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History Suspension 5



Basically, one had already achieved a certain ideal right at the beginning of the automobile era. The rigid axle wasn't actually that bad at all, it kept the wheel at a camber of 0°, as long as the other wheel remained on the road. Unfortunately however, the two wheels were not independent of each other and for a driven-axle, the additional partial weight of the cardan shaft, the final drive and the half-axles was, by no means ideal.

In the history of the suspension, as soon as one got rid of the rigid axles, the annoying problem with the camber started. Have a look at a VW-Beetle which has '00'' at the end of it's type description. When, shortly before a curve the springs are extended, it goes into the curve with a positive camber. One might say, the danger of tipping over is built in. With the introduction of the radial- or belted tyre, this malfunction was more pronounced because these tyres stayed more doggedly in track.

'What is to be done?' said Zeus. As soon as the wheels are individually suspended, at least one joint is needed in their vicinity, to decouple the tipping of the coachwork from that of the wheels. Should the wheel be driven, an additional homo-kinetic joint belongs in the drive shaft as well. Thus, the wheels develop their own wheel-travel kinematics. Such demands can't be met by, e.g., the longitudinal link- or the torsion beam axle. One reason for the introduction of the multi-link suspension in front-wheel drives.

Apart from it's own rotation, how then, does a wheel behave when the springs are compressed? For this it must be given a wheel guide, in the simplest case, a suspension strut, well known as a McPherson strut. First of all, we would like to install this doubly strained damper vertical to the road surface, something which doesn't happen in reality of course. This is assisted by a lower lying wishbone, whose steering axis, to keep it simple, will be mounted parallel to the vehicle longitudnal axis.

We'll exclude influences from the steering, which certainly do play a part. Now we can observe, that a thus guided wheel, from the extended spring condition up to the horizontal position of the wishbone, takes on an increasingly negative camber, regardless of whether this moves from positive to zero or from zero to negative. With further compression of the spring, it once again moves towards positive. Looking at it with this example in mind, the manufacturer must ensure that when the spring compresses, the wishbone does not travel above the horizontal.

The shock absorber however, is thus mounted that the top end slants towards the rear, so that the caster, with increasing spring compression, also increases. The same thing occurs with track-spreading and a negative steering roll radius, if the shock absorber is mounted with the top end slanting slightly inwards. Thereby, I have assumed a swivel axis on the wheel, which connects the lower ball-joint with the center of the upper dome bearing. 03/17

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