The Audi R8: Engine and Drivetrain
From the racetrack to the road Even more so than for any other vehicle concept, the engine is the nerve centre of a sports car. As well as being a source of dynamism, performance and sprinting ability, it must be capable of generating excitement through its spontaneous response and free-revving character. Finally, its sound is sheer music to the ears of every true sports car enthusiast. Audi initially demonstrated the performance of V8 engines with FSI petrol direct injection on the racetrack: Audi R8 sports racing cars first appeared with the FSI concept in the 2001 Le Mans 24 Hours and captured a superb double triumph, marking the start of an unprecedented string of achievements. The year after that, the combination of a superior power characteristic and reduced fuel consumption even paved the way for a one-two-three victory. There was not a single instance of the R8 failing to complete any of its 79 races due to engine failure. The new Audi R8 now transfers this superiority from the racetrack to the road: like its role-model from Le Mans, it derives its power from a high-revving V8, located ahead of the rear wheels as a mid-engine. The 4.2-litre engine is a new development that features a full array of motor racing technology in the guise of dry-sump lubrication, straight intake ports and an exhaust manifold with equal-length pipes for all cylinders. Impressive performance figures This engineering achievement is suitably reflected by a host of impressive figures: the engine’s top speed is a notable 8,250 rpm. The engine delivers its peak output of 420 bhp at 7,800 rpm. With its displacement of 4,163 cm3, this outstanding engine breaks through the magic barrier for a production vehicle of 100 bhp per litre. The high-revving concept also means that the maximum piston speed is 24.1 metres per second at the engine’s rated speed. Every piston thus changes direction around 275 times per second. The torque is equally impressive: the peak value of 430 Newton-metres is achieved between engine speeds of 4,500 and 6,000 rpm. Better still, at least 90 percent of this figure is achieved across the impressively wide speed range from 3,500 to 7,500 rpm. This assures thrust across an extensive range of engine speeds and therefore superb pulling power, enabling the driver to drive in a relaxed style without frequent gear changes. The road performance is correspondingly impressive: the R8 dashes to 100 km/h from a standstill in just 4.6 seconds, whether with manual gearbox or with R tronic sequential gearshifting. Thanks to its quattro drive and perfect weigh distribution, problems of traction are an alien concept to it. It touches the 200 km/h mark after 14.9 seconds. Thanks to its refined aerodynamics, the engine’s propulsive power is only finally harnessed by drag at a top speed of 301 km/h. Compact sports engine The V8 is very compact in design. This keeps its weight low, improves the vibrational behaviour and is beneficial in terms of installed position and weight distribution. The crankcase, with its angle of 90 degrees between cylinder banks, is only 43 cm long and 52 cm wide. The cylinder bore is 84.5 mm, with a stroke of 92.8 mm. The engine block is made from a high-strength aluminium alloy by low-pressure die-casting. The camshaft and auxiliaries such as oil pump and air conditioning compressor have a reliable, space-efficient chain drive. In the interests of achieving a low centre of gravity, a sports car’s drivetrain should be as low down as possible. Thanks to its dry-sump lubrication, the R8’s eight-cylinder engine is much flatter than a conventional engine. This has allowed it to be positioned well down, close to the road surface. Dry-sump lubrication means that instead of being collected in a large oil sump beneath the crankshaft, the engine oil is delivered to a separate tank by a scavenge pump via an oil cooler, and from there pumped back to the bearing points via the oil filter. The oil cooler is another example of precision measures at the vehicle’s centre of gravity. It has been positioned very low down in the space frame, behind the left-hand sideblade. The radiators are located in the forward structure: two behind the large air guides at the sides, and a third in the centre, behind the single-frame grille. The dry-sump lubrication with its oil tank moreover assures a reliable supply of lubricant even under extreme loads: the oil supply of the V8 sports engine is designed to cope with the lateral acceleration that occurs in the rough-and-tumble of motor racing. What is more, the fuel pump in the tank is also designed to ensure that the fuel supply to the engine is never interrupted by lateral acceleration, however extreme it is. The computer is fast, too Who does not recall those breathtakingly beautiful, high intake trumpets that Formula 1 cars used to have? The V8 engine of the Audi R8 likewise draws its breath through straight, cast aluminium intake trumpets measuring 23 cm in length. They are integrated into the dual-branch intake system that starts on both sides of the R8 beneath the sideblades and directs the fresh air to the two throttle valves via a 27-litre filter box. At low engine speeds and loads, a tumble flap is activated in the lower section of the intake manifold, producing torque-boosting swirl in the mixture. The engine speeds of up to 8,250 rpm call for high computing power and speed. That is why the fastest processor currently available for this purpose, the “Green Oak”, is used for the engine management. Two Motronic 9.1 engine management systems complement each other according to the master-and-slave principle and supply their digital commands to the mapped ignition with solid-state high-voltage distribution.
Pressure where it is needed in the cylinders, not the exhaust On the V8 FSI engine, the fuel is injected directly into the combustion chamber via a single-hole swirl-type nozzle. This supports the very good full-load performance, cools the cylinder from inside, reduces susceptibility to knocking and paves the way for the compression ratio of 12.5. Both camshafts of the four-valve engine have fully variable adjustment, assuring a sports engine characteristic with a steady rise in torque across an extensive engine-speed band. On a sports car, performance is the overriding objective likewise when configuring the exhaust system. The requirements include low exhaust back pressure and an exhaust manifold that is performance and torque-optimised by means of specific lengths for each cylinder. The two close-coupled preliminary catalytic converters are integrated into the manifold module and ensure that the exhaust emission control lights off rapidly. The two main catalytic converters are housed in the silencer. This is installed behind the engine and above the transmission, and made entirely of stainless steel. It has been possible to reduce its weight by around five kilograms by optimising the wall thicknesses. The large volume of the silencer, the systematic separation of the exhaust branches and the two exhaust flaps are instrumental in giving the R8 its unmistakably ample sound. The sound sensation The sound of a sports car’s engine has to be electrifying. Every movement of the accelerator and every change in engine speed must be accompanied by a powerful change in sound that does not merely reflect the engine’s performance and power flow, but also reinforces how these are perceived. In contrast to the sound of the engine, other driving noises (wind, tyres) should keep a lower profile. After all, sports car drivers too want to arrive relaxed and refreshed after a long, high-speed stretch of motorway. Noise and vibrational comfort were therefore a particularly important aspect in the development of the R8. Before the engineers can actively indulge in acoustic design, all undesirable frequencies need to be damped and eliminated by means of exhaustive fine-tuning. The extremely rigid space-frame construction aluminium body provides an excellent basis for low transmission of structure-borne sound. A key component of the mid-engine concept is the bulkhead between the passenger and engine compartments. The sheet metal surfaces of this firewall are insulated with special materials on both sides, and the glass pane too is made from special acoustic glass a laminated dual pane with a thick soundproofing film. Playing with the frequencies That is of course merely a condition of how to play with the “right” frequencies. The engine sound, for instance, is dominated by the intake and exhaust system. If the exhaust flaps are closed, for example, the silencer is transformed into a sound-absorbing reflection silencer. Open exhaust flaps, on the other hand, create a sportily voluminous sound pattern. The air cleaner housing has likewise been intensively tuned: the intake sound now penetrates the engine compartment in carefully measured doses through special sound apertures, and is acoustically filtered by the firewall as it passes into the passenger compartment. The frequency spectrum moreover has to be right: the V8 supplies a rich array of sounds without any one frequency being interferingly dominant. The extensive fine-tuning has unquestionably been worth while: the higher the engine speed, the higher the load and the sportier the sound produced by the R8. More than a mere adjunct: the transmission The dynamic character of a sports car stems not only from its performance and torque: the transmission ratios have to be right, too. The transmission in the R8 has six of these, which can be operated either by clutch and gear lever or, for even more sports racing flair, sequentially by the R tronic. Whichever option is used, the transmission ratios are always the same: short, and crisply engaged. The manual gearbox is very compact in design. In conjunction with the small-diameter double-plate clutch, this allows it to be installed low down. The manual gearbox features very short shift travel and utterly precise guiding of the gear lever into the open gear lever gate. It is made from stainless steel, is agreeable to the touch and enjoys exquisite sports-car looks. Crisp gearshifts, by order The R tronic sequential gearbox provides even better performance and swifter gear-changing. It adds another dimension to the R8 experience: with manual gearshifts via the steering-wheel paddles or the newly designed sequential gear lever, with an automatic mode comprising two levels, and not least with Launch Control for lightning-fast starts. The R tronic’s electro-hydraulic shifting unit has a separate oil pump with electric pump, permanently supplying the pressure of 40 to 50 bar required for the gear changes. The clutch is operated by the hydraulics, and a second valve block takes the place of the mechanical gearshift control. Other than this, the mechanical gearbox, with its optimum efficiency, remains unchanged. The shift commands from the steering wheel or gear lever are transferred by wire, in other words purely electrically. Compared with similar competitor solutions, the newly developed, comprehensively optimised R tronic is notable on the one hand for the minimal interruption to the power flow, and on the other hand for the smooth gear changes. The operating speed varies according to engine speed and transmission program. The S mode achieves extremely short gearshift times: in this mode, the R tronic shifts significantly faster than even a well-routined driver. The S mode is available both for manual operation and the automatic program. The threshold engine speeds are then higher than in the standard program. For pole position starts With its superior traction, the R8 is an excellent sprinter: it reaches 100 km/h from a standstill in a mere 4.6 seconds assuming of course a lightning-fast start and ultra-fast gearshifts at the optimum engine speed of 8,250 rpm. But there is a far easier way to experience the same utterly overwhelming acceleration: with the R tronic’s Launch Control. Here, the transmission control unit takes charge by optimally controlling the throttle angle and clutch travel. The system is straightforward to use: the S mode needs to be activated and the ESP switched off. If the foot brake and accelerator are both pressed right down, the system automatically establishes the engine speed needed for optimum traction and power transmission. When the brake is now released, the R tronic engages the clutch with ultimate efficiency and accelerates the R8 at maximum speed. Driving fun and safety, from the inventor of quattro In unveiling the first quattro, now all of 27 years ago, Audi revolutionised the automotive scene and quattro permanent four-wheel drive rapidly became established as the superior drive system. From rally courses to circuits and hill-climb races such as the legendary Pikes Peak, Audi quattro racing cars have dominated almost every category of motor sport over the years, wherever the competition rules have not prohibited this principle due to its crushing superiority. On ordinary roads, too, quattro makes the most of blending driving fun with safety. The demand-controlled distribution of the propulsive power to all four wheels improves both traction and directional stability in every driving situation. Then of course there is the safety gain in adverse weather conditions, such as rain, ice and snow. Because of its mid-engine concept, the R8’s drivetrain differs in design from all previous quattro models; the driveshaft runs from the transmission through the engine’s oil sump, to the newly developed front differential. Here, a viscous coupling distributes the power between the rear and front wheels. With an axle load distribution of 44:56 in favour of the rear axle, the weight balance of the mid-engine R8 is extremely good. The viscous coupling correspondingly diverts between 10 and 35 percent of the propulsive power to the front wheels. This assures maximum traction, but also preserves the typically agile handling of a mid-engine sports car. The asymmetric limited-slip differential on the rear axle makes a further contribution towards maintaining balanced handling of the Audi R8. The locking ratio is 25 percent when accelerating and 45 percent when coasting. In conjunction with ingenious axle kinematics, this avoids abrupt load reversal reactions, for instance if the driver switches from accelerating to braking while cornering. The equipment, data and prices stated here refer to the model range offered for sale in Germany. Subject to amendment; errors and omissions excepted.
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