1

OUR VISION

The prime objective of SAEINDIA NIT Kurukshetra Collegiate Club is to

provide a platform to the budding engineers and help them to practically

apply the theoretical knowledge; to bring dynamism in their vision and

thinking; to find solutions to the problem in the existing field of

automobile by connecting the minds of future engineers along with those

pioneering in the industry.

The idea, vision and objectivity of the club and its working can be

uniformly summarized under the club motto –

Dream. Create.

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INDEX

1. Introduction to Automotive……………………………………………………………………………………………..4

1.1 Automotive………………………………………………………………………………………………4

1.2 Automobile………………………………………………………………………………………………4

1.3 Components of an auto mobile………………………………………………………………..4

2. Basic Terminology…………………………………………………………………………………………………………….5

2.1 Vehicle Axis System………………………………………………………………………………….5

2.2 Some Common terms used in automobiles………………………………………………5

3. Chassis………………………………………………………………………………………………………………………………6

3.1 Introduction………………………………………………………………………………………………6

3.2 Types of chassis………………………………………………………………………………………..6

4. Aerodynamic fundamentals……………………………………………………………………………………………..8

4.1 Introduction………………………………………………………………………………………………8

4.2 Aerodynamic forces………………………………………………………………………………….8

4.3 Spoilers…………………………………………………………………………………………………....9

4.4 Automotive Wings…………………………………………………………………………………….9

5. Engine…………………………………………………………………………………………………………………………….10

5.1 Introduction……………………………………………………………………………………………...10

5.2 Steam and Combustion engines………………………………………………………………..10

5.3 Classification of engines…………………………………………………………………………...10

5.4 Basic engine parts……………………………………………………………………………………..12

5.5 Petrol Engine v/s Diesel Engine………………………………………………………………...18

5.6 New Technologies………………………………………………………………………………….….18

6. Transmission……………………………………………………………………………………………………………………20

6.1 Introduction………………………………………………………………………………………………20

6.2 Clutch………………………………………………………………………………………………………..20

6.3 Gear Ratio…………………………………………………………………………………………..…….20

6.4 Manual Transmission…………………………………………………………………………………21

6.5 Continuously Variable Transmission (CVT)…………………………………………………22

6.6 Automatic Transmission…………………………………………………………………………….23

6.7 Differentials………………………………………………………………………………………………24

6.8 Types of Driveline……………………………………………………………………………………..26

7. Steering System ……………………………………………………………………………………………………………….27

7.1 Introduction………………………………………………………………………………………………27

7.2 Types of steering System ………………………………………………………………………...27

7.3 Steering Geometry…………………………………………………………………………………...29

7.4 Four Wheel Steering………………………………………………………………………………….30

7.5 Power Steering………………………………………………………………………………………….30

8. Suspension System…………………………………………………………………………………………………………...32

8.1 Introduction………………………………………………………………………………………………32

8.2 Suspension Geometry……………………………………………………………………………….32

8.3 Types of suspension systems…………………………………………………………………….32

8.4 Macpherson struts vs. Double Wishbone………………………………………………..…33

9. Brakes……………………………………………………………………………………………………………………………….35

9.1 Introduction………………………………………………………………………………………………35

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9.2 Brake Fade……………………………………………………………………………………………..……35

9.3 Types of Brakes………………………………………………………………………………………..….35

9.4 Methods to reduce brake fade…………………………………………………………………....36

9.5 Types of calipers……………………………………………………………………………………..……37

9.6 Hydraulic Brakes……………………………………………………………………………………..……37

9.7 Proportioning valve…………………………………………………………………………………..…38

9.8 Anti-lock Braking System (ABS)……………………………………………………………….…..38

9.9 Types of Brake Fluids……………………………………………………………………………….…..38

9.10 Regenerative Brakes…………………………………………………………………………….….…39

10. Wheel………………………………………………………………………………………………………………………………..40

10.1 Tubeless tyres……………………………………………………………………………………….…..40

10.2 Wheel Alignment………………………………………………………………………………….…...40

10.3 Tire Size notations………………………………………………………………………………...…..42

10.4 The wheel Assmebly………………………………………………………………………………...43

11. Electrical System…………………………………………………………………………………………………………………44

11.1 Ignition System………………………………………………………………………………….…..….44

11.2 Ignition Coil………………………………………………………………………………………………..44

11.3 Distributor………………………………………………………………………………………………...45

11.4 Spark Plug………………………………………………………………………………………………….45

# Appendix ………………………………………………………………………………………………………………………………46

# Common Abbreviations…………………………………………………………………………………………………………..49

# Test Yourself………………………………………………………………………………………………………………………….50

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1. INTRODUCTION TO AUTOMOTIVE

1.1 Automotive: It is a branch of engineering dealing with automobiles or anything automatically

in motion. Automotive engineering includes:

1.Mechanical engineering

2.Vehicle dynamics

3.Engine design

4.Drive train engineering

1.2 Automobile: The word automobile comes, via the French automobile, from the Ancient Greek

word αὐτός (autós, "self") and the Latin mobilis ("movable"); meaning a vehicle that moves itself. A

vehicle moving itself rather than being pulled by an animal or other vehicle which can be used to carry

passengers and goods. Each of these vehicles is operated by engine which consumes gasoline (petrol),

diesel, natural or LPG gas etc.

The first practical automobile with a petrol engine was built by Karl Benz in 1885 in Mannheim, Germany.

Benz was granted a patent for his automobile. After that the automobile became a primary mode of

transportation for all countries. In 1806, Francois Isaac de Rivaz of Switzerland invented an internal

combustion engine that used a mixture of hydrogen and oxygen for fuel. Further developments led to the

introduction of modern gasoline- or petrol- fuelled internal combustion engine in 1885.

1.3 COMPONENTS OF AN AUTOMOBILE

The main units of an automobile

are:

The superstructure or chassis

The power plant or Engine

Transmission system or power

train

Steering system

Suspension system

Brakes

Wheels

Electrical System

Figure 1 - Various components of an automobile

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2. BASIC TERMINOLOGY

2.1 VEHICLE AXES SYSTEM

2.1.1 Longitudinal axis:

The line passing through the front and rear roll

center of the vehicle (vehicle rolls about this line)

represented as X axis.

2.1.2 Lateral axis:

Axis about which vehicle pitches, represented by

Y axis.

2.1.3 Vertical axis: Axis about which vehicle experiences yaw

movement.

2.2 SOME COMMON TERMS USED IN AUTOMOBILES

2.2.1 Wheel base:

Wheel base is the longitudinal distance measured

between contact patches of front to rear wheel.

2.2.2 Track width:

The lateral distance between the contact patches

of left and right wheel is track width of vehicle.

2.2.3 Turning Radius:

It is actually a misnomer as it is the diameter of

the circle of the outside wheels that a car turns

through while turning at full lock.

Figure 2 - Axes of motion of a vehicle

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3. CHASSIS

3.1 INTRODUCTION

Chassis consists of an internal framework that

supports the vehicle body. It is analogous to

skeleton. Following section covers different types

of chassis.

3.2 TYPES OF CHASSIS

3.2.1 Ladder frame chassis Its construction looks like a ladder- two

longitudinal rails inter connected by several lateral

and cross braces. The longitudinal members are

the main stress bearing members. They deal with

static load and also the load transfer during

acceleration and braking. The lateral and cross

members provide resistance to the lateral forces

produced during cornering and further increases

torisional rigidity.

3.2.2 Tubular space frame chassis

As ladder chassis is not strong enough, motor

racing engineers developed a 3 dimensional

design – Tubular space frame. It employs several

circular-section tubes, a square section can also be

used for better connection to body panel, but

circular cross section provides maximum strength

against forces from anywhere. These tubes are

welded together and form a very complex

structure. For high strength required by high

performance sports cars, tubular space frame

chassis usually incorporates a strong structure

under both doors, hence results in a difficult

access to the cabin.

Figure 4 - Tubular frame chassis of a formula SAE car

3.2.3 Monocoque frame chassis

Monocoque is one piece structure which defines

the overall shape of car. While ladder and tubular

space frame provide only stress bearing members

and need to build body around them, monocoque

chassis is already incorporated with the body in

single piece. Actually many pieces are welded

together. The floor-pan which is the largest piece

and other pieces are pressed by big stamping

machines. They are spot welded together within

minutes.

Figure 3 - Ladder frame chassis of a truck

Figure 5 - Monocoque chassis of Lamborghini Aventedor

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3.2.4 Uslab monocoque chassis Pressing sheet metal to make chassis creates

inhomogeneous thickness at the edges hence to

maintain minimum thickness designers have to

choose a thicker sheet metal. By the Hydro form

technique thin steel tubes are used. The steel tubes

are placed in a die which defines the desired

shape, then fluid at very high pressure will be

pumped into the tube, which expands the latter to

the inner surface of die. The thickness of steel

tube remains uniform which results in lighter

design.

3.2.5 Backbone frame chassis

A strong tubular backbone (usually rectangular

section) connects the front and rear axle and

provides all strength required. The whole drive-

train, engine and suspensions are connected to

both the ends of backbone. A body build on the

backbone is usually made of glass fiber. It is

strong enough for the sports car but not up to the

job for high ends ones.

3.2.6 Aluminum space frame chassis It consists of an extruded aluminum section;

vacuum die cast components and

aluminum sheets of different thickness. They are

made of high strength aluminum alloys. At the

highly stressed corners and joints, extruded

section is connected by complex aluminum die

casting. It is very complex and production cost is

far higher than steel monocoque.

3.2.7 Carbon fiber monocoque The carbon fiber called Kevlar offers highest

rigidity-to-weight ratio. Kevlar can be found in

body panels of exotic cars, although most of them

simultaneously use other kind of carbon fiber in

relatively large amount.

Carbon fiber panels are made by growing carbon

fiber sheets on either side of aluminum foil, the

foil which defines the shape of the panel, is

stacked with several layers of carbon fiber sheets

impregnated with resin, then cooked in oven for 3

hours at 120°C and 90 psi pressure. The carbon

fiber layers will be melted and forms uniform

rigid panel.

Figure 7 - Carbon fiber chassis of a Super Sports Car

Figure 6 - Backbone frame chassis of a lotus esprit

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4. AERODYNAMIC FUNDAMENTALS

4.1 INTRODUCTION

Following section covers different types of

aerodynamic forces, and aerodynamic devices

(spoiler etc.) deployed in a vehicle.

4.2 AERODYNAMIC FORCES

It plays a major role in high performance cars

through its contribution to Road Load.

The force due to friction of air interacts with the

moving vehicle and causes drag, lift (or

downward), momentum roll, pitch, yaw and

noise hence decreases fuel economy, handling etc.

The fluid flow follows Bernoulli‘s equation for

automotive aerodynamics

P (static) + P (dynamic) =P (total)

4.2.1 Side force The lateral wind component will impose a side

force on the vehicle, attempting to change the

direction of travel. In case of a strong cross wind

the side force is greater than the drag force, such

that the angle of overall wind force is much

greater than the relative wind angle.

4.2.2 Drag It is the largest and most important aerodynamic

force encountered by a passenger car at normal

highway speed. More than 65% of drag arises

from the body (fore-body, after-body, underbody

and skin friction. After-body is the major

contributor of drag as it contains a

separation zone. Slope angle of 15° consistently

reduces drag.

Figure 8 - Drag forces with (upper) and

without (lower) spoiler

DA = ½ ρ v2

CD A

CD = Aerodynamic drag coefficient

A= Front area of vehicle

ρ= Air density

½ρv2

is the dynamic pressure of air. The Drag

properties of a car are characterized by the value

of product of Coefficient of Drag and Front area

of the vehicle.

4.2.3 Lift

The pressure difference between the top and

bottom of a vehicle causes a lift force. These

forces are significant as they influence driving

stability and handling through reduced control

forces available at tires. Front lift that reduces

steering controllability is reduced by deploying a

front bumper spoiler and by rear ward inclination

of front surface.

Figure 9 - Uplift produced due to air-flow

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The lift at the rear of the vehicle which reduces

traction and stability is variable with vehicle

design. This lift can be reduced by spoilers etc.

4.3 SPOILERS

A spoiler is an automotive aerodynamic device

whose function is to 'spoil' unfavourable air

movement across a body of a vehicle in motion.

Spoilers on the front of a vehicle are called air

dams, because in addition to directing air flow

they also reduce the amount of air flowing

underneath the vehicle which reduces

aerodynamic lift. Spoilers are often fitted to race

and high-performance sports cars, although they

have become common on passenger vehicles as

well. Some spoilers are added to cars primarily for

styling purposes and have either little

aerodynamic benefit or even make the

aerodynamics worse.

Spoilers for cars are often incorrectly confused

with, wings. Automotive wings are devices whose

intended design is to generate down force as air

passes around them, not simply disrupt existing

airflow patterns.

Figure 10 - Spoiler in a Nissan car

The main role of a spoiler in passenger vehicles is

to reduce drag and increase fuel efficiency Front

spoilers, found beneath the bumper, are mainly

used to direct air flow away from the tires to the

under-body where the drag coefficient is less.

Rear spoilers, which modify the transition in

shape between the roof & the rear and the trunk &

the rear, act to minimize the turbulence at the rear

of the vehicle.

4.4 AUTOMOTIVE WING

A wing in this context is an aerodynamic device

intended to generate down force on an automobile.

The angle of attack of the wing on some cars can

be adjusted to increase downward force over the

rear wheels, but drag is also increased.

Spoilers are often confused with wings, and the

terms are frequently (but incorrectly) used

interchangeably. Spoilers reduce the lift created

by a car's shape, and also reduce drag by

eliminating the induced drag associated with that

lift. Wings increase the road grip by producing

down-force, at the expense of additional induced

drag. Although identical in form to the wing of an

aircraft, wings used in automotive applications are

usually inverted (oriented upside-down) and

sometimes reversed (oriented backwards) by

comparison.

DID YOU KNOW?

Nowadays DRS (Drag reduction system) is

used in Formula one races. At certain

stretches in the circuit the driver lagging

behind by 1 second can adjust the rear wing

so as to reduce Drag force and attain

greater speed in the stretch.

Figure 11 - Aerodynamic wing in a motor-sport car

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5. ENGINE

5.1 INTRODUCTION

Engine is a device designed to convert chemical

energy of the fuel into useful mechanical energy.

5.2 EXTERNAL & INTERNAL

COMBUSTION ENGINES: 5.2a STEAM ENGINES

A steam engine is a heat engine that performs

mechanical work using steam as its working fluid.

Steam engines are typically external combustion

engines, where heat is supplied to the working

fluid from fuel burned outside the engine. The

water turns to steam in a boiler and expands

greatly in volume, and can be used to generate

mechanical power, usually via pistons or turbines.

5.2b INTERNAL COMBUSTION

ENGINES

A combustion engine is also a heat engine that

burns fuel containing chemical energy to get heat

energy and then converts this heat energy in to

mechanical energy.

5.3 CLASSIFICATION OF ENGINES

5.3.1 On the basis of Basic Engine

Design They are classified as follows:

• Rotary Engine

• Reciprocating Engine

5.3.1a Rotary engines

In rotary engines, a rotor rotates inside the

engine to produce power. Example: Wankel

engine.

5.3.1.b Reciprocating Engine In the case of the reciprocating engines, a piston

reciprocates within a cylinder. Reciprocating

engines have different layouts or cylinder

configurations including the straight or inline

configuration, the more compact V configuration,

and the wider but smoother flat or boxer

configuration. More unusual configurations such

as the H, U, X, and W have also been used.

Figure 13 - Various configurations of an engine

Figure 12 - A Wenkel engine & its 4-Strokes

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5.3.2 On the basis of Working Cycle They are classified as:

• Two stroke engines

• Four stroke engines

5.3.2a Two stroke engines In the case of the two stroke engine, for every two

strokes of the piston inside the cylinder the fuel is

burnt. This means for every single rotation of the

wheel the fuel is burnt. In the case of four-stroke

engines, the fuel is burnt for every four strokes of

the piston inside the cylinder. That means each

time the fuel is burnt there are two rotations of the

wheels of the vehicle. The stroke is the distance

traveled by the piston inside the cylinder; it is

usually equal to the length of the cylinder.

5.3.2b Four stroke engines Since the 4-stroke engines produce two rotations

while 2-stroke engine produces single rotation

each time the fuel is burnt, the efficiency of 4-

stroke engines is greater than in 2-stroke engines.

Ideally the efficiency of 4-stroke engine should be

double of 2-stroke engine, but in actuality it is

never so.

Almost all cars currently use what is called a

four-stroke combustion cycle to convert gasoline

into motion. As their name implies, operation of

four stroke internal combustion engines have four

basic steps that repeat with every two revolutions

of the engine.

The four-stroke approach is also known as the

Otto cycle, in honour of Nikolaus Otto, who

invented it in 1867. The four strokes are as

follows:

Intake stroke: The piston starts at the top,

the intake valve opens, and the piston moves

down to let the engine take in a cylinder-full of air

and gasoline. This is the intake stroke. Only the

tiniest drop of gasoline needs to be mixed into the

air for this to work

.Compression stroke: Then the piston

moves back up to compress this fuel/air mixture.

Compression makes the explosion more powerful.

Combustion stroke: When the piston

reaches the top of its stroke, the spark plug emits a

spark to ignite the gasoline. The gasoline charge

in the cylinder explodes, driving the piston down.

Exhaust stroke: Once the piston hits the

bottom of its stroke, the exhaust valve opens and

the exhaust leaves the cylinder to go out the

tailpipe

Figure 14 - Working cycle of a 4-Stroke engine

5.3.3 On the basis of Ignition They are classified as:

• Spark ignition

• Compression Engines

5.3.3a Spark ignition In SI engines, the burning of fuel occurs by a

spark generated by the spark plug located in the

cylinder head of engine. Due to this fact they are

called spark ignition engines. In these engines the

fuel used is petrol or gasoline, hence SI engines

are also known as Petrol or Gasoline Engines.

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5.3.3b Compression ignition In the case of CI engines, burning of the fuel

occurs because of the high pressure exerted on the

fuel. The fuel is compressed to high pressures and

it starts burning, hence these engines are called

compression ignition engines. In CI engines the

fuel used is diesel; hence they are also called

Diesel engines.

5.4 BASIC ENGINE PARTS

5.4.1Cylinder head The cylinder head is a casting bolted to the top of

the cylinder block, injector location holes, forms

the upper face of the combustion chamber. The

coolant passages, cavities, intake and exhaust

ports, and the spark plug are also located within

the head casting. The cylinder head is detachable

for easy access to the valves and piston tops and to

facilitate machining of the cylinder bore,

combustion chamber and valve ports. The

materials generally used for the cylinder head are

grey cast iron and aluminum alloys.

5.4.2 Cylinder block

The cylinder block is the portion of the engine

between the cylinder head and sump. All the

engine parts are mounted on it or in it and this

holds the parts in alignment. Large diameter holes

in the block-castings form the cylinder bores

required to guide the pistons. Both spark-ignition

and compression-ignition cylinder blocks are

similar but later blocks are relatively heavier and

stronger to withstand high compression ratios and

internal pressure.

Figure 16 - Cylinder block of a 4-Cylinder engine

Within the cylinder, combustion process produces

rapid and periodic rises in temperature and

pressure. These induce circumferential and

mechanical properties such as strength, toughness,

hardness, and corrosion and wear resistance.

Cylinder liners provide prolonged cylinder life,

which outweighs the extra cost. The liners can be

made from lightly alloyed cast iron. They are

centrifugally cast into the cylindrical sleeve,

machined, the then heat-treated to produce the

optimum wear-resisting properties

5.4.3 Crank case and Crank shaft The crankcase supports the individual main

journals and bearings of the crankshaft and also

DID YOU KNOW?

Bugatti Veyron Super Sport is the fastest car

in production. It features an 8.0L W16

Quad-Turbocharged engine which churns

out 1200 HP and can attain a maximum

speed of 435 kmph.

Figure 15 - Cylinder head of a 4 cylinder engine

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maintains the alignment of the journal axes of

rotation as they are subjected to rotary and

reciprocating inertia forces and the periodic torque

impulses. The crankshaft, which is one of a series

of links between the pistons and the drive wheels,

is a one-piece part located in the bottom end of the

engine that harnesses the huge forces produced by

the explosions in the combustion chamber. The

front end of the crankshaft, known as the snout,

turns the sprocket, or timing gear, to drive the

camshaft, pulley that runs a belt connected to the

alternator, fan, water pump and power steering.

The other end of the crankshaft is connected to the

flywheel, which is toothed, allowing the starter

motor to rotate the crankshaft.

Function

When the spark plugs ignite the fuel-air mixture in

the combustion chamber, the resulting explosion

forces the pistons downward with tremendous

force. The function of the crankshaft is to change

the up-and-down motion of the pistons to a

rotating motion. This is accomplished by having

the connecting rods (which are attached to the

pistons) connect to the crankshaft in an offset

manner, so that as they go up and down their

angle changes.

5.4.4 Cam shaft Its job is to open and close the valves at just the

right time during engine rotation, so that

maximum power and efficient cleanout of exhaust

can be obtained. The camshaft drives the

distributor to electrically synchronize spark

ignition. Camshafts do their work through

eccentric "lobes" that actuate the components of

the valve train. The camshaft itself is forged from

one piece of steel, on which the lobes are ground.

On single-camshaft engines there are twice as

many lobes as there are cylinders, plus a lobe for

fuel pump actuation and a drive gear for the

distributor. The camshaft operates cam followers

that in turn operate the rest of the valve train.

Figure 18 - Camshaft of a 4-Cylinder engine

5.4.5 Rocker shafts and rocker arms

assembly

Rocker arm assembly consists of rocker arm,

rocker shaft and springs. Rocker arm comes in

contact with the valves as directed by the rotation

of the camshaft.

Rocker shaft Rocker-shaft

provides a rigid

pivot support for the

rocker-arms. These

shafts are machined

from hollow steel

tubing. These are

mounted and

clamped on cast-iron

or aluminum alloy pedestals, which are generally

fitted between each pair of rocker-arms. For

Figure 17 - Crank shaft of a 4-Cylinder engine

Figure 19 - A rocker shaft

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lubrication purposes radial holes are drilled

through the rocker-shaft to align with each rocker

arm, and both ends of the shaft are plugged to

prevent the oil leakage. One of the support

pedestals normally incorporates a vertical drilled

hole to supply the oil from the camshaft to the

hollow rocker-shaft. This hole matches with a

corresponding radial hole in the shaft. When

reassembling the rockers and shaft, these two

holes must align, to restore oil supply to the shaft.

The material for these tubular shafts is carbon

steel, a typical composition of which is 0.55%

carbon, 0.2% silicon, 0.65% manganese, and the

balance iron. After machining, the shaft is case-

hardened to withstand the rubbing action.

Rocker-Arm A rocker-arm rocks or oscillates about its pivot

and relays the push-rod up-and- down movement

to the stem of the poppet-valve. Therefore this

arm acts as a rocking beam. Rocker-arms may be

manufactured from materials which can be cast,

forged, or cold-pressed to shape. These are cast

from malleable cast iron with induction-hardening

at selected regions. For forging a medium-carbon

steel with a typical composition of 0.55% carbon,

0.2% silicon, 0.65% manganese, and the balance

(98.6%) iron can be used. This can be hardened by

quenching from a temperature of 1085 K to 1115

K and then tempering at a suitable temperature

between 825 K and 975 K. For cold-pressing a

low-carbon steel of composition 0.2% carbon,

0.8% manganese, and the balance (99%) iron can

be used. Rockers, when manufactured in this

method, incorporate a hardened-steel contact pad

attached at the valve-stem end.

5.4.6 Piston The automotive engine piston converts the

combustion pressure to a force on the crankshaft.

The piston starts, accelerates and stops twice in

each crankshaft revolution. This reciprocating

action of the piston produces large inertial forces.

The inertial force depends on the piston and less

inertia permits higher engine operating speeds.

During operation of the piston, a temperature

gradient of about 150 K from the head of the

piston to its bottom is experienced. Also it has to

support piston sealing rings. Therefore, design of

a piston is based on a compromise between

strength, weight and thermal expansion control.

The piston must have enough strength to support

combustion pressure and reciprocating loads, to

have sufficient length of the skirt to guide the

piston straight in the bore, to have expansion

control for quiet and long-life operation, and to

hold the piston rings perpendicular to the cylinder

wall.

Functions of a piston in brief are:

It must form a sliding gas and oil tight seal

within the cylinder.

It must transmit the gas load to the small end

of the connecting rod.

It generally acts as a bearing for the gudgeon

pin.

Figure 21 - Piston & its parts

Figure 20 - A rocker arm assembly

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The piston material should have properties like

good cast-ability, high hot strength, high strength-

to-mass ratio, good resistance to surface abrasion

to reduce skirt and ring-groove wear, good

thermal conductivity to keep down piston

temperatures, and a relatively low thermal

expansion to have a minimum piston-to-cylinder

clearance. To achieve low reciprocating forces of

the piston in a high speed engine, the piston

should be lighter, and hence aluminum alloy is

preferred to cast iron and steel.

Gudgeon pin The gudgeon-pin (piston pin) connects the piston

and connecting-rod. It is supported in holes bored

in the piston at right angles to the piston axis at

about mid-height position, and the centre portion

of the gudgeon-pin passes through the connecting-

rod small-end eye. This hinged joint transfers

directly the gas thrust from the piston to the

connecting-rod and allows the rod to pivot relative

to the cylinder axis with an oscillating motion.

Figure 22 -Piston and its gudgeon pin

Connecting rod The connecting rod joins the piston to the

crankshaft and transfers piston reciprocating force

to crankshaft rotation. The small end of the

connecting rod reciprocates and the large end

follows the crank pin rotational pattern. For this

dynamic movement, the connecting rod should be

as light as possible while maintain its rigidity. The

connecting rod is basically of two ring forms,

which encircle the piston pin and the crankshaft

rod journal. From each of these ring forms a

tangential fillet blends into a tapered H-section of

the rigid rod strut. Each connecting rod is fastened

to the piston by piston pins and to the crank pin

(journal) of the crankshaft by a plain split bearing.

5.4.7 Valves Train and Valve Timings

The valve train consists of valves, rocker arms,

pushrods, lifters, and the camshaft. Valve train

opening/closing and duration, as well as the

geometry of the valve train, controls the amount

of air and fuel entering the combustion chamber at

any given point in time. Timing for open/ close

duration is controlled by the camshaft that is

synchronized to the crankshaft by a chain or belt.

Valve trains are built in several configurations,

each of which vary slightly in layout but still

perform the task of opening and close the valves

at the time necessary for proper operation of the

engine. These layouts are differentiated by the

location of the camshaft within the engine:

Overhead Camshaft: The camshaft (or

camshafts, depending on the design employed) is

located above the valves within the cylinder head,

and operates either indirectly or directly on the

valves. Cam-in-block: The camshaft is located

within the engine block, and operates directly on

the valves, or indirectly via pushrods and rocker

arms. Because they often require pushrods they

are often called pushrod engines.

Cam less: This layout uses no camshafts at all.

Technologies such as Solenoids are used to

individually actuate the valves.

Intake and Exhaust Valves The valve arrangement in an engine controls the in

and out movements of charge and exhaust gases in

the cylinders in relation to the piston positions in

their bores. Now-a-days, this is located in the

cylinder head on all the engines. Among the

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commonly used sleeve, sliding, rotary, and poppet

type valves, the poppet-valve is most common

because this offers reasonable weight, good

strength and good heat transfer characteristics.

The most popular shape of the poppet-valve for

automobile application uses a small cup at one end

of the stem. The valve stem is placed in a guide

hole made centrally in a circular passage in the

cylinder head. The valve disc head opens and

closes the ported passage leading to the cylinder

during in and out movement of the stem.

To see how valve-timing works in a 4-stroke

engine cycle, let‘s show piston motion as a circle.

In this simple cycle, each stroke is shown as a

semi-circle. Theoretically speaking the intake

valve opens at top dead centre, and closes at

bottom dead centre and the exhaust valve opens at

bottom dead centre, then closes at top dead centre

before the new air-fuel mixture enters the

cylinder.

In practice, however, the intake valve usually

opens earlier than top dead centre, and stays open

a little past bottom dead centre. The exhaust valve

opens a little before bottom dead centre, and stays

open a little past top dead centre.

This intake valve opens 16° before the piston

reaches top dead centre and it closes 55° after

bottom dead centre.

The exhaust valve opens 55° before bottom

dead centre - and stays open - until 16° past

top dead centre. This gives exhaust gases more

time to leave.

By the time the piston is at 55° before bottom

dead centre on the power stroke, combustion

pressures have dropped considerably and little

power is lost by letting the exhaust gases have

more time to exit. letting the exhaust gases

have more time to exit.

When an intake valve opens before top dead

center and the exhaust valve opens before

bottom dead center, it is called lead.

When an intake valve closes after bottom

dead center, and the exhaust valve closes after

top dead center, it is called lag.

On the exhaust stroke, the intake and exhaust

valve are open at the same time for a few

degrees around top dead center. This is called

valve overlap. On this engine, it is 32°.

Different engines use different timings.

Manufacturer specifications contain the exact

information.

5.4.8 Sump or oil pan The sump is attached to the bottom of the cylinder

block underneath the crankcase. The functions of

the sump are:

To store the engine's lubrication oil for

circulation within the lubrication system.

DID YOU KNOW?

Due to physical time lag there is a limit to

which the valve springs can work up to.

To overcome this Ducati made a new

kind of valves that can run up to 18,000

RPM. The valves have separate opening

and closing lobes and are called as

‘Desmodromic Valves’

Figure 23 -Intake and exhaust valve

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To collect the oil draining from the sides of

the crankcase walls and if ejected directly

from the journal bearings.

To provide a centralized storage area for any

contaminants like liquid fuel, water,

combustion products blown past the piston

ring, and worn metal particles.

To provide a short recovery period for the hot

churned-up and possibly aerated oil before it is

re-circulated in the lubrication system.

To provide some inter-cooling between the hot

oil inside and the air steam outside.

Figure 24 -Oil Sump of an engine

The sump may be made from a single sheet-steel

pressing or it may be an aluminum-alloy casting

with cooling fins and strengthening ribs. A soft

flexible gasket is used in between to seal the joint

and is tightened down by set-screws. The sump

generally has a shallow downward slope at one

end, which changes into a relatively deep but

narrow-walled reservoir at the other end.

The incoming oil flows towards the deep end,

where it submerges the pick-up pipe and strainer

of the lubricating system. A drain plug is located

at the lowest level in the sump for easy drainage

of used oil.

5.4.9 Flywheel

The flywheel mounts at the rear of the crankshaft

near the rear main bearing. This is usually the

longest and heaviest main bearing in the engine,

as it must support the weight of the flywheel. The

flywheel stores up rotation energy during the

power impulses of the engine. It releases this

energy between power impulses, thus assuring

less fluctuation in engine speed and smoother

engine operation. The size of the flywheel will

vary with the number of cylinders and the general

construction of the engine. With the large number

of cylinders and the consequent overlapping of

power impulses, there is less need for a flywheel;

consequently, the flywheel can be relatively small.

The flywheel rim carries a ring gear, either

integral with or shrunk on the flywheel, that

meshes with the starter driving gear for cranking

the engine. The rear face of the flywheel is usually

machined and ground and acts as one of the

pressure surfaces for the clutch, becoming a part

of the clutch assembly. The functions of a

flywheel are the following:

It stores up energy to help the engine over idle

strokes of the piston i.e., suction, compression

and exhaust.

It dampens out speed fluctuations of the

crankshaft due to the varying effect of the

firing impulses during the engine cycle.

It provides a convenient mounting point for

the clutch and starter ring gear.

5.4.10 Carburetor A carburetor is a device that blends air and fuel

for an internal combustion engine. Carburetors

were the usual fuel delivery method for almost all

engines up until the mid-1980s, when fuel

injection became the preferred method of

automotive fuel delivery. The carburetor works on

Bernoulli's principle: the faster air moves, the

DID YOU KNOW?

The top speed ever achieved by a formula

one car during a race was 369.9 km/h

(229.8 mph) set during the 2004 Italian

Grand Prix at Monza, Italy by driver

Antônio Pizzonia of the BMW Williams F1

team driving the FW26 powered by a

BMW 3.0L V10.

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lower its static pressure, and the higher its

dynamic pressure. The throttle (accelerator)

linkage does not directly control the flow of liquid

fuel. Instead, it actuates carburetor mechanisms

which meter the flow of air being pulled into the

engine.

Figure 25 -Basic functioning of a carburetor

A carburetor basically consists of an open pipe, a

"throat" or "barrel" through which the air passes

into the inlet manifold of the engine. The pipe is

in the form of a venturi it narrows in section and

then widens again, causing the airflow to increase

in speed in the narrowest part. Below the venturi

is a butterfly valve called the throttle valve - a

rotating disc that can be turned end-on to the

airflow, so as to hardly restrict the flow at all, or

can be rotated so that it (almost) completely

blocks the flow of air. This valve controls the flow

of air through the carburetor throat and thus the

quantity of air/fuel mixture the system will

deliver, thereby regulating engine power and

speed. The throttle is connected, usually through a

cable or a mechanical linkage of rods and joints or

rarely by pneumatic link, to the accelerator pedal

on a car or the equivalent control on other vehicles

or equipment.

5.5 PETROL ENGINE v/s DIESEL ENGINE

5.5.1 EXPANSION STROKE: 1. In petrol engine, the air and fuel mixture is

ignited using a spark plug and burns expanding

and forcing the piston down.

2. In diesel engine, fuel is injected at a high

pressure into the hot, compressed air in the

cylinder, causing it to burn and force the piston

down. No spark is required.

5.5.2EXHAUST STROKE: In both petrol and diesel engines, the burned

mixture of air and fuel is pushed out of the

cylinder by the rising piston.

5.5.4 LIFE:

Petrol destroys lubrication and burns the engine

whereas diesel doesn‘t. So a diesel engine would

last longer than a petrol engine.

5.5.5WEIGHT: Petrol engines are lighter than diesel engines.

5.5.6LOAD CARRYING CAPACITY: Diesel engine would pull heavy loads easily than

a petrol engine. Though the pickup of a petrol

engine would be much more than that of a diesel

engine, the diesel engine would be steady and

carry heavier loads to longer distances.

5.5.7FUEL EFFICIENCY: Diesel engines have better fuel efficiency as

compared to petrol due to the fact that they have

higher compression ratio.

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5.6 NEW TECHNOLOGIES: Multi-Point Fuel Injection:

Multi-point fuel injection injects fuel into the

intake ports just upstream of each cylinder's intake

valve, rather than at a central point within an

intake manifold. MPFI (or just MPI) systems can

be sequential, in which injection is timed to

coincide with each cylinder's intake stroke;

batched, in which fuel is injected to the cylinders

in groups, without precise synchronization to any

particular cylinder's intake stroke; or

simultaneous, in which fuel is injected at the same

time to all the cylinders. The intake is only

slightly wet, and typical fuel pressure runs

between 40-60 psi.

Common Rail Direct Injection:

Figure 26 -Circuit diagram of a CRDI system

Common rail direct fuel injection is a modern

variant of direct fuel injection system for petrol

and diesel engines.

The fuel is pumped into a common rail using a

fuel pump and then injected directly into the

combustion chamber using high pressure injectors.

On diesel engines, it features a high-pressure (over

1,000 bar/15,000 psi) fuel rail feeding individual

solenoid valves, as opposed to low-pressure fuel

pump feeding unit injectors (Pumpe/Düse or

pump nozzles).

Turbo charging:

Figure 27 -A Centrifugal Turbocharger

A diesel engine is more easily turbocharged than a

petrol engine. A petrol engine cannot be easily

turbocharged due to the fact that if the

compression ratio and the pressure in the cylinder

is to high during the inlet stroke, the mixture starts

to burn to soon, while the piston is on its way up.

The diesel engine has no fuel in the cylinder, thus

letting the turbocharger suck as much air as it can

without creating any problems. (A turbo charger is

a simple air compressor which compresses air in

the combustion chamber for burning). Some diesel

engines also have an intercooler which helps in

blowing cold and oxygen rich air in the

combustion chamber.

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6. TRANSMISSION

6.1 INTRODUCTION

As the term indicates it refers to the transfer of

power. It refers to an entire assembly that

transmits power developed in an engine to the

wheels of a vehicle. The power may be

transmitted using a belt drive, chain and sprocket

system or a gear drive. This assembly includes a

clutch, gearbox (manual, automatic, cvt), propeller

shaft, differential, final drive shafts etc.

6.2 CLUTCH

A clutch is what enables you to change gears, and

sit at traffic lights without stopping the engine.

You need a clutch because your engine is running

all the time which means the crank is spinning all

the time. You need some way to disconnect this

constantly-spinning crank from the gearbox, both

to allow you to stand still as well as to allow you

to change gears. The clutch is composed of three

basic elements; the flywheel, the pressure plate

and the clutch plate(s). The flywheel is attached to

the end of the main crank and the clutch plates are

attached to the gearbox layshaft using a spline.

In the diagram here, the clutch cover is bolted to

the flywheel so it turns with the flywheel. The

diaphragm springs are connected to the inside of

the clutch cover with a bolt/pivot arrangement that

allows them to pivot about the attachment bolt.

The ends of the diaphragm springs are hooked

under the lip of the pressure plate. So as the

engine turns, the flywheel, clutch cover,

diaphragm springs and pressure plate are all

spinning together.

The clutch pedal is connected either mechanically

or hydraulically to a fork mechanism which loops

around the throw-out bearing. When you press the

clutch pedal, the fork pushes on the throw-out

bearing and it slides along the layshaft putting

pressure on the innermost edges of the diaphragm

springs. These in turn pivot on their pivot points

against the inside of the clutch cover, pulling the

pressure plate away from the back of the clutch

plates. This release of pressure allows the clutch

plates to disengage from the flywheel. The

flywheel keeps spinning at the end of the engine

crank but it no longer drives the gearbox because

the clutch plates aren't pressed up against it. As

you start to release the clutch pedal, pressure is

released on the throw-out bearing and the

diaphragm springs begin to push the pressure plate

back against the back of the clutch plates, in turn

pushing them against the flywheel again. Springs

inside the clutch plate absorb the initial shock of

the clutch touching the flywheel and as you take

your foot off the clutch pedal completely, the

clutch is firmly pressed against it. The friction

material on the clutch plate is what grips the back

of the flywheel and causes the input shaft of the

gearbox to spin at the same speed.

6.3 GEAR RATIO Gear ratio is defined as the ratio of the speed of

the input shaft to that of the output shaft. It is

calculated as the ratio of the number of teeth on

the output gear to the number of teeth on the input

gear. For example, imagine an input gear with 10

teeth, a secondary gear with 20 teeth and a final

gear with 30 teeth. From the input gear to the

secondary gear, the ratio is 20/10 = 2:1. From the

second gear to the final gear, the ratio is 30/20 = Figure 28 -Components of a diaphragm spring clutch

21

1.5:1. The total gear ratio for this system is

(2*1.5):1, or 3:1. i.e. to turn the output gear once,

the input gear has to turn three times.

This also neatly shows how you can do the

calculation and misses the middle gear ratios -

ultimately you need the ratio of input to output. In

this example, the final output is 30 and the

original input is 10. 30/10 = 3/1 = 3:1.

Figure 29 -Figure depicting gear ratios

6.4 MANUAL TRANSMISSION

6.4.1 Constant Mesh type Gearbox

You can see the helical gears meshing with each

other. The lower shaft in this image is called the

lay-shaft - it's the one connected to the clutch - the

one driven directly by the engine. The output shaft

is the upper shaft in this image. Well look at the

output shaft. You can see 5 helical gears and 3

sets of selector forks. At the most basic level, it

tells you that this is a 5-speed box (note that

example has no reverse gear). With the clutch

engaged, the lay shaft is always turning. All the

helical gears on the lay shaft are permanently

attached to it so they all turn at the same rate.

They mesh with a series of gears on the output

shaft that are mounted on

slip rings so they actually spin around the output

shaft without turning it. Look closely at the

selector forks; you'll see they are slipped around a

series of collars with teeth on the inside. Those are

the dog gears and the teeth are the dog teeth. The

dog gears are mounted to the output shaft on a

splined section which allows them to slide back

and forth. When you move the gear stick, a series

of mechanical pushrod connections move the

various selector forks, sliding the dog gears back

and forth.

Observing the close-up of the area between third

and fourth gear, when the gearstick is moved to

select fourth gear, the selector fork slides

backwards. This slides the dog gear backwards on

the splined shaft and the dog teeth engage with the

teeth on the front of the helical fourth gear. This

locks it to the dog gear which itself is locked to

the output shaft with the splines. When the clutch

is let out and the engine drives the lay shaft, all the

gears turn as before but now the second helical

gear is locked to the output shaft and- fourth gear.

Figure 30 - A Constant mesh gearbox

Figure 31 - Gear selection in a constant mesh gearbox

22

6.4.2 Reverse Gear Reverse gear is normally an extension of

everything explained above but with one extra

gear involved. Typically, there will be three gears

that mesh together at one point in the gearbox

instead of the customary two. There will be a gear

each on the lay-shaft and output shaft, but there

will be a small gear in between them called the

idler gear. The inclusion of this extra mini gear

causes the last helical gear on the output shaft to

spin in the opposite direction to all the others. The

principle of engaging reverse is the same as for

any other gear - a dog gear is slid into place with a

selector fork. Because the reverse gear is spinning

in the opposite direction, when you let the clutch

out, the gearbox output shaft spins the other way -

in reverse. The image the shows the same gearbox

as above modified to have a reverse gear.

Figure 32 - Idler gear being used to reverse direction of

motion

6.4.3 Synchromesh A synchro is a device that allows the dog gear to

come to a speed matching the helical gear before

the dog teeth attempt to engage.

In this way, you don't need to 'blip' the throttle and

double-clutch to change gears because the synchro

does the job of matching the speeds of the various

gearbox components for you. To the left is a

colour-coded cutaway part of my example

gearbox. The green cone-shaped area is the

synchro collar. It's attached to the red dog gear

and slides with it.

As it approaches the helical gear, it makes friction

contact with the conical hole. The more contact it

makes, the more the speed of the output shaft and

free-spinning helical gear are equalized before the

teeth engage. If the car is moving, the output shaft

is always turning (because ultimately it is

connected to the wheels). The lay-shaft is usually

connected to the engine, but it is free-spinning

once the clutch has been operated. Because the

gears are meshed all the time, the synchro brings

the lay-shaft to the right speed for the dog gear to

mesh. This means that the lay-shaft is now

spinning at a different speed to the engine, but

that's OK because the clutch gently equalizes the

speed of the engine and the lay-shaft, either

bringing the engine to the same speed as the lay-

shaft or vice versa depending on engine torque

and vehicle speed.

Figure 33 - Cone Shaped synchro collars

6.5 Continuously Variable Transmission (CVT)

Figure 34 - CVT at high speed

23

The most basic CVT has two variable pulleys and

either a steel-core rubber pull-belt or a steel alloy

push-belt. One pulley is connected to the flywheel

and the other to the gearbox output shaft. The belt

loops around between the two. On simple scooter-

type CVTs, the pulleys change geometry simply

by rotational forces - the faster the engine pulley

spins, the more it closes up and the faster the

output pulley spins, the more it opens out. In

automotive applications, the geometry of the

pulley is governed by a hydraulic piston

connected to the ECU (Electronic Control Unit).

The pulley itself is basically a splined shaft with a

pair of sliding conical wedges on it

(called 'Sheaves'). The closer the wedges are

together, the larger the radius 'loop' the belt has to

make to get around them. The further they are

apart, the smaller the radius 'loop' the belt has to

make. Based on the principles of intermeshing

gears, if the flywheel pulley has a small radius and

the output pulley has a large radius, then the

transmission is essentially in low gear. As the car

gets up to speed, the two pulleys are adjusted

together so that they present an infinitely changing

series of radii to the belt which ends up with the

flywheel pulley having the largest radius and the

output pulley having the smallest.

The first image shows the basic layout of a pulley-

based CVT with the two sliding pulleys and the

drive belt. This is the equivalent of 'low gear' - the

drive pulley spins two or three times for each

rotation of the output pulley. It's the equivalent of

a small gear meshing with a large gear in a regular

manual gearbox. The second image shows the

same system in 'high gear'. The drive pulley has

closed up forcing the drive belt to travel a larger

radius. At the same time, the output pulley has

pulled apart giving a smaller radius. The result is

that for each turn of the drive pulley, the output

pulley now spins two or three times. It's the

equivalent of a large gear meshing with a small

gear in a regular manual gearbox. The difference

here is that to get from the low gear to the high

gear, the infinite adjustment of the position of the

pulleys basically means an infinite number of

gears ratios in between.

6.6 AUTOMATIC TRANSMISSION

Automatic gearboxes are totally different from

manual gearboxes. First of all they don‘t have any

clutch pedal or u can say they don‘t have any

clutch at all. Instead of clutch they use torque

converter. In automatic gearboxes apart from

torque converter they have a planetary gear set. In

an automatic gearbox the planetary gearbox

produces all the different gear ratios in one go and

with only one set of gears.

A planetary gear set has three components-

1. The sun gear

2. The planet gears

3. The ring gear

DID YOU KNOW?

Most of the innovations come from

Formula 1. One of them being the Dog

Box transmission with fewer, larger and

straighter teeth. A strain gauge sends a

signal to the ECU to stop the ignition

which in turn unloads power long enough

for a super quick shift.

Figure 35 - CVT at low speed

24

They are arranged like a solar system. You can

imagine the sun gear being in the centre

surrounded by the planetary gears

and then the whole assembly (the sun gear and the

planetary gears) is contained in the ring gear. In

other words, the sun gear is in the centre and with

it the planetary gears are meshed n at the same

time the planetary gears are meshed with the inner

side of the ring gear. In planetary gearset we can

have the gear ratio by locking one of the gear from

the above three components and using the other

two as input and output gears.

In the simplest planetary gear system we can have

three gear ratio i.e. two for forward and one for

reverse.

But in the compound planetary system there are

two sun gears and two sets of intermeshing planet

gears but it still contain one ring gear which

contained the whole assembly inside in it. In this

system we can now have four forward gear ratio

and one reverse gear. In the arrangement shown

we have two sets of planet gears that are arranged

as inner and outer planets and the inner one are

shorter and only engage the smaller sun gear and

the outer planet gears. And then the outer planet

gear in turn rotates the larger sun gear at the

bottom and the outermost ring gear.

6.7 DIFFERENTIALS

The differential is a device that or a gear assembly

between two shafts that permits the shafts to turn

at different speeds (if necessary) while continuing

to transmit torque. It is used in axles to allow

different rates of wheel rotation on curves. They

are classified as follows.

6.7.1 Open Differentials

Open differentials are most commonly used and

they supply the same amount of torque to each

output. Open differentials have a few essential

components, illustrated below. The input pinion

gear is the gear that is driven from the drive-train -

typically the output shaft from the transmission. It

drives the ring gear which, being larger, is what

gives that final gear reduction. Attached to the

ring gear is the cage, containing two captive

pinion gears that are intermeshed with the two

output pinion gears, one connected to each axle.

The captive pinions are free to rotate how they

wish. As the input pinion spins, it meshes with the

ring gear. The ring gear spins, spinning the cage

and the two captive pinions.

When the vehicle is travelling in a straight line,

neither drive pinion is trying to spin any

differently from the other, so the captive pinions

Input Output Locked gears Caluclation

Sun Planet Carrier Ring 1+(Ring/Sun)

Planet Carrier Ring Sun 1/((1+(Ring/Sun))

Sun Ring Planet Carrier Ring/Sun

Figure 36 - Sun and Planet gears arrangement in an

automatic transmission Figure 37 - An Open differential

25

don't spin and the turning of the ring gear is

translated directly to both drive pinions.

These are connected to the drive-shafts to the

wheels so effectively that the ring gear spins the

wheels at the same speed that it is turning. When

the vehicle starts to turn a corner, one of the

wheels spins more quickly than the other. At this

point, the captive pinions come into play, allowing

the two drive pinions to spin at slightly different

speeds whilst still transmitting torque to them.

One can check whether a vehicle's differential is

working properly by jacking the driven axle up off

the ground and spinning one wheel. Now gearbox

is stationary, it holds the ring gear solid, the

captive pinions spin in opposite directions, and the

other wheel on the axle spins the other way

around. This also explains why a two-wheel-drive

vehicle can get into trouble when one wheel has

less friction with the ground than the other. The

open differential cannot compensate for this. If

one drive pinion is held solid compared to the

other, then all the input gets redirected to the drive

pinion that has the least resistance. This is why

when you gun a two-wheel-drive car with one

wheel on ice and the other on the road, the wheel

on the ice spins and the wheel on the road doesn't.

The vehicle doesn‘t go anywhere because all the

engine power is directed to the wheel with least

resistance - the one on the ice. Imagine the same

scenario on a four-wheel-drive vehicle that has

open differentials on the front and rear. If you're

off-roading in such a vehicle and get it into a

situation where one front wheel and one rear

wheel are off the ground, you're stuck. This is

where the limited slip differentials are of great

help.

6.7.2 Limited slip Differentials Sometimes known by "positraction" moniker, the

simplest form of limited-slip differential is

designed to combat the scenario outlined above.

Physically there's not a lot of difference in the

design of a limited-slip differential and an open

differential. It still has all the components of an

open differential but there are two crucial extra

elements. The first are spring pressure plates

which are a pair of springs and pressure plates

nestled in the cage between the two drive pinions.

These push the drive pinions outwards where the

second extra element comes into play - clutch

packs. The backside of the drive pinions have

friction material on them which presses against

clutch plates built into the cage. This means that

the clutch is always going to try to behave as if the

car was moving in a straight line by attempting to

make both output pinions spin at the same speed

as the ring gear and cage. However, when a car

with a limited-slip differential goes into a corner,

there are enough forces at play that the drive

Pinions begin to slip against the clutch material,

thus allowing them to turn at different speeds

again. The stiffness of the spring pack coupled

with the friction of the clutch pack together

determines the amount of torque required to

overcome the clutch. So let‘s go back to our

hapless driver stuck with one wheel on the ice and

another on the road.

With a limited-slip differential, because of the

spring- and clutch-packs, even though one wheel

is on the ice, the differential is going to attempt to

spin both drive pinions at the same speed. With

low engine revs and steady throttle control, the

wheel on the road will get enough spin to move

the vehicle forwards. If the engine is revved hard

though, it can still generate sufficient torque to

Figure 38 - A Limited slip differential

26

overcome the clutch pack and once again, only the

wheel on the ice will spin. To get around this, it's

a good idea to try to pull away in second gear -

that gives the limited-slip differential a chance to

do its job. The render here shows the generic open

differential from above modified to be a limited-

slip differential.

6.8 TYPES OF DRIVELINE

6.8.1 2-Wheel Drive This is by far the most common type of drive-train

in any car today. The engine drives the gearbox

which sends its output to an open differential

either on the front or rear axle, which in turn

drives those wheels. If one of the driven wheels

comes off the ground, or gets on a slippery surface

like ice, the car gets stuck because all the torque is

being sent to that wheel whilst the other three sit

there helpless. (Refer appendix 1, 2).

6.8.2 4-Wheel Drive A vehicle with a four wheel drive (4WD) has a

drive train that can send power to all the four

wheels. This provides maximum traction for off-

roading. It also provides maximum traction when

the road surface is slippery or covered with ice or

with snow. Some vehicles have a four wheel drive

system that that engages automatically or remains

engaged all the time. Other vehicles have a

selective arrangement that permits the driver to

shift from 4WD to 2WD and back according to

driving conditions. (Refer appendix-3).

6.2.3 All Wheel Drive Some passenger vehicles have an all wheel drive

system. This is a version of 4WD used in vehicles

primarily for on road use. It provides improved

traction primarily on slippery or snow covered

surfaces. A two speed transfer case is not used.

When the wheels on one axle slip the system

automatically transmits power to that axle which

has better traction. The engine drives the gearbox

which drives two output shafts. One goes to the

front open differential and the other goes to the

viscous coupling, the output of which is connected

to the rear open differential.

DID YOU KNOW?

A Dual Clutch Transmission takes less than

10 milliseconds to shift between gears,

which is less than time taken by one

revolution of the crankshaft.

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7. STEERING SYSTEM

7.1 INTRODUCTION

The main purpose of the steering system is to

provide the directional control to a vehicle. Most

of the steering systems are made up of the

following components

Steering wheel

Steering column-that connects the steering

wheel to the track rod

Tie rods, connected to the track rod

Steering arm, connected to the tie rods

The track rod, tie rod and the steering arm are

connected to each other by ball and socket joints

respectively.

7.2 TYPES OF STEERING SYSTEM

The different types of steering systems are:

Pitman arm type steering system

Rack and pinion type steering system

7.2.1 Pitman Arm Type Steering

System A pitman arm type of steering system involves the

use of a ‗steering gearbox‘ that is connected to the

steering wheel by the steering column at its one

end and at its other end it is connected to the track

rod via a pitman arm and other relay linkages,

which is further connected to the tie rods. The

track rod is supported in its place by idler arms.

This type of steering system is generally used in

heavy duty vehicles, eg: trucks, busses etc.

The steering gearboxes are further classified into

the following:

7.2.2 Worm and sector

In this type of steering box, the end of the shaft

from the steering wheel has a worm gear attached

to it. It meshes directly with a sector gear (so

called because it's a section of a full gear wheel).

When the steering wheel is turned, the shaft turns

the worm gear, and the sector gear pivots around

its axis as its teeth are moved along the worm

gear. The sector gear is mounted on the cross shaft

which passes through the steering box and out the

bottom where it is splined, and the pitman arm is

attached to the splines. When the sector gear turns,

it turns the cross shaft, which turns the pitman

arm, giving the output motion that is fed into the

mechanical linkage on the track rod.

7.2.3 Worm and roller

The worm and roller steering box is similar in

design to the worm and sector box. The difference

Figure 39 - Worm and Sector steering system

Figure 40 - Worm and Roller steering system

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here is that instead of having a sector gear that

meshes with the worm gear, there is a roller

instead. The roller is mounted on a roller bearing

shaft and is held captive on the end of the cross

shaft. As the worm gear turns, the roller is forced

to move along it but because it is held captive on

the cross shaft, it twists the cross shaft.

Typically in these designs, the worm gear is

actually an hourglass shape so that it is wider at

the ends. Without the hourglass shape, the roller

might disengage from it at the extents of its travel.

7.2.4 Re-circulating ball This is by far the most common type of steering

box for pitman arm systems. In a re-circulating

ball steering box, the worm drive has many more

turns on it with a finer pitch.

A box or nut is clamped over the worm drive that

contains dozens of ball bearings. These loop

around the worm drive and then out into a re-

circulating channel within the nut where they are

fed back into the worm drive again. As the

steering wheel is turned, the worm-drive turns and

forces the ball bearings to press against the

channel inside the nut. This forces the nut to move

along the worm drive. The nut itself has a couple

of gear teeth cast into the outside of it and these

mesh with the teeth on a sector gear which is

attached to the cross shaft just like in the worm

and sector mechanism.

7.2.5 Cam and lever

These are very similar to worm and sector

steering boxes. The worm drive is known as a cam

and has a much shallower pitch and the sector

gear is replaced with two studs that sit in the cam

channels. As the worm gear is turned, the studs

slide along the cam channels which forces the

cross shaft to rotate, turning the pitman arm.

One of the design features of this style is that it

turns the cross shaft 90° to the normal so it exits

through the side of the steering box instead of the

bottom.

7.2.6 Rack And Pinion Type Steering

System It consists of a steering column, connected to a

pinion gear, connected to a rack rod, which is

further connected to tie rods in its both sides via

ball and socket joints. The rotational movement of

the steering wheel and hence the pinion gear is

converted to linear motion by the rack rod which

is a linear gear.

Figure 41 - Re-Circulating balls steering system Figure 42 - Cam and Lever steering system

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The main advantage of this type of steering

system is that it has a better feedback and direct

steering feel, but the disadvantage is that it is not

adjustable, so that when it wears out and develops

lash, the only cure is replacement.

7.3 STEERING GEOMETRY

All the steering systems used in passenger cars use

ACKERMANN GEOMETRY; this prevents the

slipping of tires. In this type of geometry the

wheels pivot about a common point while turning.

It is a trapezoidal geometry. A simple

approximation to perfect Ackermann steering

geometry may be generated by moving the

steering pivot points inward so as to lie on a line

drawn between the steering arm and the centre of

the rear axle.

Steering Ratio: It is defined as the ratio of the angle turned by the

steering wheel to the angle turned by the wheels

on the ground. For example: if the steering ratio of

any car is 20:1, it means that if you turn the

steering wheel 20° and the front wheels only turn

1°. The lock to lock angle of the steering wheel is

the twice of the product of steering ratio and the

lock angle of front wheels. For example: if the

steering ratio is 22 and the average lock angle of

the front wheels is 25deg, then the lock to lock

angle of the steering wheel is 1100 deg and the

steering wheel will undergo approximately 3 full

rotations.

DID YOU KNOW?

Ackerman geometry was not invented by

Ackerman. It was invented by the

German carriage builder Georg

Lankensperger in Munich in 1817, and

then patented by his agent in England,

Rudolph Ackermann (1764–1834) in 1818

for horse drawn carriages. Erasmus

Darwin may have a prior claim as the

inventor dating from 1758.

Figure 43 - Rack and Pinion steering system

Figure 44 - Ackerman steering geometry

Figure 45 - Different steering angles in inner and outer

wheels

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7.4 FOUR WHEEL STEERING

Four-wheel steering (or all wheel steering) is a

system employed by some vehicles to improve

steering response, increase vehicle stability while

maneuvering at high speed, or to decrease turning

radius at low speed. It is of two types:

7.4.1 Passive Four Wheel Steering

System:

Many modern vehicles offer a form of passive rear

steering to counteract normal vehicle tendencies.

For example: to correct for the rear wheel's

tendency to toe-out. On many vehicles, when

cornering, the rear wheels tend to steer slightly to

the outside of a turn, which can reduce stability.

The passive steering system uses the lateral forces

generated in a turn (through suspension geometry)

and the bushings to correct this tendency and steer

the wheels slightly to the inside of the corner. This

improves the stability of the car, through the turn.

This effect is called compliance under steer and it,

or its opposite, is present on all suspensions.

Typical methods of achieving compliance under

steer are to use a Watt's Link on a live rear axle, or

a pan hard rod at the rear axle.

7.4.2 Active Four Wheel Steering

System:

In most active four-wheel steering systems, the

rear wheels are steered by a computer and

actuators. The rear wheels generally cannot turn as

far as the front wheels. In active four wheel

steering system the rear wheels turn in a direction

opposite to that of the front wheels to reduce the

turning radius, sometimes critical for large or

vehicles with trailers.. Whereas, at high speeds the

rear wheels turn in the same direction as the front

wheels in order to improve the traction and

maneuverability and prevent under steer.

7.5 POWER STEERING

As vehicles have become heavier and switched to

front wheel drive, the effort to turn the steering

wheel manually has increased - often to the point

where major physical exertion is required. To

alleviate this, power steering system has

developed. There are two types of power steering

systems:

7.5.1Hydraulic Power Steering (HPS):

It uses hydraulic pressure supplied by an engine-

driven pump to assist the motion of turning the

steering wheel. Most power steering systems work

by using a hydraulic system to steer the vehicle's

wheels. The hydraulic pressure typically comes

from a gyrator or rotary vane pump driven by the

vehicle's engine. A double-acting hydraulic

DID YOU KNOW?

The Steering wheel of a F1 Car costs about

$50,000. It is made up of carbon fiber and

has more than 15 mounted controls.

Figure 46 - A watt's link

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cylinder applies a force to the steering gear, which

in turn steers the road wheels. The steering wheel

operates valves to control flow to the cylinder.

The more torque the driver applies to the steering

wheel and column, the more fluid the valves allow

through to the cylinder, and so the more force is

applied to steer the wheels. Since the hydraulic

pumps are positive-displacement type, the flow

rate they deliver is directly proportional to the

speed of the engine. This means that at high

engine speeds the steering would naturally operate

faster than at low engine speeds. Because this

would be undesirable, a restricting orifice and

flow-control valve direct some of the pump's

output back to the hydraulic reservoir at high

engine speeds. A pressure relief valve prevents a

dangerous build-up of pressure when the hydraulic

cylinders piston reaches the end of its stroke.

7.5.2 Electric/electronic power

steering (EPS):

It is more efficient than the hydraulic power

steering, since the electric power steering motor

only needs to provide assistance when the steering

wheel is turned, whereas the hydraulic pump must

run constantly. In EPS the assist level is easily

tuneable to the vehicle type, road speed, and even

driver preference. An added benefit is the

elimination of environmental hazard posed by

leakage and disposal of hydraulic power steering

fluid.

DID YOU KNOW?

Audi’s electromechanical steering,

electronic control motor only consumes

energy when steering actions are actually

being performed. Sensors detect steering

torque and speed at which driver is

turning & transfer this information to the

ECU. This leads to a fuel saving of about

0.2L per 100 km.

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8. SUSPENSION SYSTEM

8.1 INTRODUCTION

The following topic covers suspension geometry,

types of suspension system.

8.2 SUSPENSION GEOMETRY

The suspension system deals with how the sprung

mass of the vehicle is connected to the un-sprung

mass.

These connections:

1. Control forces transmitted among them.

2. Provide wheel travel so that the wheel can

follow uneven road surface.

3. Keep wheel in proper alignment (caster,

camber, etc.)

5. Control forces produced during roll, pitch and

yaw.

6. Maintain proper traction in the wheels.

8.3 TYPES OF SUSPENSION SYSTEM

8.3.1 Dependent suspension system Wheels are mounted on a rigid beam so any

movement of one wheel is transmitted to the other

and produces roll or bump steer and camber

change. Used in rear suspension of cars and

trucks.

Wheel camber is not affected by body roll. Wheel

alignment is maintained to a great extent, hence

reduces the tire wear. But some steering vibrations

are produced.

8.3.1a Hotchkiss drive

It consists of a solid axle with leaf spring mounted

longitudinally, their ends connected to chassis and

axle attached near the midpoint. The leaf spring is

relatively stiff in lateral and longitudinal direction;

only vertical deflection is allowed.

Used widely in the rear axle of early passenger

cars, still used in light and heavy trucks.

8.3.1b Four link

The lower control arm provides longitudinal

control over the axle while the upper absorbs

lateral forces and driving torque. Use of coil

spring provides better ride and elimination of

coulomb friction.

Figure 48 - A Four link suspension system

Figure 47 - A Hotchkiss suspension system with leaf

springs

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It provides better control over roll center*

location, anti-squat and anti-dive performance and

roll steer properties

8.3.2Independent Suspension System In such a suspension system each wheel moves

vertically without affecting the opposite wheel.

All passenger cars and light trucks use this type of

suspension as it provides better resistance to

steering vibration and provides higher roll

stiffness.

Easy control over the roll center* height by

changing the geometry of control arms, larger

deflection, greater roll stiffness for given

suspension vertical rate.

8.3.2a McPherson suspension system A telescopic strut member incorporating damper

is rigidly attached to the wheel at its lower end

and upper end to chassis. Absorbs both lateral and

longitudinal force and maintains the wheel in

camber direction.

Uses small packing space hence used in front

suspension of front-wheel-drive cars. Fewer

numbers of parts and capability to spread

suspension load to body structure over wide area.

High installation height leads to disadvantages.

8.3.2b Wishbone and double

wishbone suspension system (SLA) This system basically contains equal or unequal

upper and lower control arms. Such an

arrangement precludes camber change during

suspension deflection. However under cornering

conditions when suspension deflection is due to

body roll, such a system produces camber change.

8.3.2c Trailing arm suspension

system It is one of the most simple and economic design

of an independent suspension system used by

Volkswagen and Porsche around the time of

Second World War. It uses parallel equal length

trailing arm connected at the front arm to the

lateral torsion bar (a spring is connected to this

bar). There is very little chamber change with

body roll.

8.3.2d Swing axle suspension system Swing axle suspension is the easiest way to obtain

independent rear suspension. The camber behavior

is established entirely by the axis shafts pivoting

at the U joint adjacent to the differential. The

swing radius is small thus camber change with

jounce and rebound movements will be large.

Hence difficulty arises to get consistent cornering

performance.

8.3.4 Hydro-gas Suspension System Instead of a spring, a nitrogen filled spherical

spring chamber is welded to the double conical

shaped displacement chamber. Hydraulic damper

in the form of a pair of rubber compression blocks

separates both spherical spring and displacer

chamber; it controls the flow of the fluid as it

passes to and fro between the two chambers. The

displacer chamber is sealed at its lower end by a

load absorbing nylon reinforced rubber diaphragm

which rolls between the conical piston and tapered

displacer chamber skirt as the suspension deflects

up and down.

Butyl rubber diaphragm separates the sphere into

nitrogen charged upper region and lower region

Figure 49 - A Macpherson Strut on a lower control arm

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filled with fluid. A water based fluid containing

50% industrial alcohol and small percentage of

anti-corrosion additive is pumped into chamber

at the pressure of 23 bars so that reaches the

nitrogen charging pressure.

8.4 Macpherson Struts vs.

Double wishbone

In a double wishbone assembly, the wheel sits

besides the suspension system and is guided by

two "A" arms or wishbones. The spring and shock

assembly is connected at the top to the frame of

the vehicle and at the bottom to the lower

wishbone.

Figure 50 - A Macpherson setup

The design of a double wishbone assembly allows

for a very compact suspension system compared

to a Macpherson type assembly. This allows for a

suspension system to be lower in the vehicle and

making it ideal for transmitting loads and

providing excellent road handling. This, of course,

is a very basic explanation because a double

wishbone suspension is very complex and

contains more minute parts and pieces than a

Macpherson assembly.

Figure 51 - A Double wishbone setup

With a Macpherson suspension system, the wheel

is located below the spring and shock assembly.

The spring and shock assembly sits on a ball joint

of a single lower arm connected by a tie rod. The

single lower arm is usually an "A" arm. The top

piston rod of the shock is used as a swivel axis.

This is necessary, because with a Macpherson

suspension, when the wheel is turned, the whole

suspension system turns with the wheel, not true

with a double wishbone. On a wishbone

suspension the wheel assembly is independent of

the shock assembly and so when the wheel

assembly turns, the shock assembly is stationary.

While different automotive experts will argue for

each suspension type, there is no clear winner.

Auto manufacturers and professional racing teams

alike use both suspensions.

*Roll Centre is the point about which the body rotates while rolling.

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9. BRAKES

9.1 INTRODUCTION Brakes are essentially a mechanism to change

energy types. When you're travelling at speed,

your vehicle has kinetic energy. When you apply

the brakes, the pads or shoes that press against the

brake drum or rotor convert that energy in to

thermal energy via friction.

They should stop the vehicle within minimum

possible distance.

To increase the maneuverability by locking all the

four wheels together in the least time possible.

9.2 BRAKE FADE

With continuous use, the brake shoes in a drum

brake or brake pads in a disc brake will get heated

and get no time to cool. When the brake is applied

again the components are already so hot that they

cannot absorb more heat. In every brake pad there

is the friction material which is held together with

resin. Once this lot starts to get too hot, the resin

holding the pad material starts vaporizing,

forming a gas. That gas forms a thin layer between

the two whilst trying to escape. The result is very

similar to hydroplaning; hence the pads lose

contact with the rotor, thus reducing the amount of

friction

9.3 TYPES OF BRAKES

9.3.1 Drum brakes Two semicircular brake shoes sit inside a spinning

drum which is attached to the wheel. When brakes

are applied the shoes are expand outward to press

against the inside of the drum. This creates

friction, which creates heat, which transfers

kinetic energy, which slows you down. When the

actuator is twisted, it is forced against the brake

shoes and in turn forces them to expand outwards.

The return spring is what pulls the shoes back

away from the surface of the brake drum when the

brakes are released.

The "single leading edge" refers to the number of

parts of the brake shoe which actually contact the

spinning drum. Because the brake shoe pivots at

one end, simple geometry means that the entire

brake pad cannot contact the brake drum.

The leading edge is the term given to the part of

the brake pad which does contact the drum, and in

the case of a single leading edge system, it's the

part of the pad closest to the actuator. When the

shoes are pressed outwards, the part of the brake

pad which first contacts the drum is the leading

edge.

9.3.2 Drum brakes - double leading

edge The drawbacks of the single leading edge style of

drum brake can be eliminated by adding a second

return spring and turning the pivot point into a

second actuator. Now when the brakes are

applied, the shoes are pressed outwards at two

points. So each brake pad now has one leading

and one trailing edge. Because there are two brake

shoes, there are two brake pads, it mean there are

two leading edges.

9.3.3 Disc brakes Disc brakes are better at stopping vehicles than

drum brakes, that is why you'll find disc brakes on

the front of almost every car and motorbike built

today also in sportier vehicles with higher speeds

need better brakes to slow them down.

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Disc brakes are again a two-part system: a disc or

rotor, brake caliper assemblies. The caliper

assemblies contain one or more hydraulic pistons

which push against the back of the brake pads,

clamping them together around the spinning rotor.

The harder they clamp together, more is the

friction generated, which means more

heat, which means more kinetic energy transfer,

which slows you down.

Standard disc brakes have one or two cylinders in

them - also known as one or two-pot calipers.

Where more force is required, three, or more

cylinders can be used.

9.4 METHODS TO REDUCE BRAKE FADE

9.4.1 Drilled Rotors Drilled rotors are typically use in race cars. The

drilled holes give more bite hence more friction

and also allow air currents (eddies) to blow

through the brake disc to assist cooling and

ventilating gas. Typically found in race cars.

There are some other types of rotors such

grooved, grooved-drilled rotors which give

more bite hence more friction as they pass

between the brake pads, and they also allow the

gas to vent from between the pads.

9.4.2 Master cylinder The master cylinder is a control device that converts

force provided by the driver at the brake paddle into

hydraulic pressure, in order to move other devices

which are located at the other end of the hydraulic

system, such as one or more slave cylinders. The

movement of piston inside master cylinder is

transferred through the hydraulic fluid, to result in

a movement of the slave cylinder. The hydraulic

pressure created by moving a piston toward the

slave cylinder compresses the fluid evenly, but by

varying the comparative surface-area of the master

cylinder or each slave cylinder, one will

vary the amount of force and displacement applied

to each slave cylinder

Figure 52 - Various components of a disc brake setup Figure 53 - A Drilled Rotor

Figure 54 - Various parts of a master cylinder

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9.4.3 Tandem Master Cylinder

Tandem master cylinder is characterized by two

pistons operating in series within a common bore.

In rear-wheel drive applications the piston that's

located closer to the pedal (labeled "Piston 1")

applies the vehicle's front brakes. In normal

operation, fluid displaced and pressurized by

Piston 1 also causes movement of a second piston

("Piston 2"). Piston 2 applies the vehicle's rear

brakes.

The following two illustrations show how a

tandem master cylinder isolates leaks in the front

and rear brake plumbing respectively. (In both

illustrations, the pedal has already been depressed

to the point of brake application.)

As shown in Illustration 1, if a leak develops in

the front brake system, Piston 1 will move

forward until it contacts Piston 2. Force from the

brake pedal will be transmitted mechanically

through Piston 1 to Piston 2. Although overall

braking performance will be severely

compromised, the rear brakes will still be

functional provided sufficient pedal travel is

available. The pedal will need to travel further

than normal to fully engage the rear brakes. Also,

it should be appreciated that trying to stop quickly

with just the rear brakes is very tricky because the

rear tires will easily reach the point of lock-up. As

the car is slowing, weight transfers forward and

the rear wheels lose some of their much needed

traction.

9.5 TYPES OF CALIPERS

9.5.1 Fixed calipers: Fixed calipers are rigidly

fixed to its mounting surface. It requires minimum

of two pistons one on each side. When the brakes

are applied, each piston drives its corresponding

brake pad into contact with the rotor

9.5.2 Floating calipers: Floating calipers can

slide side to side on its mounting surface. Thus the

piston is required only on one side. When the

brakes are applied, each piston drives its brake

pad into contact with the rotor. This results in the

reaction force that causes the calipers to slide

away from the rotor. This sliding motion brings

the opposite pad in contact with the rotor, and the

brakes are fully applied.

Most passenger cars use floating because fewer

components are involved than fixed calipers. On

the other hand, most high performance cars use

fixed calipers with multiple positions on either

side of calipers to generate higher application

forces that the performance of vehicle requires.

9.6 HYDRAULIC BRAKES

This type of brake system is used on most cars

and motorbikes today. Single-circuit hydraulic

systems have three basic components - the master

cylinder, the slave cylinder and the reservoir.

They're joined together with hydraulic hose and

filled with a non -compressible hydraulic fluid

(see brake fluid below). When you press your foot

on the brake, or squeeze the brake lever, you

compress a small piston assembly in the master

Figure 56 - Functioning of a Tandem Master Cylinder

Figure 55

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cylinder. Because the brake fluid does not

compress, that pressure is instantaneously

transferred through the hydraulic brake line to the

slave cylinder where it acts on another piston

assembly, pushing it out. That slave assembly is

either connected to a lever to activate the brakes,

or more commonly, is the brake caliper itself, with

the slave cylinder being the piston that acts

directly on the brake pads. Because of the

arrangement of the slave cylinder, heat from the

brakes can be transferred back in to the brake

fluid.

9.7 PROPORTIONING VALVE

Proportioning valve reduces the pressure in the

rear brakes lines. Regardless of what type of

brakes a car has, the rear brakes require less force

than the front brakes.

The amount of brake force that can be applied to a

wheel without locking it depends on the amount

of weight on the wheel. More weight means more

brake force can be applied. For equal braking

force applied at all four wheels during a stop, the

rear wheels would lock up before the front wheels.

The proportioning valve only lets a certain portion

of the pressure through to the rear wheels so that

the front wheels apply more braking force.

9.8 ANTI LOCK BRAKING SYSTEM (ABS)

ABS is a form of electronic braking which was

invented to help driver to steer the vehicle under

heavy braking and preventing the wheel from

locking.

As during heavy braking there is a chance that

wheel stop rotating before the car comes to rest

this happens because the braking force on the

wheel is not transferred efficiently to stop the

vehicle due to the fact that tire is sliding upon the

road, which leads to greater stopping distance and

loss in control over vehicle.

The electronic control unit constantly monitors the

rotational speed of each wheel; if any wheel

rotating slower than the others; it actuates the

valves to reduce hydraulic pressure to the brake at

the affected wheel, thus reducing the braking force

on that wheel; the wheel then turns faster.

If the ECU detects any wheel rotating faster than

the others, brake hydraulic pressure to the wheel is

increased so the braking force is reapplied,

slowing down the wheel. This process is repeated

continuously at the rate of 16 times per second.

9.9 TYPES OF BRAKE FLUIDS

DOT 3 and 4

The main characteristics of this type brake fluid

are as follows:

Poly-glycol based

Most commonly used

Compatible with one another

Inexpensive

Destroys paint

Ruined by moisture

DOT 5

The main characteristics of DOT5 type of brake

fluid are:

Silicone Based

Used only for heavy duty applications

Not Compatible with 4&5

Very Expensive

Does not damage paint

Where DOT- Department of Transportation

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9.10 NEW TECHNOLOGY:

9.10.1 Regenerative braking:

Every time you step on your car's brakes, you're

wasting energy. Is there anything that you, the

driver, can do to stop wasting this energy? Not

really. In most cars it's the inevitable by-product

of braking and there's no way you can drive a car

without occasionally hitting the brakes. But

automotive engineers have given this problem a

lot of thought and have come up with a kind of

braking system that can recapture much of the

car's kinetic energy and convert it into electricity,

so that it can be used to recharge the car's

batteries. This system is called regenerative

braking. At present, these kinds of brakes are

primarily found in hybrid vehicles like the Toyota

Prius, and in fully electric cars, like the Tesla

Roadster. In vehicles like these, keeping the

battery charged is of considerable importance.

However, the technology was first used in trolley

cars and has subsequently found its way into such

unlikely places as electric bicycles and even

Formula One race cars.

In a traditional braking system, brake pads

produce friction with the brake rotors to slow or

stop the vehicle. Additional friction is produced

between the slowed wheels and the surface of the

road. This friction is what turns the car's kinetic

energy into heat. With regenerative brakes, on the

other hand, the system that drives the vehicle does

the majority of the braking. When the driver steps

on the brake pedal of an electric or hybrid vehicle,

these types of brakes put the vehicle's electric

motor into reverse mode, causing it to run

backwards, thus slowing the car's wheels. While

running backwards, the motor also acts as an

electric generator, producing electricity that's then

fed into the vehicle's batteries. These types of

brakes work better at certain speeds than at others.

In fact, they're most effective in stop-and-go

driving situations. However, hybrids and fully

electric cars also have friction brakes, as a kind of

back-up system in situations where regenerative

braking simply won't supply enough stopping

power. In these instances, it‘s important for

drivers to be aware of the fact that the brake pedal

might respond differently to pressure. The pedal

will sometimes depress farther towards the floor

than it normally does and this sensation can cause

momentary panic in drivers.

Figure 57 - Functioning of Regenerative braking system

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10. WHEEL A wheel is a circular component that is

intended to rotate on an axial bearing. The

wheel is one of the main components of the

wheel and axle which is one of the six simple

machines. Wheels, in conjunction with axles,

allow heavy objects to be moved easily

facilitating movement or transportation while

supporting a load.

10.1 TUBELESS TIRES Tubeless tires are pneumatic tires, the tire is built

in such a way that it can contain the air by itself. It

does not require a tube within it. The tire and rim

assembly form an air container, to ―Seal‖ and

―Contain‖ the compressed air inside the assembly.

Friction between the tire & tube is not

experienced, thus lower rolling resistance,

improved fuel efficiency, less vibrations, less heat

generation and better comfort.

The inner liner of the tubeless tire is constructed

of halo-butyl/chloro-butyl and other materials.

This performs, in essence, the important core of

substantially reducing the permeation of air, as

compared to the natural rubber inner liner, a

function of which is why we use a butyl tube in a

tubed tire.

10.2 WHEEL ALIGNMENT

10.2.1 Caster angle The caster angle is the angle between the steering

axis and the vertical plane viewed from the side of

the tire. The caster trail is defined as the distance

at the ground between the center of the contact

patch and the point at which the steering axis

intersects the ground.

It is important that the caster angle and caster trail

be positive because both of these quantities will

affect the aligning moment.

The aligning moment is the moment that will act

against the driver as he/she is trying to steer the

vehicle.

10.2 Camber angle The camber angle is defined as the inclination of

the tire with respect to the road surface in the

vertical plane (when looking at the vehicle from

the front view).

Figure 58 - Side view of the front wheel

Figure 58 - Front view of the front wheel

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41

Negative camber occurs when the top of tire

points in towards the vehicle, and positive camber

occurs when the top of the tire points.

Camber on a wheel will produce a lateral force

which is known as camber thrust. A rolling tire

that is cambered will produce a lateral force which

is in the direction the tire is tilting from the

vehicle. It is best to go with a static negative

camber angle because it improves the effective

cornering stiffness of the tire. A large camber

angle (negative or positive) increases tire wear

which is undesirable. Camber change reduces the

contact patch area thus grip, and also introduces

non-neutral steering.

For best performance the camber angle should

remain between -2 and -7 degrees throughout the

suspension travel.

10.2.3 Toe angle The toe angle is defined as the angle between the

longitudinal axis of the vehicle and a line passing

through the center of the tire when viewed from

the top. Toe in occurs when the front of the tire

points in towards the vehicle, and toe out occurs

when the front of the tire points away from the

vehicle. There will be usually some elastic

deformation of the

suspension under driving or braking that will

cause changes in the toe angle.

Therefore, initial toe angle (-2°) is given

suspension system so that the deformation in the

system will force the tire to straighten when the

vehicle is driving or braking.

10.2.4 Steering axis inclination The angle between the steering axis and the

vertical plane, when viewing the tire from the

front is termed as Steering Axis Inclination. The

scrub radius is the distance measured at the

ground level between the center of the contact

patch and the point where the steering axis

intercepts the ground.

The Kingpin angle affects the camber angle as the

wheel is steered about the steering axis. With a

positive kingpin angle, the tire will lean out as it is

steered about the steering axis. Therefore the

greater the steering angle, the greater the amount

of positive camber generated, and the greater the

kingpin angle the greater the amount of change in

the camber angle.

Driving and braking forces will introduce a torque

about the steering axis and this torque will be

proportional to the moment arm, the scrub radius.

If the driving and braking forces are different on

any side of the vehicle then the driver will feel a

net steering torque acting to steer the vehicle. The

amount of tire scrub against the ground as the

wheel turns is dependent on the tire scrub if one

wheel losses traction when the vehicle is braking

Figure 59 - Bottom view of the front axle

Figure 60 - Steering axis inclination or the King Pin

inclination

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42

then the opposing wheel will toe an amount that is

determined by the compliance in the steering

system. This will tend to steer the car in the

straight line even though the braking force is same

on both lines. In general, a small amount of

negative scrub is required.

Typically, a small positive scrub radius(6-10 mm)

is used on vehicles with a small to moderate

kingpin angle (5°-10°) is used.

10.3 Tyre size notations:

When you look at your car and discover that it is shod with a nice, but worn set of 185-65HR13's (from the

tyre marking). Any tyre mechanic will tell you that he can replace them, and he will. You'll cough up and

drive away safe in the knowledge that he's just put some more rubber on each corner of the car that has

the same shamanic symbols on it as those he took off. So what does it all mean?

DID YOU KNOW?

Aircraft requires special tires to allow for

short duration but excessively high-impact

use, particularly when a plane comes in to

land and the weight of the aircraft

impacts the runway. For this purpose the

tires are filled with nitrogen or helium to

minimize the pressure differential

between the high altitude and the

compressed gas inside.

This is the width in

mm of the tire from

sidewall to sidewall

when it's unstressed

and you're looking at

it head on (or top-

down). This is known

as the section width.

This is the ratio of the

height of the tyre

sidewall, (section

height), expressed as a

percentage of the

width. It is known as

the aspect ratio. In this

case, 65% of 185mm is

120.25mm - the section

height.

This is the

speed rating

of the tyre.

This tells you

that the tyre is a

radial

construction.

This is the

diameter in inches

of the rim of the

wheel that the tyre

has been designed

to fit on.

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43

10.4 The Wheel Assembly:

10.4.1 The Hub (1):

The hub serves as housing for the wheel's bearings (5) and spacers and is the central support around which

the entire wheel revolves on the axle.

10.4.2 The rotor (2):

The rotor or disk is attached onto the hub of the wheel and the first impact of the brakes comes onto it and

further stops the wheel.

10.4.3 The Knuckle (6):

Knuckle is the stationary part and supports the Suspension and steering system. The knuckle is attached to

one of the edges of a bearing (5) using a sleeve (3) or directly.

10.4.4 The Caliper (4):

The brake caliper is mounted onto the knuckle (6) and thus remains stationary. When the brakes are applied

it clamps onto the rotor/disk (2) and thus slows down the wheel.

Figure 61 - The wheel assembly: (1) Hub, (2) Rotor, (3) Sleeve, (4) Caliper, (5) bearing, (6)

Knuckle.

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10 ELECTRICAL SYSTEM

11.1 IGNITION SYSTEM

Most four-stroke engines in the past used a

mechanically timed electrical ignition system. The

heart of the system is the distributor. The

distributor contains a rotating cam driven by the

engine's drive, a set of breaker points, a

condenser, a rotor and a distributor cap. External

to the distributor is the ignition coil, the spark

plugs and wires linking the distributor to the spark

plugs and ignition coil.

The system is powered by a lead-acid battery,

which is charged by the car's electrical system

using a dynamo or alternator. The engine operates

contact breaker points, which interrupts the

current to an induction coil (known as the ignition

coil).

The ignition coil consists of two transformer

windings sharing a common magnetic core—the

primary and secondary windings. An alternating

current in the primary induces alternating

magnetic field in the coil's core. Because the

ignition coil's secondary has far more windings

than the primary, the coil is a step-up transformer

which induces a much higher voltage across the

secondary windings. For an ignition coil, one end

of windings of both the primary and secondary are

connected together. This common point is

connected to the battery (usually through a

current-limiting ballast resistor). The other end of

the primary is connected to the points within the

distributor. The other end of the secondary is

connected, via the distributor cap and rotor, to the

spark plugs.

11.2 Ignition Coil The coil is a simple device - essentially a high-

voltage transformer made up of two coils of wire.

One coil of wire is called the primary coil.

Wrapped around it is the secondary coil. The

secondary coil normally has hundreds of times

more turns of wire than the primary coil. Current

flows from the battery through the primary

winding of the coil. The primary coil's current can

be suddenly disrupted by the breaker points, or by

a solid-state device in an electronic ignition.

If you think the coil looks like an electromagnet,

you're right - but it is also an inductor. The key to

the coil's operation is what happens when the

circuit is suddenly broken by the points. The

magnetic field of the primary coil collapses

rapidly. The secondary coil is engulfed by a

powerful and changing magnetic field. This field

induces a current in the coils -- a very high-

voltage current (up to 100,000 volts) because of

the number of coils in the secondary winding. The

Figure 62 - Circuit diagram of a battery ignition system

Figure 63 - An ignition Coil

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secondary coil feeds this voltage to the distributor

via a very well insulated, high-voltage wire.

11.3 Distributor The distributor handles several jobs. Its first job is

to distribute the high voltage from the coil to the

correct cylinder. This is done by the cap and rotor.

The coil is connected to the rotor, which spins

inside the cap. The rotor spins past a series of

contacts, one contact per cylinder. As the tip of

the rotor passes each contact, a high-voltage pulse

comes from the coil. The pulse arcs across the

small gap between the rotor and the contact (they

don't actually touch) and then continues down the

spark-plug wire to the spark plug on the

appropriate cylinder. When you do a tune-up, one

of the things you replace on your engine is the cap

and rotor - these eventually wear out because of

the arcing. Also, the spark-plug wires eventually

wear out and lose some of their electrical

insulation. This can be the cause of some very

mysterious engine problems.

Older distributors with breaker points have

another section in the bottom half of the

distributor -- this section does the job of breaking

the current to the coil. The ground side of the coil

is connected to the breaker points.

A cam in the center of the distributor pushes a

lever connected to one of the points. Whenever

the cam pushes the lever, it opens the points. This

causes the coil to suddenly lose its ground,

generating a high-voltage pulse. The points also

control the timing of the spark. They may have a

vacuum advance or a centrifugal advance. These

mechanisms advance the timing in proportion to

engine load or engine speed. Spark timing is so

critical to an engine's performance that most cars

don't use points. Instead, they use a sensor that

tells the engine control unit (ECU) the exact

position of the pistons. The engine computer then

controls a transistor that opens and closes the

current to the coil.

11.4 Spark plug The spark plug is quite simple in theory. It forces

electricity to arc across a gap, just like a bolt of

lightning the electricity must be at a very high

voltage in order to travel across the gap and create

a good spark. Voltage at the spark plug can be

anywhere from 40,000 to 100,000 volts. The

spark plug must have an insulated passageway for

this high voltage to travel down to the electrode,

where it can jump the gap and, from there, be

conducted into the engine block and grounded.

The plug also has to withstand the extreme heat

and pressure inside the cylinder, and must be

designed so that deposits from fuel additives do

not build up on the plug. Spark plugs use a

ceramic insert to isolate the high voltage at the

electrode, ensuring that the spark happens at the

tip of the electrode and not anywhere else on the

plug; this insert does double-duty by helping to

burn off deposits. Ceramic is a fairly poor heat

conductor, so the material gets quite hot during

operation. This heat helps to burn off deposits

from the electrode.

Some cars require a hot plug. This type of plug is

designed with a ceramic insert that has a smaller

contact area with the metal part of the plug. This

reduces the heat transfer from the ceramic, making

it run hotter and thus burn away more deposits.

Cold plugs are designed with more contact area,

so they run cooler.

APPENDIX

46

Figure 64

APPENDIX

47

Figure 65

APPENDIX

48

Figure 66

COMMON ABBREVIATIONS

49

CRDi Common Rail Direct injection

i-VTEC Intelligent Variable(valve) timing (and lift) Electronic Control

ABS Antilock Brake System

DOHC Double Overhead Camshaft

DDIS Diesel Direct injection System

TDI Turbocharged Diesel Injection

ARC Automatic Ride Control

A/T Automatic Transmission

HCCI Homogeneous Charge Compression Ignition

VVTi Variable Valve Timing with Intelligence

ECU Electronic Control Unit

IRS Independent Rear Suspension

ARAI Automotive Research Association of India

DCRV Deceleration Conscious Regulating Valve

GPS Global Positioning System

ABRS Airbags Restraint System

MPFI Multi Point Fuel Injection

PGM-Fi Programmed Fuel Injection

MUV Multi Utility Vehicle

DCT Dual Clutch Transmission

VAPS Variable Assist Power Steering

FSI Fuel Stratified Injection

TEST YOURSELF

50

1. What is turning radius?

2. What is the difference between valves and ports?

3. What principle does a CVT work on?

4. Why by-passing is done in a carburetor?

5. Why two compression rings in a piston are placed in the opposite direction?

6. Why Mobil oil is added in a 2-stroke engine but not in a 4 stroke engine?

7. What is the difference between leading edge and trailing edge?

8. What are airbags and what is their inflation speed?

9. Why teeth are cut on the flywheel of an engine?

10. What is the difference between indicated power and brake horsepower?

11. What will happen if we use diesel in a petrol engine?

12. Which is better: Double wishbone or Macpherson strut? And Why?

13. What is the firing order of a V6 engine?

14. What are the factors that affect the power output of an engine?

15. What is the difference between pan-hard bar and an anti-roll bar?

16. What are the differences between a 2-Stroke and 4-Stroke engine?

17. What is the difference between Petrol and a Diesel engine?

18. What is the ‗Octane number‘?

19. What are the factors that determine the ‗Octane Number‘ of the fuel to be used?

20. What would happen if diesel comes in contact with a burning matchstick?

21. What is the function of glow plugs in a diesel engine?

22. What are the properties of a good braking fluid?

23. In case drum brakes, why brake pads have uneven thickness after a lengthy duration

of use?

24. How ‗Tandem master cylinder‘ is different from ‗Master Cylinder‘?

25. What are the conventions for numbering the cylinders in an engine?

TEST YOURSELF

51

For the Auto maniacs:

1. Who is called as ‗The Doctor‘ in the world of Motorsports?

2. Who has the record of attaining the highest speed in Moto GP ever? And what was the

speed?

3. What is Hill decent control?

4. Where are the headquarters of FERRARI?

5. What does BMW‘s logo signify?

6. What is penny test for wear and tear of tyres?

7. What is the meaning of ‗Superleggera‘?

8. Volkswagen is the parent co. of how many companies? Name them.

9. Mazda comes from which country?

10. Quattro is a system used by which company? How does it work?

11. Connect the name of a small car and a famous footballer.

12. This company is the tyre sponsor of the Formula 1 racing and also, is the T-Shirt

sponsor of the football club Internazionale. Which is this company?

13. How was the event BAJA named as it is?

14. Who is the youngest Formula 1 Driver to win a race?

15. Which Driver has the maximum F1 race wins?