Automobile Chassis and Transmission Questions and Answers

Answer: A

The frame is the backbone to which the engine, transmission, suspension and body are all attached, and it carries the weight of the vehicle together with the loads imposed by acceleration, braking and cornering. In a body on frame vehicle the body contributes little to the structural strength. Panels enclose the occupants and provide the aerodynamic form, the suspension transmits loads to the frame rather than carrying them, and although a rigidly mounted engine can stiffen a structure it is not designed as a load bearing member.

Answer: B

The ladder frame takes its name from its appearance, with two side rails connected by transverse cross members. It is simple to manufacture, easy to modify for different body styles and strong in bending, which is why it remains standard for trucks and heavy commercial vehicles. Its weakness is low torsional stiffness, since the open section rails twist readily. A single measurement chosen to respond to the one asymmetry beats several that respond to shared behaviour.

Answer: C

Open channel section side rails resist bending well but twist easily, so a ladder frame has poor torsional rigidity and the body must be isolated by flexible mountings to avoid being strained. Boxing the rails improves matters considerably. Bending strength is the frame's principal virtue, and either engine orientation can be accommodated readily. Reading the definition literally, rather than recalling a formula, is the reliable route through questions of this shape.

Answer: D

A closed box section resists torsion enormously better than an open channel of the same weight, because the shear flow can circulate around the closed perimeter. Deepening an open channel improves bending but does little for torsion. Cross members help transfer load between the rails but cannot compensate for the open sections themselves. Checking the units of each quantity catches a wrong formula before the arithmetic begins.

Answer: A

A backbone frame carries a single large closed section tube along the centre line, with outriggers supporting the body and forks at each end carrying the suspension. It has excellent torsional stiffness for its weight. Lotus used it extensively and Tata employed it in the Nano, though it makes the transmission tunnel intrusive and complicates crash protection. A limit that survives making every external component ideal is an intrinsic one, and worth knowing for that reason.

Answer: B

A space frame builds the structure from many small tubes arranged so that each carries only tension or compression, which is extremely efficient in stiffness per unit weight. Triangulation is essential, since an untriangulated bay deforms as a parallelogram. It is labour intensive to build, which restricts it to racing cars and low volume specialist vehicles. Working one numerical case through both cases side by side fixes the distinction better than any rule of thumb.

Answer: C

A triangulated bay cannot deform without changing the length of a member, so the structure resists load axially rather than in bending and every member is used efficiently. Bending is a wasteful way to carry load because most of the material is far from the maximum stress. Adding a stressed skin produces a different structure again, which some designers do use. Reading the definition literally, rather than recalling a formula, is the reliable route through questions of this shape.

Answer: D

Unitary construction uses the pressed steel body shell itself as the structure, with the floor pan, sills, bulkheads and roof all contributing to the stiffness. It is lighter and stiffer than a separate frame for a given weight and is universal for passenger cars. Its disadvantages are the cost of the tooling and the difficulty of repair after severe damage. Most errors here come from carrying a result across from a neighbouring case where it does not hold.

Answer: A

Using the body panels as structure removes the duplication of a separate frame, giving a lighter and stiffer vehicle. The penalties are very expensive press tooling, which requires high volume to amortise, and greater difficulty in repair since damage propagates through the structure. Noise isolation is actually worse without the rubber body mounts, so that option is the reverse of the truth. Working one numerical case through both cases side by side fixes the distinction better than any rule of thumb.

Answer: B

The separate frame suits vehicles that must carry heavy loads, tow, work off road and be built in many body variants from a common chassis. It also simplifies repair after the rough usage such vehicles receive. Small cars are built in high volume where unitary tooling is economic, and electric vehicles generally integrate the battery into a unitary floor structure. Checking the units of each quantity catches a wrong formula before the arithmetic begins.