Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Vehicle subsystem or accessory control
Reexamination Certificate
1999-03-25
2001-07-24
Louis-Jacques, Jacques H. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Vehicle subsystem or accessory control
C701S036000, C280S005500, C280S124157, C280S124158, C060S407000, C060S415000
Reexamination Certificate
active
06266590
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention concerns a pneumatic suspension leveling system for vehicles, in particular for motor vehicles, with the characteristics of the introductory clause of claim
1
. Such a pneumatic suspension leveling system is known to the art, for example, from DE 38 08 395 A1.
2. Description of Related Art
Pneumatic suspension leveling systems of the kind designated above are advantageously equipped with a central pressure accumulator in order, for example, to make short-term, quick level lifts possible for the vehicle for which the maximum lifting flow of the compressor used does not, as a rule, suffice. Moreover, with the aid of such a central pressure accumulator lifting actions can be carried out without the use of a compressor, whereby, on the one hand, the compressor can remain turned off and is consequently spared and, on the other, level adjustment can respond considerably faster because a compressor warmup phase is eliminated.
The compressed air stored in advance in such a central pressure accumulator is at a pressure level which, in any case, must be higher than the air pressure in the pneumatic suspension leveling elements assigned to the vehicle's wheels when the vehicle is fully loaded. In order to be able to constantly guarantee this pressure level, the pressure in the central pressure accumulator must be monitored, for which purpose an accumulator pressure sensor is provided.
An electronic control device of the pneumatic suspension leveling system implements in this connection, among other things, pressure regulation of the prevailing central pressure accumulator air pressure. At the same time air pressure in the central pressure accumulator is expediently maintained between an upper cutoff pressure and a lower cutoff pressure. In this connection, the lower cutoff pressure corresponds to the minimum pressure with which a lifting action can still be performed for the fully loaded vehicle. The upper cutoff pressure is the maximum pressure up to which the central pressure accumulator can be charged by the compressor. The upper cutoff pressure results, for example, from the functional capacity of the compressor used.
If, for example in the course of a vehicle leveling lift, air pressure in the central pressure accumulator falls below the lower cutoff pressure, the control device induces a recharging or refilling of the central pressure accumulator by the compressor. Such filling or charging action is ended as soon as the air pressure in the central pressure accumulator reaches its upper cutoff pressure.
Usually, with pneumatic suspension leveling systems of the kind designated at the outset, electrically driven, single-stage piston compressors or piston pumps are used. The volume flow delivered by such an electric compressor to a considerable extent is dependent on the respective ambient pressure and back pressure in the central pressure accumulator. Vehicles equipped with a pneumatic suspension leveling system of the kind designated at the outset (e.g., trucks and their trailers or busses) should ordinarily operate to full functional capacity in a range of elevation between 0 meters and 4,000 meters above sea level, which corresponds to an ambient pressure range of approximately 0.625 bar (4,000 meters above zero sea level) to approximately 1 bar (0 meters above zero sea level).
As a consequence of this relatively great pressure range for ambient pressure, the maximum air pressure attainable by the compressor used to charge the central pressure accumulator at low ambient pressure, i.e., at great elevations, is available to a considerably lesser extent at lower elevations than at great ambient pressure, i.e., at sea level. Trials have shown that with a specific compressor type at an ambient pressure of 1 bar a maximum charging pressure for the central pressure accumulator of 18 bar is attainable, while the maximum pressure attainable at an ambient pressure of 0.625 bar with the same compressor type is just 13 bar. In order that reliable charging of the central pressure accumulator can be guaranteed for this compressor type also at an ambient pressure of 0.625 bar, the upper cutoff value for the air pressure in the central pressure accumulator must be set to a value smaller than 13 bar. This means, however, that for the overwhelming majority of all operating conditions in which the vehicle equipped with a pneumatic suspension leveling system of the kind designated at the outset finds itself at an elevation lower than 4,000 m above sea level, the functional capacity of the compressor and, consequently, the advantages resulting from the use of a central pressure accumulator can be taken advantage of only to a reduced extent.
SUMMARY OF THE INVENTION
The present invention concerns itself with the problem of improving the functional capacity of a pneumatic suspension leveling system of the kind designated at the outset.
This problem is solved in accordance with the invention by a pneumatic suspension leveling system with the characteristics of claim
1
.
The invention is based on the general idea of selecting the upper cutoff pressure, up to which the central pressure accumulator can be filled with air, in function of the respectively prevailing ambient pressure. In this manner it is possible, at higher ambient pressure, to fill the central pressure accumulator it higher air pressure than would be possible at a lower ambient pressure. The resulting consequence is that at higher ambient pressures the central pressure accumulator can make available a significantly greater air volume flow, whereby the functional capacity, in particular the speed with which an increase in pressure can be carried out in the pneumatic suspension leveling elements, is considerably increased. Only at extreme elevations, i.e., at low ambient pressures, does the pneumatic suspension leveling system in accordance with the invention exhibit the same functional capacity as a comparable conventional pneumatic suspension leveling system without the phasing in accordance with the invention of the upper cutoff pressure in the central pressure accumulator in function of the ambient pressure.
Modification of the upper cutoff pressure and the upper threshold signal value of the accumulator pressure sensor correlating to it expediently takes place approximately proportional to the ambient pressure and to the signal value of the ambient pressure sensor correlating to it.
In a preferred special embodiment of the pneumatic suspension leveling system in accordance with the invention the control device is able to vary the lower threshold signal value correlating to the lower cutoff pressure in the central pressure accumulator in function of the ambient pressure sensor signal values correlating to the ambient pressure. In this manner it is guaranteed that in cases of increased upper cutoff pressure an increased lower cutoff pressure likewise exists. By matching the upper and lower threshold value for the start of central accumulator charging and for the end of central accumulator charging, it is guaranteed that, at different ambient pressures, the pressure differential between these threshold values remains approximately equal, with the result that at different ambient pressures central pressure accumulator charging frequencies of the same magnitude are to be expected. The raising of the lower threshold value at high ambient pressure has the advantage that as a result thereof driving at lower elevations a distinctly higher minimum pressure can always be made available for system supply. On the other hand, lowering of the lower threshold value at low ambient pressure (e.g., mountain driving) has as a result that central pressure accumulator charging frequency does not increase, whereby the compressor is spared. This measure additionally results in the fact that, with decreasing ambient pressure, e.g. during travel through a pass, unnecessarily frequent accumulator charging actions are avoided, whereby the compressor is also spared.
In an especially preferred
Kutscher Eberhard
Lang Joachim
Lohrmann Gerhard
Schneider Reiner
Walter Udo
Calcaterra Mark P.
Daimler-Chrysler AG
Louis-Jacques Jacques H.
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