On the structure and function of the universal joint is a bit like human limbs joints, it allows the Angle between the connected parts changes within a certain range. For, adapt to and meet the power generated by jumping up and down when the car running changes caused by the Angle, front drive cars drive axle, axle shaft is connected to a common universal joint between wheel and axle. But due to the restrictions on the size of the axial, Angle but also is bigger, a single universal joint can not make the output shaft and the shaft into the shaft of the instantaneous angular velocity are equal, easy to cause vibration, adding parts damaged, and generate a lot of noise, so widely used in a variety of patterned constant speed universal joint. In before the drive motor vehicles, each half shaft with two patterned constant speed universal joint, the universal joint near the transaxle is half shaft inside of the universal joint, near the lateral axle is half shaft universal joint. The rear drive vehicle, engine, clutch and transmission as a whole is installed on the frame, and connected to the frame, drive axle by elastic suspension, there is a distance between the need for connection. Beat in the operation of the road is rough cars, poor load changes or two assembly installed, can make the gearbox output shaft and the Angle between the drive axle of main reducer input shaft and the distance change, so in the form of universal joint drive a car powered with double universal joint, is to have a universal joint on both ends of the transmission shaft, its role is to make the shaft ends of equal Angle, so as to ensure the instantaneous angular velocity of the input shaft and output shaft are always equal.