Audi S4 (2009)

The supercharger is a so-called Roots blower. Inside it, two four-vane rotary pistons counter-rotate at a speed of up to 23,000 rpm, with the air gap between them measuring just a few thousandths of a millimeter. The rotors can deliver 1,000 kilograms (2204.62 lb) of air per hour and force it into the combustion chambers at a boost pressure of up to 0.8 bar. Two intercoolers made of aluminum, connected to a separate coolant circuit, are integrated into the housing in a particularly efficient way. Here, the compressed and thus heated intake air is cooled down again in order to increase the volume of air required for the combustion process.

The three-liter V6 engine itself belongs to Audi's family of ultramodern V engines. In addition to the standard cylinder angle of 90 degrees, their attributes include systematic lightweight construction - the three-liter's crankcase, which is made from cast aluminum/silicon, tips the scales at just 33 kilograms (72.75 lb). The entire engine, including the supercharger, weighs 189 kilograms (416.67 lb). The bore measures 84.5 millimeters (3.33 in) and the stroke 89.0 millimeters (3.5 in), producing a swept volume of 2,995 cc.

Audi has included a whole array of refined high-tech features on the 3.0 TFSI. The crankcase has been adapted to the higher prevailing pressures and all components are frictionally optimized. The intake camshafts can be adjusted through a 42- degree crankshaft angle. In the intake ports, tumble flaps aid mixture preparation.

The injection system is a fundamentally new design. A common rail system with six-hole injectors injects the fuel directly into the combustion chambers at a pressure of up to 150 bar. The injectors' highly dynamic response permits up to three fuel injections per operating cycle across an extensive range of the characteristic map. The high compression ratio of 10.3:1 also contributes to optimum combustion and therefore superior efficiency. The direct injection principle is once again the key, because the intensively swirled fuel cools the combustion chamber, reducing the tendency to knock.

Transmissions

Audi delivers the Audi S4 and S4 Avant with a six-speed manual transmission as standard - its short and precise lever travel and low operating force make every gear change a delight. Special selector fork mountings decouple the gear lever from the driveline so that the driver does not sense any vibration.

Internal friction in the transmission has been minimized, improving the already high level of efficiency still further. A change-up display in the driver information system helps the driver to adopt a more economical driving style. It shows which gear is in use and recommends a different gear if this would be a better choice. The dual-mass flywheel and the hydraulically actuated single dry-plate clutch are not bolted to the crankshaft in the usual way, but supported on the transmission input shaft. On the Audi S4 and S4 Avant, the differential is located in front of the clutch. Output to it is via a hollow shaft, which features a so-called beveloid gear on both sides, enabling it to be installed at an inclined angle of 7.2 degrees.

Interchanging the components has moved the front axle forward by 154 millimeters (6.06 in) compared with the previous model. This has many advantages - a long wheelbase, a short front overhang and good weight distribution. It results in handling characteristics that set new standards in terms of dynamism, precision and stability.

Dynamic and efficient: the seven-speed S tronic

On request the new Audi S4 and S4 Avant leave the assembly line equipped with the seven-speed S tronic transmission, which is exceptionally dynamic and at the same time remarkably efficient. The innovative dual-clutch transmission can be used in various ways. The fully automatic mode features the D (Drive) and S (Sport) programs. The gears can also be manually switched with the shift selector lever or with the paddles on the steering wheel - an amazingly fast process. The gearshift feel is dynamic, comfortable and very precise - typically Audi.

The seven-speed S tronic consists of two separate transmissions and uses two multi-plate clutches that control the various gears. The large outer K1 clutch transmits the power through a solid shaft to the gear wheels for gears 1, 3, 5 and 7; they are located at the rear of the aluminum transmission housing. A hollow shaft rotates around the solid shaft. It is connected to the compact K2 clutch, which is integrated into the inside of its larger sibling, and which controls the gear wheels for gears 2, 4 and 6, as well as reverse gear. All gear wheels are arranged one behind the other on both output shafts, in the order 4, 6, 2, R, 1, 3, 7 and 5.

Both transmission structures are continuously active, but only one is powered at a time by the engine. For example, when the driver accelerates in third gear, the fourth gear is already engaged in the second transmission structure. The shifting process takes place as the clutch changes - K1 opens and K2 closes with lightning speed. The gear change takes only a few hundredths of a second and is completed without interrupting traction. It is so fluid and smooth that the driver hardly notices it.

Each component of the new seven-gear S tronic attests to Audi's innovative approach and to the company's uncompromising quality standards. Carbon-coated synchronizer rings guarantee synchronization of unsurpassed quality and stability. The gears one through three and reverse are also designed as three-cone synchronizations. Both multi-plate clutches are managed with supreme precision when driving off and shifting between gears thanks to the compact pressure cylinders, electronically controlled speed compensation and optimized coil spring packages.

quattro drive and the sport differential

Since 1980, quattro has been a synonym for cars with outstanding driving dynamics. In its basic setting, the torque-sensing centre differential delivers 40 percent of the tractive force from the engine to the front axle and 60 percent to the rear axle. Since the latest Audi RS4 was introduced in 2005, this degree of rearward bias has been standard on all new Audi models; it guarantees a high level of driving pleasure. The torque-sensing differential redistributes engine output without delay if road surface conditions change, and is thus the most advanced technical principle on the market.

This exceptionally good traction puts the quattro system at an extremely high level as far as dynamics in a forward direction are concerned. But quattro technology also has distinct advantages in terms of lateral dynamics. By distributing traction among all four wheels, each wheel has greater potential to resist lateral forces, and tire grip is maintained for significantly longer. The action of the electronic differential lock (EDL) and the typical Audi settings adopted for the ESP electronic stabilization system also add to driving pleasure and a high level of stability.

Superimposed stages for acceleration

The superimposed output stage rotates ten percent faster than the half-shaft that normally drives the wheel; the two drivelines can be connected together by the multi-plate clutch. If the clutch is engaged, the wheel is accelerated by the superimposed stage that is running at a higher speed, and thus receives an additional torque input. The differential reduces the tractive force reaching the opposite wheel accordingly. In most driving situations, almost the complete input torque can be diverted to one rear wheel in this way. The maximum difference in torque between the wheels is 1,800 Newton-meters (1327.61 lb-ft).

The sport differential is even capable of completely eliminating the classic loadreversal reactions when the accelerator is lifted or the brakes applied suddenly while cornering; the driver can specify this function by selecting 'comfort' mode. If the accelerator pedal is released, torque distribution between the wheels is adjusted almost instantaneously.

Unlike other systems, the Audi sport differential is just as effective when the engine is driving the wheels as it is on the overrun or when the car is coasting freely. In simplified terms, here too one wheel is braked and the other accelerated with the aid of the superimposed drive stages. This diverts the torque to the wheels and the vehicle is given a precisely calculated impulse in the required direction.

A technically superior solution

The task of distributing a high level of torque with minimum losses by way of a transmission that is compact and light in weight was an extremely challenging one. The solution arrived at by Audi's engineers is as ingenious as it is innovative. A new transmission stage, consisting of two sun wheels and a ring gear, performs the task in a very simple fashion. The ingenuity lies in the fact that the ring gear is displaced in relation to the sun wheels. The resulting generous gear tooth overlap enables torque transfer to take place using a minimum number of components.

This is the first time that this principle has been used in a road-vehicle driveline. The system needs no maintenance throughout its life, and operates at a high level of efficiency. The additional fuel consumption needed for the active sport differential is so small that it is hardly measurable. The device takes effect extremely quickly and has a very high level of control accuracy.

Thanks to its control unit, the sport differential is an intelligent unit. Audi developed the necessary software, which uses a unique operating principle, inhouse. The computer obtains the information it needs from the steering angle, wheel speed, lateral acceleration and yaw-rate sensors and from current engine data. Twin yaw-rate and lateral acceleration sensors are installed for the sport differential. This explains the system's extremely high reaction speed: data from both sensors are continuously compared in the control unit, which means that reliable results are available more rapidly.

Audi drive select - the unique high-tech package

The quattro driveline with active sport differential is part of Audi drive select, the innovative dynamic driving system premiered on the new Audi A4. As part of an optimal combination with Audi dynamic steering and electronic shock absorber control, the permanent four-wheel driveline and the sport differential demonstrate their immense capabilities with regard to driving dynamics.

Audi drive select integrates the technical components that determine the quality of the driving experience: engine, transmission, steering, shock absorbers and the sport differential. Drivers can adjust the characteristics of these systems at any time to suit their personal preferences. Audi drive select is a successful synthesis of comfort and convenience with dynamic sportiness at a previously unattained level.

Buttons on the centre console enable drivers to vary the operation of Audi drive select in three stages ranging from comfortable to sporty, or to put together a profile that suits their personal preferences. The engine's throttle response characteristic can be determined first, followed by that of the servotronic speeddependent power steering and, if the car has automatic transmission, its shift points.

Three operating modes for the sport differential

The functions of the sport differential can also be varied to suit the driver's individual wishes. In the 'comfort' mode, driving safety and the car's stability have absolute priority, with optimal damping of load reversals. In the 'auto' mode the program achieves a harmonious balance between all the functions. Finally, the 'dynamic' mode emphasizes the functions contributing towards agility, so that the dynamic effect of the sport differential is most easily felt. In this case, response to load reversals is both agile and easily controllable.

Electronic damper control

Audi drive select with the sport differential can be combined with electronic damping control. The gas-filled hydraulic shock absorbers have an additional valve with a continuous opening action. The control unit computes the optimal damping force at a cycle frequency of 1,000 per second.

The electromagnetically controlled valve selects a damping characteristic to match the current driving situation at any given moment. Higher damping force may be needed to resist body movement when cornering rapidly or braking, whereas a lower damping force will be appropriate on potholed roads and a moderate setting on poor country roads.

Dynamic suspension

The dynamic suspension of the new Audi S4 and S4 Avant is based on the layout that has made the A4 the sportiest car in the midsize class. Numerous suspension components made of aluminum reduce unsprung masses. The five-link front suspension can handle longitudinal and lateral forces separately; a firmly mounted subframe ensures exceptional rigidity for the front section. The springs and shock absorbers of the self-tracking trapezoidal rear suspension, which permits a wide luggage compartment thanks to its compact design, are aligned separately to improve response.

In keeping with the dynamic performance of the Audi S4 and S4 Avant, the suspension has been retuned. Stiffer bearings for the control arms guarantee elastokinematics for a sporty performance; lateral and camber rigidity are clearly enhanced. The minimal body movements lend the Audi S4 and the S4 Avant maximum stability, even when braking. The shock absorbers have firmer settings and the body has been lowered by 20 millimeters (0.79 in).

Handling precision - without compromise

All these measures lend the Audi S4 and the S4 Avant the driving dynamics of a sports car - their reactions are smooth, almost reflex-like; handling precision knows no compromise. The steering connects the driver with the road to provide sensitive, well-differentiated feedback.

The low-mounted steering gear transmits the steering forces via the track rods to the wheels over the shortest distance, its ratio of 16.5:1 is sporty and direct. The regulated vane-type pump, which supplies the system with hydraulic energy, always delivers only as much oil as is needed; in this way it too contributes towards high consumption efficiency. As a servotronic system, it bases the amount of assistance on road speed.

The new Audi S4 and S4 Avant are fitted with impressive cast aluminum wheels, which carry size 245/40 tires on 8J x 18 rims. As well as the standard 5 parallelspoke wheel in the S design, an additional design is available. Furthermore, there is a choice of winter wheels in two different widths, one of which is suitable for snow chains. quattro GmbH offers three 19-inch wheels with size 255/35 tires: the 5 segment-spoke design, 7 twin-spoke design and 20-spoke design (twopiece).

The large wheels provide space for a 17-inch brake system developed for maximum performance. All four disks are ventilated, the front having a diameter of 345 millimeters (13.58 in), the rear 330 millimeters (12.99 in). An innovative concept, which dispenses with the conventional cooling ducts, ensures impressive power and stability: the two halves of the disk are connected by hundreds of small metal cubes, between which a high volume of heated air can flow in a very short time. This design also lowers the weight - here too, drivers will experience the reduction in unsprung masses in the form of enhanced driving dynamics.

The black-painted brake calipers - sporting the S4 logo at the front - are of a composite design based on the floating caliper principle. The areas subject to high loads are made of nodular cast iron; the bolted-on piston housing made of aluminum conducts the heat effectively, and the calipers are extremely rigid despite being light in weight. Compared with the predecessor model, the surface of the brake pads has increased by 25 percent at the front, and as much as 60 percent at the rear. New materials increase the amount of friction.

The brakes on the Audi S4 and S4 Avant set new standards in terms of power and precision, not to mention accurate feedback provided to the driver. The electronic stabilization program ESP also uses high-precision hydraulic valves, which control pressure build-up with great accuracy. It intervenes at a later stage and is more subtle. The ESP can be switched off completely: the driver can deactivate the traction control function separately at a speed below 70 km/h (43.50 mph).

Design

The very design of the front section alludes to the power of the new Audi S4 and S4 Avant. The LED daytime driving lights in the standard-specification xenon plus headlights can be seen from afar. The single-frame grille, in platinum gray, has the typical look of the S models from Audi - its vertical double struts bear chromed inserts and the S4 badge. Two ribs define the lower trapezoidal air vents and chrome rings encase the front fog lights. An aluminum-look "blade" forms the centerpiece of the striking bumper.

The side view also reflects the athletic character of the Audi S4 and S4 Avant. Sill trims painted in the body color emphasize the width of the body; the aluminum-look exterior mirror housings gleam. The new midsize athletes have a powerful stance on the road with their 18 or 19-inch wheels, the rim spokes allow the blackpainted brake calipers to shine through. The so-called high-gloss package adds elegant touches all round the side windows with aluminum strips and black trims.

At the rear, too, the new Audi S4 and S4 Avant remain unmistakable - thanks to the badge on the trunk lid, the LED lights and the quadruple oval tailpipes. The rear bumper, incorporating a diffuser, has also been redesigned, its blade likewise in aluminum look. The spoiler - on the trunk lid of the sedan and the roof edge of the Avant - separates the airflow in a clean, defined way, further enhancing driving stability at high speeds.

Audi offers its midsize athletes in four solid colors - Ibis White, Brilliant Red, Brilliant Black and Imola Yellow - and in seven metallic and pearl effect finishes. These are Ice Silver, metallic, Quartz Gray, metallic, Meteor Gray, pearl effect, Phantom Black, pearl effect, Deep Sea Blue, pearl effect, Sprint Blue, pearl effect and Garnet Red, pearl effect. Imola Yellow and Sprint Blue are reserved exclusively for the S models.

The Audi S4 and S4 Avant are large midsize cars with a high level of everyday suitability. They are 4,717 millimeters (185.71 in) in length, with a wheelbase of 2,811 millimeters (110.67 in), 1,826 millimeters (71.89 in) in width and 1,406 (55.35 in) and 1,415 millimeters (55.71 in) in height respectively. The luggage compartment of the sedan has a capacity of 480 liters (16.95 cu. ft); the Avant has a basic capacity of 490 liters (17.30 cu. ft) and 1,430 liters (50.50 cu. ft) when the rear seat backs are folded down.

Interior

Dynamic, elegant, sophisticated - this is the interior of the new Audi S4 and S4 Avant. The ergonomics are exemplary, the amount of space generous; the electromechanical parking brakes leaves room on the centre tunnel. The interior in cool black - the roof lining is optionally available in silver - creates an atmosphere of sporty and technical expertise, underlined by the uncompromising craftsmanship so typical of Audi.

The many meticulously thought-out details are another characteristic of the brand. The S4 logos are found on the door sill trims, the leather multifunction sports steering wheel, the remote control key and on the instruments, the dials of which are gray, the needles white. Understated aluminum-look inlays provide subtle highlights; the versions with seven-speed S tronic sport aluminum-look shift paddles, mounted behind the steering wheel.

The electric sports seats feature lumbar supports and pull-out thigh supports; the standard version is upholstered in a combination of black Alcantara/leather. For the S sports seat, Silk Nappa leather is also available, with the option of a bi-color look with contrasting stitching. The climate-controlled comfort seats represent the high-end option; they are equipped with small cooling fans in the seat backs and are upholstered in black or brown leather. Customers who appreciate firm support can order the strongly contoured S sports seat with integrated head restraints. A sliding front center armrest including two 12-volt sockets comes as standard with all seat versions.

The inlays in the new Audi S4 and S4 Avant also have a sporty and individual look. Matt brushed aluminum is standard. Carbon, fine gray birch wood and genuine stainless steel mesh are optionally available. The filigree structure, consisting of numerous steel threads, feels slightly rough, but is fascinating to the touch.

Equipment and trim

The new Audi S4 and S4 Avant come off the assembly line with a wide range of standard equipment. The highlights - besides quattro drive, 18-inch wheels, sports suspension and servotronic - include many comfort and convenience features, namely automatic air conditioning, driver information system, a lighting package for the interior, leather multifunction sports steering wheel, electric sports seats with lumbar support and folding rear backrests - also for the sedan. Xenon plus headlights with LED daytime running lights and LEDs in the rear lights give the Audi S4 a highly distinctive look.

Audi delivers the new Audi S4 and S4 Avant, on request, with a range of high-tech systems that make driving an even more supreme and relaxed experience. These include the parking aid Audi parking system advanced with rear-view camera and Audi side assist, which monitors the blind spot during lane changes. The adaptive cruise control regulates the speed and distance from the car in front, while braking guard warns the driver of an imminent bumper-to-bumper collision.

The standard-fit tire pressure monitoring system informs the driver as soon as the tire pressure in one or several tires drops and thus provides added safety.

Audi also sets new standards when it comes to multimedia. The Audi Music Interface (AMI) allows an iPod and its entire range of control functions to be connected; an up-to-date mobile phone and its functions can be fully integrated into the Bluetooth car phone. The navigation system with DVD is combined with the competition-beating MMI operating system. The radio tuner receives digital programs on request and the luxury sound system from the exclusive Danish brand Bang & Olufsen boasts a 505-watt amplifier that controls 15 speakers through ten channels.

The range of options for the Audi S4 and S4 Avant includes other excellent features such as a three-zone automatic air conditioning system, a convenient key for keyless entry, a high-beam assistant and the dynamic cornering light system adaptive light. An electric tailgate and a large panoramic glass sunroof are available for the Audi S4 Avant. The 19-inch wheels, the active sport differential, the seven-speed S tronic and dynamic driving system Audi drive select incorporating adaptive damping and dynamic steering underscore the leading role in terms of sporty expertise that the Audi S4 and S4 Avant enjoy in their competitive field.

Audi will begin delivery of its new S models in March 2009. The basic price is particularly competitive: 50,950 euros for the sedan, 52,600 euros for the Avant.