What is the function of the leaf spring

Classic car market

The vast majority of all vehicles have steel springs. The leaf spring is the oldest steel suspension. Rigid axles guided by longitudinal leaf springs have long been the state of the art and transverse leaf springs have often taken over the work of wishbones in independent wheel suspensions.

The three types of steel springs are leaf spring, coil spring and torsion bar spring (also called torsion spring). These springs are practically always made from special spring steel. These are alloyed steels with additions of silicon and manganese, sometimes also of chromium and vanadium.
The basic rule is that a certain amount of a certain steel can absorb a certain amount of energy, that is, it can perform spring work - in theory. In practice, however, the design of the spring also plays a role.

Robust but simple

Leaf springs make the worst use of the possibilities of the material. They usually consist of several spring leaves (layered leaf springs), the cross-section, length and number of which determine the suspension properties. The leaves are connected in the middle by heart bolts or core screws, several spring clips and sometimes special bulges prevent them from shifting sideways. Since the spring length changes when the spring deflects, length compensation must also be guaranteed.

_ The simple packages also take care of axis-guiding tasks. In the picture the transverse leaf spring of the DKW suspension axis_

Basically, many spring leaves lead to a particularly hard, resilient suspension and soft suspension can be achieved with only three or four leaves. A normal leaf spring - like all steel springs that are not specially designed - has a straight characteristic curve. This means that the spring travel is linear to the load acting on the spring. However, by combining several spring assemblies with different characteristics, a progressive identification can be achieved in which the spring hardens disproportionately under heavy loads. In trucks, a roller bearing also ensures length compensation, which shortens the resilient length of the leaf spring during compression, which also hardens the spring effect.
Leaf springs are heavy and large, if only because they do not make optimal use of the energy that steel can absorb. Leaf springs with many spring layers also develop a certain amount of self-damping during their movements thanks to the resulting friction, which makes it difficult for the suspension to respond precisely.
Of course, they are not entirely without advantages: In contrast to coil springs, they can take over or support the axis guidance.

The other types of steel suspension: torsion bars and coil springs