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Vehicle Body Construction

Motor vehicles are a combination of many differentsystems all made up of separate items. All these

systems have to be brought together and mounted on

some form of frame or body shell to form a chassis. The

chassis comprises the following.

Frame or body shellforms the skeleton of the vehicle

Engineacts as the power unit

Transmissionconveys the drive to the road wheels

Suspensionabsorbs the road shocks Steeringcontrols the direction of movement

Brakesslows down the vehicle

Electrical equipmentprovides lighting, engine starting

and other driver needs.

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All vehicles are made up of separate systems and components, they

have their own purpose and operation, however, all of these systems

are brought together to give us the modern motor vehicle.

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Mojor Road Vehicle Systems And

Layouts Saloon CarThe basic body shape is the Saloon with two or four

doors and a permanent rigid roof, this design can be broken downinto three compartments, the first would normally be the engine

compartment, the centre would be for the occupants, the rear would

normally be used for storage, often referred to as the Boot The

three compartments are blended together to give a pleasing and

aero dynamic shape. Estate CarAlso known as a Shooting Brake or Station Wagon, in

this design the roof panel is extended to the rear to increase the

storage area, the rear seats are designed to fold down to increase

the floor area. The rear door is referred to as the tailgate and opens

as wide as possible. The rear suspension is up rated to support the

extra.

HatchbackThis design gives some of the advantages of the

Estate car, the tailgate is counted as one door and the rear seats

fold down to give a flat floor. Hatchbacks are made in three and five

door versions.

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Road Vehicle Systems And Layouts

ConvertibleSome times referred to as a Cabriolet or DropHead

Coupe. This design allows the removal of the roof panel or panels orthe lowering of the roof frame which is normally covered in fabric.

The roof frame may be operated by hand or by powered means.

Due to lack of a rigid roof the vehicle body is strengthened.

Coupe Normally a two door type vehicle with a rigid roof,

sometimes referred to as 2+2 with accommodation for the driver andfront passenger and limited rear seat space for children or

occasional adult use.

Light Commercial Vehicles are used for the movement of relatively

light loads. The size of the van is generally given as the maximum

load that is designed to carry. Car and Van components parts are

similar in appearance, but components such as the clutch,

suspension springs etc are up rated to with stand more strenuous

duties. Manufactures normally offer body sizes and shapes to suit

customers needs e.g. a Pick Up. Most vans have a load carrying

capacity of about half a tonne

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Road Vehicle Systems And Layouts

Heavy Commercial Vehicles are very robust and normally used for

long distance transportation of goods, the vehicles are referred to asTrucks and have a gross vehicle weight greater than about three

tonne. A large flat platform is used to carry the load. To carry heavy

loads the rear wheels either have twin tyres fitted side by side, or

wide section tyres. Vehicles exceeding a certain total loaded weight

are required to have six wheels carried on three axles, even heavierloads are required to have eight wheels. These are legal

requirements laid down in the construction and use regulations.

Trucks are allowed to tow a trailer on which an additional load can

be carried. A Articulated vehicle consists of two parts, a four or six

wheel tractor which does not carry any load, which is connected by

a special coupling referred to as the fifth wheel to the front end of

the trailer, which itself has two or four wheels at its rear end. The

trailer has retractable wheels on which it can be supported allowing

the tractor to be uncoupled and used elsewhere. Loads carried must

not exceed the gross train weight.

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Light And Heavy Vehicle Frames

In the early days of vehicle production even small cars would beconstructed using a chassis and separately constructed body. As

design and production methods improved, it was found that an all

steel body could be constructed from individual panels that were

able to withstand the load placed on them. This frameless or integral

arrangement gave a stiff light construction, this unitary structure

provides sufficient strength to allow the elimination of a separateframe.

Heavy commercial vehicles use a separate steel frame which can be

likened to a strong ladder consisting of two side members and a

number of cross members. These members can be either tubular,

channel or box section to reduce the frames weight while still beingstrong enough to resist bending and twisting forces. The shape of

the frame may be altered to allow for movement of the steering and

suspensions components and fitment of the engine and

transmission. The body is made separately and bolted to the frame.

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Composite

Construction

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Integral Construction

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Passive Safety Systems

Passive safety systems start operating in the event of an accident.

Air BagsIn the event of an accident these bags explode onto

position to cushion the driver and passenger. Antiburst door locksThese door locks prevent the doors from

flying open.

Collapsible steering columnused to try prevent chest injuries tothe driver, the steering column collapses and is pulled down away

from the driver in the event of a front end collision. Crumple zonesWhen an impact occurs, the movement energy

has to be dispersed. If this is passed through to the passengers,then serious injury will result. Crumple zones absorb as much of theenergy as possible, reducing the risk to the occupants.

Padded steering wheelhelps to reduce injury to the drivers chest.

Rollover cageIn the event of the vehicle rolling over, a cageprevents the cabin from collapsing.

Seat belt tensionersPull the seat belt tighter at the instant ofimpact.

Side impact barsBars in the door which strengthen the side of the

vehicle

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Active Systems

Active safety systems are operating all the time i.e. they are not

waiting for an accident to occur. Antilock brakesElectronically controlled system to prevent the

wheels from locking and skidding when the brakes are applied. Thishelps the driver maintain control when braking.

Aerodynamic stabilityA stable car is less likely to go out of control

Dual circuit brakesStandard on all modern cars, if one brake pipebursts, the brakes will still work on at least two wheels.

Comfortable driving positionThe driver is more likely to be able toreact to potential trouble.

Safety glassToughened glass shatters on impact into small roadgranules which do not cause cuts, but vision is impaired. Modernlaminated glass resists heavy impacts without shattering and visionremains good

Good ventilationHelps to keep the driver awake and alert.

Efficient bad weather equipmentGood lights and good windscreenwipers, to name just two parts, ensure the driver can see and beseen.

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Seat Belts

Seat belts are used to restrain

passengers in their seats during

an accident. They are made

from tough nylon straps.

The seat belt buckle provides a

strong locking mechanism, but must

also be easy to lock and unlock.

Seat belts have a retractor that

ensures the belt is constantlykept under slight tension.

When the belt is removed, the

retractor automatically recoils

the strap out of the way.

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Seat Belts

Some vehicles incorporate a seat belt reminder

system. When a seat belt is not fastened correctly,

a warning lamp is illuminated on the dashboard.

Some systems also use an audible warning.

These systems usually use two switches,

the seat belt buckle switch and a pressure

sensitive switch, under the seat.

The control module fires a pyrotechnicdevice,

which tensions the seat belt, keeping the driver

in a safe position, ready for air bag activation.

A modern vehicle has seat belts that are fitted

with pretensioners. They are activated in the

event of a crash.

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Air Bag

Impact Sensors.

Safing Sensor.

Control Module.

Air Bag Module.

The air bag helps to protect the driver(and passengers in most vehicles)

from serious injury.

The system works by rapidly inflating

a nylon air bag, immediately after a

large impact.

When the ignition is switched on, the air

bag lamp is illuminated, until a self test

of the air bag circuit is completed.

An air bag system comprises the

following components:

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Air-bag and seat belt pre-tensioner systems

The component parts of these systems consist of crash detection sensors -

Typically a piezoelectric accelerometer formed by a silicon micro machined cantilever and signal

conditioning amplifier all mounted on one substrate within a hermetically sealed case filled with

silicon oil.

A microcontroller which runs a crash algorithm to distinguish between crashes and normal

vehicle dynamics, igniter (squib) triggering for the pyrotechnic inflator used for both air-bag

deployment and seat belt tightening, and system monitoring. The allowable forward passenger

travel with an air-bag system is 12.5 cm but with seat belt tensioning systems this figure drops to

about 1cm. Approximately 30 ms are required to inflate air-bags and the time required to tension

a seat belt with a pyrotechnically activated seat belt retractor is approximately 10 ms. Thus,

triggering commands must be given by the time maximally allowable forward displacement will

be reached minus the activation time of the respective restraining device.

Manufacturers have produced designs with varying numbers of both sensors and sensor mounting

positions when employing electromechanical sensors to provide the required performance but

current electronic based units are normally single-point systems such as the one illustrated in

Figure 1.

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When air-bag deployment is called for, the microcontroller or ECU

turns on the firing current switches, allowing current to flow through

the igniter, which initiates a gas generation reaction inside the

inflation module. A central energy reserve capacitance maintainspower for the system, allowing deployment even if the vehicle

battery becomes disconnected during the crash.

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Extra Safety Features

WHIPS (Whiplash Protection

System) are speciallydesigned seats that absorb

sharp movement, protecting

the neck and back.

Inflatable curtains are available

that drop down from a vehicles

roof to cover both front and rear

side windows, giving better

head protection than SIPS.

SIPS (Side Impact Protection System) uses impact sensors in vehicle doors

to detect a side impact. These sensors trigger air bags in the side of the seat.

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Fascia instrument panel and

warning lights

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Vehicle Body Components

Roof

All vehicle component locations are identified by sitting in the driving seat.

These are front, rear, left and right. In the diagram below, the left front wing

can easily be identified.

The front and rear

bumpers offer some

protection in low speed

front or rear impacts.

The roof, front wings and rear quarters can

be used to help strengthen the vehicle body.Other parts can also help to strengthen the

vehicle body e.g. glass, doors, sub-frames,

chassis and floor-pan.

On convertible vehicles that do

not have a rigid roof the floor pan

and centre tunnel are normallymade stronger and stiffer.

Front wing

Front

bumper

Rear quarter

Rear

bumper

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Parts of the Vehicle Body

Bonnet

Boot lid/

Tailgate

Doors

The bonnet is a hinged cover for the engine compartment. It can be hinged

to open toward the windscreen toward the front of the vehicle, or in some

cases toward either wing.

The boot lid is a hinged

cover over the boot. The

boot is used as an area

to store luggage or

other items.

The doors are used as a means

for the vehicle passengers to

enter and leave the vehicle.

When closed, the doors help to

strengthen the vehicle.

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Typical Engine Configurations

Front engine, front wheel drive

Front engine, rear wheel drive

Front engine, front wheel drive

can help with the drive-ability of

the vehicle. The engine weightover the driven wheels gives

greater traction. This can be

particularly useful in adverse

weather conditions.

The front engine, rear wheeldrive configuration has the

advantage of better weight

distribution. However, some

traction can be lost because the

bulk of the weight is not over the

driving wheels.

The engine may be placed in different positions within the vehicle, each

having its own advantages. There are four main engine configurations.

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Typical Engine Configurations

Rear engine, rear wheel drive

Mid-engine, rear wheel drive

Rear engine, rear wheel drive

provides a larger load to the rear

driving wheels. However, it can

become tail heavy which affects

handling of the vehicle. It also

reduces luggage space (which isnow in the front), as the passenger

seats need to be moved forward in

order to accommodate the engine.

Mid-engine, rear wheel drive

engines provide good vehiclehandling and good traction at the

rear wheels. They are normally

found on two-seat sports cars

where these factors are important.

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Drive Train/ Transmission

Layouts

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Terminology

ChassisThe basic frame for a motor vehicle

A Post - The post on which the front door hinges are fixed. Body mountingFittings for mounting the body to the chassis for

older type cars or heavier vehicles.

Composite construction - The chassis and body of the vehicle are

built as two separate units,

Integral constructionMost modern light vehicles use this method,also called mono or unity construction. The body and chassis are

combined.

Car derived vanA van which is based on a similar car.

Body panelsWings, bonnet and door for example.

BC PostThe centre post, the B post has the front door striker

plate and the C has the hinges for the rear doors. Only appropriate

to four/five door vehicles.

D PostThe rear post on which the rear door striker is fitted. Front

door striker if a two/three door vehicle.

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Terminology

FWDFront Wheel Drive

RWDRear Wheel Drive

AWDAll Wheel Drive

4WDFour Wheel Drive

Off sideIn the UK, this is the right hand side when in the drivers

seat.

Near sideIn the UK, this is the left hand side when in the driversseat.

Light VehicleNormally classified as a car or van of less than three

tonnes

Light vehicle typesThese range from small two seater sports cars

to quite large people carriers (such as the Ford Galaxy). Alsoincluded are light commercial vehicles such as vans and pick-up

trucks.

Vehicle systemsA set of related components on the vehicle. For

example, all components used to make the brakes work are

described simply as the braking system