Using a combination of gears allowing motion in both directions, the energy-harvesting shock absorber works by converting the vertical vibrations of a moving car's suspension into a rotational motion that turns a generator. The generated electricity is then delivered directly to the car's battery or electronic devices, reducing demands on the alternator.
According to Lei Zuo, associate director of the Virginia Tech Center for Energy-Harvesting Materials and Systems, a car's shock absorbers should be able to provide between 100 and 400 W on normal roads (and even more on bumper roads). Tests of the energy harvesting shock absorber on campus roads, he says, have shown that the system can capture about 60% of the available energy.
The test model was constructed by students using off-the-shelf components. According to Zuo, who has previously created other types of energy-harvesting shock absorbers - including linear electromagnetic and hydroelectric absorbers - an efficiency of 85% should be achievable if this system is built using precision components and manufacturing.
The device is also retrofittable and, says Zuo, "can be integrated in the car directly without changing anything in the car." The next phase of development will focus on cost and performance - areas of obvious concern to both drivers and manufacturers.
Currently the system would not be cost efficient for vehicle owners who drive less than an hour or so a day, so the initial focus will be on commercial vehicle applications. In terms of performance, Zuo is looking into a microprocessor-controlled system using self-powered semi-active control, where suspension settings would adjust automatically to vehicle and road conditions to provide the smoothest ride and most efficient harvesting of energy.