Shock absorber assures driving comfort - and generates electric energy

August 27, 2013 // By Christoph Hammerschmidt
Mechatronic expert ZF Friedrichshafen AG and Levant Power jointly develop active suspension that turns kinetic energy into electricity. The system is intended to utilize the advantages of an active damper and at the same time minimize energy consumption, complexity and cost.

The Holy Grail for many automotive OEMs is a suspension system that combines handling with the comfort of a luxury car. The difficulty lies the trade-off between both extremes: good comfort requires a soft cushioning that levels out bumps while for a sporty handling the damping should be rather stiff. So far, attempts to develop an active suspension system with a wide bandwidth have failed due to high cost, complexity and the exuberant energy consumption of such a system. The cooperation agreement between ZF and Levant Power aims at developing a system that combines the many benefits of an active suspension, but at very low energy consumption and acceptable cost.

The technological basis of the active recuperating suspension system to be developed is a novel functional unit mounted at the outside of a shock absorber from ZF and a specific valve technology. The compact component consists of a dedicated Electronic Control Unit (ECU), an electric motor and an electro-hydraulic pump. The latter one controls the oil circulation within the shock absorber, driven by an electronically controlled motor. "For dynamics, comfort and safety it crucial that this enables the system to feed forces into the suspension", explained Rolf Heinz Rueger, head of the shock absorbers in ZF's suspension technology division.

Thus, the shock absorber characteristics automatically adapt to any driving situation, and pitching motions of the car body during abrupt braking manoeuvres as well as rolling movements during fast avoiding manoeuvres can be eliminated almost completely. In addition, the technology can level off every single wheel. Whenever the driving situation permits, the valve system utilizes the up and down movement of the damper piston to recuperate kinetic energy and transform it into electricity.

In such cases, the system deviates the direction of oil flow to drive the electric pump motor. As a consequence, this motor works as a generator and feeds the electric energy generated into the vehicle's electric system. This