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 Engine Oil-Finder

Lightweight Driven Rigid Axle


Although invented as early as 1893 by the French company De Dion, this construction took a relatively long time to assert itself. In sports cars it made frequent appearances a good 30 years later, and then on and off, right up into the 80s. The reason for the hesitant acceptance may lie in the relatively expensive, and space-consuming construction method.

Perhaps one can use the Opel company to illustrate the problem clearly. In 1964 they brought three new, top of the range models onto the market, and wanted, in the next 4 years, to customise the technology underneath the body-work to suit the changed requirements. The original vehicles have rear-wheel drive, and rigid rear axles. Because the coach-work was built according to American design, there is ample room for change. In this particular case the conversion to the De Dion axle turns out to be sensible, particularly as the higher costs are justifiable in the top of the range vehicles. This would be rewarded with very good driving characteristics and with all the advantages of the rigid axle but without their disadvantages: a distinctive, very difficult to harness, will of its own, breaking out of the complete vehicle rear-end on corrugated road surfaces.

How it works

In the first picture, only the most important components are to be seen. First of all, the light axle casing, which connects both wheel-bearing mountings. In the middle, the final drive, which can now be bolted, together with the cardan shaft, to the vehicle floor, because it is not rigidly connected with the wheels, but through articulated axle drive shafts which also provide for a steady transmission of torque when the springs compress and rebound. The linking of the axle casing onto the car body was omitted here for purposes of clarity. An example can be seen in figure 2, here it is guided by two trailing arms (green) and a wishbone (blue). The grey coil-springs with internal shock absorbers and the red stabiliser make up the rest of the wheel suspension.

This is only one example of the guiding of the axle casing. As a part of the unsprung mass, it is important that it has little weight. By this, all components are meant, which are associated with the road directly, and not through the vehicle suspension. Large unsprung masses, such as the powered rigid axle, make it very difficult for the suspension/shock absorbers to keep everything under control. In the end, what's left are the undiminished advantages of the rigid axle, the track and camber stability. It does not matter how the construction moves, if both wheels remain on a relatively level road, the maximum contact surface between tyre and road is maintained. 08\06

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