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TRAINING REPORT SUBMITTED TO THE DEPARTMENT OF MECHANICAL ENGINEERING OF LUDHIANA COLLEGE OF ENGINEERING AND TECHNOLOGY, KATANI KALAN, LUDHIANA AS PART OF COURSE WORK OF B.TECH. (MECHANICAL ENGINEERING) PUNJAB TECHNICAL UNIVERSITY KAPURTHALA SUBMITTED BY Harminder Singh B- Tech., Mech. Engg.

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Page 1: Diesel Shed

TRAINING REPORT

SUBMITTED TO THE DEPARTMENT OF MECHANICAL ENGINEERING

OF

LUDHIANA COLLEGE OF ENGINEERING AND TECHNOLOGY,

KATANI KALAN, LUDHIANA

AS PART OF COURSE WORK OF

B.TECH. (MECHANICAL ENGINEERING)

PUNJAB TECHNICAL UNIVERSITY

KAPURTHALA

SUBMITTED BY

Harminder Singh

B- Tech., Mech. Engg.

Univ. Roll No. – L-90491175389.

Page 2: Diesel Shed

CONTENTS

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PREFACE

The globe is shrinking. The world is taken over by the technicians. A day after day

a new technology arises. A technician without practical knowledge is zero, don’t matter

how many books you have studied. Practical know how is must to be successful.

Industrial training is the bridge for a student that takes him from the world of

theoretical knowledge to that of practical one.

Training in a good industry is highly conducive for:

1. Development of solid foundation of knowledge and personality.

2. Confidence building.

3. Pursuit of excellence and discipline.

4. Enhancement of creativity through motivation and drive which helps to

produce professional and well trained for the rigorous of the job/society.

The present report has been done as an industrial training of six weeks for the

completion of 4th semester of B–Tech Mechanical Engineering.

During the training I got the exposure to various equipment and machines their

maintenance and technology concerning the repairing the Diesel Locomotive and hence

was assisted in developing self-confidence. The training helped me in implementing my

theoretical knowledge to the actual industrial environment.

This training at the “NORTHERN RAILWAY DIESEL SHED LUDHIANA”

is definitely going to play an important role in developing an aptitude for acquiring

knowledge hard work and self confidence necessary for successful future.

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ACKNOLEDGEMENT

In these six weeks of industrial training, I wish to my attribute my profound

sense of gratitude without whose generous co-operation and co-ordination it would have

been highly difficult for me to have such a successful training experience in the

organization, in every game of life these are multitude of players whose are the real

heroes and this experience there are many loyal and phenomenally selfless friends, co-

workers and my bosses in industry, I am overwhelmed.

Few tasks are more enjoyable and fulfilling than acknowledging my gratitude to

all those, who have helped in this effort in so many ways. I take this opportunity to

express my sincere thanks to the management of “NORTHERN RAILWAY DIESEL

SHED LUDHIANA” of permitting me to observe and study the whole setup of factory.

I owe more than a debt of gratitude to Mr. R.P.Ram (Principal), Senior Section

Engineer Mr. Kuldeep Rai, and specially Thanks to Mr. Sarbjeet Singh (Mechanic) &

all the staff for their corporation & guidance made it possible to complete the work. I am

equally thankful to my faculty teacher for providing me this opportunity to work with

such a big company.

Page 5: Diesel Shed

Certificate

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OVERVIEW

Early internal combustion engine-powered locomotives used gasoline as their

fuel. Soon after Dr. Rudolf Diesel patented his first compression ignition engine in 1892,

its application for railway propulsion was considered. Progress was slow, however, due

to the poor power-to-weight ratio of the early engines, as well as the difficulty inherent in

mechanically applying power to multiple driving wheels on swivelling trucks (bogies).

Steady improvements in the Diesel engine's design (many developed by Sulzer

Ltd. of Switzerland, with whom Dr. Diesel was associated for a time) gradually reduced

its physical size and improved its power-to-weight ratio to a point where one could be

mounted in a locomotive. Once the concept of Diesel-electric drive was accepted the pace

of development quickened. By the mid 20th century the Diesel locomotive had become

the dominant type of locomotive in much of the world, offering greater flexibility and

performance than the steam locomotive, as well as substantially lower operating and

maintenance costs. Currently, almost all Diesel locomotives are Diesel-electric.

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NORTHERN RAILWAY, DIESEL SHED, LUDHIANA

Chapter-1 INTRODUCTION

_____________________________________________________________

Diesel Shed Ludhiana came into existence on 29.09.1977. Initially, the shed was

designed to home 60 WDM2 locos. Later, it was expanded to home 100 WDM2 locos in

the year 1987-88. Further the total holding of shed was increased to 150 locos in the year

1993-94. Present loco holding of Diesel Shed, Ludhiana is 170 having different types of

locos i.e. WDM2, WDM3A & WDG3A.

Diesel Shed, Ludhiana is presently the biggest shed on the Northern Railway and

the 3rd largest on Indian Railways. The total kilometers earning is approximately 22 lakh

kilometers per month and the shed is running a mail link of 96 locos consisting of various

prestigious Mail/Express trains.

Diesel Shed, Ludhiana is also having a Diesel Training School and Hostel attached

to it. The Training School consists of 5 classrooms and various working models of

mechanical and electrical sub assemblies of WDM2 locos. The staying capacity in the

hostel is 72 and is having 38 double-bedded rooms. This training School is being mainly

utilized for training of running staff for Diesel conversion and refresher courses of FZR

& UMB division. In addition to this, this is also being utilized for imparting training to

the maintenance staff of the shed. It is also equipped with the recreation facilities &

gymnasium with high-tech exercise machines, indoor games etc.

Presently, Diesel Shed, LDH is ISO0-14001 Certified Shed, which is headed by

under the dynamic control of Sr.Divl. Mech.Engineer (Diesel), under whom the officers

DME-I, DME-II, ADME/H, ADME/R/Mech., ADME/R/Elect, ACMT & SMM/Stores

are working.

Page 8: Diesel Shed

1.1 Various Sections In Diesel Shed:-

Turbo Section

Expressor Section

Compressor Section

Power Assembly Section

Cylinder Head Section

Machine Shop

Cross Head Section

Water Pump & Lube Oil Section

Radiator Section

Traction M/C

Governor Section

Gauge & Valve Section

Air Brake Section

Electrical Complaint Room

Auxillary M/C Section

Electrical Test Room

Magnaflux Section

Bogie Section

Valve Grinding Section

Contactor & Relay Room

Zyglo Testing Room

Fip Section

Tsc Balancing Section

Draftsman Room

Battery Section

Metallurgical Lab.

Spectro Section

Scrap Yard

Page 9: Diesel Shed

Various Sections In Diesel Shed

To maintain various parts of locomotives, Diesel Shed, Ludhiana has different

sections for electrical and mechanical repairs & maintenance. Brief details are as under:-

1. 1.1 Turbo Supercharger Section

Turbo Supercharge is a machine, which uses exhaust of the diesel engine to

compress the intake air to improve the engine efficiency to about 1.5 times. At present, 4

types of TSCs are being overhauled in this section.

(i) ALCO Turbo Supercharger

(ii) ABB Turbo Supercharger

(iii) Napier Turbo Supercharger

(iv) Hispano Suiza Turbo Supercharger

All these TSCs are fully dismantled and overhauled in this section. The strength

of staff of this section is 7.

1.1.2 Fip & Injector Section

This section is responsible for maintaining the fuel injection pump and the

injector of diesel locomotives. The fuel injection pump is responsible for maintaining

desired pressure to inject the fuel, whereas the injector has the duty to spray the fuel in

the cylinder after atomization. Two types of FIPs are being used at present.

(i) 15mm FIP

(ii) 17mm FIP

All these subassemblies are being dismantled, overhauled and tested in this

section.

Page 10: Diesel Shed

1.1.3 Expresser & Compressor Section

The expresser is used to maintain air pressure and vacuum pressure for breaking

system in the locomotive. This section is responsible for maintaining this subassembly.

Complete expressor or compressor is dismantled and overhauled in this section as per

Work Instructions issued to the section. The staff strength of the section is about 30.

1.1.4 Power Assembly Section

The piston and connecting rod assembly is called as power assembly. 16 power

assemblies are being used in one locomotive. Two types of pistons are being used in the

locomotive. Steel cap pistons are being used in fuel efficient locomotives, whereas

aluminium pistons are being used in conventional locomotives. The shed has switched

over to barrel shape piston rings to provide better fuel efficiency. The pistons and

connecting rods are dismantled, cleaned, zyglo tested and again are made ready for

service in this section. The staff strength of section is about 10.

1.1.5. Cylinder Head Section

This section is responsible for maintenance and overhauling of cylinder heads

of diesel locomotives. 16 Nos. cylinder heads are there in one locomotive. Each cylinder

head has four valves, two exhaust and two inlet valves. In fuel-efficient locomotives, the

valve angle is 300, whereas in conventional locomotives it is 450. The head is completely

dismantled and after cleaning and mating the valve & valve seat and overhauling the

complete components, the head is made ready for service in this section after various

tests. The staff strength of this section is about 7.

1.1.6. Cross Head Section

Crosshead is a subassembly, which is operated by camshaft to operate the valve

lever mechanism of the cylinder heads. There are 16 cross heads in one locomotive. The

cross heads operate the valve levers through two bush rods, one for exhaust and other for

air inlet. Cross heads are completely dismantled and overhauled and also the valve lever

Page 11: Diesel Shed

mechanism is completely dismantled and overhauled in this section. The staff strength of

this section is about 4.

1.1.7. Pump Section

The pump section is responsible for overhauling water pump and lube oil pump

of the locomotive. Both the pumps are gear driven through crankshaft split gear train.

Every loco is having one water pump and one no. lubricating oil pump. Both the pumps

are cleaned, overhauled and made ready for service in this section. The staff strength of

this section is 4.

1.1.8. Miscelleneous Sub-assembly & Heat Exchanger Section This section is responsible for maintaining rear truck traction motor blower

which is belt driven, front truck traction motor blower which is gear driven, universal

shaft, which is used to drive radiator fan, eddy current clutch gear box used to provide

drive to radiator fan, over speed trip assembly is responsible for preventing the engine

from over-speeding. In addition to above, various heat exchangers, such as radiator, turbo

aftercooler, compressor after cooler and engine lube oil cooler are cleaned, tested &

overhauled in this section. The self-centrifuging unit of locomotive is also overhauled in

this section.

1.1.9.Bogie Section

This section is responsible for complete overhauling of undergear of the

locomotive. A locomotive is driven on line through 06 No. traction motors, which are

supplied from a generator driven by the diesel engine. These motors are fitted on 6 Nos.

axles and connected to axles through a bull gear pinion arrangement. The motors are

suspended through suspension bearing which is plain bearing in some locomotives,

whereas these are roller bearings in about 50% of locomotives. Two bogie frames are

used to house six axles and wheels and called as front bogie and rear bogie. The braking

arrangement for the locomotives is given through 8 brake cylinders, 4 on each bogie and

various brake riggings, brake shoes and brake blocks. The load of locomotive is shared

by each bogie. Each bogie has two nos. side bearers and one no. central pivot. The load

Page 12: Diesel Shed

sharing between the central pivot and the side bearer is in the ratio of 60:40. The chassis

of the locomotive is having 2 Nos. central buffer couplers on each side for connection to

the train. The chassis is also having mounted 4 Nos. buffers, 2 on each side to bear

various pumps during operation. Staff strength in this section is about 70.

1.1.10. Yearly Section

Yearly section is used for complete overhauling of locomotive, engine block

and removal of various mechanical subassemblies. The yearly section carries out 24

monthly and 48 monthly schedules of the locomotives in which engine and various

subassemblies are overhauled completely. Staff strength of this section is about 90.

1.1.11. Air Brake Section

Air brake section is responsible for overhauling of brake valves of air brake

system and other safety items such as wipers, sanders, horns etc. In addition to it, various

gauges are also being maintained by this section. Staff strength of this section is about 50.

1.1.12. Valve Section

This section is responsible for maintaining fuel regulating valve, fuel relief valve,

lube oil regulating valve, lube oil relief valve, lube oil bypass valve of the locomotive.

The valves are overhauled and are set at a required pressure as per Maintenance

Instructions. Staff strength of this section is 2.

1.1.13. Speedometer Section

The speedometer section is responsible for maintaining speedometers of the

locomotive, which are responsible for recording and indicating the speed of the

locomotive. Staff strength of this section is about 16.

1.1.14. Governor Section

Governor section is responsible for maintenance of governor of the locomotive.

The governor of the locomotive is responsible for maintaining constant speed of the

engine as per requirement at every notch. At present, the shed has 3 types of governors.

Page 13: Diesel Shed

(i) Woodward governor

(ii) GE or electro hydraulic governor

(iii) Microprocessor based governor

1.2 Minor Repairs Sections

1.2.1 Mail Section

Mail Section is having 2 sections i.e. Mail/Mech. and Mail Elect. section. Mail

section is responsible for maintenance of diesel engine, various mechanical

subassemblies, undergears etc. for trip schedule, monthly schedule and quarterly schedule

for mail and passenger locomotives.

1.2.2 Goods Section

Goods section is also having goods mech. and goods electrical. Goods section is

responsible for maintenance of diesel engine, various mechanical subassemblies,

undergears etc. for trip schedule, monthly schedule and quarterly schedule for goods

locomotives.

1.2.3 Quarterly & Half Yearly Section

Quarterly and half yearly section is responsible for 8 monthly, 12 monthly and 16

monthly schedules of diesel locomotives.

1.2.4 Out-Of-Course Section

OOC section is responsible for attending various major repairs of the locomotives,

which cannot be covered during minor schedule.

1.2.5 M & P Of The Shed

The shed, in its bogie section, is having two 40tonne cranes and one 10 tonne

crane. These cranes are used to lift bogies, engine blocks and various major

subassemblies. Heavy Repair Bay subassembly sections are having two cranes, 0ne

10tonne and the other is 3tonne crane. These are used for handling various

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subassemblies. Every minor repair bay i.e. goods, mail, quarterly half yearly sections are

also having 3 tonne self operated cranes which are used to lift various subassemblies of

the locomotive. The shed is also having 3 Nos. fork lifters for material handling.

1.2.6 SCHEMATIC DIAGRAM OF DIESEL – ELECTRIC LOCOMOTIVE

Fig. 1 schematic diagram of diesel electric locomotive

1.2.7BLOCK DIAGRAM OF DIESEL LOCOMOTIVE

Fig. 2 Block diagram of diesel locomotive

A Diesel locomotive is a type of railroad locomotive in which the prime mover is a

Diesel engine

RADIATOR AFTER FRAME

BO

GG

IE

EXPRESSOR OR

COMPRESSOR ROOM

ENGINE ROOM

GENERATOR ROOM

DRIVER CABIN

NOTCH COMPART

MENT

BO

GG

IE

Page 15: Diesel Shed

1.2.8 SALIENT FEATURES

Sanctioned staff strength = 1331

Staff on roll = 1206

Total covered area = 12,577 sq. meters.

Berthing capacity = 32 locos.

%age of staff housed = 21%.

Fuel storage capacity = 730 kiloliters.

Average off take of diesel oil per day = 0.3 lakh liters (approx).

Lube oil storage capacity = 350 kiloliters.

Average off-take of lube oil per day = 2700 liters (approx).

Annual budget of shed = Rs.___________ (approx).

Average kms earned/month = 21.61 lakh kilometers.

Stock items in the stores depot. = 1969

Present mail link = 96

Present loco holding = 170

(a) WDM2 = 62(b) WDG3A = 44(c) WDM3A = 64

Total = 170Direct maintenance staff per loco = 4.30

SFC Mail (Lts/1000GTKM) (2008-09) = 3.72

SFC Goods (Lts/1000GTKM) (2008-09) = 2.03

ACTIVITIES IN SHED SCHEDULES GIVEN BY SHOPSSchedules Periodicity Schedules Periodicity

Trip 15/20 days. IOH/M48 (By CB Shop) 4 yearsT2 30 days. POH/M96(By CB Shop) 8 years. M2 60 days. RB (By DMW/PTA) 16-22 years M4 120 days.M12 12 months. NO.OF SCHEDULES UNDERTAKEN IN

A MONTHM24 24 months. Type of Sch No. of Sch.M48 48 months. Trip 280M72 72 months T2 82

M2 40M4/8/16/20 27M12 08M24/48 04

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1.2.9 Engine Description

Diesel Engine

Main Alternator

Auxiliary Alternator

Motor Blower

Air Intakes

Rectifiers / inverters

Electric Controls

Control Stands

Batteries

Cab

Traction Motor

Pinion Gear

Fuel Tank

Air compressor

Drive Shaft

Gear Box

Radiator and Radiator Fan

Turbo charging

Sand Box

Truck Frame

Wheel

Brakes

Mechanical Transmission

Fluid Coupling

Final Drive

Hydraulic Transmission

Wheel Slip

Page 17: Diesel Shed

Chapter-2 Diesel Engine

_____________________________________________________________

The diesel engine was first patented by Dr Rudolf Diesel (1858-1913) in

Germany in 1892 and he actually got a successful engine working by 1897. By 1913,

when he died, his engine was in use on locomotives and he had set up a facility with

Sulzer in Switzerland to manufacture them. His death was mysterious in that he simply

disappeared from a ship taking him to London.

The diesel engine is a compression-ignition engine, as opposed to the petrol (or

gasoline) engine, which is a spark-ignition engine. The spark ignition engine uses an

electrical spark from a "spark plug" to ignite the fuel in the engine's cylinders, whereas

the fuel in the diesel engine's cylinders is ignited by the heat caused by air being suddenly

compressed in the cylinder. At this stage, the air gets compressed into an area 1/25th of

its original volume. This would be expressed as a compression ratio of 25 to 1. A

compression ratio of 16 to 1 will give an air pressure of 500 lbs/in² (35.5 bar) and will

increase the air temperature to over 800° F (427° C).

The advantage of the diesel engine over the petrol engine is that it has a higher thermal

capacity (it gets more work out of the fuel), the fuel is cheaper because it is less refined

than petrol and it can do heavy work under extended periods of overload. It can however,

in a high speed form, be sensitive to maintenance and noisy, which is why it is still not

popular for passenger automobiles.

2.1 Diesel engine: Mode of Operation

1. Suction stroke: Pure air gets sucked in by the piston sliding downward.

2.Compression stroke: The piston compresses the air above and uses thereby work,

performed by the crankshaft.

3.Power stroke: In the upper dead-center, the air is max. Compressed: Pressure and

Temperature are very high. Now the black injection pump injects heavy fuel in the hot

Page 18: Diesel Shed

air. By the high temperature the fuel gets ignited immediately (auto ignition). The piston

gets pressed downward and performs work to the crankshaft.

4.Expulsion stroke: The burned exhaust gases are ejected out of the cylinder through a

second valve by the piston sliding upward again.

Fig. 3 4 stroke compression ignition (diesel) engine cycle

2.2 Diesel-electric control

A Diesel-electric locomotive's power output is independent to road speed, as long as

the units generator current and voltage limits are not exceeded. Therefore, the unit's

ability to develop tractive effort (also referred to as drawbar pull or tractive force, which

is what actually propels the train) will tend to inversely vary with speed within these

limits.

The diesel engine ideally should operate with maximum fuel economy as long as

maximum power is not required. Maintaining acceptable operating parameters was one of

the principal design considerations that had to be solved in early Diesel-electric

locomotive development, and ultimately led to the complex control systems in place on

modern units where all these parameters are solved and regulated by computer modules.

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The prime mover's power output is primarily determined by its rotational speed

(RPM) and fuel rate, which are regulated by a governor or similar mechanism. The

governor is designed to react to both the throttle setting, as determined by the engineer

(driver), and the speed at which the prime mover is running.

Locomotive power output, and thus speed, is typically controlled by the engineer (driver)

using a stepped or "notched" throttle that produces binary-like electrical signals

corresponding to throttle position. This basic design lends itself well to multiple unit

(MU) operation by producing discrete conditions that assure that all units in a consist

respond in the same way to throttle position. Binary encoding also helps to minimize the

number of train lines (electrical connections) that are required to pass signals from unit to

unit. For example, only four train lines are required to encode all throttle positions.

In older locomotives, the throttle mechanism was ratcheted so that it was not

possible to advance more than one power position at a time. The engineer could not, for

example, pull the throttle from notch 2 to notch 4 without stopping at notch 3. This

feature was intended to prevent rough train handling due to abrupt power increases

caused by rapid throttle motion ("throttle stripping," an operating rules violation on many

railroads). Modern locomotives no longer have this restriction, as their control systems

are able to smoothly modulate power and avoid sudden changes in train loading

regardless of how the engineer (driver) operates the controls.

2.3 WORKING OF DIESEL LOCOMOTIVE

When the throttle is in the idle position, the prime mover will be receiving minimal

fuel, causing it to idle at low RPM. Also, the traction motors will not be connected to the

main generator and the generator's field windings will not be excited (energized)—the

generator will not produce electricity with no excitation. Therefore, the locomotive will

be in "neutral." Conceptually, this is the same as placing an automobile's transmission

into neutral while the engine is running.

To set the locomotive in motion, the reverser control handle is placed into the correct

position (forward or reverse), the brake is released and the throttle is moved to the run 1

position (the first power notch). An experienced engineer (driver) can accomplish these

steps in a coordinated fashion that will result in a nearly imperceptible start. The

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positioning of the reverser and movement of the throttle together is conceptually like

shifting an automobile's automatic transmission into gear while the engine is idling

Placing the throttle into the first power position will cause the traction motors to be

connected to the main generator and the latter's field coils to be excited. It will not,

however, increase prime mover RPM. With excitation applied, the main generator will

deliver electricity to the traction motors, resulting in motion. If the locomotive is running

"light" (that is, not coupled to a train) and is not on an ascending grade it will easily

accelerate. On the other hand, if a long train is being started, the locomotive may stall as

soon as some of the slack has been taken up, as the drag imposed by the train will exceed

the tractive force being developed. An experienced engineer (driver) will be able to

recognize an incipient stall and will gradually advance the throttle as required to maintain

the pace of acceleration.

As the throttle is moved to higher power notches, the fuel rate to the prime mover will

increase, resulting in a corresponding increase in RPM and horsepower output. At the

same time, main generator field excitation will be proportionally increased to absorb the

higher power. This will translate into increased electrical output to the traction motors,

with a corresponding increase in tractive force. Eventually, depending on the

requirements of the train's schedule, the engineer (driver) will have moved the throttle to

the position of maximum power and will maintain it there until the train has accelerated

to the desired speed.

As will be seen in the following discussion, the propulsion system is designed to produce

maximum traction motor torque at start-up, which explains why modern locomotives are

capable of starting trains weighing in excess of 15,000 tons, even on ascending grades.

Current technology allows a locomotive to develop as much as 30 percent of its loaded

driver weight in tractive force, amounting to some 120,000 pounds of drawbar pull for a

large, six-axle freight (goods) unit. In fact, a consist of such units can produce more than

enough drawbar pull at start-up to damage or derail cars (if on a curve), or break couplers

(the latter being referred to in North American railroad slang as "jerking a lung").

Therefore, it is incumbent upon the engineer (driver) to carefully monitor the amount of

power being applied at start-up to avoid damage. In particular, "jerking a lung" could be a

calamitous matter if it were to occur on an ascending grade.

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As previously explained, the locomotive's control system is designed so that the

main generator electrical power output is matched to any given engine speed. Due to the

innate characteristics of traction motors, as well as the way in which the motors are

connected to the main generator, the generator will produce high current and low voltage

at low locomotive speeds, gradually changing to low current and high voltage as the

locomotive accelerates. Therefore the net power produced by the locomotive will remain

constant for any given throttle setting.

In older designs, the prime mover's governor and a companion device, the load

regulator, play a central role in the control system. The governor has two external inputs:

requested engine speed, determined by the engineer's throttle setting, and actual engine

speed (feedback). The governor has two external control outputs: fuel injector setting,

which determines the engine fuel rate, and load regulator position, which affects main

generator excitation. The governor also incorporates a separate over speed protective

mechanism that will immediately cut off the fuel supply to the injectors and sound an

alarm in the cab in the event the prime mover exceeds a defined RPM. It should be noted

that not all of these inputs and outputs are necessarily electrical.

The load regulator is essentially a large potentiometer that controls the main

generator power output by varying its field excitation and hence the degree of loading

applied to the engine. The load regulator's job is relatively complex, because although the

prime mover's power output is proportional to RPM and fuel rate, the main generator's

output is not (which characteristic was not correctly handled by the Ward Leonard

elevator drive system that was initially tried in early locomotives).

As the load on the engine changes, its rotational speed will also change. This is detected

by the governor via a change in the engine speed feedback signal. The net effect is to

adjust both the fuel rate and the load regulator position. Therefore, engine RPM and

torque will remain constant for any given throttle setting, regardless of actual road speed.

In newer designs controlled by a “traction computer,” each engine speed step is

allotted an appropriate power output, or “kW reference”, in software. The computer

compares this value with actual main generator power output, or “kW feedback”,

calculated from traction motor current and main generator voltage feedback values. The

computer adjusts the feedback value to match the reference value by controlling the

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excitation of the main generator, as described above. The governor still has control of

engine speed, but the load regulator no longer plays a central role in this type of control

system. However, the load regulator is retained as a “back-up” in case of engine

overload. Modern locomotives fitted with electronic fuel injection (EFI) may have no

mechanical governor, however a “virtual” load regulator and governor are retained with

computer modules.

Fig.4 3200Hp Diesel Locomotive Engine

Traction motor performance is controlled either by varying the DC voltage output of

the main generator, for DC motors, or by varying the frequency and voltage output of the

VVVF for AC motors. With DC motors, various connection combinations are utilized to

adapt the drive to varying operating conditions.

Fig. 5 Top View of Diesel Locomotive Engine

Here are some of the specifications of this engine:

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Number of cylinders: 12

Compression ratio: 16:1

Displacement per cylinder: 11.6 L (710 in3)

Cylinder bore: 230 mm (9.2 inches)

Cylinder stroke: 279 mm (11.1 inches)

Full speed: 904 rpm

Normal idle speed: 269 rpm

At standstill, main generator output is initially low voltage/high current, often in

excess of 1000 amperes per motor at full power. When the locomotive is at or near

standstill, current flow will be limited only by the DC resistance of the motor windings

and interconnecting circuitry, as well as the capacity of the main generator itself. Torque

in a series-wound motor is approximately proportional to the square of the current.

Hence, the traction motors will produce their highest torque, causing the locomotive to

develop maximum tractive effort, enabling it to overcome the inertia of the train. This

effect is analogous to what happens in an automobile automatic transmission at start-up,

where it is in first gear and thus producing maximum torque multiplication.

As the locomotive accelerates, the now-rotating motor armatures will start to

generate a counter-electromotive force (back EMF, meaning the motors are also trying to

act as generators), which will oppose the output of the main generator and cause traction

motor current to decrease. Main generator voltage will correspondingly increase in an

attempt to maintain motor power, but will eventually reach a plateau. At this point, the

locomotive will essentially cease to accelerate, unless on a downgrade. Since this plateau

will usually be reached at a speed substantially less than the maximum that may be

desired, something must be done to change the drive characteristics to allow continued

acceleration. This change is referred to as "transition," a process that is analogous to

shifting gears in an automobile.

2.4 Starting:

A diesel engine is started (like an automobile) by turning over the crankshaft

until the cylinders "fire" or begin combustion. The starting can be done electrically or

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pneumatically. Pneumatic starting was used for some engines. Compressed air was

pumped into the cylinders of the engine until it gained sufficient speed to allow ignition,

then fuel was applied to fire the engine. The compressed air was supplied by a small

auxiliary engine or by high pressure air cylinders carried by the locomotive.

Electric starting is now standard. It works the same way as for an automobile,

with batteries providing the power to turn a starter motor which turns over the main

engine. In older locomotives fitted with DC generators instead of AC alternators, the

generator was used as a starter motor by applying battery power to it.

2.5 Transition methods include:

Series / Parallel or "motor transition."

o Initially, pairs of motors are connected in series across the main generator. At

higher speed, motors are re-connected in parallel across the main generator.

Field shunting," "field diverting" or "weak fielding."

o Resistance is connected in parallel with the motor field. This has the effect of

increasing the armature current, producing a corresponding increase in motor

torque and speed.

Note: Both methods may also be combined, to increase the operating speed range.

Generator transition

o Reconnecting the two separate internal main generator stator windings from

parallel to series to increase the output voltage.

In older locomotives, it was necessary for the engineer to manually execute

transition by use of a separate control. As an aid to performing transition at the right time,

the load meter (an indicator that informs the engineer on how much current is being

drawn by the traction motors) was calibrated to indicate at which points forward or

backward transition should take place. Automatic transition was subsequently developed

to produce better operating efficiency, and to protect the main generator and traction

motors from overloading due to improper transition.

The hybrid diesel locomotive is an incredible display of power and ingenuity. It

combines some great mechanical technology, including a huge, 12-cylinder, two-stroke

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diesel engine, with some heavy duty electric motors and generators, throwing in a little

bit of computer technology for good measure.

This combination of diesel engine and electric generators and motors makes the

locomotive a hybrid vehicle. In this article, we'll start by learning why locomotives are

built this way and why they have steel wheels. Then we'll take a look at the layout and

key components.

2.6 Size Does Count

Basically, the more power you need, the bigger the engine has to be. Early

diesel engines were less than 100 horse power (hp) but today the US is building 6000 hp

locomotives. For a UK locomotive of 3,300 hp (Class 58), each cylinder will produce

about 200 hp, and a modern engine can double this if the engine is turbocharged.

The maximum rotational speed of the engine when producing full power will be

about 1000 rpm (revolutions per minute) and the engine will idle at about 400 rpm.

These relatively low speeds mean that the engine design is heavy, as opposed to a high

speed, lightweight engine. However, the UK HST (High Speed Train, developed in the

1970s) engine has a speed of 1,500 rpm and this is regarded as high speed in the railway

diesel engine category. The slow, heavy engine used in railway locomotives will give

low maintenance requirements and an extended life.

There is a limit to the size of the engine which can be accommodated within the

railway loading gauge, so the power of a single locomotive is limited. Where additional

power is required, it has become usual to add locomotives. In the US, where freight

trains run into tens of thousands of tons weight, four locomotives at the head of a train are

common and several additional ones in the middle or at the end are not unusual.

2.7 Important Maintenance Instruction For Cylinder Head.

Study the condition of cylinder head combustion chamber face, cooling jackets

and its valves thoroughly before its dismantling.

Clean cylinder head thoroughly especially cooling jackets.

Do RDF of cylinder head combustion face, defect any cracks.

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Check cylinder head hydraulically at 5kg/sq. cm and 8. Temp of water up to a min

of 15 minutes.

Check the diameter of valve guide after removing its carbon deposits.

Check the clean nozzle, cooling sleeves seat of cylinder head.

Use liquid nitrogen for valve seat insert fitting.

Check valve seat inserts for cracks by RDF (After grinding).

Before final assembly check all valve seat inserts as well as of nozzle cooling

sleeve.

Compare seat should be lapped thoroughly and it should be 1/16” thick all over.

2.8 Cylinder Head

Fig. 6 Cylinder Head

2.9 To V or not to V

Diesel engines can be designed with the cylinders "in-line", "double banked" or in

a "V". The double banked engine has two rows of cylinders in line. Most diesel

locomotives now have V form engines. This means that the cylinders are split into two

sets, with half forming one side of the V. A V8 engine has 4 cylinders set at an angle

forming one side of the V with the other set of four forming the other side. The

crankshaft, providing the drive, is at the base of the V. The V12 was a popular design

used in the UK. In the US, V16 is usual for freight locomotives and there are some

designs with V20 engines.

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2.10 Tractive Effort, Pull and Power

Before going too much further, we need to understand the definitions of tractive

effort, drawbar pull and power. The definition of tractive effort (TE) is simply the force

exerted at the wheel rim of the locomotive and is usually expressed in pounds (lbs) or

kilo Newtons (KN). By the time the tractive effort is transmitted to the coupling between

the locomotive and the train, the drawbar pull, as it is called will have reduced because of

the friction of the mechanical parts of the drive and some wind resistance.

Power is expressed as horsepower (hp) or kilo Watts (kW) and is actually a rate of

doing work. A unit of horsepower is defined as the work involved by a horse lifting

33,000 lbs one foot in one minute. In the metric system it is calculated as the power

(Watts) needed when one Newton of force is moved one metre in one second. The

formula is P = (F*d)/t where P is power, F is force, d is distance and t is time. One

horsepower equals 746 Watts.

The relationship between power and drawbar pull is that a low speed and a high

drawbar pull can produce the same power as high speed and low drawbar pull. If you

need to increase higher tractive effort and high speed, you need to increase the power. To

get the variations needed by a locomotive to operate on the railway, you need to have a

suitable means of transmission between the diesel engine and the wheels.

One thing worth remembering is that the power produced by the diesel engine is

not all available for traction. In a 2,580 hp diesel electric locomotive, some 450 hp is lost

to on-board equipment like blowers, radiator fans, air compressors and "hotel power" for

the train.

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Chapter-3 WDM-2 Diesel Locomotive

_____________________________________________________________

The first few prototype WDM-2s were imported. After Diesel Locomotive Works

(DLW) completed construction of its factory in Varanasi, production of the locomotives

began in India. The first 12 locos were built using kits imported from ALCO in the

United States. After that DLW started manufacturing the WDM-2 locomotives from their

own components. Since then over 2,800 locomotives have been manufactured and the

WDM-2 has become the most popular locomotive in India.

However, even before the arrival of WDM-2 another type of diesel locomotive

was imported from ALCO beginning in 1957. This locomotive was classified as WDM-1.

Later a number of modifications were made and a few subclasses were created.

This includes WDM-2A, WDM-2B and WDM-3A (formerly WDM-2C).

The WDM-2 is the diesel workhorse of the Indian Railways, being very reliable

and rugged.

The class WDM-2 is Indian Railways' workhorse diesel locomotive. The first

units were imported fully built from the American Locomotive Company (Alco) in 1962.

Since 1964, it has been manufactured in India by the Diesel Locomotive Works (DLW),

Varanasi. The model name stands for broad gauge (W), diesel (D), mixed traffic (M)

engine. The WDM-2 is the most common diesel locomotive of Indian Railways.

The WDM-2A is a variant of the original WDM-2. These units have been retro-

fitted with air brakes, in addition to the original vacuum brakes. The WDM-2B is a more

recent locomotive, built with air brakes as original equipment. The WDM-2 locos have a

maximum speed of 120 km/h (75 mph), restricted to 100 km/h (62 mph) when run long

hood forward. The gear ratio is 65:18.

Types of Diesel locomotives

WDM2 BG Main Line Locomotive 2600HP

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WDM3 BG Main Line Locomotive 3100HP

WDM6 BG Main Line Locomotive 1350HP

WDM7 BG Main Line Locomotive 2150HP

WDG4BG Main Line Goods Locomotive 4000HP

WDP4 BG Main Line Passenger Locomotive 4000HP

WDS6 BG Shunting Locomotive 1350HP

WDP1 BG Inter City Express Locomotive 2300HP

WDP2 BG High HP Passenger Locomotive 3100HP

WDG3A BG High Goods Locomotive 3100HP

WDG3C BG High HP Goods Locomotive 3300HP

YDM4 MG Main Line Locomotive 1350HP

3.1 Technical specifications

Builders Alco, DLW

Engine

Alco 251-B, 16 cylinder, 2,600 hp (2,430 hp site rating) with Alco

710/720/?? Turbo supercharged engine. 1,000 rpm max, 400 rpm idle;

228 mm x 266 mm bore/stroke; compression ratio 12.5:1. Direct fuel

injection, centrifugal pump cooling system (2,457 l/min at 1,000 rpm),

fan driven by eddy current clutch (86 hp at 1,000 rpm).

Governor GE 17MG8 / Woodward’s 8574-650.

TransmissionElectric, with BHEL TG 10931 AZ generator (1,000 rpm, 770 V, 4,520

amps).

Traction motorsGE752 (original Alco models) (405 hp), BHEL 4906 BZ (AZ?) (435 hp)

and (newer) 4907 AZ (with roller bearings)

Axle load 18.8 tones, total weight 112.8 t.

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Bogies Alco design cast frame trimount (Co-Co) bogies

Starting TE30.4 t, at adhesion 27%.

Length over

buffer beams15,862 mm.

Distance

between bogies10,516 mm.

The above requirement, in the year 1987, led to the creation of test beds at Engine

Development Directorate of RDSO at Lucknow having state of the art facilities for

developmental testing of all the variants of diesel engines being used by Indian Railways.

It included the computer based test facility for both data logging and control of engines.

The above facilities comparable to the best facilities in the world were created to

meet the following objectives:

Development of technology for improving existing Rail Traction Diesel Engines for

1. Better Fuel Efficiency

2. Higher Reliability

3. Increased Availability

Development of technology for increasing power output of existing Diesel Engines.

Develop capability for designing new Rail Traction Diesel Engines for meeting future needs of Indian Railways.

To provide effective R&D backup to Railways and Production units to

1. Maintain Quality

2. Facilitate Indigenization

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3.2 Broad Gauge Main Line Freight Locomotive WDG 3A

3.2.1 Technical Information Diesel Electric main line, heavy duty goods service locomotive, with 16 cylinder ALCO

engine and AC/DC traction with micro processor controls.

Wheel Arrangement Co-Co

Track Gauge 1676 mm

Weight 123 t

Length over Buffers 19132 mm

Wheel Diameter 1092 mm

Gear Ratio 18 : 74

Min radius of Curvature 117 m

Maximum Speed 105 Kmph

Diesel Engine Type : 251 B,16 Cyl.- V

HP 3100

Brake IRAB-1

Loco Air, Dynamic

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Train Air

Fuel Tank Capacity 6000 litres

3.3 Broad Gauge Main Line Mixed Service LOCO WDM 3D

3.3.1 Technical Information Diesel Electric Locomotive with micro processor control suitable for main line

mixed Service train operation.

Wheel

Arrangement

Co-Co

Track Gauge 1676 mm

Weight 117 t

Max. Axle

Load

19.5 t

Length over

Buffer

18650 mm

Wheel

Diameter

1092 mm

Gear Ratio 18 : 65

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Maximum

Speed

120 Kmph

Diesel Engine Type: 251 B-16 Cyl. ‘V’ type

HP 3300 HP (standard UIC condition)

Transmission Electric AC / DC

Brake IRAB-1 system

Loco Air, Dynamic, Hand

Train Air

Fuel Tank

Capacity

5000 litres

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3.4 Broad Gauge Shunting Locomotive WDS 6AD

3.4.1Technical Information

A heavy duty shunting Diesel Electric Locomotive for main line and branch line

train operation. This locomotive is very popular with Steel Plants and Port Trusts.

Wheel Arrangement Co-Co

Track Gauge 1676 mm

Weight 113 t

Length over Buffer 17370 mm

Wheel Diameter 1092 mm

Gear Ratio 74 : 18

Maximum Speed 50 Kmph

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Diesel Engine Type : 251 D-6 Cyl. in-line

HP 1350 / 1120 HP (std.)

Transmission Electric AC / DC

Brake IRAB-1

Loco Air

Train Air

Fuel Tank Capacity 5000 litres

3.5 Engine Test Bed Facilities

The test bed facilities in RDSO are equipped with four Test Cells. These Test Cells

house four (16 cylinders GMEMD, 16 cylinders ALCO, 12 cylinders ALCO, 6 cylinders

ALCO) types of DLW manufactured Engines. Each test cell has its own microprocessor

controlled data acquisition and control systems and Video Display Unit (VDU) for

pressure, temperature and other parameters. Various transducers relay the information

from the test engines to the microprocessor based test commander for further processing

with the help of sophisticated software. Each test cell has an instrumentation catering to

60 to 120 pressures / temperature transducers along with sophisticated equipments like

gravimetric fuel balance for measurement of fuel consumption and the equipment for

measurement of air flow.

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Fig. 8 Test Bed 3.6 Fuel Consumption on 8th Notch

Since the fuel consumption at 8th notch is highest and also since Locomotives run

at this notch for longer duration as compared to other notches, fuel consumption at this

notch is one of the important fuel efficiency index. This is measured in terms of gm / bhp

- hr.

3.7 Fuel Consumption Over Duty Cycle

An Engine runs in the field at different notch as per requirement of speed / load of

the locomotive. The notch wise percentage running of locomotive over duty cycle for

passenger and freight operations of Indian Railways locomotives is as under:

3.8 Speed at different Notch position

Notch Speed (RPM)1 4002 4503 5504 6505 7506 8507 915

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8 1000

3.9 Driving a Locomotive

You don't just hop in the cab, turn the key and drive away in a diesel locomotive.

Starting a train is a little more complicated than starting your car.

The engineer climbs an 8-foot (2.4-m) ladder and enters a corridor behind the cab. He or

she engages a knife switch (like the ones in old Frankenstein movies) that connects the

batteries to the starter circuit. Then the engineer flips about a hundred switches on a

circuit-breaker panel, providing power to everything from the lights to the fuel pump.

Next, the engineer walks down a corridor into the engine room. He turns and holds

a switch there, which primes the fuel system, making sure that all of the air is out of the

system. He then turns the switch the other way and the starter motor engages. The engine

cranks over and starts running.

Next, he goes up to the cab to monitor the gauges and set the brakes once the

compressor has pressurized the brake system. He can then head to the back of the train to

release the hand brake.

Finally he can head back up to the cab and take over control from there. Once he

has permission from the conductor of the train to move, he engages the bell, which rings

continuously, and sounds the air horns twice (indicating forward motion).

The throttle control has eight positions, plus an idle position. Each of the throttle

positions is called a "notch." Notch 1 is the slowest speed, and notch 8 is the highest

speed. To get the train moving, the engineer releases the brakes and puts the throttle into

notch 1.

In this General Motors EMD 710 series engine, putting the throttle into notch 1

engages a set of contactors (giant electrical relays). These contactors hook the main

generator to the traction motors. Each notch engages a different combination of

contactors, producing a different voltage. Some combinations of contactors put certain

parts of the generator winding into a series configuration that results in a higher voltage.

Others put certain parts in parallel, resulting in a lower voltage. The traction motors

produce more power at higher voltages.

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As the contactors engage, the computerized engine controls adjust the fuel injectors

to start producing more engine power.

Chapter-4 Main Parts Of An Engine

_____________________________________________________________

4.1 Main Alternator

The diesel engine drives the main alternator which provides the power to move the

train. The alternator generates AC electricity which is used to provide power for the

traction motors mounted on the trucks (bogies). In older locomotives, the alternator was

a DC machine, called a generator. It produced direct current which was used to provide

power for DC traction motors. Many of these machines are still in regular use. The next

development was the replacement of the generator by the alternator but still using DC

traction motors. The AC output is rectified to give the DC required for the motors.

4.2 Auxiliary Alternator

Locomotives used to operate passenger trains are equipped with an auxiliary

alternator.  This provides AC power for lighting, heating, air conditioning, dining

facilities etc. on the train.  The output is transmitted along the train through an auxiliary

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power line.  In the US, it is known as "head end power" or "hotel power". In the UK, air

conditioned passenger coaches get what is called electric train supply (ETS) from the

auxiliary alternator.  

4.3 Motor Blower

The diesel engine also drives a motor blower.  As its name suggests, the motor

blower provides air which is blown over the traction motors to keep them cool during

periods of heavy work.  The blower is mounted inside the locomotive body but the

motors are on the trucks, so the blower output is connected to each of the motors through

flexible ducting.  The blower output also cools the alternators.  Some designs have

separate blowers for the group of motors on each truck and others for the alternators. 

Whatever the arrangement, a modern locomotive has a complex air management system

which monitors the temperature of the various rotating machines in the locomotive and

adjusts the flow of air accordingly.

4.4 Air Intakes

The air for cooling the locomotive's motors is drawn in from outside the locomotive.  It

has to be filtered to remove dust and other impurities and its flow regulated by

temperature, both inside and outside the locomotive.  The air management system has to

take account of the wide range of temperatures from the possible +40° C of summer to

the possible -40° C of winter.

4.5 Rectifiers/Inverters

The output from the main alternator is AC but it can be used in a locomotive with

either DC or AC traction motors.  DC motors were the traditional type used for many

years but, in the last 10 years, AC motors have become standard for new locomotives. 

They are cheaper to build and cost less to maintain and, with electronic management can

be very finely controlled.  To see more on the difference between DC and AC traction

technology try the Electronic Power Page on this site.

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To convert the AC output from the main alternator to DC, rectifiers are required.  If the

motors are DC, the output from the rectifiers is used directly.  If the motors are AC, the

DC output from the rectifiers is converted to 3-phase AC for the traction motors. 

In the US, there are some variations in how the inverters are configured.   GM

EMD relies on one inverter per truck, while GE uses one inverter per axle - both systems

have their merits.   EMD's system links the axles within each truck in parallel, ensuring

wheel slip control is maximized among the axles equally.    Parallel control also means

even wheel wear even between axles. However, if one inverter (i.e. one truck) fails then

the unit is only able to produce 50 per cent of its tractive effort.  One inverter per axle is

more complicated, but the GE view is that individual axle control can provide the best

tractive effort.  If an inverter fails, the tractive effort for that axle is lost, but full tractive

effort is still available through the other five inverters.  By controlling each axle

individually, keeping wheel diameters closely matched for optimum performance is no

longer necessary.

4.6 Electronic Controls:

Almost every part of the modern locomotive's equipment has some form of

electronic control.  These are usually collected in a control cubicle near the cab for easy

access. 

The controls will usually include a maintenance management system of some

sort which can be used to download data to a portable or hand-held computer.

Fig.9 Controls, indicators and the radio

4.7 Control Stand

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This is the principal man-machine interface, known as a control desk in the UK

or control stand in the US.  The common US type of stand is positioned at an angle on the

left side of the driving position and, it is said, is much preferred by drivers to the modern

desk type of control layout usual in Europe and now being offered on some locomotives

in the US.

4.8 Batteries

Just like an automobile, the diesel engine needs a battery to start it and to provide

electrical power for lights and controls when the engine is switched off and the alternator

is not running.

The locomotive operates on a nominal 64-volt electrical system. The locomotive has

eight 8-volt batteries; each weighing over 300 pounds (136 kg). These batteries provide

the power needed to start the engine (it has a huge starter motor), as well as to run the

electronics in the locomotive. Once the main engine is running, an alternator supplies

power to the electronics and the batteries.

4.9 Cab

Most US diesel locomotives have only one cab but the practice in Europe is two

cabs.  US freight locos are also designed with narrow engine compartments and

walkways along either side.  This gives a reasonable forward view if the locomotive is

working "hood forwards".  US passenger locos, on the other hand have full width bodies

and more streamlined ends but still usually with one cab.  In Europe, it is difficult to tell

the difference between a freight and passenger locomotive because the designs are almost

all wide bodied and their use is often mixed. The cab of the locomotive rides on its own

suspension system, which helps isolate the engineer from bumps. The seats have a

suspension system as well.

4.10 Traction Motor

Since the diesel-electric locomotive uses electric transmission, traction motors are

provided on the axles to give the final drive.  These motors were traditionally DC but the

development of modern power and control electronics has led to the introduction of 3-

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phase AC motors. There are between four and six motors on most diesel-electric

locomotives.  A modern AC motor with air blowing can provide up to 1,000 hp.

Propulsion: The traction motors provide propulsion power to the wheels. There is one

on each axle. Each motor drives a small gear, which meshes with a larger gear on the axle

shaft. This provides the gear reduction that allows the motor to drive the train at speeds of

up to 110 mph.

Fig. 10 Traction Motor

Each motor weighs 6,000 pounds (2,722 kg) and can draw up to 1,170 amps of electrical

current.

4.11 Fuel Tank

A diesel locomotive has to carry its own fuel around with it and there has to be

enough for a reasonable length of trip.  The fuel tank is normally under the loco frame

and will have a capacity of say 1,000 imperial gallons (UK Class 59, 3,000 hp) or 5,000

US gallons in a General Electric AC4400CW 4,400 hp locomotive.  The new AC6000s

have 5,500 gallon tanks.  In addition to fuel, the locomotive will carry around, typically

about 300 US gallons of cooling water and 250 gallons of lubricating oil for the diesel

engine. Air reservoirs are also required for the train braking and some other systems on

the locomotive.  These are often mounted next to the fuel tank under the floor of the

locomotive.

This huge tank in the underbelly of the locomotive holds 2,200 gallons (8,328 L)

of diesel fuel. The fuel tank is compartmentalized, so if any compartment is damaged or

starts to leak, pumps can remove the fuel from that compartment.

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4.12 Governor

Once a diesel engine is running, the engine speed is monitored and controlled through a

governor.  The governor ensures that the engine speed stays high enough to idle at the

right speed and that the engine speed will not rise too high when full power is demanded. 

The governor is a simple mechanical device which first appeared on steam engines.  It

operates on a diesel engine as shown in the diagram below.

The governor consists of a rotating shaft, which is driven by the diesel engine.  A pair

of flyweights is linked to the shaft and they rotate as it rotates.  The centrifugal force

caused by the rotation causes the weights to be thrown outwards as the speed of the shaft

rises.  If the speed falls the weights move inwards. The flyweights are linked to a collar

fitted around the shaft by a pair of arms.  As the weights move out, so the collar rises on

the shaft.  If the weights move inwards, the collar moves down the shaft.  The movement

of the collar is used to operate the fuel rack lever controlling the amount of fuel supplied

to the engine by the injectors.

Fig. 11 Principle of Governor

4.12.1 Function and types of governors

The purpose of a governor is to control the speed of an engine. If an engine is loaded

beyond its rated capacity, it will slow down or may even stop. Governors act through the

fuel injection system to control the amount of fuel delivered to the cylinders. The

quantity of fuel delivered, in turn, governs the power developed.

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The two types of governors, each of which serves a distinctly different purpose, are :

over speed governor and regulating governor. The over speed type is used on most

marine engines where the speed of the engine is variable. By necessity, the marine engine

requires flexibility in speed due to the maneuvering of the ship. This type of governor is

installed as a safety measure and comes into action when the engine approaches

dangerous over speed. This condition could occur before the operator had time to bring

the engine under control by other means. The over speed trip functions only if the

regulating governor fails. This governor controls all abnormal speed surges.

Overspeed governors are of the centrifugal type; that is, the action of the governor

depends upon the centrifugal force created as the governor weights revolve. Centrifugal

force is the force that tends to move a body away from the axis about which it is

revolved. This force is transmitted to the fuel injection system by means of levers

connected to the governor collar and a linkage system. In some types of over speed

governors the action merely cuts off the fuel until the engine has slowed to a point of

safety and then allows the resumption of normal operation. The other type trips a fuel

cutout mechanism and affects a complete stopping of the engine. The F-M engines

employ an F-M design over speed governor and the GM engines use Woodward over

speed governors.

For this discussion governors will be classified as either hydraulic or mechanical.

The mechanical type embodies the principle of centrifugal force similar to the over speed

type, while the hydraulic type employs a centrifugally actuated pilot valve to regulate the

flow of a hydraulic medium under pressure. The mechanical governor is more applicable

to the small engine field not requiring extremely close regulation while the hydraulic type

finds favor with the larger installations demanding very close regulation. The regulating

governor is much more sensitive to slight speed fluctuations than is the overspeed

governor. Its duty is to control the speed within very narrow limits when an engine is

operating under varying loads. It takes the place of the operator's manual control of the

throttle. When the load on the engine increases, and before the engine's speed has

appreciably dropped, it permits an increase of fuel to the cylinders, thus maintaining the

engine speed at the set rate. To perform this function, the governor must be sensitive to

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the slightest variation in speed. The Woodward hydraulic governor of the regulating type

is widely used in the United States Navy & Railway Engines.

4.12.2 Description and operation

The type of regulating governor used on all submarine main engines is the

Woodward SI hydraulic type governor. On F-M engines, it is driven from the lower

crankshaft, and on GM engines, from one of the camshafts. The purpose of the governor

is to regulate the amount of fuel supplied to the cylinders so that a predetermined engine

speed will be maintained despite variations in load. Figure 10-2 is a schematic diagram of

the governor. The principal parts of the governor are a gear pump and accumulators

which serve to keep a constant oil pressure on the system at all times; a pilot valve

plunger, pilot valve bushing, and flyweights which control the amount of oil going to the

power assembly; a speed adjusting spring whose tension governs the speed setting of the

governor; the power element, consisting of the power spring, power piston, and power

cylinder; and the compensating assembly which consists of the actuating compensating

plunger, the receiving compensating plunger, the compensating spring, and two

compensation needle valves. The pilot valve plunger is constructed with a land which

serves to open or close the port in the pilot valve bushing leading to the power cylinder.

In this governor the flyweights are linked hydraulically to the fuel control

cylinder. The downward pressure of the power spring is balanced by the hydraulic lock

on the lower side of the power piston. The amount of oil below the power piston is

regulated by the pilot valve plunger controlled by the flyweights.

Fig. 12 Woodward regulating governor installed

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When the engine is running at the speed set on the governor, the land on the pilot

valve plunger covers the regulating port in the bushing. The plunger is held in this

position by the flyweights. However, if the engine load decreases, the engine speeds up

and the additional centrifugal force moves the flyweights outward, raising the pilot valve

plunger. This opens the regulating port of the bushing, and trapped oil from the power

cylinder is then allowed to flow through the pilot valve cylinder into a drainage passage

to the oil sump. As the trapped oil drains to the oil sump, the power spring forces the

piston down, actuating the linkage to the fuel system controls, and the supply of fuel to

the engine is diminished. As the engine speed returns to the set rate, the flyweights

resume their original position and the, pilot valve plunger again covers the regulating

port.

Fig. 13 Schematic diagram of Woodward regulating governor

If the load increases, the engine slows down, and the flyweights move inward. This

lowers the pilot valve plunger, allowing pressure oil to flow through the pilot valve

chamber to the power cylinder. This oil supplied by a pump is under a pressure sufficient

to overcome the pressure of the power spring. The power piston moves upward, actuating

the linkage to increase the amount of fuel injected into the engine cylinders. Once again,

as the speed returns to the set rate, the flyweights resume their central position. The gear

pump that supplies the high-pressure oil is driven from the governor drive shaft and takes

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suction from the governor oil sump. A spring-loaded accumulator maintains a constant

pressure of oil and allows excess oil to return to the sump.

To prevent overcorrection in the regulating governor a compensating mechanism

is used. This acts on the pilot valve bushing so as to anticipate the pilot valve movement

and close the regulating port slightly before the centrifugal flyballs would normally direct

the pilot valve to cover the port. A compensating plunger on the power piston shaft

moves in a cylinder that is also filled with oil. When the engine speed increases and the

power piston moves downward, the actuating compensating plunger is also carried down,

drawing oil into its cylinder. This creates a suction above the receiving compensating

plunger which is part of the pilot valve bushing. The bushing moves upward, closing the

port to the power piston. Thus the power piston is stopped, allowing no time for

overcorrection. As the flyweights and pilot valve return to their central position, oil

flowing through a needle valve allows the compensating spring to return to its central

position. To keep the port closed, the bushing and plunger must return to normal position

at exactly the same speed. Therefore, the needle valve must be adjusted so that the oil

passes through at the required rate for the particular engine.

When the engine speed drops below the set rate, the actuating compensating

plunger moves upward with the power piston. This increases the pressure above the

actuating compensating plunger and consequently above the receiving compensating

piston which therefore moves down, carrying with it the pilot valve bushing. As before,

the lower bushing port is closed. The excess oil in the compensating system is now forced

out through the needle valve as the compensating spring returns the bushing to its central

position.

The governing speed of the engine is set by changing the tension of the speed adjusting

spring. The pressure of this spring determines the engine speed necessary for the

flyweights to maintain their central position. Oil allowed to leak past the various plungers

for lubricating purposes is drained into the governing oil sump.

In actual operation, the events described above occur almost simultaneously.

4.12.3 Regulating governor sub-assemblies:-

The governor consists of five principal subassemblies as follows:

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a. Drive adapter: - The drive adapter assembly serves as a mounting base for the

governor. The upper flange of the casting is bored out at the center to form a bearing

surface for the hub of the pump drive gear and for the upper end of the drive shaft.

b. Power case assembly:- This assembly includes the governor oil pump, oil pump

check valves, oil pressure accumulators, and compensating needle valves.

The oil pump drive gear turns the rotating sleeve to which it is attached. The

pump idler gear is carried on a stud and rotates in a bored recess in the power case. These

two gears and their housing constitute the governor oil pump. On opposite sides of the

central bore in the power case, and parallel to it, are two long oil passages leading from

the bottom of the power case to the top of the accumulator bores. Check valve seats are

arranged at the top and bottom of each chamber. Both check valves have openings

leading from the space between the valves to the oil pump. In this way the pump is

arranged for rotation in either direction, pulling oil through the lower check valve on one

side and forcing it through the upper check valve on the opposite side.

There are two oil pressure accumulators. Their function is to regulate the

operating oil pressure and insure a continuous supply of oil in the event that the

requirements of the power cylinder should temporarily exceed the capacity of the oil

pump. There is no adjustment for oil pressure, as this pressure is determined by the size

of the springs in the accumulators. The two compensating needle valves control the size

of the openings in the two small tapered ports in the passage that connects the area above

the actuating compensating plunger in the Servo motor and the space above the receiving

compensating plunger in the pilot valve bushing of the rotating sleeve assembly. These

ports open the compensating oil passage to the oil sump tank. Only one needle valve and

one port are necessary for operation, but two are provided so that adjustment can be made

on the one that is more accessible.

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Fig. 14 Governor-sections through adapter, power, case, power cylinder and rotating sleeve assembly.

c. Power cylinder assembly: - The power cylinder assembly consists of the cylinder,

power piston, piston rod, power spring, and the actuating compensating plunger. The

power piston is single acting. Any oil pressure acting on the lower side forces the piston

up against the power spring, thereby increasing the fuel flow. If no oil pressure is present,

the power spring acting on the upper side forces the piston down to decrease the fuel

flow.

The area underneath the power piston is connected to the pilot valve regulating

ports. An oil drain is provided in the space above the power piston to permit any oil that

may leak by the piston to drain into the governor case oil sump. No piston rings are used

in the closely fitting piston. A shallow, helical groove permits equal oil pressure on all

sides of the piston, thus preventing wear and binding.

An adjustable load limit stop screw is provided in the power cylinder. This screw

prevents the power piston from traveling beyond the predetermined load limit. The screw

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can be adjusted by removing the cap nut on top of the power cylinder, loosening the lock

nut, and turning the screw up or down with a screwdriver.

d. Speed control column:- The basic speed control column assembly includes the

speeder plug screw, speed adjusting spring, rack shaft, rack shaft gear, and the speed

adjustment knob with gear train. The gear train consists of the dial shaft gear, dial shaft

pinion, and the pinion shaft gear and pinion. Movement of the gear train changes the

compression of the speed adjusting spring. The amount of compression determines the

speed at which the flyballs will be vertical. Hence, the compression determines the

engine speed. The speeder plug screw allows the adjustment of the governor speed setting

to match the actual speed of the engine.

e. Rotating sleeve assembly: - The principal parts of the rotating sleeve assembly

(Figure 10-13) are: the pump drive gear, pilot valve bushing, pilot valve plunger,

ballhead, and flyballs. The central bore in the power case forms a bearing for the entire

rotating sleeve. The port grooves in the sleeve align with the ports in the power case

(Figure 10-10). Since these grooves extend completely around the diameter of the

rotating sleeve, the results are the same as if the sleeve were stationary and the ports were

permanently in line with those in the case. From top to bottom the ports are as follows:

accumulator pressure to pilot valve, regulating pressure to power cylinder, drain from the

lower end of the pilot plunger, compensating pressure from the power piston to the

receiving compensating plunger on the pilot valve bushing, and drain from the lower side

of the receiving compensating plunger.

4.12.4 ADJUSTMENTS

a. Speed adjustment: - The speed setting of the governor is changed by increasing or

decreasing the compression of the speed adjusting spring which opposes the centrifugal

force of the flyballs. Increasing the spring compression will make it more difficult for the

flyballs to move outward; consequently a higher flyball (and engine) speed must be

attained to move the flyballs outward and thereby reduce the fuel supply.

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Conversely, decreasing the compression of the speed adjusting spring will permit

the flyballs to move outward when they, and the engine, are running at a lower speed.

Thus, decreasing the spring compression decreases the speed at which the engine will

run.

Speed adjustments may be made manually at the governor, or electrically from the

governor control cabinet in the maneuvering room as follows:

1. Manual adjustment:- The manual adjustment is made by means of the speed

control knob located on the front of the regulating governor. This knob is connected

through a gear train to the rack shaft which in turn is- geared to a rack on the speed

adjusting plug. The knob also actuates a pointer that travels over a dial graduated to

show engine speeds corresponding to deflection of the speed adjusting spring.

2. Electrical adjustment:- For electrical control, a Selsyn receiving motor is also

geared to the rack shaft. This receiving motor operates in parallel with a Selsyn

transmitter generator in the governor control cabinet mounted on the main control

cubicle instrument panel in the maneuvering room. When the speed setting is

changed at the transmitter generator, the receiving motor in the governor moves to

establish the same setting in the governor.

b. Compensating needle valve adjustment:- This adjustment is made with the engine

running from 200 rpm to 300 rpm as set by the speed adjustment knob or by remote

control.

Either of the two needle valves may be used for adjustment. The one not used must be

turned in against its seat. When performing the adjustment, the more accessible valve is

opened a full turn or more and the engine is allowed to surge for approximately 30

seconds to eliminate trapped air. Then the valve is closed until surging is just eliminated.

The needle valve will usually be open about one-fourth of a turn for best performance.

However, the adjustment depends on the characteristics of the engine. The needle valve

should be kept open as far as possible to prevent sluggishness. Once the valve has been

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adjusted correctly for the engine, it should not be necessary to change the adjustment

except for a permanent temperature change affecting the viscosity of the oil.

4.12.5 Air Compressor

The air compressor is required to provide a constant supply of compressed air for

the locomotive and train brakes.  In the US, it is standard practice to drive the compressor

off the diesel engine drive shaft.  In the UK, the compressor is usually electrically driven

and can therefore be mounted anywhere.  The Class 60 compressor is under the frame,

whereas the Class 37 has the compressors in the nose.

4.12.6 Gear Box

The radiator and its cooling fan is often located in the roof of the locomotive.

Drive to the fan is therefore through a gearbox to change the direction of the drive

upwards.

4.12.7 Fuel Injection

Ignition is a diesel engine is achieved by compressing air inside a cylinder until it

gets very hot (say 400° C, almost 800° F) and then injecting a fine spray of fuel oil to

cause a miniature explosion.  The explosion forces down the piston in the cylinder and

this turns the crankshaft.  To get the fine spray needed for successful ignition the fuel has

to be pumped into the cylinder at high pressure.  The fuel pump is operated by a cam

driven off the engine.  The fuel is pumped into an injector, which gives the fine spray of

fuel required in the cylinder for combustion. 

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Fig. 15 Fuel injection pump Fig. 16 FIP cut section

The original fuel injection pumps used on ALCO Engines had plunger diameter of

15 mm. The plunger diameter of the fuel injection pump was increased from 15 mm to 17

mm. This modification led to sharper fuel injection i.e. injection at higher-pressure. The

modification resulted in increase of peak fuel line pressure from 750 to 850 bars and,

thus, improvement in the fuel efficiency.

The estimated fuel and lube oil economy with this modification is approx. 1.5%

and 4% respectively.

4.12.8 FIP Testing

Ensure the level of servo calibration. Oil is above the low mark in storage tank of test

stand.

Heat the oil to 100° F to 120° F.

Mount the m/c nozzle according to FIP type to be used on m/c.

Mount the overhauled FIP on cam housing & tighten. The FIP rack should be against

the spring loaded plunger.

Screw the fuel inlet union.

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Connect the high pressure tube b/w FIP discharge & calibrating nozzle.

Keep the control rack in full fuel oil position & insert horse shoe space according to

FIP type to be tested b/w the rack positioning tool & FIP face.

Reset the counter to zero.

Operate the calibrating m/c & set the oil pressure 25-30 psi.

Measure the oil delivery in beaker for 300 strokes. Do this process five times & check

the average of last three measurement of oil delivery.

If specified delivery is not achieved adjust the rack by rotating rack position tool in

the required direction to get the specified delivery & when it is found within specified

limit, stop the m/c.

Adjust the pointer of full fuel position to proper mm reading. Remove the horse shoe

space & ensure rack length is at idle fuel length i.e. at 9 mm & record the full fuel

delivery in calibration data nozzle.

4.12.9 Injector Assembly Sequence

1. Nozzle holder body.

2. Compensating washer.

3. Spring.

4. Spindle with guide bush.

5. Intermediate disc.

6. Nozzle.

7. Nozzle cap nut.

4.12.9.1 Maintenance Instruction Of Injector While Re-Conditioning

Nozzle value lift 0.024˝ max.

Testing pressure

Min. 3100 Psi-260 kg/cm

Max. 4100 Psi-290 kg/cm

Spring pattern should be uniform.

Nozzle should give healthy chartering sound.

Seat tightness test, there should be no dribbling.

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4.12.9.2Tool, Gauges, Torque Wrenches Used In FIP Section

Torque Wrench – 100 to 400 ft. lbs.

Torque Wrench – 450 to 750 ft. lbs.

Socket – 1 (⅜)˝ & 2((⅜)˝

Box Spanner 36 mm & 70 mm.

Reamer 23/32 HSS.

Centering Sleeve For Injector Nozzle.

True Running Tool For Injection.

Pin Vice Kit.

Dial Gauge.

Temp. Gauge 0 to 110° C.

Pressure Gauge 0 to 100 psi.

Pressure Gauge 0 to 8960 psi.

Nose Plier.

Clean all the components once again using clean HSD oil & assemble them wet.

Place the injector nozzle holder body in the fixture with nozzle & upward.

Position the spring seat & spring in the body.

Keep spindle with guide bush & intermediate disc on spring.

Place assemble nozzle over the intermediate disc & screw the nozzle cap nut & torque

to 105 ft. lbs.

4.13 Fuel Control

In an automobile engine, the power is controlled by the amount of fuel/air mixture

applied to the cylinder.  The mixture is mixed outside the cylinder and then applied by a

throttle valve.  In a diesel engine the amount of air applied to the cylinder is constant so

power is regulated by varying the fuel input.  The fine spray of fuel injected into each

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cylinder has to be regulated to achieve the amount of power required.  Regulation is

achieved by varying the fuel sent by the fuel pumps to the injectors.

Fig. 17 Fuel System

The amount of fuel being applied to the cylinders is varied by altering the effective

delivery rate of the piston in the injector pumps.  Each injector has its own pump,

operated by an engine-driven cam, and the pumps are aligned in a row so that they can all

be adjusted together.  The adjustment is done by a toothed rack (called the "fuel rack")

acting on a toothed section of the pump mechanism.  As the fuel rack moves, so the

toothed section of the pump rotates and provides a drive to move the pump piston round

inside the pump.The fuel rack can be moved either by the driver operating the power

controller in the cab or by the governor.  If the driver asks for more power, the control

rod moves the fuel rack to set the pump pistons to allow more fuel to the injectors.   The

engine will increase power and the governor will monitor engine speed to ensure it does

not go above the predetermined limit.The limits are fixed by springs limiting the weight

movement.

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Fig.18 Fuel Supply system

4.14 Radiators

They are used for cooling internal combustion engines, chiefly in automobiles but

also in piston-engined aircraft, railway locomotives, motorcycles, stationary generating

plant or any similar use of such an engine.

They operate by passing a liquid coolant through the engine block, where it is heated,

then through the radiator itself where it loses this heat to the atmosphere. This coolant is

usually water-based, but may also be oil. It's usual for the coolant flow to be pumped,

also for a fan to blow air through the radiator.

In railway with a liquid-cooled internal combustion engine a radiator is connected to

channels running through the engine and cylinder head, through which a liquid (coolant)

is pumped. This liquid may be water (in climates where water is unlikely to freeze), but is

more commonly a mixture of water and antifreeze in proportions appropriate to the

climate. Antifreeze itself is usually ethylene glycol or propylene glycol (with a small

amount of corrosion inhibitor).

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The radiator transfers the heat from the fluid inside to the air outside, thereby

cooling the engine. Radiators are also often used to cool automatic transmissions, air

conditioners, and sometimes to cool engine oil. Radiators are typically mounted in a

position where they receive airflow from the forward movement of the vehicle, such as

behind a front grill. Where engines are mid- or rear-mounted, it is common to mount the

radiator behind a front grill to achieve sufficient airflow, even though this requires long

coolant pipes. Alternatively, the radiator may draw air from the flow over the top of the

vehicle or from a side-mounted grill. For long vehicles, such as buses, side airflow is

most common for engine and transmission cooling and top airflow most common for air

conditioner cooling.

4.14.1 Radiator Construction

Railway radiators are constructed of a pair of header tanks, linked by a core with

many narrow passageways, thus a high surface area relative to its volume. This core is

usually made of stacked layers of metal sheet, pressed to form channels and soldered or

brazed together. For many years radiators were made from brass or copper cores soldered

to brass headers. Modern radiators save money and weight by using plastic headers and

may use aluminium cores. This construction is less easily repaired than traditional

materials.

An earlier construction method was the honeycomb radiator. Round tubes were

swaged into hexagons at their ends, then stacked together and soldered. As they only

touched at their ends, this formed what became in effect a solid water tank with many air

tubes through it.

Fig.19 Honeycomb Radiator Tubes

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Temperature Control

4.14.2 Water Flow Control

The engine temperature is primarily controlled by a wax-pellet type of thermostat, a

valve which opens once the engine has reached its optimum operating temperature.

Fig.20 Radiator Thermostat

When the engine is cold the thermostat is closed, with a small bypass flow so that the

thermostat experiences changes to the coolant temperature as the engine warms up.

Coolant is directed by the thermostat to the inlet of the circulating pump and is returned

directly to the engine, bypassing the radiator. Directing water to circulate only through

the engine allows the temperature to reach optimum operating temperature as quickly as

possible whilst avoiding localized "hot spots". Once the coolant reaches the thermostat's

activation temperature it opens, allowing water to flow through the radiator to prevent the

temperature rising higher.

Once at optimum temperature, the thermostat controls the flow of coolant to the

radiator so that the engine continues to operate at optimum temperature. Under peak load

conditions, such as labouring slowly up a steep hill whilst heavily laden on a hot day, the

thermostat will be approaching fully open because the engine will be producing near to

maximum power while the velocity of air flow across the radiator is low. (The velocity of

air flow across the radiator has a major effect on its ability to dissipate heat.) Conversely,

when cruising fast downhill on a motorway on a cold night on a light throttle, the

thermostat will be nearly closed because the engine is producing little power, and the

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radiator is able to dissipate much more heat than then engine is producing. Allowing too

much flow of coolant to the radiator would result in the engine being over cooled and

operating at lower than optimum temperature. A side effect of this would be that the

passenger compartment heater would not be able to put out enough heat to keep the

passengers warm.

The thermostat is therefore constantly moving throughout its range, responding to

changes in vehicle operating load, speed and external temperature, to keep the engine at

its optimum operating temperature.

4.14.3 Airflow Control

Other factors influence the temperature of the engine including radiator size and the type

of radiator fan. The size of the radiator (and thus its cooling capacity) is chosen such that

it can keep the engine at the design temperature under the most extreme conditions a

vehicle is likely to encounter (such as climbing a mountain whilst fully loaded on a hot

day).

Airflow speed through a radiator is a major influence on the heat it loses. Vehicle speed

affects this, in rough proportion to the engine effort, thus giving crude self-regulatory

feedback. Where an additional cooling fan is driven by the engine, this also tracks engine

speed similarly.

4.14.4 Coolant

Before World War II, radiator coolant was usually plain water. Antifreeze was used

solely to control freezing, and this was often only done in cold weather.

Development in high-performance aircraft engines required improved coolants with

higher boiling points, leading to the adoption of glycol or water-glycol mixtures. These

led to the adoption of glycols for their antifreeze properties too.

Since the development of aluminium or mixed-metal engines, corrosion inhibition has

become even more important than antifreeze and in all regions and seasons too.

Because the thermal efficiency of internal combustion engines increases with

internal temperature the coolant is kept at higher-than-atmospheric pressure to increase

its boiling point. A calibrated pressure-relief valve is usually incorporated in the radiator's

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fill cap. This pressure varies between models, but is typically 9 psi (0.6 bar) - 15 psi

(1.0 bar).

4.14.5 Boiling Or Overheating

On this type system, if the coolant in the overflow container gets too low, fluid

transfer to overflow will cause an increased loss by vaporizing the engine coolant.

Severe engine damage can be caused by overheating, by overloading or system defect,

when the coolant is evaporated to a level below the water pump. This can happen without

warning because, at that point, the sending units are not exposed to the coolant to indicate

the excessive temperature.

To protect the unwary the cap often contains a mechanism that attempts to relieve the

internal pressure before the cap can be fully opened. Some scalding of one's hands can

easily occur in this event. Opening a hot radiator drops the system pressure immediately

and may cause a sudden ebullition of super-heated coolant which can cause severe burns

(see geyser).

4.14.6 Radiator Thrust

An aircraft radiator comprises a duct wherein heat is added. As a result, this is

effectively a jet engine. High-performance piston aircraft with well-designed low-drag

radiators (notably the P-51 Mustang) derived a significant portion of their thrust from this

effect. At one point, there were even plans to equip the Spitfire with a ramjet, by injecting

fuel into this duct after the radiator and igniting it. Although ramjets normally require a

supersonic airspeed, this light-up speed can be reduced where heat is being added, such

as in a radiator duct.

4.14.7 Steam Cooling

Pressurized cooling systems operate by adding heat to the coolant fluid, causing it

to rise in temperature in inverse proportion to its specific heat capacity. With the need to

keep the final temperature below boiling point, this limits the amount of heat that a given

mass-flow of coolant can dissipate.

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Attempts were made with aero-engines of the 1930s, notably the Rolls-Royce

Goshawk, to exceed this limit by allowing the coolant to boil. This absorbs an amount of

heat equivalent to the specific heat of vaporization, which for water is more than five

times the energy required to heat the same quantity of water from 0°C to 100°C.

Obviously this allows the necessary cooling effect with far less coolant requiring to be

circulated.

The practical difficulty was the need to provide condensers rather than radiators.

Cooling was now needed not just for hot dense liquid coolant, but for low-density steam.

This required a condenser far larger and with higher drag than a radiator. For aircraft,

especially high-speed aircraft, these were soon realized to be unworkable and so steam

cooling was abandoned.

Work instruction Radiator Fan Assembly Stripping & Cleaning

Remove the radiator fan assembly from the loco and place on the sand.

Remove the radiator fan from bearing housing.

Clean bearing housing externally with diesel oil and place it on work bench.

Dismantle the components in the following sequence:

o Universal end hub.

o Bearing housing covers.

o Shaft & bearing using hydraulic press.

Open bearing seal plate.

Clean the bearing with HSD oil and water and dry air.

Pack the bearing with servogen 3 grease and seal.

Press bearing to shaft by hydraulic press.

Apply both bearing covers duly ensuring for free rotation of shaft.

Fit hub at universal end.

Fix the bearing housing in the fixture.

Set the fan end key to fan and fan shaft.

Fix the fan to the shaft and tighten the nut and secure the split pin.

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Chapter-5 Cooling System

_____________________________________________________________

Like an automobile engine, the diesel engine needs to work at an optimum

temperature for best efficiency.  When it starts, it is too cold and, when working, it must

not be allowed to get too hot.  To keep the temperature stable, a cooling system is

provided.   This consists of a water-based coolant circulating around the engine block, the

coolant being kept cool by passing it through a radiator. 

The coolant is pumped round the cylinder block and the radiator by an electrically or belt

driven pump.  The temperature is monitored by a thermostat and this regulates the speed

of the (electric or hydraulic) radiator fan motor to adjust the cooling rate.  When starting

the coolant isn't circulated at all.  After all, you want the temperature to rise as fast as

possible when starting on a cold morning and this will not happen if you a blowing cold

air into your radiator.  Some radiators are provided with shutters to help regulate the

temperature in cold conditions.

Fig. 21 Piping System

If the fan is driven by a belt or mechanical link, it is driven through a fluid

coupling to ensure that no damage is caused by sudden changes in engine speed.  The fan

works the same way as in an automobile, the air blown by the fan being used to cool the

water in the radiator.  Some engines have fans with an electrically or hydrostatically

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driven motor.  An hydraulic motor uses oil under pressure which has to be contained in a

special reservoir and pumped to the motor.  It has the advantage of providing an in-built

fluid coupling.

A problem with engine cooling is cold weather.  Water freezes at 0° C or 32° F

and frozen cooling water will quickly split a pipe or engine block due to the expansion of

the water as it freezes.  Some systems are "self draining" when the engine is stopped and

most in Europe are designed to use a mixture of anti-freeze, with Gycol and some form of

rust inhibitor.  In the US, engines do not normally contain anti-freeze, although the new

GM EMD "H" engines are designed to use it.  Problems with leaks and seals and the

expense of putting 100 gallons (378.5 litres) of coolant into a 3,000 hp engine, means that

engine in the US have traditionally operated without it.  In cold weather, the engine is left

running or the locomotive is kept warm by putting it into a heated building or by

plugging in a shore supply.  Another reason for keeping diesel engines running is that the

constant heating and cooling caused by shutdowns and restarts, causes stresses in the

block and pipes and tends to produce leaks. Water up to 1210lts used.

Shown below are the percentages of useful work and various losses obtained

from the combustion of a fuel oil in a diesel cylinder:

To useful work (brake thermal efficiency) 30-35 percent

To exhaust gases 30-35 percent

To cooling water and friction 30-35 percent

Radiation, lube oil, and so forth 0- 5 percent

There are three practical reasons for cooling an engine:

1. To maintain lubricating oil film on pistons, cylinder walls, and other moving

parts: - This oil film must be maintained to insure adequate lubrication. The

formation of an oil film depends in large degree on the viscosity of the oil. If the

engine cooling system did not keep the engine temperature at a value that would

insure the formation of an oil film, insufficient lubrication and consequent excessive

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engine wear would result. If the engine is kept too cool, condensation takes places in

the lube oil and forms acids and sludge.

2. To avoid too great a variation in the dimensions of the engine parts: - Great

differences between operating temperatures at varying loads cause excessive changes

in the dimensions of the moving parts. These excessive changes also occur when

there are large differences between the cold and operating temperatures of the parts.

These changes in dimensions result in a variation of clearances between the moving

parts. Under normal operating conditions these clearances are very small and any

variation in dimension of the moving parts may cause insufficient clearances and

subsequent inadequate lubrication, increased friction, and possible seizure.

3. To retain the strength of the metals used: - High temperatures change the strength

and physical properties of the various ferrous metals used in an engine. For example,

if a cylinder head is subjected to high temperatures without being cooled, the tensile

strength of the metal is reduced, resulting in possible fracture. This high temperature

also causes excessive expansion of the metal which may result in shearing of the

cylinder bolts.

Cylinder heads, cylinder jackets, cylinder liners, exhaust headers, valves, and exhaust

elbows usually are cooled by water. Pistons may be cooled either by water or oil. In

present fleet type submarine installations, the pistons are cooled by lubricating oil which

is in turn cooled by engine cooling water. It is important to keep all parts of the engine at

as nearly the same temperature as possible. This can be accomplished to some extent by

engine design. For instance, the water jacket should cover the entire length of the piston

stroke to avoid possible unequal expansion of various sections of the cylinder and

cylinder liner.

It requires time to conduct heat through any substance, therefore the thicker the metal, the

slower the conduction. This is one of the reasons the size of cylinders in diesel engines is

limited, because the larger the cylinder, the thicker the material necessary for liners and

cylinder heads in order to withstand the pressures of combustion. Thicker metals cause

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the inside surfaces to run hotter, because the heat is not conducted so rapidly to the

cooling water.

5.1 Water pump:

Fig.22 Water cooling system

5.1.1 Inspection and maintenance

Examine impeller for wear & score marks.

Examine bearing and see that there are no damage balls or chattered races.

Ensure while pressing, pressure should be applied only against the inner race of

bearing.

Lubricating ball bearing with a light grease before final assembly.

Examine visually the impeller and remove any slight burs or Feathers.

Check seal plate for erosion and cavitation damages.

Check the run out of shaft and don’t permit more than 2 thou.

The torquing of the impeller nut should be done at 125lbs.

Use only stainless steel split pin.

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Check the locking properly of the lock nut.

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Chapter-6 Lubrication

_____________________________________________________________

Like an automobile engine, a diesel engine needs lubrication.  In an arrangement

similar to the engine cooling system, lubricating oil is distributed around the engine to the

cylinders, crankshaft and other moving parts.  There is a reservoir of oil, usually carried

in the sump, which has to be kept topped up, and a pump to keep the oil circulating

evenly around the engine.  The oil gets heated by its passage around the engine and has to

be kept cool, so it is passed through a radiator during its journey.  The radiator is

sometimes designed as a heat exchanger, where the oil passes through pipes encased in a

water tank which is connected to the engine cooling system. 

The oil has to be filtered to remove impurities and it has to be monitored for low

pressure.  If oil pressure falls to a level which could cause the engine to seize up, a "low

oil pressure switch" will shut down the engine.  There is also a high pressure relief valve,

to drain off excess oil back to the sump.

Fig. 23 Lube oil system

6.1 Lubricating Oil: WDM2 – 910lts WDM3 – 1110lts

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Chapter-7 Turbocharger

________________________________________________________________________

A turbocharger, or turbo, is a gas compressor used for forced-induction of an

internal combustion engine. Like a supercharger, the purpose of a turbocharger is to

increase the density of air entering the engine to create more power. However, a

turbocharger differs in that the compressor is powered by a turbine driven by the engine's

own exhaust gases.

Fig. 24 Air foil bearing-supported turbocharger

7.1 Nomenclature

Early manufacturers of turbochargers referred to them as "turbosuperchargers". A

supercharger is an air compressor used for forced induction of an engine. Logically then,

adding a turbine to turn the supercharger would yield a "turbosupercharger". However,

the term was soon shortened to "turbocharger". This is now a source of confusion, as the

term "turbosupercharged" is sometimes used to refer to an engine that uses both a

crankshaft-driven supercharger and an exhaust-driven turbocharger.

Some companies such as Teledyne Continental Motors still use the term

turbosupercharger in its original sense.

7.2 Working Principle

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A turbocharger is a small radial fan pump driven by the energy of the exhaust gases

of an engine. A turbocharger consists of a turbine and a compressor on a shared shaft.

The turbine converts heat to rotational force, which is in turn used to drive the

compressor. The compressor draws in ambient air and pumps it in to the intake manifold

at increased pressure, resulting in a greater mass of air entering the cylinders on each

intake stroke.

The objective of a turbocharger is the same as a supercharger; to improve the

engine's volumetric efficiency by solving one of its cardinal limitations. A naturally

aspirated automobile engine uses only the downward stroke of a piston to create an area

of low pressure in order to draw air into the cylinder through the intake valves. Because

the pressure in the atmosphere is no more than 1 atm (approx 14.7 psi), there ultimately

will be a limit to the pressure difference across the intake valves and thus the amount of

airflow entering the combustion chamber. Because the turbocharger increases the

pressure at the point where air is entering the cylinder, a greater mass of air (oxygen) will

be forced in as the inlet manifold pressure increases. The additional oxygen makes it

possible to add more fuel, increasing the power and torque output of the engine.

Because the pressure in the cylinder must not go too high to avoid detonation and

physical damage, the intake pressure must be controlled by controlling the rotational

speed of the turbocharger. The control function is performed by a wastegate, which

routes some of the exhaust flow away from the exhaust turbine. This controls shaft speed

and regulates air pressure in the intake manifold.

Fig. 25 Principle of turbocharger

7.3 History

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The turbocharger was invented by Swiss engineer Alfred Büchi. His patent for a

turbocharger was applied for use in 1905. Diesel ships and locomotives with

turbochargers began appearing in the 1920s.

7.4 Aviation

During the First World War French engineer Auguste Rateau fitted turbo chargers to

Renault engines powering various French fighters with some success.

In 1918, General Electric engineer Sanford Moss attached a turbo to a V12 Liberty

aircraft engine. The engine was tested at Pikes Peak in Colorado at 14,000 feet (4,300 m)

to demonstrate that it could eliminate the power losses usually experienced in internal

combustion engines as a result of reduced air pressure and density at high altitude.

Turbochargers were first used in production aircraft engines in the 1930s before World

War II. The primary purpose behind most aircraft-based applications was to increase the

altitude at which the airplane could fly, by compensating for the lower atmospheric

pressure present at high altitude. Aircraft such as the P-38 Lightning, B-17 Flying

Fortress, and P-47 Thunderbolt all used turbochargers to increase high altitude engine

power.

7.5 Design And Installation

7.5.1 Components:

Fig. 26 On the left, the brass oil drain connection. On the right are the braided oil supply line and water

coolant line connections.

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Fig.27 Compressor impeller side with the cover removed.

Fig.28 Turbine side housing removed.

Fig.29 A wastegate installed next to the turbocharger:

The turbocharger has four main components. The turbine (almost always a radial

turbine) and impeller/compressor wheels are each contained within their own folded

conical housing on opposite sides of the third component, the center housing/hub rotating

assembly (CHRA).

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The housings fitted around the compressor impeller and turbine collect and direct the gas

flow through the wheels as they spin. The size and shape can dictate some performance

characteristics of the overall turbocharger. Often the same basic turbocharger assembly

will be available from the manufacturer with multiple housing choices for the turbine and

sometimes the compressor cover as well. This allows the designer of the engine system to

tailor the compromises between performance, response, and efficiency to application or

preference. Twin-scroll designs have two valve-operated exhaust gas inlets, a smaller

sharper angled one for quick response and a larger less angled one for peak performance.

The turbine and impeller wheel sizes also dictate the amount of air or exhaust that can be

flowed through the system, and the relative efficiency at which they operate. Generally,

the larger the turbine wheel and compressor wheel, the larger the flow capacity.

Measurements and shapes can vary, as well as curvature and number of blades on the

wheels. Variable geometry turbochargers are further developments of these ideas.

The center hub rotating assembly (CHRA) houses the shaft which connects the

compressor impeller and turbine. It also must contain a bearing system to suspend the

shaft, allowing it to rotate at very high speed with minimal friction. For instance, in

automotive applications the CHRA typically uses a thrust bearing or ball bearing

lubricated by a constant supply of pressurized engine oil. The CHRA may also be

considered "water cooled" by having an entry and exit point for engine coolant to be

cycled. Water cooled models allow engine coolant to be used to keep the lubricating oil

cooler, avoiding possible oil coking from the extreme heat found in the turbine. The

development of air-foil bearings has removed this risk.

In the automotive world, boost refers to the increase in pressure that is

generated by the turbocharger in the intake manifold that exceeds normal atmospheric

pressure. Atmospheric pressure is approximately 14.5 psi or 1.0 bar, and anything above

this level is considered to be boost. The level of boost may be shown on a pressure gauge,

usually in bar, psi or possibly kPa. This is representative of the extra air pressure that is

achieved over what would be achieved without the forced induction. Manifold pressure

should not be confused with the volume of air that a turbo can flow.

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In contrast, the instruments on aircraft engines measure absolute pressure in

inches of mercury. Absolute pressure is the amount of pressure above a total vacuum.

The ICAO standard atmospheric pressure is 29.92 inches (760 mm) of mercury at sea

level. Most modern aviation turbochargers are not designed to increase manifold

pressures above this level, as aircraft engines are commonly air-cooled and excessive

pressures increase the risk of overheating, pre-ignition, and detonation. Instead, the turbo

is only designed to hold a pressure in the intake manifold equal to sea-level pressure as

the altitude increases and air pressure drops. This is called turbo-normalizing.

Boost pressure is limited to keep the entire engine system, including the turbo, inside its

thermal and mechanical design operating range. The speed and thus the output pressure

of the turbo is controlled by the wastegate, a bypass which shunts the gases from the

cylinders around the turbine directly to the exhaust pipe.

The maximum possible boost depends on the fuel's octane rating and the inherent

tendency of any particular engine towards detonation. Premium gasoline or racing

gasoline can be used to prevent detonation within reasonable limits. Ethanol, methanol,

liquefied petroleum gas (LPG) and diesel fuels allow higher boost than gasoline, because

of these fuels' combustion characteristics.

To obtain more power from higher boost levels and maintain reliability, many engine

components have to be replaced or upgraded such as the fuel pump, fuel injectors,

pistons, valves, head-gasket, and head bolts.

7.5.2 Wastegate

By spinning at a relatively high speed, the compressor turbine draws in a large volume of

air and forces it into the engine. As the turbocharger's output flow volume exceeds the

engine's volumetric flow, air pressure in the intake system begins to build. The speed at

which the assembly spins is proportional to the pressure of the compressed air and total

mass of air flow being moved. Since a turbo can spin to RPMs far beyond what is

needed, or of what it is safely capable of, the speed must be controlled. A wastegate is the

most common mechanical speed control system, and is often further augmented by an

electronic or manual boost controller. The main function of a wastegate is to allow some

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of the exhaust to bypass the turbine when the set intake pressure is achieved. Passenger

cars have wastegates that are integral to the turbocharger.

7.5.3 Anti-Surge/Dump/Blow off Valves:

Turbocharged engines operating at wide open throttle and high rpm require a large

volume of air to flow between the turbo and the inlet of the engine. When the throttle is

closed compressed air will flow to the throttle valve without an exit (i.e. the air has

nowhere to go).

This causes a surge which can raise the pressure of the air to a level which can damage

the engine. If the pressure rises high enough, a compressor stall will occur, where the

stored pressurized air decompresses backwards across the impeller and out the inlet. The

reverse flow back across the turbocharger causes the turbine shaft to reduce in speed

quicker than it would naturally, possibly damaging the turbocharger. In order to prevent

this from happening, a valve is fitted between the turbo and inlet which vents off the

excess air pressure. These are known as an anti-surge, bypass, blow-off valve (BOV) or

dump valve. It is basically a pressure relief valve, and is normally operated by the excess

pressure in the intake manifold.

The primary use of this valve is to maintain the turbo spinning at a high speed. The air is

usually recycled back into the turbo inlet but can also be vented to the atmosphere.

Recycling back into the turbocharger inlet is required on an engine that uses a mass-

airflow fuel injection system, because dumping the excessive air overboard downstream

of the mass airflow sensor will cause an excessively rich fuel mixture. A dump valve will

also shorten the time needed to re-spool the turbo after sudden engine deceleration.

7.5.4 Charge cooling:

Compressing air in the turbocharger increases its temperature, which can cause a number

of problems. Excessive charge air temperature can lead to detonation, which is extremely

destructive to engines. When a turbocharger is installed on an engine, it is common

practice to fit the engine with an intercooler, a type of heat exchanger which gives up

heat energy in the charge to the ambient air. In cases where an intercooler is not a

desirable solution, it is common practice to introduce extra fuel into the charge for the

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sole purpose of cooling. The extra fuel is not burned. Instead, it absorbs and carries away

heat when it changes phase from liquid to vapor. The evaporated fuel holds this heat until

it is released in the exhaust stream. This thermodynamic property allows manufacturers

to achieve good power output by using extra fuel at the expense of economy and

emissions. Diesels are particularly suitable for turbocharging for several reasons:

Turbocharging can dramatically improve an engine's specific power and power-to-

weight ratio, performance characteristics which are normally poor in non-

turbocharged diesel engines.

Diesel engines are optimized to operate within a relatively narrow rpm range,

reducing problems with turbo lag and compressor stall caused by sudden

accelerations and decelerations.

Diesel engines are not prone to detonation because diesel fuel requires much higher

pressures to detonate than gasoline does. Because of this, diesel engines can use much

higher boost pressures than spark ignition engines, limited only by the engine's ability

to withstand that pressure.

The turbocharger's small size and low weight have production and marketing advantage

to vehicle manufacturers. By providing naturally-aspirated and turbocharged versions of

one engine, the manufacturer can offer two different power outputs with only a fraction

of the development and production costs of designing and installing a different engine.

The compact natures of a turbocharger mean that bodywork and engine compartment

layout changes to accommodate the more powerful engine are not needed or minimal.

Parts commonality between the two versions of the same engine reduces production and

servicing costs.

Today, turbochargers are most commonly used on gasoline engines in high-performance

automobiles and diesel engines in transportation and other industrial equipment. Small

cars in particular benefit from this technology, as there is often little room to fit a large

engine. Volvo, Saab, and Subaru have produced turbocharged cars for many years, the

turbo Porsche 944's acceleration performance was very similar to that of the larger-

engined non-turbo Porsche 928, and Chrysler Corporation built numerous turbocharged

cars in the 1980s and 1990s.

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7.5.5 Sand Box:

Locomotives always carry sand to assist adhesion in bad rail conditions.   Sand is

not often provided on multiple unit trains because the adhesion requirements are lower

and there are normally more driven axles.

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Chapter-7 Truck Frame Or Bogie

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A bogie (pronounced /bogie/) is a wheeled wagon or trolley. In mechanics terms, a

bogie is a chassis or framework carrying wheels, attached to a vehicle. It can be fixed in

place, as on a cargo truck, mounted on a swivel, as on a railway carriage or locomotive,

or sprung as in the suspension of a caterpillar tracked vehicle.

Archbar type truck with journal bearings as used on some steam locomotive tenders.

Fig.30 bogie function

Bettendorf-style freight car truck displayed at the Illinois Railway Museum. This

one uses journal bearings.

A bogie in the UK, or a wheel truck, or simply truck in the USA and Canada as

well as Mexico, is a structure underneath a train to which axles (and, hence, wheels) are

attached through bearings.

Bogies serve a number of purposes:

To support the rail vehicle body.

To run stably on both straight and curved track.

To ensure ride comfort by absorbing vibration, and minimizing centrifugal forces

when the train runs on curves at high speed

To minimize generation of track irregularities and rail abrasion

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Usually two bogies are fitted to each carriage, wagon or locomotive, one at each end. An

alternate configuration often is used in articulated vehicles, which places the bogies under

the connection between the carriages or wagons.

Most bogies have two axles as it is the simplest design, but some cars designed

for extremely heavy loads have been built with up to five axles per bogie. Heavy-duty

cars may have more than two bogies using span bolsters to equalize the load and connect

the bogies to the cars.

Usually the train floor is at a level above the bogies, but the floor of the car may

be lower between bogies, such as for a double decker train to increase interior space

while staying within height restrictions, or in easy-access, stepless-entry low-floor trains.

Key components of a bogie include:

The bogie frame itself.

Suspension to absorb shocks between the bogie frame and the rail vehicle body.

Common types are coil springs, or rubber airbags.

At least one wheelset composed of an axle with a bearings and wheel at each end.

Axle box suspension to absorb shocks between the axle bearings and the bogie frame.

The axle box suspension usually consists of a spring between the bogie frame and

axle bearings to permit up and down movement, and sliders to prevent lateral

movement. A more modern design uses solid rubber springs.

Brake equipment . Two main types are used: brake shoes that are pressed against the

tread of the wheel, and disc brakes and pads.

In powered vehicles, some form of transmission, usually an electrically powered

traction motors or a hydraulically powered torque converter.

The connection of the bogie with the rail vehicle allows a certain degree of rotational

movement around a vertical axis pivot (bolster), with side bearers preventing excessive

movement. More modern bolster less bogie designs omit these features, instead taking

advantage of the sideways movement of the suspension to permit rotational movement.

7.1 Types of Bogie

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7.1.1 BR1 bogie:

The British Railways Mark 1 coach brought into production in 1950 utilized the BR1

bogie, which was rated to run at 90 mph (145 km/h). The wheels were cast as a one-piece

item in a pair with their axle. The simple design involved the bogie resting on four leaf

springs (one spring per wheel) which in turn were connected to the axles. The leaf springs

were designed to absorb any movement or resonance and to have a damping effect to

benefit ride quality.

Each spring was connected to the outermost edge of the axle by means of a roller

bearing contained in oil filled axle box. The oil in these boxes had to be topped up at

regular maintenance times to avoid the bearing running hot and from seizing.

There was also a heavy-duty version designated BR2.

7.1.2 Commonwealth bogie:

Fig. 31 Commonwealth bogie as used on BR Mark 1 and CIE Park Royals.

The SKF or Timken manufactured Commonwealth bogie was introduced in the late

1950s for all BR Mark 1 vehicles. The bogie was a heavy cast steel design weighing 6.75

ton with fitted sealed roller bearings on the axle ends, avoiding the need to maintain axle

box oil levels.

The leaf springs were replaced with coil type springs (one per wheel) running

vertically rather than horizontally. The advanced design gave a superior ride quality to

the BR1, being rated for 100 miles per hour (160 km/h).

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The side frame of the bogie was usually of bar construction, with simple horn

guides attached, allowing the axle boxes vertical movements between them. The axle

boxes had a cast steel equaliser beam or bar resting on them. The bar had two steel coil

springs placed on it and the bogie frame rested on the springs. The effect was to allow the

bar to act as a compensating lever between the two axles and to use both springs to soften

shocks from either axle. The bogie had a conventional bolster suspension with swing

links carrying a spring plank.

7.1.3 B4 bogie:

B4 bogie as used on BR Mark 2 and Irish Cravens.

The B4 bogie was introduced in 1963. It was a fabricated steel design as versus cast iron

and was hence 1.55 tons lighter than the Commonwealth, weighing in at 5.2 tons. It also

had a speed rating of 100 miles per hour (160 km/h).

Axle/spring connection was again with fitted roller bearings. However, now two coil

springs rather than one were fitted per wheel.

Only a very small amount of Mark 1 stock was fitted with the B4 bogie from new, it

being used on the Mark 1 only to replace worn out BR1 bogies. The British Rail Mark 2

coach however carried the B4 bogies from new. A heavier duty version, the B5, was

standard on Southern Region Mk1 based EMUs from the 1960s onwards. Some Mark 1

catering cars had mixed bogies—a B5 under the kitchen end, and a B4 under the seating

end. Some of the B4 fitted Mark 2s, as well as many B4 fitted Mark 1 BGs were allowed

to run at 110 miles per hour (180 km/h) with extra maintenance, particularly of the wheel

profile, and more frequent exams.

7.1.4 BT10 Bogie

BT10 High speed bogie as used on MK3.

The BT10 bogie was introduced on the British Rail Mark 3 coach in the 1970s. Each

wheel is separately connected to the bogie by a swing-arm axle.

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There is dual suspension

Primary suspension via a coil spring and damper mounted on each axle.

Secondary suspension via two air springs mounted on the pivot plank. This is

connected to the bogie by pendulum links. A constant coach height is maintained by

air valves.

Most diesel locomotives and electric locomotives are carried on bogies (UK) or trucks

(US). Trucks used in the USA include AAR type A switcher truck, Bloomberg B, HT-C

truck and Flexicoil.

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Chapter-8 Suspension

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The trucks also provide the suspension for the locomotive. The weight of the locomotive

rests on a big, round bearing, which allows the trucks to pivot so the train can make a

turn. Below the pivot is a huge leaf spring that rests on a platform. The platform is

suspended by four, giant metal links, which connect to the truck assembly. These links

allow the locomotive to swing from side to side.

Fig.32 Suspension System

The weight of the locomotive rests on the leaf springs, which compress when it passes

over a bump. This isolates the body of the locomotive from the bump. The links allow the

trucks to move from side to side with fluctuations in the track. The track is not perfectly

straight, and at high speeds, the small variations in the track would make for a rough ride

if the trucks could not swing laterally. The system also keeps the amount of weight on

each rail relatively equal, reducing wear on the tracks and wheels

8.1 Wheels

Ever wonder why trains have steel wheels, rather than tires like a car? It's to reduce

rolling friction. When your car is driving on the freeway, something like 25 percent of

the engine's power is being used to push the tires down the road. Tires bend and deform a

lot as they roll, which uses a lot of energy. The amount of energy used by the tires is

proportional to the weight that is on them. Since a car is relatively light, this amount of

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energy is acceptable (you can buy low rolling-resistance tires for your car if you want to

save a little gas).

Since a train weighs thousands of times more than a car, the rolling resistance is a

huge factor in determining how much force it takes to pull the train. The steel wheels on

the train ride on a tiny contact patch -- the contact area between each wheel and the track

is about the size of a dime.

By using steel wheels on a steel track, the amount of deformation is minimized,

which reduces the rolling resistance. In fact, a train is about the most efficient way to

move heavy goods. The downside of using steel wheels is that they don't have much

traction. In the next section, we'll discuss the interesting solution to this problem.

8.2 Traction:

Traction when going around turns is not an issue because train wheels have

flanges that keep them on the track. But traction when braking and accelerating is an

issue.

This locomotive can generate 64,000 pounds of thrust. But in order for it to use

this thrust effectively, the eight wheels on the locomotive have to be able to apply this

thrust to the track without slipping. The locomotive uses a neat trick to increase the

traction.

In front of each wheel is a nozzle that uses compressed air to spray sand, which is

stored in two tanks on the locomotive. The sand dramatically increases the traction of the

drive wheels. The train has an electronic traction-control system that automatically starts

the sand sprayers when the wheels slip or when the engineer makes an emergency stop.

The system can also reduce the power of any traction motor whose wheels are slipping.

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Chapter-9 Transmission

Like an automobile, a diesel locomotive cannot start itself directly from a stand.  It will

not develop maximum power at idling speed, so it needs some form of transmission

system to multiply torque when starting.  It will also be necessary to vary the power

applied according to the train weight or the line gradient.  There are three methods of

doing this:  mechanical, hydraulic or electric.  Most diesel locomotives use electric

transmission and are called "diesel-electric" locomotives.  Mechanical and hydraulic

transmissions are still used but are more common on multiple unit trains or lighter

locomotives.9.1 Mechanical Transmission

A diesel-mechanical locomotive is the simplest type of diesel locomotive.   As the

name suggests, a mechanical transmission on a diesel locomotive consists a direct

mechanical link between the diesel engine and the wheels.  In the example below, the

diesel engine is in the 350-500 hp range and the transmission is similar to that of an

automobile with a four speed gearbox.  Most of the parts are similar to the diesel-electric

locomotive but there are some variations in design mentioned below.

Fig.33 diesel mechanical locomotive

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9.2 Gearbox

This does the same job as that on an automobile.  It varies the gear ratio between the

engine and the road wheels so that the appropriate level of power can be applied to the

wheels.  Gear change is manual.  There is no need for a separate clutch because the

functions of a clutch are already provided in the fluid coupling. 

9.3 Final Drive

The diesel-mechanical locomotive uses a final drive similar to that of a steam engine. 

The wheels are coupled to each other to provide more adhesion.  The output from the 4-

speed gearbox is coupled to a final drive and reversing gearbox which is provided with a

transverse drive shaft and balance weights.  This is connected to the driving wheels by

connecting rods.

9.4 Hydraulic Transmission

Hydraulic transmission works on the same principal as the fluid coupling but it allows a

wider range of "slip" between the engine and wheels.  It is known as a "torque

converter".  When the train speed has increased sufficiently to match the engine speed,

the fluid is drained out of the torque converter so that the engine is virtually coupled

directly to the locomotive wheels.  It is virtually direct because the coupling is usually a

fluid coupling, to give some "slip".  Higher speed locomotives use two or three torque

converters in a sequence similar to gear changing in a mechanical transmission and some

have used a combination of torque converters and gears. 

Some designs of diesel-hydraulic locomotives had two diesel engines and two

transmission systems, one for each bogie.  The design was poplar in Germany (the V200

series of locomotives, for example) in the 1950s and was imported into parts of the UK in

the 1960s.  However, it did not work well in heavy or express locomotive designs and has

largely been replaced by diesel-electric transmission.

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Chapter-10 Dynamic braking________________________________________________________________________ A common option on Diesel-electric locomotives is dynamic (rheostat) braking.

Dynamic braking takes advantage of the fact that the traction motor armatures are always

rotating when the locomotive is in motion and that a motor can be made to act as a

generator by separately exciting the field winding. When dynamic braking is utilized, the

traction control circuits are configured as follows:

The field winding of each traction motor is connected across the main generator.

The armature of each traction motor is connected across a forced-air cooled

resistance grid (the dynamic braking grid) in the roof of the locomotive's hood.

The prime mover RPM is increased and the main generator field is excited,

causing a corresponding excitation of the traction motor fields.

Fig 34 air brake system The aggregate effect of the above is to cause each traction motor to generate

electric power and dissipate it as heat in the dynamic braking grid. Forced air-cooling is

provided by a fan that is connected across the grid. Consequently, the fan is powered by

the output of the traction motors and will tend to run faster and produce more airflow as

more energy is applied to the grid.

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Ultimately, the source of the energy dissipated in the dynamic braking grid is the

motion of the locomotive as imparted to the traction motor armatures. Therefore, the

traction motors impose drag and the locomotive acts as a brake. As speed decreases, the

braking effect decays and usually becomes ineffective below approximately 16 km/h (10

mph), depending on the gear ratio between the traction motors and axles.

Dynamic braking is particularly beneficial when operating in mountainous

regions, where there is always the danger of a runaway due to overheated friction brakes

during descent (see also comments in the air brake article regarding loss of braking due to

improper train handling). In such cases, dynamic brakes are usually applied in

conjunction with the air brakes, the combined effect being referred to as blended braking.

The use of blended braking can also assist in keeping the slack in a long train stretched as

it crests a grade, helping to prevent a "run-in," an abrupt bunching of train slack that can

cause a derailment. Blended braking is also commonly used with commuter trains to

reduce wear and tear on the mechanical brakes that is a natural result of the numerous

stops such trains typically make during a run.

Advantages:

Regenerative braking.

No gear shifting.

No backlash and breaking of couplings during shifting.

Constant availability of maximum diesel generator power.

Easy addition of multiple power units.

Less maintenance with modern ac generators and motors without commutators.

Disadvantages:

More weight.

Less efficient in fuel use.

Needs high tech electronics with use of ac generators and motors.

10.1 BRAKE: A traditional clasp brake: the brake shoe (brown) bears on the surface

(tyre) of the wheel (red), and is operated by the levers (grey) on the left

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Fig.35 brake

Brakes are used on the vehicles of railway trains to slow them, or to keep them standing

when parked. While the principle is familiar from road vehicle usage, operational features

are more complex because of the need to control trains, i.e. multiple vehicles running

together, and to be effective on vehicles left without a prime mover.

10.2 Early days:

In the earliest days of railways, braking technology was primitive. The first trains had

brakes operative on the locomotive tender and on vehicles in the train, where “porters”

or, in the United States brakemen, traveling for the purpose on those vehicles operated

the brakes. Some railways fitted a special deep-noted brake whistle to locomotives to

indicate to the porters the necessity to apply the brakes. All the brakes at this stage of

development were applied by operation of a screw and linkage to brake blocks applied to

wheel treads, and these brakes could be used when vehicles were parked. In the earliest

times, the porters travelled in crude shelters outside the vehicles, but “assistant guards”

who travelled inside passenger vehicles, and who had access to a brake wheel at their

posts supplanted them.

The braking effort achievable was limited, and an early development was the application

of a steam brake to locomotives, where boiler pressure could be applied to brake blocks

on the locomotive wheels.

As train speeds increased, it became essential to provide some more powerful braking

system capable of instant application and release by the train driver, described as a

continuous brake because it would be effective continuously along the length of the train.

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However there was no clear technical solution to the problem, because of the necessity of

achieving a reasonably uniform rate of braking effort throughout a train, and because of

the necessity to add and remove vehicles from the train at frequent points on the journey.

(At these dates, unit trains were a rarity).

The chief types of solution were:

The chain brake, such as the Heberlein brake, in which a chain was connected

continuously along the train.

When pulled tight it activated a friction clutch that used the rotation of the wheels to

tighten a brake system at that point; this system has severe limitations in length of train

capable of being handled, and of achieving good adjustment.

The simple vacuum system. An ejector on the locomotive created a vacuum in a

continuous pipe along the train, and the vacuum operated brake cylinders on every

vehicle. This system was very cheap and effective, but it had the major weakness that

it became inoperative if the train became divided or if the train pipe was ruptured.

The automatic vacuum brake. This system was similar to the simple vacuum system,

except that the creation of vacuum in the train pipe exhausted vacuum reservoirs on

every vehicle and released the brakes. If the driver applied the brake, his driver's

brake valve admitted atmospheric air to the train pipe, and this atmospheric pressure

applied the brakes against the vacuum in the vacuum reservoirs. Being an automatic

brake, this system applies braking effort if the train becomes divided or if the train

pipe is ruptured. Its disadvantage is that the large vacuum reservoirs were required on

every vehicle, and their bulk and the rather complex mechanisms were seen as

objectionable.

Fig.36 Rotair Valve Westinghouse Air brake Company

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The Westinghouse air brake system. In this system, air reservoirs are provided on

every vehicle and the locomotive charges the train pipe with a positive air pressure,

which releases the vehicle brakes and charges the air reservoirs on the vehicles. If the

driver applies the brakes, his brake valve releases air from the train pipe, and triple

valves at each vehicle detect the pressure loss and admit air from the air reservoirs to

brake cylinders, applying the brakes. The Westinghouse system uses smaller air

reservoirs and brake cylinders than the corresponding vacuum equipment, because a

moderately high air pressure can be used. However, an air compressor is required to

generate the compressed air and in the earlier days of railways, this required a large

reciprocating steam air compressor, and this was regarded by many engineers as

highly undesirable.

10.3 Later British practice:

In British practice, only passenger trains were fitted with continuous brakes until about

1930, and goods and mineral trains ran at slower speed, and relied on the brake force

from the locomotive and tender, and the brake van – a heavy vehicle provided at the rear

of the train and occupied by a guard.

Goods and mineral vehicles were provided with hand brakes, by which the brakes could

be applied by a hand lever operated by staff on the ground. These hand brakes were used

where necessary when vehicles were parked, but also when these trains needed to

descend a steep gradient; the train then stopped before descending, and the guard walked

forward to pin down the handles of sufficient brakes to give adequate braking effort.

Early goods vehicles had brake handles on one side only, and random alignment of the

vehicles gave the guard sufficient braking, but from about 1930 so-called "either-side"

brake handles were provided. These trains, not fitted with continuous brakes were

described as "unfitted" trains and they survived in British practice until about 1985.

However from about 1930 semi-fitted trains were introduced, in which some goods

vehicles were fitted with continuous brakes, and a proportion of such vehicles marshalled

next to the locomotive gave sufficient brake power to run at somewhat higher speeds than

unfitted trains.

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In the early days of diesel locomotives, a purpose-built brake tender was attached to the

locomotive to increase braking effort when hauling unfitted trains. The brake tender was

low, so that the driver could still see the line and signals ahead if the brake tender was

propelled (pushed) ahead of the locomotive, which was often the case.

10.4 Continuous brakes:

As train loads, gradients and speeds increased, braking became a problem. In the late

19th century, significantly better continuous brakes started to appear. The earliest type of

continuous brake was the chain brake which used a chain, running the length of the train,

to operate brakes on all vehicles simultaneously.

The chain brake was soon superseded by air operated or vacuum operated brakes. These

brakes used hoses connecting all the wagons of a train, so the driver could apply or

release the brakes with a single valve in the locomotive.

These continuous brakes can be simple or automatic, the essential difference being what

happens should the train break in two. With simple brakes, pressure is needed to apply

the brakes, and all braking power is lost if the continuous hose is broken for any reason.

Simple non-automatic brakes are thus useless when things really go wrong, as is shown

with the Armagh rail disaster.

Automatic brakes on the other hand use the air or vacuum pressure to hold the brakes off

against a reservoir carried on each vehicle, which applies the brakes if pressure/vacuum is

lost in the train pipe. Automatic brakes are thus largely "fail safe", though faulty closure

of hose taps can lead to accidents such as the Gare de Lyon accident.

The standard Westinghouse Air Brake has the additional enhancement of a triple valve,

and local reservoirs on each wagon that enable the brakes to be applied fully with only a

slight reduction in air pressure, reducing the time that it takes to release the brakes as not

all pressure is voided to the atmosphere.

Non-automatic brakes still have a role on engines and first few wagons, as they can be

used to control the whole train without having to apply the automatic brakes.

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10.5 Types Of Brakes

10.5.1 Air versus vacuum brakes:

In the early part of the 20th century, many British railways employed vacuum brakes

rather than the air brakes used in America and much of the rest of the world. The main

advantage of vacuum was that the vacuum can be created by a steam ejector with no

moving parts (and which could be powered by the steam of a steam locomotive), whereas

an air brake system requires a noisy and complicated compressor.

However, air brakes can be made much more effective than vacuum brakes for a given

size of brake cylinder. An air brake compressor is usually capable of generating a

pressure of 90 psi (620 kPa) vs only 15 psi (100 kPa) for vacuum. With a vacuum system,

the maximum pressure differential is atmospheric pressure (14.7 psi or 101 kPa at sea

level, less at altitude). Therefore, an air brake system can use a much smaller brake

cylinder than a vacuum system to generate the same braking force. This advantage of air

brakes increases at high altitude, e.g. Peru and Switzerland where today vacuum brakes

are used by secondary railways. The much higher effectiveness of air brakes and the

demise of the steam locomotive have seen the air brake become ubiquitous; however,

vacuum braking is still in use in India, in Argentina and in South Africa, but this will be

declining in near future.

10.5.2 Air brake enhancements:

One enhancement of the automatic air brake is to have a second air hose (the main

reservoir or main line) along the train to recharge the air reservoirs on each wagon. This

air pressure can also be used to operate loading and unloading doors on wheat wagons

and coal and ballast wagons. On passenger coaches, the main reservoir pipe is also used

to supply air to operate doors and air suspension.

Air Brake System: Most air brake equipped vehicles on the road today are using a dual

air brake system. The system has been developed to accommodate a mechanically

secured parking brake that can be applied in the event of service brake failure. It also

accommodates the need for a modulated braking system should either one of the two

systems fail. It is actually two brake systems in one, with more reservoir capacity

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resulting in a much safer system. At first glance, the dual system might seem

complicated, but if you understand the basic air brake system described so far, and if the

dual system is separated into basic functions, it becomes quite simple.

As its name suggests, the dual system is two systems or circuits in one. There are

different ways of separating the two parts of the system. On a two–axle vehicle, one

circuit operates the rear axle and the other circuit operates the front axle. If one circuit

has a failure, the other circuit is isolated and will continue to operate.

Fig.37 Compressor

In the illustration, air is pumped by the compressor (1) to the supply/wet reservoir

(5) (blue), which is protected from over pressurization by a safety valve (4). Pressurized

air moves from the supply/wet reservoir to the primary/dry reservoir (8) (green) and the

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secondary/dry reservoir (10) (red) through one–way check valves (7). At this point, the

dual circuits start.

Air from the primary/dry reservoir is directed to the foot valve (31). Air is also directed

from the secondary/dry reservoir to the foot valve. The foot valve is similar to the one

described earlier in the basic air brake system, but is divided into two sections (two foot

valves in one). One section of this dual foot valve controls the primary circuit and the

other controls the secondary circuit. When a brake application is made, air is drawn from

the primary reservoir through the foot valve and is passed on to the rear brake chambers.

At the same time, air is also drawn from the secondary reservoir, passes through the foot

valve and is passed on to the front brake chambers. If there is air loss in either circuit, the

other will continue to operate independently. Unless air is lost in both circuits, the vehicle

will continue to have braking ability. The primary and secondary circuits are equipped

with low air pressure warning devices, which are triggered by the low air pressure

indicator switch (9) and reservoir air pressure gauges (29) located on the dash of the

vehicle.

10.5.3 Electro pneumatic brakes:

A higher performing EP brake has a train pipe delivering air to all the reservoirs on the

train, with the brakes controlled electrically with a 3-wire control circuit. This can give

seven levels of braking, from mild to severe, and allows the driver greater control over

the level of braking used, which greatly increases passenger comfort. It also allows for

faster brake application, as the electrical control signal is propagated effectively instantly

to all vehicles in the train, whereas the change in air pressure which activates the brakes

in a conventional system can take several seconds or tens of seconds to propagate fully to

the rear of the train. This system is not however used on freight trains due to cost.

The system adopted on the Southern Region of British Railways in 1950 is more fully

described at Electro-pneumatic brake system on British railway trains

10.5.4 Electronically controlled pneumatic brakes:

Electronically controlled pneumatic brakes (ECP) are a development of the late 20th

Century to deal with very long and heavy freight trains, and are a development of the EP

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brake with even higher level of control. In addition, information about the operation of

the brakes on each wagon can be returned to the driver's control panel.

With ECP, a power and control line is installed from wagon to wagon from the front of

the train to the rear. Electrical control signals are propagated effectively instantaneously,

as opposed to changes in air pressure which propagate at a rather slow speed limited in

practice by the resistance to air flow of the pipe work, so that the brakes on all wagons

can be applied simultaneously rather than from front to rear. This prevents wagons at the

rear "shoving" wagons at the front, and results in reduced stopping distance and less

equipment wear.

There are two brands of ECP brakes under development, one by New York Air Brake and

the other by Wabtec. A single standard is desirable, and it is intended that the two types

be interchangeable.

10.5.5 Brake Control:

The brake control varies the air pressure in the brake cylinders to apply pressure to the

brake shoes. At the same time, it blends in the dynamic braking, using the motors to slow

the train down as well.

The engineer also has a host of other controls and indicator lights.

Fig. 38 The brake and throttle controls

A computerized readout displays data from sensors all over the locomotive. It can

provide the engineer or mechanics with information that can help diagnose problems. For

instance, if the pressure in the fuel lines is getting too high, this may mean that a fuel

filter is clogged.

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Fig. 39 This computerized display can show the status of systems all over the locomotive.

10.5.6 Reversibility:

Brake connections between wagons may be simplified if wagons always point the same

way, such as in Tasmania. An exception would be made for locomotives which are often

turned on turntables or triangles.

On the new Fortescue railway opened in 2008, wagons are operated in sets, although their

direction changes at the balloon loop at the port. The ECP connections are on one side

only and are unidirectional

10.5.7 Vacuum brake:

The vacuum brake is a braking system used on trains. It was first introduced in the mid

1860s and a variant, the automatic vacuum brake system became almost universal in

British train equipment, and in those countries influenced by British practice.

It enjoyed a brief period of adoption in the USA, primarily on narrow gauge railroads.

Its limitations caused it to be progressively superseded by compressed air systems, in the

United Kingdom from the 1970's.

The vacuum brake system is now obsolescent; it is not in large-scale use anywhere in the

world, supplanted in the main by air brakes.

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10.5.8 How the automatic vacuum brake works:

Fig40 Vacuum brake cylinder in running position: the vacuum is the same above and below the piston

Fig. 41 Air at atmospheric pressure from the train pipe is admitted below the piston, which is forced up

In its simplest form, the automatic vacuum brake consists of a continuous pipe -- the train

pipe -- running throughout the length of the train. In normal running a partial vacuum is

maintained in the train pipe, and the brakes are released. When air is admitted to the train

pipe, the air pressure acts against pistons in cylinders in each vehicle. A vacuum is

sustained on the other face of the pistons, so that a net force is applied. A mechanical

linkage transmits this force to brake shoes which act by friction on the treads of the

wheels.

The fittings to achieve this are therefore:

A train pipe: a steel pipe running the length of each vehicle, with flexible vacuum

hoses at each end of the vehicles, and coupled between adjacent vehicles; at the end

of the train, the final hose is seated on an air-tight plug;

An ejector on the locomotive, to create vacuum in the train pipe;

controls for the driver to bring the ejector into action, and to admit air to the train

pipe; these may be separate controls or a combined brake valve;

A brake cylinder on each vehicle containing a piston, connected by rigging to the

brake shoes on the vehicle; and

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A vacuum (pressure) gauge on the locomotive to indicate to the driver the degree of

vacuum in the train pipe.

The brake cylinder is contained in a larger housing - this gives a reserve of vacuum as the

piston operates. The cylinder rocks slightly in operation to maintain alignment with the

brake rigging cranks, so it is supported in trunnion bearings, and the vacuum pipe

connection to it is flexible. The piston in the brake cylinder has a flexible piston ring that

allows air to pass from the upper part of the cylinder to the lower part if necessary.

When the vehicles have been at rest, so that the brake is not charged, the brake

pistons will have dropped to their lower position in the absence of a pressure differential

(as air will have leaked slowly into the upper part of the cylinder, destroying the

vacuum).

When a locomotive is coupled to the vehicles, the driver moves his brake control

to the "release" position and air is exhausted from the train pipe, creating a partial

vacuum. Air in the upper part of the brake cylinders is also exhausted from the train pipe,

through the ball valve.

If the driver now moves his control to the "brake" position, air is admitted to the

train pipe. According to the driver's manipulation of the control, some or all of the

vacuum will be destroyed in the process. The ball valve closes and there is a higher air

pressure under the brake pistons than above it, and the pressure differential forces the

piston upwards, applying the brakes. The driver can control the severity of the braking

effort by admitting more or less air to the train pipe.

Practical considerations:

The automatic vacuum brake as described represented a very considerable technical

advance in train braking. In practice steam locomotives had two ejectors, a small ejector

for running purposes (to exhaust air that had leaked into the train pipe) and a large ejector

to release brake applications. Later Great Western Railway practice was to use a vacuum

pump instead of the small ejector.

Graduable brake valve (right) and the small (upper) and large ejector cocks from a GWR

locomotive

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The driver's brake valve was usually combined with the steam brake control on the

locomotive.

The ejectors on steam locomotives are set to create a certain degree of vacuum in the

train pipe; in British practice a full release is 21 inches of mercury (533.4 Torr). An

absolute vacuum is about 30 inches of mercury (760 Torr), depending on atmospheric

conditions; the Great Western Railway adopted 25 inches of mercury (635 Torr) as its

standard degree of vacuum.

Release valves are provided on the brake cylinders; when operated, usually by manually

pulling a cord near the cylinder, air is admitted to the upper part of the brake cylinder on

that vehicle. This is necessary to release the brake on a vehicle that has been uncoupled

from a train and now requires to be moved without having a brake connection to another

locomotive, for example if it is to be steam ejector shunted.

In the United Kingdom the pre-nationalization railway companies standardized around

systems operating on 21 inches of vacuum, with the exception of the Great Western

Railway, which used 25 inches. This could cause problems on long distance cross-

country services when a GWR locomotive was replaced with another company's engine,

as the new engine's large ejector would sometimes not be able to fully release the brakes

on the train. In this case the release valves on each vehicle in the train would have to be

released by hand. This time consuming process was not infrequently seen at large GWR

stations such as Paddington and Bristol Temple Meads.

The provision of a train pipe running throughout the train enabled the automatic vacuum

brake to be operated in emergency from any position in the train. Every guard's

compartment had a brake valve, and the passenger communication apparatus (usually

called "the communication cord" in lay terminology) also admitted air into the train pipe

at the end of coaches so equipped. This is called pulling the tail.

When a locomotive is first coupled to a train, or if a vehicle is detached or added, a brake

continuity test is carried out, to ensure that the brake pipes are connected throughout the

entire length of the train.

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Limitations:

The progress represented by the automatic vacuum brake nonetheless carried some

limitations; chief among these were:

The practical limit on the degree of vacuum attainable means that a very large brake

piston and cylinder are required to generate the force necessary on the brake blocks;

when a proportion of the British ordinary wagon fleet was fitted with vacuum brakes

in the 1950's, the physical dimensions of the brake cylinder prevented the wagons

from operating in some private sidings that had tight clearances;

For the same reason, on a very long train, a considerable volume of air has to be

admitted to the train pipe to make a full brake application, and a considerable volume

has to be exhausted to release the brake (if for example a signal at danger is suddenly

lowered and the driver requires to resume speed); while the air is traveling along the

train pipe, the brake pistons at the head of the train have responded to the brake

application or release, but those at the tail will respond much later, leading to

undesirable longitudinal forces in the train. In extreme cases this has led to breaking

couplings and causing the train to divide.

The existence of vacuum in the train pipe can cause debris to be sucked in. An

accident took place near Ilford in the 1950's, due to inadequate braking effort in the

train. A rolled newspaper was discovered in the train pipe, effectively isolating the

rear part of the train from the driver's control. The blockage should have been

detected if a proper brake continuity test had been carried out before the train started

its journey.

A development introduced in the 1950's was the direct admission valve, fitted to every

brake cylinder. These valves responded to a rise in train pipe pressure as the brake was

applied, and admitted atmospheric air directly to the underside of the brake cylinder.

American and continental European practice had long favoured compressed air brake

systems, the leading pattern being a proprietary Westinghouse system. This has a number

of advantages, including smaller brake cylinders (because a higher air pressure could be

used) and a somewhat more responsive braking effort. However the system requires an

air pump. On steam engines this was usually a reciprocating steam pump, and it was quite

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bulky. Its distinctive shape and the characteristic puffing sound when the brake is

released (as the train pipe has to be recharged with air) make steam locomotives fitted

with the Westinghouse brake unmistakable, for example in old films.

In the UK, the Great Eastern Railway, the North Eastern Railway, the London Brighton

and South Coast Railway and the Caledonian Railway adopted the Westinghouse system.

It was also standard on the Isle of Wight rail system. Inevitably this led to compatibility

problems in exchanging traffic with other lines. It was possible to provide through pipes

for the braking system not fitted to any particular vehicle so that it could run in a train

using the "other" system, allowing through control of the fitted vehicles behind it, but of

course with no braking effort of its own.

10.6 Dual brakes:

Vehicles can be fitted with dual brakes, vacuum and air, provided that there is room to fit

the duplicated equipment. It is much easier to fit one kind of brake with a pipe for

continuity of the other. Train crew need to take note that the wrong-fitted wagons do not

contribute to the braking effort and make allowances on down grades to suit. Many of the

earlier classes of diesel locomotive used on British Railways were fitted with dual

systems to enable full usage of BR's rolling stock inherited from the private companies

which had different systems depending on which company the stock originated from.

Fig.42 Dual Brake System

When spring brakes are added to a dual air brake system, the same type of dash control

valve discussed previously is used. Blended air is used to supply the spring parking brake

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control valve (27). Blended air is air taken from the primary and secondary circuits

through a two–way check valve (26). With this piping arrangement the vehicle can have a

failure in either circuit without the spring brakes applying automatically. If air is lost in

both circuits, the spring brakes will apply.

Air brakes need a tap to seal the hose at the ends of the train. If these taps are incorrectly

closed, a loss of brake force may occur, leading to a dangerous runaway. With vacuum

brakes, the end of the hose can be plugged into a stopper which seals the hose by suction.

It is much harder to block the hose pipe compared to air brakes.

10.6.1 Twin pipe:

Vacuum brakes can be operated in a twin pipe mode to speed up applications and release.

Braking is provided by a mechanism that is similar to a car drum brake. An air-powered

piston pushes a pad against the outer surface of the train wheel.

Fig.43 The brakes are similar to drum brakes on a car.

In conjunction with the mechanical brakes, the locomotive has dynamic braking. In this

mode, each of the four traction motors acts like a generator, using the wheels of the train

to apply torque to the motors and generate electrical current. The torque that the wheels

apply to turn the motors slows the train down (instead of the motors turning the wheels,

the wheels turn the motors). The current generated (up to 760 amps) is routed into a giant

resistive mesh that turns that current into heat. A cooling fan sucks air through the mesh

and blows it out the top of the locomotive -- effectively the world's most powerful hair

dryer.

On the rear truck there is also a hand brake -- yes, even trains need hand brakes. Since the

brakes are air powered, they can only function while the compressor is running. If the

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train has been shut down for a while, there will be no air pressure to keep the brakes

engaged. Without a hand brake and the failsafe of an air pressure reservoir, even a slight

slope would be enough to get the train rolling because of its immense weight and the very

low rolling friction between the wheels and the track.

The hand brake is a crank that pulls a chain. It takes many turns of the crank to tighten

the chain. The chain pulls the piston out to apply the brakes.

10.7 Vacuum brakes in 2007:

Today's largest operators of trains equipped with vacuum brakes are the Railways of

India and Spoornet (South Africa), however there are also trains with air brakes and dual

brakes in use. Other African railways are believed to continue to use the vacuum brake.

Other operators of vacuum brakes are narrow gauge railways in Central Europe, largest

of them is Ferrovia Retica.

Vacuum brakes have been entirely superseded on the National Rail system in the UK,

although they are still in use on most heritage railways. They are also to be found on a

number (though increasingly fewer) main line vintage specials.

C & E has developed the automatic vacuum brake and designed it in its simplest form;

the automatic vacuum brake consists of a continuous pipe -- the train pipe -- running

throughout the length of the train.

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Chapter-11 Engine Control

________________________________________________________________________

11.1 Engine Control Development:

So far we have seen a simple example of diesel engine control but the systems used by

most locomotives in service today are more sophisticated.  To begin with, the drivers

control was combined with the governor and hydraulic control was introduced.  One type

of governor uses oil to control the fuel racks hydraulically and another uses the fuel oil

pumped by a gear pump driven by the engine.  Some governors are also linked to the

turbo charging system to ensure that fuel does not increase before enough turbocharged

air is available.  In the most modern systems, the governor is electronic and is part of a

complete engine management system.

11.2 Power Control:

The diesel engine in a diesel-electric locomotive provides the drive for the main

alternator which, in turn, provides the power required for the traction motors.  We can see

from this therefore, that the power required from the diesel engine is related to the power

required by the motors.  So, if we want more power from the motors, we must get more

current from the alternator so the engine needs to run faster to generate it.   Therefore, to

get the optimum performance from the locomotive, we must link the control of the diesel

engine to the power demands being made on the alternator.

In the days of generators, a complex electro-mechanical system was developed to achieve

the feedback required to regulate engine speed according to generator demand.  The core

of the system was a load regulator, basically a variable resistor which was used to very

the excitation of the generator so that its output matched engine speed.  The control

sequence (simplified) was as follows:

1. Driver moves the power controller to the full power position

2. An air operated piston actuated by the controller moves a lever, which closes a

switch to supply a low voltage to the load regulator motor.

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3. The load regulator motor moves the variable resistor to increase the main generator

field strength and therefore its output.

4. The load on the engine increases so its speed falls and the governor detects the

reduced speed.

5. The governor weights drop and cause the fuel rack servo system to actuate.

6. The fuel rack moves to increase the fuel supplied to the injectors and therefore the

power from the engine.

7. The lever (mentioned in 2 above) is used to reduce the pressure of the governor

spring.

8. When the engine has responded to the new control and governor settings, it and the

generator will be producing more power.

On locomotives with an alternator, the load regulation is done electronically.  Engine

speed is measured like modern speedometers, by counting the frequency of the gear teeth

driven by the engine, in this case, the starter motor gearwheel.  Electrical control of the

fuel injection is another improvement now adopted for modern engines.  Overheating can

be controlled by electronic monitoring of coolant temperature and regulating the engine

power accordingly.  Oil pressure can be monitored and used to regulate the engine power

in a similar way.

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My Activities

I joined my training on_____. I used to observe the working of machines, different manufacturing process, use of gauges and measuring instruments and added a lot to our knowledge. It was my first chance to get knowledge about different machines used for the maintenance of engines.

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