August 15, 2003
Text and pictures courtesy of Audi of America
The 2004 Audi A8 L displays an exemplary sporting character, clean design, innovative technology and superior quality. Completely redesigned and reengineered, the all-new flagship Audi model features the latest in technology and innovation, including a first-in-class, fully pneumatic suspension system.
Exclusive to the 2004 Audi A8 L, the Audi Adaptive Air Suspension system resolves the classic conflict of how to combine a luxury ride with sport handling in a single suspension setup. Prior to now, luxury sport sedans came with suspension systems that provided either a decidedly “luxury” ride which proved too soft for spirited driving or a “sport” suspension that was too stiff to be comfortable.
The unique suspension system on the all-new 2004 A8 L replaces the conventional steel suspension of the preceding model for improved ride, handling and performance with significant weight savings. It also offers drivers a choice of suspension settings to match their particular ride and handling preference, and to match varying road conditions.
The newly engineered Audi Adaptive Air Suspension system has continuously variable damper settings and four pre-defined settings for adjusting the suspension resistance to the driving conditions. For smooth roads and highway speeds, the suspension can be stiffened and lowered for increased stability from a lower center of gravity and improved fuel economy through better aerodynamics. Uneven roads are more easily managed with softer damper settings and increased ground clearance.
The electronically controlled damping system uses sensors to signal continuous adjustment depending on the rate of acceleration, vertical wheel movements, turning angle, steering wheel position and brake and accelerator pedal pressure. When damping force requirements are constant — such as driving straight on a smooth road — the damping settings are neutral, while specific force adjustments at each wheel reduce pitch, dive and roll during starts, stops and cornering. The suspension height is kept constant irrespective of load as air is pumped into and discharged from the springs as load is added and removed, providing for a consistent ride and stance.
Components and Function
The components of the Adaptive Air Suspension system on the 2004 Audi A8 L are “layered” to enable excellent running characteristics while maintaining the sensitive response needed to handle minor roadway imperfections. At all four wheels, air suspension bellows are arranged concentrically around continuously variable, twin-tube shock absorbers and air spring suspension struts.
The air spring struts are pressurized from an air reservoir at the rear of the vehicle, fed by an electric air compressor in the engine compartment. A special multi-layered elastomer material with polyamide cord inserts increases the constructive strength of the air suspension bellows and helps absorb the forces produced in the air spring.
Feed lines carry the air to the individual components, while electromagnetic valves regulate airflow. Seven acceleration sensors — four on the axles and three on the body — send data to a suspension control unit which determines the immediate driving situation and adjusts individual shock absorbers in milliseconds to maintain optimum driving dynamics and ride comfort.
Attached to the aluminum chassis of the 2004 Audi A8 L is an aluminum-alloy, four-link front suspension and self-tracking, trapezoidal-link rear suspension. This is a similar architecture responsible for the precision steering and agility characterized in the preceding model. On the all-new A8 L this setup has been moved forward by 2.5 inches for a more favorable axle load to maximize handling advantages.
Lightweight components in the front axle setup help reduce unsprung mass and discourage undesirable wheel hop. Sheet metal shells reduce weight 20 percent compared to previous generations, helping to reduce the overall curb weight.
The trapezoidal-link rear suspension also has been improved with reduced toe-in across the entire spring travel to enhance directional stability and handling. As with the front suspension architecture, this rear suspension layout is also made of lightweight aluminum-alloy.
Combined with weight savings elsewhere in the production process, the weight distribution of the 2004 A8 L is now 56.4 percent in front and 43.6 percent in the rear, compared to 58 and 42 percent in the previous model. The improved weight distribution adds to the performance characteristics and driving traits of the new Audi flagship.
Influenced Driving Dynamics
The Audi Adaptive Air Suspension system allows drivers to choose a specific suspension set-up from four pre-selected damping traits and suspension heights:
- Automatic level, with an initial ground clearance of 4.7 inches
- Dynamic level, with a ground clearance of 3.9 inches
- Comfort level, with a constant ground clearance of 4.7 inches
- Lift level, with a ground clearance of 5.7 inches
While stationary and for typical road conditions and driving speeds, Automatic level sets the 2004 A8 L at 4.7-inches of ground clearance. To maximize aerodynamic advantages when speed exceeds 75 miles per hour for longer than 30 seconds, the Adaptive Air Suspension system automatically lowers the car one inch to a dedicated Freeway (“Motorway”) setting of 3.7-inches for improved handling and performance. When an aerodynamic posture is less of an issue, such as at speeds below 44 mph for longer than 30 seconds, the vehicle automatically lifts to its original ground clearance. The Freeway setting is automatically selected and de-selected by the Adaptive Air Suspension control center.
For active driving, Dynamic level lowers the 2004 A8 L to 3.9-icnhes of ground clearance and sets firmer springs and damping characteristics for a more performance ride and driving feel. As in Automatic level, if speed exceeds 75 mph for longer than 30 seconds, the vehicle is automatically lowered to the Freeway setting to maximize aerodynamic advantages. When vehicle speed remains below 44 mph for over two minutes, or immediately if speed falls below 22 mph, the suspension automatically returns to the Dynamic level.
In Comfort level, ground clearance is 4.7-inches. In this mode, damping force is adjusted less frequently to maximize compression travel for extra-smooth bump control.
Lift level adds nearly an inch (.98) of ground clearance for a total of 5.7-inches to cover uneven terrain at speeds below 50 mph. The suspension automatically lowers to the most recent previously selected mode when terrain and conditions permit speeds above 62 mph.
For added safety, a dedicated “Jack” mode sets the suspension at a single height and holds it constant while this setting is selected. This prevents any alteration of the suspension during routine maintenance or service to avoid any undesired automatic height adjustment.