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A group of UK companies are working on a mechanical flywheel-based energy recovery system for Formula One. This could subsequently be used for road cars.

The development is a response to new rules to make F1 more relevant. From 2009, the sport’s governing body, the FIA, will allow teams to run kinetic energy recovery systems (KERS) to reuse braking energy for acceleration. Battery-electric may be the first thing that comes to mind for passenger car developers, but some race engineers, even at Toyota F1, are focusing on high-speed flywheels to store the energy.

The group of companies is led by Flybrid Systems, set up by former technical director of Renault Formula One’s engine division Jon Hilton. It is working with transmission companies Xtrac and Torotrak.

Hilton said: “Weight is the main issue. Batteries and supercapacitors need a big device to get the power into them. It would weigh at least 50kg. Our flywheel system weighs less than 25kg.”

The firm expects to compete on cost too. The harder you cycle a battery, the shorter its life. An 80-lap grand prix could be the total lifespan of a battery. Flybrid expects a 2,000km service life for its F1 system.

The company already has one F1 customer, but Hilton declined to name it, saying only that it was not Renault.

Conforming to FIA rules, Flybrid’s F1 system can recover up to 400kJ, producing output of 60kW output. Efficiency is about 90 per cent one-way, so 8`1 per cent of the energy can return to the wheels.

The flywheel is connected to the car’s gearbox by a Torotrak toroidal continuously variable transmission (CVT). Changing the ratio controls the energy recovery.

Similar systems have been used on prototype buses in the past, but weight and gyroscopic forces of the flywheel made them impractical. Because Flybrid’s system rotates at up to 64,500rpm, the flywheel can be much smaller and lighter. The disc has a filament-wound carbon fibre rim with a steel hub and weighs 4.8kg.

It runs in a vacuum but this is created during manufacturing, not by a vacuum pump in the car. Flybrid has registered patents for the sealing concept.

Physical testing has started on a specially made test rig. Results and more details of the system’s design will be published later this year.

Some F1 teams could develop their own flywheels in-house and buy in the CVT from Xtrac. But its technical director, Adrian Moore, pointed to particular issues with that, saying: “The mechanical efficiency, compactness and mass of the variator system influences packaging and response of a flywheel KERS system.”

The development is good news for Torotrak. The UK firm has struggled to find automakers willing to license its toroidal CVT gearbox for mainstream car applications. Formula One success may open doors to OEMs.

Some have already expressed interest in Flybrid’s system for road applications. “The benefits of a system scaled for passenger cars are significant,” said Hilton. “It could store between 200 and 250kW – even cars with the least powerful engines still have brakes that can generate 500kW. The Prius can store 20kW.”

Peter Digby of Xtrac said: “There is potential to transfer this into mainstream use – particularly on sports cars.”