Volvo has completed--on public roads--an extensive testing of its experimental kinetic flywheel technology, with the results confirming that it "is a light, financially viable and very eco-efficient solution."
"The testing of this complete experimental system for kinetic energy recovery was carried out during 2012," said Volvo Car Group powertrain engineering vice president Derek Crabb. "The results show that this technology, combined with a four-cylinder turbo engine, has the potential to reduce fuel consumption by up to 25% compared with a six-cylinder turbo engine at a comparable performance level. Giving the driver an extra 80hp, it makes a car with a four-cylinder engine accelerate like one with a six-cylinder unit."
Known as Flywheel KERS (Kinetic Energy Recovery System), the experimental system is fitted to the rear axle. During retardation, brake energy causes the flywheel to spin at up to 60,000rpm. When the car starts moving off again, the flywheel's rotation is then transferred to the rear wheels via a specially designed transmission.
Since the flywheel is activated by braking, and the duration of the energy storage is limited, the system is most effective during stop-and-start driving, which means fuel savings will be greatest when driving in busy urban traffic and 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 80hp. Thanks to the swift torque buildup, this translates into rapid acceleration, cutting the 0-100kph time by seconds. In the experimental S60 model that carried the system, the car accelerated from zero to 100kph in 5.5 seconds.
According to the Swedish carmaker, flywheel propulsion assistance was first tested in a Volvo 260 back in the 1980s. However, the flywheel then was made of steel, which is large and heavy and has a limited rotational capacity, making it an unviable option. However, with the experimental system's flywheel being made of carbon fiber, it's not only lighter and smaller but also 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," added Crabb. "The next step after completing these successful tests is to evaluate how the technology can be implemented in our upcoming car models."