Assignment

In motor cars, the coil spring has almost completely edged out all other spring types. This has a lot to do with the compact construction form. It can, e.g., be wrapped around the shock absorber. Even though the torsion bar spring requires very little space in an axle tube, firstly, longer tubes in the axle construction have become rarer, and secondly, the torsion bar spring is not available with progressive performance.
In contrast to the leaf spring, the the coil spring can not take over functions of the wheel suspension. So it is from the manufacturer required additional effort for possibly longitudinal or lateral arm. One can clearly see this on the rigid axle with leaf- or helical springs.

Function

A coil spring is basically, a torsion bar spring which is formed on both ends thus, that a fairly level surface is achieved for the spring-seat. Consequently, torsion (twisting) demends are also made on the wire of the coil spring. The compression limitation of the spring is, as a rule clearly defined. The individual loops lie one on top of the other (if they have the same diameter). However, contact between the loops does not occur. Before the limits are reached, an additional progressive rubber-spring comes into play. This material is often necessary between the spring-ends and the spring seats.
The above shown coil spring, for the rear axle of a front-wheel drive vehicle, looks, at first sight, as though the coils are evenly wound. Taking a closer look, one discovers that, in the center, compared with the two ends, the wire is slightly thicker. This indicates more a progressive- than a linear performance.By using different wire thicknesses or a differing spiral-pitch/loop-diameter, the properties of the spring can be altered in such a way that the force to be used for a long spring travel, slowly increases more than proportionally (progressively). An additional spring, which comes into play after a certain amount of spring travel, is also possible. The above shown picture shows a space saving Minibloc-spring. Through its progressive performance, comfortable driving without a load is combined with a large loading capacity.

Manufacture

First of all, the loop diameter and the spiral incline of the suitable coil spring is formed from a special alloy, which is mostly kept secret by the manufacturer, then cut to size in an automatic process. Then, for the better adaptation to the respective rubbers in the spring seats, it is ground at a precise angle. Of course, at the end of the process, the spray-painting and quality control takes place.