Swedish automaker Volvo is developing technology that will use vehicle momentum to give a boost in fuel efficiency and performance.

Volvo's technology uses Kinetic Energy Recovery System (KERS). Cars like the Toyota Prius have long stored energy from braking to help propel the car, but the new Volvo system uses a unique method that doesn't require a large battery pack or a hybrid-style electric motor.

In the Prius, the rotating wheels are connected to a power generator. During braking, the spinning motion of the wheels creates electricity, which is stored in batteries. The batteries provide power to an electric motor that helps move the car. This is the most common way to recover braking energy.

Volvo's approach to KERS is very different. When a driver hits the brakes, energy is stored in a flywheel connected to the car's wheels. This works sort of like a high-tech version of 'spinner' style wheels (where part of the wheel keeps spinning when the car stoops). Just like those wheels, the flywheel keeps spinning when the driver brakes.

When the driver presses the accelerator, the spinning flywheel reconnects to the car's rear wheels and uses its stored energy to drive the car forward.

Volvo says its flywheel can spin at speeds up to 60,000 RPM, allowing it to store extra energy. That's more than nine times the redline limit in a Volvo C30 engine.

The constant stop and go of driving in traffic is very inefficient, which is why cars get much poorer fuel economy in the city than on the highway. Volvo says the new KERS system may allow a car's engine to shut off completely at red lights, saving the car from inefficient idling.

According to Volvo, the new system may be able to increase fuel efficiency by as much as 20 percent. But the system doesn't just provide better fuel economy. It could also give cars an extra 80 horsepower boost accelerating from a stop.

The technology could be available in new Volvo cars in the next two years.

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J. Mark Sternberg is an automotive journalist, car enthusiast and writer with a degree from the University of Arizona. Mark is a devoted Formula 1 fan and also enjoys boating, flying and attending the occasional track day.

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