EP1497559B1 - Hydraulic control system using load-sensing technology - Google Patents

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

The invention is based on a hydraulic control arrangement in load-sensing Technique, according to the preamble of claim 1, a first directional control valve, can be supplied via the pressure medium to a first hydraulic consumer, and at least one further directional control valve, via the pressure medium to another hydraulic Consumable can be supplied and preferably with the first directional control valve is summarized to a valve block, and a load-sensing control having.

A hydraulic control arrangement according to the preamble of the claim 1 is e.g. known from DE 197 15 021 A1. It is a hydraulic one Control arrangement according to the load-sensing principle, at a variable displacement pump or a constant pressure pump associated bypass pressure balance depending on one with the highest load pressure of the actuated hydraulic consumer changing control pressure, preferably in dependence from the load pressure itself, each set so that the pump pressure by a certain pressure difference, the control Δp, above the highest load pressure lies. For this purpose, the control pressure is a load-sensing control valve, which by a Control valve of the variable displacement pump or is realized by the bypass pressure compensator, fed via a load signaling line. This is made up of one of the number of Directional valves corresponding number of line sections together. each Directional control valve has an individual signaling channel. Shuttle valves serve to the highest pressure leading individual signaling channel with the load reporting line and their line sections to connect with each other.

Hydraulic consumers, the pressure medium flows through adjustable, usually Metering orifices formed on the spools of the directional control valves to, between an outgoing from the variable delivery pipe and the hydraulic consumers are arranged. Because of the highest Load pressure independent pressure difference between the highest load pressure and the pump pressure depends on the speed at which the highest pressure pressure hydraulic, consumer moves, solely from the flow area of the corresponding Metering off.

By the metering orifices upstream or downstream so-called individual pressure compensators can be achieved that the movement speed of all simultaneously actuated hydraulic consumers regardless of the load pressures is. With the individual pressure balances and the pressure difference over the associated with low-pressure hydraulic consumers associated metering orifices kept constant. so that the hydraulic consumer flowing Pressure medium amount only from the flow area of the respective Zumeßblende depends. If a Zumeßblende further opened, so must more pressure medium flow over them to produce the specific pressure difference. The variable pump or the bypass pressure balance is adjusted in each case so that the required Pressure medium quantity is delivered. Therefore, one 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 thereby to a Limit pressure are limited, that in the connected to the control valve, first line section of the load-sensing line provides a nozzle and between this and the control valve to the first line section a pressure relief valve followed. The pump pressure will not increase by more than that Control Δp above the limit pressure set with the pressure relief valve. In addition, also the load pressure with which a hydraulic consumer maximum can be applied, individually adjusted. This is according to DE 197 15 021 to the individual reporting channel of the corresponding directional valve section downstream of a nozzle, a pressure relief valve connected. This limits the control pressure in the spring chamber of the individual pressure compensator. Namely, the pressure balance closes when the pressure upstream of the orifice greater than the control pressure increased by the control Δp of the individual pressure compensator. The load pressure can therefore only rise to a pressure which is around the Control Δp of the individual pressure compensator above the set pressure of the pressure relief valve lies. However, this is in the directional valve section of the hydraulic Consumer an individual pressure balance necessary.

The invention is based on the object, a hydraulic control arrangement, having the features of the preamble of claim 1, so to further develop, that the load pressure for a hydraulic consumer to cost Way to a lower value than for another hydraulic one Consumer is limited, regardless of the lower value is limited, whether the second function alone or together with the first function is pressed. This is intended to safely protect the second function from excessive pressure become.

The desired goal is inventively achieved in that in the hydraulic Control arrangement with the features of the preamble of the claim 1 the Vorsteuerventitanordnung at a certain, in another Line section of the load-sensing line pending pressure from a high, first Limit pressure to a lower, second limit pressure is adjustable and that the individual message channels, from the first line section of the load reporting line from the perspective of decreasing maximum load pressure of hydraulic consumers connectable to the successive line sections of the load signaling line are. A control arrangement according to the invention serves to actuate two or more groups of one or more hydraulic consumers, where the groups differ in maximum Different load pressures. From the control valve, are located So in the load message line so first the line sections, the on Shuttle valve with an individual reporting channel of a directional valve connectable are, with whom 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 maximum Load pressure, then the pipe sections for the group with the third highest Load pressure and so on. Usually, this order is for the sake of simple bore and the same possible design of the individual Directional valve sections also correspond to the order in a valve block, so that in this on the directional valve sections for the group of consumers with the highest maximum load pressure the directional control valve sections for the group follow the second highest maximum load pressure. If more than two different maximum load pressures are provided, then follow the directional valve sections for the group with the third highest maximum load pressure. Overall, then in the valve block, the directional valve sections after falling maximum load pressure orderly. Is a hydraulic consumer from a group that does not have the has the highest maximum load pressure actuated, so is via the associated shuttle valve the corresponding line section of the load reporting line with the Load pressure applied. With this pressure, the pilot valve arrangement is so controlled, that the pressure in the first line section of the load signaling line between the nozzle and the control valve a lower maximum load pressure at least then do not exceed the corresponding maximum control pressure can if the lower maximum load pressure at the corresponding consumer is reached. Does the group include several hydraulic consumers and thus a plurality of directional control valves and a plurality of line sections of the load-signaling line, see above is sufficient pressure tap in the front, that is in the control valve on Next located this line sections, as the pressure from further back located line sections via one or more shuttle valves in the reaches the leading line section. In a hydraulic according to the invention Control arrangement are no individual pressure compensators necessary for the hydraulic Consumers have different maximum load pressures.

Advantageous embodiments of a hydraulic control arrangement according to the invention can be found in the dependent claims.

Basically, it is conceivable that the pressure in a further line section of the Lastmeldeleitung with a pressure sensor to detect and the pilot valve assembly to adjust electrically. However, from the effort it seems easier if according to claim 2, the pilot valve assembly hydraulically over a control line is adjustable, which is connected to the further line section of the Lastmeldeleitung is connected.

From the space requirements forth, it seems particularly advantageous if the pilot valve assembly according to claim 3 a between the first line section and a discharge line arranged pilot valve, whose set pressure For example, between two pressure levels is changeable. Especially the pilot valve can be a pressure relief valve with two pressure levels be and be with a valve element that of the directly at the valve inlet applied pressure in the opening direction is applied. It is, too possible that the valve element one between the first line section of the Lastmeldeleitung and a discharge line arranged or in between switchable pilot valve in the opening direction of the pressure on the control valve the remote side of the nozzle is applied. The pilot valve is then the control pressure in the line section between the nozzle and the control valve, to it with its main entrance separated from a control entrance is connected to one of the control Δp below the set pressure limit lying pressure.

A first possibility to obtain two pressure stages of the pilot valve is, as stated in claim 4, therein, the bias of a Valve spring to change the movable valve element of the pilot valve against a pressure force generated on an active surface of the valve element in the direction a closed position acted upon.

Preferably, according to claim 5, an auxiliary piston is used to over the the biasing force of the valve spring between two by a first fixed stop and a second fixed stop defined values is changeable. The auxiliary piston has an effective area which is larger than the effective area on Valve element, so that upon application of the two active surfaces on the valve element and at the auxiliary piston with the same pressure of the auxiliary piston, the valve spring first biasing more, before with further increasing pressure the pilot valve opens, and then its by the higher value of the spring preload defining stop certain situation safely maintains. Depending on the determined by the pressure in the other line section of the load-sensing line Switching position of a changeover valve is the effective area on the auxiliary piston relieved of pressure or acted upon by pressure. By use a switching valve is sufficient, a very low pressure in the other line section the load-sensing line to the pilot valve on the low To set limit pressure.

It is particularly advantageous if according to claim 6, the two stops independently adjustable by turning two setscrews are. In particular structurally advantageous embodiments of the hydraulic Control arrangement according to claim 5 or 6 can be found in the Claims 7 to 9 is particularly preferred, inter alia, that the valve spring at the valve element remote end of the auxiliary piston is supportable, so this end of the auxiliary piston is displaceable. This appears structurally simpler than a principle also possible change of the spring preload by a displacement of a valve seat for the valve element.

The response pressure of a valve, on the valve element in the opening direction or more generally, in one direction a compressive force and in the opposite Direction a spring force acts, can not be changed only by a change the spring bias, but also by a change in the effective Change effective area for the upcoming pressure. The latter succeeds according to claim 10 at a pilot valve of a hydraulic according to the invention Control arrangement in a structurally simple manner in that the valve element by a in the first line section of Lastmeideleitüng and at a first control surface applied pressure in the opening direction acted upon is and that a second control surface is present on an auxiliary piston, the on the valve element acts and as a function of the pressure in the another line section of the load-sensing line certain switching position of a Reversing valve of pressure relieved or pressurizable. Preferably is according to claim 11 or 12, the valve element by a on the second control surface applied pressure in the closed position, wherein the second control surface is smaller than the first control surface.

The switching valve can be a simple and inexpensive 2/2 way valve with a single control edge, if it according to claim 13 in series with a nozzle between the load-sensing line and a discharge line arranged is, with the control chamber on the auxiliary piston at the connection between the nozzle and 2/2 way valve is located. However, the switching valve can according to claim 14 also be a 3/2 way valve, which has a control chamber on the auxiliary piston in one Seed position with the load indicator line and in the other switching position with connects a discharge line. Here you have in any position of the switching valve a loss of control oil, as the 3/2 way valve in both switching positions disconnects the load-sensing line from the discharge line.

Direct-operated valves that operate in stages at different set pressures are adjustable, are rarely needed, are special constrictions and are therefore relatively expensive to manufacture. Made in mass production Valves may be used for the pilot valve assembly, if these according to claim 15, a first, between the first line section and a relief line arranged or switchable between pilot valve and a second, between the load-sensing line and the discharge line arranged or interposed switchable pilot valve and the set pressure of the second pilot valve is less than the set pressure of the first Pilot valve is.

Particularly preferred is an embodiment according to claim 16, after which the two pilot valves are pressure relief valves and the second pilot valve with its input via a function of the in Another line section of the load-sensing line pending pressure switchable switching valve with the first line section is connectable. Also here can be used as a switching valve, a small valve, which in high Quantities produced inexpensively.

In an embodiment according to claim 17, the following is achieved. Thereby that the entrance of the second as. Pressure relief valve trained pilot valve downstream of a nozzle with a first further line section of Lastmeldeteitung or connected to the associated individual Lastmeldekanal is, in the solo mode of the associated function (directional valve section) is the system pressure limited by the response pressure of the second pilot valve. In parallel operation this function (directional valve section) with a further forward and on a higher pressure safe function (directional valve section) against it The pump pressure may rise to the higher value because of the LS branch the front function reported a higher control pressure to the control valve can be. Upon actuation of the function (directional valve section), the one first further line section assigned to the rear following line section is, the switching valve is switched and thereby the pressure in the first Line section of the load signaling line to the low set pressure of the limited second pilot valve, so that the system pressure on the low Value is limited.

According to claim 18, the second pilot valve between the first Line section and a discharge line arranged and its valve element in the closing direction of a valve spring and in the opening direction of the in the further line section pending pressure acted upon. No here Used directional valve. In this training, the system pressure at a Parallel operation of several hydraulic consumers over the by the set pressure of the second pilot valve. conditional value increase, as long as the Load pressure of the lower pressure protected hydraulic consumer is below the set pressure of the second pilot valve. Only when the load pressure on the response pressure of the second pilot valve increases limited this the control pressure on the control valve to one by the control Δp below the set pressure value.

The claims 19 to 21 relate to the advantageous housing the pilot valve assembly in a directional control valve section with single-acting Function in which the free space of unnecessary consumer connection is available. The switching valve is advantageously perpendicular to the Plane of the directional valve disc arranged as the perpendicular to the disc planes extending control line for the pressure signal for adjusting the pilot valve assembly directly on the flange surface of the single-acting directional valve section can open into the switching valve.

Several embodiments of a hydraulic control arrangement according to the invention are as a circuit diagram and partly as a construction in the. drawings shown. With reference to the figures of these drawings, the invention will now be closer explained.

Figur 1

ein Schaltbild des ersten Ausführungsbeispiels, bei dem der Steuerdruck durch ein einziges Druckbegrenzungsventil auf zwei durch unterschiedlich starke Federvorspannung bestimmte Werte begrenzbar ist und die Verstellung durch Umschaltung eines 2/2 Wegeventils erfolgt,

Figur 2

eine erste Anordnung und konstruktive Ausgestaltung des Druckbegrenzungsventils und des 2/2 Wegeventils aus Figur 1 innerhalb einer Wegeventilscheibe,

Figur 3

eine zweite Anordnung und konstruktive Ausgestaltung des Druckbegrenzungsventils und des 2/2 Wegeventils aus Figur 1 innerhalb einer Wegeventilscheibe,

Figur 4

schematisch eine weitere. Anordnung des Druckbegrenzungsventils aus Figur 3 in einem Schnitt senkrecht zu dem aus Figur 3,

Figur 5

ein Schaltbild des zweiten Ausführungsbeispiels, bei dem gegenüber dem ersten Ausführungsbeispiel das 2/2 Wegeventil durch ein 3/2 Wegeventil ersetzt ist,

Figur 6

ein Schaltbild des dritten Ausführungsbeispiels, bei dem der Steuerdruck durch ein einziges Druckbegrenzungsventil auf zwei durch unterschiedlich große Druckwirkflächen bestimmte Werte begrenzbar ist und die Verstellung durch Umschaltung eines 2/2 Wegeventils erfolgt,

Figur 7

die Anordnung und konstruktive Ausgestaltung des Druckbegrenzungsventils und des 2/2 Wegeventils aus Figur 6 innerhalb einer Wegeventilscheibe,

Figur 8

ein Schaltbild des vierten Ausführungsbeispiels, das zwei auf unterschiedlich hohe Ansprechdrücke eingestellte Druckbegrenzungsventile aufweist und bei dem das Druckbegrenzungsventil mit dem niedrigeren Ansprech druck nach dem Umschalten eins 2/2 Wegeventils wirksam werden kann,

Figur 9

ein. Schaltbild des fünften Ausführungsbeispiels, das wie das vierte Ausführungsbeispiel zwei Druckbegrenzungsventile und ein 2/2 Wegeventil aufweist und bei dem das Druckbegrenzungsventil mit dem niedrigeren Ansprechdruck stromab einer Düse an den zweiten Leitungsabschnitt der Lastmeldeleitung in der zweiten Wegeventilsektion angeschlossen ist und das 2/2 Wegeventil den individuellen Meldekanal der ersten Wegeventilsektion mit dem zweiten Leitungsabschnitt verbinden kann,

Figur 10

ein Schaltbild des sechsten Ausführungsbeispiels, bei dem im Unterschied zum fünften Ausführungsbeispiel das 2/2 Wegeventil den ersten Leitungsabschnitt der Lastmeldeleitung mit dem Eingang des Druckbegrenzungsventils mit dem niedrigeren Ansprechdruck verbinden kann,

Figur 11

ein Schaltbild des siebten Ausführungsbeispiels, bei dem ein auf einen hohen Ansprechdruck eingestelltes Druckbegrenzungsventil und ein von dem Druck in einem weiteren Leitungsabschnitt der Lastmeldeleitung gesteuertes Drosselventil zwischen einer Düse und dem Regelventil an den ersten Leitungsabschnitt der Lastmeldeleitung angeschlossen sind,

Figur 12

ein Schaltbild des achten Ausführungsbeispiels, bei dem drei auf unterschiedlich hohe Ansprechdrücke eingestellte Drosselventile vorhanden sind, und

Figur 13

ein Schaltbild eines Ausführungsbeispiels-, bei dem Konstantpumpe und Bypassdruckwaage durch eine load-sensing geregelte Verstellpumpe ersetzt sind.

Show it

FIG. 1

a circuit diagram of the first embodiment, in which the control pressure can be limited by a single pressure relief valve to two determined by different degrees of spring preload values and the adjustment is done by switching a 2/2 way valve,

FIG. 2

a first arrangement and structural design of the pressure relief valve and the 2/2-way valve of Figure 1 within a directional control valve disc,

FIG. 3

a second arrangement and structural design of the pressure relief valve and the 2/2 way valve of Figure 1 within a directional control valve disc,

FIG. 4

schematically another one. Arrangement of the pressure relief valve of Figure 3 in a section perpendicular to that of Figure 3,

FIG. 5

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

FIG. 6

a circuit diagram of the third embodiment, in which the control pressure can be limited by a single pressure relief valve to two determined by different sized pressure acting surfaces values and the adjustment is done by switching a 2/2 way valve,

FIG. 7

the arrangement and structural design of the pressure relief valve and the 2/2 way valve of Figure 6 within a directional control valve disc,

FIG. 8

a circuit diagram of the fourth embodiment, which has two set to different high response pressures pressure relief valves and in which the pressure relief valve with the lower response pressure can be effective after switching a 2/2 way valve,

FIG. 9

one. Circuit diagram of the fifth embodiment, which has as the fourth embodiment, two pressure relief valves and a 2/2 way valve and in which the pressure relief valve is connected to the lower response pressure downstream of a nozzle to the second line section of the load reporting line in the second directional control valve section and the 2/2 way valve individual signaling channel of the first directional valve section can connect to the second line section,

FIG. 10

a circuit diagram of the sixth embodiment, in which, in contrast to the fifth embodiment, the 2/2 way valve can connect the first line section of the load reporting line with the input of the pressure relief valve with the lower set pressure,

FIG. 11

a circuit diagram of the seventh embodiment, in which a set to a high set pressure relief valve and a controlled by the pressure in another line section of the load reporting line throttle valve between a nozzle and the control valve to the first line section of the load reporting line are connected

FIG. 12

a circuit diagram of the eighth embodiment, in which there are three set to different high set pressures throttle valves, and

FIG. 13

a diagram of an exemplary embodiment, are replaced by a load-sensing regulated variable displacement pump and bypass pressure compensator.

According to the circuit diagrams shown includes a control block 15, which is for a forklift is provided, four-way valve disks 16, 17, 18 and 19, an input disk 20 having an inlet port 21 and a drain port 22, and an end plate 23, with the one from the inlet port 21 through the input disk and the directional valve discs through inlet passage 24 closed is. From the drain port 22 goes through the input disk and the directional valve discs through a drain channel 25 which leads into the end plate. From the drain port 22 hydraulic oil can flow to a tank 26. The inlet connection is connected to the pressure connection of a hydraulic pump 27, thus promote the sucked from the tank hydraulic oil into the inlet channel 24 can. According to their order from the input disk 20, let the directional valve disk be 16 the first or foremost, the directional control valve disc 17 the second, the Directional valve disc 18, the third and the way valve disc 19, the last or rearmost. If in the following components or channels within a directional valve disc be named as first, second, third or last, this should be clearly on their Indicate affiliation to the appropriate directional valve disc.

Each directional valve disc includes a proportionally adjustable directional control valve 28, 29, 30 and 31, with a hydraulic consumer, in a forklift Hydraulic cylinder, controlled according to the amount and direction of the speed can. The directional valve 28 of the first directional valve disc 16 is the function "lifting" associated with the fork, for a single-acting hydraulic cylinder is sufficient. The directional valve 29 of the second-way valve disc 17 is the function "tilt" the mast and the directional valves 30 and 31 of the directional control valves 18 and 19 are additional functions such as "extension of the fork" and "sideways movement of the Fork "for these functions are the hydraulic consumers double-acting hydraulic cylinders.

Except for a directional control valve, a shuttle valve is located in each directional control valve disc 35, 36, 37 and 38 with a valve body 39. Depending on the pressure conditions a shuttle valve connects one from the center port of the shuttle valve starting LS-Kanat 40, 41, 42 and 43 a directional valve disc with an individual Signal box 44, 45, 46 and 47 a directional control valve disc or with the LS channel of the following directional control valve disc. The one side port of the shuttle valve 38 of the last directional valve disc is on the end plate 23 with the Drain channel 25 connected. The individual signaling channel of each directional valve disc in turn, via the associated directional control valve in a working position of Directional valve connected to the flow to the hydraulic consumer, so that in it the load pressure of the hydraulic consumer is present, and in the neutral position of the directional control valve to the drain line relieved of pressure. In the first LS channel 40, a nozzle 50 is inserted.

In the embodiments according to the circuit diagrams of Figures 1, 5, 6 and 8 to 12, the hydraulic pump 27 is a constant displacement pump. The load-sensing controller will formed by a pressure compensator 51, which housed in the input disk 20 is and between the inlet channel 24 and the drain channel 25 is located. A control piston the pressure compensator is in the opening direction of the pump pressure in the inlet channel 24 charged. In the closing direction act on the control piston of the Pressure balance, a compression spring 52 and a control pressure in the LS channel 40 on of the shuttle valve 35 remote side downstream of the nozzle 50 is present. The Both surfaces on which the control pressure and the pump pressure act are same size. Thus, the control piston is free of force when the pump pressure around the Pressure equivalent of the compression spring 52 is higher than the control pressure. This pressure difference is also referred to as a rule Δp and usually has a value between 5 bar and 20 bar.

In the embodiment of Figure 13, the hydraulic pump 27 is a variable displacement pump with a schematically indicated load-sensing control valve 53 whose Regulating piston in the sense of an adjustment of the hydraulic pump in the direction of larger Stroke volume of the control pressure downstream of the nozzle 50 and a control spring and is acted upon by the pump pressure in the direction of smaller displacement. Here, too, a pump pressure is adjusted, which is the pressure equivalent of the Control spring corresponding control Δp above the control pressure downstream of the nozzle 50th lies. The use of a load-sensing regulated variable pump brings less Loss of unusable energy with it, because not only the pump pressure, but also the pump delivery is limited to the necessary level. at In the exemplary embodiment according to FIG. 13, the LS channel 40 is in the input disk 20 continued and via a LS connection 54 and a line with the on the Hydraulic pump 27 constructed control valve 53 connected.

In the embodiments of Figures 1 to 4, 5, 6, 8 to 11 and 13 is within the directional control valve disk 16, a directly controlled pressure relief valve 55, whose entrance to the downstream of the nozzle 50 lying part of the LS channel 40 and whose output is connected to the drain channel 25. Directly controlled pressure relief valve means that from the figures 2 and 3 apparent movable valve element 56 in the opening direction of an effective Effective area of the pressure at the entrance of the valve and in the closing direction of a Valve spring 57 is acted upon. The pressure relief valve 55 leaves the Pressure at its entrance only to a limit pressure rise, which at the Active surface generates a compressive force that is equal to the spring force.

In the embodiments according to Figures 1 to 4 and 5, the spring force between two determined by two stops for one end of the valve spring 57 Values changeable. The valve element 56 remote end of Valve spring 57 can do this by an auxiliary piston 58 in the direction of a valve seat be moved on the in the closed state of the valve 55 the Valve element 56 is seated. The auxiliary piston adjoins with an effective surface to one Control chamber 59, the pressurization of the switching position of a switchable between two switching positions and also in the directional control valve disc 16 built-way valve depends. This is in the embodiment according to the figures 1 to 4, a directional control valve 60 with two terminals, so a 2/2 way valve, which is in series with a nozzle 61 and downstream of this the LS channel 40 upstream of the nozzle 50 and the drain channel 25 is arranged. Thus, when the directional control valve 60 locks, the auxiliary piston 58 with the in the LS channel upstream of the nozzle 50 applied pressure and spans the Valve spring strong before, so that the limit pressure is high. If the directional valve is open, so the auxiliary piston is relieved of pressure. The valve spring 57 is less biased and the limit pressure is lower

A valve piston 62 of the directional control valve 60 is in the closing direction of a compression spring 63 loaded and in the opening direction via a through the directional control valve plate 17th passing control line 64 from that in the third LS channel 42 pending Pressure acted upon. In this case, the force of the compression spring 63 can be selected be that the directional valve already at a very low pressure of, for example 10 bar opens. However, the compression spring can also be set to a higher pressure be, but in any case is so low that when operated directional control valve 30 the pressure limiting 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 Figure 1 let For example, assume that the high limit for the control pressure at 120 bar and the low limit at 60 bar. The control ap is 10 bar. Becomes one of the functions "lifting" or "tilting" is operated alone or parallel to the other, so is in the LS channel 40 upstream of the nozzle 50, the highest load pressure of the activated functions. The two further directional valves 30 and 31 are not operated, so that the control line 64 is relieved of pressure and the directional control valve 60 occupies the switching position shown in Figures 1 to 3. The auxiliary piston 58 is acted upon by the highest load pressure and has the valve spring 57 strongly biased. The pressure relief valve 55 limits the control pressure downstream of Nozzle 50 to 120 bar, so that the pump pressure and thus the load pressure to the hydraulic consumers for the functions "lifting" and "tilting" to a maximum 130 bar increases.

If one of the directional control valves 30 or 31 is actuated, the third LS channel 42 is in the third position Pressure on. Switches the directional control valve 60, for example, already at 10 bar pressure in the Control line 64 um, then, as soon as this load pressure on one of the directional control valves 30 and 31 controlled consumer occurs, the pressure relief valve adjusted to the low limit pressure of 60 bar. The pump pressure can then to a maximum of 70 bar. The load pressure can be higher on the third or fourth Consumers will not. Will be the first or second consumer at the same time controlled, this only moves when its load pressure is lower than 70 bar is.

However, the load pressure at the third or fourth consumer is then also at 70 bar limited when the directional control valve 60 switches only at 70 bar. This brings it though with the fact that the pump pressure at a simultaneous actuation of the third or fourth consumer and the first or second consumer to over 70 bar may increase when the load pressure at the third or fourth consumer smaller than 70 bar. The pump pressure is then via the Zumeßblende in the directional control valve 30 or 31 to the load pressure of the third or fourth hydraulic consumer throttled. If this consumer finally reaches an attack, it rises its load pressure to 70 bar, so that the directional control valve 60 switches and the Pressure relief valve 55 adjusted to the low limit pressure of 60 bar becomes. The pump pressure goes back to 70 bar; so that even with open directional valve 30 or 31 and without oil flow the load pressure at the third or fourth hydraulic Consumer remains limited to 70 bar.

According to Figure 2, the valve body 39 of the shuttle valve 35 is in a Recess 70 in the voltage applied to the directional control valve disc 17 flange surface the directional valve disk 16. In alignment with each other open eccentrically into the recess 70 of the LS channel 40 of the directional control valve disk 16, in which the nozzle 50th located, and the LS-channel 41 of the directional control valve disk 17. Also opens into the Recess of the individual signaling channel 44 of the directional control valve disc 16. As appropriate in which channel the higher pressure is present, the valve body 39 takes a such a situation that the LS channel 41 or the message channel 44 with the LS channel 40 is connected.

The two valves 55 and 60 are in the directional control valve disc 16 perpendicular to the plane the directional valve disc 16 of the voltage applied to the directional control valve disk 17 Flange surface installed. Between the valve piston 62 of the directional valve 60th and the bottom of a blind bore 65, the compression spring 63 is clamped. These seeks to hold the valve piston in contact with the directional valve disc 17. In the Blind bore 65 opens a transverse channel 71, the upstream of the nozzle 50 of the LS channel 40 goes out and in which the nozzle 61 is located. In addition, the Blind bore 65 cut by a channel 72, which is connected to the drain channel 25th connected is. Also, the space in which the compression spring 63 is located, depressurized. Axial opens into the blind bore 65 in the directional control valve 17th extending control channel 64.

The valve piston 62 takes under the influence of the compression spring 63 a rest position a, in which he is pressed to the directional valve disc 17. In this rest position the two channels 71 and 72 are sealed against each other. Exceeds the by the pressure in the control channel 64 at the cross-sectional area of the valve piston 62 generated compressive force the spring force, the valve piston is to the stop moved to the bottom of the blind bore 65 in its second switching position, in the downstream of the nozzle 61 lying part of the channel 71 with the channel 72nd connected and thus relieved of pressure.

The individual parts of the pressure limiting valve 55 are in a blind bore 73, in the center at the bottom of a downstream of the nozzle 50 with the LS channel 40th connected channel 74 opens The mouth edge of the channel 74 forms a seat for the formed as a ball valve element 56 of the pressure relief valve. The Ball is held in a spring plate 75 for the valve spring 57, which extends over a another spring plate 76 at one to a stop in the blind hole 73 screwed screw 77 can support. The distance of two spring plate from each other when supporting the one on the ball 56 on Seat and the other on the screw determines a low bias the valve spring 57. By washers between the screw 77 and the spring plate 76, this bias can be adjusted. The room in which the valve spring 57 is connected via the channel 72 to the drain channel 25 and thus relieved of pressure, in a central axial bore of the Schraubeinsatzes the auxiliary piston 58 is guided tightly sliding. With a stop collar 78 is the auxiliary piston in the control chamber 59, behind the Screw insert 77 formed in the directional control valve disk 16 and a channel 79 is connected downstream of the nozzle 61 to the channel 71. The guide cross section, with the auxiliary piston 58 is guided in the screw 77 and the equal to the effective area for the pending in the control chamber 59 and the auxiliary piston is to be applied in the direction of the valve element 56 pressure is greater than the seat cross-section for the valve element 56, so that when closing the Wegeventüs 60 of the auxiliary piston 58, first the valve spring 57 to the abutment of the stop collar 78 on the screw 77 will bias more, before continuing on rising pressure in the LS channel 40, the pressure relief valve opens. The higher one Preload the valve spring 57 can by washers on the stop collar 78 to be adjusted.

In the design of Figures 3 and 4, the directional control valve 60 is the same as formed in Figure 2 and as well as there perpendicular to the plane of the disc Directional valve disc 16 arranged in this in a blind bore 65. The items the pressure relief valve 55, however, are in a blind hole 73, whose axis is parallel to the disc plane and perpendicular (Figure 3) or parallel extends to the axis of the valve bore, of which the spool 10 of the directional control valve 28 is recorded. At this one recognizes the formation of the metering diaphragm by control grooves 11. In the directional valve disk 16 is, far this Disk is provided for the actuation of a single-acting hydraulic cylinder and therefore has only one consumer outlet, especially a lot of room for the Housing the valves 55 and 60 available.

The pressure relief valve of Figure 3, which is parallel to the one consumer terminal protrudes from the directional control valve disc, has a screwed Valve seat 80 for the again designed as a ball valve element 56. The Valve spring 57 is supported on the spring plate 75 on the ball 56 from. Above the Spring plate 76 is able to support the valve spring 57 on the screw insert 77, which is now provided with a radial seal and to adjust the low Pretension of the valve spring can be rotated. The twist is, however only possible if another provided with a radial seal Screw insert 81 is not located in the bore 73. On the screw 81 is the auxiliary piston 58 mounted with its stop collar 78. Thus one can, by one twisted the screw 81, the high bias of the valve spring 57 set. This is possible from the outside. The screw 81 can with a Lock nut secured and sealed with a protective cap.

Due to the opposite to Figure 2 different arrangement of the pressure relief valve 55 run the channels in Figure 3 differently than in Figure 2. Circuit technology however, there is no difference. Upstream of the nozzle 50 in the LS channel 40 branches the Channel 71 from which leads to the directional control valve 60 and in which the nozzle 61 is located. Downstream of the nozzle 61 connected to the channel 71, the channel 79 extends to the control chamber 59 between the two. Screw inserts 77 and 81 of the Pressure relief valve 55. The spring chamber of this valve is in turn with the Relief channel 72 connected.

In the embodiment of Figure 5 is the same pressure relief valve 55 used as in the embodiment of Figure 1. However, they are 2/2 way valve 60 and the nozzle 61 of Figure 1 replaced by a 3/2 way valve 85, in its one switching position, it under the action of a spring 63 occupies the control chamber on the auxiliary piston 58 upstream of the nozzle 50 with the LS channel 40 connects and in its other switching position in which it is from the pressure is brought in the control line 64, the control room to the drain line 25 out relieved. Here occurs when relief of the auxiliary piston no loss of control oil. Moreover, the function of the embodiment of Figure 5 is the same of the embodiment of Figure 1.

The embodiment of Figures 6 and 7 uses like that after Figure 1, the 2/2 way valve 60 and the nozzle 61 to the adjustment of a pressure relief valve 55, with its entrance in turn downstream of the Nozzle 50 to the LS channel 40 and connected with its output to the drain channel 25 is. As in the embodiment of Figure 2, the items of the Pressure limiting valve 55 according to Figures 6 and 7 in a blind bore 73rd housed in the centrally located at the bottom of the channel 74. The mouth rim the channel 74 in turn forms the seat for the valve element designed as a ball 56. The ball is held in the spring plate 75 for the valve spring 57, the Furthermore, now directly on the screwed into the blind hole 73 Screw insert 77 is supported. The screw 77 is with a radial seal provided, with the aid of the control chamber 59 to the pressure-relieved spring chamber is sealed. By turning the screw 77, the bias the valve spring 57 are adjusted.

In the embodiment of Figures 6 and 7, the pressure relief valve 55 not by changing the spring preload, but by a change in the effective effective area for the valve element acting on Pressure adjusted between two different high pressure settings. To is in turn in a central axial bore of the screw 77 an auxiliary piston 58 slidably guided, corresponding to one of its guide cross-section Acting surface acted upon by the pending in the control chamber 59 pressure is. Unlike the embodiments of Figures 1 to 4 does not lift the auxiliary piston 58 now one end of the valve spring 57 of the Screw insert 77 from but acted on the spring plate 75 directly the valve element 56 in the closing direction. The guide cross section with which the Auxiliary piston 58 is guided in the screw 77, is smaller than the seat cross-section for the valve element 56.

For the description of the operation of the control arrangement according to the figures Again, assume 6 and 7 that the control Δp is 10 bar. Will one the directional control valves 30 or 31 is actuated, 42 is in the third LS-channel pressure. Switches the directional control valve 60, for example, already at 10 bar pressure in the control line 64 um, then, as soon as this load pressure at one of the directional control valves 30 and 31 controlled consumers occurs, the control chamber 59 and thus the Auxiliary piston 58 relieved of pressure. The auxiliary piston thus exerts no force on the Valve element 56 from. The pressure downstream of the nozzle 50 in the LS channel 40, as long as the pressure relief valve 55 is closed, equal to the pressure upstream the nozzle 50 is acted upon the valve element 56 at a seat cross-section corresponding active surface and opens the pressure relief valve at a low limit pressure of for example 60 bar. The pump pressure can then go up increase to a maximum of 70 bar: higher may be the load pressure on the third or fourth Consumers will not.

Will one of the functions "lift" or "tilt" be alone or parallel to the other actuated, so is in the LS channel 40 upstream of the nozzle 50, the highest load pressure of the operated functions. The two further directional 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 switching position shown in Figures 6 and 7. The auxiliary piston 58 is subjected to the highest load pressure, the auxiliary piston with the whose active surface generated force in the closing direction against the valve element 56th suppressed. As long as the pressure relief valve 55 is closed, the pressures are before and behind the nozzle 50 the same size. So the pressure relief valve starts to open when the at an effective effective area equal to the differential area between the seat cross section for the valve element 56 and the guide cross section of the auxiliary piston 58, acting pressure produces a force as large as the force of the valve spring 57 is. The after opening start flowing through the nozzle 50 Oil flow creates a pressure difference across the nozzle 50, so that after the Opening the pressure relief valve of the auxiliary piston 58 acting Pressure in the control chamber 59 is greater than the pressure in the channel 74. In a static State is the pressure difference equal to the control Δp. In the static state is So the valve element in the opening direction of a pressure force resulting from the Pressure downstream of the nozzle 50 and the seat cross section results, and in the closing direction from the low limit pressure determining force of the spring 57 and a Compressive force applied, resulting from the opposite to the pressure in the channel 74 to the control Δp increased pressure in the control chamber 59 and the guide cross-section of the Hitfskolbens 58 results. For example, is the ratio between the guide cross section and the seat cross section 1/2, so is at a control Δp of 10 bar and a lower limit pressure of 60 bar, the upper limit pressure 130 bar. With an area ratio of 1/3, the upper limit pressure is 95 bar.

The embodiment of Figure 8, in addition to a simple, one high limit pressure set pressure relief valve 55, with its input downstream of the nozzle 50 is permanently connected to the LS channel 40, a second simple pressure relief valve 86, which is at a low limit pressure is set. Between the entrance of this second pressure relief valve 86 and the LS-channel downstream of the nozzle 50, a 2/2 way valve 60 is arranged, close by a compression spring 63 in the direction. and over the control line 64 open from the upcoming in the third LS-carial 42 pressure in the direction is charged. If the directional control valve 60 is closed, then the pressure relief valve 86 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, then the pressure limiting valve 86 determines the maximum control pressure for the Pressure balance 51 and thus the maximum inlet pressure.

In the two embodiments of Figures 9 and 10 is like in the Embodiment of Figure 8 a set to a high set pressure simple pressure relief valve 55 present, the downstream of the nozzle 50 at the LS channel 40 is connected. The entrance of a second, on a low Set pressure set pressure relief valve 86 is now downstream of one located in the second LS-channel 41 nozzle 87 continuously with the LS channel 41 connected.

This means, first, that in a single operation of the first directional control valve 28, the pressure relief valve 55 and a single or parallel Actuation of the directional control valves 29, 30 and 31, the pressure relief valve 86 the maximum control pressure for the pressure compensator 51 determined.

There is still a 2/2 way valve 60 in both embodiments, the locks in a caused by the spring 63 switching position and by a in the third LS-channel 42 pending pressure placed in an open switching position can be. In the embodiment of Figure 9 connects the Directional valve 60 in the open switching position the individual reporting channel 44th the directional valve disc 16 downstream of a nozzle 88 and in the embodiment of Figure 10, the LS channel 40 downstream of the nozzle 50 with the input of Pressure limiting valve 86. This ensures that upon actuation of the Directional valve 30 or 31, even with simultaneous operation of the directional control valve 28th the set to the low limit pressure relief valve 86 the maximum control pressure for the pressure compensator 51 determined. Be against it at the same time only the directional valves 28 and 29 is actuated, so determines the pressure relief valve 55 with the higher limit pressure the maximum control pressure for the pressure compensator 51, since the directional control valve 60 remains in its blocking position.

In the embodiment of Figure 11 is in the same manner as in the Embodiments of Figures 9 and 10, the high maximum control pressure for the pressure compensator 51 determined by a simple pressure relief valve 55 Furthermore, a throttle valve 90 is present, the input downstream the nozzle 50 with the LS channel 40 and the output to the drain channel 25th connected is. The throttle valve 90 decreases under the action of a compression spring 91 a blocking position and can against the force of the spring of one of the third LS channel 42 from the control line 64 pending pressure proportionally adjusted will be so widely opened. The spring constant is small for that. The pressure at which the valve 90 responds is equal to the low maximum permitted load pressure for those controlled by the directional control valves 30 and 31 hydraulic consumers.

For the explanation of the operation, it is assumed that the throttle valve For example, it responds at a pressure of 60 bar. Is activated by a or both directional control valves 30 or 31 without operation of a directional control valve 28 or 29 reaches a load pressure of 60 bar, the throttle valve 90 opens a Throttle cross-section from the control side of the pressure compensator 51 to the outlet channel 25th and keeps the pressure on the control side by the control Δp under the load pressure of 60 bar, with a control Δp of 10 bar, ie at 50 bar.

It will now be the tilting or lifting function, so the directional control valve 28 or 29 actuated, wherein the load pressure of this function is greater than 60 bar, for example 100 be bar. Upstream of the nozzle 50 are then no longer 60 bar in the LS channel 40, but 100 bar. With unchanged position of the throttle valve 90 would thus also the pressure downstream of the nozzle 50 and thus on the control side of the pressure compensator 51 increase. This would have an increase in the inlet pressure and an increase the load pressure at the controlled with the directional control valve 30 or 31 hydraulic Consumers result, for example, is at a stop. Indeed already leads to a slight change in the pressure in the LS channel 42 to one Enlargement of the throttle cross-section of the valve 90, so that an increase in pressure the control side of the pressure compensator 51 only in the context of the opening characteristic of Valve 90 occurs. Even with a parallel operation of a directional control valve 30 or 31 and a directional control valve 28 or 29 is thus the maximum load pressure for the third and limits the fourth hydraulic consumer to the low value.

In the embodiment of Figure 11, the high maximum inlet pressure with a pressure relief valve and the low maximum inlet pressure with a Throttle valve adjusted. Both valves are housed in the directional control valve disk 16.

In contrast, in the embodiment of Figure 12 only throttle valves used for setting the pressure levels. Here is a high pressure level for the two with the directional control valves 28 and 29 controlled hydraulic Consumers, a mean pressure level for the controlled with the directional control valve 30 hydraulic consumers and a low pressure level for the with the Directional valve 31 controlled hydraulic consumers provided. Accordingly three throttle valves 90 are present, of which the high set pressure set in the directional control valve disk 16, the middle set pressure set in the directional valve disc 18 and on the low Set pressure set in the directional control valve disc 19 is housed. The Inputs of the throttle valves are via a leading through the directional control valves Line 92 downstream of the nozzle 50 to the LS channel 40 is connected. A control line 64 for the throttle valve in the directional control valve disk 16 is upstream of Nozzle 50 to the LS channel 40, the control line 64 for the throttle valve in the Directional valve disc 18 is at the LS-channel 42 and the control line 64 for the Throttling valve in the directional control valve disc 19 connected to the LS channel 43.

Upon actuation of the directional control valve 31, the throttle valve 90 holds the directional valve disc 19 in the same manner as described with reference to FIG Pressure on the control side of the pressure compensator 51 to such a value that the Pressure in the LS channel 43, equal to the load pressure of the corresponding hydraulic Consumer is, the low set pressure of the valve does not exceed. The load pressure is therefore limited to the low value. Likewise, the two work other throttle valves at the medium and high pressure levels.

Claims (21)

1. A hydraulic control arrangement using load-sensing technology, with a first directional control valve (28, 29), via which pressure medium can. be supplied to a first hydraulic consumer, and
   with at least one further directional control valve (30, 31), via which pressure medium can be supplied to a further hydraulic consumer and which is preferably combined with the first directional control valve to form a valve block (15),
   with a load sensing line, via which a control side of a load-sensing regulating valve (51, 53) can be acted upon by a control pressure dependent on the highest load pressure of the actuated hydraulic consumer and which has a first line segment (40), nearest to the regulating valve (51, 53) and having the control pressure, and at least one further line segment (41, 42, 43), in each case a line segment being connectable via a changeover valve (35, 36, 37, 38) to the following line segment or an individual sensing duct (44, 45, 46, 47) of a directional control valve,
   and with a pilot valve arrangement, by means of which the control pressure is limited to a limit pressure,
   characterized by the fact that, in the case of a defined pressure occurring in a further line segment (42) of the load sensing line, the pilot valve arrangement can be set from a high first limit pressure to a lower second limit pressure, and that, as seen from the first line segment (40) of the load sensing line, the individual sensing ducts (44, 45, 46, 47) can be connected to the successive line segments of the load sensing line according to falling maximum load pressure of the hydraulic consumers.
2. A hydraulic control arrangement according to claim 1, characterized by the fact that the pilot valve arrangement can be adjusted hydraulically via a control line (64) which is connected to the further line segment (42) of the load sensing line.
3. A hydraulic control arrangement according to claim 1 or 2,
   characterized by the fact that the pilot valve arrangement has a pilot valve (55) which is arranged between the first line segment (40) and a relief line (25) and the response pressure of which can be varied,
4. A hydraulic control arrangement according to claim 3, characterized by the fact that the pilot valve has a moveable valve element (56) acted upon by a valve spring (57) in the direction of a closing position and by a pressure force at an active face in the direction of an opening position, and that the prestressing force of the valve spring (57) can be varied as a function of the pressure in the further line segment (42) of the load sensing line.
5. A hydraulic control arrangement according to claim 4, characterized by the fact that the prestressing of the valve spring (57) can be varied via an auxiliary piston (58) between two values defined by a first fixed abutment (77) and a second fixed abutment (77, 81), that the auxiliary piston (58) has an active face which is larger than the active face on the valve element (56) and which can be relieved of pressure or can be acted upon with pressure as a function of the switching position of a changeover valve (60, 85), said switching position being determined by the pressure in the further line segment (42) of the load sensing line, and that the auxiliary piston (58) can be displaced up to the second abutment (77, 81) with the effect of increasing the spring prestress.
6. A hydraulic control arrangement according to claim 5, characterized by the fact that the two abutments (77, 81) are formed by two adjusting screws adjustable independently of one another.
7. A hydraulic control arrangement according to claim 5 or 6, characterized by the fact that the valve spring (57) can be supported at the end remote from the valve element (56) by the auxiliary piston (58).
8. A hydraulic control arrangement according to claim 7, characterized by the fact that the valve spring (57) can be supported via a spring plate (76) on the preferably screwed in insert (77) which separates a spring space relieved of pressure from a control space (59) relieved of pressure or acted upon by pressure as a function of the position of the changeover valve (60, 85), that the auxiliary piston (58), guided in a sealingly slideable manner in an axial bore of the insert (77), is arranged between the spring space and the control space (59), and that the spring plate (76) can be lifted off from the insert (77) by the auxiliary piston (58).
9. A hydraulic control arrangement according to claim 8, characterized by the fact that the valve spring (57) can be supported via a spring plate (76) on a first rotatable screwable insert (77) which forms the first abutment and which separates a spring space relieved of pressure from a control space (59) relieved of pressure or acted upon by pressure as a function of the position of the changeover valve (60, 85), that the auxiliary piston (58), guided in a sealingly slideable manner in an axial bore of the insert (77), is arranged between the spring space and the control space (59), and that on that side of the first screwable insert (77) which faces away from the spring space is located a second rotatable screwable insert (81) which is preferably adjustable from. outside and which forms the second abutment capable of being acted upon by the auxiliary piston (58).
10. A hydraulic control arrangement according to claim 3, characterized by the fact that the pilot valve (55) has a moveable element (56) acted upon by a valve spring (57) in the direction of a closing position, that the valve element (56) can be acted upon in the opening direction by a pressure occurring, downstream of a nozzle (50), in the first line segment (40) of the load sensing line and at a first control face, and that there is a second control face on an auxiliary piston (58) which acts on the valve element (56) and which is relieved of pressure or can be acted upon by pressure as a function of the switching position of the changeover valve (60), said switching position being determined by the pressure in the further line segment (42) of the load sensing line.
11. A hydraulic control arrangement according to claim 10, characterized by the fact that the valve element (56) is acted upon in the closing position by pressure occurring at the second control face, and that the second control face is smaller than the first control face.
12. A hydraulic control arrangement according to claim 11, characterized by the fact that a pressure-relieved spring space of the pilot valve (55) is sealed off, by means of an insert (77) preferably adjustable for varying the prestress of the valve spring (57), relative to a control space (59) relieved of pressure or acted upon by pressure, depending on the switching position of the changeover valve (60), and that an auxiliary piston (58) bearing against or firmly connected to the valve element (56) and having a cross-sectional face which is smaller than the first control face is guided in a sealingly slideable manner in a bore of the insert (77), said bore being open towards the control space (59).
13. A hydraulic control arrangement according to any of claims 5 to 12, characterized by the fact that the changeover valve is a 2/2-way directional control valve (60) and is arranged in series with a nozzle (61) between the load sensing line and the relief line (25), and that the control space (59) on the auxiliary piston (58) is connected to the port between the nozzle (61) and 2/2-way directional control valve (60).
14. A hydraulic control arrangement according to any of claims 5 to 12, characterized by the fact that the changeover valve is a 3/2-way directional control valve (85) and connects a control, space (59) on the auxiliary piston (58) to the load sensing line in one switching position and to a relief line (25) in the other switching position.
15. A hydraulic control arrangement according to claim 1 or 2, characterized by the fact that the pilot valve arrangement has a first pilot valve (55, 90) arranged between the first line segment (40) and a relief line (25) or connectable between these and a second pilot valve (86, 90) arranged between the load sensing line and the relief line (25) or connectable between these, and that the response pressure of the second pilot valve (86, 90) is lower than the response pressure of the first pilot valve (55, 90).
16. A hydraulic control arrangement according to claim 15, characterized by the fact that the two pilot valves are pressure limiting valves (55, 86), and that the second pilot valve (86) can be connected with its inlet to the first line segment (40) via a changeover valve (60) switchable as a function of the pressure occurring in a further line segment (42) of the load sensing line.
17. A hydraulic control arrangement according to claim 16, characterized by the fact that the second pilot valve (86) is connected with its inlet, downstream of a nozzle (87), to a first further line segment (41), and that the changeover valve (60), as a function of the pressure occurring in a further line segment (42) following the first further line segment (41) to the rear, connects or separates the first line segment (40) or an individual sensing duct (44) connectable to the latter, downstream of a nozzle (50, 88) located in said sensing duct, to or from the inlet of the second pilot valve (86).
18. A hydraulic control arrangement according to claim 15, characterized by the fact that the second pilot valve (90) is arranged between the first line segment (40) and a relief line (25), and that its moveable valve element can be acted upon in the closing direction by a valve spring (91) and in the opening direction by the pressure occurring in the further line segment (42,43)
19. A hydraulic control arrangement according to any of the preceding claims, characterized by the fact that the pilot valve arrangement is assigned locally to a directional control valve (28) having a single-acting function.
20. A hydraulic control arrangement according to claim 19, characterized by the fact that the pilot valve arrangement (55) is arranged with its axis in or parallel to a plane spanned by the axis of the directional control valve (28) and a work port, preferably parallel to the axis of the directional control valve.
21. A hydraulic control arrangement according to claim 20, characterized by the fact that the changeover valve (60) is arranged with its axis perpendicular to the plane.

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