Hybrid technology is coming to the world-famous 24 Hours of Le Mans this month, and no matter whether the winner is Audi (as expected) or Toyota (which would be an upset), it represents a significant nod toward sustainability in motor racing. According to the race organizers, Automobile Club de l’Ouest (ACO), Le Mans is “performing its role as a racing laboratory more than ever.”
What’s most intriguing to me is not who wins or loses, but rather the transfer of technology in both directions – racecar to road car and road car to racecar.
Two Approaches on the Road
Audi, like its parent company VW AG, is big on diesels, or more specifically, modern turbocharged direct-injection (TDI) diesels. In the U.S. market, Audi sells TDI A3 wagons and Q7 sport utilities. While the company has shown hybrid concepts, there are no hybrid Audi models available here.
Toyota, it goes without saying, is the hybrid king. In fact, it has sold over 3.5 million hybrid cars worldwide. In the U.S., Prius models account for about half of all hybrids sold. At the same time, Toyota has no diesel models in the U.S.
Audi’s Approach at Le Mans
Although you can be sure that both Audi and Toyota considered the ACO rules very carefully, it’s fair to say that the direction they took had as much to do with promoting their road cars as it did winning at Le Mans.
Audi has been victorious at Le Mans with turbo-diesels since 2006, and they hope to garner their 11th victory this month with their turbo-diesel/hybrid drivetrain. Just to cover their bets, however, Audi is also racing two “conventional” TDI racecars in the LMP1 (Le Mans Prototype Class 1) category. In fact, visually, the R18 Ultra (TDI) and the R18 e-tron quattro (hybrid) are identical.
The Audi hybrid racer uses a 510-horsepower, 3.7-liter TDI V6 engine to drive the rear wheels, and an electric motor to drive the front, giving the car sporadic all-wheel-drive traction. I say sporadic, because the ACO rules limit the front-drive boost from the electric motor to speeds above about 75 mph, and only for a few seconds.
Both Audi and Toyota use Kinetic Energy Recovery Systems (KERS) to generate electricity during braking – basically, the same type of regenerative braking used on production electric vehicles, like the Nissan Leaf and Chevrolet Volt. However, rather than use a battery to store electrical energy, Audi’s KERS setup feeds electricity into a flywheel accumulator before it is released to the electric motor to power the front wheels.
Unlike the limited use of KERS in Formula One, the Audi and Toyota systems are totally automatic in operation – the driver cannot control them directly – and they are much more powerful.
Summing up Audi’s approach: Diesel rear-drive plus electric motor front-drive with a flywheel electric storage device.
Toyota’s Approach at Le Mans
Toyota has developed a purpose-built 3.4-liter V8 gasoline engine without turbocharging, and a rear-mounted (actually within the transmission casing) electric motor for its hybrid TS030 racecar. No info has been released on horsepower.
Because of the ACO rules, the operation of Toyota’s electric motor is not limited to any set speed. In other words, the race organizers figured the Audi’s all-wheel-drive advantage, particularly in case of rain, would be offset by giving Toyota broader use of its hybrid system throughout the race, not just coming out of curves after braking.
In a marked departure from its road-going hybrids, the Toyota racecar uses supercapacitors instead of batteries to store and release electrical energy. These capacitors can be charged and discharged much more quickly than batteries, and they can go through many cycles of operation without any degradation in performance.
Summing up Toyota’s approach: Gasoline rear-drive plus electric motor rear-drive with a capacitor electric storage device.
Rules & Advantages
The Circuit de la Sarthe at Le Mans is about 8.5 miles long, and has been modified so that no straightaway is longer than about a mile and a quarter. Top speeds still approach 200 mph, but there are plenty of curves and lots of braking to feed the KERS devices.
To be considered a hybrid by the ACO, an LMP1 racecar must be able to travel the entire length of pit lane at 37 mph under KERS electric power alone. Regulations also limit the amount of energy the KERS devices can deliver to about 100 horsepower for 6 seconds. Again, Audi’s AWD system can only operate above 75 mph; Toyota’s rear-drive system can run at any speed.
All LMP1 cars must weigh a minimum of 1,984 pounds. The Toyota’s naturally aspirated V8 is the maximum permissible displacement of 3.4 liters; the Audi’s 3.7-liter turbo-diesel is also the largest allowed. Gasoline hybrids are allowed to carry 19.3 gallons of fuel, while diesel hybrids can only carry 15.3 gallons. Of course, diesel fuel consumption should be much less.
As you can see, there are plenty of situations where pit stops, fuel economy and weather may determine the race.
More than anything, however, Le Mans is about endurance, and if both hybrids finish the race – driving about 3,100 miles in 24 hours – it will be a major accomplishment.
I’ll let the two companies’ execs say it best.
“Audi has always consciously selected championships and categories in racing that have a close relationship to production, and therefore have technical relevance for the Audi customer,” notes Head of Audi Motorsport Dr. Wolfgang Ullrich.
“Hybrid is a core technology of Toyota so it is important to demonstrate this in a motorsport arena,” says Toyota Motorsport President Yoshiaki Kinoshita. The team’s Technical Director, Pascal Vasselon, sums it up nicely: “For any given performance level, a hybrid powertrain will achieve this with less fuel, so it is an extremely relevant technology and one we are excited to be bringing to endurance racing.”
Racing does improve the breed, as has often been noted. From rearview mirrors to fuel injection, racecars have fostered innovation. In this case, however, road-going hybrids may be influencing racing more than the other way around.