Audi R10 Diesel Race Car

This article was first published in 2006.

Audi has built a new Le Mans car – and this one’s a diesel. There have been diesel race cars before – and of course racing trucks are diesels – but no company has previously brought this level of technology to the task.

Engine

The heart of the Audi R10 is a completely new V12 TDI engine with a capacity of 5.5 litres – the maximum permitted at Le Mans. Power exceeds 650hp and a peak torque of more than 1100 Newton metres is available.

"This engine is the specifically most powerful diesel there is in the world and, up until now, the biggest challenge that Audi Sport has ever faced in its long history,” says Ulrich Baretzky, Head of Engine Technology at Audi Sport.

"There has never been anything remotely comparable. We started development with a clean sheet of paper.”
 
The V12 TDI used in the R10 is the first Audi diesel engine with an aluminium crank case. The cylinder-bank angle is 90 degrees. The V12 TDI has four valves per cylinder and twin overhead camshafts. The fuel injection system uses the Common Rail approach now found on nearly all production cars, but the injection pressure “easily exceeds” 1600 bar, so is much higher than conventional. The ignition pressures also reach values never previously seen in any Audi engine.
 
The turbo boost is produced by two Garrett turbochargers limited by the regulations to 1.94 Bar boost. The diameter of both engine air intake restrictors, stipulated by the regulations, is 2 x 39.9 millimetres. The engine management is controlled by the latest generation Bosch Motronic (MS14).
 
The engine’s usable power band lies between 3000 and 5000 rpm.
 

Unfamiliar to the driver is the low noise level and, unique for a racing engine, the smooth running V12 TDI power unit. At high speeds the engine cannot be heard from the Audi R10 prototype’s open cockpit, while Audi claims there is also hardly any vibration.

For the 24 Hours of Le Mans, the V12 TDI is equipped with a pair of diesel particle filters. Flashes of flame from the exhaust, which are created by unburned petrol in spark-ignition engines, are not seen coming from the R10.
 
One of the diesel engine’s biggest advantages is the low fuel consumption, especially at part-throttle and overrun. However, when compared to more classic circuits which demand a higher ratio of part throttle, the lower specific consumption will hardly be noticeable at Le Mans because the quota of full-throttle is almost 75 percent.
 
The enormous torque of over 1100 Newton metres posed previously unforeseen demands in the development of the R10 drive train. Even the latest generation of engine dynamometers at Audi Sport had to be reequipped with special gearboxes capable of withstanding the unusual forces.
 
Inside the V12 TDI, the extremely high pressures create forces never seen before in a racing engine. However, the main target of the Audi technicians is to reach the reliability level of the previous R8, which did not record a single engine failure in the 77 races it has contested to date.

Chassis

One of the most significant differences to its predecessor, the R8, is the integration of monocoque and bodywork. The R8 still had a traditional chassis clothed in synthetic bodywork, whereas the majority of the carbon-fibre parts belonging to the R10 monocoque are now suspended directly in the airflow and therefore require no additional fairings.

"The R8 originates from 1999 and we’ve gathered a huge amount of know-how since then,” says Wolfgang Appel, Head of Vehicle Technology at Audi Sport. "All this experience found its way into the new R10.”
   
This leads to a significant weight saving when compared with the R8, which is of particular importance since the dimensions of the 5.5 litre V12 TDI engine mated to the R10 is both longer and heavier than the 3.6 litre V8 power plant fitted to the R8. That’s why the new R10 has a significantly longer wheelbase than its predecessor.
 
The R10’s aerodynamic configuration is also refined over the R8. Although the new LM P1 regulations created by the ACO (Automobile Club de l’Ouest) targeted a 15 per cent reduction in overall downforce, the Audi Sport technicians managed to regain the majority of aerodynamic efficiency lost as a result of this through intensive wind tunnel work. The R10 silhouette is 50mm flatter than its predecessor and has a much more pointed nose.
 
The "steps” in the front splitter, the larger distance between the track and the side pods and the additional roll-over structure on the passenger side are all stipulated by the regulations.

The bulk of the changes implemented by the rule makers were made to make the powerful sport-prototypes even safer. Included in this catalogue of changes is the use of the HANS-System (Head and Neck Support), familiar in Formula 1, that protects the driver’s spine in the event of an accident.
 
Although the R10 prototype’s carbon-fibre monocoque is more waisted than that of the R8, the drivers can sit comfortably in the cockpit – a factor not to be underestimated in a 24-hour race like at Le Mans. The servo steering, which is now electric instead of hydraulic, also helps to increase comfort.
 
A similar direction to that taken in production cars was followed with the electronics. The number of electronic control units rose considerably when compared with the R8. A "network” system (CAN-Bus) runs through the entire R10; all important functions are controlled centrally by computers. Even the indicators and headlights are no longer directly activated by the driver, he simply makes a manual impulse – everything else is done by the on-board computers.
 
Together with electronic partner Bosch, a new vehicle data logging system (FDE) was developed for the R10. All data is transmitted by telemetry to the pits and shown in the cockpit on a steering wheel mounted display. The most important functions are controlled by buttons mounted on the steering wheel, which is equipped with a micro-processor and was developed together with the specialist company Megaline.

The Megaline experts were also involved in the development of the electro-pneumatic shift mechanism, which is activated in the R10 by two steering-wheel mounted paddles. The gearbox itself originates from X-trac and, despite the enormous torque produced by the TDI engine, is lighter than that of the R8.
 
Thanks to the turbo-diesel engine’s characteristics, the number of gear changes made during a 24-hour race falls significantly – an important factor concerning durability, particularly as the transmission system is subject to extremely high loads.
 
Because of the high level of torque produced by the V12 TDI, the forces acting on the R10 transmission system are even greater than those experienced by a Formula 1 racing car. The gearbox was conceived to withstand these forces, as are the driveshafts which are thicker than the ones on the R8. The same is valid for the novel ceramic clutch that was developed together with ZF Sachs.
 
The greater thermal discharge and the corresponding increase in cooling requirements are also diesel-specific. Higher side pods, in which the larger coolers are fitted, are the result. The wider front tyres, which were commissioned by tyre partner Michelin, are completely new to the LM P1 class. The use of traction control reduces the high loads created by the torque fed to the rear tyres, and helps the driver to modulate the V12 TDI engine’s power delivery, particularly in wet conditions.

The refuelling system, re-developed with specialist company Stäubli, allows a fast and virtual splash-free refuelling process. In contrast to petrol, spilled diesel does not evaporate. As was the case with the R8, various coloured LEDs located close to the refuelling inlet vent act as initial visual information indicating the diesel, engine oil and water levels to the mechanics during a pit stop.
 
Fans at Le Mans will no longer be able to see glowing brake discs on the Audi R10: the carbon-fibre brakes discs are fully enclosed in a cowling. Just like on Formula 1 cars, the brake discs are no longer fed with cooling air through pipes but are cooled by air channelled through carbon-fibre ducts mounted directly to the suspension.
 
The daytime low-beam lights use a row of white light-emitting diodes and the rear lights are also LEDs.

Development

The idea to develop a diesel sportscar for the 24 Hours of Le Mans had already emerged in 2002 but things became very serious in September 2003 when the concept guidelines for the new Audi R10 were determined.

"That was the most important stage,” says Ulrich Baretzky, Head of Engine Technology at Audi Sport. "You have to define the number of cylinders, the engine’s length, bore and stroke. Everything else results from these basic dimensions. If you make a mistake at this stage, it is almost impossible to correct later. That’s why we considered every facet very carefully before we fixed the package.”
 
In Spring 2004, the decision was made to select a twelve-cylinder engine with the maximum permissible cubic capacity of 5.5 litres allowed for Le Mans, which also affected the chassis.

"Compared with the R8, the engine’s length has grown through the number of cylinders, and because of a diesel’s typical power and strength,” says Wolfgang Appel, Head of Vehicle Technology at Audi Sport.

"In this respect we had to react by making everything as light as possible on the chassis side.”

The Le Mans V12 TDI ran for the first time on the test bed in July 2005.

"It was incredibly interesting, because we really have explored completely new territory with this engine,” says Ulrich Baretzky. "Previously, together with our colleagues from the production car development, we had made basic tests with modified production engines and a single-cylinder model. That was all!”
 
The new power unit had already clocked-up approximately 1000 test-bench hours, including several endurance runs, before the R10 prototype’s roll-out.
 

See Direct To Go for details on the direct injected, V8-powered R8, Audi’s previous Le Mans car.

Specifications
Le Mans-Version 2006
 
Model
Audi R10
 
Vehicle
Vehicle type
Le Mans Prototype ("LM" P1)
 
Monocoque
Carbon-fibre composite construction with aluminium honeycomb core. Complies with the strict FIA crash and safety standards.
 
Engine

90 degree V12 turbo-charged engine, 4 valves per cylinder, DOHC, 2 Garrett-turbo chargers, 2 x 39.9 mm engine-air intake restrictors (defined by regulations) and maximum turbo pressure of 2.94 bar absolute, diesel direct injection TDI, stressed aluminium crankshaft case
 
Engine management system
Bosch MS14
 
Lubrication system
Dry sump, Shell oil
 
Cubic capacity
5500 cc
 
Power
over 650 hp
 
Torque
over 1100 Nm
 
Drive
Rear wheel drive
 
Clutch
Ceramic clutch
 
Gearbox
Pneumatically-actuated sequential race gearbox, partner X-trac
 
Differential
Viscous-mechanical locking differential
 
Drive shafts
Constant velocity tripod plunge-joint driveshafts

Steering
Electronically controlled power steering (rack and pinion)
 
Suspension
Independent front and rear double-wishbone suspension, pushrod-system with torsion bar and adjustable dampers
 
Brakes
Dual-circuit hydraulic braking system, mono-block light-alloy brake calipers, front and rear ventilated carbon fibre brake discs, driver adjustable infinitely variable brake-balance
 
Wheels
O.Z. magnesium forged wheels, front: 13x 18 inch, rear: 14.5 x 18 inch
 
Tyres
Michelin radial, front: 33/68-18, rear: 37/71-18
 
Length
4650 mm
 
Width
2000 mm
 
Height
1030 mm
 
Minimum weight
925 kg
 
Fuel tank capacity
90 litres