In the steering drive axle, the front wheel is both the driving wheel and the steering wheel. When steering, the deflection Angle is very large, up to more than 40°. At this time, the traditional and small deflection Angle of the ordinary universal joint can not be used. When the deflection Angle of the common universal joint is large, the speed and torque will fluctuate greatly. It is difficult to transmit the power of the automobile engine to the wheels smoothly and reliably, and it will also cause the vibration, impact and noise of the automobile. Therefore, the constant velocity universal joint with large deflection Angle, stable power transmission and uniform angular velocity must be adopted to meet the requirements. The basic principle of constant velocity universal joint In mechanical transmission, a typical example is bevel gear transmission to solve the constant speed power transmission with an Angle between shafts. As shown in the figure below, for a pair of bevel gears of the same size, the Angle between the axes of the two gears is A, the meshing point P of the two gears is located on the bisector of the intersection Angle, and the vertical distance from point P to the two axes is equal to R. At point P the circumferential velocity of the two gears is equal, and therefore the angular velocity of rotation of the two gears is equal. According to this principle, if the force transfer point of the universal joint is always located in the Angle bisector when the Angle between the joint changes, the relationship of equiangular speed transmission can be maintained. The basic principle of constant velocity universal joint is to ensure that the force transmission point of the universal joint is always located on the bisector of the Angle between the master and slave moving axes during the working process.