A universal joint with no apparent elasticity in the direction of torsion. It can be divided into unequal universal joint, quasi-constant universal joint and constant universal joint. [1]

① Nonuniform universal joint. When the Angle between the two axes connected by the universal joint is greater than zero, the universal joint with the same average angular velocity moves between the output axis and the input axis at varying instantaneous angular velocity ratio.

The cross shaft type rigid universal joint is composed of universal joint fork, cross shaft, needle roller bearing, oil seal, sleeve, bearing cover and other parts. The working principle is: one of the rotating forks drives the other fork to rotate through the cross shaft, and at the same time can swing around the center of the cross shaft in any direction. The needle roller in the needle roller bearing can rotate during rotation to reduce friction. The shaft connected with the input power is called the input shaft (also known as the active shaft), and the shaft output by the universal joint is called the output shaft (also known as the driven shaft). Working under the condition that there is an included Angle between the input and output shafts, the angular velocity of the two shafts is not equal, which will lead to torsional vibration of the output shaft and the transmission parts connected with it and affect the life of these parts.

② Quasi constant velocity universal joint. A universal joint that transmits motion at the same instantaneous angular velocity at the designed Angle and at approximately the same instantaneous angular velocity at other angles. It is divided into: a) double quasi-constant velocity universal joint. Refers to the universal joint where the length of the drive shaft in the constant speed transmission device of the universal joint is reduced to the minimum. B) Convex block quasi-constant velocity universal joint. It consists of two universal joints and two convex blocks of different shapes. The two convex blocks are equivalent to the middle drive shaft and two cross pins in the double universal joint device. C) Three-pin quasi-constant velocity universal joint. It consists of two three-pin shafts, active eccentric shaft forks and driven eccentric shaft forks. D) Spherical roller quasi-constant velocity universal joint. It consists of a pin shaft, a spherical roller, a universal joint shaft and a cylinder. Roller can do axial movement in the groove, play the role of expansion spline. Roller contact with groove wall can transfer torque.