Abstract
Overdrive is defined as gearing which provides a higher ratio than that given by the final drive crown wheel and pinion. The ratio requirements of the modern car are discussed. All types of overdrive gearing are reviewed and the Laycock unit, being the only separate unit now produced in the U.K., is considered in detail. This unit is of particular interest since ratio changes are made under torque. It is, therefore, necessary to consider the changes in rotational energy which result. The paper analyses the factors involved and presents equations relating clutch torque, time, and inertias. Expressions are given for energy transfer to the output shaft and the rate of energy dissipation at the clutch. Some details of the epicyclic gearing and planet bearing loads and life factors are given. Control systems are briefly discussed.
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