We've just gotten back from Sebring where we watched a test of Audi's Le Mans R18 e-tron quattro. Two days after whipping the competition while winning the with the "old" R18, Audi was running two new versions—finished in a mysterious black—at the historic Florida circuit.
In most ways, the cars are identical. One is the R18 Ultra. The other is Audi's high-speed hybrid, the e-tron quattro. The Ultra is an updated version of the mid-engine R18 that won the last June. The e-tron earns the quattro label because its hybrid drive adds power to the front axle.
Updating the winning R18 wasn't easy. First Audi had to figure out how to take their already lightweight R18 and trim about 175 lb. from it to compensate for the added weight of the hybrid system. This would include the flywheel, the front motor and axles, the accessory components that go with the layout. The good news was that they could then distribute that weight in the non-hybrid R18 as ballast that could bring still better balance. Still, a weight reduction of 175 lb. was tough. Among the changes was a new gearbox in a carbon-fiber housing.
The Same Only Different
Though they have different paint schemes, the two cars share bodywork and the mid-mounted 510-bhp turbodiesel. To create the hybrid, Audi adds the front-drive motor and axles, which capture energy under deceleration, then transfer it to a flywheel that can shoot it back to the front axle for added acceleration. Under Le Mans' rules, the braking takes place into a corner, but feeding the power back to the front axles can only happen when the car has exceeded 75 mph.
Dr. Wolfgang Ullrich, Audi's racing guru, explains that this rule was disappointing as they had hoped to use the added power under any acceleration mode, but the 75-mph rule means "...at present it's a part-time quattro."
While Toyota's Le Mans hybrid uses supercapacitors to capture energy, Audi has opted for a flywheel. Ullrich says they feel the flywheel "...is overall the better concept system and we think there is quite some way to improve the development."
What Happens if There's an Accident?
This is not the same flywheel used in Porsche's GT3 R Hybrid. It is made of carbon fiber, has a diameter of 30 centimeters, a height of 20 centimeters, spins at up to 45,000 rpm in a vacuum and fits tightly in its enclosure. The precision fit is for safety in an accident. Ullrich explains, "If the flywheel runs out of its normal position, it touches the housing. Then the temperature goes up and because of that, the resin in the carbon fiber burns away and so the flywheel destroys itself automatically without pieces that have energy. It falls into fibers and they just create some dust and this stays inside the housing."
Wondering about any gyroscopic effect of the flywheel on the car's handling? You can tell they have checked into this, but Ullrich points out the influence of the flywheel is so small it is not a problem.
Tom Kristensen, Audi driver and 8-time winner of Le Mans, agrees and adds, "You can hear the flywheel, particularly when the engine is off but it's like a whoo whoo sound."
He gives us the driver's perspective: "We recover the energy when braking into the corner. That gives us stability into corners and you can rotate the car a little bit more because there's resistance in the front axle. That's a nice feedback to the driver. Then when you are coming out of a corner after 120 kilometers per hour (75 mph) the regulations allow you to use the recovered energy, and that's when you get the boost. Sometimes you get the boost quite aggressively and you can feel that from the front axle. It's not as much as the engine, of course, as that's the most powerful drivetrain on the car. We've driven it a little bit in damp conditions and there it feels like it can help you certain times because it gives you feedback from both axles."
So why is Audi running both the R18 Ultra and hybrid e-tron quattro? Because it likes to win and even with extensive testing, the hybrid will be a question mark going into the French classic. Audi has, however, upped the hybrid's chances by assigning it two solid driver lineups: the 2011 winning team of André Lotterer, Marcel Fässler and Benoît Tréluyer, multiple Le Mans winners Tom Kristensen, Allan McNish and Dindo Capello.