JP2010065733A - Hydraulic control circuit for working machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydraulic control circuit for a working machine, having simple construction for accurately supplying a flow amount of operating oil as required by an attachment while improving the working performance with another actuator. <P>SOLUTION: Variable throttle valves 1A, 1B whose openings are changeable with pilot pressure control are mounted in a hydraulic circuit connecting an attachment actuator 46a and hydraulic pumps 10A, 10B to each other. A control relief valve 5D is mounted in a center bypass of an attachment control valve. An attachment relief valve 5C and a low pressure relief valve 5E are mounted in the hydraulic circuit. A variable throttle valve control circuit is provided for introducing one operating hydraulic pressure out of negative control pressure in the hydraulic circuit and operating hydraulic pressure during relief, whichever higher, as pilot pressure on the variable throttle valves 1A, 1B to control the openings of the variable throttle valves 1A, 1B. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a hydraulic control circuit suitable for use in a work machine in which an attachment is attached to the tip of a front work machine.

Conventionally, a technique is known in which a hydraulic drive circuit for an attachment attached to a front work machine of a hydraulic excavator is prepared separately from hydraulic drive circuits for other actuators, and the flow rate of hydraulic oil distributed to each circuit is appropriately controlled. Yes.
For example, Patent Document 1 discloses an operation having a configuration in which hydraulic oil discharged from a hydraulic pump is diverted by a pressure compensation type diverter valve and is supplied to a running circuit for driving a crawler belt and an independent attachment circuit for attachment. A hydraulic circuit for the machine is disclosed. In this technique, in the pressure-compensated shunt valve, the differential pressure between the hydraulic pressures P _A1 and P _A2 supplied to the independent attachment circuit side and the hydraulic pressures P _B1 and P _B2 supplied to the traveling circuit side is maintained at a constant value. Thus, stable diversion is possible regardless of the discharge pressure of the hydraulic pump.

In general, a control valve is interposed in such an independent attachment circuit, and the flow rate of hydraulic oil supplied to the actuator for driving the attachment is adjusted by opening and closing the opening of the control valve. Yes. For example, when attachments such as a hydraulic breaker or a crusher are installed, the opening of the control valve is appropriately controlled so that the hydraulic oil flow required by the hydraulic motor that drives them is obtained. Yes.
JP 2000-73409 A

  However, in the circuit configuration as disclosed in Patent Document 1, the hydraulic oil flow supplied to the independent attachment circuit is controlled only by the control valve, so that the hydraulic oil flow required for the independent attachment circuit is the work load. In the case where it fluctuates according to the above, it is not always possible to ensure a sufficient hydraulic oil flow rate. In particular, in the case of an attachment having a plurality of actuators such as a rotary cutter and grapple, it is difficult to control the hydraulic oil flow rate.

  The present invention has been made in view of such a problem. With a simple configuration, the hydraulic oil flow rate required for the attachment can be accurately supplied, and the interlocking with other actuators can be improved. An object of the present invention is to provide a hydraulic control circuit for a work machine.

  In order to achieve the above object, a hydraulic control circuit for a work machine according to a first aspect of the present invention is for an attachment for driving a front actuator for driving a front work machine of the work machine and an attachment attached to the front work machine. In a hydraulic control circuit of a work machine provided with a hydraulic pump as a drive source of an actuator, an attachment hydraulic circuit that connects the attachment actuator and the hydraulic pump, and an interposition on the attachment hydraulic circuit, and by pilot pressure control A variable throttle valve that can be changed in opening, a front hydraulic circuit that connects the upstream side of the variable throttle valve and the front actuator on the first hydraulic circuit, the attachment hydraulic circuit, and the front hydraulic pressure Both of the circuit, the attachment hydraulic circuit and A pressure compensation valve having a pressure compensation spool that maintains a differential pressure of the front hydraulic circuit and ensures a constant flow rate of hydraulic fluid supplied to the attachment actuator; and a downstream side of the variable throttle valve in the attachment hydraulic circuit; A first pressure compensation circuit for connecting the one end side of the pressure compensation spool to drive the pressure compensation spool in a direction to increase the flow rate of hydraulic fluid to the attachment hydraulic circuit; and the variable throttle valve in the front hydraulic circuit A second pressure compensation circuit for connecting the upstream side of the pressure compensation spool and the other end side of the pressure compensation spool to drive the pressure compensation spool in a direction to increase the flow rate of hydraulic fluid to the front hydraulic circuit, and the attachment hydraulic circuit Controls the flow rate and flow direction of the hydraulic oil that is interposed downstream of the variable throttle valve and supplied to the attachment actuator. An attachment control valve, a control relief valve interposed on the center bypass of the attachment control valve, an attachment relief valve for setting a hydraulic pressure upper limit value of the attachment hydraulic circuit, and the attachment relief valve A low pressure relief valve that is provided downstream and relieves hydraulic oil to the tank at a pressure lower than that of the attachment relief valve; an hydraulic pressure between the attachment control valve and the control relief valve; and the attachment relief valve; A shuttle valve that selects one of the hydraulic pressures among the hydraulic pressures between the low-pressure relief valves, and a variable throttle valve that introduces the hydraulic pressure selected by the shuttle valve as a control pilot pressure of the variable throttle valve And a control circuit.

  The relief valve for control is a relief valve for taking out the negative control pressure (attachment negative control pressure) in the attachment hydraulic circuit. The attachment negative control pressure is high when the attachment actuator is not operated, but decreases according to the amount of operation when the attachment actuator is operated. The attachment relief valve is a relief valve interposed on a relief circuit for the attachment hydraulic circuit.

The hydraulic pump side on the hydraulic circuit is the upstream side, and the actuator side or the tank side is the downstream side.
According to a second aspect of the present invention, there is provided a hydraulic control circuit for a work machine according to the present invention, in addition to the configuration of the first aspect, the opening characteristic of the variable throttle valve is such that the opening area becomes narrower as the control pilot pressure becomes higher. Thus, the opening area is set to be larger as the control pilot pressure is lower.

  According to a third aspect of the present invention, there is provided a hydraulic control circuit for a work machine according to the present invention, in addition to the configuration according to the first or second aspect, front operation amount detection means for detecting an operation amount to the front actuator by an operator Front required flow rate setting means for setting a first required flow rate of hydraulic oil required for the front actuator based on the operation amount detected by the front operation amount detection means, and the variable throttle valve control circuit A pressure sensor for detecting the control pilot pressure, and an attachment required flow rate setting means for setting a second required flow rate of the hydraulic fluid required for the attachment actuator based on the control pilot pressure detected by the pressure sensor And a pump flow rate control means for controlling the discharge flow rate of the hydraulic pump to the sum of the first required flow rate and the second required flow rate. It is characterized in.

  According to a fourth aspect of the present invention, there is provided a hydraulic control circuit for a work machine according to the present invention, comprising: a front actuator for driving a front work machine of the work machine; and a drive source for an attachment actuator for driving an attachment attached to the front work machine; In the hydraulic control circuit of a work machine equipped with a hydraulic pump, the variable throttle formed on the attachment hydraulic circuit for connecting the actuator for attachment and the hydraulic pump and capable of changing the opening degree by pilot pressure control A valve, an attachment control valve that is interposed downstream of the variable throttle valve on the attachment hydraulic circuit, and that controls a flow rate and flow direction of hydraulic oil supplied to the attachment actuator; and a control valve for the attachment Interposed on the center bypass A relief valve for control, an attachment relief valve for setting the hydraulic pressure upper limit value of the attachment hydraulic circuit, and a relief oil that is interposed downstream of the relief valve for attachment and lowers the hydraulic oil to the tank than the relief valve for attachment. One of the hydraulic pressures among the low pressure relief valve, the hydraulic pressure between the attachment control valve and the control relief valve, and the hydraulic pressure between the attachment relief valve and the low pressure relief valve is selected. A shuttle valve and a variable throttle valve control circuit that introduces a hydraulic pressure selected by the shuttle valve as a control pilot pressure of the variable throttle valve are provided.

  According to the hydraulic control circuit for a working machine of the present invention (Claims 1 and 4), the attachment is controlled by pilot-controlling the opening of the variable throttle valve based on the hydraulic pressure introduced from the center bypass of the attachment control valve. A flow rate corresponding to the operation amount can be supplied to the attachment actuator. Further, when the hydraulic pressure of the attachment hydraulic circuit becomes high and the hydraulic oil is relieved from the attachment relief valve, the flow rate of the hydraulic oil in the attachment hydraulic circuit can be reduced by narrowing the opening of the variable throttle valve. With these control actions, the hydraulic oil flow rate to the attachment hydraulic circuit can be adjusted in accordance with changes in the hydraulic fluid flow rate required by the attachment actuator, improving the interlocking operability between the front work machine and the attachment. be able to.

In particular, according to the hydraulic control circuit for a working machine of the present invention (Claim 1), a constant hydraulic fluid flow rate can be ensured on the attachment hydraulic circuit side when the attachment is operated by the action of the pressure compensation valve. Interoperability with the front work machine can be further enhanced.
According to the hydraulic control circuit for a working machine of the present invention (Claim 2), the opening area of the variable throttle valve is increased as the control pilot pressure is lower, so that the amount of operation to the attachment is increased. The hydraulic oil flow rate to the attachment actuator can be increased.

  According to the hydraulic control circuit for a work machine of the present invention (Claim 3), the hydraulic pump is discharged from the hydraulic pump in the amount of addition of the first required flow rate of the front actuator and the second required amount of the attachment actuator. Therefore, the hydraulic oil can be supplied to the front actuator and the attachment actuator without excess or deficiency.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 to 6 are diagrams for explaining a hydraulic control circuit according to an embodiment of the present invention, and FIG. 1 is a side view showing an overall configuration of a hydraulic excavator to which the hydraulic control circuit is applied. Is a hydraulic circuit diagram and a control block diagram showing the overall configuration of the hydraulic control circuit, FIG. 3 is a hydraulic circuit diagram relating to an operating lever of a front actuator in the hydraulic circuit, and FIG. 4 is an operation of an attachment actuator in the hydraulic control circuit. FIG. 5 is a partial control block diagram of a controller according to the present hydraulic control circuit, and FIG. 6 is a graph showing opening characteristics of the variable throttle valve of the present hydraulic control circuit.

[1. Hydraulic excavator configuration]
The hydraulic control circuit of this embodiment is applied as a hydraulic circuit of the hydraulic excavator 40 shown in FIG. The hydraulic excavator 40 includes a lower traveling body 42 equipped with a crawler-type hydraulic traveling device, and an upper revolving body 41 that is rotatably mounted on the lower traveling body 42 via a turning device. . A boom 43 and an arm 44 as a front working machine are pivotally supported at the front end of the upper swing body 41, and a twin header 46 (rotary cutting attachment) is attached to the tip of the boom 43 and the arm 44 as an attachment.

  A hydraulically driven boom cylinder 43a (one of front actuators) that swings the boom 43 in the vertical direction is interposed between the frame of the upper swing body 41 and the boom 43. The boom 43 is provided so as to be raised and lowered with respect to the upper swing body 41 by expansion and contraction of the boom cylinder 43a. Similarly, the arm cylinder 44a (one of the front actuators) and the bucket cylinder 45a shown in FIG. 1 are hydraulic actuators for moving the posture of the arm 44 and the twin header 46, respectively.

  A hydraulic motor 46 a (attachment actuator) is built in the base of the twin header 46. The hydraulic motor 46a is a drive source for the twin header 46, and the earth and sand wall surface can be cut by rotating the pick at the tip. The hydraulic control circuit according to the present invention is a hydraulic circuit for driving the hydraulic actuators 43a, 44a, 45a, the hydraulic motor 46a, and the like.

In addition, a cab 47 on which an operator gets on the left side of the vehicle body of these front work machines. Inside the cab 47, the above-described hydraulic actuators 43a, 44a, 45a and the hydraulic motor 46a, as well as operation levers of various devices such as a traveling device and a turning device of the hydraulic excavator 40, various operation switches, seats and the like are arranged. ing.
In the engine room 48 provided in the upper swing body 41, two hydraulic pumps driven by the engine 13 are provided. Hereinafter, one hydraulic pump is referred to as a first hydraulic pump 10A, and the other is referred to as a second hydraulic pump 10B.

[2. Hydraulic circuit configuration]
FIG. 2 schematically shows a hydraulic circuit to which the hydraulic control circuit is applied. FIG. 2 shows a schematic configuration of a hydraulic circuit related to driving of the boom cylinder 43a, the arm cylinder 44a, and the hydraulic motor 46a, and a description of hydraulic circuits related to other actuators is omitted.

  This hydraulic circuit mainly includes a first hydraulic circuit L1 for driving the boom cylinder 43a, a second hydraulic circuit L2 for driving the arm cylinder 44a, a third hydraulic circuit L3 and a fourth hydraulic circuit L4 for driving the hydraulic motor 46a. , A priority circuit L10 for allocating the flow rate of hydraulic oil supplied to these hydraulic circuits, a negative control circuit L11 related to so-called negative control, and the like.

[2-1. First and second hydraulic circuit (front hydraulic circuit) L1, L2]
The first hydraulic circuit L1 is a front hydraulic circuit that connects the first hydraulic pump 10A and the boom cylinder 43a to form a hydraulic fluid passage. The second hydraulic circuit L2 is a front hydraulic circuit that connects the second hydraulic pump 10B and the arm cylinder 44a. The first hydraulic pump 10A and the second hydraulic pump 10B are variable displacement pumps provided with regulators 11A and 11B, respectively.

  As shown in FIG. 2, in the middle of each of the first hydraulic circuit L1 and the second hydraulic circuit L2, a main control valve 4A for adjusting the flow rate and flow direction of hydraulic oil to the boom cylinder 43a and the arm cylinder 44a, 4B is interposed. These main control valves 4A and 4B are configured as electromagnetic flow control valves capable of variably controlling the flow rate and flow direction of hydraulic oil by switching the flow control spool (stem) position to a plurality of positions.

  Further, negative control relief valves 5A and 5B are interposed on a circuit (that is, a bleed-off circuit) connecting the main control valves 4A and 4B and the tank 15. These negative control relief valves 5A and 5B are relief valves for taking out the negative control pressure in the front hydraulic circuits L1 and L2, and function to maintain the hydraulic pressure of the center bypass of the front hydraulic circuits L1 and L2. ing. Note that a negative control circuit, which will be described later, is formed by branching from these circuits.

[2-2. Third, fourth hydraulic circuit (attachment hydraulic circuit) L3, L4]
The third hydraulic circuit L3 is an attachment hydraulic circuit that connects the first hydraulic pump 10A and the hydraulic motor 46a, and the fourth hydraulic circuit L4 is an attachment hydraulic circuit that connects the second hydraulic pump 10B and the hydraulic motor 46a. As shown in FIG. 2, these circuits L3 and L4 are joined together on the downstream side of the check valve.

An attachment control valve 4C is interposed on the downstream side of the junction. The attachment control valve 4C is configured as an electromagnetic flow rate control valve similar to the main control valves 4A and 4B, and is used to adjust the flow rate and flow direction of hydraulic fluid supplied to the hydraulic motor 46a.
Further, a control relief valve 5D is interposed on a bleed-off circuit connecting the attachment control valve 4C and the tank 15. The control relief valve 5D is a relief valve for taking out the negative control pressure (attachment negative control pressure) in the attachment hydraulic circuits L3 and L4, and functions to maintain the hydraulic pressure of the center bypass.

Hereinafter, the hydraulic pressure between the attachment control valve 4C and the control relief valve 5D is referred to as an attachment negative control pressure. The attachment negative control pressure is high when the attachment actuator is not operated, but decreases according to the amount of operation when the attachment actuator is operated.
Further, as shown in FIG. 2, a hydraulic circuit L15 for taking out the attachment negative control pressure is connected between the attachment control valve 4C and the control relief valve 5D.

  An attachment relief valve 5C and a low-pressure relief valve 5E are interposed on a relief circuit branched from the attachment hydraulic circuits L3, L4 to the tank 15 immediately upstream of the attachment control valve 4C. The attachment relief valve 5C functions to set an upper limit value of the working hydraulic pressure in the attachment hydraulic circuits L3 and L4.

  On the other hand, the low pressure relief valve 5E is a relief valve in which a relief pressure lower than that of the attachment relief valve 5C is set. By installing a low pressure relief valve 5E downstream of the attachment relief valve 5C, when the hydraulic fluid is relieved from the attachment hydraulic circuits L3 and L4, a pressure corresponding to the relief amount is applied to the attachment relief valve 5C. And the low-pressure relief valve 5E.

  In addition, a hydraulic circuit L16 for extracting this pressure is connected between the attachment relief valve 5C and the low pressure relief valve 5E. The hydraulic circuits L15 and L16 are joined together via a shuttle valve 19 that selects a high-pressure circuit. Hereinafter, the joined circuit is referred to as a variable throttle valve control circuit L14. The hydraulic pressure in the variable throttle valve control circuit L14 is the hydraulic pressure of one of the hydraulic circuits L15 and L16, which is a high pressure.

For example, the hydraulic pressure on the hydraulic circuit L15 side is selected during normal operation of the hydraulic motor 46a in which the hydraulic oil is not relieved from the attachment relief valve 5C, and as the lever operation amount of the twin header 46 increases. The hydraulic pressure of the variable throttle valve control circuit L14 decreases. On the other hand, when the load acting on the hydraulic motor 46a increases and the relief state is reached, the hydraulic pressure on the hydraulic circuit L16 side becomes high, and the hydraulic pressure on the variable throttle valve control circuit L14 also increases.
A pressure sensor 7A is interposed on the variable throttle valve control circuit L14. Hydraulic pressure P _H1 of the variable throttle valve control circuit L14 detected here are input to the later-described controller 20.

[2-3. Priority circuit L10]
The priority circuit L10 distributes the flow rate of the hydraulic oil supplied from the first hydraulic pump 10A to the first hydraulic circuit L1 and the second hydraulic circuit L2, and the flow rate of the hydraulic oil supplied from the second hydraulic pump 10B. This is a circuit for distributing to the third hydraulic circuit L3 and the fourth hydraulic circuit L4.

As shown in FIG. 2, the hydraulic oil supply line led from the first hydraulic pump 10A is branched into a first hydraulic circuit L1 and a second hydraulic circuit L2 inside the priority circuit L10. The hydraulic oil supply line led from the second hydraulic pump 10B is branched into a third hydraulic circuit L3 and a fourth hydraulic circuit L4 inside the priority circuit L10.
The priority circuit L10 includes a variable throttle valve 1, a pressure compensation valve 2, and an electromagnetic switching valve 3. Note that the priority circuit L10 may be formed as a valve unit in which these plural types of valves are integrally combined.

The circuit for distributing hydraulic oil between the first hydraulic circuit L1 and the second hydraulic circuit L2 and the circuit for distributing hydraulic oil between the third hydraulic circuit L3 and the fourth hydraulic circuit L4 have the same configuration. ing. Hereinafter, the components related to the former will be described in detail. In FIG. 2 and below, description will be made by adding A to the end of the reference numerals of the former component and adding B to the latter.
As shown in FIG. 2, the variable throttle valve 1 </ b> A is a flow rate adjusting valve interposed on the third hydraulic circuit L <b> 3, and can adjust the opening degree (flow rate) by pilot control. As shown in FIG. 6, the opening characteristic of the variable throttle valve 1A is set such that the opening area becomes narrower as the input control pilot pressure becomes higher, and the opening area becomes wider as the control pilot pressure becomes lower. ing. Note that the variable throttle valve 1A completely opens the third hydraulic circuit L3 when no control pilot pressure is input. As described above, the opening characteristic that the opening area becomes wider as the control pilot pressure is lower, the hydraulic oil flow rate to the third hydraulic circuit L3 (hydraulic motor 46a) is increased as the operation amount to the attachment is increased. Be able to.

The aforementioned variable throttle valve control circuit L14 is connected to the pilot port of the variable throttle valve 1A. As a result, the variable throttle valve 1A is controlled to open and close according to the hydraulic pressure of the variable throttle valve control circuit L14.
The first hydraulic circuit L1 is formed to branch from the upstream side of the variable throttle valve 1A in the third hydraulic circuit L3. The discharge pressure of the hydraulic oil from the first hydraulic pump 10A acts on the upstream side of the variable throttle valve 1A as it is. On the other hand, a pressure compensating valve 2A is connected downstream of the variable throttle valve 1A.

  The pressure compensation valve 2A is a valve interposed across the first hydraulic circuit L1 and the third hydraulic circuit L3, and controls the hydraulic oil flow rates of both circuits simultaneously. As shown in FIG. 2, two channels of a first channel 2a and a second channel 2b are formed in the pressure compensation valve 2A, and each channel opening has a single spool ( The pressure compensation spool) is simultaneously changed by the movement of the pressure compensation spool. Here, the first flow path 2a is interposed on the third hydraulic circuit L3, and the second flow path 2b is interposed on the first hydraulic circuit L1.

  Two pilot circuits for driving the spool of the pressure compensation valve 2A are prepared. A sixth hydraulic circuit L6 (first pressure compensation circuit) and a fifth hydraulic circuit L5 (second pressure compensation circuit). First, among the spools of the pressure compensation valve 2A, a fifth hydraulic circuit L5 that guides hydraulic fluid upstream of the variable throttle valve 1A is provided at one end on the side where the second flow path 2b is formed in the sliding direction of the spool. It is connected. The discharge pressure of the first hydraulic pump 10A acts on the fifth hydraulic circuit L5 as it is. On the other hand, a sixth hydraulic circuit L6 that guides hydraulic fluid downstream of the variable throttle valve 1A is connected to the other end of the spool (one end on the side where the first flow path 2a is formed in the sliding direction of the spool). As shown in FIG. 2, an orifice 16 is interposed on the sixth hydraulic circuit L6.

  By providing the two pilot circuits L5 and L6 in this way, the spool of the pressure compensation valve 2A is controlled to a position where the differential pressure between the upstream side and the downstream side of the first flow path 2a is kept constant. Therefore, the flow rate on the first flow path 2a side is controlled to be constant regardless of the discharge pressure of the first hydraulic pump 10A, and the remaining flow rate flows to the second flow path 2b side. That is, it can be said that the pressure compensation valve 2A has a pressure compensation spool that secures a constant flow rate of hydraulic fluid supplied to the hydraulic motor 46a side.

  The hydraulic oil in the sixth hydraulic circuit L6 acts to move the spool in the direction of decreasing the hydraulic oil flow rate on the second flow path 2b side while increasing the hydraulic oil flow rate on the first flow path 2a side. ing. Further, the hydraulic oil in the fifth hydraulic circuit L5 acts to move the spool in a direction to decrease the hydraulic oil flow rate on the first flow path 2a side while increasing the hydraulic oil flow rate on the second flow path 2b side. Yes. For example, when the discharge pressure of the first hydraulic pump 10A increases, the flow rate of the hydraulic oil in the first flow path 2a increases, but is pushed by the hydraulic pressure in the fifth hydraulic circuit L5 that increases accordingly. Since the spool moves to the left in FIG. 2 and the valve opening is reduced, the hydraulic oil flow rate on the downstream side of the first flow path 2a does not change.

A priority switching circuit L9 connected to the tank 15 is provided downstream of the orifice 16 in the sixth hydraulic circuit L6. An electromagnetic switching valve 3A is interposed on the priority switching circuit L9.
The electromagnetic switching valve 3 </ b> A is a two-position switching valve controlled by the controller 20. Since the priority switching circuit L9 is shut off (closed) when the electromagnetic switching valve 3A is ON, the downstream side of the variable throttle valve 1A is connected to one end of the spool of the pressure compensation valve 2A via the sixth hydraulic circuit L6 as described above. The hydraulic pressure is applied. On the other hand, when the electromagnetic switching valve 3A is turned off, the priority switching circuit L9 is opened (relieved) to the tank 15 so that the hydraulic pressure in the sixth hydraulic circuit L6 is reduced to the tank pressure.

  That is, when the electromagnetic switching valve 3A is turned off, the spool of the pressure compensation valve 2A moves to the left in FIG. 2 regardless of the throttle opening state of the variable throttle valve 1A, and the first flow path 2a is completely closed. In addition, the second flow path 2b is completely opened. The electromagnetic switching valve 3A functions to forcibly stop the pressure compensation control in the pressure compensation valve 2A. Also, the flow rate adjustment by the variable throttle valve 1A works only when the electromagnetic switching valve 3A is on.

  As described above, the configuration of the priority circuit L10 on the second hydraulic pump 10B side is the same as that on the first hydraulic pump 10A side. The controller 20 can individually control the electromagnetic switching valves 3A and 3B, but in the present embodiment, the same control is simultaneously performed.

[2-4. Negative control circuit L11]
The negative control circuit L11 is a circuit for negative control in the regulators 11A and 11B. In the negative control, the discharge flow rates at the first and second hydraulic pumps 10A and 10B are decreased or increased so as to correspond to the hydraulic pressure of the negative control circuit L11, and the output of each pump is kept constant. Hereinafter, the hydraulic pressure introduced to the regulators 11A and 11B via the negative control circuit L11 is also referred to as negative control pressure. The negative control circuit L11 is provided with a negative control circuit L12 on the first hydraulic circuit L1 side and a negative control circuit L13 on the second hydraulic circuit L2 side.

  A second electromagnetic switching valve 6A and a shuttle valve 12A are provided on one negative control circuit L12. Similarly, the second electromagnetic switching valve 6B and the shuttle valve 12B are also provided on the other negative control circuit L13. An electromagnetic proportional pressure reducing valve 8 is connected to both of these circuits L12 and L13. Hereinafter, since each negative control circuit L12, L13 has the same configuration, the negative control circuit L12 on the first hydraulic circuit L1 side will be described as an example.

  The second electromagnetic switching valve 6A is a two-position switching valve that is controlled by a controller 20 to be described later, and is responsible for introducing and blocking the working hydraulic pressure bleed off from the first hydraulic circuit L1 side. On the other hand, the electromagnetic proportional pressure reducing valve 8 is a proportional pressure reducing valve controlled by the controller 20, and forcibly changes the negative control pressure by introducing hydraulic oil supplied from the pilot pump 14 into the negative control circuit L12. .

  When the electromagnetic proportional pressure reducing valve 8 is turned on (excited state), the hydraulic oil supplied from the pilot pump 14 flows downstream. Further, the electromagnetic proportional pressure reducing valve 8 can arbitrarily set the downstream hydraulic pressure by adjusting the opening degree. As shown in FIG. 2, the electromagnetic proportional pressure reducing valve 8 is also connected to the tank 15, and its secondary pressure is set to the lowest pressure (tank pressure) when it is off (non-excited state). ing. On the other hand, when the electromagnetic proportional pressure reducing valve 8 is on (excited state), the secondary pressure can be adjusted to an arbitrary pressure.

The shuttle valve 12A is a selection valve interposed at a connection portion between the circuit from the first hydraulic circuit L1 side and the circuit from the pilot pump 14 side. Of these circuits, the high pressure side is automatically selected by the shuttle valve 12A and supplied to the regulator 11A of the first hydraulic pump 10A.
Note that the regulator 11A is a known pump displacement variable means. The regulator 11A is configured to decrease the discharge flow rate of the first hydraulic pump 10A as the negative control pressure is higher, and to increase the discharge flow rate as the negative control pressure is lower. The board control is performed.

[3. Front control lever]
FIG. 3 is a hydraulic circuit diagram illustrating a configuration related to the operation levers of the boom 43 and the arm 44. Each of the front remote control valves 26a to 26d transmits a pilot pressure having a magnitude corresponding to the lever operation amount to the control valves (the control valve 4A of the boom cylinder 43a and the control valve 4B of the arm cylinder 44a) of the front working machine. It has become. Each of the front remote control valves 26a to 26d is provided with shuttle valves 27a to 27d to select a high secondary pressure. Further, the pilot pressure introduction circuit selected by the shuttle valves 27a to 27d is connected to the tournament type via the shuttle valves 27e to 27g as shown in FIG. Thus, has been the pilot pressure P _H2 selected highest level of the shuttle valve 27 g, of the lever operation of the boom 43 and the arm 44, the magnitude of the pilot pressure corresponding to that operation amount is the largest. The pilot pressure _PH2 is detected by a pressure sensor 7B (front operation amount detection means) and input to the controller 20. The pressure _PH2 is used for setting the flow rate required for the boom cylinder 43a and the arm cylinder 44a (first required flow rate).

[4. Operation lever for attachment]
FIG. 4 is a hydraulic circuit diagram relating to the operation lever of the twin header 46. The attachment remote control valve 18 transmits a pilot pressure having a magnitude corresponding to the lever operation amount to the flow control spool of the attachment control valve 4C. A shuttle valve 17 is provided inside the attachment remote control valve 18 to select a high secondary pressure. The selected pressure _PH3 is detected by the pressure sensor 7C and input to the controller 20. The pressure _PH1 is used for setting the flow rate required for the hydraulic motor 46a (second required flow rate).

[5. Control configuration]
As shown in FIG. 2, the hydraulic excavator 40 includes a controller (control) for controlling the electromagnetic switching valves 3A and 3B of the priority circuit L10, the second electromagnetic switching valves 6A and 6B and the electromagnetic proportional pressure reducing valve 8 of the negative control circuit L11. Means) 20 is provided. The controller 20 is an electronic control device configured by a microcomputer, and is provided as an LSI device in which a known microprocessor, ROM, RAM, and the like are integrated. As described above, the controller 20, pressure sensors 7A, 7B, each pressure P _H1 detected by 7C, P _H2, P _H3 is input. Based on the input information, the controller 20 performs the following control.

[5-1. Control of electromagnetic switching valves 3A and 3B]
The controller 20 detects the presence or absence of lever operation of the twin header 46 based on the pressure P _H3 detected by the pressure sensor 7C, control electromagnetic switching valve 3A, and 3B on (blocked) when the lever is being operated To do. That is, the pressure compensation control by the pressure compensation valves 2A and 2B is performed only in a state where the hydraulic motor 46a is actually operating.

  On the other hand, when the lever of the twin header 46 is not operated, the electromagnetic switching valves 3A and 3B are controlled to be off (distributed). As a result, when only the front working machine such as the boom 43 and the arm 44 is single-acting, the hydraulic oil flow in the first flow path 2a of each of the pressure compensation valves 2A and 2B is blocked, and the third hydraulic circuit L3 and the fourth hydraulic circuit L4. The supply of hydraulic oil to will stop.

[5-2. Control of second electromagnetic switching valves 6A and 6B]
Further, the controller 20 controls the second electromagnetic switching valves 6A and 6B to be on (blocked) when the lever of the twin header 46 is operated. On the other hand, when the lever operation is not performed, the second electromagnetic switching valves 6A and 6B are controlled to be off (distributed). That is, the operating hydraulic pressures of the first and second hydraulic circuits L1 and L2 related to normal negative control are introduced into the negative control circuits L12 and L13 only when the front working machine is single-acting. Further, when the twin header 46 is operated, the hydraulic pressure from the first and second hydraulic circuits L1 and L2 is cut off, so that the negative control pressures of the negative control circuits L12 and L13 are controlled according to the control of the electromagnetic proportional pressure reducing valve 8 described later. Will be forcibly changed.
Thus, when the pressure P _H3 detected by the pressure sensor 7C in the present embodiment is a pressure during operation of hydraulic motor 46a (i.e., if it is preset predetermined pressure or higher), electric switching valve 3A , 3B and the second electromagnetic switching valves 6A, 6B are turned on.

[5-3. Control of electromagnetic proportional pressure reducing valve]
A control block diagram relating to the setting of the control amount of the electromagnetic proportional pressure reducing valve 8 is shown in FIG. The controller 20 includes an attachment required flow setting device 21 (attachment request flow setting device), a front required flow setting device 22 (front required flow setting device), an adder 23, a limiter 24, and a valve command value converter 25. ing.

First, the attachment required flow rate setting device 21 determines the required flow rate F _R (attachment request) according to the pressure P _H1 detected by the pressure sensor 7A, that is, the operating hydraulic pressure in the variable throttle valve control circuit L14. Flow rate). Here, as shown by the graph in FIG. 5, the map so that the required flow rate F _R as the pressure P _H1 is high becomes smaller is set. Here, it sets the required flow rate F _R is, will be controlled to be equal to the sum of the hydraulic oil supplied from both of the third hydraulic circuit L3 and the fourth hydraulic circuit L4. Further, the required flow rate F _R of the attachment is input to the multiplier 23.

Subsequently, the front required flow rate setter 22 based on the hydraulic pressure P _H2 detected by the pressure sensor 7B, the boom cylinder 43a and the arm required to be supplied to the cylinder 44a flow rate F _m (i.e., the main control valve 4A, 4B The total required flow rate) is set. Here, as shown by the graph in FIG 5, operating as pressure P _H2 is high (boom 43, the larger the operating amount of the operating lever arm 44) the required flow rate F _m is set map to increase Yes. Here set the required flow rate F _m is input to similarly flow ratio calculator 23 and the required flow rate F _R of the attachment.

The adder 23 outputs the sum of the required flow rates F _R and F _m input from the attachment required flow rate setting device 21 and the front required flow rate setting device 22 (that is, F _R + F _m ) to the limiter 24. That is, the output of the adder 23 is the sum of the hydraulic fluid flow rates required by the first hydraulic circuit L1, the second hydraulic circuit L2, the third hydraulic circuit L3, and the fourth hydraulic circuit L4.
In each limiter 24, the actual supply flow rate is set by limiting the maximum value and the minimum value of the flow rate so that the output from the adder 23 does not become too large or too small. The actual supply flow rate set here is converted into a spool drive signal by the valve command value converter 25 and output as a control signal for the electromagnetic proportional pressure reducing valve 8. The control signal output here is a control signal for generating a negative control pressure by the electromagnetic proportional pressure reducing valve 8 at which the hydraulic fluid flow discharged from each of the hydraulic pumps 10A and 10B becomes equal to the actual supply flow. As a result, the total amount of hydraulic fluid discharged from the first hydraulic pump 10A and the second hydraulic pump 10B becomes equal to the hydraulic fluid flow rate required for the first hydraulic circuit L1 to the fourth hydraulic circuit L4.

  The control contents in the controller 20 according to the present invention are summarized as follows.

As described above, the attachment required flow rate setter 21, the first request of the working oil which is required in a boom cylinder 43a and the arm cylinder 44a based on the pressure P _H2 detected by the pressure sensor 7B of the front operation amount detecting means functions as means for setting the flow rate F _R. The front requested flow setting unit 22, and functions as means for setting the second required flow rate F _m of the working oil which is required to the hydraulic motor 46a on the basis of the control pilot pressure P _H1 detected by the pressure sensor 7A Yes. Further, the adder 23, the limiter 24, and the valve command value converter 25 control the discharge flow rate of the hydraulic pumps 10A and 10B to the addition amount F _R + F _m of the first required flow rate F _R and the second required flow rate F _m. It functions as a pump flow rate control means.

[6. Action]
With this configuration, the hydraulic control circuit operates as follows.
[6-1. During single-acting front operation]
For example, when operating a such a boom 43 and arm 44 front attachment only, since the attachment remote control valve 18 is not operated, the operating lever is operated for the attachment pressure P _H3 detected by the pressure sensor 7C is a minimum value It is judged that it is not done. Thereby, the electromagnetic switching valves 3A and 3B are controlled to be turned off (circulate), and the sixth hydraulic circuit L6 and the eighth hydraulic circuit L8 are opened to the tank 15. Therefore, the spool of the pressure compensation valve 2A moves to the left side in FIG. 2, the spool of the pressure compensation valve 2B moves to the right side in FIG. 2, and the first flow path 2a is completely closed.

  That is, the hydraulic oil flow rate on the first flow path 2a side becomes zero, all the hydraulic oil discharged from the first hydraulic pump 10A is supplied to the first hydraulic circuit L1, and the hydraulic oil discharged from the second hydraulic pump 10B is All are supplied to the second hydraulic circuit L2. Therefore, all the outputs of the hydraulic pumps 10A and 10B are assigned to drive the boom cylinder 43a and the arm cylinder 44a.

  At this time, since the second electromagnetic switching valves 6A and 6B are also controlled to be off (circulate), the working hydraulic pressures of the first hydraulic circuit L1 and the second hydraulic circuit L2 are guided to the negative control circuits L12 and L13. . On the other hand, since the electromagnetic proportional pressure reducing valve 8 is controlled to be off, the secondary pressure of the electromagnetic proportional pressure reducing valve 8 becomes the tank pressure. Accordingly, in the shuttle valves 12A and 12B, the operating hydraulic pressures of the first hydraulic circuit L1 and the second hydraulic circuit L2 are selected as the negative control pressure, and normal negative control is performed.

[6-2. When the attachment is activated]
When the twin header 46, which is an attachment, is operated (including single acting and interlocking), the amount of operation of the attachment operating lever is detected as a pressure fluctuation (increase) by the pressure sensor 7C, so the electromagnetic switching valves 3A, 3B The second electromagnetic switching valves 6A and 6B are controlled to be turned on (cut off), and the priority switching circuit L9 is cut off. Thereby, each of the sixth hydraulic circuit L6 and the eighth hydraulic circuit L8 functions as a pilot circuit for the pressure compensation valves 2A and 2B.

Since the hydraulic pressures of the sixth hydraulic circuit L6 and the eighth hydraulic circuit L8 are pressures introduced through the orifices 16, they are smaller than the discharge pressures of the hydraulic pumps 10A and 10B. On the other hand, the discharge pressures of the hydraulic pumps 10A and 10B are introduced into the other pilot pressures of the pressure compensation valves 2A and 2B via the fifth hydraulic circuit L5 and the seventh hydraulic circuit L7, respectively.
Thereby, since the differential pressure between the upstream side and the downstream side of the first flow path 2a in the pressure compensation valves 2A and 2B is kept constant, constant hydraulic fluid is always supplied to the third hydraulic circuit L3 and the fourth hydraulic circuit L4. It becomes possible to distribute. For example, on the first hydraulic pump 10A side, the flow rate of hydraulic fluid flowing through the third hydraulic circuit L3 is constant without being affected by the pump discharge pressure, and the flow rate is determined by the opening of the variable throttle valve 1A. Become. The same applies to the second hydraulic pump 10B side, and the hydraulic oil flow rate of the fourth hydraulic circuit L4 is constant even if the discharge pressure of the second hydraulic pump 10B changes. Further, the remaining hydraulic oil flows to the first hydraulic circuit L1 and the second hydraulic circuit L2 side.

When the attachment remote control valve 18 is operated to gradually increase the operation amount, the spool of the attachment control valve 4C shifts and the flow rate of hydraulic oil supplied to the hydraulic motor 46a increases. At this time, since the passage on the center bypass side of the attachment control valve 4C is gradually closed, the pressure on the upstream side of the control relief valve 5D (that is, the negative control pressure for the attachment) decreases, and the variable throttle valve control circuit hydraulic pressure P _H1 of L14 also decreases.

On the other hand, as shown in FIG. 6, since the variable throttle valves 1A and 1B have a characteristic of opening the valve opening as the input pilot pressure decreases, the third hydraulic circuit is provided via the variable throttle valves 1A and 1B. The flow rate of hydraulic oil supplied to L3 and the fourth hydraulic circuit L4 increases.
The electromagnetic proportional pressure reducing valve 8, total negative control pressure of the hydraulic pumps 10A, size discharged from 10B with the required flow rate F _R that is required by the required flow rate F _m and twin header 46 which is required by the arm 44 The opening degree is controlled so as to obtain Thereby, the opening degree of the electromagnetic proportional pressure reducing valve 8 is adjusted so as to obtain a negative control pressure that gives a pump flow rate necessary for driving both the attachment and the front.

  That is, each discharge amount of the hydraulic oil from the hydraulic pumps 10A and 10B is controlled to an appropriate amount necessary and sufficient for driving the arm cylinder 44a and the hydraulic motor 46a by the regulators 11A and 11B. Therefore, hydraulic oil is supplied to all the hydraulic circuits from the first hydraulic circuit L1 to the fourth hydraulic circuit L4 without excess and deficiency, and the interlocking between the arm 44 and the twin header 46 is improved.

  Further, when the load acting on the twin header 46 is increased and the attachment control valve 4C is in the relief state, the hydraulic oil is relieved from the attachment relief valve 5C, and pressure is established between the low pressure relief valve 5E. Since the pressure is higher than the attachment negative control pressure detected on the center bypass side, the pressure is transmitted to the variable throttle valve control circuit L14 via the hydraulic circuit L16 and the shuttle valve 19. Thereby, since the valve opening degree of the variable throttle valves 1A, 1B is throttled, leakage from the relief circuit (relief loss) is reduced.

[7. effect]
According to this hydraulic pressure control circuit, the opening degree of the variable throttle valves 1A and 1B is pilot-controlled based on the hydraulic pressure introduced from the center bypass of the attachment control valve 4C, so that the operation amount of the twin header 46 can be adjusted. The flow rate can be supplied to the hydraulic motor 46a. Further, when the hydraulic pressure of the attachment hydraulic circuits L3 and L4 becomes high and hydraulic fluid is relieved from the attachment relief valve 5C, the pressure of the hydraulic fluid relieved by the low-pressure relief valve 5E is raised so that the variable throttle valve The hydraulic fluid flow rate in the attachment hydraulic circuits L3 and L4 can be reduced by narrowing the openings 1A and 1B.

With these control actions, the hydraulic fluid flow rate to the attachment hydraulic circuits L3 and L4 can be adjusted in accordance with the change in hydraulic fluid flow rate required by the hydraulic motor 46a, and the operability of the front work machine and the attachment is linked. Can be improved.
In addition, the pressure compensation valves 2A and 2B allow a constant hydraulic fluid flow rate to be secured to the attachment hydraulic circuits L3 and L4 when the twin header 46 is operated, further improving the operability of the attachment and the front work machine. Can be increased.

Further, according to this hydraulic pressure control circuit, by controlling the electromagnetic proportional pressure reducing valve 8 to control the negative control pressure, the required flow rate F _m to be supplied to the boom cylinder 43a and the arm cylinder 44a and the hydraulic motor 46a should be supplied. required flow rate F _R and the addition amount of the hydraulic oil hydraulic pumps 10A, since that will be discharged from 10B, can be supplied in just proportion hydraulic oil to the boom cylinder 43a, an arm cylinder 44a and the hydraulic motor 46a.

Even when a plurality of attachment actuators are provided, the hydraulic fluid flow rate required by all of the actuators can be supplied to the third hydraulic circuit L3 and the fourth hydraulic circuit L4 without excess or deficiency.
Further, in the present embodiment, the first hydraulic circuit L1 and the second hydraulic circuit L2 have a simple configuration in which the second electromagnetic switching valves 6A and 6B are interposed in the negative control circuits L12 and 13 and only the front work machine is operated. This negative pressure is introduced into the hydraulic pumps 10A and 10B (that is, through normal negative control) to ensure a sufficient and sufficient hydraulic oil flow rate for the operation of each actuator. In addition, when the attachment hydraulic motor 46a is operated, the second electromagnetic switching valves 6A and 6B are closed to arbitrarily set a necessary and sufficient hydraulic fluid flow rate in the negative control circuit L11. Dynamic and linked workability can be improved.

Further, by interposing the pressure compensation valves 2A and 2B in the priority circuit L10, it becomes easy to secure the flow rate of hydraulic fluid flowing to the circuits L3 and L4 to the attachment side.
Moreover, since the pressure compensation action in the first pressure compensation valve 2A and the second pressure compensation valve 2B is stopped by opening the electromagnetic switching valves 3A and 3B on the priority switching circuit L9, the supply of hydraulic oil to the attachment is stopped. It is also easy. Thereby, the working efficiency at the time of the single action | operation of a front work machine can be improved. Further, the pump flow rate can be effectively utilized, and waste of hydraulic energy can be suppressed.

[8. Others]
Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.
For example, in the above-described embodiment, the hydraulic circuit related to the driving of the boom 43, the arm 44, and the twin header 46 is illustrated, but the hydraulic control circuit of the present invention is a hydraulic circuit that includes an attachment and other hydraulic actuators. Widely applicable. That is, the present invention may be applied to a hydraulic circuit including a hydraulic circuit that drives actuators such as a hydraulic cylinder 45a other than the boom cylinder 43a and the arm cylinder 44a, a turning device for the upper turning body 41, and a running device for the lower traveling body 42. Further, not only the twin header 46 but also various hydraulic devices driven by a hydraulic cylinder and a hydraulic motor such as a breaker, a magnet and a grapple cutter can be applied to a hydraulic circuit provided as an attachment.

  The priority circuit L10 and the negative control circuit L11 in the above-described embodiment are not essential and can be omitted as appropriate. Moreover, although the hydraulic control circuit provided with two hydraulic pumps is illustrated in the above-mentioned embodiment, the number of hydraulic pumps is not limited to this, and may be one or three or more. At least the variable throttle valve may be controlled using the negative control pressure (attachment negative control pressure) in the attachment-side hydraulic circuit as the control pilot pressure.

  In the above-described embodiment, output control of the hydraulic pumps 10A and 10B using the negative control pressure introduced from the negative control circuit L11 is performed, but the configuration related to the negative control circuit L11 can be omitted. Similarly, regarding the opening control of the electromagnetic switching valves 3A and 3B and the second electromagnetic switching valves 6A and 6B, control is performed via the controller 20 in the above embodiment, but instead of such electronic control. It is also conceivable to employ a configuration including a pilot control mechanism that physically opens and closes these electromagnetic switching valves 3A, 3B, 6A, and 6B. It is sufficient that at least the opening degree of each valve is controlled by the correspondence relationship described in Table 1 above.

In the above-described embodiment, as shown in FIG. 3, the operation amount to the operation lever of the twin header 46 is detected using the pressure sensor 7B. For example, in the case of an electronic operation lever, the operation amount is electrically operated. It is good also as a structure which detects quantity.
In the above-described embodiment, the present invention is applied to the hydraulic circuit of the excavator 40. However, the application target of the present invention is not limited to this, and various operations such as a bulldozer, a wheel loader, and a hydraulic crane are performed. It can be applied to the hydraulic circuit of a machine.

1 is a side view showing an overall configuration of a hydraulic excavator to which a hydraulic control circuit according to an embodiment of the present invention is applied. 1 is a hydraulic circuit diagram and a control block diagram showing an overall configuration of a hydraulic control circuit according to an embodiment of the present invention. FIG. 3 is a hydraulic circuit diagram relating to an operation lever of a front actuator in the hydraulic control circuit according to the embodiment of the present invention. FIG. 3 is a hydraulic circuit diagram relating to an operation lever of an attachment actuator in the hydraulic control circuit according to the embodiment of the present invention. It is a control block diagram of the controller concerning the hydraulic control circuit concerning one embodiment of the present invention. It is a graph which shows the opening characteristic of the variable throttle valve of the hydraulic control circuit which concerns on one Embodiment of this invention.

Explanation of symbols

1A, 1B Variable throttle valve 2A, 2B Pressure compensation valve 2a First flow path 2b Second flow path 3A, 3B Electromagnetic switching valve 4A, 4B Main control valve 4C Attachment control valve 5A, 5B Negative control relief valve 5C Attachment relief valve 5D Relief valve for control 5E Low pressure relief valve 6A, 6B Second electromagnetic switching valve 7A Pressure sensor 7B Pressure sensor (front operation amount detection means)
7C Pressure sensor 8 Proportional pressure reducing valve 10A First hydraulic pump 10B Second hydraulic pump 11A, 11B Regulator 12A, 12B, 17, 19, 27a-27g Shuttle valve 13 Engine 14 Pilot pump 15 Tank 16 Orifice 18 Remote control valve for attachment 26a ~ 26d Front remote control valve 20 Controller 21 Attachment required flow rate setting device (attachment required flow rate setting means)
22 Front required flow rate setting device (Front required flow rate setting means)
23 Adder (one of pump flow control means)
24 limiter (one of pump flow control means)
25 Valve command value converter (one of pump flow rate control means)
40 Hydraulic Excavator 41 Upper Revolving Body 42 Lower Traveling Body 43 Boom (One of Front Work Machine)
43a Boom cylinder (first actuator)
44 Arm (one of the front work machines)
44a Arm cylinder (second actuator)
45a Bucket cylinder 46 Twin header (attachment)
46a Hydraulic motor (Actuator for attachment)
47 Cab 48 Engine room L1 First hydraulic circuit (front hydraulic circuit)
L2 Second hydraulic circuit (front hydraulic circuit)
L3 Third hydraulic circuit (attachment hydraulic circuit)
L4 Fourth hydraulic circuit (attachment hydraulic circuit)
L5 Fifth hydraulic circuit (second pressure compensation circuit)
L6 Sixth hydraulic circuit (first pressure compensation circuit)
L7 Seventh hydraulic circuit (second pressure compensation circuit)
L8 Eighth hydraulic circuit (first pressure compensation circuit)
L9 priority switching circuit L10 priority circuit L11 negative control circuit L12 first negative control circuit L13 second negative control circuit L14 variable throttle valve control circuit L15, L16 hydraulic circuit

Claims (4)

In a hydraulic control circuit for a work machine including a front actuator that drives a front work machine of the work machine and a hydraulic pump that is a drive source of the attachment actuator that drives an attachment attached to the front work machine,
An attachment hydraulic circuit for connecting the actuator for attachment and the hydraulic pump;
A variable throttle valve interposed on the attachment hydraulic circuit and formed so that the opening degree can be changed by pilot pressure control;
A front hydraulic circuit connecting the upstream side of the variable throttle valve and the front actuator on the first hydraulic circuit;
Pressure compensation, which is interposed in both the attachment hydraulic circuit and the front hydraulic circuit, maintains a differential pressure between the attachment hydraulic circuit and the front hydraulic circuit and ensures a constant flow rate of hydraulic fluid supplied to the attachment actuator. A pressure compensation valve having a spool;
A first pressure that connects the downstream side of the variable throttle valve in the attachment hydraulic circuit and one end of the pressure compensation spool to drive the pressure compensation spool in a direction that increases the flow rate of hydraulic oil to the attachment hydraulic circuit. A compensation circuit;
A second side for connecting the upstream side of the variable throttle valve in the front hydraulic circuit and the other end side of the pressure compensation spool to drive the pressure compensation spool in a direction to increase the flow rate of hydraulic fluid to the front hydraulic circuit. A pressure compensation circuit;
An attachment control valve that is interposed downstream of the variable throttle valve on the attachment hydraulic circuit and controls the flow rate and flow direction of hydraulic oil supplied to the attachment actuator;
A control relief valve interposed on the center bypass of the attachment control valve;
An attachment relief valve for setting an upper hydraulic pressure value of the attachment hydraulic circuit;
A low-pressure relief valve interposed downstream of the attachment relief valve and relieving hydraulic oil to the tank at a lower pressure than the attachment relief valve;
A shuttle valve that selects one of the operating hydraulic pressures that is high among the operating hydraulic pressure between the attachment control valve and the control relief valve and the operating hydraulic pressure between the attachment relief valve and the low pressure relief valve;
A hydraulic control circuit for a work machine, comprising: a variable throttle valve control circuit that introduces an operating hydraulic pressure selected by the shuttle valve as a control pilot pressure of the variable throttle valve. The opening characteristic of the variable throttle valve is set such that the opening area becomes narrower as the control pilot pressure becomes higher, and the opening area becomes wider as the control pilot pressure becomes lower. A hydraulic control circuit for a work machine according to claim 1. Front operation amount detection means for detecting an operation amount to the front actuator by an operator;
Front required flow rate setting means for setting a first required flow rate of hydraulic oil required for the front actuator based on the operation amount detected by the front operation amount detection means;
A pressure sensor for detecting the control pilot pressure of the variable throttle valve control circuit;
An attachment required flow rate setting means for setting a second required flow rate of hydraulic oil required for the attachment actuator based on the control pilot pressure detected by the pressure sensor;
The hydraulic pressure of the working machine according to claim 1 or 2, further comprising pump flow rate control means for controlling a discharge flow rate of the hydraulic pump to an addition amount of the first required flow rate and the second required flow rate. Control circuit. In a hydraulic control circuit for a work machine including a front actuator that drives a front work machine of the work machine and a hydraulic pump that is a drive source of the attachment actuator that drives an attachment attached to the front work machine,
A variable throttle valve that is interposed on an attachment hydraulic circuit that connects the attachment actuator and the hydraulic pump, and is configured to be able to change the opening degree by pilot pressure control;
An attachment control valve that is interposed downstream of the variable throttle valve on the attachment hydraulic circuit and controls the flow rate and flow direction of hydraulic oil supplied to the attachment actuator;
A control relief valve interposed on the center bypass of the attachment control valve;
An attachment relief valve for setting an upper hydraulic pressure value of the attachment hydraulic circuit;
A low-pressure relief valve interposed downstream of the attachment relief valve and relieving hydraulic oil to the tank at a lower pressure than the attachment relief valve;
A shuttle valve that selects one of the operating hydraulic pressures that is high pressure among the operating hydraulic pressure between the attachment control valve and the control relief valve and the operating hydraulic pressure between the attachment relief valve and the low pressure relief valve;
A hydraulic control circuit for a work machine, comprising: a variable throttle valve control circuit that introduces an operating hydraulic pressure selected by the shuttle valve as a control pilot pressure of the variable throttle valve.

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