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2012 24 Hours of Le Mans: Diesel Vs. Gas

Racing with Hybrid Technology

Text By: , Joe Rae, Photography by

If you liked the 2010 movie Clash of the Titans, the mythical adventure about Perseus and his quest to battle the Kraken monster in order to save the princess Andromeda, then you’ll love the 2012 version of the 24 Hours of Le Mans. Le Mans is an automotive endurance race, and at this year’s event, two titans of the automobile industry—number one Toyota, and number three Volkswagen (the owner of Audi)—locked horns in a battle that is ultimately for world supremacy in automotive sales.

Defending Le Mans champion Audi brought its 3.7L V-6 diesel- powered, carbon-fiber race cars to the party but this year upped the ante with the addition of a nifty flywheel-electric hybrid system (called E-Tron) and the return of its Quattro all-wheel drive. Not to be outdone, the Toyota brain trust, in a return to Le Mans after a 13-year hiatus, brought a 3.4L, 90-degree V-8 gas car, also with a hybrid system.

Diesel’s World Domination
The story begins in mid-January, when Audi’s archrival, the very successful diesel-powered Peugeot team, announced it was dropping out of the World Endurance Championship (WEC) series that had been developed by The Automobile Club de l’Ouest (ACO), leaving Audi holding the proverbial bag. Without another manufacturer in the series, no World Championship could be awarded, throwing a very wet rag on Audi’s aspirations of promoting its foray into the hybridization of its brand through racing. That’s when Toyota stepped in to replace Peugeot and give the LMP1 class the competitive life it required.

Toyota’s 3.4L V-8 Super Capacitor Hybrid
Toyota had not planned for the 2012 season to be a racing year, and according to Rob Leupen, Director of Business Operations Toyota Motorsport BmbH, it was to be a testing year, with a debut as a race team in 2013.

Indeed, Toyota missed the first two races of the series, at Sebring and at Spa. It had planned to bring its TSO30 Hybrid to Spa, but a crash during practice prior to Spa kept the team away from the race. While the Toyota team understood it faced an uphill battle against the experienced Audi team, it was not as if they were bringing a knife to a gunfight. As the world leader in hybridization of automobiles, Toyota had been working on the integration of its technology into a race car since 2006. Indeed, Toyota used the super capacitor system for regeneration on a Supra HV-R hybrid race car that won the Tokachi 24-Hour endurance race in July 2007. This Supra became the first hybrid car in the history of motorsport to win such a race.

Additionally, Toyota hired drivers from the Peugeot Le Mans team. This trio, Alexander Wurz (a two-time 24 Hours of Le Mans winner), Stephane Sarrazin, and Anthony Davidson brought an immediate infusion of knowledge and focus to the Toyota team.

Diesel Hybrid vs. Gasoline Hybrid
In this East-meets-West battle, the two teams used two different solutions to hybridization for a race car. The first challenge for each team is that batteries simply aren’t able to charge and discharge fast enough to be of any significant use in a racing scenario. Innovation is the name of the game at Le Mans, and each team brought its own vision of the future to the race track.

Audi chose a flywheel-based, power storage system, which it dubbed E-Tron and reintroduced its famous Quattro all-wheel drive with the car. Toyota took advantage of a super capacitor it believed gave it a better power-to-weight advantage. Toyota also toyed with an all-wheel-drive car, but when all was said and done, the decision was to go with a rear-wheel-drive car.

How Audi’s Diesel-Electric Hybrid Works
Audi’s E-Tron hybrid uses the concept of a kinetic energy recovery system (KERS), a concept that was actually formulated by the Nobel Prize-winning physicist Richard Feynman in the 1950s. Essentially, the idea is to accumulate energy during the braking of the car, and then use this energy either for additional acceleration out of the corner, or to improve fuel efficiency.

Audi has already showed the world the benefit of a clean-burning diesel engine, and now it’s looking for the most efficient method to harness regenerative braking energy. Its solution was to add what it calls a motor generator unit (MGU) to the front wheels of the car and mate it with an electronic flywheel accumulator to store this energy. It sounds challenging (and to a certain extent it is), but it’s a very elegant solution that allowed Audi the ability to take advantage of Feynman’s idea and stay within the limitations of the rules currently placed on hybrid cars.

Audi reengineered its R18’s Le Mans-winning design in an effort to save weight to make up for the extra weight of the hybrid system. For example, it reduced the mass of the 3.7L V-6 diesel to the point that it now weighs less than the 3.6L gasoline engine of a decade ago, yet it has about the same horsepower, more torque, and better fuel economy.

Special Rules For Hybrids
In an effort to keep the playing field somewhat level, while allowing all-wheel drive for hybrid cars, the use of the hybrid power was limited to speeds in excess of 70 mph. Having reduced the power of the diesel engine by 7 percent and further reducing the size of the fuel tanks for diesel-powered cars, it seemed to many as if Audi was being asked to fight the battle of Le Mans with one arm tied behind its back. The ACO also stipulated braking zones where the Audi and Toyota could use their recuperative power. On the Circuit du la Sarthe, there were seven zones, whereas at the shorter Spa track there were only five. In addition, the ACO required that the maximum amount of energy that could be transferred in one of these zones is 500 kilojoules.

Inside E-Tron
Here is how Audi solved the problem: The front wheels of the R18 E-Tron have two halfshafts, which are driven by the MGU. The MGUs were developed in partnership between Audi and Bosch. These units are water-cooled and have all electronics integrated into them. Each unit can generate about 100 hp. What is most amazing is that the total weight for the MGUs is less than 50 pounds. Under braking, the MGUs are driven by the wheels of the car to recuperate energy. The MGUs use electricity to accelerate a carbon-fiber flywheel (developed by Williams WHP), which is sealed in a vacuum enclosure next to the driver. This flywheel (or technically speaking, accumulator) will reach 60,000 rpm, so obviously there is a concern about safety with this mass holding so much energy and sitting next to the driver. However, the enclosure has a Plexiglas floor, and in the event of a major failure, the carbon flywheel will disintegrate and exit out this sacrificial floor.

Planetary gears adapt the transmission ratio during acceleration and braking. Each of the independently powered axles on the E-Tron Quattro (that drive the MGUs) are synchronized via electronic control strategies, which replaces the traditional center differential in previous versions of Quattro all-wheel drive. This control occurs automatically without driver intervention. The entire charging process (recuperation) is controlled by two parameters: the braking process, and the accumulator’s state of charge. The energy emission process (boost) is defined by the minimum speed of 75 mph stipulated by the regulations, the race strategy selected, the throttle pedal movement, and acceleration of the car.

By , Joe Rae
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