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Volvo is set to test a new system called Flywheel KERS (Kinetic Energy Recovery System), which it claims will make a four-cylinder engine feel like a six-cylinder and at the same time reduce fuel consumption by up to 20%. The company has received a 6.57 million Swedish kronor grant from the Swedish Energy Agency for development, in a joint project together with Volvo Powertrain and SKF.

The Flywheel KERS is fitted to the rear axle – during retardation, the braking energy causes the flywheel to spin at up to 60,000 revs per minute, and when the car starts moving off again, the flywheel’s rotation is transferred to the rear wheels via a specially designed transmission.

The combustion engine that drives the front wheels is switched off as soon as the braking begins – the energy in the flywheel can be used to accelerate the vehicle or to power the vehicle once it reaches cruising speed.

The flywheel’s stored energy is sufficient to power the car for short periods. How it will have a major impact on fuel consumption is this: based on calculations, the combustion engine will be able to be turned off about half the time when driving in a New European Driving Cycle mode.

Since the flywheel is activated by braking, and the duration of the energy storage (the length of time the flywheel spins) is limited, the technology is at its most effective during driving featuring repeated stops and starts, which means busy urban traffic.

Combining the flywheel’s energy with the combustion engine’s full capacity promises a significant boost in horsepower, and with swift torque build-up in attendance, this translates into rapid acceleration.

The flywheel – which spins in a vacuum to minimise frictional losses – that Volvo will use in its test car is made of carbon fibre, and weighs about 6 kg with a diameter of 20 cm. It’s not the first time flywheel propulsion assistance has been tested by the company – a Volvo 240 also did so back in the 1980s, but the heavy steel-based flywheel wasn’t very efficient.

Volvo also isn’t the first manufacturer to test flywheel technology, but it is in applying 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, expect cars with flywheel technology to reach the showrooms within a few years, the company says.