Shock absorbers that generate electricity, which are being developed by Cambridge, MA-based Levant Power, can lower fuel consumption by 1.5 to 6 percent, depending on the vehicle and driving conditions. The system can also improve vehicle handling.

Levant has demonstrated the technology in road tests with a Humvee and will expand testing to trucks, buses, and other vehicles this summer. The shock absorbers look like conventional ones from the outside, except for a power cord coming out of one end, and they can be installed in ordinary vehicles by mechanics. They plug into a power management device that can also manage power from other sources, such as regenerative braking systems, thermoelectric devices that convert waste heat into electricity, or solar panels. The power is then fed into the car's electrical system to reduce the amount of load on the alternator.

As in a conventional shock absorber, the Levant technology uses a piston moving through oil to damp down movement. But Levant has developed a modified piston head that includes parts that spin as it moves through the oil, turning a small generator housed within the shock absorber. To improve vehicle handling, the power controller uses information from accelerometers and other sensors to change the resistance from the generators, which stiffens or softens the suspension. For example, if the sensors detect the car starting a turn, the power controller can increase the resistance from the shock absorbers on the outer wheels, improving cornering, says David Diamond, the vice president of business development at Levant.

The system performs best on heavy, off-road vehicles moving quickly over rough terrain, so the company is targeting military applications. The company has emphasized using off-the-shelf parts, where possible, to keep down costs. Diamond notes that active shock absorbers have failed commercially in the past because they were too expensive. What distinguishes the new system is its relatively low cost and ability to generate electricity, he says. The shock absorbers and control electronics will cost slightly more than conventional shock absorbers, he says, but in applications such as commercial trucking, the fuel savings are expected to pay for the extra costs within 18 months.

Lei Zuo, a professor of mechanical engineering at Stony Brook University, says researchers at Tufts University and General Motors have filed patents on their own electricity-generating shock-absorber designs. He is also developing systems of his own that use no fluids, only electromagnetic resistance. He says one of the biggest challenges in designing such systems is making them small enough to fit into existing vehicles, yet ensuring they are still capable of converting a useful amount of electricity.

Levant does not plan to manufacture the technology itself, but rather to license it to a manufacturer or create a joint venture.

Copyright Technology Review 2010.