The function of the universal joint is to make the Angle between the two ends of the transmission shaft equal, so as to ensure that the instantaneous angular velocity of the output shaft and the input shaft is always the same. Universal joint is universal joint, is to achieve variable Angle power transmission parts, for the need to change the direction of the transmission axis position, it is the automotive drive system of the universal transmission device "joint" parts. The following is the classification of universal joints:

1. Unconstant velocity universal joint: when the Angle between the two shafts connected by the universal joint is greater than zero, the output shaft and the input shaft transfer motion at varying instantaneous angular velocity ratio, but the average angular velocity is equal to the universal joint;

2. Quasi-constant velocity universal joint: refers to the universal joint that transmits motion at the same instantaneous angular velocity at the designed Angle and at the approximately equal instantaneous angular velocity at other angles;

3. Constant velocity universal joint: the output shaft and the input shaft connected by the universal joint transfer the universal joint with the same instantaneous angular velocity all the time;

4, flexible universal joint: universal joint has obvious elasticity in the direction of torsion.