Volvo tests confirm 25% better fuel economy with flywheel

Results confirm technology is light, cheap, and very eco-efficient

Published: April 25, 2013, 5:00 PM
Updated: November 22, 2021, 4:01 PM

Volvo flywheel technology

Volvo Car Group completed its extensive testing of kinetic flywheel technology on public roads and concluded that the system has the potential to reduce fuel consumption by 25% compared to a six-cylinder turbo engine at a comparable performance level. Vice-president of powertrain technology Derek Crabb said it gives the driver an extra 80 horsepower, making a car with a four-cylinder engine accelerate like a six.

The experimental system is fitted to the rear axle. Braking energy causes the flywheel to spin at up to 60,000 rpm. When the car starts moving again, the rotation is transferred to the rear wheels via a specially designed transmission. The engine driving the front wheels is switched off when braking begins, and the energy in the flywheel can be used to accelerate the vehicle to move off or power it when it reaches cruising speed.

"The flywheel's stored energy is sufficient to power the car for short periods. This has a major impact on fuel consumption. Our calculations indicate that it will be possible to turn off the combustion engine about half the time when driving according to the official New European Driving Cycle," says Derek Crabb.

Because the flywheel is activated by braking and the duration of the storage is limited, the technology works best in busy urban traffic and active driving.

Volvo tested flywheel propulsion technology in the '80s but the traditional steel units are large and heavy and have limited rotational capacity. This system uses carbon fibre and weights only about 6 kg with a diameter of 20 cm. It spins in a vacuum to minimize frictional losses.

"We are the first manufacturer that has applied flywheel technology to the rear axle of a car fitted with a combustion engine driving the front wheels. The next step after completing these successful tests is to evaluate how the technology can be implemented in our upcoming car models," Crabb said.