Another special feature of the A-Class chassis is an innovative selective damping system. Celebrating its world premiere in automotive construction, this new technology provides a straightforward yet extremely clever answer to a dilemma which has teased engineers for many a year. Should they favour a stiff shock absorber set-up in the interests of active safety and driving dynamics or is a softer, more comfortable setting the better all-round solution?

With the selective damping system in the new A-Class, Mercedes-Benz has killed these two birds with one stone. Working according to hydromechanical principles, this system achieves its aims without the need for complex sensors or electronics.

A brief insight into the workings of a modern shock absorber helps to clarify the func-tioning of this new development. After all, this is where the desired damping effect is generated, with wheel movements causing a valve system on the damper piston to compress oil. In so doing, flexible valve plates initiate the pre-defined resistance characteristics of the shock absorber.

With the new selective damping system, part of the oil flows through an additional valve body positioned above the damper piston itself. Inside is the control piston, which splits the valve body into two areas.

If the shock absorber experiences only minor vertical movement – consistent with a normal driving style – the control piston sits in a central position, keeping a bypass channel open, which clears the way for part of the oil to flow through the piston pin (see diagram). This oil moves past the damping valve, reducing the overall hydraulic resistance of the shock absorber. The effect is “softer” shock absorber characteristics, ensuring less road roar and tyre vibration.

If the shock absorbers are more active - during dynamic cornering or evasive manoeuvres, for example - the oil pushes the control piston in the valve body down-wards or upwards, automatically closing the bypass channel. The driver can thus rely on the full damping effect and the A-Class is stabilised to maximum effect.