Power plants – Pressure fluid source and motor – Condition responsive control of pump or motor displacement
Patent
1992-10-15
1994-03-29
Look, Edward K.
Power plants
Pressure fluid source and motor
Condition responsive control of pump or motor displacement
91518, F16D 3102
Patent
active
052973816
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a hydraulic system which is substantially free of instabilities in fluid flow arising from the load demand outstripping the capacity of the feed pump.
German Patent Publication DE 26 51 325 and corresponding U.S. Pat. No. 3,987,622 disclose a hydraulic system wherein the pressure extant at the pump as well as the highest load pressure are applied to a control valve. When the pump cannot furnish the volume flow required by the control valves and their associated consumers, the pressure difference between the pressure of the pump and the highest load pressure is reduced. As a result, the control valve reduces its supply to control pressure transducers by means of which the valves associated with the consumers are actuated. As a result, the flow through the valves is restricted. This restriction, however, becomes effective only when an excess demand already exists. When this restriction becomes effective, the consumers can no longer be controlled by means of their control valves.
In the system disclosed in German Patent Publication DE 35 46 336 and corresponding U.S. Pat. No. 4,759,183, the electrical control signals of the actuated multipleway valves are added. The volume flow which corresponds to the sum of the control signals is compared with the highest possible pump flow. When the sum of the control signals exceeds the possible pump flow, the control signals are reduced. In this system, it is necessary to evaluate all the control signals. Furthermore, it is necessary by means of a computer to take into consideration the dependence of the valve flows on the control signals.
It is the object of the invention to configure the hydraulic systems so that it is not subject to fluctuations, and that, moreover, it becomes possible to effect a desired weighting or apportioning and adjustment of the individual consumer flows relative to the operating parameters of the pump.
SUMMARY OF THE INVENTION
The above and other objects and advantages of the present invention are achieved in the embodiments illustrated herein by the provision of a hydraulic system for feeding hydraulic fluid to a plurality of loads (or consumers) from a common controllable pump which comprises individual control valves associated with each of the loads and responsive to respective external control signals, means for measuring the feed pressure of the pump and the load pressure of each of the plurality of loads, and means for determining the difference between the feed pressure and the highest one of the load pressures and for deriving a difference signal representative of the difference. Means are also provided for adjusting the feed pressure of the pump in response to the difference signal, and means are provided for comparing the difference signal with a predetermined minimum pressure difference signal and for generating a first signal when the pressure difference signal is at least equal to the predetermined minimum difference signal and generating a second signal when the pressure difference signal is less than the predetermined minimum different signal. Further, the hydraulic system also comprises means for adjusting the external control signals in response to the first and second signals.
The invention as defined above has the advantage that the response range of the means for adjusting the external control signals is not exceeded, and as a result, the individual consumers remain controllable even at a high consumption, whereas in the known system, the speed of the individual consumers is no longer controllable when the maximum possible input pump flow is exceeded. A further advantage resides in the fact that not only the pressure difference, but preferably also the change in pressure difference and the direction of change of the pressure difference can be detected. As a result, reduced consumption may commence as soon as a deficiency (i.e. the sum of the said consumer flows exceeds the highest possible input pump flow (maximum pump flow)) is evident as a result of the amo
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Eich Otwin
Salz Franz-Peter
Barmag AG
Look Edward K.
Nguyen Hoang
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