Transmission (mechanics)
A machine consists of a power source and a power transmission system, which provides controlled application of the power. Merriam-Webster defines
transmission as an assembly of parts including the speed-changing gears and the propeller shaft by which the power is transmitted from an engine to a live axle. Often
transmission refers simply to the
gearbox that uses gears and gear trains to provide speed and torque conversions from a rotating power source to another device. In British English, the term
transmission refers to the whole drivetrain, including clutch, gearbox, prop shaft, differential, and final drive shafts. In American English, however, the term refers more specifically to the gearbox alone, and the usage details are different. The most common use is in motor vehicles, where the transmission adapts the output of the internal combustion engine to the drive wheels. Such engines need to operate at a relatively high rotational speed, which is inappropriate for starting, stopping, and slower travel. The transmission reduces the higher engine speed to the slower wheel speed, increasing torque in the process.