EP1497559A1

EP1497559A1 - Hydraulic control system using load-sensing technology

Info

Publication number: EP1497559A1
Application number: EP03724956A
Authority: EP
Inventors: Gottfried Olbrich
Original assignee: Bosch Rexroth AG
Current assignee: Bosch Rexroth AG
Priority date: 2002-04-12
Filing date: 2003-04-04
Publication date: 2005-01-19
Anticipated expiration: 2023-04-04
Also published as: JP2006505746A; DE50302004D1; US20050178116A1; DE10216119A1; WO2003087585A1; ATE313715T1; EP1497559B1

Abstract

At a certain pressure in the reporting line sector (42) the servo-valve switches from a first higher limit pressure to a second lower limit pressure. The individual reporting channels (44-47), as viewed from a first line sector, are such that the consumers connect to the succeeding line in falling order of pressure. The servo-valve itself is switched over by a control line (64) which is connected to next reporting line sector (42). The servo-valve system valve (55) is arranged between the first line sector (40) and a discharge line (25) having variable response pressure. The servo-valve has a valve element (56) which is sprung (57) shut and can be loaded by pressure to its open setting. The force of the spring (57) changes in accordance with the pressure in reporting line sector (42).

Description

description

Hydraulic control arrangement in load-sensing technology

The invention is based on a hydraulic control arrangement in load-sensing technology which, according to the preamble of claim 1, has a first directional valve via which pressure medium can be fed to a first hydraulic consumer, and at least one further directional valve via which pressure medium can be fed to a further hydraulic consumer and which is preferably combined with the first directional control valve to form a valve block and has a load-sensing control.

A hydraulic control arrangement according to the preamble of claim 1 is e.g. known from DE 197 15 021 A1. This is a hydraulic control arrangement based on the load-sensing principle, in which a variable pump or a bypass pressure compensator assigned to a constant pump depends on a control pressure that changes with the highest load pressure of the hydraulic consumers actuated, preferably in Dependency on the load pressure itself, is set so that the pump pressure is a certain pressure difference, the control Δp, above the highest load pressure. For this purpose, the control pressure is fed to a load-sensing control valve, which is implemented by a control valve of the variable displacement pump or by the bypass pressure compensator, via a load signaling line. This consists of a number of line sections corresponding to the number of directional valves. Each directional valve has an individual signaling channel. Shuttle valves are used to connect the highest pressure individual signaling channel with the load signaling line and its line sections with each other.

The pressure medium flows to the hydraulic consumers via adjustable metering orifices, which are usually formed on the control slides of the directional control valves and which flow between an inlet line coming from the variable displacement pump and the hydraulic consumers are arranged. Due to the pressure difference between the highest load pressure and the pump pressure, which is independent of the highest load pressure, the speed at which the hydraulic consumer with the highest pressure moves depends solely on the flow cross section of the corresponding metering orifice.

By means of the metering orifices upstream or downstream so-called individual pressure compensators it can be achieved that the speed of movement of all hydraulic consumers actuated at the same time is independent of the load pressures. With the individual pressure compensators, the pressure difference across the metering orifices associated with the hydraulic consumers with lower load pressure is also kept constant, so that the amount of pressure medium flowing to a hydraulic consumer only depends on the flow cross section of the respective metering orifice. If a metering orifice is opened further, more pressure medium must flow over it in order to generate the specific pressure difference. The variable displacement pump or the bypass pressure compensator is adjusted so that the required quantity of pressure medium is supplied. One therefore speaks of a demand flow control.

As shown in DE 197 15 021 A1, the pump, inlet or system pressure in a load-sensing hydraulic control arrangement can be limited to a limit pressure by providing a nozzle in the first line section of the load signaling line connected to the control valve and between it and connects the control valve to the first line section with a pressure limiting valve. The pump pressure then does not increase by more than the control Δp above the limit pressure set with the pressure relief valve. In addition, the load pressure with which a hydraulic consumer can be subjected to a maximum can also be set individually. For this purpose, according to DE 197 15 021, a pressure relief valve is connected to the individual signaling channel of the corresponding directional valve section downstream of a nozzle. This controls the control pressure in the spring chamber of the individual pressure compensator borders. This is because the pressure compensator closes when the pressure upstream of the orifice plate exceeds the control pressure increased by the control Δp of the individual pressure compensator. The load pressure can therefore only increase to a pressure that is higher than the response pressure of the pressure relief valve by the control Δp of the individual pressure compensator. However, an individual pressure compensator is required in the directional valve section of the hydraulic consumer.

The invention is based on the objective of further developing a hydraulic control arrangement which has the features from the preamble of patent claim 1 in such a way that the load pressure for a hydraulic consumer is economically limited to a lower value than for another hydraulic consumer, regardless of whether it is limited to the lower value, whether the second function is operated alone or together with the first function. This is to protect the second function from excessive pressure.

The desired aim is achieved according to the invention in that, in the hydraulic control arrangement with the features from the preamble of patent claim 1, the pilot valve arrangement can be adjusted from a high, first limit pressure to a lower, second limit pressure at a certain pressure present in a further line section of the load-signaling line and that the individual reporting channels, viewed from the first line section of the load reporting line, can be connected to the successive line sections of the load reporting line after the maximum load pressure of the hydraulic consumers has dropped. A control arrangement according to the invention is used to actuate two or more groups of one or more hydraulic consumers, the groups differing from one another by different maximum load pressures. Viewed from the control valve, the load signaling line initially contains the line sections that can be connected via a shuttle valve to an individual signaling channel of a directional control valve with which a hydraulic consumer from the group with the highest maximum load pressure is controllable. Then follow the line sections for the group of hydraulic consumers with the second highest load pressure, then the line sections for the group with the third highest load pressure and so on. Usually this sequence will correspond to the sequence in a valve block for reasons of simple drilling and the same possible design of the individual directional valve sections, so that the directional valve sections for the group with the second highest are applied to the directional valve sections for the consumer group with the highest maximum load pressure follow maximum load pressure. If more than two different maximum load pressures are provided, then the directional valve sections for the group with the third highest maximum load pressure follow. Overall, the directional valve sections are then arranged in the valve block according to the falling maximum load pressure. If a hydraulic consumer from a group that does not have the highest maximum load pressure is actuated, the corresponding line section of the load signaling line is acted upon with the load pressure via the assigned shuttle valve. With this pressure, the pilot valve arrangement is controlled so that the pressure in the first line section of the load signaling line between the nozzle and the control valve cannot exceed a maximum control pressure corresponding to the lower maximum load pressure at least when the lower maximum load pressure is reached at the corresponding consumer. If the group includes several hydraulic consumers and thus several directional control valves and several line sections of the load signaling line, the pressure tap in the front line, i.e. in the line section closest to the control valve, is sufficient, since the pressure from line sections located further back via one or more shuttle valves in the reaches the foremost line section. In a hydraulic control arrangement according to the invention, no individual pressure compensators are necessary in order to have different maximum load pressures for the hydraulic consumers.

Advantageous embodiments of a hydraulic control arrangement according to the invention can be found in the subclaims. In principle, it is conceivable to detect the pressure in a further line section of the load-signaling line using a pressure sensor and to electrically adjust the pilot valve arrangement. However, it seems simpler in terms of effort if, according to claim 2, the pilot valve arrangement is hydraulically adjustable via a control line which is connected to the further line section of the load-signaling line.

In terms of space requirement, it appears particularly advantageous if the pilot valve arrangement has a pilot valve arranged between the first line section and a relief line, the response pressure of which can be changed, for example, between two pressure stages. In particular, the pilot valve can be a pressure limiting valve with two pressure stages and can be provided with a valve element which is acted upon by the pressure in the opening direction which is present at the valve inlet. However, it is also possible for the valve element of a pilot valve arranged between the first line section of the load-sensing line and a relief line or switchable therebetween to be acted upon in the opening direction by the pressure on the side of the nozzle remote from the control valve. The pilot valve will then limit the control pressure in the line section between the nozzle and the control valve, to which it is connected with its main input separated from a control input, to a pressure which is below the response pressure by the control Δp.

A first possibility of obtaining two pressure stages of the pilot valve consists, as stated in claim 4, of changing the bias of a valve spring which acts on the movable valve element of the pilot valve against a pressure force generated on an active surface of the valve element in the direction of a closed position , An auxiliary piston is preferably used for this purpose, via which the preload force of the valve spring can be changed between two values defined by a first fixed stop and a second fixed stop. The auxiliary piston has an effective area that is larger than the effective area on the valve element, so that when the two effective areas on the valve element and the auxiliary piston are acted upon with the same pressure of the auxiliary piston, the valve spring will initially bias more before the pilot valve opens when the pressure increases, and then its position determined by the stop which defines the higher value of the spring preload is reliably maintained. Depending on the switching position of a changeover valve, which is determined by the pressure in the further line section of the load-signaling line, the effective area on the auxiliary piston can be relieved of pressure or pressurized. By using a changeover valve, a very low pressure in the further line section of the load signaling line is sufficient to set the pilot valve to the low limit pressure.

It is particularly advantageous if, according to claim 6, the two stops can be adjusted independently of one another by turning two adjusting screws. Particularly advantageous in terms of design, the hydraulic control arrangement according to claim 5 or 6 can be found in claims 7 to 9. It is particularly preferred, among other things, that the valve spring at the end remote from the valve element can be supported by the auxiliary piston, that is to say this end is displaceable from the auxiliary piston. This appears to be structurally simpler than a change in the spring preload that is also possible in principle by displacing a valve seat for the valve element.

The response pressure of a valve, on whose valve element acts in the opening direction or more generally, in one direction a compressive force and in the opposite direction a spring force, can be changed not only by changing the spring preload, but also by changing the effective area for the pressure change. The latter succeeds according to claim 10 in a pilot valve of a hydraulic control arrangement according to the invention in a structurally simple manner in that the valve element can be acted upon in the opening direction by a pressure in the first line section of the load-signaling line and on a first control surface, and in that a second control surface is present on an auxiliary piston which acts on the Valve element acts and which can be relieved of pressure or pressurized depending on the switching position of a changeover valve determined by the pressure in the further line section of the load signaling line. Preferably, according to claim 11 or 12, the valve element is acted upon by a pressure applied to the second control surface in the closed position, the second control surface being smaller than the first control surface.

The changeover valve can be a simple and inexpensive 2/2 way valve with a single control edge, if it is arranged according to claim 13 in series with a nozzle between the load signaling line and a relief line, the control chamber on the auxiliary piston at the connection between the nozzle and 2/2 Directional control valve is located. However, the changeover valve can also be a 3/2-way valve, which connects a control chamber on the auxiliary piston in one switching position to the load signaling line and in the other switching position to a relief line. There is no control oil leakage flow in any position of the changeover valve, since the 3/2 way valve separates the load signal line from the relief line in both switching positions.

Directly operated valves, which can be set to different response pressures during operation, are rarely required, are special designs and are therefore relatively expensive to manufacture. Large-volume valves can be used for the pilot valve arrangement if, according to claim 15, a first pilot valve arranged between the first line section and a relief line or switchable therebetween and a second one between the. Load control line and the relief line arranged or interposed pilot valve and the connection speaking pressure of the second pilot valve is less than the response pressure of the first pilot valve.

Particularly preferred is an embodiment according to claim 16, according to which the two pilot valves are pressure relief valves and the second pilot valve can be connected to the first line section with its input via a switch valve that is switchable depending on the pressure applied in a further line section of the load signaling line. Here, too, a small valve can be used as a changeover valve, which is inexpensive to produce in large quantities.

With an education according to claim 17, the following is achieved. Because the input of the second pilot valve, designed as a pressure relief valve, is connected with its input downstream of a nozzle to a first further line section of the load signaling line or to the associated individual load signaling channel, the system pressure is the response pressure in solo operation of the associated function (directional valve section) of the second pilot valve is limited. In parallel operation of this function (directional valve section) with a function located further to the front and secured to a higher pressure (directional valve section), on the other hand, the pump pressure can rise to the higher value, since a higher control pressure can be reported to the control valve via the LS branch of the front function , When the function (directional valve section) is assigned, which is assigned to a line section following the first further line section to the rear, the primary switching valve is switched and the pressure in the first line section of the load signaling line is thus limited to the low response pressure of the second pilot valve, so that the system pressure also is limited to the low value.

According to claim 18, the second pilot valve is arranged between the first line section and a relief line and its valve element in the closing direction of a valve spring and in the opening direction of that in the pressure applied to another line section. No directional valve is needed here. With this configuration, the system pressure can increase when several hydraulic consumers are operated in parallel above the value caused by the response pressure of the second pilot valve, as long as the load pressure of the hydraulic consumer protected with the lower pressure is below the response pressure of the second pilot valve. Only when the load pressure rises to the response pressure of the second pilot valve does this limit the control pressure at the control valve to a value which is below the response pressure by the control Δp.

Claims 19 to 21 relate to the advantageous accommodation of the pilot valve arrangement in a directional valve section with a single-acting function, in which the free space of the unnecessary consumer connection is available. The changeover valve is advantageously arranged perpendicular to the plane of the directional control valve disc, since the control line for the pressure signal for adjusting the pilot valve arrangement, which runs perpendicular to the disc planes, can open directly into the changeover valve at the flange surface of the single-acting directional control valve section.

Several exemplary embodiments of a hydraulic control arrangement according to the invention are shown in the drawings as a circuit diagram and partly as a construction. The invention will now be explained in more detail with reference to the figures of these drawings.

Show it

FIG. 1 shows a circuit diagram of the first exemplary embodiment, in which the control pressure can be limited to two values determined by different spring preloads by means of a single pressure relief valve and the adjustment is carried out by switching over a 2/2 way valve, Figure 2 shows a first arrangement and design of the

Pressure relief valve and the 2/2 way valve from Figure 1 within a directional valve disc,

3 shows a second arrangement and structural design of the pressure relief valve and the 2/2 way valve from FIG. 1 within a directional valve disk, FIG.

FIG. 4 schematically shows a further arrangement of the pressure relief valve from FIG. 3 in a section perpendicular to that from FIG. 3,

FIG. 5 shows a circuit diagram of the second exemplary embodiment, in which the 2/2 way valve is replaced by a 3/2 way valve compared to the first exemplary embodiment,

FIG. 6 shows a circuit diagram of the third exemplary embodiment, in which the control pressure can be limited by a single pressure relief valve to two values determined by different effective pressure areas and the adjustment is carried out by switching over a 2/2 way valve,

Figure 7 shows the arrangement and design of the

Pressure relief valve and the 2/2 way valve from Figure 6 within a directional valve disc,

FIG. 8 shows a circuit diagram of the fourth exemplary embodiment, which has two pressure relief valves set to differently high response pressures and in which the pressure relief valve with the lower response pressure can take effect after switching over a 2/2 way valve,

Figure 9 is a circuit diagram of the fifth embodiment, which is like the fourth

Embodiment has two pressure relief valves and a 2/2 way valve and in which the pressure relief valve with the lower response pressure is connected downstream of a nozzle to the second line section of the load signaling line in the second directional valve section and the 2/2 way valve connects the individual signaling channel of the first directional valve section with the can connect the second line section, Figure 10 is a circuit diagram of the sixth embodiment, in which, in contrast to the fifth embodiment, the 2/2 way valve the first Line section of the load signaling line can connect to the inlet of the pressure relief valve with the lower response pressure,

FIG. 11 shows a circuit diagram of the seventh exemplary embodiment, in which a pressure relief valve set to a high response pressure and a throttle valve controlled by the pressure in a further line section of the load signaling line are connected between a nozzle and the control valve to the first line section of the load signaling line,

FIG. 12 shows a circuit diagram of the eighth exemplary embodiment, in which there are three throttle valves set to differently high response pressures, and

FIG. 13 shows a circuit diagram of an exemplary embodiment in which the constant pump and bypass pressure compensator are replaced by a load-sensing controlled variable pump.

According to the circuit diagrams shown, a control block 15, which is provided for a forklift truck, includes four directional valve disks 16, 17, 18 and 19, an input disk 20, which has an inlet connection 21 and an outlet connection 22, and an end plate 23, with which one of the inlet connection 21 through the inlet disk and the directional valve disks inlet channel 24 is closed. From the outlet connection 22, an outlet channel 25 passes through the input disk and the directional valve disks and leads into the end disk. Hydraulic oil can flow from the drain connection 22 to a tank 26. The inlet connection is connected to the pressure connection of a hydraulic pump 27, which can thus convey hydraulic oil sucked from the tank into the inlet channel 24. According to their order from the input disk 20, the directional valve disk 16 is the first or foremost, the directional valve disk 17 the second, the directional valve disk 18 the third and the directional valve disk 15 the last or rearmost. If components or ducts within a directional valve disc are named first, second, third or last in the following, this should clearly indicate their affiliation with the corresponding directional valve disc. Each directional valve disc contains a proportionally adjustable directional valve 28, 29, 30 or 31, with which a hydraulic consumer, in the case of a forklift a hydraulic cylinder, can be controlled according to the amount and direction of the speed. The directional control valve 28 of the first directional control valve disc 16 is assigned to the “lifting” function of the fork, for which a single-acting hydraulic cylinder is sufficient. The directional control valve 29 of the second directional control valve disc 17 is the “tilt” function of the lifting frame and the directional control valves 30 and 31 of the Directional valve disks 18 and 19 are assigned additional functions such as “extending the fork” and “moving the fork sideways”. The hydraulic consumers are double-acting hydraulic cylinders for these functions.

In addition to a directional valve, there is a shuttle valve 35, 36, 37 and 38 with a valve body 39 in each directional valve disk. Depending on the pressure conditions, a shuttle valve connects an LS channel 40, 41, 42 or 43 of a directional valve disk starting from the center connection of the shuttle valve an individual signaling channel 44, 45, 46 or 47 of a directional valve disc or with the LS channel of the following directional valve disc. One side connection of the shuttle valve 38 of the last directional valve disk is connected to the outlet channel 25 via the end disk 23. The individual signaling channel of each directional valve disc is in turn connected via the associated directional valve in a working position of the directional valve to the flow to the hydraulic consumer, so that the load pressure of the hydraulic consumer is present in it, and in the neutral position of the directional valve to the drain line, pressure is relieved , A nozzle 50 is inserted into the first LS channel 40.

In the exemplary embodiments according to the circuit diagrams in FIGS. 1, 5, 6 and 8 to 12, the hydraulic pump 27 is a constant pump. The load-sensing controller is formed by a pressure compensator 51, which is accommodated in the input disk 20 and lies between the inlet channel 24 and the outlet channel 25. A control piston of the pressure compensator is acted upon in the opening direction by the pump pressure in the inlet channel 24. In the closing direction act on the control piston Pressure compensator, a compression spring 52 and a control pressure which is present in the LS channel 40 on the side remote from the shuttle valve 35 downstream of the nozzle 50. The two areas on which the control pressure and the pump pressure act are the same size. The control piston is therefore free of forces when the pump pressure is higher than the control pressure by the pressure equivalent of the compression spring 52. This pressure difference is also referred to as control Δp and usually has a value between 5 bar and 20 bar.

In the exemplary embodiment according to FIG. 13, the hydraulic pump 27 is a variable displacement pump with a schematically indicated load-sensing control valve 53, the control piston of which, in the sense of an adjustment of the hydraulic pump in the direction of a larger stroke volume, from the control pressure downstream of the nozzle 50 and from a control spring and in the direction smaller stroke volume is acted upon by the pump pressure. Here, too, a pump pressure is adjusted which is below the control pressure downstream of the nozzle 50 by the control Δp corresponding to the pressure equivalent of the control spring. The use of a load sensing regulated variable pump means less loss of useless energy, since not only the pump pressure, but also the pump delivery rate is limited to the necessary amount. In the exemplary embodiment according to FIG. 13, the LS channel 40 is continued in the input disk 20 and is connected via an LS connection 54 and a line to the control valve 53 constructed on the hydraulic pump 27.

In the exemplary embodiments according to FIGS. 1 to 4, 5, 6, 8 to 11 and 13, a directly controlled pressure-limiting valve 55 is arranged within the directional valve disk 16, the inlet of which is connected to the part of the LS channel 40 which is downstream of the nozzle 50 and the latter Output is connected to the drain channel 25. Directly controlled pressure relief valve means that the movable valve element 56 shown in FIGS. 2 and 3 is acted upon by a valve spring 57 in the opening direction on an effective effective area by the pressure at the inlet of the valve and in the closing direction. The pressure relief valve 55 leaves the The pressure at its inlet only increases up to a limit pressure that generates a compressive force on the active surface that is equal to the spring force.

In the exemplary embodiments according to FIGS. 1 to 4 and 5, the spring force can be changed between two values determined by two stops for one end of the valve spring 57. The end of the valve spring 57 remote from the valve element 56 can be displaced by an auxiliary piston 58 in the direction of a valve seat on which the valve element 56 is seated when the valve 55 is closed. The auxiliary piston adjoins with an active surface on a control chamber 59, the pressurization of which depends on the switching position of a switching valve which can be switched between two switching positions and which is also built into the directional valve disk 16. In the exemplary embodiment according to FIGS. 1 to 4, this is a directional control valve 60 with two connections, that is to say a 2/2 directional control valve, which is in series with a nozzle 61 and downstream of it between the LS channel 40 upstream of the nozzle 50 and the outlet channel 25 is arranged. Thus, when the directional control valve 60 locks, the auxiliary piston 58 is acted upon by the pressure present in the LS channel upstream of the nozzle 50 and preloads the valve spring strongly so that the limit pressure is high. If the directional control valve is open, the auxiliary piston is relieved of pressure. The valve spring 57 is less pretensioned and the limit pressure is lower

A valve piston 62 of the directional valve 60 is loaded in the closing direction by a compression spring 63 and can be acted upon in the opening direction by the pressure present in the third LS channel 42 via a control line 64 passing through the directional valve disk 17. The force of the compression spring 63 can be selected so that the directional control valve opens at a very low pressure of, for example, 10 bar. The compression spring can, however, also be set to a higher pressure, which, however, is in any case so low that when the directional valve 30 is actuated, the pressure relief valve 55 is set to the low limit pressure before the higher limit pressure is reached. For the description of the operation of the control arrangement according to FIG. 1, it is assumed, for example, that the high limit value for the control pressure is 120 bar and the low limit value is 60 bar. The rule Δp is 10 bar. If one of the “lifting” or “tilting” functions is operated alone or in parallel with the other, the highest load pressure of the actuated functions is present in the LS channel 40 upstream of the nozzle 50. The two further directional control valves 30 and 31 are not actuated, so that the control line 64 is relieved of pressure and the directional control valve 60 assumes the switch position shown in FIGS. 1 to 3. The auxiliary piston 58 is acted upon by the highest load pressure and has strongly pre-tensioned the valve spring 57. The pressure limiting valve 55 limits the control pressure downstream of the nozzle 50 to 120 bar, so that the pump pressure and thus the load pressure at the hydraulic consumers for the functions “lifting” and “tilting” increases to a maximum of 130 bar.

If one of the directional control valves 30 or 31 is actuated, pressure is present in the third LS channel 42. If the directional control valve 60 switches over, for example, at a pressure of 10 bar in the control line 64, the pressure relief valve is set to the low limit pressure of 60 bar as soon as this load pressure occurs at one of the consumers controlled by the directional control valves 30 and 31. The pump pressure can then rise to a maximum of 70 bar. The load pressure at the third or fourth consumer cannot get any higher. If the first or second consumer is activated at the same time, it only moves when its load pressure is lower than 70 bar.

However, the load pressure at the third or fourth consumer is also limited to 70 bar if the directional valve 60 only switches over at 70 bar. This does mean that the pump pressure can increase to over 70 bar when the third or fourth consumer and the first or second consumer are actuated at the same time if the load pressure at the third or fourth consumer is less than 70 bar. The pump pressure is then via the metering orifice in the directional control valve 30 or 31 to the load pressure of the third or fourth hydraulic consumer throttled. When this consumer finally comes to a stop, its load pressure rises to 70 bar, so that the directional control valve 60 switches over and the pressure limiting valve 55 is adjusted to the low limit pressure of 60 bar. The pump pressure drops to 70 bar, so that even when the directional valve 30 or 31 is open and without oil flow, the load pressure at the third or fourth hydraulic consumer remains limited to 70 bar.

According to FIG. 2, the valve body 39 of the shuttle valve 35 is located in a recess 70 in the flange surface of the directional valve disc 16 lying against the directional valve disc 17. In alignment with one another, the LS channel 40 of the directional valve disc 16, in which the nozzle is located, eccentrically lead into the recess 70 50 is located, and the LS channel 41 of the directional valve disk 17. In addition, the individual message channel 44 of the directional valve disk 16 opens into the recess. Depending on the channel in which the higher pressure is present, the valve body 39 assumes such a position that the LS channel 41 or the message channel 44 is connected to the LS channel 40.

The two valves 55 and 60 are installed in the directional valve disk 16 perpendicular to the plane of the directional valve disk 16 from the flange surface abutting the directional valve disk 17. The compression spring 63 is clamped between the valve piston 62 of the directional control valve 60 and the bottom of a blind bore 65. This tries to keep the valve piston in contact with the directional valve disk 17. A transverse channel 71 opens into the blind bore 65, which extends upstream of the nozzle 50 from the LS channel 40 and in which the nozzle 61 is located. In addition, the blind bore 65 is cut by a channel 72 which is connected to the drain channel 25. The space in which the compression spring 63 is located is also depressurized. The control channel 64 running in the directional valve disk 17 opens axially into the blind bore 65.

The valve piston 62 assumes a rest position under the influence of the compression spring 63, in which it is pressed against the Wegeveηtil disc 17. In this rest position the two channels 71 and 72 are sealed against each other. If the pressure force generated by the pressure in the control channel 64 on the cross-sectional area of the valve piston 62 exceeds the spring force, the valve piston is shifted as far as the stop at the bottom of the blind bore 65 into its second switching position, in which the part of the channel 71 located downstream of the nozzle 61 also moves the channel 72 connected and thus relieved of pressure.

The individual parts of the pressure relief valve 55 are located in a blind hole 73, into which a channel 74, which is connected downstream of the nozzle 50 to the LS channel 40, opens centrally at the bottom. The mouth edge of the channel 74 forms a seat for the valve element 56 of the pressure limiting valve, which is designed as a ball. The ball is held in a spring plate 75 for the valve spring 57, which is able to be supported via a further spring plate 76 on a screw insert 77 screwed into the blind bore 73 up to a stop. The spacing of the two spring plates from one another when one is supported by the ball 56 on the seat and the other on the screw insert determines a low preload of the valve spring 57. This preload can be adjusted by washers between the screw insert 77 and the spring plate 76. The space in which the valve spring 57 is located is connected to the outlet channel 25 via the channel 72 and is thus relieved of pressure. The auxiliary piston 58 is guided so as to slide tightly in a central axial bore of the screw insert. The auxiliary piston is located in the control chamber 59 with a stop collar 78, which is formed behind the screw insert 77 in the directional valve disc 16 and is connected to the channel 71 via a channel 79 downstream of the nozzle 61. The guide cross section with which the auxiliary piston 58 is guided in the screw insert 77 and which is equal to the effective area for the pressure to be applied in the control chamber 59 and the auxiliary piston in the direction of the valve element 56 is larger than the seat cross section for the valve element 56 , so that when the directional valve 60 of the auxiliary piston 58 closes, the valve spring 57 will first preload more strongly until the stop collar 78 abuts the screw insert 77 before the pressure relief valve opens when the pressure in the LS channel 40 increases further. The higher one The preload of the valve spring 57 can be adjusted using washers on the stop collar 78.

In the design according to FIGS. 3 and 4, the directional control valve 60 is designed in exactly the same way as in FIG. 2 and, just as there, is arranged in a blind bore 65 in the blind valve 65 perpendicularly to the plane of the disc. The individual parts of the pressure relief valve 55, on the other hand, are located in a blind bore 73, the axis of which runs parallel to the disk plane and perpendicular (FIG. 3) or parallel to the axis of the valve bore from which the control slide 10 of the directional control valve 28 is received. This recognizes the formation of the metering orifice by control grooves 11. In the directional valve disk 16, because this disk is intended for the actuation of a single-acting hydraulic cylinder and therefore has only one consumer connection, a particularly large amount of space is available for accommodating the valves 55 and 60 ,

The pressure relief valve according to FIG. 3, which projects parallel to the one consumer connection from the directional valve disk, has a screwed-in valve seat 80 for the valve element 56, which is again designed as a ball. The valve spring 57 is supported on the ball 56 via the spring plate 75. Via the spring plate 76, the valve spring 57 can be supported on the screw insert 77, which is now provided with a radial sealing ring and can be rotated to adjust the low preload of the valve spring. However, the rotation is only possible if a further screw insert 81 provided with a radial drawing ring is not in the bore 73. The auxiliary piston 58 is suspended with its stop collar 78 on the screw insert 81. Thus, by turning the screw insert 81, the high preload of the valve spring 57 can be set. This is possible from the outside. The screw insert 81 can be secured with a lock nut and sealed with a protective cap.

Due to the different arrangement of the pressure limiting valve 55 compared to FIG. 2, the channels in FIG. 3 run differently than in FIG. 2 however, there is no difference. Upstream of the nozzle 50 in the LS channel 40, the channel 71 branches off, which leads to the directional control valve 60 and in which the nozzle 61 is located. Connected downstream of the nozzle 61 to the channel 71, the channel 79 runs to the control chamber 59 between the two screw inserts 77 and 81 of the pressure limiting valve 55. The spring chamber of this valve is in turn connected to the relief channel 72.

In the exemplary embodiment according to FIG. 5, the same pressure relief valve 55 is used as in the exemplary embodiment according to FIG. 1. However, the 2/2 way valve 60 and the nozzle 61 from FIG. 1 are replaced by a 3/2 way valve 85, which in its one switching position , which it occupies under the action of a spring 63, connects the control chamber on the auxiliary piston 58 upstream of the nozzle 50 to the LS channel 40 and in its other switching position, into which it is brought by the pressure in the control line 64, the control chamber to the drain line 25 relieved. No control oil leakage occurs when the auxiliary piston is relieved. Otherwise, the function of the exemplary embodiment according to FIG. 5 is the same as that of the exemplary embodiment from FIG. 1.

The exemplary embodiment according to FIGS. 6 and 7, like that according to FIG. 1, uses the 2/2 way valve 60 and the nozzle 61 to control the adjustment of a pressure relief valve 55, which in turn is connected to the LS channel 40 downstream of the nozzle 50 and is connected with its outlet to the drain channel 25. As in the embodiment according to FIG. 2, the individual parts of the pressure relief valve 55 according to FIGS. 6 and 7 are accommodated in a blind bore 73, into which the channel 74 opens centrally at the bottom. The mouth edge of the channel 74 in turn forms the seat for the valve element 56 designed as a ball. The ball is held in the spring plate 75 for the valve spring 57, which is now also supported directly on the screw insert 77 screwed into the blind bore 73. The screw insert 77 is provided with a radial sealing ring, with the help of which the control chamber 59 leads to the pressure-relieved spring chamber is sealed. The pretension of the valve spring 57 can be adjusted by turning the screw insert 77.

In the exemplary embodiment according to FIGS. 6 and 7, the pressure limiting valve 55 is not adjusted by changing the spring preload, but by changing the effective effective area for the pressure acting on the valve element between two response pressures of different heights. For this purpose, an auxiliary piston 58 is in turn guided in a central axial bore of the screw insert 77 in a tightly sliding manner, which is acted upon by the pressure in the control chamber 59 on an active surface corresponding to its guide cross section. In contrast to the exemplary embodiments according to FIGS. 1 to 4, the auxiliary piston 58 does not now lift one end of the valve spring 57 from the screw insert 77, but rather acts directly on the valve element 56 in the closing direction via the spring plate 75. The guide cross section with which the auxiliary piston 58 is guided in the screw insert 77 is smaller than the seat cross section for the valve element 56.

For the description of the mode of operation of the control arrangement according to FIGS. 6 and 7, it is again assumed that the control Δp is 10 bar. If one of the directional control valves 30 or 31 is actuated, pressure is present in the third LS channel 42. If the directional control valve 60 switches over, for example, at a pressure of 10 bar in the control line 64, as soon as this load pressure occurs at one of the consumers controlled by the directional control valves 30 and 31, the control chamber 59 and thus also the auxiliary piston 58 are relieved of pressure. The auxiliary piston therefore does not exert any force on the valve element 56. The pressure downstream of the nozzle 50 in the LS channel 40, which, as long as the pressure relief valve 55 is closed, is equal to the pressure upstream of the nozzle 50, acts on the valve element 56 at an effective area corresponding to the seat cross section and opens the pressure relief valve at a low limit pressure of Example 60 bar. The pump pressure can then rise to a maximum of 70 bar. The load pressure at the third or fourth consumer cannot get any higher. If one of the “lifting” or “tilting” functions is operated alone or in parallel with the other, the highest blast pressure of the actuated functions is present in the LS channel 40 upstream of the nozzle 50. The two further directional valves 30 and 31 are not actuated, so that the control line 64 is relieved of pressure and the directional valve 60 assumes the switching position shown in FIGS. 6 and 7. The auxiliary piston 58 is acted upon by the highest load pressure, which presses the auxiliary piston against the valve element 56 in the closing direction with the force generated on its active surface. As long as the pressure relief valve 55 is closed, the pressures in front of and behind the nozzle 50 are the same. The pressure limiting valve therefore begins to open when the pressure acting on an effective effective area, which is equal to the difference between the seat cross section for the valve element 56 and the guide cross section of the auxiliary piston 58, generates a force which is as large as the force of the valve spring 57. The oil flow flowing through the nozzle 50 after the start of opening creates a pressure difference across the nozzle 50, so that after the pressure limiting valve is opened, the pressure acting on the auxiliary piston 58 in the control chamber 59 is greater than the pressure in the channel 74. In a static state it is Pressure difference equal to the control Δp. In the static state, the valve element is thus acted upon in the opening direction by a pressure force which results from the pressure downstream of the nozzle 50 and the seat cross section, and in the closing direction by the force of the spring 57 which determines the low limit pressure and a pressure force which acts from the opposite the pressure in the channel 74 by the control Δp increased pressure in the control chamber 59 and the guide cross section of the auxiliary piston 58. For example, if the ratio between the guide cross-section and the seat cross-section is 1/2, the upper limit pressure is 130 bar with a control Δp of 10 bar and a lower limit pressure of 60 bar. With an area ratio of 1/3, the upper limit pressure is 95 bar.

The exemplary embodiment according to FIG. 8 has, in addition to a simple pressure relief valve 55 which is set to a high limit pressure and which is permanently connected to the LS channel 40 at its inlet downstream of the nozzle 50 second simple pressure relief valve 86, which is set to a low limit pressure. A 2/2-way valve 60 is arranged between the inlet of this second pressure limiting valve 86 and the LS channel downstream of the nozzle 50, which valve closes in the direction of a compression spring 63 and via the control line 64 the pressure in the third LS channel 42 is acted towards open. If the directional control valve 60 is closed, the pressure limiting valve 86 is not effective. The maximum control pressure for the pressure compensator 51 and thus the maximum inlet pressure is determined by the pressure relief valve 55. If the directional control valve is opened by the pressure in the LS channel 42, the pressure limiting valve 86 determines the maximum control pressure for the pressure compensator 51 and thus the maximum inlet pressure.

In the two exemplary embodiments according to FIGS. 9 and 10, as in the exemplary embodiment according to FIG. 8, there is a simple pressure relief valve 55 which is set to a high response pressure and is connected to the LS channel 40 downstream of the nozzle 50. The inlet of a second pressure limiting valve 86, which is set to a low response pressure, is now permanently connected to the LS channel 41 downstream of a nozzle 87 located in the second LS channel 41.

This means first of all that when the first directional valve 28 is actuated alone, the pressure relief valve 55 and when the directional valves 29, 30 and 31 are actuated alone or in parallel, the pressure relief valve 86 determines the maximum control pressure for the pressure compensator 51.

In both exemplary embodiments, there is also a 2/2-way valve 60 which blocks in a switching position caused by the spring 63 and can be brought into an open switching position by a pressure present in the third LS channel 42. In the exemplary embodiment according to FIG. 9, the directional valve 60 connects the individual signaling channel 44 of the directional valve disk 16 downstream of a nozzle 88 and in the embodiment shown in the open switching position. 10 the LS channel 40 downstream of the nozzle 50 with the input of the pressure relief valve 86. This ensures that when the directional control valve 30 or 31 is actuated and the simultaneous actuation of the directional control valve 28, the pressure relief valve 86 set to the low limit pressure reaches the maximum Control pressure for the pressure compensator 51 determined. If, on the other hand, only the directional control valves 28 and 29 are actuated at the same time, the pressure relief valve 55 with the higher limit pressure determines the maximum control pressure for the pressure compensator 51, since the directional control valve 60 remains in its blocking position.

In the embodiment according to FIG. 11, the high maximum control pressure for the pressure compensator 51 is determined in the same way as in the embodiments according to FIGS. 9 and 10 by a simple pressure relief valve 55. There is also a throttle valve 90, the input of which is connected downstream of the nozzle 50 to the LS channel 40 and the output of which is connected to the outlet channel 25. The throttle valve 90 assumes a blocking position under the action of a compression spring 91 and can be adjusted proportionally against the force of the spring from a pressure present from the third LS channel 42 via the control line 64, that is to say opened to different degrees. The spring constant is small. The pressure at which the valve 90 responds is equal to the low maximum permitted load pressure for the hydraulic consumers controlled by the directional control valves 30 and 31.

For the explanation of the mode of operation it is assumed that the throttle valve responds, for example, at a pressure of 60 bar. If a load pressure of 60 bar is reached when one or both directional control valves 30 or 31 are actuated without actuation of a directional control valve 28 or 29, the throttle valve 90 opens a throttle cross-section from the control side of the pressure compensator 51 to the outlet channel 25 and maintains the pressure on the Control side around the control Δp under the load pressure of 60 bar, i.e. with a control Δp of 10 bar at 50 bar. Now the tilt or lift function, i.e. the directional control valve 28 or 29, is actuated, the load pressure of this function being greater than 60 bar, for example 100 bar. Upstream of the nozzle 50 there are then no more than 60 bar in the LS channel 40, but 100 bar. With an unchanged position of the throttle valve 90 thus also the pressure would downstream of the ^'nozzle 50 and thus increase on the control side of the pressure balance 51st This would result in an increase in the inlet pressure and an increase in the load pressure on the hydraulic consumer controlled by the directional control valve 30 or 31, which is at a stop, for example. However, even a slight change in the pressure in the LS channel 42 leads to an increase in the throttle cross section of the valve 90, so that an increase in pressure on the control side of the pressure compensator 51 occurs only within the scope of the opening characteristic of the valve 90. Even if a directional control valve 30 or 31 and a directional control valve 28 or 29 are actuated in parallel, the maximum load pressure for the third and fourth hydraulic consumers is therefore limited to the low value.

In the exemplary embodiment according to FIG. 11, the high maximum inlet pressure is set with a pressure limiting valve and the low maximum inlet pressure with a throttle valve. Both valves are accommodated in the directional valve disk 16.

In contrast, in the exemplary embodiment according to FIG. 12 only throttle valves are used for setting the pressure levels. Here, a high pressure level is provided for the two hydraulic consumers controlled by the directional control valves 28 and 29, a medium pressure level for the hydraulic consumer controlled by the directional control valve 30 and a low pressure level for the hydraulic consumers controlled by the directional control valve 31. Accordingly, there are three throttle valves 90, of which the one set to the high response pressure is accommodated in the directional valve disk 16, the one set to the medium response pressure in the directional valve disk 18, and the one set to the low response pressure is accommodated in the directional valve disk 19. The inputs of the throttle valves are via a through the directional valve disks de line 92 connected downstream of the nozzle 50 to the LS channel 40. A control line 64 for the throttle valve in the directional valve disk 16 is upstream of the nozzle 50 at the LS channel 40, the control line 64 for the throttle valve in the directional valve disk 18 is at the LS channel 42 thereof and the control line 64 for the throttle valve in the directional valve disk 19 connected to their LS channel 43.

When the directional valve 31 is actuated, the throttle valve 90 of the directional valve disk 19 maintains the pressure on the control side of the pressure compensator 51 in the same manner as described with reference to FIG. 11 at a value such that the pressure in the LS channel 43 is equal to the load pressure of the corresponding hydraulic consumer, does not exceed the low response pressure of the valve. The load pressure is therefore limited to the low value. The other two throttle valves also work at the medium and high pressure levels.

Claims

claims

1. Hydraulic control arrangement in load-sensing technology with a first directional valve (28, 29), via which pressure medium can be fed to a first hydraulic consumer, and with at least one further directional valve (30, 31), via the pressure medium to another Hydraulic consumers can be supplied and which is preferably combined with the first directional valve to form a valve block (15), with a load signaling line, via which a control side of a load-sensing control valve (51, 53) with a control pressure dependent on the highest load pressure of the hydraulic consumers actuated The first line section (40) closest to the control valve (51, 53) is supplied with the control pressure and at least one further line section (41, 42, 43), one line section each via a shuttle valve (35, 36, 37, 38) can be connected to the following line section or an individual signaling channel (44, 45, 46, 47) of a directional valve, and mi t of a pilot valve arrangement, by means of which the control pressure is limited to a limit pressure, characterized in that the pilot valve arrangement can be adjusted from a high, first limit pressure to a lower, second limit pressure at a certain pressure present in a further line section (42) of the load signaling line and that the individual reporting channels (44, 45, 46, 47), viewed from the first line section (40) of the load reporting line, can be connected to the successive line sections of the load reporting line after the maximum load pressure of the hydraulic consumers has dropped.

2. Hydraulic control arrangement according to claim 1, characterized in that the pilot valve arrangement is hydraulically adjustable via a control line (64) which is connected to the further line section (42) of the load signaling line.

3. Hydraulic control arrangement according to claim 1 or 2, characterized in that the pilot valve arrangement has a between the first line section (40) and a relief line (25) arranged pilot valve (55), the response pressure is variable.

4. Hydraulic control arrangement according to claim 3, characterized in that the pilot valve has a movable valve element (56) acted upon by a valve spring (57) in the direction of a closed position and by a pressure force on an active surface in the direction of an open position, and in that the biasing force of the valve spring (57) can be changed as a function of the pressure in the further line section (42) of the load signaling line.

5. Hydraulic control arrangement according to claim 4, characterized in that the biasing force of the valve spring (57) can be changed via an auxiliary piston (58) between two values defined by a first fixed stop (77) and a second fixed stop (77, 81) is that the auxiliary piston (58) has an effective area which is larger than the effective area on the valve element (56) and which, depending on the switching position of a changeover valve (60,) determined by the pressure in the further line section (42) of the load signaling line 85) acted upon by pressure is relieved, or compressed, and that the auxiliary piston (58) to the effectiveness of the second stop (77, 81) ^is' slidably in the sense of an increase of the spring bias.

6. Hydraulic control arrangement according to claim 5, characterized in that the two stops (77, 81) are formed by two independently adjustable adjusting screws.

7. Hydraulic control arrangement according to claim 5 or 6, characterized in that the valve spring (57) at the end remote from the valve element (56) can be supported by the auxiliary piston (58).

8. Hydraulic control arrangement according to claim 7, characterized in that the valve spring (57) via a spring plate (76) on a preferably screwed-in insert (77) can be supported, one of. Pressure-relieved spring chamber from a pressure-relieved or pressurized control chamber (59) depending on the position of the change-over valve (60, 85) separates that the auxiliary piston (58), guided in an axial bore of the insert (77), sliding tightly between the spring chamber and the Control chamber (59) is arranged and that the spring plate (76) can be lifted off the insert (77) by the auxiliary piston (58).

9. Hydraulic control arrangement according to claim 8, characterized in that the valve spring (57) via a spring plate (76) on a first rotatable and the first stop forming screw insert (77) can be supported, which is relieved of pressure by a spring chamber depending on The position of the changeover valve (60, 85) separates the pressure-relieved or pressurized control chamber (59) so that the auxiliary piston (58), guided in an axial bore in the insert (77), is arranged between the spring chamber and the control chamber (59) that on the side of the first screw insert (77) facing away from the spring chamber there is a second rotatable screw insert (81) which is preferably adjustable from the outside and which forms the second stop which can be acted upon by the auxiliary piston (58).

10. A hydraulic control arrangement according to claim 3, characterized in that the pilot valve (55) has a movable valve element (56) acted upon by a valve spring (57) in the direction of a closed position, that the valve element (56) by a in the first line section ( 40) of the load signaling line downstream of a nozzle (50) and pressure present at a first control surface in the opening direction, and that a second control surface is provided on an auxiliary piston (58) which acts on the valve element (56) and which is dependent on the the pressure in the further line section (42) of the load signaling line determined switching position of a changeover switching valve (60) is relieved of pressure or can be pressurized.

11. Hydraulic control arrangement according to claim 10, characterized in that the valve element (56) by an on the second control surface

5 standing pressure is applied in the closed position and that the second control surface is smaller than the first control surface.

12. Hydraulic control arrangement according to claim 11, characterized in that a spring chamber relieved of pressure of the pilot valve (55)

10 is sealed by a preferably adjustable insert (77) for changing the pretension of the valve spring (57) against a control chamber (59) which is relieved of pressure or pressurized depending on the switching position of the changeover valve (60) and that a valve element (56) is applied to it or fixedly connected auxiliary piston (58) with a cross-sectional area that is smaller than the first control surface

15 is tightly guided in a bore of the insert (77) which is open towards the control chamber (59).

13. Hydraulic control arrangement according to one of claims 5 to 12, characterized in that the changeover valve is a 2/2 way valve (60) and

20 is arranged in series with a nozzle (61) between the load signaling line and a relief line (25) and that the control chamber (59) on the auxiliary piston (58) is connected to the connection between the nozzle (61) and the 2/2 way valve (60) ,

25 14. Hydraulic control arrangement according to one of claims 5 to 12, characterized in that the switching valve is a 3/2 way valve (85) and a control chamber (59) on the auxiliary piston (58) in one switching position with the load signaling line and in the other Switch position connects with a relief line (25).

J o

15. Hydraulic control arrangement according to claim 1 or 2, thereby indicates that the pilot valve arrangement has a first pilot valve (55, 90) arranged between the first line section (40) and a relief line (25) or switchable therebetween, and a second pilot valve (arranged between the load signaling line and the relief line (25) or switchable therebetween) 86, 90) and that the response pressure of the second pilot valve (86, 90) is less than the response pressure of the first pilot valve (55, 90).

16. Hydraulic control arrangement according to claim 15, characterized in that both pilot valves are pressure limiting valves (55, 86) and that the second pilot valve (86) with its input via a depending on that in a further line section (42) of the load signaling line Pressure switchable changeover valve (60) can be connected to the first line section (40).

17. Hydraulic control arrangement according to claim 16, characterized in that the second pilot valve (86) with its input downstream of a nozzle (87) is connected to a first further line section (41) and that the changeover valve (60) in dependence on that in one the first further line section (41), the further line section (42) following to the rear is pressurized by the first line section (40) or an individual signaling channel (44) that can be connected to it, downstream of a nozzle (50, 88) located therein with the inlet of the second pilot valve ( 86) connects or disconnects.

18. Hydraulic control arrangement according to claim 15, characterized in that the second pilot valve (90) between the first line section (40) and a relief line (25) is arranged and that its movable valve element in the closing direction of a valve spring (91) and in the opening direction can be acted upon by the pressure in the further line section (42, 43). .

19. Hydraulic control arrangement according to one of the preceding claims, characterized in that the pilot valve arrangement is locally assigned to a directional control valve (28) with a single-acting function.

20. Hydraulic control arrangement according to claim 19, characterized in that the pilot valve (55) is arranged with its axis in or parallel to a plane spanned by the axis of the directional control valve (28) and a working connection, preferably parallel to the axis of the directional control valve.

21. Hydraulic control arrangement according to claim 20, characterized in that the switching valve (60) is arranged with its axis perpendicular to the plane.