VolvoVolvoSweden, 1927 > present49 models
4535 photos
6 videos
has revealed a new flywheel hybrid for its cars that it claims improves fuel economy by 25%. It tested the system on public roads and confirmed that it is an efficient solution. 

"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. Giving the driver an extra 80 horsepower, it makes car with a four-cylinder engine accelerate like one with a six-cylinder unit," said Derek Crabb, head of powertrain engineering at Volvo.

The Volvo unit uses a flywheel kinetic energy recovery system at the rear axle. Under braking, the internal combustion engine that drives the front wheels shuts off, and the flywheel spins at up to 60,000rpm. When the car starts moving again the inertia is transferred to the rear wheels, and the engine starts again. 

The flywheel is made from carbon fiber and weighs about 6kg (13.2lb) with a 20cm (7.87in) diameter. It spins in a vacuum to minimize friction. 

The flywheel is not enough to drive the car for significant distances like a battery hybrid might, but it does provide enough power for the car to set off without using the engine. That saves the fuel usually used to accelerate the car up to speed. The system sees its biggest gains in city driving because of its frequent starts and stops. 

It also offers major performance gains. The S60Volvo S60 Gen.2Sweden, 2009 > present252 versions
436 photos
1 video
test car with a four-cylinder engine and the flywheel hybrid could accelerate to 100km/h in 5.5 seconds, which is even faster than a S60 T6Volvo S60 T6Sweden, 2010 > present1 photo
by 0.4 seconds.