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PEC/DoME AUTOMOBILE ENGINEERING UNIT I

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UNIT I VEHICLE STRUCTURE AND ENGINES 9Types of automobiles, vehicle construction and different layouts, chassis, frame and body,

resistances to vehicle motion and need for a gearbox, components of engine-their forms,

functions and materials

Development of the Automobile:

The progress of means for transportation has been intimately associated with the progressof civilization.

Transportation on land has evolved from the slow moving oxcart to the high-speed

automobile.A self-propelled vehicle used for transportation of goods and passengers on land is called

an automobile or automotive or motor vehicle.


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Types of Automobiles:The different types of automobiles found on roads are presented in Chart in a

comprehensive manner.

There are in general three main classifications of the various types of vehicle.

Based on the Purpose :o Passenger VehiclesCar, Jeep, Buso Goods VehiclesTruck

Based on the Capacity:o Light Motor vehiclesCar, Motor cycle,

scooter

o Heavy Motor vehiclesBus, coach, andtractor.

Based on the Fuel Used:o Petrol vehicles,o Diesel vehicles,o

Alternate fuelBased on the No. of wheels:o Two wheelerso Three wheelerso Four wheelerso Six wheelerso Ten wheelers etc.

Based on the Drive of the vehicles:o Single wheel driveo Two wheel driveo Four wheel drive.o Also Front wheel drive, rear wheel drive

and all wheel drive.

Based on the body style:

o closed cars,o open carso special styles

Based on the transmission:o

Conventional,o semi-automatic,o fully automatic

Classification of vehicles:


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The characteristics of ground vehicle may be described in terms of Performance: (Traction, acceleration, brake, maximum speed) Is the ability of the

vehicle to accelerate, to develop drawbar pull, to overcome obstacles and to decelerate.

Handling: (Steering) is the response of the vehicle to drivers commands.

Ride: (Comfort, suspension, vibration, noise) Is the effect of surface irregularities,

vibration, and noise on passengers and goods.

Fuel consumption, pollution, service, spare parts, Management cost, operation life,safety, price

Theory of ground vehicle The theory of ground vehicle is concerned with the study of performance, handling and

ride, and their relation with the design of ground vehicles under various operation

environments.

The behavior of a ground vehicle represents the results of the interaction between thedriver, the vehicle and the environment.

Automobile Systems and ComponentsPerformance:

Engine: Fuel system, ignition system, inlet system, exhaust system, cooling system,

lubrication system, charging system, starting system, emission control system, engine

management system.

Power train: Clutch, gearbox (transmission), propeller shaft, deferential, axle, wheels

and tires. Car body: Mass, weight distribution, CG, shape, aerodynamics, roll center.

Tire: Tire radius, rolling resistance, radial and lateral stiffness.

Brake system: Brake force distribution, stopping time, skid, slip, radial and lateral

stiffness.

Car: Maximum speed, maximum gradient and acceleration, stopping time and distance,

Fuel consumption.


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Handling and stability:

Steering system: Steering wheel, steering column, gears, linkages and other components.

Stability system:Ride:

Suspension system: Springs, shock absorber, anti roll ba.

Braking system:

Brake pedal, hydraulic system, wheel brake, booster, hand brake, brake valves, ABS.

Vehicle AssembliesThe main components of an automobile can be sub-grouped in the following assemblies:

(i) Engine or power plant, (ii) Running gear or basic structure, (iii) Driving system, (iv)

Basic Control system, (v) Electrical system, (vi) Accessories


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Construction of an Automobile:Automobile consists of the Basic structure, the Power plant, the transmission system, the

auxiliaries, the controls and the superstructure

Basic Structure:This is the unit on which are to be built the remainder of the units required to turn it into a

power operated vehicle.

It consists of the frame, the suspension systems, axles, wheels and tyresPower Plant:It provides the motive power for all the various functions which the vehicle or any part of

it, may be called upon to perform.

It generally consists of an IC engine which may be either of spark-ignition, or of

compression ignition type.

The Transmission system:It consists of a clutch, a gear box, a transfer case, a propeller shaft, universal joints, final

drive, and differential gear.

The auxiliaries:It consists of supply system (Battery and generator), the starter, the ignition system, and

ancillary devices ( Driving lights, signaling, other lights, Miscellaneous items like radio,

heater, fans, electric fuel pump, windscreen wipers, etc.)

The ControlsIt consists of steering system and brakes.

The superstructureIt may be body attached with frame, frameless construction.

Engine Position

Front engineThe large mass of an engine at the front of the car gives the driver protection in the event

of a head on collision.

Engine cooling is simpler to arrange


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In addition the cornering ability of a vehicle in normally better if the weight is

concentrated at the front.

Rear engineIt increases the load on the rear driving wheels, giving them better grip of the road.

Most rear-engine layouts have been confined to comparatively small cars, because the

heavy engine at the rear has an adverse effect on the handling of the car by making it

tail-heavy.Also it takes up good deal of space that would be used on a front-engine car for carrying

luggage.

Most of the space vacated by the engine at the front end can be used for luggage, but this

space is usually less than that available at the rear.

Central and mid-engineThese engine situations generally apply to sports cars because the engine sitting gives a

load distribution that achieves both good handling and maximum traction from the

driving wheel.

These advantages, whilst of great importance for special cars, are outweighed in the caseof everyday cars by the fact that the engine takes up space that would normally be

occupied by passengers.

The mid-engine layout shown combines the engine and transmission components in one

unit. The term mid-engine is used because the engine is mounted in front of rear axle

line.

Automobile Layouts:

An automobile layout is the orientation of the wheels, engine, and drive components inrelation to each other.


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Front engine and rear-wheel drive:Advantages

Better axle load distribution

Better road grip

Comfort riding Better cooling

Less noise (long exhaust pipe)

Use a long engine

Disadvantages

Heavy (more weight)

The passenger compartment has the

propeller shaft tunnel.

Front engine and front-wheel drive:Advantages

More space in passenger compartment.

Easy to place the fuel tank (bigger)

More safe in the event of head oncollision. (engine mass)

Shorter car length and better passenger

compartment

Better cooling

No problem in steering the car in a

slippery road.

Disadvantages:

The need to a power steering

More tire wear in the front axle

Less brake efficiency, 75% front and 25%rear.

Less climbing ability

Less accessibility for engine parts

(maintenance)

Rear engine and rear wheel drive:Advantages

Good brake distribution on the axles

Better climbing ability and acceleration

Less steering effort

Disadvantages

More rear wheel tire wear.

Bad cooling

Less space for luggage

Sensitive to the wind.

Less safety (front fuel tank)


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Four-wheel drive

Another common type of automobile layout is the front engine, four wheel driveconfiguration.

Advantages

Better traction

Less risk of wheel spin

Minimizes the possibility of wheel lock-

up when braking the car.

More gradient ability

Disadvantages

Heavier

Increase the fuel consumption

Tire wear if driven on a paved road.

Power transmission components:Clutch

Gear box (transmission)

Universal joints

Propeller shaft

Final drive and differential

Live rear axle

Wheels and tires


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Car Dimensions Definitions

Motor vehicle length

The distance between two vertical planes perpendicular to the longitudinal median plane(of the vehicle) and touching the front and rear of the vehicle respectively.

All parts of the vehicle, including any parts projecting from front or rear (towing-hooks,bumpers, etc.) are contained between these two planes.

Motor vehicle length

Vehicle height (unladen)

Vehicle height (unladen):

The distance between the supporting surface and a horizontal plane touching the topmostpart of a vehicle.

All fixed parts of the vehicle are contained between these two planes.

The vehicle is in operating order and unladen.

Vehicle width:

The distance between two planes parallel to the longitudinal median plane (of the

vehicle) and touching the vehicle on either side of the said plane. All parts of the vehicle, including any lateral projections of fixed parts (wheel hubs,

door handles, bumpers, etc.) are contained between these two planes, except the rear-

view mirrors, side marker lamps, tire pressure indicators, direction indicator lamps,

position lights, customs seals, flexible mud- guards, retractable steps, snow chains and

the deflected part of the tire walls immediately above the point of contact with the

ground.

Vehicle width

Motor vehicle or trailer wheel space


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Motor vehicle or trailer wheel space

The distance between the perpendicular lines constructed to the longitudinal medianplane (of the vehicle) corresponding to two consecutive wheels situated on the same side

of the vehicle.

If the values of right and left wheel spaces are different, both dimensions are stated,separated by a dash, the first corresponding to the left wheels.

For vehicles with three or more axles, the wheel spaces between consecutive wheels areindicated, going from the foremost to the rear most wheels: the total wheel space for right

or for left is the sum of these distances.

Semi-trailer wheel space

The distance from the axis of the fifth wheel kingpin in a vertical position to the verticalplane through the axis of the semi-trailers first axle.

In the case of a semi-trailer with two or more axles, the same rule should be applied asor vehicles with three or more axles.

Semi-trailer wheel space Track

Track:

In the case of two single wheels corresponding to the same real or imaginary axle, thetrack is represented by the distance between the axes of the traces left by the wheels on

the supporting surface.

In case of dual wheel, the track is represented by the distance between the middle oftraces left by the dual wheels on the supporting surface.

Ground clearance The distance between the ground and the lowest point of the centre part of the vehicle.

The centre part is that part contained between two planes parallel to and equidistant fromthe longitudinal median plane (of the vehicle) and separated by a distance which is 80%

of the least distance between points on the inner edges of the wheels on any one axle.


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Ground clearanceVertical clearanceVertical clearance

The vertical displacement of a wheel in relation to the suspended part of the vehicle fromthe position corresponding to the maximum permissible load to the position from which

any additional vertical travel is impossible.

Front overhang

The distance between the vertical plane passing through the centers of the front wheelsand the foremost point of the vehicle, taking into consideration lashing hooks,

registration number plate, etc., and any parts rigidly attached to the vehicle.

Front overhang Rear overhang

Rear overhang

The distance between the vertical plane passing through the centers of the rearmostwheels and the rearmost point of the vehicle, taking into consideration the towing

attachment, registration number plate, etc., and any parts rigidly attached to the vehicle.

Ramp angle

The minimum acute angle between two planes, perpendicular to the longitudinal medianplane of the vehicle, tangential, respectively, to the tires of the front and the rear wheels,

static loaded, and intersecting at a line touching the lower part of the vehicle, outside

these wheels.

This angle defines the largest ramp over which the vehicle can move.

Ramp angleApproach angle


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Approach angle

The greatest angle between the horizontal plane and planes tangential to the static loadedfront wheel tires, such that no point of the vehicle ahead of the axle lies below these

planes and that no part rigidly attached to the vehicle lies below these planes.

Departure angle The greatest angle between the horizontal plane and planes tangential to the static loaded

rear wheel tires, such that no point of the vehicle behind the axle lies below these planes

and that no part rigidly attached to the vehicle lies below these planes.

Departure angle

LiftLift

The height to which a wheel may be lifted without any other wheels leaving theirsupporting surface.

Turning clearance circles

The turning clearance circles (the steering wheel being turned to full lock) are

1) The diameter of the smallest circle enclosing the projections onto the supporting planeof all points of the vehicle.

2) The diameter of the largest circle beyond which are located the projections onto thesupporting plane of all the points of the vehicle.

Each vehicle has right-hand and left-hand turning clearance circles.

Turning clearance circles Turning circles

Turning circles

The diameters of the circles circumscribing the extensions on the supporting plane of themid planes of the steered wheels (the steering wheel being turned to full lock).

The smaller diameter of the circle circumscribing the extension on the supporting plate ofthe mid-plane of an inner non steered wheel is also of practical interest.

Each vehicle has left-hand and right-hand turning circles.


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Castor

The distance between two points p and q this distance is the projection onto a planeparallel to the longitudinal median plane (of the vehicle) of the acute angle formed by

the vertical and the real or imaginary swiveling axis of the stub axle.

It is positive when p is ahead of q in the direction of normal travel.

Castor Kingpin inclination

Kingpin inclination

The projection onto a plane perpendicular to the longitudinal median plane (of thevehicle) of the acute angle, formed by the vertical and the real or imaginary swiveling

axis of the stub axle.

Kingpin offset

The distance from the extension of the swiveling axis of the stub axle onto the supportingsurface to the extension onto the same plane of the mid-plane of the wheel.

The kingpin offset shown on the drawing is positive.

Kingpin offsetToe-in (length)

Toe-in (length)

The length defined as follows: The ends of the horizontal diameters of the interiorcontours of the rims corresponding to the same axle are the apices of an isosceles

trapezium.

The difference between the length of the rear base and that of the forward base of the

trapezium is the toe-in, the difference being positive when the wheels are closer togetherin front than behind, and negative in the contrary case.

Toe-in (angle)

The angle formed by the horizontal diameter of the wheel and the longitudinal medianplane (of the vehicle) or the acute angle formed by the vertical plane G passing through


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the axis of the axle-pin and a vertical plane H perpendicular to the longitudinal median

plane (of the vehicle).

Toe-in (angle) Camber angle

Camber angle

The acute angle between the axis of the axle-pin and a horizontal line in the vertical planethrough that axis. The angle is positive when the point of the V formed by straight lines

supporting the wheel axles is directed downwards.

This angle is equal to the acute angle formed by a vertical line and the mid-plane of thewheel. These two angles, considered in the same plane, have their sides perpendicular to

each other.Vehicle Weights

Basic Curb weight

It is the weight of the vehicle including a full tank of fuel and all standard equipment. Itdoes not include passenger, cargo, or optional equipment.

Vehicle Curb weight

It is the weight of your vehicle when picked from the authorized dealer plus anyaftermarket equipment.

Pay load

It is the combined weight of cargo and passengers that the vehicle is carrying. Themaximum pay load for the vehicle can be found on the tire label on the B-pillar or the

edge of the drivers door.

Cargo weight

Includes all weight added to the Base Curb weight including cargo and optionalequipment. When towing, trailer tongue load weight is also part of cargo weight.

GAW (Gross Axle Weight)

It is the total weight placed on each axle (front or rear), including vehicle curb weightand all payload.

GAWR (Gross Axle Weight Rating)

It is the maximum allowable weight that can be carried by a single axle (front or rear).These numbers are shown on the safety compliance certification label lasted on the B-

pillar or the edge of the drivers door. The total load on each axle must never exceed itsGAWR.

GVW (Gross Vehicle Weight)

It is the vehicle curb weight + cargo + passenger.GVWR (Gross Vehicle Weight Rating)


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It is the maximum allowable weight of the fully loaded vehicle (Including all options,equipment, passenger and cargo).

The GVWR is shown on the safety compliance certification label located on the B-Pillaror the edge of the driver door.

The GVW must not exceed the GVWR.GCW (Gross Combined Weight)

It is the weight of the loaded vehicle (GVW) plus the weight of the fully loaded trailer.GCWR (Gross Combined Weight Rating)

It is the maximum allowable weight of the vehicle and the loaded trailer including allcargo and passenger. GCW must never exceed the GCWR.

Specifying an Automobile

For describing an automobile, the various factors taken into consideration are:

o Type: Whether scooter, motor cycle, car, lorry, truck etc.o Carriage capacity: Whether 1/4 tonne, 1 tonne, 3 tones, etc. or 2 seater, 4 seater, 6

seater, 30 seater, 40 seater etc.o Make. The name allotted by the manufacturer. It is generally the name of the power

unit indicating kW or number of cylinders or shape of the engine block.

o Model: The year of manufacture or a specific code number allotted by themanufacturer.

o Drive, (i) Whether left hand or right hand drive, i.e. the steering is fitted on the lefthand side or right hand side. (ii) Two wheel drive, four wheel drive, or six wheel

drive.

As an example for specifying a truck, the typical specifications are given below: (i) Type

: Truck 312 L (ii) Capacity : 17,025 kg (iii) Drive: Right hand, 6x4 wheels, (iv) Make:

Tata Mercedes-Benz (v) Model: OM 312


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CHASSIS FRAME AND BODY

Chassis is a French term and was initially used to denote the frame parts or BasicStructure of the vehicle.

It is the back bone of the vehicle.

A vehicle with out body is called Chassis.

The components of the vehicle like Power plant, Transmission System, Axles, Wheelsand Tyres, Suspension, Controlling Systems like Braking, Steering etc., and also

electrical system parts are mounted on the Chassis frame.

It is the main mounting for all the components including the body. So it is also called asCarrying Unit.

Layout of Chassis and its main Components:


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Longitudinal torsion Lateral bending Lozenging.

Classification of Chassis:

Conventional control chassis: The engine is mounted in front of the drivers cabin.

Semi-forward control chassis: The engine is so mounted that half of it is in the drivers

cabin, whereas the other half is in front, outside the drivers cabin.

Full forward control Chassis: The engine is mounted completely inside the driverscabin.

Main components of the Chassis are

Frame: it is made up of long two members called side members riveted together with the

help of number of cross members. Engine or Power plant: It provides the source of power

Clutch: It connects and disconnects the power from the engine fly wheel to thetransmission system.

Gear Box

U Joint

Propeller Shaft

Final Drive

Differential

FUNCTIONS OF THE CHASSIS FRAME:1. To carry load of the passengers or goods carried in the body.

2. To support the load of the body, engine, gear box etc.,

3. To withstand the forces caused due to the sudden braking or acceleration

4. To withstand the stresses caused due to the bad road condition.


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5. To withstand centrifugal force while cornering

TYPES OF CHASSIS FRAMES:

There are three types of frames:

1. Conventional frame: It has two long side members and 5 to 6 cross members joinedtogether with the help of rivets and bolts. The frame sections are used generally. a.

Channel Section - Good resistance to bending b. Tabular Section - Good resistance toTorsion c. Box Section - Good resistance to both bending and Torsion.

2. Integral Frame: This frame is used now a days in most of the cars. There is no frameand all the assembly units are attached to the body. All the functions of the frame carried

out by the body itself. Due to elimination of long frame it is cheaper and due to less

weight most economical also. Only disadvantage is repairing is difficult.

3. Semi - Integral Frame: In some vehicles half frame is fixed in the front end on whichengine gear box and front suspension is mounted. It has the advantage when the vehicle

is met with accident the front frame can be taken easily to replace the damaged chassis

frame. This type of frame is used in FIAT cars and some of the European and Americancars.

Various loads acting on the frame:

Various loads acting on the frame are1. Short duration Load - While crossing a broken patch.

2. Momentary duration Load - While taking a curve.

3. Impact Loads - Due to the collision of the vehicle.

4. Inertia Load - While applying brakes.

5. Static Loads - Loads due to chassis parts.6. Over Loads - Beyond Design capacity.

Body Of The Vehicle:

Automobile bodies are divided in two groups are Passenger Body and Commercial body

According to Chassis design the body can divided intoo 1. Conventional Type


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o 2. Integral Typeo 3. Semi- Integral Type

According to other usage:o 1. Light vehicle Bodies - cars, jeepso 2. Heavy vehicle BodiesBusses, Lorrieso 3. Medium vehicle Bodies - Vans, Metadoors

Requirements of bodies for various types of vechile:

The body of the most vehicle should fulfill the following requirements:1. The body should be light.

2. It should have minimum number of components.

3. It should provide sufficient space for passengers and luggage.

4. It should withstand vibrations while in motion.

5. It should offer minimum resistance to air.

6. It should be cheap and easy in manufacturing.

7. It should be attractive in shape and colour.8. It should have uniformly distributed load.

9. It should have long fatigue life

10. It should provide good vision and ventilation.

Car Types

Coach Types

Microbus Minibus


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City bus City bus

Tour buses Double-decker bus

Trucks

Platform type Tractor for trailer

Trailers


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Tanker

DumpTruck

Delivery Van

Station Wagon


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Pickup

JeepTractor


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Rigid 4x2 truck

Rigid 6x4 truck Rigid 8x4 truck


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Articulated Tractor and Semi-trailer:

Rigid 4x2 tractor and single-axle 2 articulated Rigid 6x4 tractor and tandem-axle 4

articulated trailers. trailers.

Rigid 6x2 tractor and tri-axle 6 articulated trailers.

Advantages of Frameless construction:

Reduced weight and consequent saving in fuel consumption Lower manufacturing cost. During collision the body crumbles, thereby absorbing the shock due to impact and

thus providing safety to the passengers. Compared to framed construction lower body position may be obtained, thus resulting

in increased stability of the automobiles.

Disadvantages of frameless construction: Reduction of strength and durability Economical only if frameless construction is adopted in mass production. Increased cost of repairs in case of damage to body during accidents. Topless cars are difficult to design with the frameless construction.

Sub Frames:

Backbone frame


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Many times, the various components of the automobile are mounted on a separate frame

called sub-frame.

This sub-frame is further supported by the main frame at three points.

In this way the components are isolated from the effects of twisting and flexing of the

main frame.

The mass of the sub-frame alone helps to damp vibrations.

The provisions of sub-frame simplifies production on the assembly line and facilitatessubsequent overhaul or repair,

Defects in frames:

The dumb irons or side members may be bent.

Cross members may be buckled.

Some rivets may be loose or broken.

The frame also is subjected to the worst corrosive environment.

Chassis Frame Sections:

Chassis-member sections(A) Square solid bar (B) Round solid bar (C) Circular tube with longitudinal slit (D) Circular closed

tube (E) C-section (F) Rectangular box section (G) Top-hat-section (H) I-section (I) Channel flitch

plate.

During movement of a vehicle over normal road surfaces, the chassis frame, is subjected

to both bending and torsional distortion as discussed in the previous section.

Box section frame

Under such running conditions, the various chassis-member cross-section shapes, which

find application, include.


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o (i) Solid round or rectangular cross-sections,o (ii) Enclosed thin-wall hollow round or rectangular box-sections,o (iii) Open thin-wall rectangular channeling such as 'C, T, or 'top-hat' sections.

Backbone-type frame. Energy-absorbing frame

Body work and Integral Construction:

Some Terminology Pertaining to Body:Cab: It is the driver's cabin, which may be a closed region separated from the rest of the

body (as in truck) or may be an open region being a part of the body (as in car).

Fascia. It is the frontage of the vehicle visible to the driver. It includes the dash board(instrument board), tape recorder housing, globe box etc.

Dash board. It houses various indicators such as fuel level indicator, engine temperature

indicator, speedometer, voltmeter, ammeter, odometer, air-conditioner's control panel,

ignition switch, light switches, side indicator switch, various controls switches, automatic

operation switches, etc.

Legroom. It is the space provided for the movement of legs of the driver and passengers.

Sufficient legroom is essential for a comfortable driving, riding and traveling.

Headroom. It is the vertical distance inside the body between the floor to ceiling. This

dimension is based on the stability consideration of the vehicle, as position of CG fromthe ground level depends on this height.

Shoulder Room. It is the clear horizontal distance available inside the body.

Boot Space. This is the storing space available below the rear hood.

Body Work Requirements:The body work has to be structurally strong, easily accessible and of good finish.

Some of the important considerations for a good body work include the following :


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1. Attractive body styling.2. Upholstery work should be well trimmed and comfortable.3. Body structure should be rust preventing.4. Paint work and other finishing should be appealing.5. Body should be structurally strong and light. Therefore, construction material should

be of light weight, strong and cheap.

6. Doors and windows should be conveniently located, and easier to operate.7. Controls should be located at convenient positions and should be easily approachable.8. Arrangement of hand controls and foot pedals should be fool proof and untiring.9. Provision of sufficient space for accommodating accessories, instruments and

controls.

10.Drivers and passengers seats should be comfortable and adjustable, and should beconveniently located.

11.Interior cabin should be dust proof and sound proof.12.Body should be equipped with sufficient safety provisions.

Main Parts of the body:

The body work includes the following main parts.

1. Body safety,2. Bonnet,3. Side pillars,4. Rear hood,5. Front side panel,6. Rear side panel,7. Door pillars,

8. Windshield pillar,9. Rear quarter pillar,10.Body sill,11.Roof,12.Door Panels,13.Front bumper,14.Rear bumper


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Integral Construction:

Integral body construction

Body ShapeBody shape depends on a number of factors; these include appealing shape to the buyer,

providing comfort, and a good performance during its movement through the air.

A car body with the aerodynamic shape passes with least resistance through the air; as a

consequence the fuel economy is improved.

For a vehicle without aerodynamic shape of the body, a lot of engine power is required to

drive through the air. The air resistance increases very fast as the velocity of the vehicle

relative to the air becomes high (Fig.).

The air resistance of a vehicle is measured through wind tunnel tests.

Knowing the cross-sectional area of the vehicle and its velocity relative to the air,

aerodynamic drag coefficient (Cd) can be determined.

Force required for overcoming air resistance

A streamlined body has a low Cd so that it provides minimum resistance when passes

through the air.

Since most of the resistance is caused by the low-pressure region at the rear of thevehicle, the body shape returns the air to this region with the minimum of turbulence after

the air has flowed over the body.

Since resistance is directly proportional to the cross-sectional area, a low and sleek

sports-type car can provide good performance.

Separation of flow at the downstream side of the vehicle, and the difference in pressure

on the upstream and downstream side of the vehicle give rise to the phenomenon called


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wake. As wake is undesirable, it should be avoided or minimized by proper profiling of

the body.

The contour of body should be such that in addition to minimizing drag coefficient, the

separation of flow on any part of the body should not occur and the above pressure

difference should be minimum.

Wake depends on the body shape and drag coefficient depends on wake. To minimize

wake rear spoiler is added to aerodynamic styling of the body.Several improvements are incorporated in the body to reduce air drag.

Air dam and spoiler (A) Air dam. (B) Rear spoilerThese include the recessing of protruding items such as door handles and the shaping of

the body below the front bumper to form an air dam (Fig. A).

Airflow control devices are sometimes fitted to the rear of the vehicle.

These devices, depending on their shape and location, smooth out the air flow to reduce

the disturbance, or act as a spoiler to deflect the air upwards so that the adhesive force

acting on the rear wheels is increased (Fig. B).

Although these arrangements are beneficial on racing cars, their usage on domestic cars

may be regarded as 'image creation' embellishments.

AERODYNAMICS

An automobile is a small object submerged amid vast surrounding of air. The motion of the vehicle takes place through a large mass of either stationary air, or air

in motion. The air exerts force on the auto vehicle. It is the superstructure (body) of the vehicle which is mainly exposed to the air. An arbitrary shaped body will experience a large air resistance which implies that there is

more loss of engines power.

Consequently less power will be available to propel the automobile thereby causing less

load carrying capacity and slow speed for the same fuel consumption. Thus, there existsa need to profile aerodynamically suitable body.


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The force exerted by air on a moving auto vehicle had two components, one in thedirection of motion and the other in a direction perpendicular to the motion.

The force in the direction of motion is called drag FD and that in the perpendiculardirection is known as lift Ft, Fig.

The body profile of an automobile should be such that the lift force FL is zero ornegligible, and then the total force on the body is drag force FD.

The viscosity of air is mainly responsible for drag on the body. The arbitrary shaped body of an automobile, held stationary in a stream of air moving at a

uniform velocity V, experiences shear force along its tangentia1 direction and pressure

force in the normal direction Fig.

The shear forces are calledfrictional drag force FDf and the pressure forces are known aspressure drag force FDp

Total drag on the body is therefore the sum of friction and pressure drags.

Thus The magnitudes of friction drag and pressure drag depend on shape of the body. For

example, a flat plate portion, Fig. (a) Experiences only friction drag (.: FDp= 0).

While the flat portion perpendicular to the direction of flow, Fig. (b), feels only pressuredrag due to pressure difference on the upstream and downstream sides of the body.

In this case FDf=0.

There can be several body profiles in between the two extreme cases described above.


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For those cases the drag and lift may be calculated from

Where CDis coefficient of drag and CLis coefficient of lift, A is characteristic area of thebody which is the largest projected area of body on a plane perpendicular to the direction

of flow of the air.

Wake : Quite often we see on the downstream side of a fast moving vehicle that thesmall and light objects such as papers, pebbles etc. lift-up and move in a haphazard way.

It is due to a phenomenon called wake. Theseparation of flow, and the difference of pressure on the upstream and downstream

sides of the moving vehicle are responsible far the wake. Wake is an undesired situation.

It should be avoided or minimized by proper profiling of the body. The contouring of body should be such that the separation of flow does not occur, and the

pressure difference is not much on the upstream and downstream sides.

To achieve it, the modern cars employ a rear spoiler that adds to aerodynamic styling ofthe body.

The formed wakes can be of different sizes according to shape of the body. The magnitude of pressure drag depends on the size of the wake. The size of the wake will be large in a body such as circular disc, in the above figure

bluff body profile, having sharp edges than well-rounded bodies.

The wake and therefore the drag force are extremely small in case of streamlined body. In a well streamlined object, the friction drag is larger than the pressure drag; even

though the total drag is about 0.02 to 0.03 only to that of the circular disc.

Flow pattern around a streamlined body is shown in following Fig a. and the pressuredistribution in Fig. b.

The term v

2

/2 is called the dynamic pressure of the flowing air. Racing Car Profiling: The coefficient of drag depends on shape of the body in high

velocity air streams.

Ascompared to flat headed body in which CD= 0.85 at 300 kmph, this value is only 0.15in sharp pointed projection of racing cars.

Hence the racing cars are made of the profile as shown in Fig.


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The lift coefficient is related to the angle of attack by

As we desire CL to be a minimum, preferably zero, hence the body should be alignedin front of the upstream air so that = 0. The drag coefficient varies little with theangle of attack.

Coefficient of Drag : The aerodynamically streamlined body of Fiat Uno car with anoutstanding drag coefficient of 0.30.

In fact, such studies and intensive studies of fluid dynamics and wind tunnel testingsare a continued process in better body profiling to obtain lower coefficient of drag.

Values ofCD for different categories of vehicles and also for some specific vehiclesare given in Table.

Resistances acting on vehicle:

Tractive Resistance (TR):When a vehicle is traveling at constant speed, its resistance to

motion, termed the tractive resistance, it consists of:

Rolling resistance (RR): This depends mainly upon the nature of the ground, the tires

used, the weight of the vehicle, and to a lesser extent, the speed (the last variation isusually ignored).

Air resistance (AR): Air resistance (wind resistance) depends upon the size and shape of

the vehicleits degree of streamlining- and increases approximately as the square of the

speed through the air.


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Gradient resistance (GR): This is determined by the steepness of the hill and the weight

of the vehicle, which must, in effect, be lifted from the bottom to top.

Air Resistance (AR)

Aerodynamics effects on vehicle functions:

Air forces and Moments:

Directional Control (Driving Safety) [pitching, yaw, and rolling moments]-leftand cross wind force.

Driving Performance and Fuel consumption [air resistance]tangential

forces.

Air flow behavior, and pressure distribution: Comfort [wind noises, passenger compartment ventilation, dirty interior].

Clear Visibility [Dirty windows and lamps, Prevention of windshield misting]. Auxiliary equipment functions [engine cooling, engine compartment

ventilation, brake cooling, air conditioning].

Aerodynamic forces and moments:Aerodynamic resistance, aerodynamic lift, and aerodynamic pitching moment have

significant effects on vehicle performance at moderate and higher speeds.

The increase emphasis on fuel economy and on energy conservation has stimulated new

interest in improving the aerodynamic performance of road vehicles.

As a result of the air stream interacting with the vehicle, forces and moments are

imposed.

These may be defined systemically as the three forces and three moments, acting about

the principal axes of the car.


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The reactions are as follows:

Direction Force MomentLongitudinal (x-axis, positive rearward) Drag Rolling moment

Lateral (y-axis, positive to the right) Side force Pitching moment

Vertical (z-axis, positive upward) Lift Yawing moment

Aerodynamics drag:

Drag is the largest and most important aerodynamic force encountered by passenger cars

at normal highway speeds.

The overall drag on a vehicle derives from contributions of many sources.

Approximately 65% (.275/.42) of the drag arises from the body (fore body, after body,

underbody and skin friction).The major contributor is the after body because the drag produced by the separation zone

at the rear.

Effect of different factors on the car drag: Fore body and after body (depend upon the car shape) 55% - 60%

Skin friction (depend upon the car finish and the long of the body) 8%-l0% Flow resistance in the front grille and radiator 10% - 15%


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Air hits the outer components and car openings (luggage rack, side mirror and

windows) 8% - 12%

The air force equation is usually expressed in the following form (semi-empirical

formula):

AR=(1/2) Cd Afv2

o where: AR = air resistance [N], = air density [kg/m3], A = the car frontal area [m

2],

v = car speed [m/s], Cd = the coefficient of aerodynamic resistance [dimensionless]o The term [(1/2 v

2] in the above equation is the dynamic pressure of the air

[(kg/m3)(m

3/s

2)], [N/m

2].

o The drag properties of the car sometimes characterized by the value of (Cd Af).

Air density ():

o The air density is usually equal to 1.202 kg/m3

and it depends on the air temperature

and pressure: = 1.225 (pr / 101.325) (288.16/(273.16+Tr)) [kg/m3] = 3.48 (pr / (273.

16+Tr))

where: Pr = atmospheric pressure [kPa], Tr = air temperature [degree Celsius C]

Coefficient of aerodynamic resistance (Cd):

Cd is the coefficient of aerodynamic resistance that represents the combined effects of

form drag, skin friction, and resistance due to air flow through the radiator and interior of

the vehicle.

Typical values of Cd


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Factors affecting the value of Cd:

Aerodynamic effects on vehicle functions:


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Automobile Engines:

Automobile Engines ClassificationAutomobile engines are classified in many several different ways as follows:

1. Types of Cycles2. Types of Fuel Used3. Number of Cylinders

4. Arrangement of Cylinders

5. Firing Order6. Arrangement of valves7. Type of Cooling

8. Reciprocating or Rotary Engines

Engine Construction:The major components of an automobile reciprocating piston engine are the

cylinder block, oil pan, cylinder head, intake manifold, exhaust manifold, crankshaft,

flywheel, camshaft, oil seals, bearings, connecting rod, piston, piston rings, valve

train etc.


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Cylinder Block:

Fig. Monoblock cylinder block and crankcase Fig. Cylinder block with detachable crankcase

Fig. Closed-deck cylinder block.Fig. Open-deck cylinder block.


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Fig. Horizontally opposed cylinder with detachable crankcase Fig. Horizontally opposed cylinderwith divided

crankcase

Fig. Monoblock V cylinder withblock and crankcaseFig. 'V cylinder blockwith detachable

crankcase

Cylinder Liners:

Dry Liners:

A. Plain force-fit B. Flanged slip-fit.

Wet Liners:

A. Single sleeve support with open-deck.B. Double sleeve support with closed-deck.


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Cylinder Block Attachments:A number of parts are attached to the engine to enclose it and to adapt it to the vehicle.

These include covers, housings, and mounts.

Cylinder Head:

Fig. Overhead-camshaftcylinder head

Lubrication System:

Wetsump Lubrication Drysump lubrication

Cooling System of Engine:


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Intake and Exhaust Valves Functions and Arrangements:

Fig. Valve assembly parts

Fig. Valves and valve lifters. Valve in L-head engine.


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Fig. Valves and valve lifters -Overhead valve.

The Poppet-valve:

Fig. Identification of a poppet valve. Fig. Valve guides.

Rocker-shaft assembly:

Rocker-arm:

Fig. Valve rocker-arms A. Forged or cast rocker-arm with central pivot and end adjustment. B. Pressed-steel-sheet rocker-arm with central pivot and end adjustment. C. Cast or pressed-sheet rocker-arm with central pivot and adjustment.

D. Forged or cast rocker-arm with end pivot and adjustment. E. Geometrically best rocker-to-valve-stem layout.


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Cam Follower (Tappet) and Lifter:

Fig. Cam followers (tappet).

A. Mushroom follower. B. Bucket or barrel follower.C. Enclosed bucket follower with helical slots. D. Roller follower.

Camshaft:

Fig. Camshafts chain driven by the crankshaft.

Timing the Valve of an Engine:During the assembling of an engine the drive between the crankshaft and the camshaft must

be connected properly so that the valves open and close at the correct times in relation to the

movement of the crankshaft and the piston. This operation is known as timing the valves.

For the engine with more than one camshaft, each one has to be timed individually.

1. Set the crankshaft in the position in which one of the valves should open or close. (It is

usual to work on the opening point of the inlet valve, but any other point can be used.)


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2. Set the camshaft in the position in which it is about to open the inlet valve (or whatever

point is chosen).

3. Connect up the drive to the camshaft.

Suitable parts of the engine are usually marked, to assist in timing the valves.

The timing gear or sprocket is keyed to the crankshaft and can be fitted in one position only.

The camshaft gear or sprocket is similarly fixed to the camshaft in such a way that it can be

attached in one position only.

Fig. The timing gears

By lining up marked teeth on these gears, the crankshaft and camshaft are placed in the

correct positions for connecting up the camshaft drive.


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Intake Manifold:

Fig. Intake manifold of a six-cylinder in-line engine.

Fig. Intake manifold of an in-line engine.

Fig. Two-plane intake manifold.

Different Types of Intake Manifold

Exhaust Manifold:


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Catalytic converter

Exhaust system with a catalytic converter

Mufflers:

A muffler is a part of a car's exhaust system that is designed to reduce the amount of noise that an engineproduces.

Performance mufflers not only seek to reduce sound levels, but to also reduce back pressure. Adding a performance muffler to the car or truck can increase your engines performance and efficiency.

They can also help to reduce wear on engine components, by reducing engine heat and boosting exhaustflow.


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Fan-belt Pulley Attachment:


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Dynamic Oil Seals:Dynamic oil seals are used between surfaces having relative motion such as a shaft and

housing.

The seals keep liquid and gases in and keep contaminants out.

Oil seals must not press very hard against the moving parts to minimize surface wear and

must provide minimum drag or friction.

Seal selection is made considering the rubbing speed, fluid pressure, operating temperature,

shaft surface requirements, and space available.Some dynamic seals, such as piston rings, are designed to withstand a lot of pressure, while

others such as front and rear crankshaft oil seals, seal against little pressure.

Seals around rotating shafts in an engine are called as radial positive contact seals.

Three most common types of seals are, (a) the radial-packing seal (b) the radial-lip seal, and

(c) the spiral-thread clearance seal.

Dynamic seals used in automotive engines are most commonly made from a rope packing or

from synthetic rubber.

Rope packing is the least expensive type of dynamic seal and has very low friction and wear

characteristics.Lip-type dynamic seals used in automobile engines are made from synthetic rubber.

They can stand more shaft eccentricity and run-out than rope type seals.

They can operate at higher shaft speeds, but they require a finer shaft finish, for longer

sealing life.

Lip seals place more load on the shaft than the rope type seal, and therefore, they seal better.

Lip seals are usually held in a steel case or are supported by bonding on to a steel support

member.


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The seals must run with a very thin flow of lubrication otherwise it would wear the shaft

very quickly.

Engine Bearings:Engine bearings support the operating loads of the engine at all engine speeds and along

with lubricant, minimize friction.

Most engine bearings are plain or sleeve bearing, in contrast to roller, ball and needle

bearings, called anti-friction bearings, which are used where minimum lubrication isavailable.

The lubricating system in automotive engines continuously supplies lubricant to each

bearing so that the shaft actually rolls on a film of lubricant in plain bearings.

The friction caused, in this case, is almost same as in antifriction bearings.

It is important that the bearing surface must be large enough so that the bearing unit load is

within safe limits.

Bearing load capacity is the bearing load per unit of the bearing projected area.

Bearing Materials:

Selection of Bearing Materials:The properties required in a bearing material include the following:

High Fatigue Strength: This permits the bearing to resist the high fluctuating pressure in

the lubricant film due to the periodic reciprocating-inertia and gas loads.

High Melting Point and Hot Strength: This resists damage by high temperature lubricant

films and the reduction of yield strength of bearing alloys at elevated temperatures. The oil

temperatures in big-end bearings can reach around 423 K.

High Resistance to Corrosion: This permits the bearing surface to resist attack from

degraded acidic lubricants at elevated temperatures.

Adequate Hardness: This allows the relatively soft bearing surface to resist abrasive wear

and cavitation erosion caused by high-velocity oil and to sustain static and dynamic loads,but without sacrificing conformability and embeddability.

Good Conformability: This is the ability of the bearing surface to tolerate misalignment

between the bearing and the crankshaft. In general, conformability is inversely related to

bearing hardness.

Good Embeddability: Due to this property the bearing surface absorbs dirt particles being

carried round by the lubricant and prevents scoring of the journal under high loads.

Good Compatibility: This property provides resistance to steel journal against local

welding or pick-up from the bearing when loaded under boundary-lubrication conditions, but

with a rotational speed insufficient to provide a thick hydrodynamic oil film.Classification of Plain-journal-bearing Materials:Journal bearing material can be categorized into three broad groups:

1. Lead- or tin-based white metal (Babbitt metal),2 Copper based alloys and

unit i ohp

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