Next time you're driving along a bumpy road, consider this: someday, your car may be able to harvest previously wasted energy from that uneven road surface, simply by having a new set of shock absorbers fitted.

Researchers at the College of Engineering at Virginia Tech say they are working on a system that could use a car's suspension to recover some normally wasted energy.

Only between 10 and 16 percent of the gasoline a car burns is actually used to overcome road resistance and air drag to drive the car forward; most of the rest is lost to heat and other inefficiencies, says mechanical engineering professor Lei Zuo.

There are three areas where otherwise wasted energy might be recovered or generated; the wasted heat given off by the car's engine, the kinetic energy absorbed when the car brakes and — the focus of Zuo's work — the vibrational energy dampened by the vehicle's shock absorbers.

An energy-harvesting shock absorber could generate between 100 and 400 watts of energy in a car being driven over a normal road, and even more over rough roads, Zuo estimates.

The shock absorber he's developing can translate the vertical movement of the car's suspension into rotary motion that could drive a generator, which could provide electricity directly to the vehicle's battery or electrical systems, reducing the demand on the car's alternator.

That could translate to an increase in fuel efficiency of one to five percent, which could mean an annual fuel savings of $13 billion to $19 billion, Zuo says.

His shock absorbers utilize a unique combination of gears allowing bidirectional, up-and-down motion to be converted into the unidirectional rotational motion needed to drive a generator.

This solves a challenge inherent in converting two-way vibrational energy into constant one-way rotary motion to essentially double the amount of energy recovered, he says.

Zuo and his students have tested prototypes of the shock absorbers — built with off-the-shelf components — on campus roads and found they could harvest around 60 percent of the available vibrational energy.

With further development, 85 percent efficiency is possible, Zuo says.

No modification to existing cars would be needed, and the energy-harvesting shocks "can be integrated in the car directly without changing anything in the car," he says.

In its current form, they wouldn't be cost-effective for car owners who drive less than an hour daily, he acknowledges, which is why he's focusing on developing them for large commercial vehicles that are in motion on the roads for long stretches of time.

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