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Engineers found a way for cars to get energy from bumps in the road

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Staff writer ▼ | August 7, 2015
Lei Zuo, an associate professor of mechanical engineering in Virginia Tech's College of Engineering, found a way for harvesting energy from the car's suspension.
New technology   An innovative way to save some energy
Zuo explained that only 10 to 16 percent of the fuel a car consumes is actually used to drive—that is, to overcome road resistance and air drag. Most of the rest is lost to heat and other inefficiencies. With clever engineering, however, that deficit can be reduced.

Three major opportunities exist for recovering or generating energy while driving: the waste heat given off by the engine, the kinetic energy absorbed during braking, and the vibrational energy dampened by the shock absorbers, he said.

Zuo estimates that a car's shock absorbers should be able to provide between 100 and 400 watts of energy on normal roads and even more on rougher roads. By comparison, the average cell phone call uses about 1 watt. That corresponds to an increase in fuel efficiency between 1 and 5 percent, which would add up to an annual fuel savings of $13 billion to $19 billion.

His energy-harvesting shock absorber works by translating the vertical vibrations of the suspension into rotational motion that turns a generator. The generator delivers electricity directly to the car's battery or electrical devices, reducing the demand on the alternator.

This system has solved a major challenge in harvesting vibrational energy: converting bidirectional, up-and-down motion into the unidirectional motion needed to drive a generator. A unique combination of gears allows motion in both directions to be converted into electricity, essentially doubling the amount of energy that can be recovered.

Zuo, who is affiliated with the Institute for Critical Technology and Applied Science, explains that this innovation allows the generator to work at a steady speed and reduces the load on the gear teeth, making the system more efficient and reliable. Moreover, the generator keeps rotating even after the vibration has stopped, maximizing the amount of energy recovered.

He and his students have tested the shock absorber on campus roads. Their current model, which the students have built using off-the-shelf components, can harvest about 60 percent of the available energy—a substantial improvement over other designs.

Zuo said he is confident that with precision components and manufacturing the system could reach 85 percent efficiency.