Forget batteries and capacitors: Volvo is developing a new hybrid system that uses a spinning flywheel to help recoup and store energy. According to Volvo, the system could improve vehicle fuel economy by 20 percent and make a four-cylinder engine feel as powerful as a V-6.
The experimental system is called Flywheel KERS, which stands for Kinetic Energy Recovery System. (Racing fans will note the same acronym is used for a controversial hybrid technology in Formula 1.) At the system’s core is a carbon-fiber flywheel encased in a vacuum-sealed steel hub, which is mounted near the vehicle’s rear axle. The flywheel weighs 13.2 pounds and measures 7.9 inches in diameter.
When the driver brakes, a clutch connects the flywheel to the drive axle, rotating the former at up to 60,000 rpm. This captures energy that would otherwise be lost as heat when braking, much like the generator function in a traditional hybrid. When the driver accelerates, a special transmission links the flywheel to the rear axle, providing up to 80 hp of assistance. The flywheel mechanism should be able to propel the car for short distances without any engine intervention. Moreover, the car’s engine can be turned off during braking and when the car is stopped.
There are some limits to this technology. The laws of physics cannot be defeated, so the flywheel will eventually slow down and lose some of its stored energy. As such, Volvo says Flywheel KERS is best suited to city driving with frequent stops and starts — it won’t maintain very much energy after a 30-minute freeway slog, for instance.
Volvo claims to have tested the idea with in a 240 sedan back in the 1980s, but using steel for the flywheel mechanism meant it was too heavy to be practical. The new flywheel setup is said to be cheaper and lighter than the batteries and motors needed for today’s hybrid vehicles. Volvo will begin tests of the flywheel system in a car later this year, and claims that cars with the hybrid setup will go on sale “within a few years.”
A similar system was demonstrated by Porsche in the GT3 R Hybrid and 918 RSR Hybrid. Porsche’s system is designed with racing in mind, and combines electric motors with a flywheel energy-storage system. Conversely, Volvo’s system uses a mechanical flywheel connection and appears to be designed for mainstream vehicles.