Audi takes a two-pronged approach this year in the 24 Hours of Le Mans and the newly created FIA World Endurance Championship (WEC) – the 2012 Audi R18 is available with and without hybrid drive. The trick: the base of both cars is completely identical, which is why the additional logistical effort is kept to a minimum for Audi Sport and the race team.
When Audi Sport designed the R18 TDI for Le Mans 2011, the technicians already had the future electrification in the back of their minds. It was not foreseeable that the new, smaller power plants would be subject to further limitations by the regulations after their first season. From the very inception of project ‘R18’ Audi Sport focused on a compact 3.7 liter V6 TDI with innovative architecture and equipped with a mono-turbocharger. This specifically now pays dividends: the engine is very compact and plays its role in compensating for the hybrid system’s additional weight. In spite of the latest restrictions imposed by the Automobile Club de l’Ouest (ACO) Audi Sport still extracts over 375 kW (510 hp) and a maximum torque exceeding 850 Nm from the power unit thanks to the efficiency of the overall concept.
At first sight the R18 ultra does not look much different to last year’s Le Mans winning R18 TDI. However, under the guidance of Technical Director Dr. Martin Mühlmeier the Audi Sport engineers have done a great job and left hardly a single area of the car untouched. The result is a largely new LMP1 prototype – including a modified carbon-fiber monocoque, which continues to excel through its one-piece construction.
“To compensate for the weight, the subject of lightweight design and construction was the focus throughout the entire car,” says Christopher Reinke, Technical Project Leader LMP at Audi Sport. “We have systematically and logically pursued ultra lightweight design and construction without compromising the aspects of safety and reliability. The same applies to the monocoque just as it does for the engine, gearbox and other components.”
Almost every component in the V6 TDI engine was completely reworked and adapted to suit the new regulations, which targeted a reduction in engine power of around seven per cent, which was achieved in the form of a smaller engine air intake restrictor (45.8 instead of 47.4 mm diameter) and a reduction in the maximum the boost pressure from 3.0 to 2.8 bar. In addition, the fuel cell volume was reduced from 65 to 60 liters and even 58 liters for the diesel hybrid.
“The target was to compensate for this as best as possible, for example through the reengineering of the combustion process and the optimization of the gas exchange – and we are extremely satisfied with the result,” says Ulrich Baretzky, Head of Engine Development at Audi Sport. “We also succeeded in making a significant weight reduction so that our 3.7 liter V6 TDI is now lighter than the 3.6 liter V8 TFSI of ten years ago – and this for approximately the same engine power, substantially more torque and considerably less fuel consumption. This is remarkable progress when you consider that diesel engines are often regarded as being
inherently heavier due to greater component load. This once again emphasizes Audi’s technical expertise.”
Innovation in the power transmission area
There is a genuine innovation in the area of the transmission: a new carbon-fiber composite gearbox housing was developed for the R18 – a premiere in endurance racing. Innovative materials and manufacturing processes to reduce mass are also used in the suspension area. The electromechanical steering, which gives the drivers even more precise feedback, is completely new.
The extremely advanced aerodynamic configuration from 2011 was initially adapted to suit the new regulations, which stipulate openings above the wheel arches. Additionally, the product concept catalogue also specified a further significant reduction in aerodynamic drag despite the increased cooling requirements for the hybrid components. Vision out of the closed cockpit was also improved through detailed optimization in the area of windshield cleaning and the area illuminated by the full LED headlights.
Fundamentally, the hybrid drive results in a slightly longer front section which also has positive effects on the overall balance of the conventionally powered twin brother that more than lives up to its model name ‘R18 ultra’: it is the lightest Le Mans prototype that Audi Sport has ever built. Accordingly, the engineers can position the additional ballast weight exactly where it is required – even if both cars have exactly the same overall weight. The regulations for LMP1 cars stipulate
“The new R18 ultra is a distinct evolution of last year’s Le Mans race winning car,” summarizes Head of Audi Motorsport Dr. Wolfgang Ullrich. “Our drivers’ impressions were positive from the first moment. Without the weight optimized R18 ultra we would have not been capable of realizing the R18 e-tron quattro which is absolutely identical with the exception of the hybrid system.”
Technical data Audi R18 ultra
Vehicle type: Le Mans Prototype (LMP1)
Monocoque: Carbon-fiber composite with aluminum honeycomb, tested according to the strict FIA crash and safety standards
Battery: Lithium ion batteries
Engine: Turbocharged 120° V6, 4 valves per cylinder, DOHC, 1 Garrett turbocharger, mandatory intake air restrictor of 1 x 45.8 mm diameter and turbo boost pressure limited to 2.8 bar absolute, diesel direct injection TDI, fully stressed aluminum cylinder block, diesel particle filter
Engine management: Bosch MS24
Engine lubrication: Dry sump, Castrol
Displacement: 3,700 cc
Power: Over 375 kW / 510 hp
Torque: Over 850 Nm
Type of drive: Rear wheel drive, traction control (ASR)
Clutch: Carbon clutch
Gearbox: Sequential, electrically activated 6-speed racing gearbox
Differential: Limited-slip rear differential
Gearbox housing: Carbon-fiber composite with titanium inserts
Driveshafts: Constant velocity sliding tripod universal joints
Steering: Electrical assisted rack and pinion steering
Suspension: Front and rear double wishbone independent suspension, front pushrod system and rear pull rod system with adjustable dampers
Brakes: Hydraulic dual circuit brake system, monobloc light alloy brake calipers, ventilated carbon disc brakes front and rear, infinitely manually adjustable front and rear brake balance
Wheels: O.Z. magnesium forged wheels
Tires: Michelin Radial, Front: 360/710-18, rear: 370/710-18
Length: 4,650 mm
Width: 2,000 mm
Height: 1,030 mm
Minimum weight: 900 kg
Fuel tank capacity: 60 liters