Propeller Shaft / Drive Shaft, A Universal joint | 2 Major Types and Functions of the Propeller Shaft

Propeller shaft or Drive shaft or Prop shaft or Cardan shaft

The propeller shaft connects the transmission shaft to the pinion shaft at the wheel axle. The propeller shaft is also called the driveline shaft or drive shaft.

The propeller shaft transmits the driving power generated by the engine to the axles in four-wheel drive and rear-wheel drive vehicles. The propeller shaft is built of steel tubes that are very resistant to bending and torsional stresses. It is dynamically balanced, and a balance weight is occasionally welded outside the tube to keep it balanced.

The propeller shaft carries the power from the engine, clutch, and transmission unit to the driving wheels of the vehicle, through the final drive and differential unit. 

When a vehicle makes a right turn, for instance, its innermost wheels must travel less distance and the vehicle’s speed will be reduced. However, in comparison to the inner wheels, the outermost wheels will have to travel a greater distance and at faster speeds. With the aid of the differential, this may be accomplished.

Functions of the propeller shaft

In most automotive vehicles, the engine is located at the front and the rear wheels of the vehicle are being driven. This arrangement stipulates a longer propeller shaft to be used. In some arrangements, two or three propeller shafts are used to make up the length.

In cars, the engine is located in the front, and the vehicle’s front wheels are driven. In some cars, the engine is located in the back, and the rear wheels drive. To accomplish this, each wheel is driven by a miniature propeller shaft.

The engine and transmission units are mounted to the vehicle’s frame using flexible mountings or bearings. The rear axle, differential, and wheels are all connected to the vehicle frame by a suspension spring.

To sum up, the propeller shaft does the following functions:

1. It transmits the rotary motion of the gearbox output shaft to the differential and then to the wheels through the axle shafts.
2. It transmits motion at an angle that is varying frequently.
3. It accommodates changes in length between the gearbox and rear axle.
4. It reduces rotary vibrations

In the case of cars, where the overall length of the vehicle is not too much, the propeller shaft is of a single length. On the other hand, the distance between the transmission shaft and the pinion shaft of the differential is more in the case of trucks, buses, and long chassis cars. In such cases, one or more intermediate propeller shaft is connected to the gearbox main shaft and the other end to be the main propeller shaft.

The intermediate propeller shaft is supported by a bearing unit. The bearing unit consists of a bracket, a rubber pad, and a ball bearing. The bearing bracket is attached to the cross member of the vehicle frame. The intermediate shaft arrangement reduces the length of the main propeller shaft.

Propeller shaft requirements

• Durability and high torsional strength
• Excellent welding qualities
• Excessive geometric precision, such as eccentricity and roundness
• Drawing and hammering characteristics are excellent.
• The surface quality is excellent.
• Variations in wall thickness and inner/outer diameter are kept to a minimum.
• Straightness variation is kept to a minimum.
• Axial run-out and concentricity deviations are kept to a minimum.

Propeller shaft material properties

• Torsional and fatigue strength are both high.
• Adaptability to dynamic load fluctuations
• Large Deflection angles
• Excellent characteristics for reconstructing
• ductility and homogeneous strength characteristics
• Low rotational diameter of joints, lightweight construction, flexible flange connections
• Low backlash and a wear-resistant shape minimize axial pressures in the slip design.
• Excellent weldability skills
• Corrosion resistance is minimized.
• Surface imperfections such as adhesions, scratches, and dents were reduced to a minimum.

Propeller shaft Types:

1. Single piece style propeller shaft:

• Used for automobiles between the motor and the axles with a limited distance
• The frictional welding at the junction helps increase the strength, efficiency, and reliability of the propeller shaft junction.

2. Propeller shaft of 2 portion / 3 portion:

• Used as a part of automobiles with a long distance from engine to the axle, and four-wheel-drive Front engine.
• The splitting in two or three portions of the propeller shaft allows the crucial number of revolutions to be decreased so as to avoid the vibratory problem if the total shaft length is increased.

Where is the Propeller shaft-mounted?

In some vehicles, the engine is kept at the front and the front wheels of the vehicle are being driven. In some other vehicles, the engine is at the rear and the rear wheels are being driven. For such arrangements, a short propeller shaft is used to drive each wheel.

The engine and the transmission unit are attached to the vehicle frame with some flexible mounting. The rear axle housing with differential and wheels are attached to the vehicle frame by suspension springs.

Due to the above arrangement, the transmission output shaft and the input shaft to the rear axle housing are in different planes. This compels the propeller shaft that connects these two shafts to be kept inclined.

Further, whenever the rear wheels encounter irregularities in the road, the rear axle housing moves up and down, compressing and expanding the suspension springs. As this happens, the angle between the transmission output shaft and the propeller shaft changes. Further, the length to be occupied by the propeller shaft also changes.

Propeller Shaft Diagram

The variation in the length of the propeller shaft happens because the propeller shaft and the rear axle housing rotate on arcs with different points as their centers of rotation.

The rear axle housing moves in a shorter arc than that of the propeller shaft. This is because the center of the rear axle housing arc is the point of attachment of the rear spring or control arm to the vehicle frame. This aspect causes a reduction in the length occupied by the propeller shaft as the angle between the transmission and the propeller shaft increases.

Propeller shaft parts

The propeller shaft is typically constructed from a seamless steel tube with universal joint yokes welded to both ends. Some drivelines employ a central support bearing and feature two propeller shafts and three universal joints. Two propeller shafts are used in four-wheel-drive wheels, one to drive the front wheels and the other to drive the back wheels.

In practice, the propeller shaft should be as short and strong as feasible, allowing it to withstand the bending stresses and torque responses imposed during operation. If a short length is not possible, the rigidity of the shaft can be enhanced by increasing the diameter. The shafts of propellers are either solid or tubular in design. Tubular shafts are stronger than solid shafts of the same weight, and hence offer weight savings and lower production costs.

Following are the main parts of the propeller shaft:

1. U-joint
2. Tube
3. Centre bearing
4. Midship shaft
5. End yoke
6. Slip yoke and Tube yoke
7. Flanges

U-joint

A universal joint (sometimes known as a U-joint) is a mechanical connection between rotating shafts. Driveshafts and universal joints are now more common in rear-wheel drive and four-wheel drive vehicles.

A universal joint connects the two shafts mechanically and permits angular movement of one or both shafts. It also seamlessly transfers power from the gearbox to the differential.

Road shocks will deflect the springs, altering the angle of the propeller shaft relative to the gearbox and final drive, and the shaft will bend and fracture unless a universal joint is attached to either end of the propeller shaft.

Tube

A tube is a drive shaft component that may be found in both front-engine and rear-drive automobiles. The tube’s job is to keep the rear end in place when you accelerate and brake.

Centre Bearing

A center bearing connects the two parts of the driving shaft. To prevent harmonic vibrations, these bearings are intended to keep both parts of the driveshaft solid during acceleration.

Midship Shaft

Midship shafts are the most basic components of a coupling shaft, and they’re part of a driving shaft that’s attached to the frame via a center bearing.

End Yoke

An end yoke is utilized for precision and longevity. An end yoke reduces noise and vibration, allowing your driveline to function more smoothly.

Slip Yoke and Tube Yoke

A universal joint links the driveshaft to the slip yoke. The slip yoke is used to transmit power by sliding into and out of the transfer case. For the U-joints to spin smoothly with the driving shaft, the tube yoke is also necessary.

Propeller shaft flanges

In vehicles, flanges connect the driveshaft to the gearbox, transfer case, and differential. Flanges link driveshafts to power take-offs, hydraulic pumps, and several other accessories.

Propeller shaft, and universal joint

It should be noted that power is transferred from the gearbox to the differential through the propeller shaft in front-engine, rear-wheel-drive vehicles. The universal joint connects the gearbox to one end of the propeller shaft. Another universal joint connects the differential to the opposite end of the propeller shaft. Because the back end of the propeller shaft is continually rising and falling owing to the up and down bending of the rear springs, universal joints are necessary.

Functions of universal joint

The universal joint serves the following purposes:

• Distribute power in a variety of directions.
• Allow the rear axle assembly to rotate as a result of the driving and braking torques.

Requirements for Universal joint

The following are the requirements for a modern universal joint:

Strength

High torque must be transferred with the least amount of frictional energy possible.

Compactness

Because space is restricted, the joint must be compact and durable.

Large drive angle

Because modern road springs allow for considerable wheel deflections, the joint must be able to tolerate the enormous driving angle that this movement generates.

Propeller Shaft balance

If the shaft deviates from its actual position, severe vibration develops, hence the joint must remain in proper alignment.

Operating speed

Under the conditions of high torque and varied drive angle, the joint must perform efficiently at a greater speed. This necessity must be balanced against the demand for a long-lasting, low-maintenance joint.

Types of universal joint

The universal joints are classified as follows:

1. Variable velocity joint
   • Cross or spider type
   • Flexible ring type
2. Constant velocity joint
   • Rzeppa joint
   • Tripod joint

Variable velocity joint

Although the driving and driven members turn at the same r.p.m., they do not turn at the same speed during each segment of a revolution in variable velocity joints. As a result, the driven and driving shafts should be in a straight line so that they can rotate at the same speed throughout each rotation. However, because the driving shaft of a car is slanted, this is not possible.

The driven shaft rotates slower than the driving shaft for half of a revolution and faster than the driving shaft for the other half of the revolution when the driven and driving shafts are at an angle. As a result, the driven shaft’s average speed is the same as the driving shafts. When the flex angle of the universal joint is increased, the speed variation in the driven shaft rises. Variable velocity joints are commonly utilized when the flex angle is minimal because of this.

When using two variable velocity universal joints in a single driveline, the yoke on the shafts connecting the universal joints should be in the same plane. It aids in the shaft’s balance.

The following are two types of variable velocity joints:

Cross or spider type:

Hooke’s joint is another name for it. It is the most popular type of universal joint found in vehicles because it is easy to build and performs well at modest angles (usually up to 200 degrees) for propeller shaft up and down movement. It is made up of two Y-shaped yokes that are joined at right angles by a cross or spider. The cross’s arms are known as trunnions. Between the yokes and cross ends, needle-type bearings are used, and the bearing cups are fastened to the yokes using circlips.

Flexible Ring type:

A flexible ring is used in this sort of joint, and it functions by flexing. Two or three armed spiders are fastened to the opposite faces of the flexible ring on the shafts. One spider’s arms are positioned in the middle of the other spider’s arms.

The flexible ring is generally constructed up of one or more rings of rubberized fabric sewn together in a unique way to provide the required strength. It should be mentioned that instead of fabric rings, a number of these steel discs are occasionally employed. The ring flexes continuously as the shafts rotate around their axes, allowing driving via a variety of angles. The benefits and drawbacks of this type of joint are listed below.

Constant velocity joint

A constant velocity joint has an output shaft speed that is identical to the input shaft speed at all shaft positions throughout the joint’s working range. When the connecting device between the driving and driven yokes is positioned in a plane that bisects the angle of drive, constant-velocity conditions are established.

Mounting two universal joints back-to-back (double Carden type) or positioned in a certain way at either end of the propeller shaft is one means of producing a consistent speed output from the propeller shaft. The relative locations of each joint must be adjusted in both configurations such that the speed change of one joint is counteracted by the other.

Rzeppa Joint:

As depicted in fig., a Rzeppa joint (also known as a Birfield Rzeppa joint) is made up of an inner race, a set of six spherical balls, and a cage to place the balls, and an outside housing. Outboard joints are what these joints are used for (i.e., wheel end of the axle shaft or drive shaft).

The steel balls are kept in the spherical recess’ grooves. The balls transfer the torque from one race to the next. Because of the circular arrangement of balls, both shafts rotate at the same speed.

Tripod Joint:

As illustrated in Fig., a tripod joint consists of a housing, a spider, and a set of three rollers. The spider and rollers can glide in the axial direction to adjust for any changes in driveshaft length induced by driveshaft angle fluctuation. Inboard joints are frequently utilized with tripod joints (i.e. differential end of axle shaft or drive shaft).

Why is the propeller shaft hollow?

Hollow and solid shafts are the two types of shafts. Hollow shafts are significantly lighter than solid shafts and can transfer the same torque as solid shafts of comparable size. Furthermore, the acceleration and deceleration of hollow shafts need less energy. As a result, hollow shafts have a lot of promise in the automobile sector for power transmission. Hollow shafts are traditionally made through forging and deep-hole drilling. Unfortunately, due to a large amount of material required for manufacture, this is an extremely expensive operation.

Propeller shaft balancing

An unbalanced rotating shaft will vibrate causing discomfort, noise, and a short time to failure. Balancing is adding (or removing) material to make the shaft rotate Unbalanced spinning shafts vibrate, producing discomfort, noise, and failure in a short period. Adding (or removing) material to make the shaft revolve without vibrating is known as balance.

After being evaluated in a dynamic balancing test rig, a set of balance weights was spot-welded onto a new driveshaft. It was the installation of a new shaft onto existing yokes in this example, which may have been necessary for a gearbox change or other alteration, but the makers follow the same procedure because the physics are the same.

Propeller Shaft vs Drive Shaft

Propeller Shaft

This shaft must be robust enough to withstand the driving torque’s twisting action, as well as robust enough to absorb torsional shocks. Because vibration occurs when the center of gravity does not coincide with the shaft’s axis, it must overcome the natural tendency to bow under its own weight.

A tubular-section propeller shaft is commonly employed because it has a low weight, a high resistance to misalignment, (particularly bow), a strong torsional strength, and a low inertial resistance to variations in angular speed that occur when a universal joint type coupling is often used to drive the shaft.

Due to its own weight, the shaft sags (i.e. forms a bow) near the center, even after a perfect static alignment. Due to the centrifugal impact, when this sagging becomes severe, rotation of the shaft causes the bow to rise. This distortion, or whipping of the shaft, causes a significant vibration when it reaches the whirling speed. The whirling speed or critical speed at which this situation occurs is determined by two key aspects: the hollow tube’s mean diameter and the hollow shaft length. The material is subjected to bending loads that are greater than the shearing stresses induced by transmitted torque.

Driveline shaft

Shafts are of relatively short length and are solidly constructed to allow for suspension movement if there is a problem in space. A short distance between the road wheel and the final drive housing with extensive road wheel movement due to suspension deflection is responsible for the maximum drive angle of the universal joints and the large variation in the shaft length. On either side of the driving shaft, the angle requirement is satisfied by a constant velocity (CV) joint and the variation in length is adjusted by a CV plunger. The road wheel is connected by a drive shaft to the fixed final drive assembly with an independent rear suspension in rear wheels driving vehicles.

Propeller Shaft material

The shaft of the propeller is composed of tubular hardened steel. The center bearing is placed between the two propeller shafts. The propeller shaft is made of alloy steel. They’re also available in spring steel.

What type of material should be utilized for the propeller shaft?

Aluminum, composite materials, carbon fiber, or a mixture of these materials can be used for propeller shafts and drive shafts. The type of material chosen is determined by the vehicle, its size, and its intended usage.

Propeller shaft lubrication

Always inspect the accurate filling of the Universal Joints with grease once the driveshafts have been mounted. The grease pumping should be kept going until the grease comes out of the seal. Universal Joints should be lubricated after 2000 hours of operation or 12 months, whichever comes first.

Propeller shaft grease

Always utilize Lithium Base Grease to regrease, such as IOC’s Servo Multipurpose, Indrol’s Multipurpose Grease, and Bharat Petroleum’s Multipurpose Grease MP II.

Propeller Shaft Alignments Methods

Signs of a Misalignment

Propeller shaft misalignment can be detected in a variety of methods. The following are some signs of misalignment:

• Shafts that sway
• Vibrations that are excessive
• The bearing temperature is too high.
• Make a lot of noise
• The pattern of bearing wear
• Wear on the coupling

Misalignment can take a variety of forms.

Parallel and angular misalignment are the two most common forms of misalignment. In both the vertical and horizontal planes, both forms can be found. In both directions, a jumble of parallel and angular misalignment is common.

Dial indicators, parallel blocks, taper gauges, feeler gauges, a tape measure, a 6-inch rule, and a tiny mirror are all important when completing alignments since each one has a role to perform. The employment of an alignment laser is a high-tech way of ensuring perfect alignment. An installer can place one or more bearings with extreme precision using a laser.

Propeller shaft bearings

To transmit power in the vehicle, a propeller shaft is included. They are subjected to enormous loads and stress, resulting in severe wheel misalignment. The force exerted in extreme degrees of misalignment can cause excessive wear and breakage of the shaft.

The propeller shaft, which also functions as a driving shaft, links the gearbox to the vehicle’s final gear through a Universal Joint and Centre Bearing. The vehicle’s propeller shaft is long enough and rotates at a high speed. As a result, propeller shaft components are engineered to resist misalignment while also effectively absorbing unwanted vibration.

A center bearing assembly connects the two components of the propeller shaft, which are joined and supported. “Through rubber and metal mountings, the center bearing retains the shaft in the appropriate position and links it to the engine or chassis body.” This helps to guard against bending and vertical variations by reducing vibration.