quattro Permanent All-wheel Drive
One in four Audi drivers already enjoys the benefits of all-wheel drive: permanent quattro all-wheel drive has long since been one of their favorite technical concepts. Almost 25 percent of all 1999 Audi A4 models were equipped with all-wheel drive; the figure will undoubtedly be higher for the new-generation Avant. Because right from the production start, Audi will supply the new A4 with engine versions from 110 kW (150 bhp) upwards as quattro models.
The major benefits consist of capabilities that have come to be regarded as a matter of course over the past twenty years: convincingly better operating dynamics and driving safety, and a distinctively superior form of travel.
On the new Audi A4 Avant, with its longitudinally installed four and six-cylinder engines, a Torsen differential automatically distributes power to all four wheels. The name "Torsen" is a contraction of the two terms "torque" and "sensing". The Torsen differential is a self-locking worm gear.
The advantage is that the locking action is only prompted by the driveline. This type of differential accommodates differences in speed when the brakes are applied and when cornering. Normally the power is split 50:50 between the two pairs of wheels, but in extreme cases the entire propulsive power can be diverted to either pair. In the event of more than one wheel encountering considerable slip, the Electronic Differential Lock EDL can even concentrate the available tractive force at one wheel.
The New Light Alloy Suspension
Audi has demonstrated "Vorsprung durch Technik" with the new A4 saloon's aluminum suspension, the strengths of which are dynamism and comfort, easy handling and active driving safety at a high level.
As far as consistent implementation of weight-saving construction principles are concerned, this suspension is unique in its class: agility and on-road comfort are equally impressive. The new A4 Avant now benefits too from the dynamic potential of this state-of-the-art design.
The aluminum suspension uses a tried-and-tested concept at the front that has been fundamentally modified: four-link front suspension, now of light alloy construction and 8.5 kilograms lighter.
The front-wheel-drive and all-wheel-drive versions of the Audi A4 both have self-stabilizing trapezoidal-link rear suspension with identical wheel control properties.
The rear suspension consists predominantly of alloy components. It is responsible for drastically reduced unsprung weight, yielding a new dimension of driving pleasure in this class.
Less means more: this lightweight construction principle is doubly significant for the suspension because every scrap of weight that can be saved here counts double, particularly in terms of comfort. The "unsprung weight" - in other words, wheels, suspension components and parts of the brake system that move up and down with the wheel - have an especially significant influence on changes in wheel loads.
The fact that all new Audi A4 cars with 96 kW (130 bhp) or more powerful engines have alloy wheels is therefore more than a question of purely visual appeal. Alloy wheels reduce the unsprung weight by several kilograms compared with steel wheels.
The lightweight components naturally make a difference to the overall weight of the vehicle as well. Fuel consumption, performance and driving dynamics: the high-tech aluminum suspension benefits drivers of the new Audi A4 in diverse ways.
The Front Suspension
Audi's four-link front suspension layout set the standard in the midsize car category, with its precise, comfortable steering action and good road behavior. This is true of front-wheel-drive A4 and quattro versions in equal measure. The advantage of this concept is that the steering axis - a virtual line around which the wheel moves when the steering is turned - runs almost perpendicularly through the wheel's center, so that virtually no driveline influences are felt at the steering.
Audi's suspension developers have now updated this highly advanced suspension concept by adopting numerous lightweight but very strong aluminum components.
On the four-link suspension layout, each wheel is located by four aluminum control arms. The swivel bearings are likewise now made from the same light alloy, a change which cuts the weight by around 40 percent compared with the conventional version. The subframe, on the other hand, is a systematic application of weight-saving design principles in steel; the use of high-strength, thin-walled sheet metal reduces the weight by around two kilograms.
Large-volume rubber/metal components are used as the upper shock absorber mounts on the new suspension design. This helps to isolate the shock absorbers acoustically.
quattro Rear Suspension Now Also on Front-wheel-drive A4
All versions of the new Audi A4 Avant are equipped with one of the most advanced and efficient rear suspensions available today: the self-stabilizing trapezoidal-link rear suspension used on quattro models is now also installed on the front-wheel-drive cars.
The trapezoidal-link rear suspension makes for top-quality ride comfort on all models, coupled with dynamic behavior that will amaze the driver of many a competing model.
The trapezoidal link is made from hollow-section aluminum. This torsionally and flexurally rigid control arm absorbs a large portion of the forces and moments acting on the wheel. Together with the track rod located behind it, it determines the elastokinematic behavior of the axle. The track rod is made from lightweight sheet steel.
This design is notable for its low weight and high functionality as well as its outstanding space efficiency. The compact design permits a low load-area floor in all versions, coupled with a generous load-area width. These were the main characteristics that have made the space efficiency and smooth surfaces of the A4 Avant's load area possible.
All wheel control elements pivot on the resiliently mounted subframe via rubber-metal mounts which isolate axle vibration very effectively from the body. Molded rubber mountings are also used for the suspension springs between the trapezoidal link and the body's longitudinal member. Here again, the material chosen provides excellent acoustic insulation.
The twin-tube gas-filled shock absorber is connected to the wheel carrier, so that direct-ratio effect is obtained. Combined with the separately mounted spring, this ensures optimum response from the shock absorber.
The Steering: Precision and Lightness
The steering contributes decisively to the A4 Avant's excellent dynamism and responsiveness. Numerous reviewers have already praised the precision of the A4 saloon's steering.
The new A4 Avant has the same hydraulic power-assisted rack-and-pinion steering, bolted rigidly to the suspension cross-member.
The improvement can also be felt at the steering wheel: a new steering valve greatly reduces steering torque tolerances. The driver registers this as greater precision and an even more spontaneous response to steering movements.
Six-cylinder versions of the new Audi A4 Avant are fitted with damping valves integrated into the steering system. They reduce steering wheel vibration and any tendency to jerk as a function of steering-wheel angular velocity.
Audi's developers have also achieved an optimum steering layout in terms of safety for the A4. Thanks to the use of two universal joints, the steering column is decoupled telescopically in the event of a crash, to isolate it from the steering gear and prevent bulkhead intrusion.
The dictates of lightweight design even extend as far as the design of the steering wheels for the Audi A4: for reasons of weight, the single-section skeletons are die-cast in magnesium.
Road Behavior: a Policy of Neutrality
Superb traction when coming out of even the tightest of curves; neutral, clearly defined self-steering characteristics, and finally, maximum agility; in short, a new best-in-class system. These were the requirements that had to be met when developing the Audi A4 Avant's suspension.
Such targets can only be attained by coordinating all new and modified elements to a high standard of precision. The role of the new self-stabilizing trapezoidal-link rear suspension in the overall package is of course particularly significant. Its elastokinematic properties ensure above all the desired precision of response, while significantly pushing back the handling limits.
On the circular test pad, the most revealing gauge of behavior close to these limits, the Audi A4 Avant needs only a slight increase in the steering wheel angle to remain on course at moderate to high lateral acceleration.
From the driver's standpoint, the effect is clear enough: the Audi A4 Avant remains unruffled even when close to the adhesion limits, and stays on the chosen line with controllable and strictly neutral behavior. Only at a very stage does its response shift to restrained, easily controlled understeer.
Body movement even in S-bends remains moderate, without any of the loss of comfort that might be expected from this dynamically firm layout. This is because the spring rate have been raised to boost roll stiffness considerably - a positive effect that is maintained in a wide variety of load conditions.
All Audi A4 models are fitted with the latest Electronic Stability Program ESP as standard. This system helps the driver to remain in control of the vehicle in potentially critical situations if the handling limits are reached.
The new Audi A4 Avant has a particularly safety-conscious, permanently alert passenger on board at all times: the electronic brake assist system. As an integral part of the latest ESP generation, it is part of the standard specification. Its task is to help the driver in emergency braking situations by automatically increasing braking pressure. Even inexperienced drivers can be sure of maximum deceleration close to the wheel-lock limit.
All versions of the Audi A4 have disc brakes at the front and rear; the front discs are ventilated. The diameter of the front discs on four-cylinder models is 288 millimeters, with 312-millimetre discs in conjunction with a six-cylinder engine. The rear disc diameter is 245 mm on four-cylinder A4 models and 255 mm on the six-cylinder versions.