Gearbox and Transmission Systems Questions and Answers

Answer: C

A sliding idler gear placed between the layshaft gear and the output gear reverses the direction of rotation, and being straight cut and unsynchronised it produces the familiar whine and requires the vehicle to be stationary. Modern gearboxes often synchronise reverse and use constant mesh with a dog clutch. The epicyclic arrangement is used in automatic transmissions. Naming the cost of a choice alongside its benefit is what turns a fact into a design decision.

Answer: D

Overall ratio is the product of the gearbox and final drive ratios, and it determines the engine speed for a given road speed together with the rolling radius of the tyre. A change of final drive therefore affects every gear equally. Tyre size enters the road speed calculation but is not part of the ratio itself. Reading the definition literally, rather than recalling a summary, avoids the usual confusion. Working the distinction through on a single concrete case fixes it more firmly than any rule of thumb.

Answer: A

A higher numerical ratio multiplies the torque more and reduces the road speed for a given engine speed, improving acceleration at the expense of top speed and cruising economy. Rally cars use short ratios and long distance cars long ones. The engine speed for a given road speed rises rather than falls. Most errors here come from carrying across a result from a neighbouring case where it does not hold. A symptom that appears under one condition and not another is what narrows the diagnosis quickly.

Answer: B

An overdrive ratio turns the output shaft faster than the input, so the engine runs more slowly for a given road speed, improving fuel consumption and reducing noise and wear. Top gear in most modern gearboxes is an overdrive ratio. Torque at the wheels is correspondingly reduced. Naming what changes and what stays the same is the reliable route through questions of this shape. The order in which the effects act is what decides the outcome, so it is worth establishing first.

Answer: C

Laycock de Normanville units used a planetary set whose sun gear was braked to give the overdrive ratio, controlled by a cone clutch operated hydraulically from a pump driven by the gearbox. They were fitted to many British cars from the nineteen fifties onward. Modern gearboxes simply include an overdrive ratio among their gears. Working the distinction through on a single concrete case fixes it more firmly than any rule of thumb.

Answer: D

Planetary sets are used because their ratios can be changed by applying brakes and clutches to different members without any component having to slide into mesh. Several sets in series give the required number of ratios. Modern designs use compound sets to obtain eight, nine or ten ratios compactly. Working the distinction through on a single concrete case fixes it more firmly than any rule of thumb. Tracing the requirement back to the physical constraint that produces it makes the answer follow.

Answer: A

The central sun gear meshes with several planets carried on a rotating carrier, and the planets also mesh with an internally toothed annulus surrounding them. Holding any one member and driving another gives a different ratio. Locking two members together gives direct drive. A symptom that appears under one condition and not another is what narrows the diagnosis quickly. Naming the cost of a choice alongside its benefit is what turns a fact into a design decision.

Answer: B

Driving the sun with the annulus held makes the planets walk around inside the annulus, carrying the carrier round more slowly than the sun in a reduction. Driving the carrier and taking the output from the sun gives the corresponding overdrive. Reverse requires the carrier to be held instead. The order in which the effects act is what decides the outcome, so it is worth establishing first. Reading the definition literally, rather than recalling a summary, avoids the usual confusion.

Answer: C

With the carrier held stationary the planets act as simple idlers, so the annulus turns opposite to the sun and reverse is obtained. Locking any two members together gives direct drive with the whole set rotating as a unit. Those three cases cover reduction, reverse and direct drive from one set of gears. Checking which component actually carries the load settles most questions of this kind at once. Most errors here come from carrying across a result from a neighbouring case where it does not hold.

Answer: D

Hydraulically applied wet multiplate clutches connect members to one another and brake bands or clutches hold members to the casing, and the control system schedules them to give each ratio. One way clutches are used to simplify the changes. All of the elements are designed to slip briefly during the change, which is why the fluid specification matters so much. The shared behaviour explains why these belong together and the differences explain why both exist.