Basic Vehicle body construction

Basic Vehicle body construction
A typical four-door saloon body can be likened to a hollow tube with holes cut in the sides. The bulkhead towards the front and rear completes the box-like form and assists in providing torsional stability. The roof, even if it has to accommodate a
sunshine roof, is usually a quite straightforward and stable structure; the curved shape of the roof panel prevents lozenging (going out of alignment in a diamond shape). The floor is a complete panel from front to rear when assembled, and is usually fitted with integral straightening ribs to prevent lozenging. With its bottom sides or sill panels, wheel arches, cross members and heelboard, it is the strongest part of the whole body. The rear bulkhead, mainly in the form of a rear squab panel, is again a very stable structure. However, the scuttle or forward bulkhead is a complex structure in a private motor car. Owing to the awkward shape of the scuttle and the accommodation required for much of the vehicle’s equipment, it requires careful designing to obtain sufficient strength. Body sides with thin pillars, large windows and door openings are inherently weak, requiring reinforcing with radiusing corners to the apertures to give them sufficient constructional strength.

A designer in a small coach building firm will consider methods necessary to build the body complete with trim and other finishing processes. The same job in a mass production factory may be done by a team of designers and engineers all expert in their own particular branch of the project. The small manufacturer produces bodies with skilled labour and a minimum number of jigs, while the mass producer uses many jigs and automatic processes to achieve the necessary output. However, the problems are basically the same: to maintain strength and stability, a good standard of finish and ease of production.

shows the build-up details of a fourdoor saloon, from the main floor assembly to the complete shell assembly. In the figure the main floor unit (1), commencing at the front, comprises a toeboard or pedal panel, although in some cases this may become a part of the scuttle or bulkhead. Apart from providing a rest for the front passengers’ feet,it seals off the engine and gearbox from the body and connects the scuttle to the main floor. The main centre floor panel (2) should be sufficiently reinforced to carry the weight of the front seats and passengers. It may be necessary to have a tunnel running the length of the floor in the centre to clear the transmission system from the engine to the rear axle, and holes may have to be cut into the floor to allow access to the gearbox, oil filler, and dipstick,
in which case removable panels or large grommets would be fitted in these access holes (3).
The front end of the main floor is fixed to the toeboard panel and the sides of the main centre floor are strengthened by the bottom sills (4) and/or some form of side members which provide the necessary longitudinal strength. The transverse strength is provided by the cross members. The floor panel itself prevents lozenging, and the joints between side members and cross members are designed to resist torsional stresses.
The rear end of the floor is stiffened transversely by the rear seat heelboard (5). This heelboard also stiffens the front edges of the rear seat panel. In addition it often provides the retaining lip for the rear seat cushion, which is usually made detachable from the body. The heelboard, together with therear panel and rear squab panel, forms the platformfor the rear seat.
The rear seat panel (6) is reinforced or swaged ifnecessary to gain enough strength to support therear passengers. Usually the rear seat panel has tobe raised to provide sufficient clearance for thedeflection of the rear axle differential housing. Thefront edge of the rear seat panel is stiffened bythe rear seat heelboard, and the rear edge of the seatpanel is stiffened by the rear squab panel. The rearsquab panel completes this unit and provides therear bulkhead across the car. It seals off the bootor luggage compartment from the main body orpassenger compartment.
The boot floor (7), which extends from the backof the rear squab panel to the extreme back of thebody, completes the floor unit. In addition to theluggage, the spare wheel has to be accommodatedhere. The front edge of the boot floor is reinforcedby the rear squab panel and the rear end by a crossmember of some form (8). The sides of the floorare stiffened by vertical boot side panels at therear, while the wheel arch panels complete thefloor structure by joining the rear end of the mainfloor and its side members. The wheel arch panels(9) themselves seal the rear road wheels from thebody.
In general the floor unit is made up from aseries of panels with suitable cross members orreinforcements. The edges of the panels are stiff-ened either by flanging reinforcing members, orby joining to the adjacent panels. The boot fram-ing is joined at the back to the rear end of the boot floor, at the sides to the boot side panels andat the top to the shelf panel behind the rear squab(10). It has to be sufficiently strong at the pointwhere the boot lid hinges are fitted to carry theweight of the boot lid when this is opened.
Surrounding the boot lid opening there is a gutterto carry away rain and water to prevent it enteringthe boot; opposite the hinges, provision is madefor the boot lid lock striking plate (11) to befixed. From the forward edge of the boot, the nextunit is the back light and roof structure (12), andthis extends to the top of the windscreen orcanopy rail (13). The roof is usually connected tothe body side frames, which comprise longitudi-nal rails or stringers and a pair of cantrails whichform the door openings (14). Provision in the roofshould be made for the interior lights and wiringand also the fixing of the interior trimming. Thescuttle and windscreen unit, including the frontstanding pillar or A-post (15), provides the frontbulkhead and seals the engine from the passengercompartment.
Accommodation has to be made for the instru-mentation of the car, the wiring, radio, windscreenwipers and driving cable, demisters and ducting,steering column support, handbrake support andpedals. The scuttle (16) is a complicated structurewhich needs to be very strong. When the front dooris hinged at the forward edge, provision has to bemade in the front pillar for the door hinges, doorcheck and courtesy light switches.
The centre standing pillar or BC-post (17) isfixed to the side members of the main floor unitand supports the cantrails of the roof unit. It pro-vides a shut face for the front door, a position forthe door lock striking plate and buffers or dovetail,and also a hinge face for the rear door; as with thefront standing pillar, provision is made for the doorhinges and door check. The rear standing pillar orD-post (18) provides the shut face for the rear endof the floor side members at the bottom, whilst thetop is fixed to the roof cantrails and forms the frontof the quarters.
The quarters (19) are the areas of the body sides
between the rear standing pillars and the back lightand boot. If the body is a six-light saloon therewill be a quarter window here with its necessarysurrounding framing, but in the case of a four-lightsaloon this portion will be more simply constructed. Apart from the doors, bonnet, boot lid and front wings this completes the structure of the average body shell.