WO2002086328A1 - Hydraulic control circuit - Google Patents

Abstract

The invention relates to a hydraulic control circuit, in which the pressure medium, supplied by a hydraulic pump, is firstly supplied to a first hydraulic user and, secondly, supplied to a second hydraulic user. The control circuit in conventional manner comprises a first metering orifice, through which the pressure fluid of the first hydraulic user (LS user) may be supplied and by means of which a constant pressure difference may be set using an upstream in-line first pressure regulator. The pressure medium may be supplied to the second hydraulic user (LUDV user) through a second metering orifice, with a downstream in-line second pressure regulator, which is pressurised in the closing direction by a control pressure in a back pressure chamber and by the pressure after the second metering orifice in the opening direction. The hydraulic pump is controllable with relation to the highest load pressure of the operating hydraulic user in such a way that the pressure in a supply line is above the highest load pressure by a certain pressure difference, whereby a load signal line from the load pressure of the second hydraulic user or pressurised by a pressure derived therefrom is connected to the back pressure chamber of the second pressure regulator and a regulator for the pressure medium source. In known hydraulic control circuits of the above type the initial pressure medium supply for the LS user is guaranteed by means of a really complicated sliding valve as priority valve. The aim of the invention is the production of a hydraulic control circuit as outlined above in a less complicated and thus more economical manner. According to the invention, said aim is achieved, whereby the priority valve is a non-return valve, open from the first connection to the second connection.

Description

 description

Hydraulic control circuit

The invention relates to a hydraulic control circuit with which a primary, first hydraulic consumer and a subordinate, second hydraulic consumer can be supplied with pressure medium and which has the features from the preamble of claim 1.

Such a hydraulic control circuit is known from DE 43 28 283 A1. The pressure medium flows to the two hydraulic consumers via a metering orifice, the first metering orifice assigned to the primary, first hydraulic consumer being preceded by a pressure compensator and a pressure compensator being connected to the second metering orifice assigned to the subordinate second hydraulic consumer. With the help of the pressure compensators, constant pressure differences are maintained via the metering orifices, regardless of the load pressures of the hydraulic consumers, so that the amount of pressure medium flowing to a hydraulic consumer only depends on the opening cross section of the respective metering orifice. An adjustable hydraulic pump is usually used as the pressure medium source and can be controlled as a function of the highest load pressure in such a way that the pressure in an inlet line is above the highest load pressure by a certain pressure difference. The pressure compensator downstream of the second metering orifice is acted upon in the opening direction by the pressure after the second metering orifice and in the closing direction by a control pressure which is present in a rear control chamber and which usually corresponds to the highest load pressure of all hydraulic consumers supplied by the same hydraulic pump.

If several hydraulic consumers, to which pressure medium flows via a metering orifice and one of these downstream pressure compensators, which is acted upon from the rear by the highest load pressure, are actuated simultaneously, then the the amount of pressure medium flowing to them is reduced proportionately if the quantity of pressure medium supplied by the hydraulic pump is smaller than the sum of the partial quantities of pressure medium required. In this case one speaks of a control with load-independent flow distribution (LUDV control). Hydraulic consumers controlled in this way are briefly called LUDV consumers. Because the LUDV control also senses the highest load pressure and an inlet pressure that is a certain Δp above the highest load pressure is generated by the pressure medium source, a LUDV control is a special case of a load-sensing or load-sensing control (LS control).

For several hydraulic consumers, to which pressure medium flows via a metering orifice with an upstream pressure compensator, which is only acted upon in the closing direction by the pressure in front of the metering orifice and in the opening direction only by the load pressure of the respective hydraulic consumer and by a compression spring, no load-independent flow distribution is obtained. You only have one LS control and LS consumer.

DE 43 28 283 A1 now discloses a priority circuit between an LS consumer and one or more LUDV consumers, in which the LS consumer is primarily supplied with pressure medium. For this purpose, a priority valve is provided which has a first connection connected to a line section between the first pressure compensator and the first metering orifice and a second connection connected to the load signaling line, and its valve member opens in the direction of the connection between the first connection and the second Connection of the load pressure of the priority hydraulic consumer, ie the LS consumer, and an additional force can be applied. The priority valve according to the control according to DE 43 28 283 A1 is acted upon by the pressure in the second connection in the direction of closing the connection between the first connection and the second connection. A hydraulic control circuit according to the preamble of claim 1 is also known from DE 197 03 997 A1. Here, just as with the hydraulic control circuit from DE 43 28 283 A1, the valve member of the priority valve is opened in the direction of opening the connection between the first connection and the second connection connected to the load signaling line by the load pressure of the priority hydraulic consumer, that is to say the LS Consumer, and a compression spring applied. The pressure present at the first connection acts on the valve element of the priority valve in the direction of closing.

A priority supply of pressure medium to the LS consumer is ensured both by the hydraulic control circuit according to DE 43 28 283 A1 and by the hydraulic control circuit according to DE 197 03 997 A1. However, quite complex slide valves have to be used as priority valves.

The invention is based on the objective of providing a hydraulic control circuit which has the features from the preamble of claim 1, with which an LS consumer is to be primarily supplied with pressure medium compared to one or more LUDV consumers, and is therefore less expensive and therefore less expensive shape.

The desired goal is achieved according to the invention in that the priority valve is a check valve that opens from the first connection to the second connection. In this extremely simple and inexpensive solution to the problem, when the pressure of the first hydraulic consumer assumes certain values with respect to the highest load pressure of simultaneously actuated second hydraulic consumers, a pressure in the load reporting line is reported via the check valve, which pressure occurs in the line section between the the first pressure compensator and the first metering orifice and which is regulated by the pressure compensator to a value which is above the load pressure of the first hydraulic consumer by the control Δp of the pressure compensator. This pressure, which is reported to the pressure medium source via the check valve, loads the second one Pressure compensators in the closing direction and is accumulated by these downstream of the second metering orifices. In the event of undersaturation, the difference between the pump pressure and the reported pressure decreases, and thus also the pressure difference across the second orifice plates. The amount of pressure medium flowing to the second hydraulic consumer is reduced. In extreme cases, the pump pressure drops to the reported pressure, so that the pressure difference across the second metering orifices is zero, while there is a pressure difference equal to or close to the desired value via the first metering orifice when the first pressure compensator is now fully open.

Advantageous embodiments of a hydraulic control circuit according to the invention can be found in the subclaims.

Thus, according to claim 2, the closing element of the check valve is advantageously acted upon in the closing direction by a weak compression spring, the pressure equivalent of which is, for example, 0.5 bar. As a result, the pressure reported via the non-return valve into the load reporting line is slightly lower than the pressure between the first pressure compensator and the first metering orifice. However, this is only noticeable in an extremely small fluctuation in the amount of pressure medium flowing to the first consumer. But it closes the check valve quickly and safely.

Claim 3 specifies how a primary pressure medium flow is generated for several first metering orifices with little effort. There are simply several check valves in parallel with one another with their second connections on the load signaling line.

An embodiment of a hydraulic control circuit according to the invention is shown in the drawings. The invention will now be explained in more detail with reference to the figures of these drawings. Show it

1 shows an overall circuit diagram of the exemplary embodiment and FIG. 2 shows the circuit diagram of a variable displacement pump including control valves, as is used in the exemplary embodiment.

According to the drawing, a variable displacement pump 10 with an adjusting device 11 draws in pressure medium from a tank 12 and releases it into a system of supply lines 13. A first hydraulic consumer 14, which is designed as a synchronous cylinder and e.g. is used as a steering cylinder, and supplies at least a second hydraulic consumer 15, which is a differential cylinder, with pressure medium. The direction and speed of the synchronous cylinder 14 is determined by a corresponding actuation of a 4/3 proportional directional control valve 16, the valve slide of which is spring-centered in a central position in which the four working connections of the directional control valve 16 are blocked and a control connection 18 to the tank is relieved. When the valve spool is displaced out of its central position in one or the other direction, a metering orifice 17 is opened to different extents, depending on the path that the valve spool is moved. The control connection 18 is connected downstream of the metering orifice with the flow to the synchronous cylinder 14.

A 2-way pressure compensator 20 is inserted between the system of the supply lines 13 and an inlet connection 19 of the directional control valve 16, the control piston of which in the direction of closing from the pressure upstream of the metering orifice 17 and in the direction of opening via a control line 61 from the pressure in the control connection 18 of the directional control valve 16 , that is, the load pressure of the synchronous cylinder 14, and is acted upon by a control spring 21. The force of the control spring 21 is designed so that it has a pressure difference of e.g. 15 bar via the orifice 17 is equivalent.

Thus, while the first pressure compensator 20 assigned to the first hydraulic consumer 14 is connected upstream of the first metering orifice 17, it is the second Hydraulic consumer 15 assigned second pressure compensator 30 downstream of a second orifice 31. For the directional control of the differential cylinder 15, a directional control valve 32 is arranged between the second pressure compensator 30 and the differential cylinder, via which, in comparison to the pressure drop at the metering orifice 31, there is no more significant pressure drop when the differential cylinder 15 is actuated. The metering orifice 31 and the control grooves necessary for directional control are formed in a known manner on the same valve slide, so that directional and speed control are in each case carried out jointly without further notice. The control piston 33 of the pressure compensator 30 will open at the front in the direction of the connection between the metering orifice 31 and the directional control valve 32 from the pressure after the metering orifice and backwards in the direction of closing the connection from a control pressure prevailing in a control pressure chamber 34 and from a weak compression spring 35, which is a Pressure of, for example, only 0.5 bar is equivalent. The front side of the control piston 33 is connected to the control pressure chamber 34 via a channel 36 running in the control piston, a check valve 37 opening towards the control pressure chamber being arranged in the channel 36.

Parallel to the metering orifice 31, the pressure compensator 30 and the directional control valve 32 for the second hydraulic consumer 15, further second metering orifices, second pressure compensators and second directional control valves for further second hydraulic consumers can be connected to the system of the feed lines 13. The control pressure chambers 34 of all pressure compensators 30 are connected to one another so that the same pressure is present in these control pressure chambers. When a second hydraulic consumer is actuated, the regulating pistons 33 of the pressure compensators seek to bring them into a position in which a pressure difference, which is only equivalent to the force of the compression spring 35, is established on their front side than in the control pressure chambers 34.

Via the channels 36 and the check valves 37, the first hydraulic consumer 14 is completely ignored, the highest one Load pressure of all actuated second hydraulic consumers 15 in the control pressure chambers 34.

The control pressure chambers 34 are connected to a load signaling line 38, which leads to the adjusting device 11 of the pump 10. In particular, as can be seen from FIG. 2, the load signaling line 38 leads to a control valve 39 with three connections, one of which is connected to an actuating cylinder 40 of the variable displacement pump 10. Another connection of the control valve 39 is connected to a feed line 13 and the third connection to tank 12. The control piston of the control valve 39 is acted upon by the pressure in the feed line 13 in the direction of a connection of the first connection to the second connection and by the pressure in the load signaling line 38 and by a control spring 41 in the direction of a connection of the first connection to the third connection. Variable pumps and control valves according to the circuit diagram according to FIG. 2 are generally known and are readily available on the market. It is therefore unnecessary to go into this in more detail. It should only be pointed out that the pump control causes a pressure to be set in the feed line 13 which is a pressure difference equivalent to the force of the control spring 41 above the pressure in the load signaling line 38. The pressure difference is e.g. 18 bar, is therefore higher than that of the force of the control spring 21 of the first pressure compensator 20 equivalent pressure difference of 15 bar.

The first hydraulic consumer 14 is to be supplied primarily with pressure medium before the second hydraulic consumer 15. For this purpose, a check valve 45 is provided, which is connected with its inlet 46, which represents the first connection, to a line section 48, which runs between the pressure compensator 20 and the inlet connection 19 of the directional control valve 16, and with its outlet 47, which represents the second connection, to the load signaling line 38, that is to say from opens from the line section 48 to the load signaling line 38 and has a closing member which acts in the open direction on the pressure in the line section 48 and in the closing direction on the pressure in the load signaling line becomes. A weak compression spring 50, the pressure equivalent of which is, for example, 0.5 bar, also acts on the closing member 49 in the closing direction.

The load signaling line 38 is connected to the tank 12 via a current regulator 55. The load signaling line is relieved of pressure via this current controller if none of the hydraulic consumers is actuated.

The first hydraulic consumer 14, which is primarily to be operated with pressure medium, is always supplied with sufficient pressure medium without the priority valve 45 having to function if the sum of its load pressure plus the control Δp of the adjusting device 11 on the variable displacement pump 10 is lower than the highest load pressure of all simultaneously actuated second hydraulic consumers 15. Because pressure medium always flows to the hydraulic consumer with the lowest load pressure.

Let us now consider the case in which the load pressure of the first hydraulic consumer 14 is higher than the highest load pressure of all the simultaneously actuated second hydraulic consumers 15. It is e.g. 80 bar, while the highest load pressure of LUDV consumers is 60 bar. When the directional valve 16 is actuated, the pressure upstream of the metering orifice 17 rises from 15 bar to 95 bar because of the pressure equivalent of the compression spring 21. The check valve reports, once you see from the closing spring 50, the pressure of 95 bar in the load signaling line 38, so that the hydraulic pump 10 delivers so much pressure medium that a pump pressure of 95 bar plus 18 bar is equal in the system of the feed lines 13 113 bar. The pressure compensator 20 throttles this 113 bar down to the 95 bar present in the line section 48. The pressure in the load reporting line of 95 bar is also present in the control pressure rooms 34 of the LUDV pressure compensators 30.

If a second hydraulic consumer 15 is now to be actuated, the corresponding metering orifice 31 is opened and the corresponding directional valve 32 shifted from its middle position. Between the metering orifice 31 and the downstream pressure compensator 30, the pressure of the compression spring 35 shows the same pressure as in the control pressure chamber 34, namely a pressure of 95 bar. Because only then is there a balance of forces on the control piston 33 of the pressure compensator 30. Since the pressure in the system of the supply lines 13 is 113 bar, the pressure difference across a metering orifice 31 is, as desired, 18 bar in accordance with the control Δp of the variable pump 10.

If now by increasing the opening cross section of a metering orifice 17 or by increasing the opening cross sections of several metering orifices 31 more and more pressure medium quantity is requested by the pump, this finally reaches its maximum adjustment, from which the pressure medium quantity can no longer be increased. This leads to a reduction in the pressure in the system of the feed lines 13 below the value of 113 bar and, because the pressure downstream of the metering orifices 31 is still kept at 95 bar by the pressure compensators 30, leads to a reduction in the pressure difference across the metering orifices 31, so that a reduced amount of pressure medium flows to the actuated second hydraulic consumers. Ultimately, the pump pressure in the feed lines can drop to 95 bar, so that the pressure difference across the metering orifices 31 is zero and the second hydraulic consumers 15 no longer receive any pressure medium. The pressure difference across the metering orifice 17 of the directional control valve 16 is still 15 bar when the pressure compensator 20 is fully open, so that the first hydraulic consumer is fully supplied with pressure medium.

The behavior of the control circuit is the same as that just described if the highest load pressure of the actuated second hydraulic consumer is between the load pressure of the first hydraulic consumer and the sum of the load pressure of the first hydraulic consumer plus the pump Δp. Even then, a load pressure of the first hydraulic consumer increased by 15 bar is reported via the check valve 45 into the load signaling line 38. The closing spring 50 tensioned to 0.5 bar has the effect that the pressure reported via the check valve 45 and thus also the pressure in the feed lines 13 is 0.5 bar lower than previously assumed. This means that in the event of extreme undersaturation with the pressure compensator 20 fully open, the pressure difference across the metering orifice 17 drops from 15 bar to 14.5 bar. This is hardly noticeable in the amount of pressure medium flowing to the first hydraulic consumer.

If there are a plurality of first hydraulic consumers 14 which can be actuated simultaneously, there are, as indicated in FIG. 1, a plurality of check valves 45 which each have a line section 48 with their first connection 46 and with the load signaling line with their second connection 47 are connected.

Claims

claims 1. Hydraulic control circuit for a priority, first hydraulic consumer (14) and for a subordinate, second hydraulic consumer (15) with a first metering orifice (17), via which pressure medium can be fed to the first hydraulic consumer (14) and through which upstream, first pressure compensator (20), a constant pressure difference can be set, with a second metering orifice (31), via which pressure medium can be fed to the second hydraulic consumer (15) and which is followed by a second pressure compensator (30), which in the closing direction of a control pressure present in a rear control chamber (34) and in the opening direction can be acted upon by the pressure after the second metering orifice (31), with a pressure medium source (10) of variable delivery quantity, which in dependence on the highest load pressure of the actuated hydraulic consumers (14, 15) can be controlled that the pressure in an inlet line (13) by a certain pressure difference is above the highest load pressure, with a load signaling line (38) which can be acted upon by the load pressure of the second hydraulic consumer (15) or a pressure derived therefrom and with the rear control chamber (34) of the second pressure compensator (30) and with a control element (11) is connected to the pressure medium source (10), with a priority valve (45) which has a first connection (46) connected to a line section (48) between the first pressure compensator (20) and the first metering orifice (17) and one with the load signaling line ( 38) connected, second connection (47), characterized in that the priority valve (45) is a check valve opening from the first connection (46) to the second connection (47). 2. Hydraulic control circuit according to claim 1, characterized in that the closing member (49) of the check valve (45) is acted upon in the closing direction by a weak compression spring (50). 3. Hydraulic control circuit according to claim 1 or 2, characterized in that a plurality of first metering orifices (17), a plurality of first pressure compensators (20) and a plurality of check valves (45) are provided, each of which has a line section (48) with its first connection (46) ) are connected between a first pressure compensator (20) and the first metering orifice (17) located downstream thereof and with its second connection (47) to the load signaling line (38).