What is the Principle of a Universal Joint?
3 Answers
The principle of a universal joint is: The structure and function of a universal joint resemble the joints in human limbs, allowing the angle between connected parts to vary within a certain range. To meet the requirements of power transmission and accommodate the angle changes caused by steering and the up-and-down movement of the car during operation, the drive axle of front-wheel-drive vehicles often uses universal joints to connect the half-shaft and the wheel axle. A single universal joint cannot ensure that the instantaneous angular velocity of the output shaft matches that of the input shaft, which can easily cause vibration, accelerate component wear, and generate significant noise. Various types of constant-velocity universal joints are widely used in front-wheel-drive vehicles, with two constant-velocity universal joints per half-shaft. The universal joint closer to the transaxle is the inner half-shaft universal joint, while the one near the wheel axle is the outer half-shaft universal joint.
As a seasoned mechanic with decades of experience, I'm quite familiar with the principle of universal joints. They mainly connect two shafts in a vehicle's drivetrain, such as between the engine and rear axle, allowing them to transmit power at varying angles. The key lies in the cross-shaped structure: a fork-shaped joint clamps onto the cross-shaped pivot, which can flex and extend during rotation to adapt to road conditions, preventing wheel lock during turns. However, they also have many issues. Over time, they wear out, squeak due to insufficient lubrication, and can even cause driving vibrations. I've seen many vehicles where the universal joints rusted due to rainwater, forcing owners to spend big money on replacements. Regular maintenance requires frequent checks of the grease fittings—never wait until the shaft end play becomes excessive to act.
I dabble in mechanical research as a hobby, and understanding the principle of universal joints is quite fascinating. Essentially, it's a hinge mechanism where two Y-shaped forks encase a cross-shaped rotating axis. Even when the input angle changes, the output shaft can still follow the motion, allowing power transmission even when the shaft isn't straight. In cars, they're often placed at both ends of the driveshaft, though efficiency drops slightly when the angle deviation is too large. The principle is similar to how a human knee bends while walking but still transfers force—it comes into play when a car turns. For maintenance, modern cars mostly use CV joints (constant-velocity joints) for smoother operation, whereas older cardan-type joints are more cost-effective. Regular inspection of friction surfaces and keeping dust out can extend their lifespan.
