Volvo Flywheel System Cuts Fuel Consumption 25%

Volvo Car Group says its kinetic flywheel system gives a turbocharged four-cylinder engine the acceleration of a six-cylinder turbo but with 25% better fuel economy.

The company's assessment is based on extensive on-road testing of the system last year in an S60 sport sedan.

The carbon fiber flywheel weighs about 6 kg (13 lbs) and is 20 cm (7.9 inches) in diameter.

The Flywheel KERS (kinetic energy recovery system) fits on the rear axle. The heart of the system is a carbon fiber flywheel that weighs about 6 kg (13 lbs) and is 20 cm (7.9 inches) in diameter.

The system collects braking energy, spinning the flywheel at speeds as high as 60,000 rpm. A special transmission then transfers the energy to the rear wheels when the car accelerates. Since the flywheel is activated by braking and slowly spins down when not used, the system is especially effective in stop-and-go traffic or during spirited driving.

Volvo says the system can deliver an extra 80 hp to the powertrain, enough to propel the vehicle for short periods. The company estimates its device would enable a car's engine to shut down during about half the New European Driving Cycle.

In the S60 test vehicle, the Flywheel KERS cut 0-100 kph acceleration to 5.5 seconds, according to Volvo. That is about 2 seconds quicker than the standard model.