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Concept
Transmission (mechanical device)
Summary
A transmission (also called a gearbox) is a mechanical device which uses gears to change the speed or direction of rotation in a machine. Many transmissions have multiple gear ratios, but there are also transmissions that use a single fixed gear ratio.
Most currently-produced passenger cars with petrol or diesel engines use transmissions with 5-8 forward gear ratios and one reverse gear ratio. Electric vehicles typically use a single-speed or two-speed transmission.
The simplest transmissions used a fixed ratio to provide either a gear reduction or increase in speed, sometimes in conjunction with a change in the orientation of the output shaft. Examples of such transmissions are used in helicopters, wind turbines and power take-offs (PTOs) for tractors. In the case of a wind turbine, the first stage of the gearbox is usually a planetary gear, to minimize the size while withstanding the high torque inputs from the turbine.
Many transmissions - especially for transportation applications - have multiple gear ratios that can be switched between while the machine is operating. The multiple ratios are used to match the range of input speeds (e.g. engine rpm) with the output speed (e.g. the speed of a car) required for a given situation.
Manual transmission
A manual transmission requires the driver to manually select the gears by operating a gear stick and clutch (which is usually a foot pedal for cars or a hand lever for motorcycles).
Most transmissions in modern cars use synchromesh to synchronise the speeds of the input and output shafts. However, prior to the 1950s, most cars used non-synchronous transmissions.
File:Cambio H.jpg |Transmission internals for a 2009 [[Volkswagen Golf]]
File:John Deere 3350 tractor cut transmission.JPG |16-speed tractor transmission (plus 8 reverse gears)
Sequential manual transmission
A sequential manual transmission is a type of non-synchronous transmission used mostly for motorcycles and racing cars. It produces faster shift times than synchronized manual transmissions, through the use of dog clutches rather than synchromesh.
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Epicyclic gearing
An epicyclic gear train (also known as a planetary gearset) consists of two gears mounted so that the center of one gear revolves around the center of the other. A carrier connects the centers of the two gears and rotates the planet and sun gears mesh so that their pitch circles roll without slip. A point on the pitch circle of the planet gear traces an epicycloid curve. In this simplified case, the sun gear is fixed and the planetary gear(s) roll around the sun gear.
Internal combustion engine
An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combustion engine, the expansion of the high-temperature and high-pressure gases produced by combustion applies direct force to some component of the engine. The force is typically applied to pistons (piston engine), turbine blades (gas turbine), a rotor (Wankel engine), or a nozzle (jet engine).
Torque converter
A torque converter is a type of fluid coupling that transfers rotating power from a prime mover, like an internal combustion engine, to a rotating driven load. In a vehicle with an automatic transmission, the torque converter connects the power source to the load. It is usually located between the engine's flexplate and the transmission. The equivalent location in a manual transmission would be the mechanical clutch.