Drivetrain: The 4.0 TDI eight-cylinder
The allroad quattro concept proudly boasts the very first eight-cylinder in Audi's new range of TDI powerplants complete with common rail technology and piezo inline injectors - the 4.0 TDI.
Like its six-cylinder counterparts with a displacement of 3.0 and 2.7 liters, this magnificent eight-cylinder features the most advanced fuel injection technology and interacts with a diesel particulate filter to outperform the demanding European EU4 emission standards not coming into force until 2006.
Displacement of the eight-cylinder version is 3,936 cc. The engine's power and performance, in turn, is expressed clearly and convincingly by some simple and very straightforward figures: 290 bhp/210 kW at 3200 rpm and maximum torque of 650 Newton-meters attained consistently from just 1600 rpm all the way to 3000 rpm for supreme acceleration throughout.
The results, obviously, are a spontaneous response to the gas pedal and enormous pulling power from very low engine speeds. Acceleration to 100 km/h from a standstill comes in just 6.4 seconds; top speed is at a governed 250 km/h.
Particularly interim acceleration on the road is an outstanding strength of this high-performance power unit, with Audi's new concept car accelerating from 80-120 km/h in just 4.9 seconds. This, believe it or not, makes it just as fast as Audi's high-performance S4 athlete.
The V8 32-valve powerplant complete with turbocharger technology and map-controlled, cooled exhaust gas recirculation is the first eight-cylinder TDI in Audi's new generation of V-engines. Both the camshafts and the oil pump are driven by chain.
Like all representatives of Audi's new V-engine family, this powerplant comes with extremely compact dimensions: Engine length is a mere 516 millimeters. This also helps to minimize the weight of the engine reduced to just 259 kg, making the 4.0 TDI the lightest diesel V8 worldwide.
Common rail technology and piezo inline injectors
Fuel is supplied to the engine by the very latest common rail injection system featuring a separate high-pressure pump and distributor rail for each row of cylinders. Injection pressure peaks at 1650 bar, 300 bar more than on former common rail systems.
This high injection pressure serves to atomize the diesel fuel even more consistently into minute particles, ensuring even better fuel/air supply and even more efficient combustion.
The most significant innovation introduced with this new common rail technology is without doubt the piezo injectors. Using the piezo effect, the injection system supplies electric tension to a ceramic unit which consequently changes its crystalline structures. The result is a minute change in geometry which, together with the effect of a hydraulic element, mechanically opens the injection jet needle.
Piezo injectors serve to minimize injection volume and maximize both the degree and accuracy of dosage control, enabling the "intelligent" injection system to vary the number of injections per operating cycle almost at random. In the case of the 4.0 V8, the engineers developing Audi's TDI power unit have opted for up to five injection processes as a function of specific requirements.
This strategy serves to minimize emissions and, at the same time, smoothen the entire combustion process, helping in particular to reduce engine noise: The 4.0 TDI is not only a lot quieter and smoother than its predecessor, but indeed clearly sets the benchmark in this respect in its class.
Audi's six-speed tiptronic is the ideal partner for the ultra-strong and powerful V8. Indeed, this unique transmission converts the full potential of the engine into genuine dynamism and ride comfort in supreme, unprecedented style.
Low weight, the fast gearshift, and the optimum gearshift strategy consistently combine the sporting performance of the allroad quattro concept with the equally superior comfort of this automatic transmission.
The transmission ratios and increments particularly in the lower gears ensure significantly enhanced acceleration and, in the higher gears, an equally significant reduction of engine speed. This, on the road, means both less noise and, at the same time, greater fuel efficiency offering the driver the best of both worlds.
Gearshift speed of the six-speed tiptronic is particularly dynamic, the driver benefiting from an even more spontaneous gearshift particularly when shifting down. At the same time the automatic intermediate gas function serves to further enhance the car's agility on the road.
The electronic control unit responds to parameters such as longitudinal and lateral acceleration as well as the way the driver moves the gas pedal both in transmission mode D and in the S sports program, thus avoiding any unwanted upward gearshift in bends.
Permanent quattro all-wheel drive
Permanent quattro all-wheel drive is a natural feature on all high-performance Audi cars. Indeed, it was precisely this technology which revolutionized the car world no less than 25 years ago and is now featured in virtually all car segments not just with Audi. One out of every three Audi cars sold is currently a quattro model, with more than 1.8 million Audi cars being built with permanent quattro all-wheel drive by the end of 2004.
Audi quattro ensures excellent traction and side stability, at the same time minimizing the influence of drive forces on the car's steering behavior. And this, in turn, is the essential prerequisite for very high speeds in bends and a high standard of driving stability.
With the engine of the new Audi allroad quattro concept fitted lengthwise, a torsen differential automatically ensures the optimum flow of power to all four wheels.
The word "torsen" incidentally comes from "torque" and "sensing", signifying the perfect balance of torque and operating smoothness provided in this way. The torsen differential is a self-locking worm gear transmission system.
The big advantage of this concept is that the differential generates its locking effect only under power, while at the same time the transmission allows different speeds during application of the brakes and in bends. Under normal circumstances 50 per cent of the engine's power goes to each axle, but under extreme conditions up to 75 per cent of the drive power may go either to the axle at the front or at the rear.