Automotive shock absorber doubles as energy harvester

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

Automotive OEMs seek 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 large energy consumption. A 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 on the outside of a shock absorber from ZF, together with 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 controls oil circulation within the shock absorber, driven by an electronically controlled motor. The shock absorber characteristics automatically adapt to any driving situation; pitching motions of the car body during abrupt braking manoeuvres as well as rolling movements during fast avoiding manoeuvres, can both be eliminated almost completely. In addition, the technology can level off each wheel individually. Whenever the driving situation permits, the valve system uses  the up and down movement of the damper piston to recover  kinetic energy and transform it into electricity.

In such cases, the system diverts 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 effect can be used best if the vehicle is driving on poor roads.

ZF is contributing its expertise in active damping system (Continuous Damping Control, CDC) to the development effort with Levant Power. CDC has been introduced in 1994 and is used in more