What is a universal joint？

Universal joint, also known as universal joint in English, is a mechanical component used to achieve variable angle power transmission. It is used to change the position of the transmission axis direction. It is a joint component of the universal transmission device in the automotive drive system. The combination of a universal joint and a transmission shaft is called a universal joint transmission device. The structure and function of a universal joint are somewhat similar to those of joints on human limbs, allowing the angle between the connected parts to vary within a certain range. To meet the requirements of power transmission, adaptation to steering, and the angle changes caused by up and down bouncing during vehicle operation, a universal joint is commonly used to connect the drive axle, half axle, and wheel axle of front drive vehicles. However, due to the limitation of axial dimensions and the requirement for a relatively large deflection angle, a single universal joint cannot make the instantaneous angular velocity of the output shaft and the input shaft equal, which can easily cause vibration, exacerbate damage to the components, and generate significant noise. Therefore, various types of constant velocity universal joints are widely used. On front drive cars, each half shaft is equipped with two constant velocity universal joints. The universal joint near the variable speed drive axle is the inner universal joint of the half shaft, and the outer universal joint near the axle is the outer universal joint of the half shaft. In rear drive cars, the engine, clutch, and transmission are installed as a whole on the frame, while the drive axle is connected to the frame through elastic suspension, with a distance between the two that needs to be connected. During the operation of a car, uneven road surfaces can cause bouncing, changes in load, or differences in the installation of two assemblies, which can cause changes in the angle and distance between the transmission output shaft and the input shaft of the drive axle main reducer. Therefore, in rear drive cars, the universal joint transmission form adopts double universal joints, which means that there is a universal joint at both ends of the transmission shaft, and its function is to make the angle between the two ends of the transmission shaft equal, Ensure that the instantaneous angular velocity of the output shaft and the input shaft is always equal.