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An axle on your vehicle is a rod or axle that turns the wheels and supports the weight of the car. Car and Driver explains that axles are essential components of any vehicle. Since axles conduct the power that turns the wheels, all vehicles need axles to function properly.
Type of Axle
- Rear Axle
- Front Axle
- Stub Axle
1. Rear Axle
The rear axle assembly supports 50% to 80% of the vehicle weight and also driving the rear wheels at the same time.
The rear axle assembly can be divided into the two half axle shaft that drives the wheels through a differential gear usually through a spline connection. floating axle
A housing completely enclose the short axle shaft and gear thereby protect them from dust, damage and water.
Rear axle housing is mounted on the leaf spring to prevent the vehicle from road vibration.
The live rear axle half shaft have to withstand the following loads
1) Shearing force due to weight of body.
2) Side thrust caused by side forces during turning.
3) Bending moment due to offset between the spring seat and road wheel.
4) Bending moment caused due to side forces and reaction by the tyres on the ground.
5) Driving torque transmitted to road wheel.
The rear axle are classified as per the mounting of bearing in the axle housing.
a) Semi-floating type
In this type bearings are installed in between the axle housing and the axle shaft and wheel is fitted directly to the flanged at outer end of shaft by bolts, while inner enf of the axle shaft is splines to the differential side gear.
It has to support all the load as side thrust and driving torque.
The vehicle load is transmitted to the axle through the casing and bearing which causes bending and shearing of the axle. It is simplest and cheapest than other type of axle and widely used in cars.
b) Full floating type
This type of axle two taper roller bearing are used. Bearing are placed between the axle housing and the wheel hub. Since the load of the vehicle is supported completely by the axle housing.
The axle only transmit driving torque. The inner end of the axle is supported in side gear of differential and outer end have a flange to which wheel hub is bolted.
Axle mey be removed or replaced from the housing without disturbing the wheel by removing the nut. This type of axle is more expensive and heavier than other axle. This tyep of axle is used in trucks or commercial vehicles.
c) Three quarter floating type
A single bearing is installed between the axle housing and the wheel hub and the wheel is fitted directly to the shaft.
Thus, the weight of the vehicle is transferred to the axle casing and only side thrust and driving torque are taken by the axle.
The axle is keyed rigidly to the hub, thus provide the driving connection and maintaining the alignment of the wheel. It is more reliable and robust one.
Different Stresses to be Resisted by Rear Axle
1) Shear force due to weight of body
2) Side thrust causal by side forces during tearing
3) Bending Moment due to offset between spring seat and road wheel.
4) Bending Moment due to side forces and reaction by the tyre on the groond.
5) Driving torque transmitted to road wheel.
2. Front Axle
The front axle is rigid axle called as dead axle. The front axle transmit the weight of front part of the vehicle to the road surface through the front wheels.It also caries the steering mechanism and absorbs shock due to road variation.
They are straight axle, double drop axle and fully drop axle. These are made by drop forging from steel having 0.4% carbon or 1.3% nickel steel.
The front axle is made of I section at the centre portion. While the ends are made either circular or elliptical. The I section construction takes bending loads due to the load of the vehicle and also the torque due to braking of the wheels.
To keep the chassis height low the centre portion of the front axle is given a downward sweep.
The rigid type front axle was used in connection with leaf springs. Two longitudinal leaf spring fixed to the two spring seat on the axle beam.
3. Stub Axle
The main front axle beam is connected to wheel spindle by mean of king pin or spindle bolt. The front wheels are mounted on the stud axle.The different four types of stub axle shown in below fig.
Reverse Elliot type is most common stud axle are made of 3% nickel steel and alloy steel containing chromium and molybolenum. This type of streering head, the steering knuckle is forked and the axle proper fit inside the fork.
In Elliot type, the steering knuckle is inserted between the forked end of the axle.
In the Lamoine type of steering head, the L shape steering knuckle is attached with the axle end by a pivot. It is used in tractors.
The reverse elliote type is most popular because
1) It is easier to manufacture.
2) Load exerted by the stub axle is equally distributed.
3) It is more adaptable for use with front brake and also allow a simpler steering arrangement.
A) In many heavy duty truck like Ashok leyland, Eicher, TATA etc.
B) Light duty vehicle like Metadoor etc.
Difference between Rear Axle and Front Axle
|Rear axle||Front axle|
|Rear axle is a rotary axle transmit power or motion to the wheel.||Front axle is a rigid axle transmit the weight of vehicle part to road surface.|
|It takes bending movement, torque reaction and driving thrust reaction and weight of body.||It take only weight of body.|
|This is not directly fixed to suspension system but through axle housing.||Directly fixed to suspension system depending upon type of drive.|
|For power transmission it brake into two half axle shaft.||It is a complete a straight axle.|
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