Reading Material

MET 285: AUTOMOTIVE TECHNOLOGY 

1 

CHAPTER 1 

INTRODUCTION TO I.C ENGINES 

Heat Engine: A heat engine typically uses energy provided in the 

form of heat to do work and then exhausts the heat, which cannot be 

used to do work. 

The characteristics of heat engine are: 

‣ They receive heat from a high temperature source (solar energy, 

oil furnace etc). 

‣ They convert part of this heat into work. 

‣ They reject the remaining waste heat to a low temperature sink. 

‣ They operate in a cycle. 

High Temperature Source 

Q i 

Heat Engine 

Q o 

Low Temperature Sink 

Fig 1.1: Heat Engine 

W 

Heat engines such as automobile engines operate in a cyclic manner, adding energy in the form of heat in 

one part of the cycle and using that energy to do useful work in another part of the cycle. In the case of 

the automobile engine, the hot reservoir is the burning fuel and the cold reservoir is the environment to 

which the combustion products are exhausted. Because the fuel is burned inside, or internally, the engine 

is known as internal combustion engine. 

**Combustion means burning 

Classification of Automotive Engines: Automotive engines can be classified in many ways depending 

on: 

1. Engine operating cycle - 4 stroke or 2 stroke 

2. Method of ignition - Spark ignition or compression ignition 

3. Type of fuel burned - petrol, diesel or natural gas 

4. Basic engine design - Reciprocating or rotary type 

5. Number of cylinders 

6. Arrangement of cylinders 

7. Method of Firing 

8. Arrangement of valves and valve trains 

9. Combustion chamber design – open chamber or divided chamber 

10. Type of cooling - Water or air cooled 

11. Mixture preparation - Carburetor or fuel injection 

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1. Engine operating cycles: 

In reciprocating engines the piston moves up and down, this motion is transferred into a rotating motion 

in the drive shaft by the connecting rod and crank mechanism. The piston comes to rest at the top center 

crank position and the bottom center crank position respectively. 

One cycle is completed in 4-strokes for a conventional 4-stroke cycle engine and 

Two strokes in a 2-stroke cycle engine. 

Four stroke cycle: The majority of engines operate on 4-stroke cycle. Each cylinder requires 4 strokes of 

its piston i.e. two crankshaft revolution to produce one power stroke. Both S.I and C.I engines use this 

cycle. The 4-stroke cycle comprises of the following stages: 

Fig 1.2: 4-Stroke Cycle 

1. Intake stroke: Intake stroke starts with the piston at TC and ends with the piston at BC. During 

the stroke the intake valve opens to allow the fresh charge in. The pressure in the cylinder is less 

than the atmospheric pressure. As a result of the difference in pressures the charge flows into the 

cylinder. To increase the mass inducted, the inlet valve opens shortly before the stroke starts and 

closes after it ends. 

2. Compression stroke: The compression stroke starts when both the valves are closed and the 

mixture inside the cylinder is compressed to a small fraction of its initial volume. Towards the end 

of the compressions stroke, combustion is initiated and the cylinder pressure rises rapidly. 

3. Power stroke/Expansion stroke: It starts when the piston is at TC and ends at BC as the high 

temperature and pressure gases push the piston down and force the crank to rotate. As the piston 

approaches BC the exhaust valve opens to initiate the exhaust process and drop the cylinder 

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pressure. 

4. Exhaust stroke: In this stroke the remaining burned gases exit the cylinder first and as the piston 

approaches TC the inlet valve opens and just after TC the exhaust valve closes and the cycle starts 

again. 

2- Stroke Engines: In 2- Stroke Engines ports are used to control the exhaust and inlet flows while the 

piston is close to BC. The 2- Stroke Engines comprises of the following stokes. 

1. Compression Stroke: It starts by closing the inlet and exhaust ports and then compresses the 

cylinder contents and draws fresh charge into the crankcase. As the piston approaches TC, 

combustion is initiated. 

2. Power Stroke: It is similar to 4- stroke until the piston approaches BC when first the exhaust 

ports and then intake ports are uncovered. Most of the burnt gases exit the cylinder in an exhaust 

blow down process. When the inlet ports are uncovered the fresh charge, which has been, 

compressed in the crankcase flows into the cylinder. 

Fig 1.3: 

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The two-stroke engine produces twice the power as the four-stroke engine. However this does not make 

the two strokes twice as powerful. When the piston opens the transfer and exhaust ports there is always 

some mixing of fresh air-fuel mixture with the exhaust gases. This reduces the amount of fresh air-fuel 

mixture that enters. Also, only part of the piston stroke helps get air-fuel mixture into the cylinder. This 

further reduces the amount of air-fuel mixture that enters. And only part of the down stroke of the piston 

produces power. 

Comparison of 2-Stroke and 4-Stroke engines: 

1. For the same speed the power of the two-stroke is twice that of four-stroke. 

2. For the same power two-stroke is lighter than four strokes and occupies less space. 

3. The two stoke engines require lighter flywheel and foundation in comparison to four-stroke 

engines. 

4. There are no valves in 2-stroke engines only ports are present. Hence mechanism is simple. 

5. Scavenging is very poor in 2-stroke engine. 

6. In 2- stroke engines inlet and outlet valve open simultaneously resulting in low thermal efficiency. 

2. Method of ignition: 

Depending upon the method of ignition the I.C engines are classified as spark ignition (S.I) and 

compression ignition ( C.I ) engines. 

In (SI) spark ignition the fuel and air mixture is prepared outside the cylinder in a carburetor. From the 

carburetor the accurately metered quantity of the fuel mixture is fed into the cylinders where it is ignited 

by an electric spark. 

In C.I engines the fuel air mixture is prepared in the cylinder. The cylinder is charged with the air and 

then it is compressed. Thus the air being heated to a very high temperature at the end of the compression 

gets a finely atomized injected under a high pressure. This fine spray of fuel coming into contact with 

very hot air gets ignited and it is called compression ignition. 

3. Type of fuel burned: Spark ignition engines usually burn gasoline (petrol) whereas compression 

ignition engines uses diesel as fuel. The S.I engine works on Otto cycle and C.I engines works on Diesel 

engine cycle. 

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Otto Cycle: 

‣ It is an ideal cycle that approximates a spark ignition internal combustion engine. 

‣ It consists of two reversible adiabatic (without loss of heat) and two constant volume processes. 

Reversible adiabatic 

4 

4 

V=C S =C 

V=C 

5 

P 3 

V=C 

1 2 

T 

S =C 

3 

2 

V=C 

5 

V 

s 

T.C 

B.C 

1-2 Intake/suction: Air/Fuel mixture is drawn into 

the cylinder. 

2-3 Compression: The mixture is compressed 

adiabatically. 

3-4 Combustion: The mixture is ignited and 

burned at constant volume. 

4-5 Expansion: The gases then expand adiabatically 

5-2 Heat is discharged at constant volume 

2-1 Gases are swept out of the cylinder at constant 

pressure. 

Fig 1.4: Otto cycle 

Ratio of compression/Ratio of expansion (r): 

V 

2 = 

Heat supplied during the process 3-4: Q i = mC v (T 4 -T 3 ) 

Heat rejected during 5-2: Q o = mC v (T 5 -T 2 ) 

Thermal efficiency for Otto cycle: η = 

W 

Q 

i 

V 

3 

i 

V 

V 

Q − Q 

5 

4 

i o 

= = 

Q 

T 

1− 

T 

2 

3 

T 

( 

T 

T 

( 

T 

5 

2 

4 

3 

−1) 

−1) 

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We know further, 

T 

T 

3 

2 

V 

= ( 

V 

2 

3 

) 

k −1 

V 

= ( 

V 

5 k−1 

) 

4 

T 

= 

T 

T4 

Therefore, = 

T 

3 

4 

5 

T 

= 

T 

5 

2 

70 

η 

T2 

k 

and η = 1− 

= 1 − r 1− 

= 1 1 

− 

T r k − 1 

3 

r 

15 

Fig 1.5: Thermal efficiency of Otto cycle as a 

function of compression ratio. 

Diesel Cycle: 

‣ In diesel engine cycle only air without fuel is compressed and at the end of the compression stroke, 

fuel is injected into the compressed air and burns immediately. 

‣ It consists of two reversible adiabatic, one constant volume and one constant pressure processes. 

Reversible adiabatic 4 

3 

4 

P=C 

S =C 

P 

5 

T 

S=C 

3 

5 

V=C 

1 2 

2 

V 

s 

Ratio of compression (r): 

1-2 Intake/suction: Air/Fuel mixture is drawn into the cylinder. 

2-3 Compression: The mixture is compressed adiabatically. 

3-4 Combustion: The mixture is ignited and burned at constant pressure. 

4-5 Expansion: The gases then expand adiabatically 

5-2 Heat is discharged at constant volume 

2-1 Gases are swept out of the cylinder at constant pressure. 

Fig 1.6: Diesel cycle 

V2 

and Cutoff ratio (rc ): 

V 

3 

Heat supplied during the process 3-4: Q i = mC p (T 4 -T 3 ) & Heat rejected during 5-2: Q o = mC v (T 5 -T 2 ) 

V 

V 

4 

3 

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1 

Thermal efficiency for diesel cycle: η =1- 

k 

kr 

−1 

rc 

( 

r 

c 

k 

−1 

) 

−1 

Comparison of Otto and diesel cycle: 

Case 1: Same state at the beginning of compression and same piston displacement and compression ratio. 

4 

4 

P 

3 

4' 

5 

T 

3 

V=C 

P=C 

4' 

5 

1 2 

2 

V 

s 

Otto cycle: 1-2-3-4-5-2-1 ; Diesel cycle: 1-2-3-4'-5-2-1 

Efficiency of Otto Cycle is higher than diesel cycle 

Case 2: Compression ratio of diesel cycle is much higher than Otto cycle 

4 

p=C 

P 

3' 4 

3 

5 3 

T 

3’ 

v=C 

5 

1 1' 2 2 

s 

V 

Otto cycle: 1-2-3-4-5-2-1 ; Diesel cycle: 1'-2-3'-4-5-2-1' 

Efficiency of Otto Cycle is lower than diesel cycle 

Differences between Petrol and Diesel Engines: 

Petrol Engine 

It costs less, but running cost is more due to 

1 

costly fuel. 

Air and petrol mixture is sucked through inlet 

2 

valve. 

Diesel Engine 

It costs more initially, but the running cost is 

less as the diesel is cheaper than petrol. 

Only air is sucked during suction stroke. 

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3 Spark plug is used to ignite the mixture. An injector injects the fuel at high pressure 

4 It works on Otto cycle. It works on Diesel cycle. 

5 Carburetor is used to prepare the mixture. Fuel pump and injector is used. 

6 Compression ratio is from 6:1 to 9:1 Compression ratio is from 12:1 to 22:1 

7 Lighter in weight. Heavier in weight. 

8 Starting is easy due to low compression ratio. 

Starting is difficult due to high compression 

ratio. 

9 Maintenance cost is higher. Maintenance cost is lower. 

10 

No vibration when the engine is running idle or 

slow. 

Due to diesel knock the vibrations are always 

there. 

Geometrical Properties of Engine: 

a. Top Center (TC): The position at which the cylinder 

volume is minimum. 

b. Bottom Center (BC): The position at which the cylinder 

volume is maximum. 

c. Cylinder Bore (B): Inside diameter of the cylinder. 

d. Piston Stroke (L): The distance between the Top center 

and bottom center. 

e. Connecting Rod Length (l): It is the length of 

connecting rod. 

f. Crank Radius (a): It is the radius of the crank. (Stroke 

and crank radius are related by L = 2a) 

g. Clearance Volume (V c ): The volume of the combustion 

chamber when the piston is at the Top center (TC). 

h. Displacement Volume (V d ): The volume swept out by 

the piston or displaced volume is defined as the difference 

between the total volume (V t ) and the clearance volume 

(Vc)(V d = Vt - V c) 

Maximum cylinder volume 

i. Compression Ratio (r c ): r c = = 

Minimum cylinder volume 

Vc + Vd 

Vc 

Fig.1.7: Geometrical details 

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Engine Parameters 

(a) Mean Piston Speed (Sp) 

(b) Brake Torque (T): 

It is a measure of an engine ability to do work. 

(c) Brake Power (P b ): 

It is the rate at which work is done. 

(d) Indicated Power (P i ): The rate of work transfer 

from the gas within the cylinder to the piston. 

(e) Friction Power (P f ): It is the power required to 

overcome friction of the bearings, piston and other 

mechanical components of the engine and to drive 

the engine accessories. 

(f) Mechanical Efficiency (η m ): The ratio of the 

brake power delivered by the engine to the 

indicated power is called the mechanical efficiency 

(g) Mean Effective Pressure (mep): It is the ratio of 

work per cycle to the displaced cylinder volume per 

cycle. 

Sp = 2LN 

T = F x b, where F is the force and b is the 

perpendicular distance. 

P = 

i 

WN 

nR 

P = 2πNT 

b 

; Where nR is the number of 

crankshaft revolutions for each power 

stroke per cylinder. 

**Four stroke n R = 2; Two stroke n R = 1 

Relation between indicated power, brake 

power and friction power 

P i = Pb +P f: 

Pb 

η m = 

P 

3 

P( 

kW ). nR.10 

mep( kPa) 

= 

3 

Vd 

( dm ). N( 

rev / s) 

6.28. nR. 

T ( N. 

m) 

= 

3 

V ( dm ) 

(h) Specific Fuel Consumption: The fuel flow rate 

m 

f 

( g / h) 

sfc( 

g / kW. 

h) 

= ; 

per unit power output. P( 

kW ) 

d 

i 

(i) Fuel Conversion Efficiency: It is measure of 

engine efficiency. 

(j) Volumetric Efficiency: It is defined as the volume 

flow rate of air into the intake system divided by 

the rate at which volume is displaced by the piston. 

1 

η = 

sfc( 

mg / J ). Q 

m 

f 

( g / s) 

sfc( 

mg / J ) = 

P( 

kW ) 

f 

HV 

( MJ / kg) 

= 

ma 

η 

v 

= 

ρ V 

a, 

i 

3600 

sfc( 

g / kW. 

h). 

Q 

d 

HV 

( MJ / kg) 

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TUTORIAL 1 

1. The compression ratio in an Otto cycle is 8. At the beginning of the compression 

stroke the pressure is 0.1 Mpa and the temperature is 15 0 C. The heat transfer to 

the mixture is 1800 kJ/kg. Determine 

(a) The pressure and temperature at the end of each process of the cycle. 

(b) The thermal efficiency 

(c) The mean effective pressure 

2. A four cylinder automotive S.I engine is being designed to provide maximum brake 

torque of 150 N.m. The maximum brake mean effective pressure is 925 Kpa. 

Estimate the required engine displacement, bore and stroke and the maximum 

brake power the engine will deliver. The maximum rated engine speed is 87 rev/s 

and assume B = L. 

3. Calculate the mean piston speed, bmep and specific power of direct injection four 

stroke six cylinder Cummins diesel engine 

Displaced volume = 10 l, bore = 125 mm, stroke = 136 mm, compression ratio = 

16.3, maximum power = 168 Kw at rated speed of 2100 rev/min. 

4. The diesel engine of problem (3) is operating at a mean piston speed of 8 m/s. 

Calculated the air flow if the volumetric efficiency is 0.92. If (F/A) is 0.05 what is 

the fuel flow rate? 

5. The compression of a diesel cycle is 18. At the beginning of the compression 

stroke the pressure is 0.1 Mpa and the temperature is 15 0 C. The heat transfer to 

the air is 1800 kJ/kg. Determine 

(a) The pressure and temperature at the end of each process of the cycle. 

(b) The thermal efficiency 

(c) The mean effective pressure 

6. An engine has a swept volume of 300 cm 3 . If the compression ration is 8.5:1, 

determine the clearance volume. 

KHORSHED ALAM

MET285: AUTOMOTIVE TECHNOLOGY 

11 

CHAPTER 2 

CONSTRUCTIONAL DETAILS OF ENGINE (I) 

Engine Types: Number and arrangement of cylinders 

Cylinders can be arranged 

1. In a row (inline) 

2. In two rows or banks set at an angle (V type) 

3. In two rows or banks opposing each other (flat, pancake, or opposedcylinder 

type) 

4. Likes spokes on a wheel 

Important Points: 

‣ In-line engines have their cylinders arranged in a row. 3, 4, 5 and 6 

cylinder engines commonly use this arrangement. 

‣ The "V" arrangement uses two banks of cylinders side-by-side and is 

commonly used in V-6, V-8, V-10 and V-12 configurations. 

‣ Flat engines use two opposing banks of cylinders and are less common 

than the other two designs. They are used in Subaru's and Porsches in 4 

and 6 cylinder arrangements as well as in the old VW beetles with 4 

cylinders. Flat engines are also used in some Ferrari's with 12 cylinders. 

Fig 2.1: Cylinder 

arrangements 

Basic components of an engine 

1. Cylinder head: A cylinder head is bolted to the top of each bank of cylinders to seal the individual 

cylinders and contain the combustion process that takes place inside the cylinder. The cylinder head 

contains at least one intake valve and one exhaust valve for each cylinder. 

Most engines have two 

Fig 2.2: Cylinder Head 

valves per cylinder, one 

intake valve and one 

exhaust valve. Some newer 

engines are using multiple 

intakes and exhaust valves 

per cylinder for increased 

engine power and 

efficiency. 

These engines are sometimes named for the number of valves that they have such as "24 Valve V6" which 

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indicates a V-6 engine with four valves per cylinder. Modern engine designs can use anywhere from 2 to 5 

valves per cylinder. 

2. Cylinder block and crankcase: The engine block or 

cylinder block is the foundation of the engine. All other 

engine parts are assembled in or someway attached to the 

cylinder block. The large holes in the block are the cylinder 

bores. Water cooled engines have passages surrounding each 

cylinder, valve and spark plug. Coolant flows through these 

spaces to pick up heat and carry it away from the engine. 

Parts attached to and installed in block: 

a) Crankshaft with main bearings 

b) Piston and piston rings 

c) Connecting rod 

d) Cylinder head 

e) Oil sump and pump 

3. Engine Manifold: For the engine to run, it must able to 

“breathe”. Passages must carry the air or air-fuel mixture to 

the intake ports in the cylinder head. Then, after combustion, 

other passages must carry the burned gases away from the 

exhaust ports in the cylinder head. 

Fig 2.3: Cylinder Block 

Fig 2.4: Engine Manifold 

4. Oil sump: The sump is steel pressing bolted to the underside of the crankcase and used to hold the oil. 

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5. Cylinders: The cylinders form the stationary part of the gas tight seal in which the piston moves. 

6. Pistons: The piston forms a sliding gas 

tight seal in the cylinder bore and transmits 

the force of the gas pressure to the small 

end of the connecting rod. The piston must 

posses the following characteristics. 

a. Rigidity to withstand the high pressure. 

b. Light 

c. Good heat conductivity 

Fig 2.5: Piston 

d. Low expansion coefficients 

** Pistons are made of aluminum because it is a 

light metal. It can either be cast or forged. 

7. Piston rings: To prevent the escape of 

expanding gases piston rings are fitted into 

the grooves of the piston. The piston rings 

also prevent oil from entering into the 

combustion chamber and also conduct heat 

from the piston to the cylinder walls. 

Usually pistons are fitted with two 

compression rings and one oil ring. 

a. Compression rings seal compression and 

combustion pressure in the combustion 

chambers and help prevent blowby. 

b. Oil rings scrapes the excess oil off the 

cylinder walls and returns the oil to the 

Fig 2.6: Piston Rings 

crankcase. 

8. Gudgeon pin: The gudgeon pin connects the piston to the connecting rod. 

Fig 2.7: Gudgeon Pin 

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9. Connecting rod: The purpose of the connecting 

rod is to connect the piston and the crankshaft at 

the same time converting up and down motion or 

reciprocating motion of the piston to rotary 

motion at the crankshaft. The small end of the 

connecting rod is connected to the piston while 

the big end is fixed to the crankshaft. 

10. Crankshaft: The crankshaft is a one piece casting 

or forging of heat treated alloy steel. Counter 

weights placed opposite the connecting rod 

journals balance the crankshaft. A journal is any 

part of a shaft that rotates in a bearing. The 

output end of the crankshaft has the flywheel or 

drive plate attached to it. The front end has the 

gear or sprocket that drives the camshaft, the 

vibration damper and the drive-belt pulley. 

Fig 2.8: Connecting Rod 

Fig 2.9: Crankshaft 

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11. Flywheel: Each power stroke delivers a sudden power impulse to the crankshaft. This causes the 

crankshaft to speed up. 

During the other three piston 

strokes, the crankshaft tries to slow 

down. However, a weight on one 

end of the crankshaft helps it 

turning smoothly. On vehicles with 

a manual transmission this weight is 

a heavy metal flywheel that bolts to 

Fig 2.10: Flywheel 

the rear end of the crankshaft. 

The flywheel helps smooth out the power flow by resisting any sudden change in the crankshaft’s 

speed of rotation. Vehicles with an automatic transmission have a light drive plate with a fluid filled 

torque converter attached to the crankshaft. Some engines have a dual or tandem mass flywheel. 

This is basically two separate flywheels, a primary flywheel and a secondary flywheel. The primary 

flywheel attaches to the crankshaft flange. As the crankshaft rotates, engine power is transmitted 

from the primary flywheel through torsional springs to the secondary flywheel. This arrangement 

allows the springs to absorb the crankshaft torsional vibration caused by the engine power impulses. 

Fig 2.11: Primary & Secondary Flywheel 

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12. Valves: Valves allow the engine to “breathe”. Intake valves open to admit air-fuel mixture toe the 

cylinders. Exhaust valves open to allow burned gases to exit or exhaust from the cylinders. Valves open 

and close at predetermined times, which vary with different engines. They are several different 

arrangements of valves and valve trains. They differ in 

a) Location of the camshaft 

b) How the camshaft is driven 

c) Type of valve train 

d) Number of valves per cylinder 

a) Location of the camshaft: The camshaft is either in the cylinder block or on the cylinder head. An 

engine with the camshaft in the block is an overhead valve (OHV) or pushrod engine. When the 

camshaft is on or in the cylinder head, the engine is an overhead camshaft (OHC) engine. 

b) Type of camshaft drive: Camshafts are driven by timing gears, sprockets and timing chain or sprockets 

and toothed timing belt. Some engines use a combination of timing chain and timing belt to drive the 

camshafts. 

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c) Type of valve train: Three types of valve trains are shown in figure below 

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d) Number of valves per cylinder: Some engines have more then two valves per cylinder. Some have 

three, four, five and even six valves in each cylinder. These are multivalve engines. 

13. Camshaft: The function of the camshaft is to operate the valves. The camshaft can either be located 

overhead or at the side of the engine. 

camp lobe with necessary figure. 

explain the 

Combustion Chamber shapes: 

The combustion chamber usually cast into the cylinder head and then machined as necessary. The greater the 

turbulence of the A/F mixture in combustion chamber the faster it burns. There are four basic shapes of the 

combustion chamber. 

1. Wedge: It increases the turbulence (Unrest) of 

the burning mixture but has high exhaust 

emissions. 

2. Hemispheric (open): It provides relatively slow 

burning. 

3. Cup (bowl): A flat cylinder head is used with a 

piston that has a cup or bowl in its tops. This 

forms a combustion chamber that improves 

turbulence in diesel, turbo charged and high 

performance engine. 

4. Crescent (pent roof): The crescent or pent roof 

can be easily be changed to vary the compression 

ratio and turbulence. Only the height and shape 

of the piston head must be changed. 

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Pre-combustion chamber: A pre-combustion chamber is a separate small combustion chamber where 

combustion begins. A primary intake valve opens into the main combustion chamber. An auxiliary 

intake valve opens into the pre-combustion chamber. Both the valves open at the same time. The 

auxiliary intake valve admits the rich mixture. The primary intake valve admits the lean mixture. The 

spark plug in the pre-combustion chamber ignites the rich mixture. 

The burning rich mixture then streams out of the pre-combustion chamber rapidly mixing with and 

igniting the lean mixture in the main combustion chamber. The effect produces high turbulence and 

good combustion. A spark-ignition engine using a pre-combustion chamber is a stratified-charged 

engine. (“Stratified” means in layers). 

** The diesel engine is a stratified charge engine 

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Knocking in S.I Engines 

Scavenging: It is a process of removing the burnt gases in internal combustion engines from the 

combustion chamber of the engine cylinder. 

Supercharging: Supercharging is supplying the intake air to the engine cylinder at a pressure greater than 

the pressure of surrounding atmosphere using blower or compressor. 

Advantages: When pressure increases, density and temperature also increases resulting in better combustion. 

Disadvantage: It increases the possibility of detonation (explosion) in petrol engines and decreases the 

knocking in diesel. 

Auto-ignition: Phenomena by which a fuel catches fire without external flame. 

Pre-ignition: It is ignition of the charge in S.I engine before the spark occurs in the spark plug. 

Ignition Lag: Time taken by the fuel after injection to reach up to auto-ignition temperature. 

Detonation: The rapid auto-ignition of a portion of a fuel causes pressure waves. These waves are of high 

intensity resulting in blow to cylinder making loud noise resulting in knocking of the engine. 

Knocking can be classified as 

‣ Knocking in SI Engine – sudden auto ignition farthest away from the spark plug. 

‣ Knocking in CI engine – sudden auto ignition of the mixture at the very beginning of the 

combustion process. 

Knocking in S.I engine: It can be prevented if the end mixture is having 

‣ Low density: Knocking increases by supercharging the engine, opening throttle, increasing the 

compression ratio and advancing the spark timing. 

‣ Low temperature: Knocking increases by supercharging, increasing the inlet air temperature, 

increasing the coolant air temperature and compression ratio. 

‣ Long ignition delay: knocking increases by decreasing the speed and turbulence and increasing the 

distance of the flame travel in combustion process. 

‣ Lean or rich mixture: Possibility of knocking increased by low self-ignition temperature, chemically 

correct mixture and short ignition delay. (Rich mixture is sometimes used to suppress knocking) 

Knocking in C.I engine: It can be prevented if the first element of the fuel and air is having high density, 

high temperature, short ignition delay and reactive mixture. 

Octane number: The percentage volume of iso-octane in a mixture of iso-octane and normal heptane (nheptane), 

which shows the tendency to knock as the given fuel when tested in a specified condition is 

known as octane number of the fuel. 

Cetane number: The percentage volume of cetane in a mixture of cetane and alpha methyl naphthalene, 

which gives the same ignition delay as the given fuel when tested in a specified condition is known as cetane 

number. 

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21 

Exercise 

1. Identify the type of engines 

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22 

CHAPTER 3 

LUBRICATION 

Engine bearing surfaces: The engine bearing surfaces in an internal combustion engines are 

1. Cylinder surfaces 2. Connecting rod bearing 3. Crankshaft bearing 4. Valve mechanism bearings 

Purpose of lubricating oil 

a. The oil lubricates moving parts to reduce wear 

b. As the oil moves through the engine, the oil picks up heat. 

c. Oil fills the clearance between bearings and rotating journals 

d. The oil helps form a gas tight seal between piston rings and cylinder walls. 

e. The oil acts as a cleaning agent. 

Note: 

1. The oil on the cylinder surfaces should provide a seal against leakage. 

2. It prevents the piston from touching the cylinder surface 

3. The lubricant must have high flash point which is higher than the inside surface temperature of the 

cylinder at this point. 

4. Higher the operating temperature the higher should be the viscous characteristics of the lubricant. 

5. For large piston clearances, oil with a heavy body should be used. 

6. Light oils should be used for connecting rod bearings and crankshaft operating at high rubbing speed 

and low loads. 

7. The power required for starting an engine at low temperature depends principally upon the viscosity of 

the oil in the bearing surface at that temperature. 

Classification of lubrication system 

Lubrication systems may be classified as follows - Splash and Pressure feed 

Splash system: The lower ends of the connecting rods, dip into the oil and splash it over the lower cylinder 

surfaces as well as the crank-case surfaces. The piston spreads the oil over the cylinder surfaces while the ducts 

or channels lead the oil from other surfaces to the crankshaft and cam-shaft bearings. The lower connecting 

rod bearings have oil forced in through a hole in the lower half during the time the rod dips into the oil. 

Disadvantage: Lack of positive circulation to the bearings which limits the bearing loading and quantity of oil 

circulated. 

Pressure Feed: The force-feed system supplies oil under pressure to the various bearings. The oil flows 

through a strainer and into the suction line of the pump, all of which is usually located in a sump in the bottom 

of the crankcase. 

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Figure 1 shows the lubricating system for an inline 4 

cylinder overhead camshaft engine. The oil pump 

picks up oil from the oil pan. The pump sends the oil 

through the oil lines to the main bearing that support 

the crankshaft. Some oil flows from the main bearing 

through oil holes drilled in the crankshaft to the rod 

bearings. The oil flows through the bearing oil 

clearance and then is thrown off the moving parts. At 

the same time, oil flows through an oil line to the 

cylinder head. There the oil flows through an oil 

gallery to lubricate the camshaft bearings and valve 

train parts. After the oil circulates to all engine parts, it 

drops back down into the oil pan. 

Fig 1: Lubricating System for a four cylinder OHV S.I Engine 

Figure 2 shows the lubricating 

system for an inline overhead valve 

(OHV) engine. Oil flows up through 

hollow pushrods to lubricate the 

rocker arms and valve stems. Some 

of the oil thrown off the connecting 

rod bearing lands on the cylinder 

walls. This lubricates the pistons, 

piston rings and piston pins. 

Fig 2: Lubricating system for an inline OHV engine 

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Lubricating System Components: 

1. Oil Pan: 

It is fitted on the bottom of the cylinder block to store the oil. 

A gasket between the pan and the block seal the joint and prevent oil leaks. 

Most pans hold 3L to 8L of oil 

2. Oil Pump: 

Two types of oil pumps used in automotive engines: gear and rotor. 

In overhead valve engines the camshaft spiral gear that drives the ignition distributor usually drives the oil 

pump. 

Some engines drive the distributor directly from the end of an overhead camshaft. The oil pump on these 

engines may be driven by a separate drive shaft or jackshaft. 

3. Pressure Relief Valve 

To prevent excessive oil pressure, the lubricating system has a pressure regulator valve or relief valve. 

It is a spring loaded ball or plunger 

4. Oil cooler 

It prevents oil from getting too hot. 

In the oil cooler, engine coolant flows past tubes carrying hot oil. The coolant picks up the heat and carries it 

to the radiator. 

5. Oil filters 

The filter allows the oil to pass through while trapping particles of dirt and carbon. 

The filter has a pleated paper filtering element. 

The filter has a spring loaded bypass valve to protect the engine from starvation if the filter clogs. 

6. Lubricating system Indicators 

Indicator Light 

Electric, electronic or digital gauge for oil pressure 

Dip stick 

Oil change indicator 

Types of filtration systems: The pump distributes the oil to the crankshaft bearings, piston and camshaft. 

The pressure feed lubrication system is of two types 

1. Full flow filtration system – The oil is filtered before it is send to the bearings. 

2. By pass filtration system - The oil is filtered after it lubricates the bearings. 

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Full flow filtration system 

By pass filtration system 

Properties of lubricating oil 

1. Proper viscosity: Engine oil should have the proper viscosity so it flows easily to all moving engine parts. 

Low viscosity reduces the ability of the oil to stay in place between moving parts. 

If the oil is too thin it is forced out from between the moving parts. Rapid wear results. 

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An oil that is too thick flows too slowly to engine parts, especially when the engine and oil are cold. This also 

caused rapid engine wear. 

2. Viscosity Index: This is a measure of how much the viscosity of an oil changes with temperature. 

Viscosity index improvers are added to engine oil so its viscosity stays more nearly the same, hot or cold. 

3. Viscosity numbers: Oils are rated for winter or for other than winter. 

Winter grade oils are SAE 5W, SAE 10 W … (SAE stands for society of automotive engineers). 

The W stands for winter. For other than winter use, single viscosity oil grades are SAE 20, SAE 30 ….. 

The higher the number, the thicker the oil 

4. Multiple viscosity oil: A multiple viscosity oil graded SAE 5W-30 has the viscosity of an SAE5W oil 

when cold and SAE30 when hot. 

5. Resistance to carbon formation and oil oxidation 

6. Corrosion and rust inhibitors 

7. Foaming resistance 

8. Detergents-dispersants 

9. Extreme pressure resistance 

10. Energy conserving oils 

11. Synthetic oil 

2 Stroke Gasoline/Petrol Lubrication 

‣ Most 2-stroke gasoline/petrol engines use a set gasoline/petrol-oil mixture for lubrication. As the air, fuel 

and oil enter the crankcase, the fuel evaporates, leaving behind enough oil to keep parts coated and 

lubricated. 

‣ Oil Injection system: An oil injection system doesn’t need the oil and gasoline/petrol mixed manually. 

An engine-driven oil pump takes oil from a tank and pumps a measured amount directly into the engine 

where it mixes with the fuel and lubricates the internal engine parts. 

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CHAPTER 4: CARBURETOR 

A Carburetor is a mixing device that can supply a 

spark ignition engine with a combustible mixture of 

air and fuel. 

Types of carburetor: 

• Fixed venturi/Variable venturi 

• Single barrel/two barrel/4 barrel 

• Feed back/ Non-feed back 

Float-type Carburetor 

• A fuel metering device that uses a float-actuated 

needle valve to maintain fuel level slightly 

below the edge of the discharge nozzle. 

• Measures the amount of air entering the engine. 

• Meter into this air the correct amount of 

atomized liquid gasoline. 

• Convert the liquid fuel into fuel vapors and 

distributes uniformly to the cylinders. 

• Varies mixture based on engine needs. 

• Internal Systems 

• Float system 

• Idling system 

• Metering System 

• Power System 

• Acceleration system 

• Choke system 

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A/F ratio with different speeds 

Choke system supplies a rich mixture for 

starting. 

As the engine warms up and its speed increases, 

the mixture leans out. 

At intermediate speed, with the throttle valve 

only partly open, both idle and main metering 

system supply fuel. 

As the throttle opens wider, the main metering 

system takes over completely. 

At full throttle and higher speeds, the power 

system comes on. It enriches the air-fuel 

mixture for full power. 

IDLE SYSTEM 

When the throttle is closed there is not enough 

air flowing to produce a pressure low enough to 

pull the fuel from the float bowl through the 

main metering jet, so a separate system is used. 

When the engine is idling all air must pass 

around the edge of a butterfly valve. 

– Airflow is restricted, causing travel 

at high velocities resulting in lower 

pressures. 

The idle mixture adjustment knob controls the 

amount of fuel flow and allows a smooth idle 

to be set at any given speed. 

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LOW SPEED OPERATION 

When the throttle valve opens slightly and the 

edge of the throttle valve moves above the idle 

port to the low speed port or transfer port. 

MAIN METERING SYSTEM 

The throttle valve is open and the main nozzle 

is discharging fuel. 

The wider the throttle opens, the faster the air 

flows through and the greater the venture 

vacuum. This causes more fuel to discharge 

from the main nozzle to maintain the proper 

air-fuel ratio. 

POWER SYSTEM 

For high speed, full power, wide open 

throttle operation, the air-fuel mixture must 

be enriched. 

When the throttle valve is open, the metering 

rod is raised so that the smaller diameter of 

the rod is in the jet. This allows additional 

fuel to flow. 

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ACCELERATION PUMP SYSTEM 

When the throttle valve opens for vehicle 

acceleration, there is a sudden rush of air 

through the carburetor. Unless additional fuel is 

immediately delivered, the air fuel mixture will 

be so lean that the engine will hesitate. 

The accelerator pump supplies the additional 

fuel needed for quick acceleration. 

CHOKE SYSTEM 

Closing the choke valve increases the vacuum 

in the carburetor; this causes the main nozzle to 

discharge fuel. 

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CHAPTER 5: ENGINE COOLING SYSTEM 

The primary job of the cooling system is to keep the engine from overheating by transferring this heat to 

the air, 

The cooling system also has several other important jobs as below; 

1. To remove the cylinder wall heat 

3. To prevent burning of lubricants 

2. To prevent preignition of charge 

4. To do away possible seizure of the piston 

Methods of cooling: Air cooling and water cooling 

Air cooled Engines: 

‣ All air cooled cylinders have extended surface (fins) to increase the rate of heat transfer. Air movement 

over the cylinders is usually accomplished by a fan or propeller. 

‣ The amount of extended surface depends upon the rate of heat transfer. 

‣ The external surface may be obtained in several ways. It can be either screwed into the cylinder wall or 

cast deep as thin ribs on the cylinder wall. 

‣ The parts of the cylinder which are subjected to the highest temperatures should be provided with the 

most surface. The hottest part of the cylinder will be the combustion chamber walls and particularly that 

part around the exhaust valve. 

‣ A study of the conductivity of metals discloses the fact that aluminum and copper transfer heat much 

more readily than cast iron. 

Advantages: 

Disadvantages: 

Lightness, operability at extreme conditions, Difficulty in maintaining even cooling, bulky fan and 

easier maintenance and early warm-up 

noisy 

Servicing requires: 

Drive belts to cooling fan, Cooling air intake ducts, Cleaning heat sink cooling fins – prevent ‘hotspots’. 

Water Cooled Engines: 

Advantages: 

Disadvantages: 

Quieter operation and greater temperature Lower power to weight, slow to reach operating 

control 

temperature and at risk of frost(ica) damage 

Main Components: 

Radiator 

Pump 

Pressure Cap and expansion reservoir Fan 

Thermostat 

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Cab heat 

exchanger 

Heater Control 

Thermostat 

Radiator 

Engine Block & 

Cylinder head 

Water Jacket 

Water 

Pump 

Fan 

Radiator: 

The function of the radiator is to ensure close 

contact of the hot coolant coming out of the 

engine with outside air, so as to ensure high 

rates of heat transfer from the coolant to air. 

A radiator consists of an upper (or 

header) tank, core and the lower (or 

collector) tank. Besides, an over flow pipe 

in the header tank and drain pipe in the lower 

tank are provided. Hot coolant from the 

engine enters the radiator at the top and is 

cooled by the cross flow of air while flowing 

down the radiator. The coolant collects in the 

collector tank from where it is pumped to the 

engine for cooling. 

There are two basic types of radiator core- tubular and cellular type. 

-In tubular core the coolant flows through the tubes and air passes around them, 

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While, in the cellular type the air passes through the tubes and coolant flows in the spaces in 

between them. 

-Tubular type is further classified depending upon the shape of the fins around the tubes which are 

meant to increase the area for heat transfer from the coolant to the cooling air. 

Water Pump 

The pump circulates the fluid whenever the engine is 

running. 

Pump Belt connected to the crankshaft of the engine. 

Hoses are connected for circulation of coolant 

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Fan - Function and Components 

Function: To drive the airflow through the radiator. 

Components: Fan and drive mechanism 

Arrangements: 

‣ Mounted on the water pump shaft (rear wheel drive). 

Thermostatic control,flexible fan blades, variable angles 

of blades and different number of blades. 

‣ Independently mounted fans (in front wheel drive cars), 

Electrical and Thermostatic control. 

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Problem: 

A water cooled four cylinder engine with cast iron cylinder walls, bore 80 mm, stroke 110 mm and wall 

thickness 7 mm is running at 3500 rpm. At this speed, 10 percent of the energy input is being transferred to 

the cylinder walls. The consumption of fuel, whose calorific value is 42,000 kJ/kg is 300 gm/min. Assume 

thermal conductivity of cast iron as 168 kJ/m hr. 0 C. Calculate: 

A. Temperature drop through cylinder walls 

B. Temperature drop from the cylinder walls to cooling water which is being circulated at a speed of 50 

cm/sec. Assume film coefficient of heat transfer at this speed as 37800 kJ/m 2 hr 0 C 

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CHAPTER 6: FUEL INJECTION SYSTEM 

In an internal combustion engine, the fuel injection system is that delivers fuel or a fuel-air mixture to the cylinders 

by means of pressure from a pump. 

Note: 

It was originally used in diesel engines because of diesel fuel's greater viscosity and the need to overcome the 

high pressure of the compressed air in the cylinders. 

A diesel fuel injector sprays an intermittent, timed, metered quantity of fuel into a cylinder, distributing the fuel 

throughout the air within. 

Fuel injection is also now used in gasoline engines in place of a carburetor. In gasoline engines the fuel is first 

mixed with air, and the resulting mixture is delivered to the cylinder. 

Computers are used in modern fuel injection systems to regulate the process. The positive effects of fuel 

injection are that there is more efficient fuel combustion, better fuel economy and engine performance and 

reduced polluting exhaust emissions. 

Continuous Injection: A Cloud of mixture is formed in the manifold, ready to be drawn into each cylinder when 

the inlet valve opens. 

Timed or Sequential Injection: Injection takes place over a limited period usually though not always once per 

revolution of the crankshaft. 

Simultaneous double-fire injection/Phased injection: Electronically control the air-fuel ratio accurately and 

injection is once every two revolution of the crankshaft. 

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Basic Function: 

-The fuel injector acts as the fuel-dispensing nozzle or supplying nozzle. It injects liquid fuel directly into the 

engine's air stream. In almost all cases this requires an external pump. 

-The process of determining the amount of fuel, and its delivery into the engine, are known as fuel 

metering. 

- Early injection systems used mechanical methods to meter fuel (non electronic, or mechanical fuel injection). 

--Modern systems are nearly all electronic, and use an electronic solenoid (the injector) to inject the fuel. A CPU 

calculates the mass of fuel to inject. 

Typical EFI (Engine Fuel Injection) Components: 

a. Injectors 

d. ECU - Electronic Control Unit; includes a digital CPU, and 

b. Fuel Pump 

circuitry to communicate with sensors and control outputs. 

c. Fuel Pressure Regulator 

e. Various Sensors 

Fuel Injectors: Fuel injector consists of a nozzle holder and an 

injection nozzle. 

Nozzle holder: The purpose of the nozzle holder assembly is 

to position and contain the injection nozzle. The holder 

assembly also provides fuel passage to and from the injection 

nozzle; provides a pressure adjustment mechanism and provides 

a means to position the injector securely in relation to the 

cylinder head. 

Injection Nozzle: The purpose of the injection nozzle is to 

direct and atomize the metered fuel into the combustion 

chamber. The combustion chamber design dictates the type of 

nozzle, the droplet size, the spray pattern and the spray angle 

required to achieve complete combustion within a given time 

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and location. 

Fuel Injectors: Differential type nozzles are the most common Their design include the short or long reach multi 

hole type, single hole type, standard pintle type, throttling type and pintaux type. Spray cones are precisely 

calculated to achieve maximum fuel efficiency to achieve complete combustion and to reduce emissions. These 

objectives are achieved through the nozzle hole size, length of the nozzle holes, spray angle and injection pressure. 

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Engine Sensors 

In order to provide the correct amount of fuel for every operating condition, the engine control unit (ECU) has to 

monitor a huge number of input sensors. Here are just a few: 

• Mass airflow sensor - Tells the ECU the mass of air entering the engine 

• Oxygen sensor(s) - Monitors the amount of oxygen in the exhaust so the ECU can determine how rich or 

lean the fuel mixture is and make adjustments accordingly 

• Throttle position sensor - Monitors the throttle valve position (which determines how much air goes into 

the engine) so the ECU can respond quickly to changes, increasing or decreasing the fuel rate as necessary 

• Coolant temperature sensor - Allows the ECU to determine when the engine has reached its proper 

operating temperature 

• Voltage sensor - Monitors the system voltage in the car so the ECU can raise the idle speed if voltage is 

dropping (which would indicate a high electrical load) 

• Manifold absolute pressure sensor - Monitors the pressure of the air in the intake manifold 

The amount of air being drawn into the engine is a good indication of how much power it is producing; and 

the more air that goes into the engine, the lower the manifold pressure, so this reading is used to gauge how 

much power is being produced. 

• Engine speed sensor - Monitors engine speed, which is one of the factors used to calculate the pulse 

width 

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4

Chapter 7:Ignition System 

The function of the ignition system is to produce spark in the engine cylinder towards the end of the 

compression stroke. 

In a fours stroke engine a spark should occur in each cylinder after two revolutions of the crankshaft whereas 

in 2 stroke engine a spark in each cylinder is requires every revolution of the cylinder. 

Requirements of an ignition system: 

1. Spark at the plug electrodes must be regular and synchronously timed with respect to the cylinder-piston 

position at all speeds and loads on the engine 

2. Spark should be sufficiently strong so as to start ignition of the charge. 

3. The spark duration should be sufficient to establish burning of the air-fuel mixture under all conditions. 

4. Ability to produce spark even when carbon, oil or water condensation deposits on electrodes. 

5. Power consumed to produce spark should be minimum 

6. Must be light/compact and easy to manufacture 

Timing: The timing of the spark is important, and the timing can either be advanced or retarded (delayed) 

depending on conditions. 

The time that the fuel takes to burn is roughly constant. But the speed of the pistons increases as the 

engine speed increases. This means that the faster the engine goes, the earlier the spark has to occur. This 

is called spark advance: The faster the engine speed, the more advance is required. 

The purpose of the ignition system is two fold: 

1. First to create a voltage high enough (20,000+) to arc cross the gap of a spark plug, thus creating a spark 

strong enough to ignite the air/fuel mixture for combustion; 

2. Second to control the timing so that the spark occurs at the right time and at the right cylinder. 

Types of ignition system: 

Conventional Ignition system (Point Type) 

• Battery Ignition System 

• Magneto Ignition System 

Battery Ignition System 

Electronic Ignition system (solid state) 

All ignition systems have two circuits; 

The Primary Circuit: The primary circuit is the low voltage circuit that controls the ignition system. The 

primary circuit consists of: 

Battery - provides the power to run the system. 

Ignition Switch - allows the driver to turn the system on and off.

Ballast Resistor - reduces battery voltage from 12 volts to 9 volts. 

Points - a mechanical switch that acts as the triggering mechanism. 

Condenser - protects the points from burning out. 

Primary Coil - produces the magnetic field which creates the high voltage in the secondary coil. 

Wires - join all the components together. 

The Secondary Circuit: The secondary circuit is the circuit which converts magnetic induction into high 

voltage electricity to jump across the spark plug gap, firing the mixture at the right time. The Secondary 

Circuit consists of: 

Secondary Coil - the part of the coil that creates the high voltage electricity. 

Coil Wire - a highly insulated wire, that takes the high voltage from the coil, to the distributor cap. 

Distributor Cap - a plastic cap which goes on top of the distributor, to hold the high tension wires in the right 

order. 

Rotor - spins around on the top of the distributor shaft, and distributes the spark to the right spark plug. 

Spark Plug Wires - another highly insulated wire that takes the high voltage from the cap to the plugs. 

Spark Plugs - take the electricity from the wires, and give it an air gap in the combustion chamber to jump 

across, to light the mixture. 

Principles 

1. When electricity flows through a coil, a magnetic field is built up around the coil. 

2. When a coil passes through magnetic lines of force, cutting them, a voltage is induced in the coil. 

3. Three things are needed to produce electricity: 

1. Magnetic Field 

2. Circuit - a path for the electricity to go through. 

3. Motion - either the wire, or the magnetic field, has to move. 

So, How Does The Ignition System Work Anyway? 

When the switch is ON the battery is connected to the ignition coil and the primary circuit is closed and the 

magnetic field is generated. 

The switch also turns the motor which rotates the crankshaft resulting in movement of the rotor in the 

distributor. The contact breaker breaks the circuit and the primary circuit is open and the magnetic field 

collapse resulting in high voltage in the secondary windings. These secondary windings are connected to the 

spark plugs. 

Primary Circuit Parts 

Ignition Coil: The coil is the device that generates the high voltages required to create a spark. It is a simple 

device -- essentially a high-voltage transformer made up of two coils of wire. The ignition coil contains both 

the primary and secondary winding circuits. The coil primary winding contains 100 to 150 turns of heavy 

copper wire. The turns of this wire must be insulated from each other or they would short out and not create 

the primary magnetic field that is required. The primary circuit wire goes into the coil through the positive 

terminal and exits through the negative terminal. The coil secondary winding circuit contains 15,000 to 30,000 

turns of fine copper wire, which also must be insulated from each other. To further increase the coils magnetic 

field both windings are install around a soft iron core. To withstand the heat of the current flow, the coil is 

filled with oil for cooling. As current flows through the coil a strong magnetic field is built up. When the 

current is shut off, the collapse of this magnetic field induces a high voltage which is released through the large 

center terminal through the distributor to the spark plugs.

Contact Points: The points are simple mechanical 

switch that turns on and off the ignition coil. The 

are opened by the distributor cam, and closed by 

the point spring. When they are closed, the 

electricity flows from the battery to the ignition 

switch on the steering column, to the positive side 

of the primary coil, and across the points to 

ground. The only way the electricity can get to 

ground is across the points, so when the points 

open, electrons can no longer flow and the 

magnetic field around the coil collapses. The 

points are the weak link in an ignition system that 

includes them. After as little as 1000 miles they 

have deteriorated significantly, and gone out of 

adjustment. By 20,000 miles the engine is not likely 

to run at all. The points must be replaced, and 

adjusted at the time of a tune-up. 

Condenser: The sole purpose of the condenser is to protect the points, and keep them from burning out 

prematurely. The condenser is merely a storage room for electrons. 

Distributor: Distributor housing contains the contact breaker, condenser, ignition advance mechanism and 

the distributor. 

As the engine rotates, the camshaft turns the distributor, which then opens and closes 

the breaker points as many as 15,000 to 25,000 times a minute. When the points are 

closed, current is allowed to flow through the ignition coil, thereby building a magnetic 

field around the windings. When the points are opened, they interrupt that current 

flow, thereby collapsing the magnetic field and releasing a high voltage surge (flow). 

This high voltage enters the top of the distributor, where an ignition rotor distributes 

that voltage through a cap to the right spark plug at the right time.

The function of the distributor is to distribute the high voltage from the coil to each 

of the sparking plugs at regularly timed intervals in the sequence of the engine firing 

order. 

The common firing orders are: 4 cylinder 1-3-4-2 or 1-2-4-3; 6 cylinder 1-5-3-6-2-4 

The distributor consists of a cap and rotor. The cap is held firmly in place by spring 

type clips or screws; the housing is attached to the engine block or head by means 

of a screw and retainer plate with a gasket in between the housing and the engine. 

This ensures the housing will not move. 

The coil is connected to the rotor, which spins inside the cap. Rotor is fitted on the 

top of the shaft carrying the breaker cam. 

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. 

• A : High voltage lead from coil 

• B: Cap- Rotor contact button 

• C: Distributor cap 

• D: High voltage to sparkplug 

Spark Plug 

The spark plug is quite simple in theory: It forces electricity to arc across a gap. 

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. 

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. 

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. 

The carmaker will select the right temperature plug for each car. Some cars with high-performance engines 

naturally generate more heat, so they need colder plugs. If the spark plug gets too hot, it could ignite the 

fuel before the spark fires; so it is important to stick with the right type of plug for your car.


Chapter # 8TRANSMISSION SYSTEM 

• When a vehicle is moving at a uniform speed, the driving force or tractive effort, at the wheels must be 

such as to exactly balance the sum of three categories of variable forces tending to oppose the motion. 

• The three forces are – 

1. aerodynamic or air resistance, 

2. gradient resistance 

3. and rolling resistance. 

• Aerodynamic resistance – The air offers a resistance to the passage of bodies through it. The magnitude 

of this resistance is dependent directly upon the shape and frontal area of the body exposed to the fluid, it 

is passing through and to the square of its velocity. 

• Gradient resistance- It depends on the steepness of the slope. 

• Rolling (Miscellaneous) resistance – All the remaining forces resisting motion at constant speed come 

under the heading of rolling resistance. E.g. Resistance of tires. 

• If traction effort is greater than total resistance, the car will accelerate, and if it is smaller, it will decelerate 

until a balance is obtained. 

The requirements for the transmission are as follows: 

1. To provide for disconnecting the engine from the driving wheel. 

2. When the engine is running, to enable the connection to the driving wheels to be made smoothly and 

without shock. 

3. To enable the leverage (force) between the engine and driving wheels to be varied. 

4. It must reduce the drive-line speed from that of the engine to that of the driving wheels in the ratio of 

somewhere between about 3:1 and 10:1 or more, according to the relative size of engine and weight of 

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vehicle. 

5. Turn the drive if necessary, through 90 0 or perhaps otherwise realign it. 

6. Enable the driving wheels to rotate at different speeds. 

7. Provide for relative movement between the engine and driving wheel. 

What is transmission & types of transmission? 

The transmission is a device that is connected to the back of the engine and sends the power from the engine 

to the drive wheels. An automobile engine runs at its best at a certain RPM (Revolutions per Minute) range 

and it is the transmission's job to make sure that the power is delivered to the wheels while keeping the 

engine within that range. It does this through various gear combinations. 

There are two basic types of automatic transmissions based on whether the vehicle is rear wheel drive or 

front wheel drive. 

On a rear wheel drive car, the transmission is usually mounted to the back of the engine and is located under 

the hump in the center of the floorboard alongside the gas pedal position. A drive shaft connects the rear of the 

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transmission to the final drive which is located in the rear axle and is used to send power to the rear 

wheels. Power flow on this system is simple and straight forward going from the engine, through the torque 

converter, then through the transmission and drive shaft until it reaches the final drive where it is split and 

sent to the two rear wheels. 

On a front wheel drive car, the transmission is usually combined with the final drive to form what is called a 

transaxle. The engine on a front wheel drive car is usually mounted sideways in the car with the transaxle tucked 

(inserted) under it on the side of the engine facing the rear of the car. Front axles are connected directly to the 

transaxle and provide power to the front wheels. 

In this example, power flows from the engine, through the torque converter to a large chain that sends the 

power through a 180 degree turn to the transmission that is along side the engine. From there, the power is 

routed through the transmission to the final drive where it is split and sent to the two front wheels through the 

drive axles. 

There are a number of other arrangements including front drive vehicles where the engine is mounted front to 

back instead of sideways and there are other systems that drive all four wheels but the two systems described 

here are by far the most popular. 

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CLUTCHES: The clutch connects the two shafts so that they can either be locked together and spin at the 

same speed, or be decoupled and spin at different speeds. 

• In a car, you need a clutch because the engine spins all the time and the car wheels don't. In order for a car to 

stop without killing the engine, the wheels need to be disconnected from the engine somehow. The clutch 

allows us to smoothly engage a spinning engine to a non-spinning transmission by controlling the slippage 

between them. 

• Flywheel is connected to the engine, and the clutch plate is connected to the transmission. 

• When your foot is off the pedal, the springs push the pressure plate against the clutch disc, which in turn 

presses against the flywheel. This locks the engine to the transmission input shaft, causing them to spin at the 

same speed. 

Friction clutches 

• Contact surfaces should develop a frictional force 

• Heat of friction should be rapidly dissipated. 

• Surfaces should be backed by a material stiff enough to ensure a reasonably uniforn distribution of pressure 

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Engage 

Disengage 

GEAR BOX: 

Function of gearbox: 

• It converts the power of the engine running at high speeds into low speeds and high torque for starting. 

• It changes the motion from forward to reverse as and when required. 

• It disconnects the engine from the driving wheel by putting the gear into neutral position. 

Constructional arrangement of gearboxes 

Gear boxes can be classified in the following types 

1. Sliding mesh gearbox 

2. Constant mesh gearbox 

3. Synchromesh gearbox 

4. Epicyclic gearbox 

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Sliding mesh gearbox: 

In earlier days this type of gearbox was used. 

But difficulty in engaging the gears and noise 

produced, improvements were made. 

1. main drive gear 

2. counter shaft (Lay shaft) 

3. main shaft 

4. I gear 

5. II gear III gear 

6. top speed engaging dogs 

Gear Ratio’s 

Khorshed Alam


Khorshed Alam


Problem: A sliding mesh type of gearbox with forward speeds only is to be designed. The gearbox should have 

the following gear ratios available 1.0, 1.5, 2.5 and 3.9. The smallest gear is to have 16 teeth and the sum of the 

meshing gear teeth’s must be equal to 48. Calculate the number of teeth of the various gears. 

Khorshed Alam


Constant Mesh gear: 

The first improvement was the use of "Constant 

Mesh" gears, which are connected to the 

mainshaft by a sliding dog. The 2nd speed gear 

(or 2nd and 3rd in a 4-speed box) is in constant 

mesh with its layshaft gear, but rotates freely on 

the mainshaft. The dog clutch slides along 

splines on the mainshaft and engages with dog 

teeth on the gear, thus connecting the drive from 

the engine to the mainshaft. 

Synchromesh gearbox: 

The basic gearbox is laid out in the same manner 

as the constant mesh, but with the addition of a 

cone clutch fitted between the dog and gear 

members, as shown in figure 

Khorshed Alam

Chapter # 9: Automatic Gearbox 

There are two big differences between an automatic transmission and a manual transmission: 

Automatic 

Manual 

There is no clutch pedal in an automatic transmission There is a clutch pedal in a manual transmission car. 

car. 

There is no gear shift in an automatic transmission There is gear shift liver in a manual transmission car. 

car. Once you put the transmission into Drive, Each transmission needs to be changed manually. 

everything else is automatic. 

In an automatic transmission, the same set of gears In the manual transmission locks and unlocks different 

produces all of the different gear ratios. The sets of gears to the output shaft to achieve the various 

planetary gear set is the device that makes this gear ratios 

possible in an automatic transmission. 

Torque Converters: In manual transmissions the engine is connected to a 

transmission by way of a clutch. Without this connection, a car would not 

be able to come to a complete stop. But cars with an automatic transmission 

have no clutch that disconnects the transmission from the engine. Instead, 

they use an amazing device called a torque converter. 

What is torque converter? - A torque converter is a type of fluid coupling, 

which allows the engine to spin somewhat independently of the 

transmission. 

If the engine is turning slowly, such as when the car is idling at a stoplight, 

the amount of torque passed through the torque converter is very small, so 

keeping the car still requires only a light pressure on the brake pedal.

Components of the torque converter: There 

are four components inside the very strong 

housing of the torque converter: Pump, 

Turbine, Stator and Transmission fluid. 

The housing of the torque converter is bolted 

to the flywheel of the engine, so it turns at 

whatever speed the engine is running at. The 

fins that make up the pump of the torque 

converter are attached to the housing, so they 

also turn at the same speed as the engine. 

The cutaway below shows how everything is connected inside the torque converter. 

The pump inside a torque converter is a type of centrifugal pump. As it spins, fluid is flung (through) to the 

outside, much as the spin cycle of a washing machine flings water and clothes to the outside of the wash tub. As 

fluid is flung to the outside, a vacuum is created that draws more fluid in at the center. The fluid then enters the 

blades of the turbine, which is connected to the transmission. The turbine causes the transmission to spin, which 

basically moves your car. This means that the fluid, which enters the turbine from the outside, has to change 

direction before it exits the center of the turbine. It is this directional change that causes the turbine to spin. 

Pump 

Turbine 

In order to change the direction of a moving object, you must apply a force to that object -- it doesn't matter if 

the object is a car or a drop of fluid. And whatever applies the force that causes the object to turn must also feel 

that force, but in the opposite direction. So as the turbine causes the fluid to change direction, the fluid causes 

the turbine to spin. The fluid exits the turbine at the center, moving in a different direction than when it entered.

If you look at the arrows in the figure above, you can see that the fluid exits the turbine moving opposite the 

direction that the pump (and engine) are turning. 

If the fluid were allowed to hit the pump, it would slow the engine down, wasting power. This is why a 

torque converter has a stator. The stator resides in the very center of the torque converter. Its job is to 

redirect the fluid returning from the turbine before it hits the pump again. This dramatically increases 

the efficiency of the torque converter. 

The stator has a very aggressive blade design that almost completely reverses the direction of the fluid. A 

one-way clutch (inside the stator) connects the stator to a fixed shaft in the transmission (the direction that the 

clutch allows the stator to spin is noted in the figure above). Because of this arrangement, the stator cannot spin 

with the fluid -- it can spin only in the opposite direction, forcing the fluid to change direction as it hits the stator 

blades. 

Something a little bit tricky happens when the car gets moving. There is a point, around 40 mph (64 kph), at 

which both the pump and the turbine are spinning at almost the same speed (the pump always spins slightly 

faster). At this point, the fluid returns from the turbine, entering the pump already moving in the same direction 

as the pump, so the stator is not needed. 

Planetary Gear sets: 

When you take apart and look inside an automatic transmission, you 

find a huge assortment of parts in a fairly small space. Among other 

things, you see: 

1. An ingenious planetary gear set 

2. A set of bands to lock parts of a gear set 

3. A set of three wet-plate clutches to lock other parts of the gear 

set 

4. An incredibly odd hydraulic system that controls the clutches 

and bands 

5. A large gear pump to move transmission fluid around

Input Output Lock Gear Ratio 

Fig (a) 

S 

S 

+ 

A 

=1:3 

Fig (b) 

Fig (c) 

Fig (d) 

S =1:2 

A 

S + A 

=3:1 

A 

S + A 

=3:1 

A 

* S – Sun gear teeth =40 and A – Ring gear teeth=80 

Characteristics of gear train: 

1. Output can be driven at a reduced speed relative to the input and in the same direction. 

2. Output can be driven at a higher speed in the same direction. 

3. Output can be driven at an alternative higher speed in the same direction. 

4. Output can be driven at a lower speed than the input but in the opposite direction 

5. If any two gears are locked, the third cannot rotate relative to the others, giving 1:1 gear ratio. 

6. All ratios are dependent on number of teeth’s.

Compound Planetary System: Automatic transmission uses a set of gears, called a compound planetary 

gearset, that looks like a single planetary gearset but actually behaves like two planetary gearsets combined. It 

has one ring gear that is always the output of the transmission, but it has two sun gears and two sets of planets. 

Gear Input Output Fixed Gear Ratio 

1st 

30-tooth 72-tooth ring Planet carrier 2.4:1 

sun 

2nd 

30-tooth Planet carrier 36-tooth ring 2.2:1 

sun 

Planet 

carrier 

72-tooth ring 36-tooth sun 0.67:1 

Total 2nd 1.47:1 

3rd 30- and 36- 

tooth suns 

72-tooth ring 1.0:1

MET 285 AUTOMOTIVE TECHNOLOGY 

OD 

Planet 72-tooth ring 36-tooth sun 0.67:1 

carrier 

Reverse 36-tooth 72-tooth ring Planet carrier -2.0:1 

sun 

Clutch Packs: A clutch pack consists of alternating disks 

that fit inside a clutch drum. Half of the disks are steel and 

have splints that fit into groves on the inside of the drum. 

The other half have a friction material bonded to their 

surface and have splines on the inside edge that fit groves 

on the outer surface of the adjoining hub. There is a piston 

inside the drum that is activated by oil pressure at the 

appropriate time to squeeze the clutch pack together so 

that the two components become locked and turn as one. 

Bands: A band is a steel strap with friction material 

bonded to the inside surface. One end of the band is 

anchored against the transmission case while the other end 

is connected to a servo. At the appropriate time hydraulic 

oil is sent to the servo under pressure to tighten the band 

around the drum to stop the drum from turning. 

Hydraulic system 

Khorshed Alam


CHAPTER 10: ENGINE BALANCE 


I. Velocity and Acceleration of piston 

sin 2θ 

The velocity of the piston is given as V p = ω . a(sinθ 

+ ) 

2R 

cos 2θ 

and acceleration a p = ω 2 . a(cosθ 

+ ) 

2R 

Where a = crank radius, l = connection rod length, ω = angular velocity of the crankshaft, θ 

is the crank angle and R =l/a. 

Case 1: Consider the piston is at TC: 

V p = …………………………………..; a p = ……………………………………… 

Case 2: Consider the piston somewhere between TC and BC: 

V p = …………………………………..; a p = ……………………………………… 

Case 3: Consider the piston at BC: 

V p = …………………………………..; a p = ……………………………………… 

KHORSHED ALAM, LECTURER, MET 

1

B 



Important Points: 

‣ The motion of the piston is not uniform. 

‣ The piston travels in one direction during the first half of a revolution and in the 

opposite direction during the second half. 

‣ Its speed of movement in the cylinder increases during the first half of each stroke 

(that is twice each revolution) and decreases during the second half of each stroke, 

the speed being greatest and most uniform about the middle of each stroke. 

‣ The speed of the piston is changing most rapidly (that is the acceleration is greatest) 

at the ends of the stroke and it follows that the force required to change the motion 

is greatest there also. At the middle of the stroke the speed is not changing at all, so 

no force is required. 

‣ The necessary force is supplied by a tension and compression in the connecting rod. 

II. Single Cylinder Engine 

F N 

l 

F I 

F 

F BV 

B 

F R 

F BH 

Let F R = Force required to accelerate the reciprocating parts 

F I = inertia force due to the reciprocating parts 

F N = Force on the sides of the cylinder walls 

F B = force acting on the crankshaft bearing 

Important Points 

‣ Since F R and F I are equal in magnitude but opposite in direction therefore they balance 

each other. 

‣ The horizontal component of F B (F BH ) acting on the line of reciprocation is also equal to 

F I . 

‣ This force F BH = F U is an unbalanced force or shaking force and required to be properly 

balanced. 

‣ The force on the sides of the cylinder walls (F N ) and the vertical component of F B (i.e. 

FBV) are equal and opposite and thus form a shaking couple of magnitude F N xs or F BV xs. 

From above we see that the effect of the reciprocating parts is to produce a shaking force 

and a shaking couple. Thus the purpose of balancing is the reciprocating masses are to 

eliminate the shaking force and a shaking couple. 


2



A. Show that 90 0 Twin Engine is perfectly balanced engine 


3



B. Comment on the unbalance forces and couples for the engines given in the figure below. 


4

Hand out # 11 BRAKING SYSTEM 

Braking of a vehicle: A brake is a device, which stops an automobile. The capacity of a brake depends upon the 

following factors: 

1. The unit pressure between the braking surfaces. 

2. The coefficient of friction between the braking surfaces. 

3. The peripheral velocity of the brake drum, 

4. The projected area of the friction surfaces and 

5. The ability of the brake to dissipate heat equivalent to the energy being absorbed. 

Principle 

In a four-wheeled moving vehicle, the brakes may be applied to 

1. The rear wheels only 

2. The Front wheels only 

3. All the four wheel 

1. Rear Wheels only 

μg 

cosα( 

L − x) 

a = 

+ g sinα 

L + μh 

2. Front Wheels only 

μgx 

cosα 

a = + g sinα 

L − μh 

3. All the four wheels 

a = g( 

μ cosα − sinα)

1. A car moving on a level road at a speed 50km/h has a wheel base 2.8m, distance of a C.G from ground 

level 600 mm, and the distance of C.G from rear wheels 1.2m. Find the distance traveled by the car 

before coming to rest when the brakes are applied. 

1. To the rear wheels 

2. To the front wheels 

3. To all the four wheels 

The coefficient of friction between the tires and the road may be taken as 0.6.

The typical brake system consists of disk brakes in 

front and either disk or drum brakes in the rear 

connected by a system of tubes and hoses that link 

the brake at each wheel to the master cylinder. 

Other systems that are connected with the brake 

system include the parking brakes, power brake 

booster and the anti-lock system. 

On a disk brake, the fluid from the master cylinder is forced into a caliper where it presses against a piston. The 

piston, in-turn, squeezes two brake pads against the disk (rotor) which is attached to the wheel, forcing it to slow 

down or stop. This process is similar to a bicycle brake where two rubber pads rub against the wheel rim creating 

friction. Disk brakes wear longer, are less affected by water, are self adjusting, self cleaning, less prone to grabbing 

or pulling and stop better than any other system around. The main components of a disk brake are the Brake 

Pads, Rotor, Caliper and Caliper Support. 

Rotor: The disk rotor is made of iron with highly machined surfaces where the brake pads contact it. Just as the 

brake pads wear out over time, the rotor also undergoes some wear, usually in the form of ridges and groves 

where the brake pad rubs against it. When the pads are replaced, the rotor must be machined smooth to allow 

the new pads to have an even contact surface to work with. Only a small amount of material can be machined 

off of a rotor before it becomes unusable.

Brake Pads: There are two brake pads on each caliper. They are 

constructed of a metal "shoe" with the lining riveted or bonded to it. The 

pads are mounted in the caliper, one on each side of the rotor. Brake pads 

wear out with use and must be replaced periodically. There are many types 

and qualities of pads available. 

Caliper & Support: There are two main types of calipers: Floating calipers 

and fixed calipers. A floating caliper "floats" or moves in a track in its 

support so that it can center itself over the rotor. As you apply brake 

pressure, the hydraulic fluid pushes in two directions. It forces the piston 

against the inner pad which in turn pushes against the rotor. It also pushes 

the caliper in the opposite direction against the outer pad, pressing it against 

the other side of the rotor. 

Drum Brakes 

With drum brakes, fluid is forced into the wheel cylinder which pushes the brake shoes out so that the friction 

linings are pressed against the drum which is attached to the wheel, causing the wheel to stop. When the pressure 

is released, return springs pull the shoes back to their rest position. In either case, the friction surfaces of the 

pads on a disk brake system, or the shoes on a drum brake convert the forward motion of the vehicle into heat. 

Heat is what causes the friction surfaces (linings) of the pads and shoes to eventually wear out and require

eplacement. While all vehicles produced for many years have disk brakes on the front, drum brakes are cheaper 

to produce for the rear wheels. The main reason is the parking brake system. On drum brakes, adding a parking 

brake is the simple addition of a lever, while on disk brakes, we need a complete mechanism, in some cases, a 

complete mechanical drum brake assembly inside the disk brake rotor! Parking brakes must be a separate system 

that does not use hydraulics. Drum brakes consist of a backing plate, brake shoes, brake drum, wheel 

cylinder, return springs and an automatic or self-adjusting system. When you apply the brakes, brake fluid is 

forced, under pressure, into the wheel cylinder which, in turn, pushes the brake shoes into contact with the 

machined surface on the inside of the drum. As the brake linings wear, the shoes must travel a greater distance to 

reach the drum. When the distance reaches a certain point, a self-adjusting mechanism automatically reacts by 

adjusting the rest position of the shoes so that they are closer to the drum. 

Anti-Lock Brakes (ABS) : The most efficient braking pressure takes place just before each wheel locks up. 

When you slam on the brakes in a panic stop and the wheels lock up, causing a screeching sound and leaving 

strips of rubber on the pavement, you do not stop the vehicle nearly as short as it is capable of stopping. Also, 

while the wheels are locked up, you loose all steering control so that, if you have an opportunity to steer around 

the obstacle, you will not be able to do so. Another problem occurs during an extended skid is that you will burn 

a patch of rubber off the tire which causes a "flat spot" on the tread that will produce an annoying thumping 

sound as you drive. Anti-lock brake systems solve this lockup problem by rapidly pumping the brakes 

whenever the system detects a wheel that is locked up. In most cases, only the wheel that is locked will 

be pumped, while full braking pressure stays available to the other wheels. This effect allows you to 

stop in the shortest amount of time while maintaining full steering control even if one or more wheels 

are on ice. The system uses a computer to monitor the speed of each wheel. When it detects that one or 

more wheels have stopped or are turning much slower than the remaining wheels, the computer sends a signal to 

momentarily remove and reapply or pulse the pressure to the affected wheels to allow them to continue turning. 

This "pumping" of the brakes occurs at ten or more times a second, far faster then a human can pump the brakes 

manually. If you step on the brakes hard enough to engage the anti-lock system, you may feel a strong vibration 

in the brake pedal. This is a normal condition and indicates that the system is working, however, it can be 

disconcerting to some people who don't expect it. If your vehicle has anti-lock brakes, read your owner's manual 

to find out more about it.The system consists of an electronic control unit, a hydraulic actuator, and wheel speed 

sensors at each wheel. If the control unit detects a malfunction in the system, it will iluminate an ABS warning 

light on the dash to let you know that there is a problem. If there is a problem, the anti-lock system will not 

function but the brakes will otherwise function normally.

STEERING & SUSPENSION SYSTEM 

STEERING SYSTEM 

The steering mechanism provides a 

means whereby the driver can place 

his vehicle as accurately as practicable 

where he wants it to be on the road, 

for selection of the course he wants to 

steer round corners and so that he can 

avoid other road users and 

obstructions. It must also, however, 

keep the vehicle stably on course 

regardless of irregularities in the 

surface over which the vehicle is 

traveling. For a car to turn smoothly, 

each wheel must follow a different 

circle. Since the inside wheel is 

following a circle with a smaller radius, 

it is actually making a tighter turn than 

the outside wheel. If you draw a line 

perpendicular to each wheel, the lines 

will intersect at the center point of the 

turn. The geometry of the steering 

linkage makes the inside wheel turn 

more than the outside wheel. 

Rack And Pinion Steering Mechanism 

Rack-and-pinion steering is quickly becoming the most common type of steering on cars. 

It is actually a pretty simple mechanism. A rack-and-pinion gearset is enclosed in a metal 

tube, with each end of the rack protruding from the tube. A rod, called a tie rod, connects 

to each end of the rack. 

MET 285 AUTOMOTIVE TECHNOLOGY – Khorshed Alam


The pinion gear is attached to the steering shaft. When you turn the steering wheel, the 

gear spins, moving the rack. The tie rod at each end of the rack connects to the steering 

arm on the spindle (see diagram above). The rack-and-pinion gearset does two things: 

• It converts the rotational motion of the steering wheel into the linear motion 

needed to turn the wheels. 

• It provides a gear reduction, making it easier to turn the wheels. 

On most cars, it takes three to four complete revolutions of the steering wheel to make the 

wheels turn from lock to lock (from far left to far right). 

The steering ratio is the ratio of how far you turn the steering wheel to how far the 

wheels turn. For instance, if one complete revolution (360 degrees) of the steering wheel 

results in the wheels of the car turning 20 degrees, then the steering ratio is 360 divided by 

20, or 18:1. A higher ratio means that you have to turn the steering wheel more to get the 

wheels to turn a given distance. However, less effort is required because of the higher gear 

ratio. Generally, lighter, sportier cars have lower steering ratios than larger cars and trucks. 

The lower ratio gives the steering a quicker response -- you don't have to turn the steering 

wheel as much to get the wheels to turn a given distance -- which is a desirable trait in 

sports cars. These smaller cars are light enough that even with the lower ratio, the effort 

required to turn the steering wheel is not excessive. 

Power Rack and Pinion 

Power Steering: There are a couple of key components in power steering in addition to 

the rack-and-pinion or recirculating-ball mechanism. 



Figure below shows an automotive power – steering example of a mechanical –hydraulic 

servo system (closed – loop system). Operation is as follows: 

1. The input or command signal is the turning of the steering wheel. 

2. This moves the valve sleeve, which ports oil to the actuator (steering cylinder). 

3. The piston rod moves the wheels via the steering linkage. 

4. The valve spool is attached to the linkage and thus moves with it. 

5. When the valve spool has moved far enough, it cuts off oil flow to the cylinder. This 

stops the motion of this actuator. 

6. Thus, mechanical feedback recenters (nulls) the valve (actually a servo valve) to stop 

motion at the desired point as determined by the position of the steering wheel. 

Additional motion of the steering wheel is required to cause further motion of the 

output wheels. 

Figure 6: 

Automotive example of mechanical – hydraulic servo system 



SUSPENSION 

Job of suspension: The job of a car suspension is to maximize the friction between the 

tires and the road surface, to provide steering stability with good handling and to ensure 

the comfort of the passengers. 

FRONT SUSPENSION 

REAR SUSPENSION

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