ZF Friedrichshafen AG and Levant Power Corp., a Woburn, Massachusetts technology company spun off from MIT, have announced what they call the first fully active suspension system that includes a regenerative function that recovers energy from the motion of the suspension. The system is branded GenShock. Active suspensions are not new, General Motors experimented with an actively suspended ZR-1 Corvette when the automaker owned Lotus, which had worked with active suspensions before the technology was banned in Formula One. Going back even farther, there were the hydropneumatic Citroens and the last true Packards’ “torsion level” suspension. With road cars the goal in using such a system would be to combine good ride with good handling, soft sometimes and stiff sometimes, depending on the driving circumstances. Early tries at developing what chassis engineers call a “high bandwidth active suspension”, capable of dealing with those varying circumstances, have run into cost, complexity and power consumption issues. The GenShock system is claimed to be affordable, simple to integrate in existing suspension designs, and not only have modest power consumption but also be able to recover energy from the suspension.
The heart of the system is what Levant Power calls the Activalve TM, a device that combines electric and hydraulic motors (the companies are calling that an “electrohydraulic gear pump”) and can be adapting to standard mono, twin, and tri-tube damper configurations. Hydraulic fluid in the shock absorber is routed from the damper body through the valve, where the electric motor can be used to control the flow of fluid through the gear pump, or alternatively, the pump can be used to drive the electric motor as a generator, recovering electricity. The poorer the road quality, the more bumps there are, the more energy is recovered. Electronic controls adapt the damping characteristics to the driving situation, reducing body pitch and roll during cornering and braking. While the system adds a little bit of weight, compared to a passive suspension, it also eliminates the need to carry a jack, since the system is capable of raising or lowering each wheel independently.
Note that this is not a perpetual motion machine, like putting a wind generator on a car. It creates no new load on the powertrain, it merely recovers energy that would normally be turned into heat. ZF and Levant Power haven’t released any figures on just how much energy is recovered and whether that exceeds the power required to run the system. Like Innowatech‘s piezoelectric roadways, BMW’s Turbosteamer concept, or Purdue professor Xianfan Xu’s work recovering electricity from engine exhaust using large scale Peltier devices, the GenShock is harvesting energy that would otherwise go to waste.