QP CODE 129 AUTOMOBILE ENGINEERING PART-A1 QP CODE 129 AUTOMOBILE ENGINEERING PART-A 1.What is the function of connecting rod? It is used to convert reciprocating motion of the piston

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QP CODE 129

AUTOMOBILE ENGINEERING

PART-A

1.What is the function of connecting rod?

It is used to convert reciprocating motion of the piston into rotary motion of the crankshaft.

2. What is scavenging process?

It is the process of forcing out the burnt gases out of the cylinder by admitting fresh charge

into the cylinder.

3. What is the function of cooling system?

• To cool the engine parts and save it from overheating.

• To maintain normal temperature under all working speeds and loads.

4. What are the types of pumps used in Lubrication system?

• Gear pump

• Rotor pump

5. What are the properties of petrol?

• Purity

• Volatility

• Sulphur content

• Gum content

• Antiknock quality

• Calorific value

• Operating economy

6. What is meant by octane number and cetane number?

Octane number :

The octane number of any fuel is the percentage of iso-octane by volume in mixture of

iso – octane and normal heptane.

Cetane number :

The cetane number is defined as the percentage by volume of normal cetane and

alpha-methyl-napthalene.

7. Write the types of injection nozzles.

• Single hole nozzle

• Multihole nozzle

• Pintle nozzle

• Pintaux nozzle

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8. What is governing?

The process of controlling the speed of the engine by adjusting the fuel supply is called

governing.

9. What is the function of a clutch?

• It is used for connecting or disconnecting the drive of the engine to the gear box.

• To disconnect the engine from the gear box as required under following situations.

o To start the engine and warm it up

o To facilitate to engage 1st or 2nd gear to move the vehicle from the rest

o Disconnect power to gear box for easy shifting of gears, so that the noise and

damage to the gear is avoided.

o Disconnecting drive from the engine to stop the vehicle after application of brakes.

• To transmit the engine power to the rear wheels without shock.

• The clutch is engaged only when the vehicle is in motion.

10.Write the causes for clutch slipping.

• Worn lining

• Lining glazed

• Grease or oil on lining

• Weak pressure spring

• Lack of free play in clutch pedal

• Worn splines on clutch

11. Write the types of gear used in final drive.

• Straight bevel gear

• Spiral bevel gear

• Hypoid bevel gear

• Worm and worm wheel

12. What is non-slip differential?

A non-slip differential is a type of differential is a type of differential that allows its two

output shafts to rotate at different speeds but limits the maximum difference between the two

shafts.

13. What is live axle and dead axle?

Live axle : It has the differential mechanism through which the engine power is transmitted to the wheels. Dead Axle : it is a dummy axle without any connections with the engine. 14. What is toe-out on turns?

The wheel may set closer at the rear than at the front in which case the difference of the

distances between the wheels at the front and the rear is called toe-out.

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15. What are the types of front independent suspension?

• Wishbone type or parallel link type

• Mac Pherson strut type

• Vertical guide type

• Trailing link type

• Swinging half axle type

16. What is shock absorber?

The shock absorber is a device which introduces resilience to the up and down movement of

the suspension spring so as to damp out the vibrations quickly.

17. Name different battery ratings.

• Twenty hour rate

• Twenty minute rate

• 25 ampere rate

• Cold rate

18. What are the two types of ignition system?

1. Compression ignition system ( Diesel )

2. Spark ignition system ( Petrol)

19. What are the various types of lighting system used in automobiles?

• Head light

• Parking light

• Directional signal light

• Blinker lights

• Stop lights

• Tail lights

• Interior lights

20. What is catalytic converter?

It is a which is used to control the emission levels of various pollutants by changing the

chemical characteristics of the exhaust gases.

PART – B

21. (A) (i) Classify the combustion chamber used in diesel engine. What type of swirl is used in these

chambers?

Classification :

I. Open Combustion chamber or Direct injection system

II. Indirect injection system

a. Pre-combustion chamber type

b. Swirl or turbulent type

c. Energy cell

2 marks

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Methods of generating air swirl in diesel engine combustion chamber

Swirl is circular motion which is given to air. In the swirl combustion chamber the air is von a

swirl. There are two types of swirl combustion chamber as shown in figure.

1. Vortex type 2. Comet type

These are designed in such a way as to introduce turbulence of the compressed air.

In the vortex type, the air at the end of the compressions stroke is pushed in the cylinder

chamber in the head, when the fuel is injected. The air is given a swirl while coming in the chamber.

So the mixing and burning of fuel takes place completely.

In the comet type, a spherical combustion chamber is separated from cylinder. The spherical

chamber connected tangentially through a narrow passage called throat to a cavity in the piston

crown. On the compression stroke air is pumped at high velocity through throat into the chamber,

thus causing a high turbulence within the chamber. As the piston approaches TDC the injector

discharges fuel. The injector is located in the chamber such that the spray of the fuel is crossed by

the produced swirl. Here the high turbulence is used to strip the fuel droplets to form a homogenous

mixture. Burning of fuel takes completely.

(ii) Explain the purpose of pressure relief valve used in lubrication system. 6 marks

• To control and limit the lubricating pressure in the oil system.

• Necessary to prevent damage caused by excessive system pressure and to ensure

that engine parts are not deprived of fuel due to a system failure.

• To return oil directly to the pan

• To avoid damage of seals because of excessive pressure

• To maintain the pressure at the pump exit is maintained at a specific value over the

engine operating range

• To avoid damage of the bearing

• To avoid engine noise

4 marks

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(B) Briefly explain with neat sketch, the construction and operation of water pump circulation

cooling system.

In water cooling system, the cooling medium used is water. In this, the engine cylinders are

surrounded by water jackets through which the cooling water flows. Heat flows from the cylinder

walls into water which goes to the radiator where it loses its heat to the air. Usually some antifreeze

is added to the cooling water, due to which it is often referred to as coolant.

A pump is used for the circulation of cooling water. It consists of radiator water pump, water

jacket, fan, thermostat valve, radiators, shutters etc.

The pump is driven by the engine which draws cold water from radiator. Then, this water is

forced to circulate through water jackets of cylinder block and cylinder head. The cold water absorbs

the heat from the engine. The hot water enters the top of radiator and flows from top to bottom.

While flowing through radiator tube, the hot water is cooled by forced air drawn by a fan. Thus, the

water is cooled and recirculated again. A drain tap is provided at the bottom of the radiator to

remove the water periodically.

A thermostat valve is provided between the engine and radiator top to control the

temperature of cooling water.

When the engine becomes hot, the radiator shutters are opened to allow more air to flow

through radiator tubes. It increases the rate of cooling.

Theory – 6 marks

Figure – 6 marks

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22. (A) (i) Briefly explain about oil bath type air cleaner with a simple sketch.

It consists of a centrifugal pre-cleaner and two filtering elements as shown, along with oil

reservoir at the bottom. The pre-cleaner gives a whirling motion to the incoming air, which causes

the impurity particles in the air to be thrown out through the slots provided. The pre-cleaned air

then impinges on the oil surface where some of the impurities are left while an emulsion of air and

oil passes through the wire-wool mesh where most of the dirty oil is absorbed. This dirty oil then

condenses and falls back into the oil reservoir, where the dirt settles down. The relatively clean air

then passes through the second wire mesh, which retains any impurities still left and the clean air is

then passed on to the engine.

(ii) Explain the diesel fuel feed system with a layout.

The function of a fuel injection system is to inject proper quantity of fuel into the engine

cylinders at the correct time and at a predetermined rate.

The fuel supply system in a diesel engine is shown in figure. It consists of a fuel tank, feed

pump, fuel filters, Fuel Injection pump (FIP), injectors (atomizer) and pipe lines. Fuel is pumped from

the fuel tank to the fuel injection pump by the fuel feed pump. Fuel filters prevent the entry of dust

particles into the injection pump.

From the fuel injection pump, the fuel is delivered to the injectors. The injectors spray fuel

Into the engine cylinder.

Theory – 3 marks

Figure – 3 marks

Theory – 3 marks

Figure – 3 marks

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(B) Write the construction and working of distributor type fuel injection pump with necessary Line

diagrams.

Construction:

• It has a fuel tank, feed pump, transfer pump, regulator valve, metering valve, distributor

port, rotor and injector.

• The fuel pump is used to pump the fuel from the fuel tank and passes through the filter.

• The transfer pump is used to deliver the fuel to metering valve at high pressure.

• The metering valve is operated by the control lever or accelerator pedal.

• When the accelerator pedal is pressed, more fuel is allowed into the rotor.

• The rotor does the job of pumping and it is rotated by the cam shaft.

Working

• In this the fuel distribution to cylinders is achieved by a rotor.

• The rotor has a central passage and two sets of radial holes.

• One set of radial holes is (A) connected to pump inlet to central passage and the other set of

radial holes (B) is connected to delivery line and injectors to various cylinders.

• The number of radial holes on each side equals to the number of cylinders of the engine.

These holes are located at different heights.

• When the pump plungers move away from each other, the fuel from inlet port A is drawn

into the central passage.

• It is then delivered via the outlet port B to the cylinder corresponding to the passage

coinciding with the outlet port.

• These type of pumps are small in size and light in weight compared to other types of

injection pumps.

Theory – 6 marks

Figure – 6 marks

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23. (A) (i) Explain the functions of a final drive and differential unit in an automobile.

Functions of final drive : 3 marks

• It transmits the drive at right angle to the rear axles.

• It provides permanent speed reduction.

• It transmits the torque to the both rear axle shafts or torque on the driving wheels gets

increased.

Functions of differential : 3 marks

• It splits the power that is received and sends the same through the two half axle shafts to

driving wheels.

• When the vehicle goes on a straight path, it allows the two driving wheels to steer to the

same magnitude.

• When the vehicle takes a turn, it allows the inner rear wheel to revolve slowly and the outer

wheel to revolve faster.

(ii) Explain the function of propeller shaft, universal joint and slip joint in vehicle power transmission

system.

Function of propeller shaft : 2 marks

• To transmit the power from gear box to differential.

• To transmit motion at varying angles which is varying frequently.

• To allow and accommodate change in length.

Function of universal joint 2 marks

• An universal joint is a joint which enables the drive shaft to transmit power at varies angles.

• Engine power is transmitted through the gear box to the differential through the propeller

shaft.

• The universal joint allows the change of angle of the propeller shaft.

• This joint absorbs some vibrations and gives smooth rotation.

• It transmits rotary motion of the gear box to various angles without any loss.

Function of slip joint : 2 marks

• To adjust length of the propeller shaft, according to the rear axle movements

• The propeller shaft will break if there is no slip joint

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(B) Briefly explain the Hotchkiss drive with a neat sketch.

This is the simplest and most widely used type of rear axle drive. In this case the springs

besides taking weight of the body, also take the torque reaction, driving thrust and the side thrust.

The propeller shaft is provided with two universal joints and also a sliding joint. The spring is fixed

rigidly in the middle, to the rear axle. The front end of the spring is fixed rigidly on the frame, while

the rear end is supported in a shackle. The driving thrust is transmitted to the frame by the front half

of the springs.

Due to the torque reaction, the spring deflects. Thus torque reaction is taken up by the

springs. Similarly, to take up the braking torque the springs would deflect in the opposite direction.

When the springs deflect in the manner shown, the bevel pinion shaft also changes its position.

Therefore if there is only one universal joint at the front end of the propeller shaft, it will bend under

this condition. To avoid this, another universal joint at the rear end of the propeller shaft is used.

Again when the rear axle moves up and down, it has to move in a circle with the front spring

support at the frame as centre. But for the propeller shaft motion, the centre is at the front universal

joint. This means that during this movement of the rear axle, the length of the propeller shaft has to

very. This is provided for by means of a sliding joint in the propeller shaft.

24. (A) (i) Define (1) Camber, (2) King pin inclination and (3) Caster.

Camber 2 marks Definition—Camber is the tilt of the car wheels from the vertical. Camber is positive if the tilt is outward at the top. Camber is also called ‘wheel rake’. King Pin Inclination (Steering Axis Inclination) 2 marks Definition—Inclination of the king pin from vertical is called the king pin inclination or king pin rake . In modern cars where the king pin has been replaced by the ball joints, this term has also been renamed as Steering Axis Inclination’ and is defined as the inclination of the ball joint-axis from the vertical . Steering axis is an imaginary line drawn through the lower and the upper steering pivot pints. SAl is non-adjustable, since it would change only if the wheel spindle or steering knuckle are bent. Castor : 2 marks Definition—The angle between the king pin centre line (or steering axis) and the vertical, in the plane of the wheel is called the Castor angle. If the king pin centre line meets the ground at a point ahead of the vertical wheel centre line, as is shown in figure., it is called positive castor while if it is behind the vertical wheel centre line, it is called negative castor.

Theory – 6 marks

Figure – 6 marks

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(ii) State the advantages and disadvantages of front independent suspension system. Explain any

one system in detail

Advantages:

• This system uses coil springs so unsprung weight is reduced.

• It gives comfortable space to engine and passengers.

• Better road holding.

• Improved steering control.

• Do not transmit the vibration to entire body of the vehicle.

• Suspension is soft. -

• Increased tyre life.

Disadvantages:

• It absorbs shocks and vibrations that wheel alone can withstand.

• Rate of weakening of wheels is very high.

TYPES OF FRONT INDEPENDENT SUSPENSION

i. Wishbone type or parallel link type.

ii. Mac Pherson strut type.

iii. Vertical guide type.

iv. Trailing link type..

v. Swinging half axle type.

Wishbone type or parallel link type:

Theory – 3 marks

Figure – 3 marks

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Construction:

• It consists of lower and upper wish bone arms, V’ in shape.

• Wish bone are pivoted on both frame and steering knuckle through ball joint.

• Springs are seated on rubber pads between lower and upper wish bone arms.

• Upper arm is shorter in length than the lower arm.

• he wish bones not only position the wheel or transmit the vehicle load to the spring but this

also resists acceleration, braking and cornering forces.

Working:

When the wheels move on a bump the upper and lower wish bones are inclined to the coil

and shock absorber is compressed.

At straight roads, it expands to its original position to absorb shocks and vibration.

Mac Pherson strut type

• Earle S.Mac Pherson, an engineer with ford USA, developed a single wish bone with a

telescopic strut type system.

• This system has a telescopic strut, a single arm and a diagonal stay.

• The whole system is known as the Mac Pherson system.

• In this type, only lower wish bones are used. A strut containing shock absorber is mounted

between the two collars to absorb road shocks. The wish bone hinged to the cross member

controls the wheel path; as well as it resists accelerating, braking & side forces.

• This type gives the maximum room in the engine compartment

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Vertical guide type

• In this type the king pin is directly attached to the cross member of the frame.

• It has two springs-main and rebound.

• It can slide up and down corresponding to the up and down motion of the wheel, there by

compressing or elongating the springs.

• The system results in constant camber and caster.

• In this design, there are two half axle links. In this, wheels are mounted rigidly on the half

• axles.

• The other end of axles is pivoted to the chassis member at the middle of car

Trailing link type

• The trailing link suspension systems use parallelogram linkage lying beside the frame side

members.

• Usually a horizontal coil spring is used in. this type of suspension.

• When the wheels move up and down, it winds and unwinds the spring.

• This system maintains the camber and the wheel track constant.

• However, the distance between the front and the rear wheels change.

• Torsion bars are used instead of horizontal coil springs.

• These types of suspensions are used in matador vans.

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Swinging half axle suspension

• In this system the wheels are mounted rigidly on the half axles.

• The axle shafts are joined to the final drive housing.

• At the centre of each axle joint, universal joints are fitted.

• The drive axles are supported by chassis frame by means of spring and shock absorber.

(B) Describe the construction and working of telescopic type shock absorber with neat sketch.

A ‘telescopic’ shock absorber derives its name from the tubular shape of early telescopes

used in ancient times, These are of two types, viz., the mono-tube type and the twin-tube type.

Referring to Figure, wherein a twin-tube type shock absorber is shown, rod G is attached to the two-

way valve A, while another similar two-way valve B is attached at the lower end of cylinder C. There

is a fluid in the space below valve assembly A, below B and also in the annular space between

cylinder C and tube D, which is connected to the space below the valve assembly B as shown. H is

gland in the head J and any fluid scrapped off by rod G is brought down into the annular space

through the inclined passage shown in the head. The eye E is connected to the axle, while the eye F

is attached to the chassis frame. The fluid generally used in shock absorbers is a mixture of 60 per

cent transformer oil and 40 per cent turbine oil.

Theory – 6 marks

Figure – 6 marks

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To understand the action of the shock absorber, consider that the vehicle has come across a

bump. Then eye E would move up and thereby the fluid will pass from the lower side of valve

assembly A to its upper side. But since the volume of the space above A is less by the volume of the

rod G, the fluid will also exert its pressure on valve assembly B and go to the underside of valve B.

This passing of the fluid through valve openings provides the damping. Similarly for downward

motion of the eye E during rebound, the fluid will pass from the upper side of the valve assembly A

to the lower side and also from the lower side of valve assembly B to its upper side.

25. (A) (i) Explain the various methods of battery testing.

BATTERY TESTING

Following are the important tests conducted to ascertain the conditions of a battery.

• Specific Gravity test

• Open volt test

• High discharge test

• Cadmium test.

Specific gravity test

This is conducted with the help of a hydrometer. The hydrometer is in the form of a glass

tubular body with a rubber bulb at the top and a sampler tube at the bottom. There is a glass float

inside the glass body. This float has a vertical density scale. To test the specific gravity of the

electrolyte, immerse the sampler tube in the cell electrolyte, squeeze the rubber bulb and release

the same which would cause a sample of the electrolyte to be drawn inside the glass body. Let the

float inside rise and then read off the scale at the surface level of the sample drawn in.

Open volt test

More and more vehicles are now fitted with maintenance-free (sealed) batteries, where the

hydrometer cannot be used to determine the state of charge. In such a case, the same can be

determined from the open volt test of the battery. The open circuit voltage of the battery cell is

measured with the help of an ordinary voltmeter. The open circuit voltage of a fully charged battery

cell is about 2.1 volts. If the car has been recently driven or the battery has been just charged, the

‘surface charge’ must be removed from the battery by running on the headlights for one minute,

turning off and waiting for about two minutes. Then with the engine and all electrical accessories

shut off, connect the voltmeter to battery terminals. In case of a 12-V battery, if the voltmeter reads

12.6 V, it is fully charged, if it reads 12.2 V it is half-full charged while below 11.9 V it may be taken as

fully discharged. It has been observed that a change of 0.01 volt of open-circuit voltage is equivalent

to a change of 0.0 10 in the specific gravity of the electrolyte. Thus the gravity measurement can be

indirectly made with an accurate voltmeter also. There is another way of expressing relation

between the open circuit voltage of a battery cell and its specific gravity. This is:

Voltage of the cell = Specific gravity + .840

High discharge test

Open circuit voltage is not representative of the cell voltage under actual operating

conditions. The cranking motor at the time of starting draws a very heavy current which causes the

cell voltage to fall. To simulate this condition a high discharge test is made with the help of a carbon

Theory – 3 marks

Figure – 3 marks

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pile or a cell voltage tester. A cell voltage tester consists of a voltmeter connected to two legs with a

high resistance placed across these. Pressing the two legs of the cell tester on the cell terminals

causes heavy current (of the order of 150 to 200 amperes) to flow. The test is made for 5-10 seconds

at the end of which the voltage should not fall below 1.5 volts- difference of cell voltages of various

cells should not exceed 0.2 volts; otherwise the battery may be taken defective.

This is a very severe test and should be made only on the fully charged or at least on half-

fully charged Even then it should not be made continuously for more than 15 seconds, otherwise the

battery will get permanently damaged.

Cadmium test

This test is conducted to know the chemical conditions of the positive and negative plates

and is performed only when the battery is either on charge or discharge.

A cadmium rod is enclosed in a perforated ebonite tube and is immersed in the battery

electrolyte. The rod is then connected to the negative terminal of a high resistance voltmeter whose

positive terminal is connected alternately to the positive and negative terminals of the battery cell.

In case of positive terminal, voltage reading should not be less than 2.5 volts if the battery is nearing

completion of its charge or 2.0 &.s if the battery is being discharged at normal rate. A lower reading

indicates defective positive plates. i the other hand, reading in case of connection with negative

battery terminal should not be more than volt when the battery is being discharged at normal rate.

A higher reading in this case will indicate defect in negative plates.

(ii) Explain about exhaust gas recirculation (EGR).

Theory – 3 marks

Figure – 3 marks

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At the time of higher temperature above 195°C, the nitrogen oxide is induced by taking

more oxygen which is in the combustion chamber. So EGR is helps to lower the higher temperature.

In this system 10% exhaust gas is again returned to intake manifold. Exhaust with less temperature

and less oxygen mixes with fresh charge. The charge is then passed to combustion chamber with less

oxygen. So, the combustion chamber is not getting so high temperature. Production of nitric oxide is

prevented. The EGR system makes the way between the inlet manifold and exhaust manifold. There

is a valve which is working in the way between inlet manifold and exhaust manifold. In the fig shows

the EGR valve. In EGR valve there is a diaphragm with a spring. A valve is fixed with the diaphragm.

The valve controls the exhaust gas which unnecessarily not passed to inlet manifold. Upper part of

the diaphragm is connected with the throttle body by means of tube. The valves closed the spring

push down the diaphragm. When the vacuum is not created in the port the valve works as before. So

the exhaust is not recirculated. The system works like that and the nitric oxide induced is less.

When throttling starts, the vacuum is created in the port. So the diaphragm pushed up and

the valve is opened the way. Then the exhaust goes to the inlet, when the throttling is more the

vacuum is less in the port. The spring force is acted on the diaphragm which is pushed down in order

to close the way. Thus the EGR valve working is not giving the obstruction to the full power engine

operation.

There is a thermal vacuum switch in many engines. The EGR may not function upto the

engine heat reached 38°C. The switch in the engine water jacket is used for closing and opening the

way when engine cold or engine hot respectively.

(B) With the help of a circuit diagram, explain the working of a battery coil ignition system.

A battery of 12 volts is generally employed. Battery ignition system for a 4-cylinder engine is

shown in figure. As in clear from figure, there are two basic circuits in the system viz, the primary

and the secondary circuits. The battery, primary winding of the ignition coil, condenser and the

contact breaker form the primary circuit, whereas the secondary winding of the ignition coil, the

distributor and the spark plugs constitute the secondary circuit.

When the ignition switch is in the ‘on’ position, the current flowing in the primary circuit will

grow exponentially during the make period of the contact breaker . The electromagnetic energy on

account of this build up of current in the primary circuit is stored in the laminated iron core of the

ignition coil. As the contact breaker points open, the magnetic field built up by the growth of the

current collapses and the energy stored during the make period is projected into the secondary

Theory – 6 marks

Figure – 6 marks