Transmission
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A transmission, also known as a tranny
or a gearbox, is a mechanical device that uses a gear set to change the speed, direction, or torque of a machine. Trannies are mainly found in vehicles, including your car. Most cars have 4-6 gears plus neutral and reverse, though some can have over ten.
Types[edit | edit source]
Fixed-ratio[edit | edit source]
Simple trannies in the past used a fixed ratio to provide either a gear reduction or an increase in speed. These trannies can be found in old helicopters and wind turbines.
Multi-ratio[edit | edit source]
A multi-ratio tranny has multiple gears that are used to change the ratio of input speed to output speed. Gear selection can be manual, semi-automatic, or automatic.
Manual[edit | edit source]
A manual tranny requires the driver to manually select gears by pressing the clutch and moving the shifter. Cars in Europe typically have manual trannies, though you can less commonly find manuals in the United States, often driven by car snobs. Of course, all cars made prior to the invention of the automatic tranny have a manual tranny.
Semi-automatic[edit | edit source]
In a semi-automatic tranny, some of the operation is automated, but it still requires input from the driver. An example of this is an AMT, which uses automatic actuation to operate the clutch.
Automatic[edit | edit source]
Automatic trannies are the most common form in the United States. They do not normally require any input from the driver to shift gears. Some automatic trannies do have a "manual" setting which allows the driver to select a gear, though the clutch operation is still automated. Some automatic trannies also have the option to keep the vehicle in a low gear, which can be used on steep inclines, when towing heavy loads, off-road, or in slippery conditions to give the driver more control and torque.
