Flywheel and compressed air hybrid cars

Alternative hybrid approaches replace the battery with compressed air or a flywheel.

Compressed Air

Scuderi has now released results of a computer simulation of its compressed air engine against a European economy-class engine of comparable power. The compressed air hybrid achieved a fuel economy figure of 65 miles per gallon, compared with 52 miles per gallon for the conventional engine. It also emitted 85 grams per kilometer of carbon dioxide, compared with 104 grams per kilometer for the conventional engine.




Direct Energy to and from the wheels Flywheel

The Renault Formula 1 team has adapted its motorsport-developed flywheel system for use with conventional vehicles. The team has formed a company, Flybrid Systems, to commercialize the technology, and has teamed up with Jaguar Land Rover to trial the Flybrid technology that was originally developed as the kinetic energy recovery system (KERS) used in Formula 1 racing to provide a boost during racing. But while most KERS systems work by using a flywheel to charge an onboard battery or supercapacitor, Flybrid uses a gearbox system to transfer kinetic energy directly to and from the wheels.

Flybrid cars transfer energy via either a continuously variable transmission or a less complex three-gear system, which allows 15 different gear ratios on a standard five-gear model. “There are always efficiency losses when you convert energy,” explains Flybrid’s technical director, Doug Cross. “This system eliminates those losses, making it far more efficient.”

The flywheel weighs five kilograms and is made from carbon fiber wrapped around a steel core. Because it is so light, it has to spin fast—at 60,000 rpm—which means that its rim is traveling at supersonic speeds. As a result, it has to operate in a vacuum, and Flybrid has developed special seals so that the wheel can be fully enclosed inside a safety container in case of a crash. At top speed, the flywheel can store 540 kilojoules of energy, which is sufficient to accelerate an average-sized automobile from a standing start to 48 kilometers per hour.

“One way you can use this technology is to boost the car during a cruise,” Cross said. “We have a system installed on a Jaguar saloon, and that has shown that during a cruise, you can actually switch the engine off for 65 percent of the journey. With a V6 diesel engine, it cuts fuel use by 26 percent, but gives you the power of a V8 petrol engine.
