A universal joint is a critical component of a vehicle's driveshaft, typically consisting of a cross shaft, cross bearings, and a flange yoke.
In front-engine, RWD vehicles, the universal joint driveshaft is installed between the transmission output shaft and the drive axle's final drive input shaft; whereas in front-engine, FWD vehicles, the universal joint is installed between the front axle half-shaft, which is responsible for driving and steering, and the wheels. Due to uneven road surfaces, load variations, or differences in assembly mounting positions during vehicle operation, the angle and distance between the transmission output shaft and the drive axle's final drive input shaft can change. Therefore, universal joints are necessary to address this issue.
Transmission Characteristics: Universal joint transmission plays a crucial role in front-engine, RWD (or AWD) vehicles because relative motion is required between the drive axle's final drive input shaft and the transmission (or transfer case) output shaft. Furthermore, to effectively prevent certain mechanisms or devices from being unable to achieve linear power transmission, universal joints are also necessary to ensure normal power transfer. Universal joint transmission must possess the following characteristics:
1. It must reliably transmit power when the relative positions of the two connected shafts vary within the expected range;
2. It must ensure uniform operation of the two connected shafts, and any additional loads, vibrations, and noise generated by the universal joint angle should be within permissible limits;
3. It must have high transmission efficiency, long service life, simple structure, ease of manufacturing, and convenient maintenance. In automobiles, the output shaft of a single cross-type universal joint rotates non-uniformly relative to its input shaft (when there is an angle between them). Therefore, a double universal joint (or multiple universal joints) drive must be used, and the two universal joint yokes connected to the same driveshaft must be arranged in the same plane, with equal angles for both universal joints. This is very important, and the universal joint angle should be minimized during design.
