Control System Could Help Flywheels Beat Battery Hybrids

Silvery metal structure consisting of four cylinders attached to each other.
Photo: Eindhoven University of Technology

When I say hybrid, you probably think of a car with a big set of batteries and an electric motor. But there might be a better way, and after four years of work engineers in Europe are nearly ready to prove it. Engineers from the Eindhoven University of Technology are developing a hybrid power train that uses a flywheel to store energy instead of a battery. Compared to a gasoline engine it offers an average of 25 percent reduction in fuel usage. Compared to a hybrid electric vehicle it should be cheaper to produce and maintain.

The flywheel hybrid project is a joint venture begun about four years ago between the Eindhoven University and five companies, including Drivetrain Innovations, SKF, Bosch, CCM, and Punch Power Train. Drivetrain Innovations invented the mechanical hybrid technology and its three founders were former PhD students from the University.

Although researchers hoped to have a hybrid car up and running powered by a flywheel around September, they still had a few obstacles to over come first. One of them is the fuel optimization control system.

“The problem is that hybrids don’t use the engine often,” he says. “This means that at least in the beginning, the engine is at lower temperatures.” Since these low temperatures could result in lower engine efficiency, researchers needed to know how starting an engine at low temperatures affects fuel consumption in this unique hybrid and whether it was going to be a problem in the design of its control system.

According to Theo Hofman, assistant professor at Eindhoven University of Technology, starting an engine at low temperatures does greatly influence fuel consumption. But it doesn’t substantially affect the optimal control of a flywheel hybrid powertrain, simplifying the control system.

Apart from the control system, the flywheel power train is quite simple, consisting of a clutch and a small metal cylindrical element rotating in a vacuum chamber. Its energy comes mostly from regenerative braking, and it can be used to either start the engine or drive the car.

The beauty of the flywheel hybrid is that it stores mechanical energy directly, minimizing losses. That’s compared to a battery system where energy is lost as heat when chemical energy is stored and then converted into electric energy.

But there are host of other reasons flywheels might beat out batteries in future hybrids, according to the Eindhoven engineers. Compared to a battery hybrid, the flywheel system has a higher efficiency, no chemical waste, no degradation of lifetime, and costs less because it doesn’t require expensive power electronics. According to Hofman, the simple design of the energy-aware control system saves the driver money because of reduced fuel consumption and its simple maintenance and design.


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