Monday, June 24, 2013

Looking beneath the skin: Comparison between Audi sports prototypes

Audi Press Release

14 years have passed since Audi competed at Le Mans for the first time. The first LMP sports car in 1999 was an Audi R8R. Today, the brand relies on the Audi R18 e-tron quattro. There is a world of difference between these two models. Dr. Martin Mühlmeier, Head of Technology at Audi Sport, has accompanied the development of the sports prototypes back then and today. A look beneath the carbon fiber skin of the race cars brings back memories of exciting developments in all areas.

Not even the mathematical calculation methods have remained the same,” says Dr. Martin Mühlmeier, Head of Technology at Audi Sport, recalling the transition period shortly before the start of the new millennium. Until 1998, all Audi race cars were still based on steel structures. Except for the 1989 Audi 90 IMSA GTO, all rally models and touring cars were directly derived from production models. “The 1999 R8R was our first concept with a stressed CFRP structure. This material exhibits a completely different behavior. While metallic materials bend or break in a crash, carbon fiber collapses. Consequently, the calculation methods used here are totally different.”

In the early phase, Dallara assisted with their experience. The Italian company acquired its expertise over many years as a constructor of ‘monoposti’ (open-wheelers) and sports prototypes. “Audi Sport ­subsequently entered the field of CFRP on its own,” Dr. Mühlmeier goes on to explain. “We implemented this know-how, strengthened our resources by recruiting highly skilled personnel and developed proprietary calculation methods. This soon made it possible for us to calculate structures, strength and crash behavior in-house.”

When comparing the 1999 R8R and the R18 e-tron quattro, 14 years of progress in all areas become evident – starting on the outside. The first car featuring a roadster concept, which laid the foundation for the ‘R’ being used in the name of the ‘R8’ model range abbreviation, looks pretty plain by today’s standards. But how can progress be measured?

Dr. Mühlmeier cites weight as an impressive example: “With the R8R we met the prescribed ­minimum weight of 900 kilograms with relatively high accuracy. Today, an R18 e-tron quattro that tips the scales at 915 kilos weighs almost the same. However, it is powered by a diesel engine, which is heavier due to its basic design, has a closed cockpit and contains a complex hybrid system. Still, it remains below the minimum weight. That’s why we can work with ballast weight on the set-up.”

How are such major strides achieved? “When we were developing our first car, a steel roll bar was typically used,” recalls Mühlmeier, who has a PhD in engineering. “As of 2000, an integrated CFRP roll bar was implemented. Since 2011, we have been fielding the R18 with a closed monocoque that is completely made of CFRP and features a one-piece design.” In the case of the body, a lot has changed as well. The first skin was designed for relatively high robustness and permitted severe body contact in duels. Now, the body consists of a very thin-layered carbon construction. The steering system is another example. In 1999, power steering was still a hydraulic system supported by the engine. Since the R10 TDI, which made its debut in 2006, the driver’s work at the wheel has been electrically assisted.

ultra-lightweight design, which achieves significant savings in current Audi production models, is desirable in all areas of racing. The suspension of the LMP sports prototypes has become notably lighter. The lithium-ion battery that has been used since the 2009 R15 TDI saved 7 kilograms of weight compared with a lead battery. One of the major single steps the engineers achieved concerned the carbon fiber transmission: Since 2012, Audi has been saving a double-digit number of kilos in just one step.

At the same time, the engineers improved the efficiency of the entire race car. Aerodynamically, the R18 e-tron quattro is a lot more efficient than the first model. Engine technology has even seen true leaps in efficiency. Not only the switch from gasoline to diesel engines in 2006 represented a major step, as the current V6 TDI engine makes very favorable fuel consumption possible. More than 20 percent fuel savings have been achieved in the diesel era. Next season, a fundamentally different set of regulations will place an even greater focus on efficiency.

But Audi has not only clearly progressed in terms of technology but also with respect to manpower. Today, a total of 250 employees are working for Audi Sport at the Ingolstadt and Neckarsulm locations. Under the direction of Audi Head of Motorsport Dr. Wolfgang Ullrich, they take care of the factory-backed motorsport commitments in the DTM and in the FIA World Endurance Championship (WEC). For 2013, new responsibilities have been established. Dieter Gass, as Head of DTM, is responsible for the program with the Audi RS 5 DTM. Chris Reinke, as Head of LMP, manages the sports car program with the Audi R18 e-tron quattro. Both report directly to Dr. Ullrich, who has overall responsibility for all factory-backed programs.

The development of the seven generations of LMP race cars

Audi R8R (1999)
On its debut, Audi opted for a conventionally designed sports car. A V8 bi-turbo unit powered the mid-engine race car. Its water radiators were installed at the front. At both the Sebring 12 Hours and the Le Mans 24 Hours, Audi celebrated a podium finish with the roadster. Its opponents at La Sarthe back then were the factory teams of Mercedes-Benz, Nissan, Toyota, BMW and Panoz.

Audi R8 (2000–2005)
Audi’s so far most successful sports prototype owes its list of 63 victories in 80 races to its concept, as well as to its long life. Five of the sports car’s six runs at Le Mans ended in victory, despite increasingly severe limitations imposed on power and performance by the regulations. In addition to constant further development of aerodynamics, the engine changed as well. In 2001, TFSI gasoline direct injection made its debut.

Audi R10 TDI (2006–2008)
Unbeaten – this is the strong track record of the Audi R10 TDI at Le Mans. Visually, the revolutionary car still bore some resemblance to its predecessor, the R8. But the V12 TDI engine with more than 650 hp was a pioneering achievement. From the cooling system to the wheelbase, from the axle load distribution to the aerodynamic concept, every area was affected by the diesel revolution.

Audi R15 TDI (2009–2010)
Audi’s last open sports car to date secured its entry in the history books. In 2010, Audi set a new distance record with the innovative roadster at the Le Mans 24 Hours. Its V10 TDI engine paved the way for VTG turbocharger technology in racing, its lithium-ion battery and LED high-beam headlights rang in a new era in other areas as well.

Audi R18 TDI (2011)
Audi ultra-lightweight technology was embodied by the R18 TDI in an exemplary way. The engineers created a lot of reserves for ideal positioning of ballast weight. Thus, the sports car powered by a V6 TDI engine excelled in delivering well-balanced handling. The closed sports car won one of the most thrilling Le Mans races in recent history with a 13.854-second advantage.

Audi R18 e-tron quattro (2012)
Visually a close relative of the R18 TDI, the R18 e-tron quattro carried the next revolution under its bodywork. The V6 TDI engine continued to drive the rear wheels. A hybrid system at the front axle completed the powertrain. A flywheel accumulator stored the recuperated energy and supplied it to the front wheels again on acceleration. The prototype immediately won the race.

Audi R18 e-tron quattro (2013)
In 2013, Audi is relying on an evolution of the revolution. The hybrid sports car has a more efficient hybrid system, new details and modern assistance systems such as the digital inside mirror and LED headlights with matrix-beam technology. Specifically for Le Mans, Audi has developed a new overall aerodynamics concept. The long-tail body catches the eye. Now, the bodywork is flush with the rear wing.