Speed reducers are generally used in low-speed, high-torque transmission equipment. They reduce the speed of a motor, internal combustion engine, or other high-speed power source by meshing a smaller gear on the input shaft with a larger gear on the output shaft. Ordinary speed reducers may also have several pairs of gears operating on the same principle to achieve the desired reduction effect. The ratio of the number of teeth on the large gear to the number of teeth on the small gear is the transmission ratio.
Speed reducers play a role in matching speeds and transmitting torque between the prime mover and the working machine or actuator. They are relatively precise machines. Their purpose is to reduce speed and increase torque. There are many types and models of speed reducers, each with different applications. Speed reducers can be classified according to transmission type (gear reducers, worm gear reducers, planetary gear reducers); according to the number of transmission stages (single-stage and multi-stage reducers); according to gear shape (cylindrical gear reducers, bevel gear reducers, and bevel-cylindrical gear reducers); and according to the transmission arrangement (open-type reducers, split-type reducers, and coaxial reducers).