Transmission (automobile)

An automobile transmission is an intermediary device for transmitting the rotary energy of the car's engine at a suitable rotation speed, to the differential and from there to the driving wheels.

The need for a transmission is a consequence of the characteristics of the internal combustion engine. Engines typically operate over a range of 600 to about 6000 revolutions per minute (though this varies from design to design), whilst the car's wheels rotate at anything from 0 rpm to about 2500 rpm. Furthermore, the engine provides its highest torque outputs approximately in the middle of its range, whilst often the greatest torque is required when the vehicle is moving from rest or travelling slowly. Therefore, a system that transforms the engine's output so that it can supply high torque at low speeds, but also operate at highway speeds with the motor still operating within its limits, is required. Transmissions perform this transformation.

There are two main transmission designs in common use - the manual transmission[?], an entirely mechanical gearing system, and the automatic transmission[?], which uses hydraulics as well as mechanical gearing, and partially automates the gear selection process. Recent developments have included electronically controlled "clutchless-manuals" which technically resemble traditional manual transmissions but from a driver perspective work like an automatic, and continuously variable transmissions[?] which rather than providing a limited set of "ratios", allow the relationship between the speed of the engine and the speed of the wheels to be varied continuously.