## What is Universal Joint?

universal joint is considered the oldest of all flexible couplings. It is commonly known for its application in automobiles and trucks. It is located where two shafts are to be joined at an angle to transmit torque.

In the transmission system of a vehicle, the output shaft of the gearbox. The propeller shaft and the differential pinion shaft are not in one line, and hence the connection between them is made by a universal joint.

Thus, it permits the torque transmission at an angle, and also while this angle is changing constantly while the vehicle is moving on the road. It is a simple and most common type of joint and is known as a Cardan joint or hook joint. They have a number of unique features that make them perfect for a range of applications.

## Purpose of Universal Joint

When a car is running on an uneven road, the differential rises and falls. Thus, the propeller shaft also changes its angle due to the rise and fall of the differential at the same time the propeller shaft is rotating.

Under such conditions, these joint allows the changes of angle of the propeller shaft without the transmission.

If the differential is directly connected from the gearbox without a universal joint during the rise and fall of the rear axle the connection fails because it is not flexible due to the absence of a universal joint.

## Parts of a Universal Joint

Following are the parts of a universal joint:

1. Driving yoke and driven yoke
2. Spider

### 1. Driving Yoke and Driven Yoke

The universal consists of two yokes, one is a driving yoke and another is a driven yoke, to form the joint.

### 2. Spider

These yokes are connected by means of a cross-shaped intermediate member called the spider. In this, a shaft can be rotated at many angles.

If the shaft is connected straight, the input shaft will rotate the cross, and the cross will turn the output shaft. It is obvious that both the input and output shafts will rotate at the same speed.

## Working of Universal Joint

As per the above figure, it consists of a driving yoke ‘1’ on one side. This is connected to the main shaft of the gearbox, and there is a driven yoke ‘3’ is connected to the propeller shaft.

These two yokes are connected by means of a crossed spider ‘2’. The four arms of the spider are known as trunnions.

When the driving shaft is rotating the driven shaft also rotates, and at the same time, the universal joint allows angular motion. Hence the power is transmitted from the gearbox to the propeller shaft at an angle.

Thus, these joints are used to make a flexible connection between two rigid shafts at an angle with each other. They permit the transmission of the power not only at an angle but also while this angle is being varied constantly.

## Functions of Universal Joint

The important functions of the universal joint are as follows:

1. It is used to connect two shafts, whose axles intersect.
2. It permits the rotation of one shaft about its axis by another shaft which rotates about its own axis.
3. They permit the transmission of power not only at an angle, but also while this angle is being changing constantly.

## Types of Universal Joint

Mainly there are 3 types of universal joints as follows:

1. Cross type or spider and two-yoke type joint
2. Ball and trunnion type joint
3. Constant velocity type joint

### 1. Cross-Type Universal Joint

In this joint, it has two Y-shaped yokes and a crosspiece (also known as a spider). One yoke is attached to the driving shaft and another one is attached to the driven shaft.

The cross piece consists of a four-arms (trunnion) that are connected to both ends of the yokes. Four bearings were also provided for each arm of the cross-piece. These bearings allow the yoke to move around the trunnion while simultaneously removing the driving and driven shafts at an angle.

### 2. Ball Trunnion Type Universal Joint

It is a combination of both universal and slip joints in one assembly. The ball trunnion type joint is consists of a ball-type head that are fastened to one end of the propeller or drive shaft.

A pin or cross shaft is pressed through this end of the shaft forming a ‘T’ shape. In this pin, two steel balls are fitted firmly. The joint helps in the rotational motion through the ball and the pin. The balls can also move axially in direction. Ball and trunnion joints are also variable velocity joints.

### 3. Constant Velocity Type Universal Joint

It is a type of universal joint, which allows both driving and driven shafts to move at a constant velocity. Because, in this case, the two joints act on the same angle.

These joints are typically used when the vehicle is in a front-wheel (axle) drive. Because the speed variation between the driving and driven shaft will present difficulty in the steering system and results in excessive tire wear.

1. Universal joints have more elastic properties than knuckle joints.
2. These joints help in torque transmission between shafts that have an angular misalignment.
3. They are cheaper in cost and are simple to be assembled and dismantled.
4. The universal joint can provide high torque transmission efficiency.
5. These joints allow angular displacement compared to other types.

1. If the joint is not lubricated properly, it may wear out.
2. It requires frequent maintenance to avoid wear.
3. These joints can cause unstable motion.
4. They cannot support axial misalignment.

## Applications of Universal Joint

Universal joints differ based on their material form and hub type. A positive mechanical joint is used to connect shafts. They are commonly seen in the propeller shafts of rear-wheel-drive cars. These are used for the purpose of transmitting motion, power, or both.

The joints with thermoplastic body members are used in light industrial applications because they offer advantages such as self-lubricating features, lightweight, negligible reactivity, corrosion resistance, and the ability to operate at high speeds.

These joints are commonly used in applications of aircraft, control mechanisms, electronics, instrumentation, medical and optical instruments, armaments, radios, sewing machines, textile machinery, and tool drives.

## Wrapping It Up

As we discussed above, a universal joint is a process of connecting rigid rods whose axes are inclined towards each other, allowing the transmission of torque and/or rotary motion.