Energy-saving technology taken a step beyond

A four-litre engine feels like a six-litre engine with the Flywheel KERS system. Photo / Supplied

Volvo will begin testing a Kinetic energy recovery system (KERS) on its road cars later this year.

It is a light, cheap and eco-efficient solution that makes a four-cylinder engine feel like a six and, at the same time, reduces fuel consumption by 20 per cent, says the carmaker.

Volvo will be one of the first to test the potential of flywheel technology on public roads.

"Our aim is to develop a complete system for kinetic energy recovery," says executive powertrain engineer Derek Crabb.

"This technology has the potential for reducing fuel consumption by up to 20 per cent. 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, known as Flywheel KERS, is fitted to the rear axle. Braking energy causes the flywheel to spin at up to 60,000 revs per minute. When the car starts moving off again, the flywheel's rotation is transferred to the rear wheels via a specially designed transmission.

Formula One has used a similar KERS system to aid overtaking on the race track.

Volvo's testing will turn off the combustion engine that drives the front wheels as soon as the braking begins. The energy in the flywheel can be used to accelerate the vehicle when it is time to move off again, or to power the vehicle once it reaches cruising speed.

"The flywheel's stored energy is sufficient to power the car for short periods," says Crabb. "However, this has a major impact on fuel consumption. Our calculations indicate that the combustion engine will be able to be turned off about half the time when driving."

The fuel savings will be greatest when driving in busy urban traffic as well as during active driving.

If the energy in the flywheel is combined with the combustion engine's full capacity, it will give the car an extra boost of 50kW, and the swift torque build-up translates into rapid acceleration, cutting zero to 100 km/h times significantly.

Flywheel propulsion assistance was tested in a Volvo 240 in the 1980s, and flywheels made of steel have been evaluated by various carmakers in recent years.

The flywheel that Volvo will test is made of carbon fibre. It weighs about 6kg and has a diameter of 20cm. The carbon-fibre wheel spins in a vacuum to minimise frictional losses.

"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," says Crabb.

"If the tests and technical development go as planned, we expect cars with flywheel technology to reach the showrooms within a few years."