8. engine mechanics fundamentals

8/12/2019 8. Engine Mechanics Fundamentals

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ENGINE MECHANICS

FUNDAMENTALS

N. V. MARATHESr. Deputy Director, Powertrain Engineering

ARAI, Pune (India)[email protected]


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.recap of topics covered in past

2 days

Basics of Engine Thermodynamics

Basics of Engine Combustion

CRDI Emission Formation & Control

Breathing and Valve train

Exposure to Engine tests

Exposure to Port testing


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CONTENTS of the moduleEngine Mechanism Fundamentals

Engine Classifications parameters

Crank mechanism Kinematics & Forces

Engine balancing

Torsional vibrations


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Engine Classification Purpose

Stationary engineelectric power plants, pumping units, etc

Variable speed engine - motor vehicles, off-road,

locomotive, ships

Type of fuel

Light liquid fuelpetrol, kerosene

Heavy liquid fueldiesel, fuel oil, bio-fuel, etc.

Gaseous fuelnatural gas, propane, hydrogen, etc

Mixed fuel

Nature of energy conversion to mechanical work

Internal Combustion (IC) enginesconventional piston engine External combustion enginesgas turbine

Method of mixture formation

External mixture formationpetrol engine

Internal mixture formationdiesel engine


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Method of ignition Positive ignition - spark ignitiongasoline engine

Compression ignitiondiesel engine

Pre-chamber ignition

Open chamber ignition Piston strokes per cycle Two stroke

Four stroke

Nature of Aspiration Naturally Aspirated ( NA ) engine

Supercharged engine

Turbocharged engine

Engine Classification


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Method of load controlcomposition of mixture Quantity control - quantity of mixture is controlled

composition of mixture unchangedpetrol engines

Quality control fuel mass is controlledcomposition of

mixture changed - diesel engines

Cooling method Liquid cooling

Air cooling

Cylinder arrangement

Inlinevertical, horizontal

V

Opposed piston

Radial

Engine Classification


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8

Vee AngleFor even firing pulses the

product of the vee angle and

the number of cylinders must

be a multiple of 360.

60o: V-6 or V-12

90o: V-8

Changing the vee angle (for

package dimensions, use of

common tooling, etc.) results

in uneven firing..

Vee Engine Design Considerations


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Engine that converts thermal energy to

mechanical work

Particularly, the architecture comprising all the

subsystems required to convert this energy to

work

Sometimes extends to drive train, whichconnects power train to end-user of power

What is a Power Train ?


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Basic Characteristics of Vehicle engines Reliability

Efficiency of conversion of heat energy into mechanical work Engine power and torque capacity

Specific powerpower per litre

Specific massengine power per unit of engine mass

Package volume - size

Exhaust emissions Noise

Reliable starting in all conditions

Durability - service life of all design elements

Design complexity

Manufacturing cost Operating cost

Service interval - Oil change period

Access to assembly and dis-assembly

Recycling

Customer perception and acceptance


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Typical Cross-section of an Engine


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Cylinder Block

Part of engine framethat contains

cylinders in which

piston moves

Supports liners &head

Structural Components


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Cylinder Head/Assembly

Serves to admit, confine, and release fuel/air

Cover to cylinder block Supports valve train

Crankcase

Engine frame section that houses the crankshaft

Oil sump

Reservoir for collecting and holding lube oil



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Three Groupsaccording to motion

Reciprocating only (pistons and valves)

Reciprocation & rotary (connecting rods)

Rotary only (crankshafts and camshafts)



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Piston Acted on by combustion gases

Lightweight but strong/durable

Piston Rings

Transfer heat from piston to

cylinder Seal cylinder & distribute lube

oil

Piston Pin

Pivot point connecting pistonto connecting rod

Connecting Rod

Connects piston & crankshaft

reciprocating rotating

motion



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Crankshaft Combines work done by each piston

Drives camshafts, generator, pumps, etc.

Flywheel Absorbs and releases kinetic energy of piston

strokes.

Smoothens rotation of crankshaft



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Valves Intake: open to admit air to

cylinder (with fuel in Otto

cycle)

Exhaust: open to allowgases to be rejected

Camshaft & Cams

Used to time the addition ofintake and exhaust valves

Operates valves via

pushrods & rocker arms

Moving Components


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Pushrod OHV (Type 5) HEMI 2-Valve (Type 5) SOHC 2-Valve (Type 2)

2-V train layout of an engine


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SOHC 4-Valve (Type 3) DOHC 4-Valve (Type 2)

DOHC 4-Valve (Type 1)Desmodromic

4-V train layout of an engine


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Air flow is an easier variable to

change than thermal efficiency

90% of restriction of induction

system occurs in cylinder head Cylinder head layouts allowing

the greatest airflow will have

highest specific power potential

Peak flow from poppet valveengines primarily a function of

total valve area

More/larger valves provide

greater valve area

Valve- train layoutSpecific Power = f(Air Flow, Thermal efficiency)


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21

Cam Drive Configuration - Example

GM ECOTEC 1.8 2.2L in-line DOHC 4cylinder


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Increased pressure of combustion

gases acts on piston. Reciprocating

motion converts to rotary motion

Can be 2 or 4 stroke engines

2-stroke: 1 power stroke per 1crankshaft rev

4-stroke: 1 power stroke per 2

crankshaft rev

Engine Operation


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Engine stroke

A stroke is a single

traverse of the

cylinder by the

piston (from TDC to

BDC)

1 revolution of

crankshaft =

2 strokes of piston

Engine Operation

R

L

Stroke S

BDC

TDC


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Vc= Clearance Volume

Vd= Displacement or Swept Volume

Vt= Total Volume

TC or TDC=

Top or Top Dead Center Position

BC or BDC=

Bottom or Bottom Dead CenterPosition

Compression Ratio (CR)c

cd

V

VVCR

Compression Ratio


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Intake stroke Intake valve open, exhaust

valve shut

Piston travels from TDC to

BDC Air or Charge drawn in

4-Stroke engine

Compression stroke

Intake and exhaust valves shut

Piston travels from BDC to TDC

Temperature and pressure of air or Charge increase

Fuel is injected at the end of the stroke ( CI engines )

Spark is ignited towards the end of the stoke ( SI engines)


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Power stroke Intake and exhaust valves shut

Fuel injected gets ignited and pressure develops

Piston forced from TDC to BDC

4-Stroke engine

Exhaust stroke Intake valve shut, exhaust

valve open

Piston moves from BDC toTDC

Combustion gases expelled


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Air system

Supplies & removes air/gases

Air supplied at constant pressure by

blower/compressor

Fuel System

Carburetor: mixes air & fuel in properproportion (NOT on diesels)

Fuel injector: sprays fuel in (more efficient)

Engine Supporting systems


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Ignition system Diesel has compression ignition

Gasoline has spark plugs

Cooling system Uses fresh water and/or salt water to cool

Lubrication system Provide lubrication and cooling

Engine Supporting systems


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Characteristics

Slider-crank mechanism has high mechanicalefficiency (piston skirt rubbing is source of 50-60% of all firing friction)

Piston-cylinder mechanism has high single-stage compression ratio capabilityleads tohigh thermal efficiency capability

Reciprocating I C engine


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Engine Mechanics

Kinematics

Static force analysis

Inertial effects

Balancing

Overview

Some simplifying assumptions are made throughout:

(a) gravity forces are small, and are ignored

(b) friction is ignored

(c) the components are rigid

(d) the motions are planar (two dimensional)

(e) the length ratio between crank-throw and con-rod issmall enough to make some simplifications

(f) the con-rod can be represented as a two-mass system.

Mechanics of I C engine


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31

approximate expression for the distance x between thecrankshaft rotation centre O and the piston centre B :

where n is a geometric ratio between the length of thecon-rod AB and the length of the crank throw OA.

O

A

B

y

x

r n r

Fig 1.2: crank-slider geometry

coscos nrrx

2/stroker

)2/stroke/(lengthconrodn



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for transverse crankpin displacement,

Or,

since

then

sinsin nrr

cos ( sin ) 1 2

sin1

1cos 22

n

nrrx

sin1

sin

n

O

A

B

y

x

r n r

Fig 1.2: crank-slider geometry



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33

2cos1

2

11cos

2

nnrx

2sin2

1sin

nrx

)2cos1

cos2sin2

1sin

2

n

rn

rx

Applying binomial theorem expansion and neglecting higher terms of

mn/1

Piston displacement

Piston velocity

Piston acceleration

M h i f I C i


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-15000

-10000

-5000

0

5000

10000

15000

20000

25000

0 30 60 90 120 150 180

Crank Angle (deg)

Accelera

tion(m/s2)

0

5

10

15

20

25

30

0 30 60 90 120 150 180

Crank Angle (deg)

Velocity(m/s)

4.3

2

Peak piston velocity increases and advances towards

BDC as n reduces Peak piston acceleration at BDC positionincreases as n reduces

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0 30 60 90 120 150 180

Crank angle BDC - TDC (deg)

PistonpositionBDC-TDC(m)

4.3

2

BDC

TDC


Pistondisplacement--

Con

rod CD

Crank

rad

(0.5 x

stroke)

Peak

piston

velocity

Piston

acceln

at BDC

n l r Vp(max) Ap(bdc)

reduce

s

reduce

s

(shortercon rod

length)

increase

s

(longerstroke)

increase

s and

shifts

towardsBDC

increase

s

BDC TDC TDCBDC


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Con Rod and Piston Stroke ratioThon e rod-to-stroke ratio is the ratio of the length of the

connecting rod to the length of the piston stroke.

A longer rod will reduce the sidewise pressure of the piston on

the cylinder wall and the stress forces, hence increasingengine life. It also increases cost and engine height and

weight.

A square engineis an engine with a bore diameter equal to

its stroke length.

An engine where the bore diameter is larger than its stroke

length is an oversquareengine.

an engine with a bore diameter that is smaller than its stroke

length is an undersquareengine

http://en.wikipedia.org/wiki/Oversquarehttp://en.wikipedia.org/wiki/Oversquare


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36

Heat Transfer Losses

As Bore/Stroke increases, surface to

volume ratio near TDC increases,

causing increased heat transfer losses.

Valve Flow Area

As Bore/Stroke decreases, there is less

room in the head for valves, and the

valve flow area decreases.

Piston Speed

As Bore/Stroke decreases, the longer

stroke dimension requires the piston to

travel further in the same amount of time.

Bore / Stroke Ratio Optimization


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37

Bore to Stroke Ratio Optimization

(Example taken for 2L per cylinder at 1800 RPM)

0

2

4

6

0

10

20

30

40

4

6

8

10

0.4 0.6 0.8 1.0 1.2 1.4 1.6

Bore to Stroke Ratio

Mean Piston Speed (100 ft/min)

Pressure drop across intake valves (psi)

Surface area to Volume at TDC (1/in.)

Optimum Range

Bore / Stroke Ratio Optimization


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38

Rotational forcedue to mass

spinning at

some offset from

the shaft

centerline

Inertia force associated

with accelerating anddecelerating

reciprocating mass

Gas pressure

forces transmittedthrough piston to

connecting rod

Moment generated bygrouping of cylinders

whose net forces try

to pivot the system

about some axis

Forces Generated within the Engine


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39

FRecip

FR

R

L

Frecip is the reciprocating forcegenerated by accelerating and

decelerating the piston, rings, pin, and

upper portion of the connecting rod.

FRRecip is the reaction force

transmitted to the block at the mainbearing saddle

Frotate is the rotating force generated

by the mass of the crankshaft and

lower portion of the connecting rodoffset from the crankshaft centerline.

FRRotate is the reaction force

transmitted to the block at the main

bearing saddle.

Forces Acting on the Engine System


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40

Reciprocating forces are calculated from Newtons

Second Law:

onAcceleratiMassForce

The mass is that of the piston, rings, piston pin, and

the upper portion of the connecting rod.

The acceleration is calculated by taking the time

derivative of the piston velocity as a function of crank

angle.

Reciprocating Forces


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41

The piston velocity versus crank angle is given by the series

expression:

Piston acceleration versus crank angle is then given by:

...4cos162cos4cos 422 aaR

dt

dV

V 2R s in 2a2s in2 4a

4s in4 ...

where: a2

LR

14RL

2 116

RL

4 15512

RL

6 ...a

4 L

R164

RL

4

3256

RL

6

...



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42

By Newtons Second Law the reciprocating forces are then:

The higher order terms are very small and can be safely

neglected. 4a2is approximately R / L, so the equation simplifies

to:

First Order Second Order

Frecip MPiston Assy dVdt

MPiston Assy

2Rcos4a

2

cos216a4

cos4...

Frecip MPiston Ass y 2

R cosRLcos2


Reciprocating Forces Engine Vibration Order


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43

ReciprocatingFor

ce

TDC 0o BDC 180o TDC 360o

First Order

Second Order

Resultant

90o 270o

Reciprocating Forces Engine Vibration Order

Engine Vibration Order= Frequency of vibration / system characteristicfrequency

For engine, the system characteristic frequency is taken as crankshaftspeed

A first order vibration is one where the force cycle repeats onceeverycrankshaft revolution

1 stroke 2 stroke

1 revolution


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44

BDC

Crank Angle

TDC 90o

Piston velocityis not sinusoidal, but is skewed

It shows higher velocities near TDC than BDC

As shown in the four-cylinder diagram,

pistons 1 and 4 nearing TDC are

decelerating at a faster rate than pistons 2

and 3 nearing BDC, resulting in anet

upward force.

One-half revolution later, pistons 2 and 3

approach TDC, while 1 and 4 approach

BDC, and the force is repeated

What is 1st& 2ndorder forces ?


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Engine Balancing

Engine balance is the design,

construction and tuning of an engineto runsmoothly.
http://en.wikipedia.org/wiki/Enginehttp://en.wikipedia.org/wiki/Engine


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Engine Balancing

Primary balance is the balance achieved bycompensating for the eccentricities of the masses inthe rotating system, including the connecting rods.

Primary balance is controlled by adding or removing

mass to or from the crankshaft, typically at each end, at

the required radius and angle. It varies both due to

design and manufacturing tolerances.

Theoretically, any conventional engine design can bebalanced perfectly for primary balance.


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Engine Balancing

Secondary balance can include compensating for :

kinetic energy of the pistons

non-sinusoidal motion of the pistons

motion of the connecting rods

sideways motion of balance shaftweights

The second of above is the main consideration for secondary balance.

There are two main control mechanisms for secondary balance

matching the phasing of pistons along the crank, so that their

second order contributions cancel,

the use of Lanchester balance shafts, which run at twice engine

speed, and so can provide a counteracting force.
http://en.wikipedia.org/wiki/Balance_shafthttp://en.wikipedia.org/wiki/Balance_shafthttp://en.wikipedia.org/wiki/Balance_shafthttp://en.wikipedia.org/wiki/Balance_shaft


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Primary forces are balanced

Secondary forces sum up. This produces a vibration in

the vertical plane at a frequency twice that of the speed of

the crank.

Direction of Primary and secondary forces in an in-line 4-cylinder engine

EXAMPLE

Engine Balancing


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49

Static Balance

Unbalanced Couplewhen shaft spins

Concept of Dynamic Couples

massestwothebetweenshaftalongcetanDisL

velocityangularshaftfromdistanceradialMass

masseachbygeneratedforceOutwardF

:where

LFMoment

2


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50

Couple balanced by adding

equal and opposite couple

Concept of Dynamic Couples


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51

The mass associated

with each cylinder

creates two equal and

opposite couples, and

forces transmitted into

the block cancel oneanother. However, two

internal couples, and

resulting moments, place

high loads on the 1, 3,

and 5 main bearings.

Counterweights asshown are used to cancel

these internal moments,

and reduce main bearing

loads.

Four Cylinder Crankshaft Representation


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Summary of unbalance forces & couples

Engine

Configurati

on

Unbalance Forces Unbalance Couples

Primary Seconda

ry

Rotary Primary Seconda

ry

Rotary

Single cyl

PRESEN

T

PRESEN

T

PRESEN

TX X X

2-cyl (1800) X PRESEN

T

X PRESE

NT

X PRESENT

2-cyl (5400)

PRESENT

PRESEN

T

PRESEN

T

X X X

3-cyl X X X PRESENT

PRESEN

T

PRESENT

4-cyl X PRESEN

T

X X X Internal

couple

In-line Engines


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Solutions for Engine Balancing

Primary balancer shaft rotating at the speed of

the engine

Balance mass on the pulley

Pair of secondary balancer shafts rotating at double

speed of the engine and in the opposite direction

of each other

Counter weights on the crank-throw


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54

Each fraction of the

counterweight has the

effect of the mass ofthat fraction acting at

its radius from the

crankshaft centerline

Reducing the arc over which

the counterweight is sweptmakes each element of mass

more effective, and reduces

overall crankshaft mass, but

increases required crankcase

size

This design eliminates mass in

the least effective areas, and aids

in packaging, with some increase

in crankcase diameter

Crankshaft Counterweights


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55

Counterweights may be shaped for

reduced aerodynamic drag

This will slightly increase overall

crankshaft mass

Counterweight Design


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Benefits of engine balancing

reduced vibrationand other stresses

reliability of the engine

Tolerates higher engine speeds

improved performance and efficiency

reduced stress on other machinery

and people near the engine

improved cost of ownership
http://en.wikipedia.org/wiki/Vibrationhttp://en.wikipedia.org/wiki/Stress_(physics)http://en.wikipedia.org/wiki/Stress_(physics)http://en.wikipedia.org/wiki/Vibration


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Focus areas to achieve engine balancing

( additional to basic design principles )

Balancing the physical engine components, is called

BLUEPRINTING

Careful machining and matching of components as a

seteach engine being unique

Flywheel, bearings, piston & rings, connecting rods,

piston pins, crank

Balancing the engine dynamics

Differing compression ratio will create imbalance and

Vibrations

Compression ratio is affected by many parameterssuch as damaged

Cylinder wall, gasket imperfections, poor valve seating,

poor spark plug

or injector sealing, camshaft uneven wear, etc.


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58

Convert reciprocating motion of pistons to rotarymotion Work extraction

Repeated cycle

Components and specific functions Connecting rod - link between reciprocating and

rotary components Crankshaft - Transfers work from engine, and definespiston travel

Vibration dampener - minimizes torsional vibration

Flywheel - minimizes cyclic speed fluctuation

Crankshaft functional requirements

Critical Crankshaft Dimensions


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59

Critical region for

durability

Journal Overlap

Web Thickness

Main Bearing

Rod Bearing

Fillet Radii

Critical Crankshaft Dimensions


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60

Crankshaft failure

mode is simple

bending across

diagonal section

Main Bearings

TDC Firing

Tensile

Compressive

TDC Valve Overlap

Compressive

Tensile

Rod Bearings

Bending across crankshaft web


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61

Fillet RadiusMax.P

rincipalStressinRodFillet Inertia Load

Firing Load

Stress

Load

d

e

a

c

b

Bearing

Web

abc

de Strain gage

locations

Importance of fillet radius


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62

Axial Loading

Bending perpendicular to crankshaft

Results from transfer of cylinder pressure and reciprocating

forces, and relationship between rod and crankshaft

position versus timeBending parallel to crankshaft

Results from crankshaft bending, or misalignments

between power cylinder and slider-crank components

Tensile loads due

to reciprocating

forces

Compressive loads due to

combination of cylinder pressure and

reciprocating forces

Connecting rod loading


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Torsional vibration is angular vibrationof an object,commonly a shaft, along its axis of rotation.

Torsional vibration is often a concern in power

transmissionsystems using rotating shafts or couplings.

It can cause failures, if not controlled.

In ideal power transmission systems using rotating parts,

the torquesapplied or reacted are "smooth" leading toconstant speeds.

In reality this is not the case. The torques generated may

not be smooth (e.g., internal combustion engines)

Torsional Vibration
http://en.wikipedia.org/wiki/Vibrationhttp://en.wikipedia.org/wiki/Power_transmissionhttp://en.wikipedia.org/wiki/Power_transmissionhttp://en.wikipedia.org/wiki/Torquehttp://en.wikipedia.org/wiki/Internal_combustion_engineshttp://en.wikipedia.org/wiki/Internal_combustion_engineshttp://en.wikipedia.org/wiki/Torquehttp://en.wikipedia.org/wiki/Power_transmissionhttp://en.wikipedia.org/wiki/Power_transmissionhttp://en.wikipedia.org/wiki/Vibration


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Torsional vibration is a concern in the crankshaftsofinternal combustion engines because of several factors.

Alternating torques are generated by the slider-crank

mechanism of the crankshaft, connecting rod, and piston. The motion of the piston mass and connecting rod

mass generate alternating torques often referred to as

"inertia" torques

The cylinder pressure due to combustion is not

constant through the combustion cycle.

The slider-crank mechanism does not output a smooth

torque even if the pressure is constant (e.g., at Top

Dead Centerthere is no torque generated)

Torsional Vibration
http://en.wikipedia.org/wiki/Crankshaftshttp://en.wikipedia.org/wiki/Top_Dead_Centerhttp://en.wikipedia.org/wiki/Top_Dead_Centerhttp://en.wikipedia.org/wiki/Top_Dead_Centerhttp://en.wikipedia.org/wiki/Top_Dead_Centerhttp://en.wikipedia.org/wiki/Crankshafts


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If torsional vibration is not controlled in acrankshaft, it can cause failure of the crankshaft

or other accessories that are being driven by the

crankshaft (typically at the front of the engine).

The inertia of the flywheel normally reduces the

vibrational motion at the rear of the engine.

Engines with several cylinders can have very

flexible crankshafts due to their long length.

Inherently little damping in a crankshaft does

not reduce the vibration

Torsional Vibration


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These curves show the amplitude

of relative twist between thevarious crankpins during the

course of one revolution.

The greater portion of the crank

twists from clockwise to

anticlockwise, while the flywheeland small portion of crank at the

rear twist in the opposite

direction.

The node is the point of zero twist

- it is the weakest point. And this

is where a crankshaft usually

breaks.

Torsional VibrationThe torsional twist varies along

the length of a crankshaft.

Each crankpin assembly is

represented by a disc that has the

same deflection properties.

NODE


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A FREQUENCY is the vibration at a specific number of cycles per

second. For example, 400 cycles per second ("hertz"), or how f requently

the oscillation occurs.

An ORDER is a specific multiple of a basic frequency. For example aneven-firing eight-cylinder, four-stroke engine produces eight torque

pulses per cycle that is four torque pulses per revolution. This is called

a fourth order excitation.

If the crankshaft in an 8-cyl engine operates at 6000 rpm, then the

frequency of the fourth order excitation is 4 x 6000 / 60 = 400 hertz,

whereas the same 4th order excitation at 7200 RPM is a frequency of

480 hertz.

Torsional Vibration

DEFINITIONS


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For Inline Engines

3 Cylinder : 1.5, 3, 4.5, 6,----

4 Cylinder : 2, 4, 6, 8,----

6 Cylinder : 3, 6, 9, 12,----

Major Critical Orders


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A crankshaft, like a plain torsion-bar, has mass and a

torsional spring rate. This causes the crankshaft system

to have its own torsional resonant frequency.

The torque peaks and valleysplus the inertia loads fromthe accelerationof the reciprocating components cause

the engine crankshaft itself to deflect (rotationally)

forward and backward while it is operating. When those

pulses (excitations) are near the crankshaft resonantfrequency, they can cause the crank to vibrate

uncontrollably and eventually break.

Torsional Vibration
http://www.epi-eng.com/piston_engine_technology/torsional_excitation_from_piston_engines.htmhttp://www.epi-eng.com/piston_engine_technology/piston_motion_basics.htmhttp://www.epi-eng.com/piston_engine_technology/piston_motion_basics.htmhttp://www.epi-eng.com/piston_engine_technology/piston_motion_basics.htmhttp://www.epi-eng.com/piston_engine_technology/piston_motion_basics.htmhttp://www.epi-eng.com/piston_engine_technology/torsional_excitation_from_piston_engines.htm


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The torsional resonant frequency of the crankshaft

system is a function of :

crankshaft length; crankshaft torsional stiffness;

crankshaft stroke;

Bob-weight mass;

moments of inertia of rotating items attached to

or driven by the engine.

Torsional Vibration


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71

Cam and accessory drive durability

Gear train

Chain or belt drives

Crank durability?

Magnitude of stress resulting from

torsionals

Noise

Torsional Vibration - importance


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Developing an Equivalent Rotor System Determination of Natural Frequencies -

HolzersForced Tabulation Method

Eigen Value Matrix Method

Fast Fourier Transformation of T- Curve. Conversion of

periodic function to harmonic function

Identification of major & minor Critical Orders

Construction of Phaser & Vector diagrams

Order Analysis for forced Vibration Amplitudes. Estimation of

Resonance & resonance amplitude.

Damper design, if required

Torsional Vibration Analysis Steps


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Equivalent Rotor SystemExample for a 3 Cyl Engine

5-Rotor system representing 3 Cyl Engine crank train


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-0.2

0

0.2

0.4

0.6

0.8

1

1.2

0 1 2 3 4

MODAL

VALUE

LOCATION

HOLZER

MATRIX

NATURALFREQENCY

Modal Value

Pulley Cyl. 1 Cyl.2 Cyl. 3 Flywheel

471 Hz 1 0.8752 0.66 0.328 -0.0497

1245 Hz 1 0.1275 -0.648 -0.619 0.0122

Method FundamentalFrequency

Second HigherFrequency

Holzer Table 471 Hz 1245 Hz

Eigen Matrix 470.5 Hz 1244.6 Hz

Modal AnalysisNatural frequency estimationExample for a 3 Cyl Engine

Mode

Shape


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75

Forcing Function

Resultant Force (Combined) curve based on cylinder pressure and inertia forces.Torque curve is developed based on Combined force data.

Combined


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-600

-400

-200

0

200

400

600

800

1000

1200

1400

0 100 200 300 400 500 600 700 800

Torque(N-m

)

Turning Moment Diagram

-150

-100

-50

0

50

100

150

0 100 200 300 400 500 600 700 800

Torque(N-M

)

1 st order harmonic

-250

-200

-150

-100

-50

0

50

100

150

200

250

0 100 200 300 400 500 600 700 800

Torque(N-m

)

2 nd order harmonic

-200

-150

-100

-50

0

50

100

150

200

0 100 200 300 400 500 600 700 800

Torque(N-m

)

6 th order harmonic

3 Cylinder Engine Case Study

Gas Torque curve

order

1storder

3rdorder

FFT analysis of Gas Torque curve


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Torsional Vibration Control

A DAMPER is a device which dissipates energy,

mainly in the form of heat.

An ABSORBER is a device which is designed to

oscillate in direct opposition to a vibration at

either a specific frequency or a specific order,depending on the design.

DEFINITIONS


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The potentially damaging torsional

vibration is often controlled by a torsional

damper that is located at the front nose of

the crankshaft, often integrated into thefront pulley.

Tuned Rubber Damper

Viscous Damper

Torsional Vibration Control


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Tuned absorber type of "dampers" often

referred to as a harmonic dampers orharmonic balancers

The tuned rubber vibration damper has a

rubber mass interposed between an

outer inertia ring and a central hub. It istypically tuned to the first torsional

natural frequency of the crankshaft.

This type of damper reduces the

vibration at specific engine speeds of

interest. Vibration amplitudes increases

at other non-critical speeds.

It is effectively employed in single speed

control engines such as constant speed

genset engines.

Torsional Vibration ControlTuned Rubber Damper

CHARACTERISTIC HELP GRAPH - 1

0

10

20

30

40

50

60

70

80

90

0 500 1000 1500 2000 2500

FREQUENCY (rad/sec)

DYNAMIC

MAGNIFICATION LOCK_TD

UNIT_TD

O_TD

OPT_TD


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Viscous dampers consist of an

inertia ring in a viscous silicon

fluid.Its viscocity changes very

little with temperature. The

torsional vibration of the

crankshaft forces the fluid throughnarrow passages that dissipates

the vibration as heat. Shearing

force in the fluid damp the

vibrations.The viscous torsional damper is

analogous to the hydraulic shock

absorberin a car's suspension.

Torsional Vibration Control Viscous Damper


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Effectiveness of TV Damper CASE STUDY ( 6 cyl diesel


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Test Engine - 6 Cylinder inline, TC

Rated Power - 200 HP @2500rpm

Test - Full Load test , Speed Sweep Test

Test Carried out with & without Damper

High Speed Data Acquisition is used to record Rotary

oscillations of Crankshaft

Accelerometer along with HSDA is used to recordsurface vibrations on the block (g levels of crankcase)

Effectiveness of TV Damper - CASE STUDY ( 6 cyl diesel

Engine )


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0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

1800 1900 2000 2100 2200 2300 2400 2500 2600

ENGINE SPEED (RPM)

AMPLITUDE(deg)

EXP

PRED

4.5 th

6 th

9 th

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

1800 2000 2200 2400 2600

ENGINE SPEED (RPM)

AMPLITUDE(deg)

EXP

PRED 6 th

4.5 th

9th

Without DamperWith Damper

Effectiveness of TV Damper - CASE STUDY ( 6 cyl diesel Engine )


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Signature Analysis

(Speed Sweep Test)

0 20 40 60 80 100 120 140

-100

0

100

g(g)

secs

max 190.3

min -196.1

Range 386.4

sd 16.16

0 20 40 60 80 100 120 1401000

1500

2000

2500ENGINE SPEED(rpm)

secs

max 2524

min 983.8

Range 1540

sd 431.7

0 20 40 60 80 100 120

-50

0

50

g(g)

secs

max 93.04min -92.5Range 185.5

sd 9.406

0 20 40 60 80 100 120

1500

2000

2500ENGINE SPEED(rpm)

secs

max 2516min 1012Range 1503

sd 521.5

Without Damper With Damper



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Campbell Diagram

1000 1500 2000 2500

0

100

200

300

400

ENGINE SPEED (rpm)

3

5

6

7

9

12 10.2

:

1000 1500 2000 2500

0

100

200

300

400

ENGINESPEED (rpm)

Frequency(Hz.)

3

5

6

7

9

1213.1

Without Damper With Damper



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Thank You

8. engine mechanics fundamentals

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