Automobile Rear Axle types- Live and Dead Axis

Automobile Rear Axle –

Rear-axle transmits power from the differential to the wheels so that vehicle may move. Rear-axle is not a single piece but it is in two parts that are connected by the differential.
This is shown in. fig. Each part of the rear axle is called the half shaft. The outer end of the rear axle carries the wheel while the inner end is connected to the sun gear of the differential. In vehicles which employ rear-wheel drive, rear wheels are driving wheels. However, in front-wheel drive vehicles, front wheels are driving wheels. Rear axles and differential are completely enclosed in a housing to protect them from dust, dirt, water, and any possible damage.
Automobile Rear axle assembly
Automobile Rear axle assembly
Functions of Rear Axle
(a) To transmit power from the differential to the wheels. This is the main function.
(b) To carry the weight of automobiles.
Types Of Rear Axle : 
1. Live axis –  It is an axle which contains differential mechanism through which the engine power flows towards the front wheels
2. Dead Axis – It has no connection with the engine means it is dead and will not carry the engine power.
3. according to Loading arrangement 
A. Semi-floating axle hub.
B. Three-quarter floating axle hub.
C. Fully floating axle hub.
Rear Dead axle ( lazy axle)
  • A dead axle, also called lazy axle, is not part of the drive train but is instead free-rotating. The rear axle of a front-wheel-drive car is usually a dead axle.
  • Many trucks and trailers use dead axles for strictly load-bearing purposes. A dead axle located immediately in front of a drive axle is called a pusher axle.
  • A tag axle is a dead axle situated behind a drive axle. Dead axles are also found on semi-trailers, farm equipment, and certain heavy construction machinery serving the same function.
  • On some vehicles (such as motorcoaches), the tag axle may be steerable. In some designs the wheels on a lazy axle only come into contact with the ground when the load is significant, thus saving unnecessary tire wear.

Front dead axles

front dead axle
front dead axle
  • The front dead axles called as rigid axles are straight axle, double drop axle, and fully drop axle type.
  • 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 center 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 the braking of the wheels.
  • To keep the chassis height low, the center portion of the front axle is given a downward sweep.
  • It reduces the swing or sway of the vehicle while cornering and give greater stability as well as safety at high speed.
  • The center of gravity of the road vehicle was lowered by dropping the entire center portion. The dead front axle transmits the weight of the front part of the vehicle to the road surface through the front wheels.
  • It also carries the steering mechanism and absorbs shock due to road variation. The rigid type front axle was used in connection with leaf springs. The two longitudinal leaf springs fixed to the two spring seat on the axle beam.
The front dead axles are four types :
(i) Elliot axle,
(ii) Reverse type,
(iii) Lemoine,
(iv) Reversed lamoine type.

Live axle vs. Dead axle
A live axle is a type of beam axle in which the shaft (or shafts, since live axles, while connected to move as a single unit, are seldom one piece) also transmits power to the wheels; a beam axle that does not also transmit power is sometimes called a dead axle. While typically used in vehicles with Hotchkiss drive, this suspension system can also be used with other types of power transmission.

Difference Between Live axle and Dead axle :

Dead AxleLive axle
1) It has no connection with the engine means it is dead and will not carry the engine power.1) It is axle that contains a differential mechanism through which the engine power flows towards the front wheels.
2) It has sufficient rigidity and strength to transmit the weight of vehicle from the springs to the front wheels.2) In addition, to transmit weight live has to supply engine power to wheels.
3) Generally, front axle is dead in front-engine real wheel drive or rear-engine rear-wheel drive.3) Generally rear axle is live axle in front-engine real wheel drive or rear engine rear-wheel drive.
Advantages
  • The principal advantage of the beam axle is its simplicity.
  • This simplicity makes it very space-efficient and relatively cheap to manufacture.
  • They are nearly universally used in heavy-duty trucks and most light and medium-duty pickup trucks, SUVs, and vans also use a beam axle, at least in the rear.
  • Beam axles have an important advantage for off-road applications, as they provide better vehicle articulation and durability in a high load environment.
  • This simplicity also makes it relatively easy to lift a vehicle.
Disadvantages
  • The drawbacks are that it does not allow each wheel to move independently in response to bumps, and the mass of the beam is part of the unsprung weight of the vehicle, which can further reduce ride quality.
  • Also the cornering ability is typically worse than other suspension designs because the wheels have zero camber angle gain during body roll.

Types Of Rear Axle/Loading of different axle-hub arrangements

A. Semi-floating axle hub.
B. Three-quarter floating axle hub.
C. Fully floating axle hub.
Axle shafts are divided into semi-floating, three-quarter floating and fully floating depending on the stresses to which the shaft is subjected. Axle half-shafts are situated on each side of the final drive and convey motion to the road-wheels. There are basically three different arrangements of supporting axle wheel hubs on the rear axle casing.
These include :
(i) Semi-floating axle hub (commonly used on cars).
(ii) Three quarter floating axle hub (rarely used today).
(iii) Fully floating axle hub (commonly used on heavy vehicles).
Half Floating Axle/Semi Floating 
In a half floating rear axle, the axle is at the center of the axle casing and the bearings are inside the axle casing. The weight of the vehicle is transmitted first to suspension spring, then to axle casing, then to the axle and finally to the ground.
Semi Floating rear axle-Types Of Rear axle
Semi Floating rear axle-Types Of Rear axle
Three-quarter Floating Axle
In a three-quarter floating rear axle, bearings are on the outer side of axle casing, i.e. between casing and wheel. In this case, the major part of vehicle weight is taken by axle casing and not by the axle. This is the main advantage of a three-quarter floating type over half floating type. Thus, axle breakdown is less in this case compared to the previous type.
Three-quarter Floating rear axle 
Three-quarter Floating rear axle

Fully floating rear axle

In a fully floating rear axle, the bearings are provided between axle casing and the wheel. In this case, all the vehicle weight is transmitted to the ground through-axle case and wheel. The axle is not supported by bearings but it is supported at both ends. This type of axle is very strong and therefore, it is used for heavy-duty vehicles. In the event of a breakdown of the axle, the wheel cannot come out. This, is safer but costly.
Fully Floating Rear Axle 
Fully Floating Rear Axle

Sachin Thorat

Sachin is a B-TECH graduate in Mechanical Engineering from a reputed Engineering college. Currently, he is working in the sheet metal industry as a designer. Additionally, he has interested in Product Design, Animation, and Project design. He also likes to write articles related to the mechanical engineering field and tries to motivate other mechanical engineering students by his innovative project ideas, design, models and videos.

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