Automobile Rear Axle types- Live and Dead Axis
Automobile Rear Axle types- Live and Dead Axis
Rear axle transmits power from differential to the wheels so that vehicle may move. Rear axle is not a single piece but it is in two parts which are connected by the differential.
This is shown in . Each part of rear axle is called the half shaft. Outer end of the rear axle carries the wheel while inner end is connected to 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.
Functions of Rear Axle
(a) To transmit power from differential to the wheels. This is main function.
(b) To carry weight of automobile.
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 asmotorcoaches), the tag axle may be steerable. In some designs the wheels on a lazy axle only come into contact with ground when the load is significant, thus saving unnecessary tire wear.
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.
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.
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 centre of the axle casing and the bearings are inside the axle casing. The weight of vehicle is transmitted first to suspension spring, then to axle casing, then to axle and finally to ground.
Three-quarter Floating Axle
In three-quarter floating rear axle, bearings are on the outer side of axle casing, i.e. between casing and wheel. In this case, major part of vehicle weight is taken by axle casing and not by axle. This is the main advantage of three-quarter floating type over half floating type. Thus, axle breakdown is less in this case compared to the previous type.
In fully floating rear axle, the bearings are provided between axle casing and the wheel. In this case, all the vehicle weight is transmitted to 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 breakdown of axle, wheel cannot come out. This, it is safer but costly.