Automobile gearboxes are often referred to as "transmissions" in automobiles; they are often referred to as "transmissions" in industrial machinery. They are mechanical or hydraulic equipment for mechanical power conversion and are one of the main components of automotive transmission systems.The actual use of the car is very complicated, such as starting, idle parking, low speed or high speed driving, acceleration, deceleration, climbing and reversing, which requires the driving force and speed of the car to vary within a considerable range. But the piston engine has a smaller range of output torque and speed.In order to adapt to the constantly changing driving conditions and at the same time to operate the engine under favorable operating conditions (higher power, lower fuel consumption), a transmission is provided in the transmission system.