Hydraulic control systems for work machines

Abstract

To avoid the situation where the pressure of an actuator oil path is raised to upper limit pressure which is set according to an individual optional hydraulic actuator at the non-operation of an optional operation tool without installing a variable relief valve in the actuator oil path which is connected to the optional hydraulic actuator.SOLUTION: By switching an optional control valve 60 to load pressure relief positions R1, R2 in which the pressure of an actuator oil path is made to flow to a load pressure introduction oil path 62 when the pressure of actuator oil paths 67, 68 exceeds upper limit pressure at the non-operation of an optional operation tool, and controlling the relief set pressure of a variable relief valve 65 connected to the load pressure introduction oil path to the upper limit pressure or lower, the pressure of the actuator oil path is made to escape to an oil tank 12 via the optional control valve, the load pressure introduction oil path and the variable relief valve.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to the technical field of hydraulic control systems for work machines such as hydraulic excavators. [Background technology]

[0002] Generally, some work machines, such as hydraulic excavators, are configured to be able to selectively mount a plurality of optional hydraulic actuators. For example, hydraulic excavators are configured to be able to detachably mount optional tools, such as hydraulically driven breakers and crushers, instead of a bucket, which is a commonly used work attachment. When a hydraulic circuit for an optional hydraulic actuator that drives such an optional tool is provided in the hydraulic circuit of a work machine, it is required that the circuit be shared by multiple optional hydraulic actuators in order to save space and reduce the number of parts, but it is also required that the circuit be able to accommodate control for each optional hydraulic actuator. For example, if a fork bucket is installed as an optional hydraulic actuator, the supply pressure to the fork cylinder that operates the fork can be lower than the supply pressure to the bucket cylinder that operates the bucket, so that the bucket can be operated powerfully and the forks can be operated softly. In this way, it is required that the circuit be able to control the supply pressure to the optional hydraulic actuator in accordance with the operating pressure of each optional hydraulic actuator. Therefore, a known technology is known in the past in which a relief valve is provided in each of a pair of actuator oil lines leading from an option control valve that controls the oil supply and discharge to the optional hydraulic actuator to the optional hydraulic actuator, and the supply pressure to the optional hydraulic actuator is controlled by the set pressure of the relief valve, and a variable relief valve whose set pressure can be changed by a control signal from a control device is used as the relief valve, thereby making it possible to arbitrarily change the supply pressure to the optional hydraulic actuator according to the individual optional hydraulic actuator (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-168738 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the device of Patent Document 1, a pair of variable relief valves are required to be arranged in each of a pair of actuator oil lines in order to control the supply pressure to the optional hydraulic actuators so that it corresponds to the operating pressure of each optional hydraulic actuator, which hinders efforts to reduce the number of parts and costs. Therefore, a circuit has been considered that can control the supply pressure to correspond to each optional hydraulic actuator even if the pair of variable relief valves are omitted. However, if the variable relief valves are omitted in this case, when the option operating device is not being operated, that is, when oil is not being supplied to or discharged from the optional hydraulic actuators, even if the pressure in the actuator oil lines increases due to external forces, gravity, or the like, the pressure cannot be released via the variable relief valves set for each optional hydraulic actuator, which creates a problem that the optional hydraulic actuators may be overloaded. This is the problem that the present invention aims to solve. [Means for solving the problem]

[0005] The present invention has been made in view of the above-mentioned circumstances and with the object of solving these problems, and the invention of claim 1 provides an option control circuit in a hydraulic control system of a work machine that is shared by a plurality of optional hydraulic actuators that are selectively attached to the work machine, the option control circuit comprising: an option control valve that controls the supply and discharge of oil to and from the optional hydraulic actuator based on the operation of an option operating tool; a pair of actuator oil lines that connect the option control valve and the optional hydraulic actuator; pressure detection means that detects the pressure in the actuator oil lines; a pressure compensation valve that is arranged upstream of the option control valve and operates to introduce inlet pressure and outlet pressure of the option control valve and maintain the differential pressure between the introduced inlet pressure and outlet pressure at a predetermined pressure; and a control device that controls the operation of the option control valve, and a load pressure introduction oil line that introduces the outlet pressure of the option control valve to the pressure compensation valve is provided with a release control signal from the control device. a variable relief valve capable of varying its set relief pressure, which is used to reduce the pressure in the load pressure introduction oil line to the set relief pressure and introduce it into a pressure compensation valve, thereby enabling variably controlling the inlet pressure of the option control valve based on changes in the set relief pressure of the variable relief valve; and a load pressure relief position is provided as a switching position for the option control valve, which does not supply or discharge oil to or from the option hydraulic actuator but allows the pressure in the actuator oil line to flow into the load pressure introduction oil line, so that when the option operating tool is not being operated and the pressure in the actuator oil line exceeds an upper limit pressure that is preset for each individual option hydraulic actuator, the option control valve is switched to the load pressure relief position and the set relief pressure of the variable relief valve is controlled to be equal to or lower than the upper limit pressure, thereby allowing the pressure in the actuator oil line that exceeds the upper limit pressure to be released into the oil tank via the option control valve, load pressure introduction oil line and variable relief valve. The invention of claim 2 is a hydraulic control system for a work machine according to claim 1, characterized in that the hydraulic control system for the work machine comprises first and second hydraulic pumps which serve as hydraulic supply sources for other hydraulic actuators provided on the work machine in addition to the optional hydraulic actuator, the optional hydraulic actuator uses either or both of these first and second hydraulic pumps as its hydraulic supply source, the option control circuit comprises first and second option supply oil passages connected to the first and second hydraulic pumps respectively, and an option junction oil passage where these first and second option supply oil passages join, and a pressure compensation valve and an option control valve are arranged in the option junction oil passage. The invention of claim 3 is a hydraulic control system for a work machine according to claim 2, characterized in that the hydraulic control system for the work machine is provided with first and second bleed valves that respectively control the bleed flow rates from the first and second hydraulic pumps to the oil tank based on control signals output from the control device, and the discharge pressures of the first and second hydraulic pumps are controlled by controlling the bleed flow rates by the first and second bleed valves, and the control device, when the optional hydraulic actuator uses only one of the first or second hydraulic pumps as a hydraulic supply source, makes the discharge pressure of the hydraulic pump that serves as the hydraulic supply source higher than the discharge pressure of the other hydraulic pump that is not a hydraulic supply source, and when the optional hydraulic actuator uses both the first and second hydraulic pumps as hydraulic supply sources, controls the bleed flow rates so that the discharge pressures of the first and second hydraulic pumps are equal. [Effects of the Invention]

[0006] By adopting the invention of claim 1, the upper limit pressure of the pressurized oil supplied to the optional hydraulic actuator can be variably controlled to a pressure corresponding to each optional hydraulic actuator, even without providing a variable relief valve in each of the pair of actuator oil lines, and the pressure in the actuator oil line when the optional operating device is not being operated can be controlled so as not to exceed the upper limit pressure set in accordance with each optional hydraulic actuator. By adopting the invention of claim 2, whether the optional hydraulic actuator uses only the first hydraulic pump, only the second hydraulic pump, or both hydraulic pumps as its hydraulic supply source, oil supply and discharge control for the optional hydraulic actuator can be performed with just one option control valve arranged in the option joint oil passage, which contributes to a reduction in the number of parts. By adopting the invention of claim 3, even if a separate valve for opening and closing the first and second option supply oil passages is not provided in the first and second option supply oil passages, whether the option hydraulic actuator uses either the first or second hydraulic pump as a hydraulic supply source or both hydraulic pumps as hydraulic supply sources, only the supply pressure oil from the hydraulic pump serving as the hydraulic supply source can be supplied to the option junction oil passage, thereby reducing the number of parts and costs. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a side view of a hydraulic excavator. [Figure 2] FIG. 1 is a hydraulic circuit diagram of a hydraulic excavator. [Figure 3] FIG. 4 is an enlarged view of an option control circuit for an optional hydraulic actuator. [Figure 4] 1A is a diagram showing the relationship between the spool movement stroke of the option control valve in the first and second load pressure relief positions and the first and second operating positions and the opening area of ​​the supply valve path, discharge valve path, and load pressure valve path, and FIG. 1B is a diagram showing the opening characteristics of the switching valve. [Figure 5] FIG. 2 is a block diagram showing the configuration of a controller. [Figure 6] FIG. 3 is a control block diagram of a first and second manipulated variable setting unit. [Figure 7] 10A, 10B, and 10C are diagrams showing the relationship between the operation amount of the operating tool and the required flow rate. [Figure 8] FIG. 3 is a control block diagram of a required flow rate setting unit and a pump control unit. [Figure 9] FIG. 4 is a control block diagram of a valve opening area control unit. [Figure 10]FIG. 4 is a control block diagram of a bleed control unit. [Figure 11] FIG. 4 is a control block diagram of first and second pump target pressure setting in a bleed control unit. [Figure 12] FIG. 4 is a flowchart showing a control procedure of load pressure relief control. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a hydraulic excavator 1, which is an example of a work machine equipped with the hydraulic control system of the present invention. The hydraulic excavator 1 is made up of various parts, such as a crawler-type lower traveling body 2, an upper rotating body 3 that is supported above the lower traveling body 2 so that it can swing freely, and a work implement 4 that is attached to the upper rotating body 3. The work implement 4 is further made up of a boom 5 that has its base end supported on the upper rotating body 3 so that it can swing freely up and down, a stick 6 that is supported at the tip of the boom 5 so that it can swing freely back and forth, and a bucket 7 that is attached to the tip of the stick 6 so that it can swing freely. The hydraulic excavator 1 is also equipped with various hydraulic actuators, such as a boom cylinder 8, a stick cylinder 9, and a bucket cylinder 10 that swing the boom 5, stick 6, and bucket 7, respectively, left and right travel motors (not shown) that travel the lower traveling body 2, and a swing motor (shown in FIG. 2) 11 that swings the upper rotating body 3. Furthermore, the hydraulic excavator 1 is capable of selectively mounting various hydraulically operated optional tools (optional attachments) such as a breaker, crusher, grapple, tilt bucket, rotary cutting attachment (none of which are shown) in place of the bucket 7, depending on the type of work being performed. When an optional tool is mounted, the bucket cylinder 10 operates as a hydraulic cylinder for swinging the optional tool relative to the stick 6.

[0009] Next, a hydraulic control system provided in the hydraulic excavator 1 will be described based on the hydraulic circuit diagram shown in Fig. 2. In Fig. 2, the hydraulic circuit related to the traveling motor is omitted. In Fig. 2, A and B are variable displacement first and second hydraulic pumps, Aa and Ba are displacement varying means for varying the displacements of the first and second hydraulic pumps A and B, and 12 is an oil tank. Also, 8, 9, 10, and 11 are the boom cylinder, stick cylinder, bucket cylinder, and swing motor, which are hydraulic actuators permanently installed in the hydraulic excavator 1. Furthermore, 13 is an optional hydraulic actuator. Optional hydraulic actuator 13 is a hydraulic actuator provided on an optional tool to drive an optional tool selectively attached to the hydraulic excavator 1. For example, if a breaker is attached as an optional tool, optional hydraulic actuator 13 is a breaker hydraulic actuator (hereinafter simply referred to as the breaker), and if a grapple is attached, optional hydraulic actuator 13 is a grapple hydraulic actuator. In this embodiment, boom cylinder 8 and stick cylinder 9 use both the first and second hydraulic pumps A and B as hydraulic supply sources, bucket cylinder 10 uses first hydraulic pump A as a hydraulic supply source, and swing motor 11 uses second hydraulic pump B as a hydraulic supply source. Furthermore, as will be described later, the optional hydraulic actuator 13 is configured to use either one or both of the first and second hydraulic pumps A and B as the hydraulic pressure supply source, depending on the flow rate required by the optional hydraulic actuator 13 and whether the optional hydraulic actuator 13 is operated independently or in conjunction with (simultaneous operation with) other hydraulic actuators. Furthermore, in this embodiment, the boom cylinder 8, stick cylinder 9, bucket cylinder 10, and swing motor 11 correspond to other hydraulic actuators of the present invention.

[0010] 2, C is a first pump line connected to the discharge side of first hydraulic pump A, and first boom supply oil passage 14, first bucket supply oil passage 15, first stick supply oil passage 16, and first option supply oil passage 17 are connected to first pump line C in parallel with one another. Also, D is a second pump line connected to the discharge side of second hydraulic pump B, and second boom supply oil passage 18, second stick supply oil passage 19, second swing supply oil passage 20, and second option supply oil passage 21 are connected to second pump line D in parallel with one another. The first and second boom supply oil passages 14, 18 are oil passages that connect the first and second hydraulic pumps A, B, respectively, to a boom control valve 23, which will be described later, the first bucket supply oil passage 15 is an oil passage that connects the first hydraulic pump A to a bucket control valve 25, the first and second stick supply oil passages 16, 19 are oil passages that connect the first and second hydraulic pumps A, B, respectively, to a stick control valve 24, and the second swing supply oil passage 20 is an oil passage that connects the second hydraulic pump B to a swing control valve 26. In addition, the first and second option supply oil passages 17, 21 are oil passages that connect the first and second hydraulic pumps A, B, respectively, to an option joint oil passage 22, which will be described later.

[0011] A boom flow control valve 31 is disposed in the second boom supply oil passage 18, controlling the supply flow rate from the second hydraulic pump B to the boom control valve 23, and first and second stick flow control valves 32 and 33 are disposed in the first and second stick supply oil passages 16 and 19, controlling the supply flow rates from the first and second hydraulic pumps A and B to the stick control valve 24, respectively. These boom flow control valve 31 and first and second stick flow control valves 32 and 33 are poppet valves that control the flow rates by pilot operation using a boom flow control electromagnetic proportional valve 41 and first and second stick flow control electromagnetic proportional valves 42 and 43 (all shown in Figures 5 and 9), which operate based on control signals output from the controller 30, and have a backflow prevention function that allows oil to flow from the first and second hydraulic pumps A and B to the boom control valve 23 and stick control valve 24, but prevents backflow.

[0012] On the other hand, no flow control valves such as the boom flow control valve 31 or the first and second stick flow control valves 32 and 33 described above are disposed in the first boom supply oil passage 14, first bucket supply oil passage 15, second swing supply oil passage 20, and first and second option supply oil passages 17 and 21, and the pressure oil supplied from first hydraulic pump A or second hydraulic pump B via these first boom supply oil passage 14, first bucket supply oil passage 15, second swing supply oil passage 20, and first and second option supply oil passages 17 and 21 is supplied directly to the boom control valve 23, bucket control valve 25, swing control valve 26, and option joint oil passage 22 without being flow rate controlled. Furthermore, check valves 34 are provided in the first boom supply oil passage 14, the first bucket supply oil passage 15, the second swing supply oil passage 20, and the first and second option supply oil passages 17, 21, respectively, so that oil is permitted to flow from the first and second hydraulic pumps A, B to the boom control valve 23, the bucket control valve 25, the swing control valve 26, and the option joint oil passage 22, but reverse flow is prevented.

[0013] Thus, pressure oil from the first hydraulic pump A via the first boom supply oil passage 14 and pressure oil from the second hydraulic pump B via the second boom supply oil passage 18 can be supplied to the pump port 23p of the boom control valve 23, and the pressure oil from the second hydraulic pump B is supplied to the boom control valve 23 in a state where its flow rate is controlled (including a shut-off state) by a boom flow control valve 31 arranged in the second boom supply oil passage 18. Furthermore, pressure oil from the first hydraulic pump A via the first stick supply oil passage 16 and pressure oil from the second hydraulic pump B via the second stick supply oil passage 19 can be supplied to the pump port 24p of the stick control valve 24, and the pressure oil from these first and second hydraulic pumps A and B is supplied to the stick control valve 24 in a state where its flow rate is controlled (including a shut-off state) by first and second stick flow control valves 32 and 33 arranged in the first and second stick supply oil passages 16 and 19, respectively.

[0014] The control valves 23-26 for the boom, stick, bucket, and swing are closed center spool valves that control the supply and discharge flow rate for the boom cylinder 8, stick cylinder 9, bucket cylinder 10, and swing motor 11, and switch the supply and discharge direction. They are equipped with pairs of pilot ports 23a, 23b-26a, 26b that are respectively connected to electromagnetic proportional valves 44a, 44b-47a, 47b (shown in FIGS. 5 and 9) for the boom, stick, bucket, and swing that output pilot pressure based on a control signal from the controller 30, supply valve passages 23c-26c that supply pressure oil from first and / or second hydraulic pumps A, B to the boom cylinder 8, stick cylinder 9, bucket cylinder 10, and swing motor 11, and discharge valve passages 23d-26d that allow discharged oil from the boom cylinder 8, stick cylinder 9, bucket cylinder 10, and swing motor 11 to flow to a tank line T that leads to an oil tank 12. When pilot pressure is not input to both pilot ports 23a, 23b to 26a, 26b, the supply valve paths 23c to 26c and the discharge valve paths 23d to 26d are closed and the valves are positioned in a neutral position N where supply and discharge control is not performed for the corresponding hydraulic actuators (boom cylinder 8, stick cylinder 9, bucket cylinder 10, swing motor 11). However, when pilot pressure is input to one or the other pilot port 23a, 23b to 26a, 26b, the valves are configured to switch to an operating position X or Y where the supply valve paths 23c to 26c and the discharge valve paths 23d to 26d are opened and supply and discharge control for the hydraulic actuators is performed. The opening areas of the supply valve passages 23c to 26c and the discharge valve passages 23d to 26d when they are located at the operating positions X or Y are controlled to increase or decrease in accordance with the movement stroke of the spool that accompanies an increase or decrease in pilot pressure output from the electromagnetic proportional valves 44a, 44b to 47a, 47b for the boom, stick, bucket, and swing to the pilot ports 23a, 23b to 26a, 26b of the control valves 23 to 26 for the boom, stick, bucket, and swing.

[0015] The supply flow rate and discharge flow rate to the bucket cylinder 10 and the swing motor 11 are controlled by the opening areas of the supply valve passages 25c, 26c and discharge valve passages 25d, 26d of the bucket and swing control valves 25, 26. Furthermore, with regard to the supply flow rate to boom cylinder 8, the supply flow rate from first hydraulic pump A via first boom supply oil passage 14, which is not provided with a flow control valve, is controlled by the opening area of ​​supply valve passage 23c of boom control valve 23, while the supply flow rate from second hydraulic pump B via second boom supply oil passage 18, which is provided with boom flow control valve 31, is "zero" when boom flow control valve 31 is closed, and is controlled by the opening area of ​​boom flow control valve 31 and the opening area of ​​supply valve passage 23c of boom control valve 23 when boom flow control valve 31 is open. On the other hand, the discharge flow rate from boom cylinder 8 is controlled by the opening area of ​​discharge valve passage 23d of boom control valve 23. Furthermore, with regard to the supply flow rate to the stick cylinder 9, the supply flow rate from the first hydraulic pump A via the first stick supply oil passage 16 in which the first stick flow control valve 32 is provided is "zero" when the first stick flow control valve 32 is closed, and is controlled by the opening area of ​​the first stick flow control valve 32 and the opening area of ​​the supply valve passage 24c of the stick control valve 24 when the first stick flow control valve 32 is open, while the supply flow rate from the second hydraulic pump B via the second stick supply oil passage 19 in which the second stick flow control valve 33 is provided is "zero" when the second stick flow control valve 33 is closed, and is controlled by the opening area of ​​the second stick flow control valve 33 and the opening area of ​​the supply valve passage 24c of the stick control valve 24 when the second stick flow control valve 33 is open. On the other hand, the discharge flow rate from the stick cylinder 9 is controlled by the opening area of ​​the discharge valve passage 24d of the stick control valve 24.

[0016] On the other hand, the optional equipment confluence oil passage 22 is an oil passage formed by the merging of the downstream side of the first optional equipment supply oil passage 17 connected to the first hydraulic pump A and the downstream side of the second optional equipment supply oil passage 21 connected to the second hydraulic pump B, and the optional equipment confluence oil passage 22 is provided with an optional equipment control valve 60 (described later) and a compensator valve (corresponding to the pressure compensation valve of the present invention) 61 located upstream of the optional equipment control valve 60.

[0017] The option control valve 60 is a closed center spool valve that controls the supply / discharge flow rate for the option hydraulic actuator 13 and switches the supply / discharge direction, and as shown in the enlarged hydraulic circuit diagram of FIG. 3, is equipped with first and second pilot ports 60a, 60b connected respectively to first and second option solenoid proportional valves 48a, 48b (shown in FIGS. 5 and 9) that output pilot pressure based on a control signal output from the controller 30, a pump port 60p connected to the option hydraulic junction oil passage 22, a tank port 60t connected to the tank line T, a first actuator port 60c connected to one port 13a of the option hydraulic actuator 13 via a first actuator oil passage 67, a second actuator port 60d connected to the other port 13b of the option hydraulic actuator 13 via a second actuator oil passage 68, and a load pressure output port 60e connected to a second pilot port 61b of a compensator valve 61 (described later) via a load pressure introduction oil passage 62. When pilot pressure is not input to the first and second pilot ports 60a, 60b, the option-operated control valve 60 closes the pump port 60p and the first and second actuator ports 60c, 60d to not control the supply and discharge of fluid to and from the option hydraulic actuator 13, and is positioned in a neutral position N where the load pressure output port 60e communicates with the tank port 60t. However, when pilot pressure is input to the first pilot port 60a, the spool moves in one direction to be positioned at the first load pressure relief position R1 or the first operating position X, and when pilot pressure is input to the second pilot port 60b, the spool moves in the other direction to be positioned at the second load pressure relief position R2 or the second operating position Y. The first and second actuator oil passages 67, 68 are oil passages that connect the option-operated control valve 60 and the option hydraulic actuator 13, and correspond to the actuator oil passages of the present invention.

[0018] The first and second operating positions X, Y of the option control valve 60 are regions where the spool movement stroke from the neutral position N is larger than that at the first and second load pressure relief positions R1, R2 (regions where the pilot pressure input to the first and second pilot ports 60a, 60b is larger than that at the first and second load pressure relief positions R1, R2). In the first operating position X, the supply valve passage 60f from the pump port 60p to the first actuator port 60c, the discharge valve passage 60g from the second actuator port 60d to the tank port 60t, and the load pressure valve passage 60h from the first actuator port 60c to the load pressure output port 60e are opened. In the second operating position Y, the supply valve passage 60f from the pump port 60p to the second actuator port 60d, the discharge valve passage 60g from the first actuator port 60c to the tank port 60t, and the load pressure valve passage 60h from the second actuator port 60d to the load pressure output port 60e are opened. The opening areas of the supply valve passage 60f and the discharge valve passage 60g are controlled to increase or decrease according to the movement stroke of the spool, which is moved by the pilot pressure output from the first and second option-operated solenoid proportional valves 48a and 48b, and the supply flow rate and discharge flow rate for the option hydraulic actuator 13 are controlled by the opening areas of the supply valve passage 60f and the discharge valve passage 60g, respectively. Furthermore, when the option-operated control valve 60 is in the first or second operating position X or Y, the outlet side pressure of the option-operated control valve 60 (the load pressure of the option hydraulic actuator 13, the pressure of the first or second actuator oil passage 67, 68 to which pressure oil is supplied from the supply valve passage 60f) is introduced into the load pressure introducing oil passage 62 by opening the load pressure valve passage 60h.

[0019] On the other hand, the first and second load pressure relief positions R1, R2 of the option control valve 60 are regions where the spool movement stroke from the neutral position N is smaller than that at the first and second operating positions X, Y (regions where the pilot pressure input to the first and second pilot ports 60a, 60b is smaller than that at the first and second operating positions X, Y). In the first load pressure relief position R1, the pump port 60p, the tank port 60t, and the second actuator port 60d are closed, while the load pressure valve passage 60h from the first actuator port 60c to the load pressure output port 60e is opened. In the second load pressure relief position R2, the pump port 60p, the tank port 60t, and the first actuator port 60c are closed, while the load pressure valve passage 60h from the second actuator port 60d to the load pressure output port 60e is opened. In other words, when the optional component control valve 60 is positioned at the first or second load pressure relief position R1, R2, the supply valve passage 60f (the valve passage from the pump port 60p to the first or second actuator port 60c, 60d) that supplies pressurized oil from the first and second hydraulic pumps A, B via the optional component junction oil passage 22 to the optional hydraulic actuator 13, and the discharge valve passage 60g (the valve passage from the second or first actuator 60d, 60c to the tank port 60t) that flows the discharged oil from the optional hydraulic actuator 13 to the oil tank 12 are closed, and no oil is supplied or discharged to the optional hydraulic actuator 13. However, by opening the load pressure valve passage 60h that runs from the first or second actuator port 60c, 60d to the load pressure output port 60e, it is possible to flow pressurized oil from the first and second actuator oil passages 67, 68 to the load pressure introduction oil passage 62.

[0020] 4(A) shows an example of the relationship between the spool movement stroke and the opening areas of the supply valve passage 60f, the discharge valve passage 60g, and the load pressure valve passage 60h when the option control valve 60 is located at the first or second load pressure relief position R1, R2 or the first or second operating position X, Y. As shown in FIG. 4(A), when the option control valve 60 is located at the first or second load pressure relief position R1, R2, the supply valve passage 60f and the discharge valve passage 60g are closed, and the load pressure valve passage 60h opens when the spool movement stroke exceeds the dead band. On the other hand, when the option control valve 60 is located at the first or second operating position X, Y, the supply valve passage 60f and the discharge valve passage 60g are opened, and their opening areas increase as the spool movement stroke increases. Furthermore, when in the first or second operating position X, Y, the load pressure valve path 60h maintains the opening area that is open to the first or second load pressure relief position R1, R2, but the opening area is smaller than the maximum opening area of ​​the supply valve path 60f and the discharge valve path 60g.

[0021] Incidentally, there are various types of optional hydraulic actuators 13, such as those that supply pressure oil in one direction, such as a unidirectional motor or a single-acting cylinder (e.g., a breaker), those that supply pressure oil in both directions, such as a bidirectional motor or a double-acting cylinder (e.g., a crusher), those that require a large flow rate (e.g., a large breaker or crusher), and those that only require a small flow rate (e.g., a small breaker or crusher), and the optional control valve 60 is used commonly with these various optional hydraulic actuators 13. In other words, by switching the optional control valve 60 between the first operating position X and the second operating position Y, pressure oil can be supplied in both directions to the optional hydraulic actuator 13, and by using only one of the operating positions, either the first operating position X or the second operating position Y, pressure oil can be supplied in one direction. However, in this embodiment, the first operating position X is used when pressure oil is supplied in one direction.

[0022] On the other hand, the load pressure introduction oil passage 62 is an oil passage that extends from the load pressure output port 60e of the option control valve 60 to the second pilot port 61b of the compensator valve 61, and a first orifice 63 is provided in the load pressure introduction oil passage 62, and a load pressure relief oil passage 66 that branches off from the load pressure introduction oil passage 62 that extends from the load pressure output port 60e of the option control valve 60 to the first orifice 63 via a second orifice 64 and a variable relief valve 65 and to the tank line T is formed. The variable relief valve 65 is an electromagnetic proportional relief valve that can change the relief set pressure LP based on a control signal from the controller 30, and when the relief set pressure LP of the variable relief valve 65 is lower than the load pressure of the optional hydraulic actuator 13 introduced into the load pressure introduction oil passage 62, the load pressure introduced into the load pressure introduction oil passage 62 flows to the oil tank 12 via the variable relief valve 65, thereby making it possible to reduce the load pressure input to the second pilot port 61b of the compensator valve 61 to the relief set pressure LP.

[0023] The compensator valve 61 is equipped with a first pilot port 61a to which a first pilot pressure is input that presses the valve element of the compensator valve 61 to the closing side, a second pilot port 61b to which a second pilot pressure that presses the valve element to the opening side is input, and a spring 61c that presses the valve element to the opening side, and the opening area is controlled so that the differential pressure between the first pilot pressure and the second pilot pressure is maintained at a predetermined pressure K determined by the spring 61c. The first pilot port 61a of the compensator valve 61 is connected to the optional equipment joint oil passage 22 on the inlet side of the optional equipment control valve 60, and the pressure of the optional equipment joint oil passage 22 is input thereto. The second pilot port 61b is connected to the load pressure introduction oil passage 62, and when the load pressure of the optional hydraulic actuator 13 is equal to or lower than the set relief pressure LP of the variable relief valve 65, the load pressure of the optional hydraulic actuator 13 is input, whereas when the load pressure of the optional hydraulic actuator 13 is higher than the set relief pressure LP, a load pressure reduced to the set relief pressure LP is input, as described above. Thus, when the optional control valve 60 is located at the first or second operating position X, Y and oil is being supplied or discharged to or from the optional hydraulic actuator 13, when the load pressure of the optional hydraulic actuator 13 is equal to or lower than the set relief pressure LP, the pressure PO in the optional hydraulic joint oil passage 22 is controlled by the action of the compensator valve 61 to be higher by a predetermined pressure K than the load pressure of the optional hydraulic actuator 13, whereas when the load pressure of the optional hydraulic actuator 13 is higher than the set relief pressure LP, the pressure PO in the optional hydraulic joint oil passage 22 is controlled to be higher by the predetermined pressure K than the set relief pressure LP. This makes it possible to variably control the relief set pressure LP of the variable relief valve 65 based on a control signal from the controller 30, thereby controlling the pressure PO of the option confluence oil passage 22 on the inlet side of the option control valve 60 to be equal to or lower than the pressure (LP+K) that is higher than the relief set pressure LP by a predetermined pressure K (PO≦(LP+K)).

[0024] On the other hand, when the optional equipment control valve 60 is positioned at the first and second load pressure relief positions R1, R2, as described above, the supply valve path 60f and the discharge valve path 60g are closed, while the load pressure valve path 60h, which introduces the load pressure of the first and second actuator oil paths 67, 68 into the load pressure introduction oil path 62, is open. When the pressure of the first and second actuator oil paths 67, 68 introduced into the load pressure introduction oil path 62 is higher than the set relief pressure LP of the adjustable relief valve 65, the pressurized oil in the first and second actuator oil paths 67, 68 flows from the load pressure valve path 60h through the load pressure introduction oil path 62 and the adjustable relief valve 65 to the oil tank 12. As a result, when the optional equipment control valve 60 is positioned at the first and second load pressure relief positions R1, R2, the pressure in the first and second actuator oil paths 67, 68 can be reduced to the set relief pressure LP of the adjustable relief valve 65.

[0025] Furthermore, first and second option relief oil passages 71 and 72 branch off from the first and second actuator oil passages 67 and 68 and lead to the tank line T via first and second option relief valves 69 and 70. The first and second option relief valves 69 and 70 operate to release the high-pressure oil to the oil tank 12 when the first and second actuator oil passages 67 and 68 become high-pressure due to dynamic pressure fluctuations such as when surge pressure is generated due to an external force such as a collision, and the set relief pressures of the first and second option relief valves 69 and 70 are set to a value that exceeds the highest driving pressure of the optional hydraulic actuators 13 selectively attached to the hydraulic excavator 1. The first and second option relief valves 69 and 70 are inexpensive valves whose set relief pressure cannot be electrically changed. In addition, relief valves similar to the first and second option relief valves 69, 70 are also provided in the oil passages connecting the boom control valve 23, the stick control valve 24, the bucket control valve 25, and the swing control valve 26 to the boom cylinder 8, the stick cylinder 9, the bucket cylinder 10, and the swing motor 11, respectively, but are omitted from FIG. 2.

[0026] 2 and 3, reference numeral 73 denotes a bypass oil passage branching off from the first or second actuator oil passage 67, 68 and leading to the oil tank 12, and a selector valve 74 is disposed in the bypass oil passage 73. As shown in FIG. 4(B), the selector valve 74 is a two-position selector valve that is turned ON / OFF by a voltage applied from the controller 30 and switches between a closed position N and an open position X. When the selector valve 74 is switched to the open position X, oil discharged from the optional hydraulic actuator 13 can flow directly to the oil tank 12 without passing through the discharge valve passage 60g of the option control valve 60. When an optional hydraulic actuator 13 that requires back pressure reduction, such as a breaker, is installed and pressure oil is supplied in one direction, the selector valve 74 can be opened (set to the open position X) to allow oil discharged from the optional hydraulic actuator 13 to flow from the bypass oil passage 73 to the oil tank 12, thereby reliably reducing the back pressure acting on the optional hydraulic actuator 13. As mentioned above, the switching valve 74 is an inexpensive device that switches ON / OFF, and is capable of performing back pressure reduction control at a lower cost than, for example, when a variable relief valve is used. Furthermore, the bypass oil passage 73 is formed by branching off from an actuator oil passage that serves as a return oil passage from the optional hydraulic actuator 13 when an optional hydraulic actuator 13 that has a unidirectional pressure oil supply direction and requires back pressure reduction is installed, and in this embodiment, the bypass oil passage 73 is formed by branching off from the second actuator oil passage 68, but when the first actuator oil passage 67 serves as a return oil passage from the optional hydraulic actuator 13, the bypass oil passage 73 is formed by branching off from the first actuator oil passage 67.

[0027] 2, E and F denote first and second bleed lines that branch off from upstream positions of all of the supply oil passages 14-21 connected to the first and second pump lines C and D and lead to the tank line T. First and second bleed valves 75 and 76 are provided in the first and second bleed lines E and F, respectively. These first and second bleed valves 75 and 76 are actuated by pilot pressures output from first and second bleed electromagnetic proportional valves 49a and 49b (shown in FIGS. 5 and 10) to increase or decrease their opening areas, thereby controlling the increase or decrease of the bleed flow rates that flow from the first and second hydraulic pumps A and B to the oil tank 12 via the first and second bleed lines E and F. The pressures in the first and second pump lines C and D (the discharge pressures of the first and second hydraulic pumps A and B) are controlled by controlling the bleed flow rates using the first and second bleed valves 75 and 76.

[0028] 2, reference numeral 77 denotes a valve block incorporating various valves for controlling the oil supply and discharge to the various hydraulic actuators (boom cylinder 8, stick cylinder 9, bucket cylinder 10, swing motor 11, and optional hydraulic actuator 13). The valve block 77 is formed by integrally assembling a main valve block 77X incorporating various valves for controlling the permanently installed hydraulic actuators (boom, stick, bucket, and swing control valves 23-26, boom and first and second stick flow control valves 31-33, etc.) and first and second bleed valves 75, 76, etc., to an optional valve block 77Y incorporating various valves for controlling the optional hydraulic actuators (option control valve 60, compensator valve 61, variable relief valve 65, first and second option relief valves 69, 70, etc.). The bypass oil passage 73 and the switching valve 74 are provided outside the valve block 77.

[0029] On the other hand, as shown in the block diagram of FIG. 5, the controller 30 (corresponding to the control means of the present invention) has, on the input side, boom operation detection means 80, stick operation detection means 81, bucket operation detection means 82, swing operation detection means 83, option operation detection means 84, which respectively detect the operation direction and operation amount of the boom operation tool, stick operation tool, bucket operation tool, swing operation tool, and option operation tool (none of which are shown), option hydraulic actuator notification means 85 which will be described later, and pressure sensors (not shown) which detect the pump pressure of first and second hydraulic pumps A and B. ), pressure sensors (none of which are shown) that detect the load pressure of the boom cylinder 8, stick cylinder 9, bucket cylinder 10, swing motor 11, first and second option pressure sensors (corresponding to pressure detection means for detecting the pressure of the actuator oil passages of the present invention) 97, 98 that detect the load pressure of the optional hydraulic actuator 13 (pressure of the first and second actuator oil passages 67, 68), etc. are connected to the output side, and capacity varying means Aa, Ba of the first and second hydraulic pumps A, B, boom flow rate control electromagnetic proportional valve 41 that outputs pilot pressure to the boom flow rate control valve 31, First and second stick flow control solenoid proportional valves 42, 43 output pilot pressure to first and second stick flow control valves 32, 33, respectively; boom, stick, bucket, and swing solenoid proportional valves 44a, 44b to 47a, 47b output pilot pressure to boom, stick, bucket, and swing control valves 23 to 26; first and second option solenoid proportional valves 48a, 48b output pilot pressure to option control valve 60; and first and second bleed solenoid proportional valves 49 output pilot pressure to first and second bleed valves 75, 76. a, 49b, a variable relief valve 65, a switching valve 74, etc. are connected, and a first and second operation amount setting unit 90, a required flow rate setting unit 91, a pump control unit 92, a valve opening area control unit 93, a bleed control unit 94, an option control unit 95, etc., which will be described later, control the discharge flow rate of the first and second hydraulic pumps A and B, control the bleed flow rate of the first and second bleed lines E and F, control the oil supply and discharge for the boom cylinder 8, stick cylinder 9, bucket cylinder 10, and swing motor 11, control the oil supply and discharge and supply pressure for the optional hydraulic actuator 13, control the load pressure relief,The optional hydraulic actuator notification means 85 is configured to perform back pressure reduction control, etc. The optional hydraulic actuator notification means 85 is a means for notifying the controller 30 of various information such as the type and specifications of the optional hydraulic actuator 13 when the optional hydraulic actuator 13 is installed, or the value of an upper limit pressure PU for the optional actuator, which will be described later. In this embodiment, a monitor device (not shown) disposed in the cab 3a of the hydraulic excavator 1 is provided as the optional hydraulic actuator notification means 85, and various information about the optional hydraulic actuator 13 can be notified to the controller 30 and various pieces of information can be changed by operating the monitor device. Also, although the optional hydraulic actuator notification means 85 is provided external to the controller 30 in FIG. 5, it is also possible to configure the controller 30 to have at least some of the information and functions stored in the optional hydraulic actuator notification means 85.

[0030] Next, the control performed by the setting section and control section provided in the controller 30 will be described. When operation signals are input from the operation detection means 80-84 for the boom, stick, bucket, swing, and option, the first and second operation amount setting unit 90 sets, based on these operation signals, a first operation amount to be performed by the first hydraulic pump A and a second operation amount to be performed by the second hydraulic pump B for each operation tool operation amount. The first and second operation amounts are set based on pre-stored data according to the first and second hydraulic pumps A and B that serve as hydraulic supply sources for the operated hydraulic actuators (boom cylinder 8, stick cylinder 9, bucket cylinder 10, swing motor 11, and optional hydraulic actuator 13), the operation tool operation amount, the hydraulic actuators to be operated in conjunction (simultaneously), and the type and specifications of the optional hydraulic actuator 13. For example, in this embodiment, since the bucket cylinder 10 uses only the first hydraulic pump A as a hydraulic supply source, when the bucket operation tool is operated, only the first bucket operation amount is set. Furthermore, since the swing motor 11 uses only the second hydraulic pump B as a hydraulic supply source, when the swing operation tool is operated, only the second swing operation amount is set. For the boom cylinder 8, first and second boom operation amounts are set when pressure oil is supplied from both the first and second hydraulic pumps A and B, but only the first boom operation amount is set when pressure oil is supplied only from the first hydraulic pump A. For the stick cylinder 9, first and second stick operation amounts are set when pressure oil is supplied from both the first and second hydraulic pumps A and B, but only the first stick operation amount is set when pressure oil is supplied only from the first hydraulic pump A, and only the second stick operation amount is set when pressure oil is supplied only from the second hydraulic pump B. For the optional hydraulic actuator 13, first and second option operation amounts are set when pressure oil is supplied from both the first and second hydraulic pumps A and B, but only the first option operation amount is set when pressure oil is supplied only from the first hydraulic pump A, and only the second option operation amount is set when pressure oil is supplied only from the second hydraulic pump B (see FIG. 6).The data for setting the first and second manipulated variables is stored as control parameters in the first and second manipulated variable setting unit 90, and can be changed using the monitor device or the like, for example, in accordance with the type of work to be performed by the hydraulic excavator 1 and the type and specifications of the optional hydraulic actuator 13.

[0031] Furthermore, a required flow rate setting unit 91 determines the required flow rates (first required flow rate for boom, second required flow rate for boom, first required flow rate for stick, second required flow rate for stick, first required flow rate for bucket, second required flow rate for swing, first required flow rate for option, and second required flow rate for option) that each hydraulic actuator (boom cylinder 8, stick cylinder 9, bucket cylinder 10, swing motor 11, optional hydraulic actuator 13) requires of the first and second hydraulic pumps A and B, based on the first and second manipulated variable set by the first and second manipulated variable setting unit 90. Furthermore, the required flow rate setting unit 91 sets first and second margin added required flow rates for option by adding a margin flow rate α to the first and second required flow rates for option, respectively (see FIG. 8). Note that the margin flow rate α is a flow rate added to the first and second required flow rates for option to avoid a shortage of pressurized oil supplied to the optional hydraulic actuator 13 due to flow rate control performed by the compensator valve 61 for adjusting the differential pressure when pressurized oil is supplied from the first and second hydraulic pumps A and B to the optional hydraulic actuator 13. Furthermore, when the first and second option-use requested flow rates are "zero," the first and second option-use margin-added requested flow rates also become "zero." 7(A), (B), and (C) show examples of the relationship between the first and second option-use operating device operation amounts, the first and second option-use required flow rates, and the total option-use required flow rate (the sum of the first option-use required flow rate and the second option-use required flow rate). FIG. 7(A) shows a case in which, in the first and second operation amount setting unit 90, when the operation amount of the operating device is small, only the first option-use operating amount is set (pressurized oil is supplied only from the first hydraulic pump A), and when the operation amount of the operating device is large, the first and second option-use operating amounts are set (pressurized oil is supplied from both the first and second hydraulic pumps A and B). FIG. 7(B) shows a case in which the first and second option-use operating amounts are set to the same value (the same amount of pressurized oil is supplied from the first and second hydraulic pumps A and B). FIG. 7(C) shows a case in which only one of the first or second operation amounts is set (pressurized oil is supplied from only either the first hydraulic pump A or the second hydraulic pump B). The required flow rate setting unit 91 is provided with data such as a map showing the relationship between the first and second operation amounts and the required flow rate for each hydraulic actuator, and uses this data to determine the required flow rate according to the operation amount of the operating tool. Such data is incorporated into the required flow rate setting unit 91 as a control parameter, and it is possible to change the value of the required flow rate corresponding to the first and second operation amounts using the monitor device, etc., depending on, for example, the work content to be performed by the hydraulic excavator 1 and the type and specifications of the optional hydraulic actuator 13.

[0032] The pump control unit 92 also calculates target discharge flow rates for the first and second hydraulic pumps A and B based on the required flow rates set by the required flow rate setting unit 91. In this case, the first and second required boom flow rates, the first and second required stick flow rates, the first required bucket flow rate, and the second required swing flow rate set by the required flow rate setting unit 91 are used for the required flow rates for the boom cylinder 8, the stick cylinder 9, the bucket cylinder 10, and the swing motor 11, and the first and second margin added required flow rates for option, to which a margin flow rate α is added, are used for the required flow rate for the optional hydraulic actuator 13. The target discharge flow rate for the first hydraulic pump A is set to the sum of the first required flow rates and first margin added required flow rates for the first hydraulic pump A of each operated hydraulic actuator (first required boom flow rate + first required stick flow rate + first required bucket flow rate + first margin added required flow rate for option), and if the total flow rate exceeds the maximum discharge flow rate of the first hydraulic pump A, the maximum discharge flow rate is set to the target discharge flow rate. Similarly, the target discharge flow rate of the second hydraulic pump B is set to the sum of the second required flow rates and second margin added required flow rates for the second hydraulic pump B of each operated hydraulic actuator (second required flow rate for boom + second required flow rate for stick + second required flow rate for swing + second margin added required flow rate for option), and if the total flow rate exceeds the maximum discharge flow rate of the second hydraulic pump B, the maximum discharge flow rate is set to the target discharge flow rate. Then, the pump control unit 92 outputs control signals to the capacity varying means Aa and Ba of the first and second hydraulic pumps A and B so as to obtain the target discharge flow rates (see FIG. 8). Note that if the first operation amounts of the hydraulic actuators are all "zero" and if the second operation amounts are all "zero", the first and second hydraulic pumps A and B are each controlled to have a minimum flow rate.

[0033] Furthermore, the valve opening area control unit 93 calculates the opening areas of the supply valve passages 23c to 26c of the boom, stick, bucket and swing control valves 23 to 26, the boom flow control valve 31, the first and second stick flow control valves 32 and 33, and the supply valve passage 60f of the option control valve 60, based on the required flow rates for the first and second hydraulic pumps A and B of each hydraulic actuator calculated by the required flow rate setting unit 91. In this case, the control process for determining the opening area differs between the control valves (control valves for boom, stick, bucket, and swing) 23-26 and flow control valves (flow control valves for boom, first and second stick) 31-33 for the permanently installed hydraulic actuators (boom cylinder 8, stick cylinder 9, bucket cylinder 10, swing motor 11) and the optional control valve 60, so first, the opening area control of the control valves 23-26 and flow control valves 31-33 for the permanently installed hydraulic actuators will be described. When calculating the opening areas of the control valves 23-26 and the flow control valves 31-33 for the permanent hydraulic actuators, the valve opening area control unit 93 first calculates the distributed flow rates for each permanent hydraulic actuator. The distributed flow rates are calculated separately for the first hydraulic pump A and the second hydraulic pump B. That is, for the distributed flow rates for the permanent hydraulic actuators supplied with pressure oil from the first hydraulic pump A, the target discharge flow rate of the first hydraulic pump A is distributed in the ratio of the first margin added required flow rate for option, the first required flow rate for boom, the first required flow rate for stick, and the first required flow rate for bucket to calculate the first distributed flow rate for boom, the first distributed flow rate for stick, and the first distributed flow rate for bucket. Furthermore, for the distributed flow rates for the permanent hydraulic actuators supplied with pressure oil from the second hydraulic pump B, the target discharge flow rate of the second hydraulic pump B is distributed in the ratio of the second margin added required flow rate for option, the second required flow rate for boom, the second required flow rate for stick, and the second required flow rate for swing to calculate the second distributed flow rate for boom, the second distributed flow rate for stick, and the second distributed flow rate for swing. If the first and second option margin added required flow rates are "zero," a distributed flow rate calculation is performed to distribute the entire target discharge flow rate to the permanent hydraulic actuators. Then, the valve opening area control unit 93 calculates the opening areas of the supply valve paths 23c-26c of the boom, stick, bucket, and swing control valves 23-26 and the boom, first, and second stick flow control valves 31-33 for supplying the first and second boom distributed flow rates, the first and second stick distributed flow rates, the first bucket distributed flow rate, and the second swing distributed flow rate from the first and second hydraulic pumps A and B to the boom cylinder 8, stick cylinder 9, bucket cylinder 10, and swing motor 11, respectively. Then, the control valves 23 to 26 are switched to operating positions X or Y in accordance with the operating directions of the operating tools for the boom, stick, bucket, and swing motor, and control signals are output to the boom, stick, bucket, and swing electromagnetic proportional valves 44a, 44b to 47a, 47b, boom flow rate control electromagnetic proportional valve 41, and first and second stick flow rate control electromagnetic proportional valves 42, 43 so as to achieve the calculated opening areas (see FIG. 9). In this way, when controlling the opening areas of the control valves 23-26 and the flow control valves 31-33 for the permanent hydraulic actuators, the discharge flow rates of the first and second hydraulic pumps A, B are divided between the first and second optional margin addition required flow rates and the required flow rate of the permanent hydraulic actuators. This means that even when the optional hydraulic actuator 13 is operated in conjunction with other hydraulic actuators (permanent hydraulic actuators) that share hydraulic pumps A and / or B, the first and second optional margin addition required flow rates are supplied to the optional hydraulic junction oil passage 22, ensuring a reliable supply flow rate to the optional hydraulic actuator 13. As an example of control, it is also possible to adjust the first and second optional margin addition required flow rates by multiplying the first and second optional margin addition required flow rates by a flow rate restriction coefficient dedicated to the conjunction operation, thereby controlling the supply flow rate to the optional hydraulic actuator 13 to be constant. On the other hand, when determining the opening area of ​​the option control valve 60, the valve opening area control unit 93 calculates the opening area of ​​the supply valve path 60f of the option control valve 60 for supplying the total flow rate of the first and second option required flow rates set by the required flow rate setting unit 91 to the option hydraulic actuator 13. Then, the option control valve 60 is switched to the first operating position X or the second operating position Y in accordance with information about the option hydraulic actuator 13 input from the option hydraulic actuator notifying means 85 and the operating direction of the option operating tool, and control signals are output to the first and second option solenoid proportional valves 48a, 48b so as to achieve the calculated opening area (see FIG. 9). In this case, the differential pressure across the supply valve path 60f of the option control valve 60 is kept constant (at a predetermined pressure K) by the compensator valve 61 described above, so that the supply flow rate from the option control valve 60 to the option hydraulic actuator 13 is controlled with high precision to be the total flow rate of the first and second option required flow rates.

[0034] In addition, the bleed control unit 94 controls the bleed flow rate flowing from the first and second hydraulic pumps A, B to the oil tank 12 based on the first and second operation amounts calculated by the first and second operation amount setting unit 90, and controls the discharge pressure of the first and second hydraulic pumps A, B by controlling the bleed flow rate. In this case, the bleed control unit 94 first determines the first and second required pressures (first required boom pressure, second required boom pressure, first required stick pressure, second required stick pressure, first required bucket pressure, second required swing pressure, first required option pressure, second required option pressure) that the corresponding hydraulic actuators require of the first and second hydraulic pumps A and B based on the first and second boom operation amounts, the first and second stick operation amounts, the first bucket operation amount, the second swing operation amount, and the first and second option operation amounts. Note that the bleed control unit 94 has data for each hydraulic actuator, such as a map showing the relationship between the first and second operation amounts and the required pressures, and determines the required pressure corresponding to the operation amount of the control tool using this data. Such data is incorporated into the bleed control unit 94 as control parameters, and it is possible to change the value of the required pressure corresponding to the operation amount depending, for example, on the work content performed by the hydraulic excavator 1 and the type and specifications of the optional hydraulic actuator 13. Next, the bleed control unit 94 calculates the first and second pump required pressures based on the first and second required pressures. In this case, the maximum value of the required pressures (first boom required pressure, first stick required pressure, first bucket required pressure, and first option required pressure) that the hydraulic actuators require of the first hydraulic pump A is set as the first pump required pressure PR1, and the maximum value of the required pressures (second boom required pressure, second stick required pressure, second swing required pressure, and second option required pressure) that the hydraulic actuators require of the second hydraulic pump B is set as the second pump required pressure PR2. Then, target pressures (first and second pump target pressures) PT1 and PT2 of the first and second hydraulic pumps A and B are set based on the first and second pump required pressures PR1 and PR2 (see FIG. 10).

[0035] In setting the first and second pump target pressures PT1, PT2, the bleed control unit 94 first determines whether or not an option operation device is being operated, and if the option operation device is not being operated (if the first and second option operation amounts are both "zero"), it sets the first and second pump required pressures PR1, PR2 as the target pressures PT1, PT2 of the first and second hydraulic pumps A, B. On the other hand, if the option operation device is being operated (if at least one of the first and second option operation amounts is not "zero"), it performs option priority control, which will be described later.

[0036] When the option priority control is performed, the bleed control unit 94 first determines whether the hydraulic pump supplying pressure oil to the option hydraulic actuator 13 is the first hydraulic pump A only (only the first option operation amount is set), the second hydraulic pump B only (only the second option operation amount is set), or both the first and second hydraulic pumps A and B (first and second option operation amounts are set).The bleed control unit 94 then compares the first pump required pressure PR1 with the second pump required pressure PR2 in each of the cases where the determination result is the first hydraulic pump A only (hereinafter referred to as determination result (A)), the second hydraulic pump B only (hereinafter referred to as determination result (B)), or both the first and second hydraulic pumps A and B (hereinafter referred to as determination result (A+B)). And, when the first pump required pressure PR1 is greater than the second pump required pressure PR2 (PR1 > PR2) in the determination result (A), these first and second pump required pressures PR1 and PR2 are set as the target pressures PT1 and PT2 of the first and second hydraulic pumps A and B, respectively. On the other hand, when the first pump required pressure PR1 is less than or equal to the second pump required pressure PR2 (PR1 ≤ PR2) in the determination result (A), the pressure obtained by adding the margin pressure β to the second pump required pressure PR2 (PR2 + β) is set as the first pump target pressure PT1, and the second pump required pressure PR2 is set as the second pump target pressure PT2. Thereby, in the case of the determination result (A), that is, when the hydraulic pump that supplies the pressure oil to the optional hydraulic actuator 13 is only the first hydraulic pump A, the target pressure PT1 of the first hydraulic pump A is set to a higher pressure than the target pressure PT2 of the second hydraulic pump B. Incidentally, the margin pressure β is a pressure added to make the discharge pressure of the hydraulic pump that supplies the pressure oil to the optional hydraulic actuator 13 surely higher than the discharge pressure of the hydraulic pump that does not supply the pressure oil to the optional hydraulic actuator 13. Also, when the first pump required pressure PR1 is greater than or equal to the second pump required pressure PR2 (PR1 ≥ PR2) in the determination result (B), the first pump required pressure PR1 is set as the first pump target pressure PT1, and the pressure obtained by adding the margin pressure β to the first pump required pressure PR1 (PR1 + β) is set as the second pump target pressure PT2. On the other hand, when the first pump required pressure PR1 is less than the second pump required pressure PR2 (PR1 < PR2) in the determination result (B), these first and second pump required pressures PR1 and PR2 are set as the target pressures PT1 and PT2 of the first and second pumps. Thereby, in the case of the determination result (B), that is, when the hydraulic pump that supplies the pressure oil to the optional hydraulic actuator 13 is only the second hydraulic pump B, the target pressure PT2 of the second hydraulic pump B is set to a higher pressure than the target pressure PT1 of the first hydraulic pump A. Furthermore, if the determination result (A+B) shows that the first pump required pressure PR1 is greater than the second pump required pressure PR2 (PR1>PR2), the first pump required pressure PR1 is set as the first and second pump target pressures PT1, PT2. On the other hand, if the determination result (A+B) shows that the first pump required pressure PR1 is equal to or less than the second pump required pressure PR2 (PR1≦PR2), the second pump required pressure PR2 is set as the first and second pump target pressures PT1, PT2. As a result, in the case of the determination result (A+B), that is, when the hydraulic pumps supplying pressure oil to the optional hydraulic actuator 13 are both the first and second hydraulic pumps A, B, the target pressures PT1, PT2 of these first and second hydraulic pumps A, B are set to be equal to the higher of the first and second pump required pressures PR1, PR2 (see FIG. 11). In this way, when the hydraulic pump supplying pressure oil to the optional hydraulic actuator 13 is either the first or second hydraulic pump A, B (in the case of the judgment result (A) or (B)), the discharge pressure of the one hydraulic pump supplying pressure oil is controlled to be higher than the discharge pressure of the other hydraulic pump not supplying pressure oil, so that the pressure oil supplied from one hydraulic pump flows preferentially to the optional equipment merged oil passage 22, and the pressure oil supplied from the other hydraulic pump does not flow to the optional equipment merged oil passage 22. On the other hand, when the hydraulic pumps supplying pressure oil to the optional hydraulic actuator 13 are both the first and second hydraulic pumps A, B (in the case of the judgment result (A+B)), the discharge pressures of both hydraulic pumps A, B are controlled to be the same, so that the pressure oil supplied from both the first and second hydraulic pumps A, B is supplied to the optional equipment merged oil passage 22 and merges.

[0037] After setting the target pressures PT1, PT2 of the first and second hydraulic pumps A, B, the bleed control unit 94 calculates the opening areas of the first and second bleed valves 75, 76 to achieve the target pressures PT1, PT2, and outputs control signals to the first and second bleed electromagnetic proportional valves 49a, 49b to achieve the opening areas, thereby controlling the bleed flow rates that flow from the first and second hydraulic pumps A, B to the oil tank 12 (see FIG. 10). Note that when the first operation amounts of the hydraulic actuators are all "zero" and when the second operation amounts are all "zero", the bleed flow rates are controlled so that the discharge pressures of the first and second hydraulic pumps A, B become the minimum discharge pressures that are set in advance.

[0038] In addition, when an operation signal of an option operating tool is input from the option operation detection means 84, the option control unit 95 performs option supply pressure control, which sets the relief setting pressure LP of the variable relief valve 65 to control the supply pressure to the option hydraulic actuator 13, based on information input from the option hydraulic actuator notification means 85. In this case, the option control unit 95 receives, from the option hydraulic actuator notification means 85, the value of an option upper limit pressure PU that is set in advance as the upper limit pressure of each option hydraulic actuator 13 in accordance with the type, specifications, etc. of the option hydraulic actuator 13. Then, it outputs a control signal to the variable relief valve 65 so as to set the relief setting pressure LP of the variable relief valve 65 to a pressure (LP = PU - K) obtained by subtracting the predetermined pressure K (a pressure determined by the spring 61c of the compensator valve 61) from the option upper limit pressure PU. As a result, the inlet side pressure PO of the option control valve 60 is controlled by the action of the compensator valve 61 described above to be equal to or lower than (LP + K) a pressure higher than the relief setting pressure LP of the variable relief valve 65 by the predetermined pressure K (PO ≦ (LP + K)), in other words, equal to or lower than the option upper limit pressure PU (PO ≦ PU). By controlling the inlet pressure of the option control valve 60 to be equal to or less than the option upper limit pressure PU by setting the relief set pressure LP of the variable relief valve 65 in this way, it is possible to make the supply pressure to the option hydraulic actuator 13 less than the option upper limit pressure PU set for each option hydraulic actuator 13, even without providing variable relief valves in the pair of first and second actuator oil passages 67, 68 leading from the option control valve 60 to the option hydraulic actuator 13.

[0039] Furthermore, when an operation signal of the option operating tool is not input from the option operation detection means 84, that is, when the option operating tool is not being operated, the option control unit 95 performs load pressure relief control to relieve the pressure in the first and second actuator oil passages 67, 68 connected to the option hydraulic actuator 13 when the pressure exceeds a preset option upper limit pressure PU, based on the information input from the option hydraulic actuator notification means 85 and the detection values ​​of the first and second option pressure sensors 97, 98. The load pressure relief control will be explained based on the flowchart shown in FIG. 12. First, the option control section 95 determines whether or not an option operating tool is being operated (step S1). Then, if it is determined that the optional operating tool is not being operated (not being operated), the high pressure holding side of the optional hydraulic actuator 13 when the optional operating tool is not being operated is recognized based on the information input from the optional hydraulic actuator notification means 85, and the pressure detection value Pd of the first actuator oil passage 67 or the second actuator oil passage 68 connected to that high pressure holding side is read from the first or second optional pressure sensor 97, 98 (step S2). Furthermore, the value of the option upper limit pressure PU, which is preset as the upper limit pressure of each option hydraulic actuator 13 depending on the type, specifications, etc. of the option hydraulic actuator 13, is read from the option hydraulic actuator notification means 85 (step S3). Subsequently, the pressure detection value Pd of the first actuator oil passage 67 or the second actuator oil passage 68 on the high pressure holding side is compared with the upper limit pressure PU for options (determining whether Pd≦PU) (step S4). If it is determined in step S4 that the detected pressure value Pd is equal to or lower than the option upper limit pressure PU (Pd≦PU), the option control valve 60 is controlled to be in the neutral position N, and the adjustable relief valve 65 is de-energized (step S5). As a result, the first and second actuator oil passages 67, 68 are placed in a state where the inflow and outflow of oil is blocked by the option control valve 60 in the neutral position N. After processing step S5, the process returns to the determination in step S1. The de-energized adjustable relief valve 65 has a maximum set relief pressure LP. On the other hand, if it is determined in step S4 that the detected pressure value Pd is greater than the optional accessory upper limit pressure PU (Pd>PU), a control command is output to the optional accessory control valve 60 to switch to the first or second load pressure relief position R1, R2 (the first load pressure relief position R1 when the first actuator oil passage 67 is on the high pressure holding side, and the second load pressure relief position R2 when the second actuator oil passage 68 is on the high pressure holding side) in order to open the load pressure valve passage 60h from the first or second actuator port 60c, 60d connected to the first or second actuator oil passage 67, 68 on the high pressure holding side to the load pressure output port 60e. Furthermore, a control command is output to the adjustable relief valve 65 so that the relief set pressure LP becomes the optional accessory upper limit pressure PU (or so that the relief set pressure LP becomes a value slightly lower than the optional accessory upper limit pressure PU) (step S6). As a result, the pressurized oil in the first or second actuator oil passage 67, 68 on the high pressure holding side flows through the load pressure valve passage 60h of the option control valve 60 to the load pressure introduction oil passage 62, and then flows to the oil tank 12 via the variable relief valve 65 connected to the load pressure introduction oil passage 62, thereby reducing the pressure in the first or second actuator oil passage 67, 68 on the high pressure holding side. After processing in step S6, the process returns to the judgment in step S1, but the control in step S6 continues until it is determined in step S1 that the option operating device has been operated, or it is determined in step S4 that the pressure detection value Pd is equal to or less than the option upper limit pressure PU (Pd≦PU). On the other hand, if it is determined in step S1 that the option operation device has been operated, the load pressure relief control described above is terminated. In other words, the load pressure relief control starts only when the option operation device is not operated, and ends when the option operation device is operated even if the load pressure relief control is in progress. When the option operation device is operated, the option control valve 60 is positioned at the first operating position X or the second operating position Y under the control of the valve opening area control unit 93 described above, and the variable relief valve 65 is controlled so that the set relief pressure LP is set by the option supply pressure control performed by the option control unit 95 described above, and is controlled to be the set relief pressure LP. By performing load pressure relief control in this manner, when the pressure in the first or second actuator oil passage 67, 68 on the high-pressure retention side exceeds the option upper limit pressure PU when the option operating device is not being operated, the pressure flows to the oil tank 12 via the option control valve 60 at the first or second load pressure relief position R1, R2, the load pressure introduction oil passage 62, and the variable relief valve 65. Thus, even if variable relief valves are not provided in the first and second actuator oil passages 67, 68, the pressure in the first and second actuator oil passages 67, 68 when the option operating device is not being operated can be controlled to be equal to or lower than the option upper limit pressure PU set for each optional hydraulic actuator. Moreover, because the load pressure relief control is performed using the load pressure valve passage 60h formed in the option control valve 60 and the variable relief valve 65 used for option supply pressure control, no separate component dedicated to load pressure relief control is required, and components can be shared. In this embodiment, the value of the upper limit pressure for options used for the supply pressure control for options and the value of the upper limit pressure for options used for the load pressure relief control are set to the same value, but different upper limit pressure values ​​for options may be set for the supply pressure control for options and the load pressure relief control.

[0040] Furthermore, when an operation signal for an optional operation tool is input from the optional operation detection means 84, the optional control unit 95 determines, based on information input from the optional hydraulic actuator notification means 85, whether the optional hydraulic actuator 13 is a hydraulic actuator that supplies pressure oil in one direction and that requires back pressure reduction, such as a breaker. If it is determined to be an applicable hydraulic actuator, it outputs a control signal to position the switching valve 74 in the open position X. This allows return oil from the optional hydraulic actuator 13 to the oil tank 12 to flow directly to the oil tank 12 without passing through the optional control valve 60, thereby ensuring that back pressure can be reduced.

[0041] Next, the control that is performed when the option operating tool is operated will be described using examples 1 to 4. In each example, if the control is the same as in other examples, a brief explanation will be given or the explanation will be omitted. [Example 1] First, a case where the optional operation tool is operated independently and pressure oil is supplied to the optional hydraulic actuator 13 only from the first hydraulic pump A will be described as Example 1. In this case, when an operation signal is input from the option-related operation detection means 84, the controller 30 first sets a first option-related operation amount, which is the operation amount to be performed by the first hydraulic pump A. Furthermore, in accordance with the first option-related operation amount, the controller 30 calculates a first option-related required flow rate that the option hydraulic actuator 13 requests of the first hydraulic pump A, and a first option-related margin-added required flow rate, which is the first option-related required flow rate plus a margin flow rate α. The controller then controls the discharge flow rate of the first hydraulic pump A using the first option-related margin-added required flow rate as a target discharge flow rate. Furthermore, the controller 30 sets a first option-related required pressure that the option hydraulic actuator 13 requests of the first hydraulic pump A in accordance with the first option-related operation amount, sets the first option-related required pressure as a first pump required pressure PR1, and further sets the first pump required pressure PR1 to a target pressure PT1 of the first hydraulic pump A, and controls the opening area of ​​the first bleed valve 75 so as to achieve the target pressure PT1. Meanwhile, the discharge flow rate and discharge pressure of the second hydraulic pump B are controlled to be minimum. The pressure oil supplied from the first hydraulic pump A flows through the first pump line C and the first optional-option supply oil passage 17 to the optional-option junction oil passage 22, and is supplied to the optional hydraulic actuator 13 through the compensator valve 61 and optional-option control valve 60 disposed in the optional-option junction oil passage 22. Furthermore, the controller 30 controls the supply pressure to the optional-option control valve 60 to be equal to or lower than the optional-option upper limit pressure PU by setting the relief setting pressure LP of the variable relief valve 65 to a pressure (LP=PU-K) obtained by subtracting a predetermined pressure K from the optional-option upper limit pressure PU set based on the type, specifications, etc. of the optional hydraulic actuator 13.Furthermore, the opening area of ​​the supply valve passage 60f of the optional equipment control valve 60 is controlled to be an opening area corresponding to the first optional equipment required flow rate, and in this case, the differential pressure before and after the optional equipment control valve 60 is maintained at a predetermined pressure K by the compensator valve 61, so that highly accurate supply flow rate control can be performed. In addition, the supply flow rate from the first hydraulic pump A is the first optional equipment margin added required flow rate, which is the first optional equipment required flow rate plus a margin flow rate α, so that even if the flow rate is controlled by the compensator valve 61 to adjust the differential pressure, the supply flow rate to the optional equipment control valve 60 will not be insufficient. Furthermore, if the optional equipment hydraulic actuator 13 is a hydraulic actuator that requires back pressure reduction, a control signal is output to the switching valve 74 to switch to the open position X, so that return oil from the optional equipment hydraulic actuator 13 can flow to the oil tank 12 via the bypass oil passage 73 without passing through the optional equipment control valve 60. In this way, in Example 1, pressure oil is supplied to the optional hydraulic actuators 13 only from the first hydraulic pump A, but in this case, the supply pressure to the optional control valve 60 is controlled to be equal to or less than the optional upper limit pressure PU set for each optional hydraulic actuator 13, and the supply flow rate to the optional hydraulic actuators 13 can be controlled with high precision.

[0042] [Example 2] Next, a case where the option operating tool is operated independently and pressure oil is supplied to the option hydraulic actuator 13 from both the first and second hydraulic pumps A and B will be described as Example 2. In this case, when an operation signal is input from the option-specific operation detection means 84, the controller 30 first sets first and second option-specific operation variables. Furthermore, the controller 30 calculates first and second option-specific required flow rates and first and second option-specific margin-added required flow rates in accordance with the first and second option-specific operation variables. The controller 30 then controls the discharge flow rates of the first and second hydraulic pumps A and B using the first and second option-specific margin-added required flow rates as target discharge flow rates. Furthermore, the controller 30 sets first and second option-specific required pressures in accordance with the first and second option-specific operation variables, and sets the first and second option-specific required pressures as first and second pump required pressures PR1 and PR2, respectively. Furthermore, the controller 30 sets the higher of the first and second pump required pressures PR1 and PR2 as target pressures PT1 and PT2 (PT1 = PT2) for both the first and second hydraulic pumps A and B, and controls the opening areas of the first and second bleed valves 75 and 76 to achieve the target pressures PT1 and PT2. This controls the discharge pressures of the first and second hydraulic pumps A and B to be equal. The pressure oil supplied from the first and second hydraulic pumps A, B passes through first and second pump lines C, D and first and second optional-unit supply oil passages 17, 21, respectively, to join at an optional-unit joint oil passage 22. In this case, because the discharge pressures of the first and second hydraulic pumps A, B are equal, the pressure oil supply from either one of the hydraulic pumps A, B is not given priority at the time of joining, and the oil supplied from both hydraulic pumps A, B flows into the optional-unit joint oil passage 22 and is supplied to the optional-unit hydraulic actuator 13 via a compensator valve 61 and an optional-unit control valve 60 disposed in the optional-unit joint oil passage 22. The opening area of ​​the supply valve passage 60f of the optional-unit control valve 60 is controlled so as to be the opening area corresponding to the total flow rate of the first and second optional-unit required flow rates. In this case, as in the case of Example 1 described above, highly accurate supply flow rate control can be performed. Furthermore, the controller 30 sets the relief set pressure LP of the variable relief valve 65 and controls the switching of the switching valve 74 as necessary, but these are the same as in Example 1 and therefore will not be described here. In this way, in Example 2, pressure oil is supplied to the optional hydraulic actuator 13 from both the first and second hydraulic pumps A and B, but in this case as well, as in Example 1, the supply pressure to the optional control valve 60 is controlled to be equal to or less than the optional upper limit pressure PU set for each optional hydraulic actuator 13, and the supply flow rate to the optional hydraulic actuator 13 can be controlled with high precision. Moreover, in this case, the discharge pressures of the first and second hydraulic pumps A and B are controlled to be equal, so that the supply of pressure oil from both hydraulic pumps A and B can be joined in the optional-element joining oil passage 22 without priority being given to the supply of pressure oil from either one of the hydraulic pumps A or B.

[0043] [Example 3] Next, we will explain, as Example 3, a case in which the option operating tool is operated in conjunction with the stick operating tool and the swing operating tool, and pressure oil is supplied to the option hydraulic actuator 13 from a first hydraulic pump A, and pressure oil is supplied to the stick cylinder 9 and swing motor 11 from a second hydraulic pump B. In this case, when operation signals are input from the option-related, stick-related, and swing-related operation detection means 84, 81, and 83, the controller 30 first sets the first option-related, second stick-related, and second swing-related operation amounts. Furthermore, the controller 30 calculates the first option-related, second stick-related, and second swing-related required flow rates and the first option-related margin-added required flow rate according to the first option-related, second stick-related, and second swing-related operation amounts. The controller 30 then controls the discharge flow rate of the first hydraulic pump A using the first option-related margin-added required flow rate as the target discharge flow rate, and controls the discharge flow rate of the second hydraulic pump B using the sum of the second stick-related required flow rate and the second swing-related required flow rate as the target discharge flow rate (or, if the total flow rate exceeds the maximum discharge flow rate of the second hydraulic pump B, the maximum discharge flow rate as the target discharge flow rate). Furthermore, the controller 30 sets the first option-related, second stick-related, and second swing-related required pressures according to the first option-related, second stick-related, and second swing-related operation amounts. The first optional-use required pressure is set to the first pump required pressure PR1, and the higher of the second stick-use and second swing-use required pressures is set to the second pump required pressure PR2. Furthermore, the first pump required pressure PR1 and the second pump required pressure PR2 are compared, and target pressures PT1 and PT2 of the first and second hydraulic pumps A and B are set based on the comparison result. In this case, by control of the above-mentioned bleed control unit 94, the target pressure PT1 of the first hydraulic pump A that supplies pressure oil to the optional hydraulic actuator 13 is set to a higher pressure than the target pressure PT2 of the second hydraulic pump B that does not supply pressure oil to the optional hydraulic actuator 13, and the opening areas of the first and second bleed valves 75 and 76 are controlled to achieve the target pressures PT1 and PT2. The pressure oil supplied from the first hydraulic pump A flows through the first pump line C and the first option supply oil passage 17 to the option joint oil passage 22. In this case, however, the discharge pressure of the first hydraulic pump A is higher than the discharge pressure of the second hydraulic pump B, so the pressure oil supplied from the first hydraulic pump A flows preferentially to the option joint oil passage 22, and the pressure oil supplied from the second hydraulic pump B does not flow to the option joint oil passage 22.The supply pressure oil from the first hydraulic pump A that flows into the optional accessory joint oil passage 22 is supplied to the optional accessory hydraulic actuator 13 via the compensator valve 61 and optional accessory control valve 60, which are arranged in the optional accessory joint oil passage 22. In this case, the control of the opening area of ​​the supply valve passage 60f of the optional accessory control valve 60, the setting of the relief set pressure LP of the variable relief valve 65, and the switching control of the switching valve 74 that is performed as needed are the same as in Example 1, so explanations will be omitted. On the other hand, the supply pressure oil from the second hydraulic pump B flows from the second pump line D to the second stick supply oil passage 19, and is supplied to the stick cylinder 9 via the second stick flow control valve 33 and the stick control valve 24, and also flows from the second pump line D to the second swing supply oil passage 20, and is supplied to the swing motor 11 via the swing control valve 26. In this case, the second stick flow control valve 33 and the opening areas of the supply valve passages 24c, 26c of the stick and swing control valves 24, 26 are controlled by the above-mentioned valve opening area control unit 93 so as to provide opening areas corresponding to the second stick distributed flow rate and the second swing distributed flow rate obtained by distributing the discharge flow rate of the second hydraulic pump B at the ratio of the second stick required flow rate and the second swing required flow rate.In addition, in Example 3, since pressure oil is supplied to the stick cylinder 9 only from the second hydraulic pump B, the first stick flow control valve 32 arranged in the first stick supply oil passage 16 is controlled to close. As described above, in Example 3, the optional operation tool is operated in conjunction with the operation tools for the other hydraulic actuators (stick cylinder 9, swing motor 11), and pressure oil is supplied to the optional hydraulic actuator 13 from the first hydraulic pump A, and pressure oil is supplied to the other hydraulic actuators from the second hydraulic pump B. However, in this case as well, as in Examples 1 and 2, the supply pressure to the optional control valve 60 is controlled to be equal to or lower than the optional upper limit pressure PU set for each optional hydraulic actuator 13, and the supply flow rate to the optional hydraulic actuator 13 can be controlled with high precision. Moreover, in this case, the discharge pressure of the first hydraulic pump A that supplies pressure oil to the optional hydraulic actuator 13 is controlled to be higher than the discharge pressure of the second hydraulic pump B, so that only the supply pressure oil from the first hydraulic pump A can be reliably flowed into the optional hydraulic junction oil path 22. Meanwhile, the discharge flow rate of the second hydraulic pump B is distributed to the other hydraulic actuators, thereby ensuring good interlocking operability between the optional hydraulic actuator 13 and the other hydraulic actuators (stick cylinder 9, swing motor 11).

[0044] [Example 4] Next, we will explain Example 4, which shows a case where the option operating tool is operated in conjunction with the boom operating tool and the swing operating tool, and where pressurized oil is supplied to the option hydraulic actuator 13 and boom cylinder 8 from a first hydraulic pump A, and pressurized oil is supplied to the swing motor 11 from a second hydraulic pump B. In this case, when operation signals are input from the option-related, boom-related, and swing-related operation detection means 84, 80, and 83, the controller 30 first sets the first option-related, first boom-related, and second swing-related operation variables. Furthermore, the controller 30 calculates the first option-related, first boom-related, and second swing-related required flow rates and the first option-related margin added required flow rate according to the first option-related, first boom-related, and second swing-related operation variables. The controller 30 then controls the discharge flow rate of the first hydraulic pump A using the sum of the first option-related margin added required flow rate and the first boom-related required flow rate as the target discharge flow rate (if the total flow rate exceeds the maximum discharge flow rate of the first hydraulic pump A, the maximum discharge flow rate is set as the target discharge flow rate), and also controls the discharge flow rate of the second hydraulic pump B using the second swing-related required flow rate as the target discharge flow rate. Furthermore, the controller 30 sets the first option-related, first boom-related, and second swing-related required pressures according to the first option-related, first boom-related, and second swing-related operation variables. The higher of the first option-operated and first boom-operated required pressures is set as the first pump required pressure PR1, and the second swing required pressure is set as the second pump required pressure PR2. Furthermore, the first pump required pressure PR1 and the second pump required pressure PR2 are compared, and target pressures PT1 and PT2 of the first and second hydraulic pumps A and B are set based on the comparison result, but in this case, by control of the above-mentioned bleed control unit 94, the target pressure PT1 of the first hydraulic pump A that supplies pressure oil to the optional hydraulic actuator 13 is set to a higher pressure than the target pressure PT2 of the second hydraulic pump B that does not supply pressure oil to the optional hydraulic actuator 13, and the opening areas of the first and second bleed valves 75 and 76 are controlled to achieve the target pressures PT1 and PT2. The pressure oil supplied from the first hydraulic pump A flows from the first pump line C to the first boom supply oil passage 14, and is supplied to the boom cylinder 8 via the boom control valve 23, and also flows from the first pump line C to the option joint oil passage 22 via the first option supply oil passage 17. In this case, however, since the discharge pressure of the first hydraulic pump A is higher than the discharge pressure of the second hydraulic pump B, the pressure oil supplied from the first hydraulic pump A flows preferentially to the option joint oil passage 22, and the pressure oil supplied from the second hydraulic pump B does not flow to the option joint oil passage 22.The supply flow rate of the pressure oil from the first hydraulic pump A supplied from the first boom supply oil passage 14 to the boom control valve 23 to the boom cylinder 8 is controlled by the opening area of ​​the supply valve passage 23c of the boom control valve 23. In this case, the opening area of ​​the supply valve passage 23c of the boom control valve 23 is controlled by the control of the valve opening area control unit 93 described above so as to be an opening area corresponding to the first boom distributed flow rate obtained by distributing the discharge flow rate of the first hydraulic pump A in the ratio of the first option-use margin added requested flow rate to the first boom-use requested flow rate. As a result, the first option-use margin added requested flow rate, which is the first option-use requested flow rate plus the margin flow rate α, flows from the first hydraulic pump A to the optional-use joined oil passage 22. The supply pressure oil from the first hydraulic pump A flowing to the optional-use joined oil passage 22 is then supplied to the optional hydraulic actuator 13 via the compensator valve 61 and the optional-use control valve 60 arranged in the optional-use joined oil passage 22. In this case, the opening area of ​​the supply valve passage 60f of the option-mounting control valve 60 is controlled to be an opening area corresponding to the first required option-mounting flow rate, but the control of the opening area, the setting of the relief set pressure LP of the variable relief valve 65, the operation of the compensator valve 61, and the switching control of the switching valve 74 performed as needed are the same as in Example 1, so explanations will be omitted. Meanwhile, supply pressure oil from the second hydraulic pump B flows from the second pump line D to the second swing supply oil passage 20 and is supplied to the swing motor 11 via the swing control valve 26. In this case, the opening area of ​​the supply valve passage 26c of the swing control valve 26 is controlled to be an opening area corresponding to the second required swing flow rate, because the swing motor 11 is the only hydraulic actuator to which pressure oil is supplied from the second hydraulic pump B. In addition, in Example 4, pressure oil is supplied to the boom cylinder 8 only from the first hydraulic pump A, so the boom flow control valve 31 arranged in the second boom supply oil passage 18 is controlled to close. As described above, in Example 4, the optional accessory operating tool is operated in conjunction with the operating tools for the two other hydraulic actuators (boom cylinder 8, swing motor 11), and pressure oil is supplied to the optional accessory hydraulic actuator 13 and one of the other hydraulic actuators from the first hydraulic pump A, while pressure oil is supplied to the other other hydraulic actuator from the second hydraulic pump B. However, even when the optional accessory hydraulic actuator 13 shares the first hydraulic pump A with the other hydraulic actuator in this way, the optional accessory first margin added required flow rate, which is the first optional accessory required flow rate plus the margin flow rate α, is supplied to the optional accessory confluent oil passage 22. Therefore, even when the flow rate is controlled by the compensator valve 61 to adjust the differential pressure, the supply flow rate to the optional accessory control valve 60 does not become insufficient, and even in this case, as in Examples 1 to 3 above, the supply pressure to the optional accessory control valve 60 is controlled to be equal to or lower than the optional accessory upper limit pressure PU set for each individual optional accessory hydraulic actuator 13, and the supply flow rate to the optional accessory hydraulic actuator 13 can be controlled with high precision. Moreover, in this case, the discharge pressure of the first hydraulic pump A that supplies pressure oil to the optional hydraulic actuator 13 is controlled to be higher than the discharge pressure of the second hydraulic pump B, so that only the pressure oil supplied from the first hydraulic pump A can be reliably flowed into the optional-use junction oil passage 22. On the other hand, the discharge flow rate of the second hydraulic pump B is supplied to the other hydraulic actuator, thereby ensuring good interlocking operability between the optional hydraulic actuator 13 and the other hydraulic actuators (boom cylinder 8, swing motor 11).

[0045] In the embodiment configured as described above, the hydraulic control system of the hydraulic excavator 1 is provided with an option control circuit that is shared by a plurality of optional hydraulic actuators 13 that are selectively attached, and the option control circuit is provided with an option control valve 60 that controls the supply and discharge of oil to and from the optional hydraulic actuator 13 based on the operation of an option operating tool, first and second actuator oil passages 67, 68 that connect the option control valve 60 to the optional hydraulic actuator 13, first and second option pressure sensors 97, 98 that detect the pressures in the first and second actuator oil passages 67, 68, respectively, a compensator valve 61 that is arranged upstream of the option control valve 60 and operates to introduce inlet pressure and outlet pressure of the option control valve 60 and maintain the differential pressure between the introduced inlet pressure and outlet pressure at a predetermined pressure K, and a controller 30 that controls the operation of the option control valve 60.Furthermore, a variable relief valve 65 capable of varying the relief set pressure LP by a control signal from the controller 30 is connected to a load pressure introduction oil passage 62 that introduces the outlet side pressure of the option control valve 60 to the compensator valve 61, and by using the variable relief valve 65 to reduce the pressure in the load pressure introduction oil passage 62 to the relief set pressure LP and introduce it into the compensator valve 61, the inlet side pressure of the option control valve 60 can be variably controlled based on changes in the relief set pressure LP of the variable relief valve 65. In this configuration, when the option control valve 60 is switched to a position where oil is not supplied or discharged to or from the option hydraulic actuator 13, the pressure in the first and second actuator oil passages 67, 68 is supplied to the load pressure introduction oil passage 62. When the pressure in the first or second actuator oil passage 67, 68 exceeds an option upper limit pressure PU that is set in advance for each individual option hydraulic actuator 13 while the option operating device is not being operated, the option control valve 60 is switched to the first or second load pressure relief position R1, R2 and the relief setting pressure LP of the variable relief valve 65 is controlled to be equal to or lower than the option upper limit pressure PU, thereby allowing the pressure in the first or second actuator oil passage 67, 68 that exceeds the option upper limit pressure PU to be released into the oil tank 12 via the option control valve 60, the load pressure introduction oil passage 62 and the variable relief valve 65.

[0046] As a result, the upper limit pressure of the pressurized oil that is flow-controlled by the option control valve 60 and supplied to the option hydraulic actuator 13 can be variably controlled to a pressure that corresponds to each option hydraulic actuator 13 by changing the relief setting pressure LP of the variable relief valve 65 connected to the load pressure introducing oil passage 62 with a control signal from the controller 30. Therefore, compared to a configuration in which variable relief valves are provided in each of the pair of first and second hydraulic actuator oil passages 67, 68 leading from the option control valve 60 to the option hydraulic actuator 13 to variably control the upper limit pressure of the pressurized oil supplied to the option hydraulic actuator 13, Furthermore, with this configuration, if the pressure in the first and second actuator oil passages 67, 68 exceeds the option upper limit pressure PU when the option operating device is not being operated, the pressure can be released to the oil tank 12 via the option control valve 60, the load pressure introduction oil passage 62, and the variable relief valve 65. Thus, even if variable relief valves are not provided in the first and second actuator oil passages 67, 68, the pressure in the first and second actuator oil passages 67, 68 when the option operating device is not being operated can be controlled to be equal to or lower than the option upper limit pressure PU set for each optional hydraulic actuator. Moreover, this control is performed using the option control valve 60, which controls the supply and discharge of oil to the optional hydraulic actuator 13 based on the operation of the operating device, and the variable relief valve 65, which is used to variably control the supply pressure to the optional hydraulic actuator 13, so no additional dedicated components are required and parts can be shared.

[0047] Furthermore, the hydraulic control system is equipped with other hydraulic actuators (boom cylinder 8, stick cylinder 9, bucket cylinder 10, swing motor 11) provided on the hydraulic excavator 1 in addition to the optional hydraulic actuator 13, and first and second hydraulic pumps A and B which serve as hydraulic supply sources for these other hydraulic actuators. The optional hydraulic actuator 13 uses either or both of these first and second hydraulic pumps A and B as its hydraulic supply source, and the optional control circuit is equipped with first and second optional supply oil passages 17 and 21 which are connected to the first and second hydraulic pumps A and B, respectively, and an optional joint oil passage 22 where these first and second optional supply oil passages 17 and 21 join, and a compensator valve 61 and an optional control valve 60 are disposed in the optional joint oil passage 22. As a result, whether the optional hydraulic actuator 13 uses only the first hydraulic pump A, only the second hydraulic pump B, or both hydraulic pumps A and B as its hydraulic supply source, oil supply and discharge control for the optional hydraulic actuator 13 can be performed with just one option control valve 60, which contributes to reducing the number of parts.

[0048] Furthermore, the hydraulic control system is provided with first and second bleed valves 75, 76 which respectively control the bleed flow rates flowing from the first and second hydraulic pumps A, B to the oil tank 12 based on control signals output from the controller 30, and is configured to control the discharge pressures of the first and second hydraulic pumps A, B by controlling the bleed flow rates using the first and second bleed valves 75, 76. In this case, when the optional hydraulic actuator 13 uses only one of the first and second hydraulic pumps A, B as its hydraulic supply source, the controller 30 makes the discharge pressure of the hydraulic pump that serves as the hydraulic supply source higher than the discharge pressure of the other hydraulic pump that is not a hydraulic supply source, and when the optional hydraulic actuator 13 uses both the first and second hydraulic pumps A, B as its hydraulic supply sources, the controller 30 controls the bleed flow rates so that the discharge pressures of the first and second hydraulic pumps A, B are equal. As a result, when the optional hydraulic actuator 13 uses only one of the first and second hydraulic pumps A, B as the hydraulic supply source, the supply pressure oil from that one hydraulic pump that is the hydraulic supply source can be preferentially made to flow to the optional device junction oil passage 22, and the supply pressure oil from the other hydraulic pump that is not the hydraulic supply source does not flow to the optional device junction oil passage 22. Furthermore, when the optional hydraulic actuator 13 uses both the first and second hydraulic pumps A, B as hydraulic supply sources, the supply pressure oil from both hydraulic pumps A, B can be made to merge in the optional device junction oil passage 22. Therefore, even if valves for opening and closing the first and second optional device supply oil passages 17, 21 are not provided in the first and second optional device supply oil passages 17, 21, respectively, only the supply pressure oil from the hydraulic pump that is the hydraulic supply source can be supplied to the optional device junction oil passage 22, whether either one of the first and second hydraulic pumps A, B is used as the hydraulic supply source or both hydraulic pumps are used as hydraulic supply sources, which allows for a reduction in the number of parts and contributes to cost reduction.Furthermore, when the optional hydraulic actuator 13 uses either the first or second hydraulic pump A, B as its hydraulic supply source, and the other hydraulic actuator uses the other hydraulic pump as its hydraulic supply source, the pressure oil supplied from one of the hydraulic pumps flows into the optional joint oil passage 22 and is used only for the optional hydraulic actuator 13, while the pressure oil supplied from the other hydraulic pump does not flow into the optional joint oil passage 22 and is entirely used only for the other hydraulic actuator, ensuring good interlocking operability between the optional hydraulic actuator 13 and the other hydraulic actuators. [Industrial Applicability]

[0049] The present invention can be used in a hydraulic control system for a work machine such as a hydraulic excavator when an optional hydraulic actuator is installed on the work machine. [Explanation of symbols]

[0050] 8 Boom cylinder 9 Stick Cylinder 10 Bucket cylinder 11 Swing motor 12 Oil Tank 13 Optional Hydraulic Actuators 17 First option oil supply line 21 Second option oil supply line 22 Optional confluence oil passage 30 Controllers 60 Optional control valve 61 Compensator valve 62 Load pressure introduction oil passage 65 Variable Relief Valve 67 First actuator oil passage 68 Second actuator oil passage 75 First bleed valve 76 Second bleed valve 94 Bleed control section 95 Option control unit 97 Pressure sensor for first option 98 Second option pressure sensor A First hydraulic pump B Second hydraulic pump R1 First load pressure relief position R2 Second load pressure relief position

Claims

1. In providing a hydraulic control system for a work machine with an option control circuit shared by a plurality of optional hydraulic actuators selectively attached to the work machine, the option control circuit comprises an option control valve that controls the supply and discharge of oil to and from the optional hydraulic actuator based on the operation of an option operating tool, a pair of actuator oil lines connecting the option control valve and the optional hydraulic actuator, pressure detection means for detecting the pressure in the actuator oil lines, and a pressure detecting means disposed upstream of the option control valve and adapted to introduce the inlet pressure and outlet pressure of the option control valve. a pressure compensating valve that operates to maintain the differential pressure between the introduced inlet side pressure and outlet side pressure at a predetermined pressure, and a control device that controls the operation of the option control valve; a variable relief valve that can vary the relief set pressure with a control signal from the control device is connected to a load pressure introducing oil line that introduces the outlet side pressure of the option control valve to the pressure compensating valve, and the pressure in the load pressure introducing oil line is reduced to the relief set pressure by the variable relief valve and introduced into the pressure compensating valve, thereby making it possible to variably control the inlet side pressure of the option control valve based on changes in the relief set pressure of the variable relief valve; a load pressure relief position is provided as a switching position of the option control valve, which does not supply or discharge oil to or from the option hydraulic actuator, but which allows the pressure in the actuator oil line to flow to the load pressure introduction oil line; and when the pressure in the actuator oil line exceeds an upper limit pressure that is preset for each option hydraulic actuator when the option operating device is not being operated, the option control valve is switched to the load pressure relief position and the relief setting pressure of the variable relief valve is controlled so that it is not more than the upper limit pressure, thereby allowing the pressure in the actuator oil line that exceeds the upper limit pressure to be released to the oil tank via the option control valve, the load pressure introduction oil line and the variable relief valve.

2. 10. A hydraulic control system for a work machine according to claim 1, comprising first and second hydraulic pumps which serve as hydraulic supply sources for other hydraulic actuators provided on the work machine in addition to the optional hydraulic actuator, the optional hydraulic actuator using either or both of the first and second hydraulic pumps as its hydraulic supply source, the optional control circuit comprising first and second optional supply oil passages connected to the first and second hydraulic pumps respectively, and an optional option junction oil passage where the first and second optional option supply oil passages join, and a pressure compensation valve and an optional option control valve are disposed in the optional option junction oil passage.

3. 3. A hydraulic control system for a working machine according to claim 2, wherein the hydraulic control system for a working machine is provided with first and second bleed valves that respectively control the bleed flow rates from the first and second hydraulic pumps to the oil tank based on control signals output from a control device, and the discharge pressures of the first and second hydraulic pumps are controlled by controlling the bleed flow rates by the first and second bleed valves, and the control device, when the optional hydraulic actuator uses only one of the first and second hydraulic pumps as a hydraulic supply source, makes the discharge pressure of the hydraulic pump that serves as the hydraulic supply source higher than the discharge pressure of the other hydraulic pump that is not a hydraulic supply source, and when the optional hydraulic actuator uses both the first and second hydraulic pumps as hydraulic supply sources, controls the bleed flow rates so that the discharge pressures of the first and second hydraulic pumps are equal.

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