Uses of Universal Joints

A regular joint just moves in one direction along a single axis. This is acceptable for simple machines, but what if a machine requires a joint to not only move up and down but also move in a rotating motion? All sorts of machines today have complicated moving parts and transfer power along shafts. Designing a shaft that is able to rotate as well as move up and down is quite a challenge, but the problem is fixed with universal joints.

Learn more about universal joints


The Special Properties of Universal Joints


Imagine a length of rods that are joined in such a way that the length as a whole can bend in almost any direction. Two such joints could move in quite a few directions, but could not bend or rotate in a cone dimension with ease. It would take several joints arranged like a chain to achieve that type of flexibility.


An alternative was innovated centuries ago, and the ancient Greeks used a similar device called the gimbals. The basic concept is to take two flexible rods with U-shaped ends and then connect both these joints onto a disk with metal hinges. Rather than relying on a chain of joints, only two joints are connected separately to a disk. With only two sections, the joint can both bend and rotate.


Early uses for this invention was on artillery pieces and clockwork devices. It had the problem that if one joint rotated, the other joint might not rotate smoothly or uniformly. As the result, the design has had to be refined more than once to avoid vibration and wear. There are disadvantages to such a joint, namely that depending on two connections rather than one has less mechanical strength.


Common Applications of Universal Joints


The most common use for this type of joint today is in vehicles and factory equipment. Most internal combustion engines use pistons that capture the energy of a small explosion made from vaporized fuel and compressed air. That force drives a piston which then converts linear energy into rotational energy. That conversion is arranged using a universal joint that is able to bend with the up and down motion of the piston while still driving a shaft.


When four or more pistons work in harmony, their universal joints are guaranteed to be perfectly calibrated. This type of joint does not rotate along its circumference but instead helps to drive a rotating object such as a wheel or a drive shaft. A similar device was invented to drive the wheels of a train, although piston joints are designed to move multiple pistons without breaking.


Joints for vehicles have to be robust and yet move smoothly because of the forces involved. drive shafts often use universal joints as well because they must transfer power to more than one system. An all-wheel drive has to be able to shift power between the front wheels and the back wheels. This can be a problem when car sections are jerking around while a car is moving. The problem is solved with a double Cardan joint. This means that two universal joints are on the same shaft in order to transfer power without the shaft getting jarred by motion.