Shock absorber harvests energy

PORTLAND, Ore. — By harvesting the energy wasted by ordinary shock absorbers, a prototype device aims to take over much of the work now performed by alternators.

In hybrid vehicles, the GenShock also could boost mileage by 10 percent. The GenShock design has been patented by Massachusetts Institute of Technology (MIT) students who formed a startup, Levant Power Corp., that is targeting heavy vehicles like Humvees and AM General's proposed Joint Light Tactical Vehicle.

In a marriage of electrical and mechanical engineering, GenShock absorbers compress hydraulic fluid as they damp the vertical motion of the shock, generating up to 1 kilowatt per shock. An active suspension system then converts into electricity the combined hydraulic pressure from all the shocks using a centralized generator.

"We have an efficient means of recovering power, one that is very effective in converting the vertical travel of a vehicle into electrical power," claimed Shakeel Avadhany, CEO of Boston-based Levant Power, who is due to graduate from MIT this fall. "We convert the vertical motion of the vehicle into rotary motion using back EMF [electromotive force] from in the generator to provide damping while converting the motion to power."

From left, Ryan Bavetta, Zack Anderson and Shakeel Avadhany, designers of the GenShock shock absorber, which can generate electricity from bumps in the road.

Ordinary shocks damp vertical motion with friction that converts energy into heat. GenShock operates similarly when the active suspension system fails or is turned off. If the active suspension electronics is working normally, however, the GenShock converts the damped vertical motion into hydraulic pressure that exactly matches the counter EMF from a centralized, hydraulically-driven electric generator.

"Our 'Eureka!' moment was when we realized that [counter] EMF mirrors the velocity-proportional damping of a shock absorber" said Avadhany.

Past attempts to generate power with shocks have used solenoid-like electricity generators inside each shock absorber. GenShock instead pressurizes hydraulic fluid, then routes all hydraulic lines to a centralized electricity generator. The generator is similar to an electric motor used to pressurize a hydraulic line, but in reverse, so that the hydraulic pressure turns the generator against the damping effect of its counter EMF.

Electronics balance and control the power-generating capabilities of each shock in the active suspension system to optimize the damping effect. This results in a smoother ride that also generates electricity from wasted energy.

Levant Power found during testing that shock absorbers on heavy trucks can generate up to a 1 kilowatt of power, or as much as as a heavy-duty alternator.

AM General is currently supplying Levant Power with a Hummer vehicle that is being used for prototyping the GenShock active suspension system. One possible use could be on the U.S. military's planned Joint Light Tactical Vehicle. The military is also interested in using GenShock to provide auxilliary power to supplement hybrid power generators used today for refrigeration.