Rigid universal joint
The universal joint has no obvious elasticity in the torsional direction. It can be divided into variable velocity universal joint, quasi constant velocity universal joint and constant velocity universal joint.
① CV joint. When the included angle between the two shafts connected by the universal joint is greater than zero, the output shaft and the input shaft transmit motion with the changing instantaneous angular velocity ratio, but the average angular velocity is the same.
The cross shaft type rigid universal joint is composed of universal joint fork, cross shaft, needle roller bearing, oil seal, sleeve, bearing cover, etc. Working principle: one of the rotating forks drives the other fork to rotate through the cross shaft, and at the same time, it can swing around the center of the cross shaft in any direction. During rotation, the needle in the needle bearing can rotate to reduce friction. The shaft connected with the input power is called the input shaft (also called the driving shaft), and the shaft output through the universal joint is called the output shaft (also called the driven shaft). When the input shaft and output shaft work at an included angle, the angular speeds of the two shafts are not equal, which will cause torsional vibration of the output shaft and its connected transmission parts and affect the life of these parts.
② Quasi constant velocity joint. It refers to the universal joint that transmits motion at the designed angle with equal instantaneous angular velocity, while transmitting motion at other angles with approximately equal instantaneous angular velocity. It is also divided into: a) Dual quasi constant velocity universal joint. It refers to the universal joint where the length of the transmission shaft in the constant speed transmission device of the universal joint is shortened to the minimum. b) Bulge type quasi constant velocity universal joint. It is composed of two universal joints and two bumps of different shapes. Two bumps are equivalent to the intermediate transmission shaft and two cross pins in the double universal joint device. c) Three pin quasi constant velocity universal joint. It is composed of two three pin shafts, a driving eccentric shaft fork and a driven eccentric shaft fork. d) Spherical roller type quasi constant velocity universal joint. It is composed of pin shaft, spherical roller, universal joint shaft and cylinder. The roller can move axially in the groove to play the role of expansion spline. The roller contacts the groove wall to transmit torque.
③ The output shaft and input shaft connected to the constant velocity universal joint transmit the universal joint at the constant instantaneous angular velocity. It is further divided into:
a) Ball and fork type constant velocity universal joint. Universal joint composed of ball fork with raceway and steel ball. The spherical fork type universal joint with circular arc groove raceway refers to the universal joint with circular arc steel ball raceway. The joint structure is characterized by that the driving fork and driven fork of the ball fork are provided with arc grooves, and the two are assembled to form four steel ball raceways, which contain four steel balls in total. The centering steel ball is installed in the spherical groove at the center of the driving and driven forks. Straight groove raceway type ball yoke type universal joint refers to the universal joint whose steel ball raceway on the ball yoke is straight groove raceway type. Its structural feature is that two spherical forks are provided with straight grooves, each of which is inclined to the centerline of the shaft at the same angle and symmetrical to each other. Four steel balls are installed in the raceway between two ball forks.
b) Ball cage constant velocity universal joint. According to whether the universal joint can move in the axial direction, it can also be divided into axial non retractable (fixed) ball cage type universal joint and retractable ball cage type universal joint. The inner surface spline of the star sleeve of the fixed ball cage universal joint on the structure is connected with the transmission shaft. Its outer surface is made of 6 arc grooves as the inner raceway of the steel ball, and the outer raceway is on the inner surface of the spherical shell. One steel ball is installed in each of the six raceways formed after the star sleeve and spherical shell are assembled, and the cage (ball cage) makes the six steel balls in the same plane. The power is transmitted from the transmission shaft through the steel ball and spherical shell (Fig. 2). The structural feature of the telescopic ball cage universal joint is that cylindrical straight grooves are made on the inner wall of the cylindrical shell and the outer side of the star sleeve, and steel balls are installed in the raceway formed after the two are assembled. The steel ball is also installed in the hole of the cage. The inner hole of the star sleeve is provided with splines to connect with the input shaft. This structure allows the star sleeve to move in the axial direction relative to the simple shell.
Flexible universal joint
Flexible universal joint: Universal joint with obvious elasticity in the torsional direction.
The flexible universal joint is mainly composed of rubber elastic elements (rubber disc, rubber block, rubber ring, rubber metal sleeve, etc.), bushings, bolts, and centering device set to ensure dynamic balance at high speed. Its working principle is that when the torque acts on the input shaft, the torque is transmitted to the rubber block after passing through the three flanges and connecting bolts on the input shaft and universal joint yoke, and the torque acts on the universal joint flange on the output shaft after passing through the rubber block. Since the rubber block is elastic, a certain included angle is allowed between the two shafts
