Extreme Aerodynamics
The Audi R15 TDI® developed in line with the Automobile Club de l’Ouest (ACO) LMP1 regulations is the first “second” generation diesel racing sports car. Apart from the basic concept it does not have much in common with its forerunner, the R10 TDI® unveiled at the end of 2005: Both are open topped roadsters with a TDI® engine, a five speed gearbox and rear wheel drive. “The step from R10 to R15 is considerably greater than it was from R8 to R10,” emphasizes Dr. Ullrich.

First Audi Prototype with "High Nose”
It is the first thing you notice about the new Le Mans sports car: The R15 TDI® is the first Audi prototype with a “high nose”. This helps to improve airflow through the roadster’s front and rear ends and reveals the basic concept of the “new one”. “The aerodynamics take precedence during the development, since they are also of great significance at Le Mans,” explains Dr. Martin Mühlmeier, Head of Technology at Audi Sport.

In the process, the Audi Sport engineers chose similar routes to the current Audi A4 from the DTM. With help of CFD calculations (Computational Fluid Dynamics) the attached airflow and specifically the airflow through the car was optimized. With the R10 TDI® the airflow was directed primarily over the bodywork, with the R15 TDI® a part of the airflow is directed through the car.

This allowed Audi Sport to reduce the car’s virtual frontal area. According to the race track, this can be used for less drag or more down force.

The design work around the rear end was particularly challenging. For the 2009 season the regulations stipulate a 40 centimeter narrower rear wing. A part of the down force lost as a result was recovered by the technicians through the extremely flat and flow optimized rear body and a novel rear wing design. The wing mountings are no longer on the underside, which is especially important for generating down force, but on the upper surface.

Also the exhaust tail pipes now emerging upwards just behind the engine have – in addition to being lighter – an aerodynamic effect: They optimize the incident flow to the rear wing.

Furthermore, to optimize the airflow the cooling air exit ducts behind the front wheels were subject to extensive refinement. They are very complex and look like gills on the R15 TDI®.

The aerodynamic concept of the front end is also entirely new featuring a high nose with air partly flowing through it. The front suspensionSuspensionSee 4-link front suspension, 4-link rear suspension, dynamic suspension, stabilizer bar, and trapezoidal-link rear suspension.Suspension cowlings are also even more refined than on the R10 TDI®.

“We are convinced that our aerodynamic concept offers a huge advantage over the R10 concept,” says Dr. Martin Mühlmeier.

The R15 project started in autumn 2007 with the engine development and the definition of the concept. The first wind tunnel tests followed at the beginning of 2008. Design work started just before the 24 Hours of Le Mans at the end of the second quarter. Every available resource was channeled into the R15 TDI® immediately after Le Mans. The maiden outing followed in December 2008.

The following development targets were given highest priority: to reduce the weight, which was partially due to the diesel engine in the R10 TDI® being heavier than a conventional gasoline engine, to decrease the slightly excessive tail-heavy weight distribution also resulting from this, in general – as is normal for every new race car – to improve the performance and to optimize the aerodynamic efficiency. To achieve this the technicians started by targeting the engine, the aerodynamics and weight.

More Compact and Lighter
Although diesel engines were restricted by the Automobile Club de l’Ouest (ACO) regulations and must now make do with approximately 10% smaller air inlets and almost 7% less turbo pressure, Audi continues to rely on TDI® power and thus the world’s arguably most efficient drive technology.

Instead of twelve, the R15 TDI® engine has ten cylinders. “In our opinion this is the best compromise for the existing ACO regulations,” says Ulrich Baretzky, Head of Engine Development at Audi Sport. “It’s not only a question of absolute power but also weight, size and drivability. This means also the engine has been subject to the strong demands of the whole package of the car.”

Two Cylinders Less
As with the V12 TDI® engine, Audi again uses the maximum displacementDisplacementThe total volume of air displaced by all the pistons within an engine block.Displacement of 5.5 liters permitted by the regulations. The removal of two cylinders, however, enables a more compact design and a significant reduction in weight. The engine therefore makes a major contribution to the R15 TDI® having a much better weight distribution than its predecessor.

The new power unit’s architecture is only partly comparable with that of the V12 TDI®; development began on September 1, 2007, the first dynamometer run was made one year later. The cylinder bank angle of 90 degrees was retained. Apart from this the engine is an entirely new development with a changed geometry.

The Audi Sport technicians did not only restrict themselves to reducing the weight and dimensions. Innovations in the used materials and the turbo-charging and fuel injection areas ensure a maximum of power and torqueTorqueTorque is what causes rotational speed to change. Just as greater net forces cause greater linear accelerations, greater torques cause greater rotational or angular accelerations.Torque and a more spontaneous throttle response and thus better engine drivability. Furthermore, the specific fuel consumption and associated CO2 emissions were further reduced.

In spite of the lower turbo pressure (2.75 instead of 2.94 bar absolute) stipulated by the regulations and the smaller air inlets (37.9 instead of 39.9 millimeter diameter) the V10 TDI® produces over 600 hp. The maximum torque still lies at about 1,000 Newton meter.

Short Exhaust Tail Pipes
The exhaust system mated to the Audi engine is completely new. The titanium tail pipes now emerge on the upper side of the bodywork directly behind the power unit. Shortening the tail pipes also saved weight. Furthermore, the gases are now channeled more perfectly onto the rear wing and, as a result, also have an aerodynamic function. The lighter, next generation diesel particle filters (DPF) are even more compact than those of the R10 TDI® and generate even less back pressure.

The new engine differs acoustically from its forerunner, the new sound is immediately evident: The V10 TDI® is still considerably quieter than a common race engine, but sounds much more aggressive and powerful than the V12 TDI®.

Proven Gearbox
Like its predecessor, the R15 TDI® also manages with five forward gears selected pneumatically via steering wheel mounted shift-paddles. The torque transmitting components of the gearbox of the gearbox are practically identical to the final lightweight version recently used in the R10 TDI®. The traction control (ASR) was further developed. The multi-function steering wheel originates from the R10 TDI® but has been given additional functions.

From Motorsport to the Production Line
In 1971 the slogan “Vorsprung durch TechnikVorsprung durch Technik"Vorsprung durch Technik" is Audi's tagline in Germany. Literally translated, it means "advancement through technology"; however, English cannot fully capture the meaning of "Vorsprung" which means "to leap ahead."Vorsprung durch Technik ” was created and since then has become the main agenda for Audi! The brand’s rise to premium manufacturer in the automobile sector was accompanied by numerous technical innovations: quattro®quattro®Audi's quattro® permanent all-wheel drive, has had over 25-year-long tradition.quattro® drive, fully galvanized bodies, the most streamlined high-volume production limousines of their day, broad introduction of gasoline engines with exhaust-gas turbo charging, development of economical direct injection diesel power units, aluminum bodyAluminum BodyThe Audi A8 is the first North American car with an aluminum body built according to the Audi Space Frame® principle. Aluminum Body , the first hybrid vehicles, gasoline direct injection and LED technology are just a few milestones in Audi’s history, which began exactly 100 years ago with the company foundation by August Horch.

Audi also demonstrates “Vorsprung durch Technik” in motorsport. The approximate 200 employees, who work under the supervision of Dr. Wolfgang Ullrich at Audi Sport in Ingolstadt and Neckarsulm, belong to the AUDI AG Technical Development (TE). And this for good reason: Audi is involved in motorsport to test new technologies and to accelerate the development. The Audi Sport engineers work closely together with their colleagues from production and pre-production development. There is a permanent exchange in both directions. Michael Dick, Member of the Board of Management with responsibility for Technical Development, is also the direct superior of Dr. Wolfgang Ullrich.

Close Cooperation Between Motorsport and Production
The new Audi R15 TDI® is an excellent example of the close cooperation between motorsport and production. The low beam light comprised solely of light emitting diodes, and fitted to the new Le Mans sports car, will be launched on the market shortly. Use at the 24 Hours of Le Mans is the final tough test for this new technology. New technologies are also used in the fuel injection and turbo charging fields which will later be introduced on the production line.

Audi frequently puts new technologies to the test initially in a motorsport environment before being introduced into road car production. Particularly impressive examples are quattro® drive, with which Audi revolutionized rallying in the 1980s and later also touring car racing, and the combination of turbo charging and gasoline direct injection (TFSI®) which was unbeatable between 2001 and 2005 at Le Mans and is found today in numerous Audi production models.

TFSI® allows a reduction in the cubic capacity, “down sizing”, of spark ignition engines, which in turn reduces the consumption and CO2 emissions. In this way Audi extracts an impressive 160 hp from a mere 1.8 liter four-cylinder engine with help of TFSI® Technology.

Accelerator Motorsport
TDI® Technology, invented by Audi, is promoted further through the motorsport program. New detail solutions are hidden in the V10 TDI® which will flow into future generations of TDI® engines.

Latest proof of the direct technology transfer from motorsport to production is the Audi Q7 V12 TDI® whose powerful 500 hp diesel engine is a close relative of the power plant that triumphed three times at Le Mans. “Audi would not be the most sporting and fastest growing brand in the premium segment today without the success in motorsport,” stresses Rupert Stadler, Chairman of the Board of Management of AUDI AG. “Everybody at Audi knows just how important motorsport is for the brand.”