Universal joint is also called cardan joint, which is used to realize the transmission of variable Angle power. It is used to change the position of the transmission axis. It is the "joint" part of the cardan transmission device of the vehicle driving system. The combination of universal joint and drive shaft is called universal joint transmission device. On the vehicle driven by the rear wheel of the front engine, the universal joint drive device is installed between the transmission output shaft and the driving axle main reducer input shaft; The front-engine front-wheel-drive vehicle omit the drive shaft, and the universal joint is installed between the front axle half shaft and the wheel, which is both responsible for driving and steering.
Structure and function: the structure and function of a cardan joint is similar to the joint on a human limb. It allows the angle between the connected parts to vary within a certain range. In order to meet the change of angle caused by power transmission, up and down jumping during the operation of the vehicle, the driving axle of the front drive vehicle is usually connected with the cardan between the semi-axle and the axle. However, due to the limitation of axial size, the deviation angle is required to be relatively large. A single universal joint cannot make the instantaneous angular velocity of the output shaft equal to that of the input shaft, so it is easy to cause vibration, aggravate the damage of machine parts and generate great noise. Therefore, various kinds of uniform universal joints are widely used. On the front drive vehicle, each half axle USES two constant speed universal joints. The universal joint near the transmission drive axle is the inner universal joint of the half axle and the outer universal joint near the axle is the outer universal joint of the half axle. On the rear drive vehicle, the engine, clutch and transmission are mounted as a whole on the frame, while the drive axle is connected to the frame through the elastic suspension. There is a distance between the two, which needs to be connected. In the process of automobile operation, the road surface undulation, load change or position difference of two assembly installation will change the Angle and distance between the transmission output shaft and the driving axle main reducer input shaft. Therefore, the driving mode of the cardan joint of the rear drive vehicle adopts the double cardan joint, that is, there is a cardan joint at both ends of the driving shaft, whose function is to make the Angle between the two ends of the driving shaft equal, and to ensure that the instantaneous angular velocity of the output shaft and the axis entering the shaft is always equal.
Maintenance: the maintenance of universal joint cross shaft shall grind gear oil. Since the lube nozzle of universal joint needle roller bearing is an ordinary yellow oil nozzle, it gives people a kind of illusion that universal joint is filled with butter to lubricate. In fact, it is very difficult to add butter from the nozzles to the needle roller bearings, even to the end of the neck of the cross shaft. Lubrication with butter (i. e. calcium base grease) will result in early damage to the large number of cross shaft needle bearings.
