| Front engine- rear/four-wheel drive or rear engine/four-wheel drive |
The cardan shaft is always used when a front-mounted engine should, exclusively or additionally, drive the rear axle. It can be also necessary if a rear engine should also drive the front axle. In the so-called standard drive, the cardan shaft connects the gearbox output by way of a tunnel, with the rear final drive. With the rigid rear axle a spline end and two 90° staggeredly arranged universal joints are necessary to compensate for the vertical movement of the axle.
| The rigid axle needs more universal joints |
First of all we'll use the example of a rear final drive which is connected with the vehicle floor (independent suspension). In this case, no great amount of vertical movement must be compensated. A simple shaft-joint,
sometimes even with dry joints and without spline ends, would be sufficient. In the case of the permanent four-wheel drive, (figure 2) more effort was
expended obviously, because
of the different movement of the engine/gearbox-unit and the final drive. In the passenger car, the cardan shaft begins mostly in the gearbox with a dry joint, goes straight up to a centre bearing to drive the rear axle
through two universal joints. In some older vehicles with a simple chassis it can even be covered in this area by a casing which transfers the driving- and braking force of the rear axle to the centre bearing. Parts of the
cardan shaft then belong to the unsprung masses.
| Cardan shafts in motorcycles, trucks, agricultural machines and roller coasters |
In a straight-mounted engine with selectable front-wheel drive, the cardan shaft also goes from the gearbox output to the front axle. In utility vehicles a
second rear axle can be also
driven by it. This type of shaft without spline end is shown on top. In agricultural machinery it appears as a connecting element between drive and machine, even the multiple-looping roller coasters at the fair-ground
can not get by without them. The word 'cardan' very rightly points out the universal usability of this shaft.
Once well known in BMW, in about 1980 the cardan shaft started its triumphal march into nearly all motorcycle brands, because it was believed, that the market was screaming for less service-intensive drives. Adding
to this, it also seemed ideal for the single-arm swinging fork. In the mean time, however, disillusionment has caught up with the motorcycle branch, where (except in 'cruisers') more value is placed on low vehicle
weight. 09/08
