UNIVERSAL JOINTS: Types, Working and Functions

INTRODUCTION OF UNIVERSAL JOINT  

Universal joints are often used when applications require correction of misalignment between mating shafts greater than 3° (usually provided by flexible coupling).  

With a single universal joint consisting of two yokes, a central bearing block, and two bolts that penetrate the block at right angles, as an angle of up to 45° at low speeds.  

There is a possibility that the deviation will occur.  

At speeds above 10 rpm, about 20° to 30° makes more sense.  

Single universal joint components

Single universal joints have the disadvantage that the speed of the output shaft is non-uniform with respect to the drive shaft.  

The double universal allows for parallelism and large misalignment of the connected shafts.  

In addition, the second joint cancels the non-uniform vibration of the first joint, allowing the input and output shafts to rotate at the same uniform speed.  

A vehicle universal joint that connects an engine or transmission to the drive wheels are used in some rear-wheel drive vehicles, light and heavy trucks, farm equipment, and construction vehicles.  

The spider assembly includes needle roller bearings on each arm.  

The far right shows the ball pivot yoke, flange yoke, and center coupling yoke that form the double cardan universal joint.  

Constant velocity joints, or just another type, simply called CV joints, are often used as a key component of front-wheel drive and an all-wheel drive vehicle powertrain.  

Double universal joint

 A double universal joint for heavy industry design.  

Some of these types include two-piece connecting tubes with splines to allow for significant changes in axial position and to accommodate angular or parallel misalignments. 

Cornay universal joint

Such new designs are called the Cornay universal joint.  

This creates a true constant velocity of the output shaft over all drive angles up to 90°.  

Compared to standard universal joint designs, Cornay joints operate faster and can accommodate the torque transmitted, the speed of rotation, and the angle at which the joint operates.  

The velocity / angle factor is calculated as the product of velocity and operating angle.  

This value determines the uptime utilization applied to the base torque load to calculate the nominal torque required for the connection.  

All manufacturers provide such data in their catalogs.  

Some drive shafts that incorporate a universal joint with a relatively long tubular section between the end joints are often referred to as torsion tubes.  

WORKING OF UNIVERSAL JOINT  

Automotive universal joints

In automobiles, the gearbox is firmly attached.  

The position of the rear axle is constantly changing due to the action of the load springs and there is play when the gearbox is attached to the rear axle via the propeller shaft.  

The universal joint consists of two yokes.  

These yokes are attached to both ends of the shaft.  

The two yokes are connected by a central or a connecting cross piece.  

The connecting cross rotates the bearings on the yoke as the angle between the shaft’s changes. 

When the shafts move diagonally, they do not transmit the movement evenly.  

Therefore, the output shaft rises to the maximum and then to the minimum.  

Exploded view of driveshaft components

The driven shaft moves up and down twice as the pivot pin rotates in a different plane each time it revolves. 

TYPES OF UNIVERSAL JOINTS 

VARIABLE VELOCTY JOINT  

In this case, even if the RPM of each part of rotation is the same, both the driven shaft and the drive shaft will not rotate at the same speed.  

The output and input axes should be aligned so that they rotate at the same speed in all parts of one rotation.  

However, in reality, this is not possible with any car.  

The drive shaft is always inclined.  

If there is an angle between the output shaft and the drive shaft, the output shaft will be half a turn smaller than the drive shaft and the other half turn will be faster than the drive shaft.  

Therefore, the average velocity of the output axis is equal to that of the input axis. The speed change of the output shaft increases according to the bending angle of the universal joint.  

When using two universal variable speed pairs with two drive trains, do not place the yokes of the shafts connected to the universal pair in different planes. 

TYPES OF VARIABLE VELOCITY JOINTS 

1. Cross or spider type: 

The universal joint connects two yokes, one connected to the drive shaft and the other connected to the output shaft at right angles to each other by a cross or spider.  

Needle bearings are mounted between the yoke and the cross end.  

These types of joints are commonly used in drive shafts. 

2. Ring type: 

This type of connection uses a flexible ring.  

There are two or three armed spiders on the shaft.  

The arm is bolted to the other side of the flexible ring.  

The arm of one spider is placed in the middle of the other arm.  

Flexible rings are made up of one or more rubber rings to provide sufficient strength.  

Instead of fabric rings, some thin steel discs are used.  

The joint itself ensures sufficient axial movement of the shaft.  

It corrects torque fluctuations and does not require lubrication.  

The main drawback is that the ring does not last long. 

3. Ball and trunnion types:  

This type uses a combination of universal joints and sliding joints in one assembly.  

At the end of the cardan shaft, a pin or horizontal axis is connected in a cross-T shape.  

Balls are attached to the needle bearings at both ends of the cross shaft.  

The entire assembly slides freely into the machined grooves in the body outside the joint.  

Heavy springs resist excessive vertical movement of the shaft.  

Power is transmitted via pivot pins, balls and cross shafts.  

The bending moment is generated by rolling the ball in one direction.  

You can also do that in the opposite direction by moving the ball vertically into the groove of the pin. 

The open end of the shaft is covered with a leather or rubber boot cover. 

CONSTANT VELOCITY JOINT  

In this type of joint, the drive shaft rotates at the same speed as the drive shaft rotates at each part of the rotation of each degree of bending.  

These joints are primarily used on front-wheel drive axles and transmit power at large angles.  

Cadillac cars use constant velocity joints of balls and sockets on the propeller shaft. 

CONSTANT VELOCITY JOINTS TYPES  

1. Rzeppa: 

It consists of spherical inner and outer ball laces with grooves cut parallel to the shaft.  

The steel ball is placed in the groove of the spherical raceway.  

Torque is transmitted from one raceway to another ball.  

The circular pattern of the ball causes the shaft to rotate at the same speed. 

2. Bendix Weiss  

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. 

3. Tracta  

This joint is different from the two joints above.  

These joint uses four yokes with two yokes attached to the shaft and two other yokes that float in the center of the joint.  

The mating part of the yoke is formed into a segment of circles.  

Both the circular segment and the floating effect of the two yokes guarantee a constant velocity joint. 

FUNCTIONS OF UNIVERSAL JOINTS  

Universal joints connect two shafts that are angled to each other and serve to transfer rotational movement from the engine to the running wheels at different rear axle positions on the gear box and chassis.  

The universal joint is used at the front and rear ends of the cardan shaft to transmit power to the wheel at different heights than the gearbox and rear axle.  

The universal joint may start the power transmission and rotational movement at a variable angle even if the axle moves up and down due to the unevenness of the road surface, the drive angle changes continuously. 

MATERIALS USED FOR UNIVERSAL JOINTS  

Universal joints can be made from almost any material, depending on the application.  

Commonly used materials include stainless steel, steel, brass, and other similar alloys for handling higher torques and temperatures.  

Plastics and thermoplastics are also used in the manufacture of universal joints because they are highly resistant to rust and corrosion and provide electrical and magnetic insulation as needed. 

APPLICATIONS OF UNIVERSAL JOINTS 

Universal joints depend on the composition of the material, the type of hub, and the application in which they are designed.  

This is a positive fitting mechanical joint used to connect the shafts.  

Universal joints are most commonly found on propeller shafts in rear-wheel drive vehicles.  

Specific applications for universal joints include aircraft, appliances, control systems, electronics, instrumentation, textile machinery, medical and optical devices, radios, weapons, sewing machines, and tool drives. 

ADVANTAGES  

Universal couplings are more flexible than toggle joints.  

Facilitates torque transmission between shafts with angular deviations.  

It’s cheap.  

Easy to assemble and disassemble.  

High efficiency of torque transmission.  

The joint allows for angular displacement. 

DISADVANTAGES  

 Wear can occur if the joints are not properly lubricated.  

 Maintenance is often required to prevent wear.  

 The universal joint creates a swaying movement. 

 Axial deviation is not supported. 

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