Rear axle
The engine’s power comes from the differential is transmitted through
the rigid shaft called as the rear axle. It is made as two parts such as left side and right side in the vehicle and used. The axle’s inner edge is connected with the sun gear by the splines and outer edge is connected to the wheel hub. This axle withstands the weight, vibrations and torque of the vehicles.
Purpose
1. To withstand rear side weight of the vehicle.
2. To transmit the engine power to rear wheels.
3. To act as axle needle for the wheels.
4. It acts as housing for the final drive,differential and half shafts.
Forces acting on the rear axle
The following forces act on the rear axle
1. Torque reaction
2. Driving torque or driving thrust
3. Side thrust
4. Weight of the body
1. Torque reaction
When the torque is transmitted from the propeller shaft through the differential,the bevel pinion is started to rotate over the crown wheel, at the time an opposite force is developed against the direction of differential housing. This force is equalbto driving torque and operates in the opposite direction. This force produces a bending moment on the propeller shaft.
2. Driving torque
It is the torque transferred from the engine to the axle casing. The force
created due to this on the rear axle is transferred to the body through chassis frame. Radius rods in the chassis are used to transmit this drive torque to the body.
3. Side thrust
This refers to the thrust developed between the axles in the longitudinal
direction. This thrust is caused by the force of air acting on sideways. By connecting panhard rods on the chassis frame the side thrust could be minimized.
4. Weight of the body
The total weight of the goods and passengers of the vehicle acting on the axle are called as unsprung mass. They act on the axle through the springs. The total weight of the vehicle develops a shear force and bending moment on the axle. For reducing these forces powerful springs must be used.
Types of rear axle
The rear axle can be classified in to three different types according to the construction of rear axle shaft and wheel hub connections, They are
1. Semi-floating axle
2. Full-floating axle
3. Three quarter floating axle
Semi- floating axle
In this type of axle a bearing is placed in-between the axle shaft and the
axle casing. The outer axle shaft is coupled with the wheel hub by using locknut and the key. The axle shaft withstands the vehicle weight, driving thrust and transmits the power to the wheels. It is simple and cheaper compared to other types. This type is used in vehicles such as fiat 100
and standard-20.
Full floating axle
In this type, one bearing is placed at the differential housing and the two
tapper roller bearings are placed between the axle housing and wheel hub. Moreover the axle shaft is kept inside the axle housing and at its other end wheel hub is fitted by using a flange. The axle casing bears the whole weight of the vehicle and axle shaft transmits only the driving torque to the
wheels. This type of axle is used in Ashok Leyland tarus, Tata 1612, 1312, Eicher 10.80, 10.90 Mondraj vehicles.
Advantages
1. As the axle shaft transmits the power only to wheels the power output is higher.
2. Without removing the wheel and hub the axle can be removed.
3. If the axle shaft is broken, the power transmission only will be stopped.
Three quarter floating axle
In this type, one bearing is at the differential side and another bearing is placed in between the axle housing and wheel hub. The axle shaft is connected tightly with lock nut and key with the wheel hub. The axle shaft receives both driving torque and end thrust completely and bears one fourth of the vehicle’s weight. The remaining weight of the vehicle is carried out by the axle housing.It is mostly used in the ambassador and Jeep like vehicle
