A universal joint is more commonly known as U-joint. Besides, it can also be called universal coupling, Cardan joint, and Hooke’s joint, etc. it is a mechanical connection between rotating shafts which are generally not in parallel, but intersecting. It can allow positive transmission of rotating power at a much larger angle than is permissible with a flexible coupling. And it can transmit torque and motion.
Universal joints can be widely used in all types of power transmission systems. They have a variety of applications. They can be used in food processing equipments, replacement for expensive gearboxes, and drives, etc. Besides, they are also commonly applied in connecting power take-off drive shafts in off-highway tractors that operate drawn machinery such as rotary grass mowers and feed grinders.
As is mentioned at the beginning of this article, a universal joint is also can be called Cardan joint or Hooke’s joint. Actually, it is the oldest and most common type of u-joint. This joint is quite popular in automotive applications. It can transmit relatively high torque with minimal radial loads. However, it also has some disadvantages. For example, by design these u-joints have difficulty compensating for parallel offset and axial misalignment. Besides, due to its design, even a lubricated Cardan u-joint will require periodic maintenance, and may leak lubricant.
Universal joints can be assigned to one of three categories: non constant velocity U-joints, near-constant velocity U-joints, or constant velocity U-joints. As to the first one, it offers the simplest and least complex units. Typical applications are to join the drive shaft and differential in automobiles and trucks. They are also widely used in mobile equipment, farm machinery, and industrial machinery.
As to the second category, the most common type of joint that produces a near-constant velocity consists of two back-to-back Cardan joints, with the second joint compensating for the speed variations of the first.
Now let us see the third one: constant velocity U-joints. It is said that this kind of joints can operate more smoothly and at higher speeds than the other two types because of their constant velocity characteristics. However, they also have many disadvantages. For example, they are more complex and expensive. Besides, they do not carry loads as heavy as non constant-velocity types.
According to the above, we can see that the universal joint is also a very important mechanical part. It plays a very important role in the power transmission. Therefore, it is also rather necessary to learn something about it.