Volvo Cars Tests of Flywheel Technology Confirm Fuel Savings of up to 25 Per Cent
LONDON, April 29, 2013 /PRNewswire/ –
Volvo Car Group has completed extensive testing of kinetic flywheel technology on
public roads – and the results confirm that this is a light, financially viable and very
“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 a car with a four-cylinder engine accelerate like one
with a six-cylinder unit.”
The experimental system, known as Flywheel KERS (Kinetic Energy Recovery System), is
fitted to the rear axle. During retardation, the 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.
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.
Most efficient in city traffic
“The flywheel’s stored energy is sufficient to power the car for short periods. This
has a major impact on fuel consumption. Our calculations indicate that it will be possible
to turn off the combustion engine about half the time when driving according to the
official New European Driving Cycle,” explains Derek Crabb.
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
If the energy in the flywheel is combined with the combustion engine’s full capacity,
it will give the car an extra 80 horsepower and, thanks to the swift torque build-up, this
translates into rapid acceleration, cutting 0 to 62 mph figures by seconds. The
experimental car, a Volvo S60
[http://www.volvocars.com/uk/all-cars/volvo-s60/Pages/default.aspx ], accelerates from 0 to
62 mph in 5.5 seconds.
Carbon fibre for a lightweight and compact solution
Flywheel propulsion assistance was tested in a Volvo 260 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 a viable option.
The flywheel that Volvo Cars
[http://www.volvocars.com/uk/sales-services/sales/business-sales/Pages/default.aspx ] used
in the experimental system is made 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
“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.