Le Mans organizers wisely avoid the tightly controlled “spec racing” approach of series like NASCAR and Formula 1. Le Mans Prototype rules encourage technological experimentation that allows engineers to exercise imagination and pursue novel ideas. It enables manufacturers to assess their latest technology in the ultimate test of automotive durability that covers a distance more than 6 times the Indianapolis 500, and approaches the combined distance of a full 20-race Formula 1 season.

It is the most prestigious auto race in the world to win.

Dynasties have been built at Le Mans, most notably Porsche (16 wins), Ferrari (9) Jaguar (7) and Bentley (6). The current leader is Audi who has won 11 races since it first raced there in 1999. Five were with gasoline engines and the last 6 with diesels.

Racing is not immune to societal concerns and it explores areas that may transfer to production cars – like reduced emissions, fuel efficiency and improved tires and brakes. For 2012 Audi launched its new R18 e-tron Quattro diesel-electric hybrid Le Mans racer.

Toyota’s hybrid entry, the TSO30 Hybrid, not surprisingly was a gasoline-electric that Toyota hoped would benefit – in both technology and image – its production gasoline-electric Prius. The two Toyota entries ran strongly until one crashed and the other’s engine failed.

While Audi does not reveal all, we know the diesel engine in its 900 kg racer is a 3.7 litre, double overhead cam, 24-valve 120-degree V6 diesel mounted longitudinally behind the driver. The exhaust valves discharge inward and the single Garrett turbocharger in the valley of the engine vee pressurizes it at up to 2.8 bar (41 psi). It develops more than 500 hp and 627 lb ft of torque, and drives the rear wheels through a 6-speed sequential transmission.

The R18 e-tron’s Audi hallmark, Quattro four-wheel drive, was achieved electrically. Only the rear wheels are engine-driven: the front wheels are motivated by a water-cooled motor/generator unit with two 100 hp electric motors. Le Mans regulations allow hybrid energy storage in battery, capacitor of flywheel.

Audi chose a flywheel specially developed from the Williams Hybrid Power flywheel kinetic energy recovery system used in Williams Formula 1 cars and Porsche racers. Flywheel advantages include higher power density than batteries or capacitors, and no deterioration in performance or life due to time or high temperature. It is rugged, light and compact and runs up to 45,000 rpm in a vacuum on ultra-efficient bearings.

A flywheel is like an electro-mechanical battery that stores energy in its mechanical rotation and releases it by slowing that rotation. Flywheels have typically been spun up mechanically, but the Williams “electric flywheel” is different. It acts as a generator or motor and there is no mechanical connection to a power source, only an electric cable.

The flywheel is formed from a mix of magnetic powder and composite material that is magnetized to create the magnetic fields. Separate permanent magnets are thus eliminated. In motor form it spins the flywheel up to speed; in generator form it draws down speed to generate electricity.

Under vehicle deceleration or braking, kinetic energy is converted to electric energy by the front wheel traction motor/generator in its generator mode. This is sent to the flywheel motor that spins the flywheel up to speed. When hybrid power is demanded (allowed only above 120 km/h) the flywheel becomes a generator supplementing the engine by energizing the front wheel traction motors. It’s an ingenious system in which electrical energy flows back and forth between the traction motor/generator and the electric flywheel as required. 

Audi ran a four-car team at Le Mans, hedging its bet on the new system with two e-trons and two non-hybrid R18 Ultra diesels. It was unnecessary caution.

The R18 e-tron hybrids validated the new technology by finishing first and second, the first hybrid win at Le Mans. The winner covered 5160 km. The conventional R18 Ultras were third and fifth. Audi’s gamble on advanced flywheel technology proved its ruggedness for possible use in production vehicles.

Bill Vance is a founding member of the Automotive Journalists Association of Canada (AJAC) and author. ( This e-mail address is being protected from spambots. You need JavaScript enabled to view it ).