Semi-automatic transmission

A semi-automatic transmission (SAT) (also known as a clutchless manual transmission, automated manual transmission, trigger shift, flappy-paddle gear shift, or paddle-shift gearbox) is an automobile transmission that does not change gears automatically, but rather facilitates manual gear changes by dispensing with the need to press a clutch pedal at the same time as changing gears. It uses electronic sensors, pneumatics, processors and actuators to execute gear shifts on input from the driver or by a computer. This removes the need for a clutch pedal which the driver otherwise needs to depress before making a gear change, since the clutch itself is actuated by electronic equipment which can synchronise the timing and torque required to make quick, smooth gear shifts. The system was designed by automobile manufacturers to provide a better driving experience through fast overtaking maneuvers on highways. Some motorcycles also use a system with a conventional gearchange but without the need for manual clutch operation.

In the 1930s, automakers began to market cars with some sort of device that would reduce the amount of clutching and de-clutching and shifting required in stop and go driving. Most typically, a fluid coupling or a centrifugal clutch replaced the standard manual clutch to allow for stop and go driving without using the clutch pedal every time the car was brought to a stop. More sophisticated systems allowed for shifting while driving without using the clutch, and some systems did away with the clutch pedal altogether. Semi-automatic transmissions were phased out as technology advanced and automatic controls were developed to take care of changing gear ratios. Smaller, lower powered cars used Semi-automatic transmissions with a dry clutch because the mechanical connection offered a more efficient powertrain compared to a fluid coupling.

Another early semi-automatic transmission was the Sinclair S.S.S. (synchro-self-shifting) Powerflow gearbox. which was applied to Huwood-Hudswell diesel mines locomotives. It was also applied to some road vehicles. It is covered by US patent 2505842.

Modern "Semi-automatic transmissions" usually have a fully automatic mode, where the driver does not need to change gears at all, operating in the same manner as a conventional type of automatic transmission by allowing the transmission's computer to automatically change gear if, for example, the driver were redlining the engine. The semi-automatic transmission can be engaged in manual mode wherein one can up-shift or down-shift using the console-mounted shifter selecter or the paddle shifters just behind the steering wheel, without the need of a clutch pedal. The ability to shift gears manually, often via paddle shifters, can also be found on certain automatic transmissions (manumatics such as Tiptronic) and continuous variable transmissions (CVTs) (such as Lineartronic).

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