Automakers Give Flywheels a Spin

Technology Review
July 12, 2011

The automakers Volvo and Jaguar are testing the possibility of using flywheels instead of batteries in hybrid electric vehicles to aid acceleration and help engines operate more efficiently. The devices could reduce fuel consumption by 20 percent and would cost a third as much as batteries. Volvo will begin road-testing a car with the technology this fall.

In a flywheel system, energy from the wheels is used to spin a flywheel at high speeds. The flywheel continues spinning, storing energy until that motion can be transferred back to the wheels via a transmission. The idea isn't new, but it's hard to make flywheels efficient—a lot of energy can be lost to friction. In 1982, for example, GM engineered a flywheel system that was intended for its 1985 vehicles, but they canceled the project after discovering that the fuel efficiency improvements were less than half of what they'd expected. Advances in the technology now have automakers taking a second look. "Industry has gone from being skeptical to thinking it can be done, but there are enormous challenges," says Derek Crabb, vice president of powertrain engineering for Volvo.

Engineers who design Formula 1 race cars have tried to overcome the challenges of a flywheel system by using composite materials to save weight. To reduce friction, they've sealed the flywheels inside a vacuum chamber. In translating that system to passenger cars, automakers face the problem of how to maintain the vacuum, since the seals that connect the flywheel to a transmission aren't perfect.

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