Most of us are conditioned to aim for the smoothest line down an aging roadway. It's more comfortable, it's easier on the hardware, and it's more efficient not to cause all that suspension friction, and heat dissipation in the shocks as fluid squishes through the damping holes. Ah, but what if that damping energy now lost as heat could be harnessed, in much the same way as braking heat energy is recovered by electric-regenerative braking?
The first patent applications for this general concept apparently were filed some 30 years ago, but two different groups are working to commercialize it this year. One is a 2008 Boston startup called Levant Power Corporation, founded by a group of freshly minted MIT engineers whose GenShock product is currently undergoing official military prototype testing. The company intends to follow up with products for commercial heavy trucks and maybe even hybrid cars eventually.
The other is Arizona-based Physics Lab of Lake Havasu, which started out to build a Progressive Automotive X-Prize contender by converting a late-'80s Chevy K5 Blazer into a 100-mpg plug-in hybrid. Regenerative shocks were just one of the waste-power harvesting concepts employed, but as the most commercially viable among them Physics Lab is working to bring its Regen-EV-Shocks to production for aftermarket applications.
If this idea is conjuring images of electromagnetic rams with magnetic pistons stroking up and down inside an electric coil, as in the fully active Bose suspension I covered in January 2005, think again (and keep your fingers crossed for the eventual development of that cool system). These shocks are fully hydraulic, but instead of the oil squeezing through restrictor-plate holes, it's routed through a turbine wheel, gerotor pump, or some other spinning gizmo that powers an electric generator.
Starting from that same basic premise, the two companies' designs are quite different. Levant envisions completely self-contained GenShocks packaged small enough to fit inside of or next to a coil spring with only an electrical connection to the vehicle. The Levant folks expect to be able to offer adjustable ride quality at each corner with their design. In an effort to keep costs as low as possible, Physics Lab routes the fluid from each of its Regen-EV-Shocks to a single pressure accumulator that drives a pump that spins a conventional alternator. Wheel-specific ride tuning will be trickier with this approach.
So how much power can these systems generate? It's still early in the development of each system, and different hydraulic impellor concepts are still revealing opportunities for improved efficiency, but Levant's Zack Anderson believes that a heavy vehicle like a Class-8 truck should be able to produce 2-5 kilowatts from the typical one-inch shock motions that occur continuously on normal highways, and those trucks typically consume around 3 kilowatts (refrigerated trailers need more). Relieving the engine alternator of that load promises fuel economy improvement of 2-10 percent.
Results in rough off-road environments could be even greater, helping to meet the much higher electric demands GPS, communications, and other gear place on military vehicles. Jim Stansbury pegs the output of his Regen-EV-Shocks at a similar 2-4 kilowatts on the rough roads his Blazer is expected to tackle. Neither company is prepared to talk cost yet, though when I ask how it might compare with the roughly $1800 Toyota is asking for a photovoltaic roof package on the Prius (including sunroof), Zack Anderson reckons GenShocks would likely produce more power for less money, adding that a set of aftermarket semi shocks would pay for themselves in one to two years, at a cost of $670/percentage point efficiency gain.
Whittle away at that price a bit, and it may become a cap-and-trade/CAFE bargain.
Illustration by Doug Fraser