Among the cars taking part in the Le Mans 24 Hours next month will be two hybrids from the German automaker Audi.
It will be the first time Audi has entered a hybrid car at the famous endurance race, which takes place in France on June 16 and 17.
Known as the Audi R18 e-tron quattro, the car is powered by a diesel engine and an electric motor. The V-6 turbo-diesel engine is on the rear axle while the car can capture brake energy in a flywheel, which it converts into electricity which powers an electric motor on the front axle.
The hybrid system has allowed the car maker to bring back its four wheel drive quattro model, which was a highly successful race and rally car until it was banned by racing authorities in 1998.
From 1981 to 1997, Audi won four titles in the World Rally Championship, eleven national Super Touring Car Championships and a Touring Car World Cup with quattro models.
However, world racing authority the FIA banned all-wheel drive models from its racing circuit program in 1998 because it was decided the technology gave drivers an unfair advantage.
Although the four-wheel drive quattro will be allowed to compete again, a clause has been introduced into the race regulations which will limit the advantage of the quattro, especially when accelerating out of tight corners. According to the clause, the electrified axle can only be used for acceleration above a speed of 75 mph.
The added fuel economy that the capture and deployment of brake energy should result in could be a decisive factor in Le Mans since it will mean fewer pit stops. However, the 24-hour race will be significant endurance test for the hybrid technology.
In a statement the head of Audi Motorsport Dr Wolfgang Ullrich said: "We're convinced that by splitting the electric drive and the combustion drive between two axles we're achieving a positive weight distribution in the vehicle while making use of at least some of the advantages of a quattro drive system.
"After presenting our concept to the ACO and the FIA for the first time we received a relatively quick response. They saw that in the case of our hybrid solution in combination with all-wheel drive the quattro factor certainly carries some weight."
According to Audi, the electric motor works much like a dynamometer. Converters built in to the motor turn the energy generated by the brakes into direct current, which in turn drives a rotating mass storage device located alongside the driver. After cornering, the stored energy is used to power the electric motor, which in turn drives the front wheels. The car maker said that up to 150 kilowatts (kW) of short-term power can be supplied to the front axle.
Toyota also recently announced plans to return to Le Mans in 2012 with a hybrid racing car. The Japanese automaker's car will use a gasoline engine alongside a hybrid electric drive system.