Air Suspension Systems—What Advanced Applications May Be Possible?
Authors: Wolf‐Monheim Friedrich 
Published: April 2015

Air suspension systems fulfill the customer expectations for high driving comfort and driving dynamics. Today there are rear air leveling systems and four‐corner air suspension systems with and without switchable additional volumes. Four‐corner air suspension systems usually have externally guided air springs with thin wall bellows, defined as flexible bladder or bag containing pressurized air, with one axial fiber layer only. This enables reduced harshness behavior compared to standard bellows with two crossed fiber layers. Four‐corner air suspension systems can reduce the air resistance and the aerodynamic lift of a vehicle during high speed driving by lowering the vehicle body. The off‐road performance of a vehicle can be improved by raising the vehicle body.

Continuously variable air suspension systems deliver a higher degree of freedom with regard to spring stiffness, compared to four‐corner air suspension systems with switchable additional volumes. To design such a system, the air volumes and/or the effective areas of the air spring modules can be varied. For systems with variable effective areas, two separate bellows can be pressurized independently from one another. The first bellow functions as the main air spring. The second bellow is attached to the rolling piston in a way that the diameter of the rolling piston can be varied with the pressure inside the bellow. As the air spring characteristics are very sensitive to changes in the effective area, already small changes in volume of the second air bellow introduce significant changes in air spring stiffness.

Air spring damper systems introduce not only springing functionality but also damping functionality to an automotive chassis system. Both the springing and the damping functionality are provided by air as the working fluid.

A further category of advanced air suspension systems are interlinked four‐corner air suspension systems. Pneumatic pipes with electromagnetic pneumatic valves interconnect the air spring modules. A left to right connection between the two front and the two rear suspension air spring modules, respectively, can be used to reduce the roll angles of the vehicle body while driving over single‐sided impacts and to reduce the roll angle oscillation accelerations while driving on uneven road surfaces. A front suspension to rear suspension connection between the air spring modules can be used to reduce the pitch angles of the vehicle body while driving over impacts and to reduce the pitch angle oscillation accelerations while driving on uneven road surfaces.

For active systems, a pneumatic connection between the front and the rear suspension air spring modules can be used to achieve active anti‐lift and/or anti‐dive pitch angle compensation during acceleration and braking maneuvers. The left to right connection can be used to achieve body roll angle compensation during lateral dynamic driving maneuvers. Active air suspension systems can be based on air mass or air volume changes. A system with an active air mass variation can be realized, for example, with a high pressure reservoir and a compressor. Active air volume change can be based on pneumatic, hydraulic, or electromechanical actuators.