Power plants – Pressure fluid source and motor – Condition responsive control of motive fluid flow
Reexamination Certificate
2002-06-24
2003-12-09
Look, Edward K. (Department: 3745)
Power plants
Pressure fluid source and motor
Condition responsive control of motive fluid flow
C060S421000
Reexamination Certificate
active
06658843
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The invention relates to a hydraulic control arrangement, by means of which preferably a plurality of hydraulic consumers are supplied with pressure medium (hydraulic fluid) in a demand-feed-regulated manner. Such a hydraulic control arrangement is used, in particular, in mobile working machines, such as, for example, dredger loaders.
A hydraulic control arrangement with demand-feed regulation or on the load-sensing principle is known from EP 0 566 449 B1. In this known control arrangement, a variable-displacement pump is set as a function of the highest load pressure of the actuated hydraulic consumers, in each case in such a way that the pump pressure is above the highest load pressure by the amount of a specific pressure difference. The pressure medium flows to the hydraulic consumers via adjustable metering diaphragms which are arranged between an inflow line, into which the pressure medium is conveyed by the variable-displacement pump, and the hydraulic consumers. What is achieved by means of pressure compensators located downstream of the metering diaphragms is that, when a sufficient quantity of pressure medium is delivered by the variable-displacement pump, there is a specific pressure difference across the metering diaphragms, irrespective of the load pressures of the hydraulic consumers, so that the pressure medium quantity flowing to a hydraulic consumer then depends only on the opening cross section of the respective metering diaphragm. When the metering diaphragm is opened further, a greater pressure medium quantity must flow across it in order to generate the specific pressure difference. The variable-displacement pump is in each case adjusted in such a way that it delivers the required pressure medium quantity. This is also therefore also referred to as demand-feed regulation.
The pressure compensators located downstream of the metering diaphragms are acted upon in the opening direction by the pressure downstream of the respective metering diaphragm and in the closing direction by a control pressure which prevails in a rear control space and which normally corresponds to the highest load pressure of all the hydraulic consumers supplied by the same hydraulic pump. When, during a simultaneous actuation of a plurality of hydraulic consumers, the metering diaphragms are opened to an extent such that the pressure medium quantity delivered by the hydraulic pump adjusted to the limit is smaller than the total pressure medium quantity required, the pressure medium quantities flowing to the individual hydraulic consumers are reduced in the same proportion, regardless of the respective load pressure of the hydraulic consumers. This is therefore referred to as control with load-independent throughflow distribution (LUDV control). Hydraulic consumers activated in this way are known, in brief, as LUDV consumers. Since, in LUDV control, the highest load pressure is also sensed and, by a variation in the pressure medium quantity required, an inflow pressure which is above the highest load pressure by the amount of a specific pressure difference is generated by the hydraulic pump, LUDV control is a special case of load-sensing control (LS control).
For a plurality of hydraulic consumers, to which pressure medium flows in each case via a metering diaphragm with an upstream pressure compensator, which is acted upon in the closing direction only by the pressure upstream of the metering diaphragm and in the opening direction only by the load pressure of the respective hydraulic consumer and by a compression spring, there is no load-independent throughflow distribution. There is a straightforward LS control and LS consumer. Such a control is known, for example, from DE 197 14 141 A1. Here, when a plurality of hydraulic consumers are actuated simultaneously and there is not a sufficient pressure medium quantity delivered by the variable-displacement pump, only the pressure medium quantity flowing to the hydraulic consumer having the highest load pressure is reduced.
DE 197 03 997 A1 discloses a hydraulic control arrangement which includes a variable-displacement pump supplying pressure medium to a plurality of LUDV consumers and to one LS consumer. The LS consumer is a hydraulic steering system in which pressure medium preferentially has to be supplied. This priority of the hydraulic steering system in relation to the LUDV consumers is achieved by means of a priority valve which has a first junction, connected to a portion of the inflow line upstream of the metering diaphragm assigned to the steering system, and a second junction, connected to the load-signaling line, and a valve member of which is acted upon in the opening direction of the connection between the first junction and the second junction by the load pressure of the steering system and the force of a compression spring and in the closing direction of the connection between the first junction and the second junction by the pressure prevailing in the first junction. When the load pressure of the steering system is higher than the load pressure of an LUDV consumer actuated in parallel with this and a variable-displacement pump conveys sufficient pressure medium for all the actuated hydraulic consumers (saturation situation), the priority valve causes so much pressure medium to flow out of the inflow line into the load-signaling line that a pressure dependent on the height of the load pressure of the steering system prevails in the latter and a pressure which is above the steering system pressure by the amount of a specific pressure difference prevails in the inflow line. When so much pressure medium is demanded that the variable-displacement pump is adjusted as far as the maximum stroke volume (undersaturation situation), then the priority valve increases the pressure in the load-signaling line to an extent such that, by a more pronounced throttling of the pressure medium stream, the LUDV pressure compensators lower the pressure difference across the LUDV metering diaphragms to an extent such that the pressure in the inflow line maintains the same level as in the saturation situation and the pressure difference across the LS metering diaphragm is exactly the same as in the saturation situation.
A control arrangement with demand-feed regulation can be implemented not only with a variable-displacement pump having an LS pump-regulating valve, but also with a fixed-displacement pump and an LS-controlled bypass pressure compensator, via which pressure medium conveyed by the hydraulic pump and not required by the hydraulic consumers flows back to a tank. In this case, however, the losses of nonutilizable energy are higher than when the variable-displacement pump is used.
A hydraulic control arrangement is known from DE 34 22 205 A1, FIG.
4
. In this, the two hydraulic pumps are fixed-displacement pumps and the two demand-feed regulators are bypass pressure compensators. An inflow line leads from the pressure outlet of the second hydraulic pump to a control block, while the first hydraulic pump conveys into the inflow line via a nonreturn valve. The two pressure compensators are acted upon in the closing direction by the pressure in the load-signaling line and a compression spring and in the opening direction by the pressure in the inflow line. By causing the compression spring to exert on the second pressure compensator assigned to the second hydraulic pump a force which corresponds to a somewhat greater pressure difference than the compression spring on the first pressure compensator assigned to the first hydraulic pump, in the case of a low demand for pressure medium, only the second hydraulic pump conveys pressure medium to the control block, while the pressure medium quantity conveyed by the first hydraulic pump flows back, pressureless, to the tank via the first pressure compensator. When the demand for pressure medium of the simultaneously actuated hydraulic consumers exceeds the conveyed quantity of the second hydraulic pump, the pressure in the inflow line falls below a value determ
Bosch Rexroth AG
Farber Martin A.
Leslie Michael
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