Geneva 2008: VIDEO:Audi R8 TDI Le Mans
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Audi is presenting a revolution in the top class – the first 12-cylinder diesel engine in a high-performance roadgoing sports car. The V12 TDI with a displacement of six liters powers a concept car based on the Audi R8. This unit generates a huge 500 hp and 1,000 Newton-meters (737.56 lb-ft) of torque. Audi is writing a new chapter in diesel technology with this power unit. Equipped with the expertise that Audi has built up through its motor sport activities, the R8 TDI Le Mans in Brilliant Red embodies superb road handling, pioneering technology and fascinating design.
The V12 TDI is closely related to the engine in the Audi R10, the two-time Le Mans winner – so it catapults the Audi R8 into supercar terrain concerning performance too. It sprints from zero to 100 km/h (62.14 mph) in just 4.2 seconds and its top speed is well over 300 km/h (186.41 mph). The peak torque, reached at only 1,750 rpm, paves the way for effortless acceleration that is unrivaled even at this level.
The new V12 TDI belongs to Audi’s family of V engines but has the ideal included angle for this engine type of 60 degrees between cylinder banks. Its highlights include the new chain drive layout that includes the two newly developed high-pressure pumps for the common rail injection system.
Its sound is as thrilling as you’d expect in a sports car of this caliber. For all the subtle smoothness that typifies this design principle, the twelve-cylinder unit is full-bodied and equipped with energetic overtones that make no secret of its performance potential.
The Drivetrain
The roadgoing version of the new V12 TDI is built at the Gyor plant, in Hungary. And the R8 TDI Le Mans still has a massive 500 hp on tap. In developing the six-liter engine, it was a clear priority to integrate it into the current family of Audi V engines, of which many thousands of versions with 6, 8 and 10 cylinders have already been built – both gasoline and TDI.
Audi’s engineers were in an ideal position to use their experience building the racing engine to develop the road version. Like the other power units in this range, the distance between cylinder bore axes on the V12 TDI is 90 mm (3.54 in.). Yet its included angle is 60 degrees, not 90 degrees. This means no free inertial forces or mass moments of inertia can occur with the V12. The results are refined in every respect.
The 83.0 mm (3.27 in.) bore and 91.4 mm (3.60 in.) stroke produce a total displacement of 5,934 cc – just like the 3.0 TDI. At only 684 mm (26.93 in.) long, this large diesel engine is very compact and just 166 mm (6.54 in.) longer than the V8 TDI. This compact length is key to accommodating the V12 in the mid-engined Audi R8.
The V12 TDI crankcase is made from gray cast iron with vermicular graphite – a high-tech material referred to as GJV-450 that is already used on the V6 and V8 TDI engines. GJV-450, made by a patented casting process, is about 40 percent more rigid and 100 percent more fatigue-resistant than gray cast iron. This enabled the developers to make its walls thinner, cutting its weight by around 15 percent compared with conventional gray cast iron.
The two cylinder heads are each made from three main elements. These are a base section made from a high-strength aluminum alloy incorporating the intake and exhaust ports, an oil-bearing upper section, and a reinforcing ladder frame supporting the two camshafts.
The valves are actuated by low-friction roller cam followers; the compression ratio is 16.0:1. Map-controlled swirl variation of the combustion air has been adopted from the V6 and V8 TDI engines. This produces permanently optimized swirl concerning both emissions and high performance.
Ultramodern Injection Technology
As is the case in the Audi V engines, the no-maintenance chain drive is mounted at the back of the engine, where it occupies little space. Its layout has changed on the new V12 TDI. The camshafts’ sprocket engages in an intermediate gear via which two Simplex chains drive the camshafts. Two more chains drive the oil pump and the two high-pressure pumps actuate the common rail injection system.
The two new dual-piston high-pressure pumps form part of the common rail injection system supplied by specialty manufacturer Bosch. The two pumps build up a pressure of up to 2,000 bar in the rails. The piezo injectors with eight-hole nozzles have also been fundamentally revised.
The high pressure distributes the mixture optimally throughout the combustion chamber. The result is that the ignition process is faster, more homogeneous and more acoustically refined. The more efficient combustion process also increases power output, cuts consumption and reduces pollutant emissions.
The current generation of so-called inline injectors makes effective use of the piezo effect: piezo crystals expand in a fraction of a millisecond when an electrical voltage is applied. The number of injection processes per operating cycle can be varied across a wide range thanks to piezo technology – reaching as many as five fuel injection operations in the case of the V12 TDI.
As well as the main injection, pilot and post injections are possible. Pilot injections tone down the acoustic harshness of the combustion process. Retarded post injections are designed specifically to increase the temperature of the exhaust gas, promoting regeneration of the two standard particulate filters.
The two turbochargers are located on the outside of the engine’s V, each of them supplying one bank of cylinders. Thanks to their variable turbine geometry, the full flow of exhaust gas always passes through the turbine, so the chargers respond slickly – even at low engine speeds – and operate very efficiently.
The two turbochargers, which generate up to 2.6 bar of boost pressure, play a crucial role in producing the huge torque of 1,000 Nm (737.56 lb-ft) that the V12 TDI maintains from 1,750 rpm to 3,000 rpm. In developing 368 kW (500 hp), the diesel achieves a specific output of 62.0 kW (84.3 hp) per liter displacement.
Two large intercoolers reduce the temperature of the compressed air. The V12 has a twin-pipe exhaust system with two particulate filters. The intake system is similar in structure with one air cleaner per cylinder bank, with an airflow meter behind it. Two control units, sharing the workload in a master/slave principle, manage events in the engine.
The Audi R8 TDI Le Mans already fulfills the Euro 6 emissions standard that is likely to take effect in 2014 and calls for sharply reduced nitrogen oxides. By also designing in ultra-precise fuel metering by the common rail system, Audi’s engineers have made full use of current clean diesel technology.
The heart of the system is a special catalytic converter downstream of the oxidizing catalyst and the particulate filter. The second component in the system is an additional tank containing an aqueous urea solution. Small quantities of the solution, known as “AdBlue,” are injected into the exhaust system. The hot exhaust gases break the solution down to form ammonia that splits the nitric oxides into nitrogen and water. The system remains effective for the entire service life of the vehicle.
The dynamic character of a sports car depends not just on its performance and torque; the transmission ratios have to be right too. In keeping with the character of a high-performance sports car with unbeatable torque potential, the transmission in the R8 TDI Le Mans has six manually operated gears.
The manual transmission is very compact in design. Together with the small-diameter double-plate clutch, this means it can be installed low down. The manual transmission has very short shift travel and utterly precise guiding of the shifter into the open gear lever gate. It is made from polished aluminum, has an agreeable feel and exquisite sports car looks.
Such a high-performance Audi also has quattro permanent all-wheel drive. In the case of this mid-engine sports car, power is distributed variably between the front and rear wheels from a starting ratio of 40:60 to optimize the handling.
The entire bodyshell of the study car weighs just 210 kilograms (462.97 lbs.). In ASF technology, the body’s supporting structure is made of extruded aluminum sections and die-castings. Aluminum panels are incorporated into this skeleton to form a positive connection and perform a load-bearing role. Each individual component of the ASF space frame is optimized for its specific task by the use of widely differing shapes and cross-sections, combining maximum stability with minimal weight. It adds up to a car that’s particularly light and rigid, an outcome that can be felt in the R8’s ultra-precise driving feel.
The aerodynamics experts at Audi have done their work so thoroughly on the study car that, as an added benefit of its elegant shape, the body actually generates downforce – unlike many other sports cars. This aids directional stability at high speeds. It is achieved partly by means of an extending rear spoiler that is much larger than on the production version, and also thanks to the fully clad diffuser underbody.
Two large-format diffuser apertures in the rear bumper demonstrate just how much aerodynamics dictate the shape of the study vehicle. The tailpipes of the exhaust system are located in pairs on the right and left above the diffuser apertures. The add-on, automatically extended rear spoiler also interacts with the air as it flows around the car. The extra downforce it provides increases the efficiency of the air intake generated by the aerodynamic design of the underbody and diffusers. At low speeds, the rear spoiler returns to its initial position.
Chassis
The precision chassis of the Audi R8 TDI Le Mans remains supremely in control of the sporty performance, but is capable of assuring relaxed driving pleasure over long distances too. The sports car is spontaneous and agile at obeying steering movements, always demonstrating exceptionally good driving safety. The suspension, with double wishbones at both the front and rear, is optimized for a neutral self-steering response and maximum ease of control.
The study car, too, has the innovative dampening technology known as Audi magnetic ride. This adapts the chassis characteristic to the profile of the road and the driver’s style within milliseconds.
Ceramic Brakes with Extreme Reserves
A generously dimensioned brake system supplies the necessary braking force. It applies a total of 24 pistons to the four brake disks, combining excellent performance with minimal weight and high durability. The disks are made from carbon fiber reinforced ceramic, a material that has repeatedly proven its worth in the aviation and aerospace sectors. The basis is very hard, frictionally resistant silicon carbide, with its diamond-like crystalline structure. Embedded in it are high-strength carbon fibers that absorb the stresses occurring in the material. The intricate geometry of cooling ducts in the ventilated disks prevents extremely high temperatures. The ceramic brake disk ring is bolted by 10 spring-loaded elements to a stainless steel central element that acts as the connection with the wheel’s hub.
The ceramic brakes are identifiable at a glance by the special red, six-piston monobloc aluminum calipers and the fixed calipers at the rear. The advantages of the ceramic brakes include a further reduction in weight of around 20 kilograms (44.09 lbs.), which in this case improves the handling characteristics and comfort. The high abrasion resistance permits an operating life of up to 300,000 kilometers (186,411 miles). Their key strength, however, is their ability to withstand very high loads. Even on the racetrack, for example, the ceramic brakes always maintain their full reserve performance.
Source: Audi
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