Hybrid cars give flywheels a spin

HE next generation of hybrid cars could get a boost from an old technology - the humble flywheel. By replacing hefty batteries in hybrid electric vehicles with a lightweight flywheel that uses a novel form of magnetic gearing, a British engineering company claims that the same fuel-efficiency savings can be achieved at a much lower cost.

The system, called Kinergy, is to be tested initially in airport buses, starting this week. It uses a carbon-fibre flywheel spinning at up to 60,000 revolutions per minute to store energy recovered from the engine and braking, which it then delivers back when needed. Engineers led by Andy Atkins of Ricardo, the Shoreham-on-Sea firm that developed the system, hope it will increase buses' energy efficiency by 13 per cent in urban driving conditions.

Storing vehicles' energy in flywheels has been tried in trains and buses for decades, but the devices have typically proven too large and heavy to be practical. Ricardo's design is just 23 centimetres in diameter and the wheel weighs only 4.5 kilograms, but can deliver 30 kilowatts of power to a vehicle's transmission.

Kinergy's high speeds are possible because it spins in a vacuum - air resistance and heat would otherwise rip it apart. To transfer energy in and out of an object spinning so fast in a vacuum-sealed chamber, the team had to devise a gearing system that makes no mechanical contact.

The system achieves this through magnetic gearing, where an array of powerful permanent magnets is set into the flywheel's shaft and another array of magnets mounted on an external shaft. In between, a ring of steel segments interferes with the magnetic fields in such a way that asone shaft turns, it causes the other to spin at a different rate. With a gearing ratio of 10 to 1, the speed of rotation becomes manageable for conventional transmissions, Atkins says.

If the bus tests are successful, they could hasten the broader adoption of flywheels to help power hybrid cars. "This is going to be very attractive in mobile applications", says Alan Ruddell of the Energy Research Unit at Rutherford Appleton Laboratory in Oxfordshire, UK.

Ricardo won't be alone. Volvo announced last week that it is developing flywheel hybrids. And Jaguar is looking at commercialising a system based on the Formula 1 kinetic-energy recovery system being used by the Hope Polevision team in Le Mans, France, this month, developed by Flybrid, in Silverstone, UK. Flywheels are coming, says Flybrid founder John Hilton. "It will make hybrid technology at between a quarter and a third of the cost of electric," which in turn will make for much more affordable hybrid cars, he says.

Source New Scientist