The universal joint is a mechanism that realizes variable-angle power transmission,used to change the position of the transmission axis, is the "joint" part of the universal transmission device of the automobile drive system. The combination of universal joint and transmission shaft is called universal joint transmission device. On vehicles with front-engine rear-wheel drive, the universal joint transmission is installed between the output shaft of the transmission and the input shaft of the main reducer of the drive axle; while vehicles with front-engine front-wheel drive omits the transmission shaft, the universal joint is installed Between the half axle of the front axle and the wheels, which are both responsible for driving and steering.