Spring devices – Vehicle – Comprising compressible fluid
Patent
1995-04-10
1997-04-29
Butler, Douglas C.
Spring devices
Vehicle
Comprising compressible fluid
138 31, 188314, 267 6425, 280708, B60G 1704, B60G 1130, F16F 906, F15B 124
Patent
active
056241054
DESCRIPTION:
BRIEF SUMMARY
The present invention pertains to a hydropneumatic suspension system, in particular for motor vehicles, comprising at least one hydraulic strut that during its deflection and rebound movements acts via a hydraulic medium upon at least one hydropneumatic piston-type accumulator that has a separating piston which separates a hydraulic accumulator chamber from a spring chamber that contains a compressible medium, in particular a gas, with a hydraulic pressure that originates from the accumulator chamber and a pneumatic pressure that originates from the spring chamber acting upon said separating piston, and with at least one supplementary spring force acting upon the separating piston of the piston-type accumulator in addition to the forces resulting from charging the separating piston with the hydraulic pressure and the pneumatic pressure.
In hydropneumatic suspension systems, a hydraulic medium is displaced during the deflection and rebound movements of the strut, i.e., due to movement of a piston inside of a cylinder. When deflecting the strut, a certain volume of the hydraulic medium flows into the accumulator chamber of a hydropneumatic accumulator such that the volume of a compressible medium, usually a gas, that is contained in said hydropneumatic accumulator is reduced. This compression causes a pressure increase and consequently an elastic spring effect that subsequently causes a backflow of the hydraulic medium for the rebound movement of the strut. In a static position of the strut, the pneumatic pressure generates via the hydraulic medium a supporting force for carrying the respective load inside the strut.
The essential advantage of hydropneumatic suspension systems can be seen in the fact that nearly constant suspension characteristics can be attained even under changing load ratios (ratio between the empty load and the full load of the strut) due to the fact that the level of the motor vehicle and consequently also the available travel of the strut can practically be maintained constant by means of a hydraulic leveling process, i.e., by introducing or removing the hydraulic medium. This means that it is practically possible to attain a suspension that does not depend on the load. Consequently, systems of this type are primarily suitable for motor trucks in which a high load ratio usually occurs.
However, this high load ratio is associated with the disadvantage that it requires that the compressible medium has a very large total volume such that the entire load ratio of the strut can be absorbed by the spring chamber or the medium contained therein while causing the smallest possible pressure changes (volume changes of the compressible medium) and--for reasons of comfort--attaining a flat, "smooth" characteristic line. However, this requires a very large structural size of the spring chamber with a long displacement path of the separating piston. This can cause installation problems in a motor vehicle and naturally is also associated with excessive costs regarding the accumulator.
U.S. Pat. No. A 4,153,237 discloses a suspension system of the initially mentioned type in which a helical pressure spring which charges the separating piston with a supplementary spring force that acts in the direction of the pneumatic pressure and opposite to the hydraulic pressure is arranged inside of the spring chamber, i.e., inside of the pneumatic pressure medium, in order to influence the spring characteristics of the piston-type accumulator. However, this is associated with the disadvantage that the helical spring substantially limits the range of travel of the separating piston in the direction of the spring chamber such that the pneumatic medium cannot be compressed arbitrarily. Consequently, the spring characteristics cannot be easily adjusted to arbitrary requirements.
European Patent No. A 0,052,782 (or the corresponding U.S. Pat. No. A 4,478,431) discloses one additional suspension system in which at least two accumulators are provided for each strut. In a few of the respective embodiments, one of the acc
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Butler Douglas C.
Hemscheidt Fahrwerktechnik GmbH & Co.
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