Volvo Tests MPG-Boosting Flywheel Technology

ROCKLIN, NJ – This fall, Volvo Car Corp. said it plans to test flywheel technology on public roads. The company received a grant from the Swedish Energy Agency to develop next-generation technology for recovering braking energy kinetically.

"Our aim is to develop a complete system for kinetic energy recovery,” said Derek Crabb, Vice President VCC Powertrain Engineering. “Tests in a Volvo car will get under way in the second half of 2011. This technology has the potential for reducing fuel consumption by up to 20 percent. What is more, it gives the driver an extra horsepower boost, giving a four-cylinder engine acceleration like a six-cylinder unit."

The new system, which Volvo is calling the Flywheel KERS (Kinetic Energy Recovery System), is fitted to the rear axle. During stopping, the braking energy makes the flywheel to spin at up to 60,000 revs per minute. When the car starts moving again, the flywheel's rotation is transferred to the rear wheels via a specially designed transmission.

The combustion engine that drives the front wheels switches off as soon as braking begins. The energy in the flywheel can then be used to accelerate the vehicle when it is time to move again, or to power the vehicle once it reaches cruising speed. If the energy in the flywheel is combined with the combustion engine's full capacity, it will give the car an extra boost of 80 horsepower.

The flywheel that Volvo will use in its test car is made of carbon fiber. It weighs around 13 lbs. (6 kg) and has a diameter of 7.8 inches. The carbon fiber wheel spins in a vacuum to minimize frictional losses, according to the company.

"We are not the first manufacturer to test flywheel technology. But nobody else has applied it to the rear axle of a car fitted with a combustion engine driving the front wheels. If the tests and technical development go as planned, we expect cars with flywheel technology to reach the showrooms within a few years," said Crabb. "The flywheel technology is relatively cheap. It can be used in a much larger volume of our cars than top-of-the-line technology, such as the plug-in hybrid. This means that it has potential to play a major role in our CO2-cutting DRIVe Towards Zero strategy."