The need for multiple gear ratios in ICE-powered motor vehicles is because the engines typically operate over a range of approximately 600-7000 rpm, while the road speed of the vehicle typically equates to a rotational speed of the wheels in the range of 0-1800 rpm. Automobiles Power and torque curves for two example car engines Applications of these devices included pumps, mills and hoists. Applications Early uses Įarly transmissions included the right-angle drives and other gearing in windmills, horse-powered devices, and steam-powered devices. Modern versions of these systems that are fully automatic in operation, such as Selespeed and Easytronic, can control both the clutch operation and the gear shifts automatically, without any input from the driver. Some of these systems are also referred to as clutchless manual systems. Many early versions of these transmissions were semi-automatic in operation, such as Autostick, which automatically control only the clutch, but still require the driver's input to initiate gear changes. Main articles: Automated manual transmission and Clutchless manual transmissionĪn automated manual transmission (AMT) is essentially a conventional manual transmission that uses automatic actuation to operate the clutch and/or shift between gears. 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. Examples of such transmissions are used in helicopters and wind turbines. 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. Electric vehicles typically use a single-speed or two-speed transmission.įixed-ratio Transmission for a Bristol Sycamore helicopter Most currently-produced passenger cars with petrol or diesel engines use transmissions with 5–8 forward gear ratios and one reverse gear ratio. Many transmissions have multiple gear ratios, but there are also transmissions that use a single fixed gear ratio. Epicyclic gearing diagram, as used in hydraulic automatic transmissionsĪ transmission (also called a gearbox) is a mechanical device which uses gears to change the speed or direction of rotation in a machine.
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