2008 Audi A4

Exterior

The new Audi A4 exudes dynamism and athleticism. Its architecture of new proportions is charged with strength and emotion and underlines the leading position Audi occupies in the area of automotive design.

With its length of 4,703 millimeters (185.16 inches), and a width of 1,826 mm (71.89 inches), the new Audi A4 clearly surpasses its most important competitors, while it stays below them in height (only 1,436 mm (56.53 inches)). These sporty proportions follow the premise of elevated dynamics. Compared to the predecessor, the new A4 has been extended nearly 12 cm (4.6 inches) in length and 6 cm (2.36 inches) in width, while, at the same time, the front overhang was shortened and the hood and wheelbase were extended. The new A4 not only provides a higher degree of stature but also more power than its predecessor.

The body: Sculpted in one piece

In the new A4, the Audi designers have reinterpreted classic themes from the range of shapes used by Audi. The result is a focused, taut design – a personality with self-assured carriage. The coupe-like, early sloping roof line turns the entire silhouette into a flow of elegance, while dynamic lines frame and emphasize curved sculpted surfaces. In its precision, the design conveys the objective of uncompromising quality to which Audi is committed.

The front end of the new Audi A4 underscores the image of self-confidence. Compared to its predecessor, the single frame is wider and lower. The grille is finished in stone gray; on the most powerful engine model – the 3.2 FSI – it comes in high gloss black. Depending on the version, headlights differ by a few details. Especially eyecatching are the chrome finished “wings,” which differ between the halogen and the xenon plus headlights. On the halogen lights, the wing shapes a second, short wing, while the xenon plus units are embedded in a single curved wing.

Both versions feature the daytime running lights. With the halogen lights, it is generated by incandescent bulbs, while the xenon plus headlights each have 14 integrated white LEDs, with a total power consumption of only nine watts. The daytime running lights, which were pioneered by Audi, not only represent a significant safety technology, but a consistent styling characteristic; they give the face of the new Audi A4 its unmistakable expression. All engine versions share halogen fog lights integrated into the air intakes in the lower front end.

Poised power: The side profile

The profile of the new Audi A4 also conveys the impression of forward-urging power. The long, powerful hood and the correspondingly set-back passenger cell paint the picture of dynamic energy. In the side view, a sophisticated interplay of ascending and descending lines produces a dynamic feel without interfering with the overall balance. The sill area is the foundation, with the dynamic line above it extending all the way to the rear of the car. It rises toward the rear in a sweeping curve, thus shifting the visual center of gravity to the middle of the new Audi A4.

The tornado line, on the other hand, located just below the windows, descends toward the back. Accented by a distinct seam, it projects beyond the front and the rear wheel wells like a line drawn by a steady hand. The “feature line,” a slightly slanted edge of the roof contour, gives the window area a flat and elongated impression.

The body

The body of the new Audi A4 employs new high-tech materials and processes, and it is stiffer and safer than its predecessor, while its weight has been reduced considerably even though it is longer and wider. With a drag coefficient of 0.27 for the sedan and 0.31 for the Avant, it glides lightly through the wind.

The new Audi A4 is unusually sizeable and spacious. With it long wheelbase of 2,808 mm (110.55 inches) it clearly beats the competition. The generous interior space, the high degree of stability, and the supreme straight-line stability all benefit from this long wheelbase.

Moving the front axle forward was what made this long wheelbase possible. This was facilitated by moving the differential 154 millimeters (6.06 inches) forward directly behind the engine – in fact, it switched places with the clutch (or the torque converter). This solution also allowed for the subtly balanced distribution of the axle loads – thus providing for the driving excellence that captivates in the new Audi A4. For the same reason, the battery was moved into the cargo area.

Lightweight steel construction

One of the great strengths of the new A4 is its low weight – benefiting both sporty driving qualities as well as low fuel consumption. The sedan and Avant are both extremely lightweight, although much larger than their predecessor. The sedan is 10 percent lighter, while the Avant is nine percent lighter.

Prime examples of the new technologies applied by Audi to the A4 are found in the body structure, where hot-formed ultra-high-strength steel materials are utilized. On the new A4, they are utilized principally in those areas where only minor deformation is permitted – for example reinforcement of the center tunnel, the inner sills, the B posts and the firewall transverse beams in the engine compartment. In hot forming, boron alloyed steel plate blanks are heated in an oven to about 950 °C (1,742 °F) and then formed in cooled presses while being quenched. The molecular structure created in this way features a tensile strength of up to 1,600 Megapascal.

As well as conventional resistance spot welding, Audi relies on a sophisticated structural bonding agent in many areas. This bonding agent increases the stability of the connection and thus improves the rigidity and crash characteristics of the body structure. In addition, Audi employs two further sophisticated joining technologies. Laserbeam welding is used for the sill area and the doors. In the visible area of the tailgate rain duct, as well as the zero-gap joint between side element and roof, the relevant components are joined by plasmatron brazing. Here, Audi’s high-tech character and quality approach are evident, complemented by close joins throughout the body. Further proof of this high standard has been provided for many years by the fully galvanized bodyshell, which enables a 12-year warranty against body penetration by rust to be offered.

The highest standard possible: Occupant protection

Occupant protection also reaches the highest possible standard in the new Audi A4. For this development, the brand makes use of the broad knowledge base acquired from its own research: All over the world, the AARU (Audi Accident Research Unit) looks into actual accident situations and evaluates relevant data.

In the United States, this research has paid off, as the last generation A4 achieved IIHS (Insurance Institute for Highway Safety) “top safety pick” results, earning top frontal, side, and rear crash safety scores for the past few years.

In a frontal collision, the new A4 protects its occupants with an exactly planned sequence of measures. At the onset of the crash, two acceleration sensors located below the headlights are activated. The front cross-member distributes the forces to the side members, which, thanks to their carefully designed deformation, absorb this energy. The aluminum subframe diverts the forces and momentum in a controlled manner into the floor and tunnel structure of the occupant cell. The steering column can be deformed backwards by up to eight centimeters (3.15 inches), while the main elements of the pedal assembly can be released from their mountings.

In a head-on crash, small people are still at considerably greater risk than tall occupants. Audi therefore has networked the occupant restraint systems more closely together than on any midsize car produced so far. Sensors on the seat rails check the front seat position; this way, the computer can calculate how far the seat occupant is from the airbag and can ensure that the amount of forward movement – during which the seat belt and airbag can restrain the body – is optimally utilized.

The airbags in the new Audi A4 are adaptive and operate based on a new strategy: they always inflate fully. If the control unit assesses the situation as relatively harmless – that is if the impact is not too violent and the seat occupant is sitting close to the cockpit – part of the gas from the airbag is discharged again through valves, so that the head and chest of the occupant are restrained relatively gently. If the crash is severe, the airbags remain fully inflated for longer. The same procedure occurs if the impact is not very strong, but if the passenger is sitting so far back that her or his torso would whip forward with great force.

Even more safety: Adaptive belt force limiters

The seat-belt force limiters also use an adaptive operating principle, with two integral torsion bars linked by gear wheels. In a less critical situation, the torsion bars are separated at an early stage in the accident. This gives the belt a greater range of movement – the torso plunges relatively deeply into the airbag and the load on the chest is reduced. In a more severe crash situation, however, the torsion bars are either disconnected later or not at all – the seat belt restrains the passenger more firmly.

Inside the car, occupants are protected by seat-integrated sidebags with a volume of 13 liters (793.31 cubic inches) for the front seats (sidebags with a volume of 12 liters (732.28 cubic inches) are an option for the rear seats) and large side curtain airbags (25.5 liters – or 1,556.10 cubic inches).

Furthermore, driver and front passenger in the new Audi A4 are effectively protected by variable-height seat belts, not available among some of its competitors, head restraints with a generous amount of vertical adjustment, and anti-submarining ramps in the seats. A sensor recognizes if the passenger seat is occupied.

Rear-end collisions also lose much of their injury potential in the new A4. The side members and the rear subframe absorb the kinetic energy by deforming, while the rear wheels make contact with the body sills if necessary. The seats and head restraints are designed to protect the upper body of front seat occupants against a whiplash impact from the rear. This integral head restraint system already has been highly praised in independent tests. In case of severe rear-end collision, the seat-belt tensioners are triggered to firmly hold the occupants in the best position in their seats.

Rigidity: Basis for comfort and dynamic handling

The rigidity of the new Audi A4’s body is the basis for the peaceful ride, with virtually no unpleasant noise or vibration. At the same time, the rigid body shell is the key to the car’s outstanding road behavior – ensuring smooth running and sporty precision in its handling.

One challenge for the development engineers was to offer the customer the same high levels of vibrational and noise insulation and comfort if a panoramic sunroof is selected in the A4 Avant. In its basic version, the panoramic roof would lead to reduction of body rigidity and a deterioration in the qualities named above. In the A4 Avant, for example, the panoramic sunroof is fixed rigidly to the body by means of a reinforcing frame. This not only secures the roof module compactly, it also considerably improves acoustic comfort.

A great degree of focus was placed by the engineers on local rigidity as well. All locations where driving operations produce interference and vibrations have been targeted for reinforcement, such as the connection of the front suspension crossmember to the wheel suspension and the body. The front crossmember, for example, distributes the frequency impulses from the wheels into a multi-element structure consisting of the side members and tunnel elements – thus greatly reducing the tire roll noises in significant body areas.

Perfect peace: The aeroacoustics

The new Audi A4 is a very quiet car. With intensive detail work, wind roar – the biggest source of noise above 120 km/h (74.56 mph) – was significantly reduced below the level on the previous model. An important development tool in this work was Audi’s extremely quiet aero-acoustic wind tunnel.

In the basic version, the new Audi A4 achieves an exemplary drag coefficient of 0.27 for the sedan and 0.31 for the Avant. This is significantly less than the previous model (sedan 0.31 and 0.33 for previous Avant). Even though the wider body increases the frontal area from 2.14 m2 (23.03 square feet) to 2.20 m2, (23.68 square feet), overall drag has been reduced by more than three percent on the sedan.

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