Rear Engine Vehicles with Live Axle

This arrangement has primary advantage in buses and coaches because it allows floor to be set at low level and to be flat and clear throughout the whole length.In the Figure 1, the engine and gearbox are made as one unit mounted transversely behind the rear axle.The clutch is interposed between these two.At the other end of box is a bevel gear pair known as the transfer drive.
Now to transfer the drive to rear axle, the gear is coupled by a universal joint to a relatively short propeller shaft which is then coupled by pinion shaft to final drive unit.


Obviously, the shorter the propeller shaft, the greater is the angle through 

which it has to swing to accommodate the relative movements of both the 

engine on its mountings and the axle on its springs. Therefore, the final drive 

unit is incorporated at one side of the axle, instead of near its centre. The 

drive is turned through much less than 90° from the propeller shaft at both

its final drive and transfer drive ends, which simplifies the design of both 

pairs of gears. A difficulty with this layout is the accommodation of the 

long engine, gearbox and transfer drive within the overall width of the 

vehicle.

For this reason, several manufacturers have installed their engines 

longitudinally 

behind the rear axle. This layout has been adopted in Figure 2, 

where the gearbox is mounted separately, in front of the axle. Because the 

universal joints on the coupling shaft between the engine and gearbox have 

to accommodate only relative movements due to deflections of the mountings 

and vehicle frame or structure – instead of movements of the axles – they can 

be of a simple type. Constant velocity joints are needed, however, on the short propeller shaft.


Disadvantages of all rear-engine installations include the lengths of the 

control runs from the driving position and the fact that the driver may not be 

able to hear the engine and judge its speed, for changing gear, especially in 

noisy urban traffic. The latter problem does not arise, however, if automatic 

transmission is used.

Transverse rear-engine installations obviously call for an angle drive, and 

several transmission manufacturers produce such a unit. It generally consists 

of a bevel gear pair in a casing that can be bolted on to the gearbox or engine 

and clutch or torque-converter assembly. In Figure, a retarder – transmission 

brake – is incorporated in the gearbox, which is bolted to the angle-drive 

casing.

A coupling connects the angle drive-shaft to the engine and clutch assembly

Next up--"Dead-Axle and Axle-less Transmission" & "Four Wheel Drive Transmission"