Automakers have long sought a suspension that allows sport cars handling while maintaining the comfort of a premium luxury sedan. The difficulty in achieving this outcome rests in balancing comfort and handling; comfort requires a soft suspension to absorb bumps, while handling requires stiffness for control. Previous attempts to achieve high-bandwidth active suspension have fallen short due to cost, complexity and power consumption.

The recently agreed cooperation between ZF Friedrichshafen AG and Levant Power Corp., based in Woburn, Mass., U.S., paves the way for advancing damper technology.

We look forward to working closely together with Levant Power. The objective is to develop the world’s first fully active and regenerative suspension, make it ready for volume production and introduce it to the market. Thus, we are promoting efficient innovations that are tailored to meet global requirements.

—Rolf Heinz Rüger, in charge of the Suspension Technology business unit of ZF’s Car Chassis Technology division

GenShock’s valve technology, known as Activalve, adapts to standard damper architectures including mono, twin, and tri-tube configurations. Fluid is re-routed from the shock through the valve, where our proprietary integrated hydraulic motor can either extract power or perform work on the fluid.

The very compact unit consists of its own control unit, an electric motor and an electrohydraulic gear pump (Gerotor). Levant’s proprietary fluid porting geometries allow for the Gerotor to perform efficiently in a damper environment. The valve can either let fluid flow drive the pump and generator to create electrical power, or it can use power to pump fluid and control damper motion.

For dynamics, comfort and safety, it is essential that active forces can be applied into the chassis.

—Rolf Heinz Rüger

Activalve contains a proprietary power electronics system that dynamically controls force from each actuator, updating 10,000 times per second. It regulates bi-directional energy, rapidly switching between regeneration in semi-active mode and power consumption in fully active mode.

The damping characteristic curve not only adapts optimally and automatically to each driving situation, but bodywork pitch motions are also virtually eliminated during abrupt braking maneuvers and rolling motions. Moreover, the technology is capable of actively raising each individual wheel.

As soon as the driving situation permits, the valve system automatically uses the swaying motion of the damper piston to recover energy. Then, the system guides the oil in the damper in such a way that it drives the electric pump motor. This then functions like a generator; it converts the generated kinetic energy into electricity and feeds it into the vehicle power supply, thus contributing to a reduction in CO₂ emissions. This effect is most powerful when the vehicle is traveling on poor quality country roads.

With this project, ZF is making use of its long-standing know-how of adaptive dampers. Continuous Damping Control (CDC) has been winning over vehicle manufacturers since its market launch in 1994 and is still doing so with its fourth generation. The production numbers continue to rise; 2011 marked the temporary record high with more than 2.2 million dampers produced for the following customers: Alpina, Audi, Bentley, BMW, Ferrari, Maserati, Opel, Rolls-Royce, Mercedes-Benz, Porsche and Volkswagen.

A total of around 14 million CDC systems have already come off the production line at ZF, and the company expects an annual production of more than three million CDC units for passenger car applications alone by 2016. In addition, there are ZF systems for buses, trucks, agricultural machines and motorcycles.