Transmission jack

Transmissions can have a single fixed-gear ratio, multiple distinct gear ratios , or continuously variable ratios. Variable-ratio transmissions are used in all sorts of machinery, especially vehicles. Early transmissions included the right-angle drives and other gearing in windmills , horse -powered devices, and steam -powered devices. Applications of these devices included pumps , mills and hoists.

Bicycles traditionally have used hub gear or Derailleur gear transmissions, but there are other more recent design innovations. Since the torque and power output of an internal combustion engine varies with its rpm , automobiles powered by ICEs require multiple gear ratios to keep the engine within its power band to produce optimal power, fuel efficiency , and smooth operation.

Multiple gear ratios are also needed to provide sufficient acceleration and velocity for safe and reliable operation at modern highway speeds. ICEs typically operate over a range of approximately — rpm, while the vehicle's speeds requires the wheels to rotate in the range of 0— rpm. In the early mass-produced automobiles, the standard transmission design was manual : the combination of gears was selected by the driver through a lever the gear stick that displaced gears and gear groups along their axes.

Transmission oil

Starting in , cars using various types of automatic transmission became available in the US market. These vehicles used the engine's own power to change the effective gear ratio depending on the load so as to keep the engine running close to its optimal rotation speed. Automatic transmissions now are used in more than two thirds of cars globally, and on almost all new cars in the US.

Most currently-produced passenger cars with gasoline or diesel engines use transmissions with 4—10 forward gear ratios also called speeds and one reverse gear ratio. Electric vehicles typically use a fixed-gear or two-speed transmission with no reverse gear ratio. 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.