Power plants – Pressure fluid source and motor – Having condition responsive control in a system of distinct...
Reexamination Certificate
2001-07-27
2003-11-11
Look, Edward K. (Department: 3745)
Power plants
Pressure fluid source and motor
Having condition responsive control in a system of distinct...
C060S446000
Reexamination Certificate
active
06644025
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The invention relates to a control arrangement which is used to supply at least two hydraulic consumers with pressure medium. The invention also relates to a pressure differential valve which is used in particular in said control arrangement.
A hydraulic control arrangement of this type is known, for example from EP 0 566 449 A1. This document relates to a hydraulic control arrangement using the load-sensing principle, in which 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 feed pressure is higher than the highest load pressure by a defined pressure difference. The pressure medium flows to the two hydraulic consumers via two adjustable meter-in variable restrictors, a first of which is arranged between a pump line leading from the variable-adjustment pump and a first hydraulic consumer, and the second of which is arranged between the pump line and the second hydraulic consumer. The pressure compensators connected downstream of the meter-in variable restrictors mean that, if a sufficient quantity of pressure medium is supplied, there is a defined pressure difference across the meter-in variable restrictors irrespective of the load pressures of the hydraulic consumers, so that the quantity of pressure medium flowing to one hydraulic consumer is only dependent on the opening cross section of the meter-in variable restrictor in question. If a meter-in variable restrictor is opened further, it is inevitable that a greater quantity of pressure medium will flow through it, in order to generate the defined pressure difference.
The variable-displacement pump is in each case adjusted in such a way that it supplies the quantity of pressure medium which is required. This is therefore known as control based on the required flow.
The pressure compensators which follow the meter-in variable restrictors are acted upon in the opening direction by the pressure downstream of the respective meter-in variable restrictor and in the closing direction by a control pressure which prevails in a rear control space and which usually corresponds to the highest load pressure of all the hydraulic consumers supplied by the same hydraulic pump. If, in the event of simultaneous actuation of a plurality of hydraulic consumers, the meter-in variable restrictors are opened so wide that the quantity of pressure medium supplied by the hydraulic pump, which has been moved all the way to its stop, is lower than the total quantity of pressure medium required, the quantities of pressure medium flowing to the individual hydraulic consumers are reduced in equal proportions irrespective of the prevailing load pressure of the hydraulic consumers. This is therefore referred to as control with load-independent flow distribution (LIFD control). Hydraulic consumers which are controlled in this way are known as LIFD consumers for short. Since, with LIFD control, the highest load pressure is also sensed and a feed pressure which lies above the highest load pressure by a defined pressure difference is generated by the pressure medium source, LIFD control is a special case of a load-sensing control (LS control).
There is no load-independent flow distribution in the case of a plurality of hydraulic consumers to which pressure medium flows in each case via a meter-in variable restrictor with upstream pressure compensator which is acted upon in the closing direction only by the pressure upstream of the meter-in variable restrictor and in the opening direction only by the load pressure of the corresponding hydraulic consumer and by a compression spring. This is a case of a simple LS control and an LS consumer. A control set-up of this type is known, for example, from DE 197 14 141 A1. In the event of simultaneous actuation of a plurality of hydraulic consumers and of insufficient quantities of pressure medium being supplied by the variable-displacement pump, in this case only the quantity of pressure medium flowing to the hydraulic consumer with the highest load pressure is reduced.
An advantage of LS control with pressure compensators connected upstream of the meter-in variable restrictors compared to LS control with pressure compensators connected downstream of the meter-in variable restrictors, however, is that, in the event of an excess quantity being supplied for a brief time by the variable-adjustment pump and an associated rise in the feed pressure, the upstream pressure compensators, by reducing their opening cross section, do not allow any increase in the pressure difference across the meter-in variable restrictors, so that no further pressure medium flows across the meter-in variable restrictors and the speed of the hydraulic consumers is not changed. The excess quantity flows back to a tank via a pressure-limiting valve. In the case of a control set-up with pressure compensators connected downstream of the meter-in variable restrictors, by contrast, the excess quantity is passed through to the hydraulic consumers.
Depending on whether the user attaches more importance to a load-independent flow distribution or to preventing excess quantities from flowing to the hydraulic consumers, he will select an LIFD control or an LS control. This has hitherto been a drawback for the manufacturers of hydraulic components, since they have to offer control blocks for both LIFD control set-ups and for LS control set-ups. These differ considerably, since very divergent structures are required depending on whether a pressure compensator is connected upstream or downstream of the corresponding meter-in variable restrictor.
SUMMARY OF THE INVENTION
By contrast, the invention is based on the objective of providing a hydraulic control arrangement which has the features of the introductory-mentioned type, i.e. in which in particular pressure compensators are connected downstream of meter-in variable restrictors, in such a way that the flow of excess quantities to the hydraulic consumers is prevented.
The desired object is achieved, according to the invention, in a hydraulic control arrangement of the generic type, wherein the control pistons of the pressure compensators can be acted on in the closing direction by a control pressure which is present in a rear control space, is derived from the feed pressure prevailing in the feed line with the aid of a valve device and changes with the feed pressure. While in the known hydraulic control arrangement with pressure compensators connected downstream of the meter-in variable restrictors these compensators are acted on in the rear control space by the highest load pressure, on which the delivery quantity of the variable-displacement pump has no influence, in a control arrangement according to the invention the control pressure which is present in the rear control space is derived from the feed pressure and changes with the latter. Therefore, if the feed pressure rises on account of a delivery quantity from the variable-displacement pump rising beyond demand, the control pressure also rises. The control pistons of the pressure compensators are moved accordingly in the closing direction, so that the pressure downstream of the meter-in variable restrictors also rises and the pressure difference across the meter-in variable restrictors does not change. However, a constant pressure difference across a meter-in variable restrictor also means a constant quantity of pressure medium flowing across the meter-in variable restrictor. Therefore, while maintaining the basic arrangement of meter-in variable restrictor and downstream pressure compensator, and therefore without fundamental changes to a control block, the same control performance as in the case of a control set-up with pressure compensators connected upstream of the meter-in variable restrictors, i.e. control blocks of altogether different construction, is achieved with minor modifications.
Therefore, the difference between the feed pressure and the control pressure, when the variable-displacement pump has not b
Oberhäusser Martin
Weickert Thomas
Bosch Rexroth AG
Farber Martin A.
Leslie Michael
Look Edward K.
LandOfFree
Control arrangement for at least two hydraulic consumers and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Control arrangement for at least two hydraulic consumers and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Control arrangement for at least two hydraulic consumers and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3178338