What is Universal Joint and how it works? Where does the universal joint used?


A universal joint is used where two shafts or axles are connected at an angle to transmit torsional power. In the transmission system of a vehicle, the main shaft, propeller shaft and the differential pinion shaft are not in one line: and hence the connection between them is made by a universal joint. One universal joint is used to connect the other end of the propeller shaft and the differential pinion shaft. Thus, the connections between the three shafts are flexible and at an angle with each other. The universal joint permits the torque
transmission not only at an angle but also while this angle is changing constantly.
universal joint
universal joint

A simple universal joint consists of two Y-shaped yokes, one on the driving shaft and other on the driven 
shaft: and a cross-piece called the spider. The four arms of spider, called as trunnions, are assembled into the ends of the two shaft yokes with bearing. The driving shaft and the driven shaft are at an angle to each other, the bearings in the yokes permit the yokes to swing around on the trunnions each revolution.

It is to be noted that simple universal joint does not transmit the motion uniformly when the shafts are operating at an angle, except in constant velocity type universal joint. Because the pivot pins do not revolve in the same plane, the driven shaft will increase to a maximum and decrease to a minimum twice in each revolution. Although the degree of variation is small, however, it may be minimized by the use of two universal joints. The two joints are arranged so that the non-uniform rotation of each joint tends to neutralize that of the other, as shown in Figure.


The universal joints may be of three types as follows:
  1. Cross-type or spider and two-yoke type.
  2. Ball and trunnion type.
  3. Constant velocity type.
The cross type universal joint is shown in Figure. Because it consists of a cross piece or spider and two yokes, therefore, it is known as cross-type or spider and two-yoke type universal joint. There are four needles bearing one for each trunnion of the spider. The bearings are held in place by rings heat drop into undercuts in the yoke-bearing holes. One commercial design of the cross type universal joint incorporates a slip joint. One yoke is integral with the hub that holds the female end of the slip joint. When the joint is used between the propeller shaft and rear axle gear shaft, the slip joint is omitted so that a direct connection is made between the two units. Other designs of cross type universal joint are ring and trunnion type used in torque tube drive, and cross ball type used in Hotch-kiss dive.

universal joint cross pin or spider.
universal joint cross pin or spider.


The ball and trunnion type universal joint consists of a ball head fastened to the end of the propeller shaft through which a pin is pressed. Two steel balls mount over the ends of the pin. The ball retains the roller bearing between them and U-shaped channel in the body. The centring bottoms and the button spring help to keep the pin properly centred. The universal joints and propeller shaft assembly is bolted to a companion flange with the gasket and grease cover between them. The companion flange (not shown) is splined to the other
shaft. The rotary motion is carried out through the pin and balls. The balls can move back and forth in the channels of the body to compensate for varying angle of the drive at the same time, they act as a slip joints by slipping into or out of the channels.
The constant velocity universal joint
The constant velocity universal joint
The constant velocity universal joint consists of two individual universal joints linked by a ball and socket. The ball and socket split the end of the two propeller shafts between the two universal joints. The type of joint permits uniform motion. Because the two joints are operating at the same angle, the acceleration resulting at any instant from the action of one universal joint is cancelled out by the deceleration of the other and vice versa.

For Better understanding about universal joint watch the animation video below:

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