What Is a Universal Joint?

A universal joint is a universal joint. The English name is universal joint. It is a mechanism to achieve variable angle power transmission. It is used to change the position of the transmission axis. The combination of a universal joint and a transmission shaft is called a universal joint transmission. In front-engine rear-wheel-drive vehicles, a universal joint transmission is installed between the transmission output shaft and the drive axle main reducer input shaft; while front-engine front-wheel-drive vehicles omit the drive shaft, the universal joint is installed Between the front axle axle and the wheels, which both drive and steer.

A universal joint is a universal joint. The English name is universal joint. It is a mechanism to achieve variable angle power transmission. It is used to change the position of the transmission axis. The combination of a universal joint and a transmission shaft is called a universal joint transmission. In front-engine rear-wheel-drive vehicles, a universal joint transmission is installed between the transmission output shaft and the drive axle main reducer input shaft; while front-engine front-wheel-drive vehicles omit the drive shaft, the universal joint is installed Between the front axle axle and the wheels, which both drive and steer.

Chinese name

Universal joint

Foreign name

universal joint

Classification

Constant velocity, quasi-constant velocity, constant velocity universal joint

Function

Change the direction of power transmission

Classification of rigid joints

Gimbal rigid joint

The universal joint has no obvious elasticity in the twist direction. It can be divided into unequal velocity universal joint, quasi-constant velocity universal joint, constant velocity universal joint. ^[1]

Unequal velocity universal joint. When the angle between the two axes connected by the universal joint is greater than zero, the motion is transmitted between the output shaft and the input shaft at a varying instantaneous angular velocity ratio, but the universal joint with the same average angular velocity.

Universal joint

Cross shaft rigid universal joint is composed of universal joint fork, cross shaft, needle bearing, oil seal, sleeve, bearing cover and other parts. The working principle is that one of the turning forks drives the other fork to rotate through the cross shaft, and at the same time can swing in any direction around the center of the cross shaft. The needle in the needle bearing can rotate during rotation to reduce friction. The shaft connected to the input power is called the input shaft (also called the driving shaft), and the shaft output by the universal joint is called the output shaft (also called the driven shaft). Working under the condition that there is an angle between the input and output shafts, the angular velocities of the two shafts are not the same, and therefore the output shaft and the transmission components connected to it will cause torsional vibration and affect the life of these components.

Quasi-constant velocity universal joint. Refers to a universal joint that transfers motion at the designed angle at equal instantaneous angular velocity, and at other angles at approximately equal instantaneous angular velocity. It is further divided into: a) double quasi-constant velocity joints. Refers to the universal joint when the length of the drive shaft in the universal joint constant speed transmission is shortened to a minimum. b) Bump type quasi-constant velocity universal joint. It consists of two universal joints and two bumps of different shapes. The two projections 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 consists of two three-pin shafts, an active eccentric shaft fork and a driven eccentric shaft fork. d) Spherical roller type quasi-constant velocity universal joint. It consists of a pin, a spherical roller, a universal joint shaft and a cylinder. The roller can move axially in the groove to play the role of telescopic spline. The roller contacts the groove wall to transmit torque.

Universal joint

The constant velocity universal joint The output shaft and the input shaft connected to the universal joint transfer the universal joint at a constant instantaneous angular velocity. It is further divided into:

a) Ball-fork constant velocity universal joint. A universal joint consisting of a ball fork with a raceway and a steel ball. The arc groove raceway ball fork type universal joint refers to the arc type universal joint of the steel ball raceway in the ball sense. The knot structure is characterized by circular arc grooves on the driving fork and driven fork of the ball fork. After the two are assembled, four steel ball raceways are formed, and a total of 4 steel balls are contained in the raceway. The centering steel ball is installed in a spherical groove in the center of the master and driven forks. Straight groove raceway ball fork type universal joint refers to the steel ball raceway on the ball fork is a straight groove raceway type universal joint. Its structure is characterized in that straight grooves are made on the two ball forks, and each straight groove is inclined with the center line of the shaft, and the inclination angle is the same and symmetrical with each other. Four steel balls are installed in the raceway between the two ball forks.

b) Ball cage type constant velocity universal joint. According to whether the universal joint can move axially, it can be divided into axially non-retractable (fixed) ball cage universal joints and retractable ball cage universal joints. The inner surface of the star sleeve of the fixed ball cage universal joint is structurally connected to the drive shaft by an internal spline. Its outer surface is made with 6 arc grooves as the inner raceway of the steel ball. On the inner surface of a spherical shell. Each of the six raceways formed after the star-shaped sleeve and the spherical shell are assembled is equipped with one steel ball, and the six steel balls are in the same plane by a cage (ball cage). Power is transmitted from the transmission shaft through steel balls and spherical shells (Figure 2). The structure of the telescopic ball cage universal joint is characterized in that a cylindrical straight groove is made on the inner wall of the cylindrical shell and the outer part of the star sleeve, and a steel ball is installed in a 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 splined to connect with the input shaft. This structure allows the star sleeve to move in the axial direction relative to the simple shell. ^[2]

Cardan joint diagram

Flexible joints

Flexible universal joint: A universal joint with obvious elasticity in the twisting 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 devices provided to ensure dynamic balance at high speeds. Its working principle is that when the torque acts on the input shaft, the torque passes through the input shaft, the three flanges on the universal joint fork and the connecting bolt, and then is transmitted to the rubber block, and the torque passes through the rubber block and then acts on the output Cardan joint flange on the shaft. Due to the elasticity of the rubber block, a certain angle between the two shafts is allowed.

Universal joint

Universal joint structure and function

The structure and function of the universal joint is similar to the joints on the human limbs, which allows the included angle between the connected parts to change within a certain range. In order to meet the angle change caused by power transmission, adaptive steering, and up-and-down jumps that occur when the car is running, the drive axles of front-drive cars are usually connected with universal joints between the axle and the axle. However, due to the limitation of the axial size, the required deflection angle is relatively large. A single universal joint cannot make the instantaneous angular velocity of the output shaft and the shaft into the shaft equal, which easily causes vibration, exacerbates the damage of components, and generates a lot of noise. Therefore, various constant velocity universal joints are widely used. In front-drive cars, two constant velocity joints are used for each semi-axle, the joints near the transaxle are the inner joints of the semi-axle, and the ones near the axle are the outer joints of the semi-axle. In rear-drive vehicles, the engine, clutch, and transmission are mounted on the frame as a whole, and the drive axle is connected to the frame through an elastic suspension. There is a distance between the two, which needs to be connected. The unevenness of the road surface during the running of the car, the load change, or the position difference between the two assembly installations will cause the angle and distance between the transmission output shaft and the drive axle main reducer input shaft to change. The universal joint transmission uses double universal joints, that is, there is a universal joint at each end of the transmission shaft, and its role is to make the included angle of 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 are always equal.

Cardan joint motion