When the two shafts connected by the WS Cardan Shaft Coupling are not on the same axis, the driving shaft will move at a constant speed, and the driven shaft will perform periodic variable speed movement within a certain range, that is, the two shafts are not synchronized. The theory of equal angular speed transmission of double cross shafts believes that if two cross shaft Cardan Shaft Coupling are used in series, the non-uniform transmission of a single cross shaft Cardan Shaft Coupling can be achieved, and constant speed transmission can be realized, but the following requirements must be met condition:

a. The three axes of the intermediate shaft, the driving shaft and the driven shaft should be in the same plane;
b. The fork openings of the fork joints at both ends of the intermediate shaft should be located in the same plane; for the double cross shaft Cardan Shaft Coupling, the driven shaft can stabilize the angular speed and torque, and the intermediate shaft can be stretched to meet the requirements of some mobile machinery. Or the requirements of the experimental equipment for the position of the main and driven shafts to change at any time in the transmission, that is, the requirements for α1 and α2 to change at any time.

However, the speed of the intermediate shaft of this type of universal joint varies, which will cause additional inertial torque, torsional vibration and vibration noise. Therefore, in order to realize the balanced operation of the drive shaft, it is usually stipulated that the inertia moment cannot exceed 8% of the rated torque of the universal joint shaft, and the maximum cannot exceed 30% of the rated torque of the universal joint shaft. In addition, the existence of the intermediate shaft increases the axial size of the universal joint, and the expansion and contraction of the intermediate shaft will lead to the generation of axial force (when the intermediate shaft is elongated, an axial tension is generated at the yoke, and when it is shortened, an axial pressure is generated. ).

The axial force acts on the cross shaft bearing, and also causes the axial load and radial load at the support of the drive shaft.