The universal joint (universal joint) is a mechanical part that realizes variable Angle power transmission and is used for the position that needs to change the direction of the transmission axis. It is the "joint" part of the universal transmission device of the automobile drive system. The combination of universal joint and drive shaft is called universal joint transmission device.

Constant velocity universal joint is an important part of car transmission system, which connects two axes which do not coincide with each other and makes them transfer motion at the same angular speed. Its function is to transfer the power of the engine from the transmission (differential) to the driving wheel of the car, meet the requirements of the outer end corner.