This invention relates to a damper for a motor vehicle suspension system that includes a pneumatic self-leveling capability to maintain the ride height of the vehicle at a desired level.
Motor vehicles, such as passenger cars and light trucks, experience wide variations in loading. Accordingly, it is desirable to adjust the spring rate and load of the suspension system to compensate for variations in vehicle loading, and accordingly maintain the ride height of the vehicle despite the variations in loading.
Several devices are known in the prior art that compensate for varying vehicle loads to maintain ride height. These devices include air springs mounted on the vehicle either parallel to the main spring or as a replacement for the main spring, and an air spring in combination with a suspension damper, commonly referred to as an xe2x80x9cair shockxe2x80x9d. All of these devices require an air compressor to provide compressed air to the device, a sensor which measures ride height and actuates the compressor, and a solenoid valve to release air when the vehicle loading is reduced. Accordingly, these devices are expensive, difficult to install, and require that the vehicle have the necessary electrical and mechanical infrastructure to permit their use. Hydro-pneumatic systems, in which hydraulic fluid is pumped into the gas chamber of a gas charged damper to adjust ride height are also used to maintain ride height. These systems also require pumps, valves, etc. and tend to be costly and heavy. Finally, a self-contained device sold by Mannesmann Sachs AG of Schweinfurt, Germany under the trade name Nivomat includes a pumping mechanism, level sensor, hydro-pneumatic spring and damper that uses normal road undulations to pump up the suspension to maintain ride height. This device is easy to install but is expensive and compromises the ride quality of the vehicle suspension.
According to the present invention, a suspension damper includes a reservoir housing with a piston slidably mounted therein and including a piston rod extending from the reservoir housing and attached to the vehicle by a mount assembly. An air chamber is defined by a sleeve or dust cover cirucmscribing the piston rod and connected to the reservoir housing by a flexible sleeve. The mount assembly includes a pumping chamber which expands and contracts in response to normal road undulations to inflate the air chamber. A valve controlled by the flexible sleeve controls communication from the air chamber to ambient atmosphere to thereby control inflation of the air chamber, thereby controlling ride height.