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This article was first published in 2006.
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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.
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See Direct To Go
for details on the direct
injected, V8-powered R8, Audi’s previous Le Mans car.
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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
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