Propeller shaft or Drive Shaft
The propeller shaft connects the transmission shaft to the pinion shaft at the wheel axle. The propeller shaft is also called driveline shaft or drive shaft.
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 of the 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.
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 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 / Components of Propeller shaft
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 centres of rotation.
The rear axle housing moves in the shorter arc than that of the propeller shaft. This is because the centre 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.
To sum up, the propeller shaft does the following functions:
1. It transmits 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 which is varying frequently.
3. It accommodates changes in length between gear box and rear axle.
In the case of cars, where the overall length of the vehicle is not too much, the propeller shaft is of 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, on or more intermediate propeller shaft is connected to the gearbox main shaft and the other end to be main propeller shaft.
The intermediate propeller shaft is supported in 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.
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 the large amount of material required for manufacture, this is an extremely expensive operation.
Propeller Shaft vs Drive 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 centre 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 centre, 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.
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 are responsible for the maximum drive angle of the universal joints and the large variation in the shaft length. At 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.
What type of material should be utilised for the propeller shaft?
Aluminum, composite materials, carbon fibre, 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 the intended usage.
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
- Bearing temperature is too high.
- Make a lot of noise
- 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 for ensuring perfect alignment. An installer can place one or more bearings with extreme precision using a laser.