Part 1 of 2 Parts
This 1994 Chrysler patriot racecar concept used a flywheel for extra power.
By Bill Visnic, Contributor
Technology developed for Formula One racing has resuscitated decade-old talk of using flywheels as the energy-storage medium for hybrid-electric passenger cars.
When the Federation Internationale de l'Automobile (FIA), the governing body of F1, quietly issued its 2009 technical regulations late last year, they included provision for F1 cars to use a "kinetic energy recovery system," or KERS. It enables the cars to recovery braking energy – as do the hybrids we drive today – and use it, on demand, as “surge power” to boost acceleration when the driver deems appropriate.
The KERS regulation effectively means F1 racecars will be hybrids come 2009.
The three British companies that cooperated on development of a kinetic system already purchased by one F1 team won the Engine Innovation of the Year award from the Professional MotorSport World Expo Awards earlier this year. The system uses a carbon-fiber composite flywheel, rather than a chemical battery, to store the braking energy.
Passenger Cars by 2012?
Underscoring the technology trickle-down theory that always has been a marketing goal of F1 racing, the companies say a similar flywheel system could be available for hybrid passenger cars as early as 2012.
Fybrid Systems LLP, Torotrak plc. and Xtrac Ltd. cooperated on development of the F1 kinetic energy system.
Flybrid is the flywheel specialist, Torotrak plc. engineered the continuously variable transmission used to transmit energy to and from the flywheel, and Xtrac, a transmission design and manufacturing company that already serves racing teams in many different motor sports, essentially acted as the transmission guru and system integrator.
The companies say the flywheel system "employs a small and sophisticated ancillary transmission manufactured by Xtrac, incorporating full toroidal traction drive technology licensed from Torotrak."
"Toroidal" means the continuously variable transmission uses a metal disc rather than pulleys and a belt or a chain to transfer torque to the drive wheels.
Xtrac, in turn, can sub-license the Torotrak transmission technology to Flybrid and other racing teams that want to use it to develop their own kinetic energy recovery systems.
Difficulties Remain
The toroidal CVT, says Torotrak marketing manager Peter O’Neill, is in low-volume pilot production now for use in ride-on lawn mowers – a long way down the evolutionary chain from F1 cars, or even passenger cars.
O'Neill acknowledges the engineering and cost difficulties Nissan Motor Co. Ltd. had with its own recent production-car toroidal CVT, but says Torotrak is working with a number of auto equipment makers and suppliers towards series production for the automotive sector.
He adds that problems Nissan had with its toroidal CVTs in cold temperatures have been overcome with help from lubrication suppliers.
It’s widely acknowledged that CVTs are efficient transmission devices – every Toyota hybrid has one. The developers say the advantage of their mechanical KERS system is that a CVT combined with a flywheel is a more efficient and effective method than chemical batteries of storing braking energy because the flywheel can more quickly accept and release large amounts of energy.
How much more efficient than batteries and a motor – the "conventional" hybrid approach?
Better Than Battery
O'Neill tells Green Car Advisor that estimated "round trip efficiency" – driveline to transmission to flywheel and back – is approximately 70 percent while the battery and motor systems also being developed for F1 cars are estimated at 31-35 per cent efficiency.
KERS flywheel (white cylinder) and CVT boost power with braking energy.
One of the main reasons for this significant difference is the number of "state changes" required for the electrical systems in moving from mechanical energy to electrical to chemical and back again, he said.
Flybrid's flywheel is a 10.6-pound composite of a carbon-fiber rim affixed to a steel hub. The entire F1 kinetic system weighs around 53 pounds, say the companies.
Safety Issue
One issue that dogged earlier flywheel energy-storage developers was assuring the flywheel would be "contained" in the event of an accident – 11 pounds spinning at 60,000 rpm has enormous potential destructive force.
Flybrid says its alloy housing, which holds the spinning flywheel in a hermetically sealed vacuum, has been crash-tested at 20-g of deceleration, reflective of a high-speed F1 impact. Nothing really broke, no high-velocity shrapnel. The housing was intact and the flywheel was still spinning.
The companies also tout the weight and packaging advantages of their KERS, which does not require a heavy battery and electric motor. The flywheel acts directly on the output shaft of the transmission via a clutch and several fixed gears. In braking-energy recovery mode, that action simply is reversed – the transmission drives the CVT, which spins the flywheel back up to its maximum speed.
Okay, it appears the award-winning mechanical KERS will be the ticket for the 2009 F1 season.
What Next?
But the racing league's rules call for a maximum limit of 60 kilowatts, about 80 horse power, that the system can recover from braking or deliver to the rear wheels. That's about a 10 percent bounce for present F1 engines that are making around 800 horsepower. The rules also limit torque output for the kinetic system to no more than 6.67 seconds of use on any single lap during a race.
A 10 percent power boost that lasts about seven seconds is great on the racetrack, but is hardly optimal for a hybrid passenger car.
So can Formula 1 flywheel-hybrid advantages translate to a family sedan?
We'll tackle that Tuesday in Part II.
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