Volvo tests flywheel-based KERS technology
This autumn, Volvo Car Corporation intends to launch the tests of its flywheel-based KERS on public roads. The system could reduce fuel consumption by as much as 20 percent and make a four-cylinder engine feel like a six six-cylinder unit, the company said.
The flywheel KERS (Kinetic Energy Recovery System) will be fitted to the rear axle. During retardation, the braking energy causes the flywheel to spin at up to impressing 60,000 rpm. 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 when it is time to move off once 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. 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 according to the official New European Driving Cycle," explained Derek Crabb, Vice President VCC Powertrain Engineering.
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. Thus, similarly to HEVs, 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 80 horsepower, and thanks to the swift torque build-up this translates into rapid acceleration, cutting 0 to 100 km/h figures significantly, Volvo engineers have reckoned.
Flywheel propulsion assistance was tested in a Volvo 240 already back in the 1980s, and flywheels made of steel have been evaluated by various manufacturers in recent times. However, since a unit made of steel is large and heavy and has rather limited rotational capacity, this is not considered a viable alternative anymore. Thus, Volvo’s flywheel will be of carbon fibre. It weighs about six kilograms and has a diameter of 20 centimetres. The carbon fibre wheel spins in a vacuum to minimise frictional losses.
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