Oct. 12, 2023
Universal Joint: Definition, Working Principle, Applications, Advantages, Disadvantages
What is universal joint?
A universal joint, also known as a U-joint, is a type of mechanical coupling that allows two shafts to be connected and transmit torque while still being able to rotate freely and move in different directions. This is achieved by using two yokes, each attached to one of the shafts, and a cross-shaped connecting piece called a cross-pin that links the two yokes together. The cross-pin is mounted in bearings in the yokes, allowing it to rotate and swivel, allowing the shafts to move and rotate relative to each other.
Universal joints are commonly used in various applications, such as drive shafts for vehicles, machinery for industrial processes, and other mechanical systems where the flexible and versatile coupling is needed. The universal joint diagram is given below.
Working Principle of Universal Joint
The working principle of a universal joint is based on using two yokes, each attached to one of the shafts to be coupled, and a cross-shaped connecting piece called a cross-pin that links the two yokes together. The cross-pin is mounted in bearings in the yokes, allowing it to rotate and swivel, allowing the shafts to move and rotate relative to each other.
When torque is applied to one of the shafts, it is transmitted through the universal joint to the other shaft, causing it to rotate. As the relative orientation of the two shafts changes, the cross-pin can rotate and swivel in the bearings in the yokes, allowing the universal joint to accommodate these changes while transmitting torque and allowing the shafts to rotate. This allows the universal joint to provide a flexible and versatile coupling between the two shafts, allowing them to move and rotate freely in different directions while transmitting torque.
Types of Universal Joints
There are several different types of universal joints, which vary in their design and application. Some common types of universal joints include
Single Cardan joint: This is the most common type of universal joint, and it consists of a single cross-shaped connecting piece that links the two yokes together. This allows the joint to accommodate changes in the relative orientation of the two shafts while transmitting torque and allowing them to rotate.
Double Cardan joint: This type of universal joint consists of two cross-shaped connecting pieces arranged in series, which link the two yokes together. This allows the joint to accommodate even larger changes in the relative orientation of the two shafts, and it is often used in applications where the shafts may be subjected to more extreme movements.
Constant velocity joint: This type of universal joint is designed to maintain a constant rotational velocity between the two shafts, even as their relative orientation changes. This is achieved by using a series of small balls or rollers that are arranged specially, allowing the joint to accommodate changes in orientation while maintaining a constant velocity.
Hooke's joint: This type of universal joint uses a series of curved arms, or levers, to link the two yokes together. This allows the joint to accommodate changes in orientation while transmitting torque and allowing the shafts to rotate.
Cross and bearing joint: This type of universal joint uses a cross-shaped connecting piece and a series of bearings to link the two yokes together. This allows the joint to accommodate changes in orientation while transmitting torque and allowing the shafts to rotate.
Applications of Universal Joints
Universal joints are commonly used in various applications due to their ability to accommodate changes in the relative orientation of the two shafts that are coupled together while transmitting torque and allowing them to rotate. Some common applications of universal joints include
In drive shafts for vehicles, such as cars, trucks, and tractors, the shaft must be able to accommodate changes in orientation as the vehicle moves over uneven terrain.
Machinery for industrial processes, such as conveyor belts, mixers, and other equipment, may require shafts that can move and rotate in different directions.
In power transmission systems, such as those used in wind turbines, the shafts may be subject to large and varying forces, requiring a flexible and versatile coupling.
In robotics, universal joints are often used to connect the different parts of a robot's body, allowing it to move and rotate freely.
In other mechanical systems where flexible and versatile coupling is needed, such as in cranes and other lifting equipment, marine propulsion systems, and various other applications.
Advantages of Universal Joints
Universal joints have several advantages over other mechanical couplings, making them useful in various applications. Some of the main advantages of universal joints include
Flexibility: Universal joints can accommodate changes in the relative orientation of the two coupled shafts, allowing them to move and rotate freely in different directions. This makes them ideal for applications where the shafts may be subject to large and varying forces or need to move and rotate in different directions.
Versatility: Universal joints can transmit torque and allow the shafts to rotate, making them useful for a wide range of applications where power transmission or rotation is needed.
Compactness: Universal joints are relatively small and compact, which makes them easy to incorporate into a wide range of mechanical systems.
Durability: Universal joints are typically designed to be robust and durable, with high-quality bearings and other components that can withstand large forces and long-term use.
Cost-effectiveness: Universal joints are generally less expensive than other types of couplings, which makes them an economical choice for many applications.
Disadvantages of Universal Joints
While universal joints have many advantages, they also have disadvantages. Some of the main disadvantages of universal joints include
Limited range of motion: Universal joints can only accommodate a limited range of changes in the relative orientation of the two coupled shafts. This means they may not be suitable for applications where the shafts may be subject to large or extreme movements.
Loss of power: Due to how universal joints are designed, some power is lost as the torque is transmitted through the joint. This means that the shafts may not rotate as efficiently as they would if coupled using a different type of coupling.
Noise and vibration: Universal joints can sometimes produce noise and vibration as the shafts rotate, which may be undesirable in some applications.
Maintenance: Universal joints require regular maintenance and lubrication to function properly and to maintain their durability and performance. This can add to the overall cost and complexity of using universal joints in some applications.
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How Does a Universal Joint Work?
A Universal Joint (often referred to as a U-Joint or Uni Joint) is a special type of pivoting joint that allows rotational power to be transmitted between two shafts that are imperfectly aligned. Universal joints are commonly found in rear-wheel drive cars where the driven axle moves independently of the gearbox. The universal joint allows the shaft to move along with the suspension while transmitting power when there isn’t a straight line between the engine and axle.
A universal joint consists of an X-shaped pivot point based on the design principles of gimbals. The universal joint connects two separate shafts and allows them to pivot and move independently, at relative angles of up to 45 degrees. Typical universal joints provide two degrees of freedom, meaning the two shafts are free to rotate along two axes simultaneously (commonly the X and Y axes). In more complex applications, the universal joint may include two separate X-shaped pivots to allow the shafts to operate at much steeper angles, up to 90 degrees.
How to check U-Joints
A propeller shaft, or propshaft, connects the rear axle to the gearbox on front-engined rear-wheel-drive cars.
At each end of the propshaft there is a universal joint (UJ), which allows the rear axle to move up and down in relation to the gearbox without bending or snapping the shaft.
Some propshafts also have a universal coupling fitted at the centre.
A universal joint consists of a cross-shaped 'spider' with needle roller bearings held on its four arms by caps and circlips. The yoked ends of two shafts have lugs which engage with the spider arms and can pivot on the roller bearings .
In most modern cars the joints are sealed for life and cannot be lubricated. In older cars, they can be dismantled from the propshaft, checked and lubricated or replaced.
If the propshaft joints on your car have grease nipples, check with the manufacturer's service schedule for greasing intervals.
The main drawback with many current car models is that the universal joints cannot normally be separated from the propshaft. When the joints wear, the propshaft must be renewed. A worn joint causes the propshaft to vibrate. As wear increases, vibration worsens.
Another sign of wear is a clonk when you accelerate or decelerate, or a regular knock when the car is moving.
A sure sign of something breaking up inside the bearings of a joint is rust-coloured dust around the spider. Fit a new joint or shaft immediately.
To check for wear when no dust is evident, grip one side of the joint firmly and try to turn the other side against holding pressure . There should be no play in the joint at all.
Make another check by inserting a large screwdriver between the yoke and the spider and levering it to see if there is any play. If you feel any play, fit a new joint or propshaft.
The symptoms of a worn joint — the clonks or apparent play — are very similar to those for excessive between two parts such as the teeth of gears. data-term-id="1310">backlash
