What is a Universal Joint? – Types, Working & Diagram

What Is A Universal Joint?

Universal Joint
Universal Joint Diagram | Universal Joint Application, Working Of Universal Joint, Types Of Universal Joint, Universal Joint In Automobile.

Universal Joint is a joint or coupling that connects rigid rods whose axes are bent to each other and are commonly used in shafts that transmit rotary motion. It consists of a pair of hinges placed close together, connected by a cross shaft, oriented at 90 ° to each other.

If we look at the history of the universal joint, Robert Hooke is commonly known as the inventor of the ‘Hooke’s Joint’ or ‘Universal Joint’. There are various names used for the universal joints such as universal coupling, U-joint, Cardan joint, Spicer or Hardy Spicer joint.

Universal Joints are mainly used to create a flexible connections between two rigid shafts at an angle. It permits the transmission of constantly varying power. It is used to connect the propeller shaft with the gearbox shaft to transmit the rotary motion.

The transmission of power under varying conditions is impossible without using a flexible device or universal joint. This flexible device is also used in vehicles having coupling shafts between clutch and gearbox, between main gearbox and auxiliary gearbox and also on driving shafts of the driven front axle.

Working Of Universal Joint

In case of an automobile, the gearbox is rigidly mounted. Due to the action of the road springs, the position of the rear axle is constantly varied and the allowance is provided if the gearbox is mounted to the rear axle by a propeller shaft. A universal joint consists of two yokes. These yokes are attached to each end of the shaft. The two yokes are joined by a central or connecting cross piece. The connecting cross piece will turn bearings of the yoke with the change in angularity between shafts. They do not transmit motion uniformly if the shafts are operating at an angle.

Therefore, the driven shaft increases to the maximum and then it decreases to the minimum. The rise and fall of the driven shaft occurs twice as the pivot pin rotates through different planes in each revolution.

Types Of Universal Joint

1. Variable Velocity Joints

In this case, both the driven and driving shafts do not rotate at the same speed even though each part of a revolution is at the same rpm. The driven and driving shafts should be placed in a straight line to turn at the same speed through each part of a revolution. But in actual practice, it will not be feasible in any automobiles. The drive shaft is always inclined.

If there is an angle between driven and driving shafts, the driven shaft will be less than the driving shaft by half revolution and faster than the driving shaft by the other half revolution. Hence, the average speed of the driven shaft is equal to the driving shaft. The speed variation in the driven shaft increases with increase in flex angle of the universal joint.

If two variable speed universal pairs are used in two drive lines, the yoke on the shaft connected to the universal pairs should not be indifferent planes. It provides the balancing to the speed variations.

Variable Velocity Joints are following These Types.

– Cross or Spider Type

In universal joints, the two yokes in which one is connected to the driving shaft and the other one is connected to the driven shaft at right angles to each other by a cross or spider. Needle type bearings are mounted between yokes and cross ends. These types of joints are generally used in driving shafts.

– Ring Type

Universal Joint
Ring Type | Universal Joint Diagram

This type of joint uses a flexible ring. The shaft has two or three armed spiders. The arms are bolted to opposite faces of the flexible ring. The arms of one spider are placed midway between the arms of the other. The flexible ring is made of one or more rings of rubber to provide enough strength. A number of thin steel discs are used instead of the fabric rings. This joint itself provides a sufficient amount of axial movement of the shaft. It smoothens the torque fluctuations and it does not require lubrication. The main drawback is that the ring does not withstand for a longer period.

– Ball and Trunnion Type :

A combination of both universal and slip joints in one assembly is used in this type. A pin or cross shaft is connected crosswise in ‘T’ fashion in the end of a universal joint shaft. A ball is mounted on the needle bearings at each end of the cross shaft. The complete assembly freely slides in grooves machined in the outer body of the joint. The heavy spring resists excessive longitudinal movement of the shaft. The power is transmitted through the trunnion, balls and cross shaft. The bending moment occurs by rolling the ball in one direction. It is also in the other direction by moving balls lengthwise in trunnion grooves. The open end of the shaft is covered by the leather or rubber boot covers.

2. Constant Velocity Joints

In this type of joint, the driven shaft is turned at the same speed as the driving shaft turns through each part of revolution at any degree of flex. These joints are mainly used in front drive axles to transmit power over large angles. Cadillac cars use ball and socket type constant velocity joints in their propeller shafts.

Constant Velocity Joints are following These Types.

– Rzeppa

Universal Joint
Rzeppa | Universal Joint Diagram

It consists of spherical internal and external ball races in which the grooves are cut parallel to the shaft. The Steel balls are placed in grooves on the spherical races. The torque transmission is done from one race to another ball. The circular pattern of balls causes shafts to turn at the same velocity.

– Bendix Weiss

Universal Joint
Bendix Weiss | Universal Joint Diagram

The principle of driving through balls placed in a circle around a sphere is used in this type of joint. Four numbers of driving balls are placed into machined races in close fitting yokes. A fifth or centre ball is held between two yokes as an inner race. The driving balls are arranged themselves in a circle in the same manner as the Rzeppa joint. The aligning action of the balls gives a constant velocity joint.

– Tracta

Universal Joint
Tracta | Universal Joint Diagram

This joint differs from the above two joints. Four yokes are used in this joint in which two yokes are fastened to shafts and the other two are floating at the centre of the joint. The mating parts of the yokes are made into segments of a circle. Both circular segments and floating action of the two yokes provide a constant velocity joint.

Also, Read | Single Plate Clutch – Types, Working, Construction & Diagram

Function Of Universal Joint

Universal joints are used for connecting two shafts inclined to one another at angle and also for transmitting the rotary motion from engine to road wheels throughout the variations in rear axle position with respect to gearbox and chassis.

So the universal joints are used at the front and rear end of the propeller shaft which transmit the power to the wheels even if the heights of transmission and rear axle are different. Also whenever the axle moves up and down due to road irregularities, the angle of drive changes continuously and the universal joint allows transmission of power and rotary motion at a varied angle.

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Materials Used For Universal Joints

Universal joints can be made from almost any material depending on the application. Common materials used include stainless steel, steel, naval brass and other similar alloys to handle greater torque and temperature. Plastics and thermoplastics are also used to create universal joints as they have greater rust and corrosion resistance as well as electrical and magnetic insulation in applications where this is required.

Also, Read | What is Gearbox : Types of Gearbox, Parts & Working

Application Of Universal Joint | Universal Joint Application

  • Universal joints vary based on their material composition, hub type and the applications for which they are designed, it is a positive mechanical joint that is used for connecting shafts.
  • Universal Joint is most commonly found in the propeller shaft of rear wheel drive cars.
  • Specific applications of universal joints include aircraft, appliances, control systems, electronics, Instrumentation, textile machinery, medical and optical equipment, radios, weapons, sewing machines and tool drives.

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Advantages And Disadvantages

Advantages Of Universal Joint

  1. Universal coupling is more flexible than knuckle joint.
  2. It facilitates torque transmission between shafts which have angular misalignment.
  3. It is cheap and cost-effective.
  4. It is simple to be assembled and dismantled.
  5. Torque transmission efficiency is high.
  6. The joint permits angular displacements.

Disadvantages Of Universal Joint

  1. Wear may occur if the joint is not properly lubricated.
  2. Maintenance is often necessary to avoid wear.
  3. Universal joint produces fluctuating motion
  4. It does not support axial misalignment.

Also, Read | What is Front Axle – Types, Parts, Function & Diagram

What Is Slip Joint

What Is Slip Joint
What Is Slip Joint | Slip Joint Diagram

A Slip Joint or Sliding Joint is used between propeller shaft and universal joint connecting the propeller shaft to compensate for this change of length and it helps to transmit the power from engine to rear axle at the same time. In cars having a torque-tube drive, a slip joint is not necessary.

The propeller shaft is inclined towards down from the transmission main shaft to the rear axle as stated earlier. The propeller shaft will also be shortened and lengthened again when the axle rises as the rear springs are compressed and at the time the axle returns to its original position.

The joint consists of a male splined end of the main shaft which slides into the corresponding grooves with the female member of the joint. The female part is integral with the universal joint hub. The splines enable the slip joint to transmit power for compensating any change of length in the propeller shaft when sliding.

Also, Read | What is Clutch? : Types of Clutch, Functions, Working

Function Of Slip Joint | Slip Joint Function

What Is Slip Joint
What Is Slip Joint | Slip Joint Diagram

If the rear wheel comes in front of the bump, then the spring compresses or expands as the differential with the rear axle housing and the wheel moves up and down. This not only changes the angle but also varies the length of the propeller shaft. The slip joint therefore allows an effective length of propeller shaft depending on the road conditions. If there is no slip joint, the propeller shaft will buckle or brake.

Also, Read | What is Differential? – Types, Parts, Function & Diagram

FAQ – Universal Joint

Q. What is Universal Joint?

Universal Joint is a joint or coupling that connects rigid rods whose axes are bent to each other and are commonly used in shafts that transmit rotary motion. It consists of a pair of hinges placed close together, connected by a cross shaft, oriented at 90 ° to each other.

Q. What is Slip Joint?

A Slip Joint or Sliding Joint is used between propeller shaft and universal joint connecting the propeller shaft to compensate for this change of length and it helps to transmit the power from engine to rear axle at the same time. In cars having a torque-tube drive, a slip joint is not necessary.

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