The Volvo Car Group has recently completed the extensive testing of its experimental Flywheel kinetic energy recovery system (KERS) on public roads which confirmed that it is a viable solution for a light, cheap and eco-efficient component.
"The testing of this complete experimental system for kinetic energy recovery was carried out during 2012. The results show that this technology combined with a four-cylinder turbo engine has the potential to reduce fuel consumption by up to 25 per cent compared with a six-cylinder turbo engine at a comparable performance level," says Derek Crabb, Vice President Powertrain Engineering at Volvo Car Group, "Giving the driver an extra 80 horsepower, it makes car with a four-cylinder engine accelerate like one with a six-cylinder unit."
The experimental system, known as Flywheel KERS, is fitted to the car's rear axle which enables it to spin at speeds up to 60,000 rpm during braking. 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 braking begins. The energy in the flywheel can then be used to accelerate the vehicle when it is time to move off 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 80 horsepower.
Since the flywheel is activated by braking, and the duration of the energy storage - that is to say the length of time the flywheel spins - is limited, the technology is at its most effective during driving featuring repeated stops and starts. In other words, the fuel savings will be greatest when driving in busy urban traffic and during active driving.
To maximize fuel consumption savings, the flywheel used in the experimental system was made of carbon fiber to offer significant weight reduction and 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," concludes Derek Crabb.