21.7.
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 travelling.
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 from the 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 :
• Attractive body styling.
• Upholstery work should be well trimmed and comfortable.
• Body structure should be rust preventing.
• Paint work and other finishing should be appealing.
• Body should be structurally strong and light. Therefore, construction material should be of light weight, strong and cheap.
• Doors and windows should be conveniently located, and easier to operate.
• Controls should be located at convenient positions and should be easily approachable.
• Arrangement of hand controls and foot pedals should be fool proof and untiring.
• Provision of sufficient space for accommodating accessories, instruments and controls.
• Driver’s and passengers seats should be comfortable and adjustable, and should be conveniently located.
• Interior cabin should be dust proof and sound proof.
• Body should be equipped with sufficient safety provisions. Main Parts. The body work includes the following main parts.
• Body safety
• Bonnet
• Side pillars
• Rear hood
• Front side panel
• Rear side panel
• Door pillars
• Windshield pillar
• Rear quarter pillar
• Body sill
• Roof
• Door Panels
• Front bumper
• Rear bumper
Integral Construction.
Around 1934, the all-steel body construction was introduced so that a separate frame could be eliminated. This frameless or integral construction provides a stiff, light construction, which is specifically suitable for mass-produced vehicles. Since 1945 light cars have used integral construction. When suitably designed the body shell is capable of withstanding the various frame stresses. Figure 21.12 illustrates some of the forces that act on a car body and the arrangement of the various body panels to form a unitary structure of sufficient strength to resist these forces. The floor and roof panels resist the sagging effect caused by the weight of the occupants. Since these two members are widely spaced, thin sheet metal is used to form a strong and lightweight box like structure. To increase torsional stiffness of the body the scuttle at the front is strengthened and behind the rear seat squab cross ties are used or a ribbed metal panel is fitted.
The thickness of the sheet metal depends on the stress to be taken by the panel. Structural members such as sills, rails and pillars are often about 1.1 mm thick, whereas panels such as the roof are 0.9 mm thick. Component attachment points are reinforced with thicker section. Some cases use a separate sub-frame to mount engine and other members. Sometimes this sub-frame is connected to the body by rubber insulation mountings.
A very low (0.1 percent) carbon steel is used to provide extremely good ductility required for the pressing of the panels. The low strength, 278 MN/m2, of this steel requires stiffening of the
structural members, which is achieved by spot welding into position of intricate sections, formed out of thin steel sheet.
Fig. 21.12. Integral body construction.
A modified construction is necessary in case the roof cannot be fully utilized as a compression member. This situation occurs on drop-head coupe models and where a sunshine roof, or very thin door pillars are used. To achieve the required strength in these cases a strong underbody frame is used. In addition, the body-shell parts, which are subjected to torsion, are provided with extra stiffness.
Fig. 21.13. Space frame.
A body-shell is normally fabricated either by spot-welding the panels, pillars and pressings together to form a strong box, or by buildings a skeleton or space frame (Fig. 21.13), which provides a high structural strength. To this frame is attached the shell, aluminium or glass-reinforced plastic (GRP) body panels, doors, roof, etc. Steel is the most common material used for manufacturing of vehicle in high volume, because production costs become lower once the initial investment on body jigs and other facilities has been recovered.
The vibration of the panels, which produces an unwanted noise called drumming, is avoided by fixing a sound-damping material on the inside of the panels. The driver and passengers are enclosed in a rigid cell for their safety. The front and rear of this rigid compartment are fixed with sub-frames, which are designed to concertina on impact (Fig. 21.14). The crumple zones of the body absorb the shock of a collision so that the rate of deceleration experienced by the occupants is reduced.
Nowadays, it is mandatory to obtain an impact test certificate from an approved centre before vehicles can be sold. The vehicle can pass this severe destructive test, provided a required standard on the level of safety of the occupants is witnessed. The doors must remain closed during impact and must open after the test. The inclusion of this test feature justifies the common use of special anti-burst locks at present.
The vehicles safety belts, or some other approved body restraint system, must be provided for the driver and all passengers. These belts must be securely anchored to suitable strengthened parts of the body. Internal body trim, fittings and controls must all conform to safety standards. The improvements made during recent years in the design of parts such as steering wheels and control knobs have considerably increased the safety of the occupants.
Fig. 21.14. Crumple zones.
