Vehicle Construction and Drive Arrangements

Vehicle Body Construction• Motor vehicles are a combination of many different

systems 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 shell – forms the skeleton of the vehicle• Engine – acts as the power unit• Transmission – conveys the drive to the road wheels• Suspension – absorbs the road shocks• Steering – controls the direction of movement• Brakes – slows down the vehicle• Electrical equipment – provides lighting, engine starting

and other driver needs.

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.

Road Vehicle Systems And Layouts• Saloon Car – The basic body shape is the Saloon with two or four

doors and a permanent rigid roof, this design can be broken down into 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 Car – Also 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.

• Hatchback – This 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.

Road Vehicle Systems And Layouts• Convertible – Some times referred to as a Cabriolet or Drop – Head

Coupe. This design allows the removal of the roof panel or panels or the 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 and front 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

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 as Trucks 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 heavier loads 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.

Light And Heavy Vehicle Frames• In the early days of vehicle production even small cars would be

constructed 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 separate frame.

• 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 being strong 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.

Composite Construction

Integral Construction

Passive Safety Systems• Passive safety systems start operating in the event of an accident.• Air Bags – In the event of an accident these bags ‘explode’ onto

position to cushion the driver and passenger.• Antiburst door locks – These door locks prevent the doors from

flying open.• Collapsible steering column – used to try prevent chest injuries to

the driver, the steering column collapses and is pulled down away from the driver in the event of a front end collision.

• Crumple zones – When 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 the energy as possible, reducing the risk to the occupants.

• Padded steering wheel – helps to reduce injury to the drivers chest.• Rollover cage – In the event of the vehicle rolling over, a cage

prevents the cabin from collapsing.• Seat belt tensioners – Pull the seat belt tighter at the instant of

impact.• Side impact bars – Bars in the door which strengthen the side of

the vehicle

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

waiting for an accident to occur.• Antilock brakes – Electronically controlled system to prevent the

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

• Aerodynamic stability – A stable car is less likely to go out of control• Dual circuit brakes – Standard on all modern cars, if one brake pipe

bursts, the brakes will still work on at least two wheels.• Comfortable driving position – The driver is more likely to be able to

react to potential trouble.• Safety glass – Toughened glass shatters on impact into small road

granules which do not cause cuts, but vision is impaired. Modern laminated glass resists heavy impacts without shattering and vision remains good

• Good ventilation – Helps to keep the driver awake and alert.• Efficient bad weather equipment – Good lights and good windscreen

wipers, to name just two parts, ensure the driver can see and be seen.

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 constantly kept under slight tension.

When the belt is removed, the retractor automatically recoils the strap out of the way.

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 pyrotechnic device, 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.

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:

Extra Safety Features

WHIPS (Whiplash Protection System) are specially designed seats that absorb sharp movement, protecting the neck and back.

Inflatable curtains are available that drop down from a vehicle’s 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 doorsto detect a side impact. These sensors trigger air bags in the side of the seat.

Fascia instrument panel and warning lights

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 normally made stronger and stiffer.

Front wing

Frontbumper

Rear quarter

Rear bumper

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.

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 weight over the driven wheels gives greater traction. This can be particularly useful in adverse weather conditions.

The front engine, rear wheel drive 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.

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 is now 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 vehicle handling and good traction at the rear wheels. They are normally found on two-seat sports cars where these factors are important.

Drive Train/ TransmissionLayouts

Terminology• Chassis – The basic frame for a motor vehicle• A Post - The post on which the front door hinges are fixed.• Body mounting – Fittings 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 construction – Most modern light vehicles use this method,

also called mono or unity construction. The body and chassis are combined.

• Car derived van – A van which is based on a similar car.• Body panels – Wings, bonnet and door for example.• BC Post – The 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 Post – The rear post on which the rear door striker is fitted. Front door striker if a two/three door vehicle.

Terminology• FWD – Front Wheel Drive• RWD – Rear Wheel Drive• AWD – All Wheel Drive• 4WD – Four Wheel Drive• Off side – In the UK, this is the right hand side when in the drivers

seat.• Near side – In the UK, this is the left hand side when in the drivers

seat.• Light Vehicle – Normally classified as a car or van of less than three

tonnes• Light vehicle types – These range from small two seater sports cars

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

• Vehicle systems – A set of related components on the vehicle. For example, all components used to make the brakes work are described simply as the ‘braking system’.