The composition and structure of an automobile driveshaft

　　The drive shaft consists of a shaft tube, a telescopic sleeve, and a universal joint. The telescopic sleeve automatically adjusts changes in the distance between the transmission and the drive axle. The universal joint ensures changes in the angle between the transmission output shaft and the drive axle input shaft, and achieves constant-velocity transmission between the two shafts.
Universal Joint
　　The universal joint is a key component of the automotive drive shaft. A car is a moving object. In rear-wheel-drive cars, the engine, clutch, and transmission are installed as a unit on the chassis, while the drive axle is connected to the chassis via elastic suspension. There is a distance between the two that needs to be connected. Uneven road surfaces cause the car to bounce during operation.
1. Function:
　　A typical universal joint consists of a cross shaft, a cross bearing, and a flange fork. The universal joint is a key component of the automotive drive shaft. In vehicles with a front-engine rear-wheel-drive configuration, the universal joint driveshaft is installed between the transmission output shaft and the input shaft of the drive axle main reducer; while in front-engine front-wheel-drive vehicles, the driveshaft is omitted, and the universal joint is installed between the front axle half-shaft (which handles both driving and steering) and the wheel. Uneven road surfaces during vehicle operation cause bouncing, load changes, or differences in the installation positions of the two assemblies, all of 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, a "flexible" device is needed to solve this problem, hence the universal joint.
2. Transmission Characteristics:
　　In vehicles with a front-engine rear-wheel-drive (or all-wheel-drive) configuration, due to suspension deformation during vehicle movement, there is often relative movement between the input shaft of the drive axle main reducer and the output shaft of the transmission (or transfer case). In addition, to effectively avoid certain mechanisms or devices (where straight-line transmission is not feasible), a device is needed to ensure normal power transmission, hence the universal joint transmission. Universal joint transmission must have the following characteristics:
　　a. Ensure reliable power transmission when the relative position of the two connected shafts changes within the expected range;
　　b. Ensure uniform rotation of the two connected shafts. Additional loads, vibrations, and noise caused by the universal joint angle should be within acceptable limits;
　　c. High transmission efficiency, long service life, simple structure, easy manufacturing, and easy maintenance. For automobiles, since the output shaft of a single cross-type universal joint rotates at a different speed than the input shaft (due to a certain angle), double universal joint (or multiple universal joint) transmission must be used, and the two universal joint forks connected to the same driveshaft must be arranged in the same plane, with equal angles between the two universal joints. This is extremely important. The angle of the universal joint should be minimized during design.
Telescopic Sleeve
　　In traditional drive shaft telescopic sleeves, the spline sleeve and flange fork are welded together, and the spline shaft is welded to the drive shaft tube. New drive shafts change the traditional structure by welding the spline sleeve and drive shaft tube into one piece, and making the spline shaft and flange fork into one piece. The rectangular spline is changed to a large pressure angle involute short-tooth spline, which increases strength and facilitates extrusion forming, meeting the needs of high-torque conditions. A layer of nylon material is applied to the tooth surfaces of the telescopic sleeve tube and spline shaft, which not only increases wear resistance and self-lubrication but also reduces the impact load damage to the drive shaft and improves buffering capacity.
　　This type of drive shaft adds a tubular sealing protective sleeve to the outside of the flange spline shaft. Two polyurethane rubber oil seals are installed at the ends of the protective sleeve, forming a completely sealed space inside the telescopic sleeve, protecting the telescopic spline shaft from external dust erosion, providing both dust and rust protection. Therefore, when assembling, applying lubricating grease once between the spline shaft and the sleeve is sufficient to meet the usage requirements, eliminating the need for oil lubrication and reducing maintenance.
Bush
　　It is designed to reduce friction and wear during shaft movement, with a function similar to bearings, and is relatively inexpensive. However, it has higher frictional resistance, so it is only used in some parts. Bushes are mostly made of copper, but plastic bushes also exist. Bushes are mostly placed between the shaft and the supporting structure, fitting tightly against the supporting structure, allowing only the shaft to rotate in the bush. When assembling the shaft and bush, lubricant is added between them to reduce friction during rotation.