he function of universal joint is to enable the transmission shaft to transmit the power of the transmission (or transfer case) to the reduction gear in the main drive in a certain angle range, so as to avoid damage to the transmission shaft parts.

There are two types of universal joints.

① It is a universal joint with unequal velocity. In one revolution of the driving shaft, the rotation angular velocity of the driven shaft is not equal. In order to achieve constant speed rotation, it should be used in pairs, that is, two universal joints are installed at both ends of the transmission shaft, so that the universal joint forks at both ends of the transmission shaft are in the same plane; the driving shaft and the driven shaft should be basically parallel, which is mainly composed of universal joint fork, cross shaft and needle roller bearing.

② Constant velocity universal joint: its transmission characteristic is that the rotation angular velocity of driving shaft and driven shaft is equal. Front axle drive cars are equipped with constant velocity universal joints (drive and steering). There are generally three forms of constant velocity universal joint.