Hydraulic Control System

Abstract

To avoid an increase in the size of a direction changeover valve and execute supply flow rate control accurately in providing a flow rate control valve on the upstream side of the direction changeover valve and making it possible to change relationships between a supply flow rate and a discharge flow rate with respect to a hydraulic actuator.SOLUTION: Supply flow rate control for a stick cylinder 8 is executed on the basis of opening areas of a stick direction changeover valve 25 and a stick flow rate control valve 28, and a target opening area of the stick flow rate control valve 28 is calculated and the stick flow rate control valve 28 is controlled so that the calculated target opening area is attained on the basis of a target supply flow rate from hydraulic pumps A and B to the stick cylinder 8, an opening area of the stick direction changeover valve 25, and a target differential pressure between the hydraulic pump A and a load pressure of the stick cylinder 8.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Generally, various hydraulic actuators are provided in working machines such as hydraulic excavators, and as a hydraulic control system for controlling the supply and discharge of hydraulic oil to such hydraulic actuators, a system that uses a single spool valve to simultaneously perform a direction switching control for switching the direction of supply and discharge of hydraulic oil to the hydraulic actuator, a supply flow rate control for controlling the supply flow rate from a hydraulic pump to the hydraulic actuator, and a discharge flow rate control for controlling the discharge flow rate from the hydraulic actuator to an oil tank has been widely known. However, when the supply flow rate control and the discharge flow rate control are performed using a single spool valve in this manner, the relationship between the opening area on the supply side and the opening area on the discharge side relative to the moving position of the spool is uniquely determined, and therefore, for example, the relationship between the supply flow rate and the discharge flow rate cannot be changed depending on the operating state, such as an individual operation in which one hydraulic actuator is driven alone or a combined operation in which multiple hydraulic actuators are driven simultaneously, or various work contents, such as light load work and heavy load work, resulting in a problem of poor work efficiency and operability. In the past, as a technique for independently controlling the supply flow rate and the discharge flow rate for a hydraulic actuator, there has been a technique that includes a flow control valve that controls the supply flow rate from a hydraulic pump to the hydraulic actuator, a directional control valve that is arranged downstream of the flow control valve and switches the supply / discharge direction of hydraulic oil to the hydraulic actuator and controls the discharge flow rate from the hydraulic actuator, and a control means that controls the flow control valve and the directional control valve (see, for example, Patent Document 1). In this technique, the opening area of ​​the supply valve passage formed in the directional control valve is set large so that the supply flow rate controlled by the flow control valve flows directly to the hydraulic actuator, so that the directional control valve is configured not to control the supply flow rate, and as a result, the supply flow rate and the discharge flow rate for the hydraulic actuator can be independently controlled by separate valves, and by giving the directional control valve two functions, supply / discharge switching control and discharge flow rate control, the number of parts is reduced compared to a case in which the direction switching control, the supply flow rate control, and the discharge flow rate control are all controlled by different valves. Furthermore, in the above-mentioned Patent Document 1, for a large flow rate hydraulic actuator using two hydraulic pumps, a first and a second hydraulic pump, as hydraulic supply sources, two flow rate control valves are provided, a first flow rate control valve for controlling the supply flow rate from the first hydraulic pump and a second flow rate control valve for controlling the supply flow rate from the second hydraulic pump, and the total flow rate from these two flow rate control valves is supplied to the hydraulic actuator by passing through a supply valve path formed in a directional control valve that performs the directional control and discharge flow rate control. As a result, even for a large flow rate hydraulic actuator supplied with pressure oil from two hydraulic pumps, the supply flow rate and the discharge flow rate can be controlled separately, while only one directional control valve is required, simplifying the circuit, and since the supply flow rate from the first hydraulic pump and the supply flow rate from the second hydraulic pump can be controlled separately, it is possible to control the pump flow rate distribution during combined operation with high accuracy. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-20604 A Summary of the Invention [Problem to be solved by the invention]

[0004] As described above, in the above-mentioned Patent Document 1, the directional control valve is set to directly flow the supply flow rate controlled by the flow control valve to the hydraulic actuator, and is configured not to control the supply flow rate. In this case, the opening area of ​​the supply valve passage of the directional control valve is set large enough so that no differential pressure occurs before and after the directional control valve, so that the supply flow rate to the hydraulic actuator can be controlled only by controlling the opening area of ​​the flow control valve. However, in order to form such a valve passage with a large opening in the directional control valve, the size of the directional control valve must be increased. In particular, for a directional control valve for a large-flow hydraulic actuator that uses two hydraulic pumps as hydraulic supply sources, a supply valve passage with a large opening is required to pass the supply flow rate from the two hydraulic pumps without a differential pressure before and after, which causes a problem that the directional control valve becomes significantly large. Therefore, it is proposed to provide a flow control valve upstream of the directional control valve without making the opening area of ​​the supply valve passage of the directional control valve large enough to prevent a differential pressure before and after. In this case, however, the flow control is affected not only by the opening area of ​​the flow control valve but also by the opening area of ​​the supply valve passage of the directional control valve, making it difficult to control the supply flow rate to the hydraulic actuator. This is the problem that the present invention aims to solve. [Means for solving the problem]

[0005] The present invention has been created in view of the above-mentioned circumstances and with the objective of solving these problems. The invention of claim 1 provides a hydraulic control system comprising a hydraulic pump and a hydraulic actuator using the hydraulic pump as a hydraulic supply source, comprising a directional control valve having a supply valve path and a discharge valve path for the hydraulic actuator and switching the supply and discharge direction, a flow control valve arranged upstream of the directional control valve and controlling the supply flow rate from the hydraulic pump to the directional control valve, and control means for controlling the operation of the directional control valve and the flow control valve, wherein the discharge flow rate control for the hydraulic actuator is performed based on the opening area of ​​the discharge valve path of the directional control valve, and the supply flow rate control is performed based on the opening area of ​​the supply valve path of the directional control valve and the opening area of ​​the flow control valve. on the other hand The control means includes a target supply flow rate setting means for setting a target supply flow rate from the hydraulic pump to the hydraulic actuator in accordance with the operation amount of a hydraulic actuator operating tool, a directional control valve opening area setting means for setting the opening areas of a supply valve passage and a discharge valve passage of the directional control valve in accordance with the operation amount of the hydraulic actuator operating tool, and a target differential pressure between the pump pressure of the hydraulic pump and the load pressure of the hydraulic actuator. In advance and a calculation means for calculating a target opening area of ​​a flow control valve for supplying the target supply flow rate to the hydraulic actuator based on the set target supply flow rate, the opening area of ​​the directional control valve supply valve path, and the target differential pressure, and the operation of the flow control valve is controlled so as to achieve the target opening area calculated by the calculation means. Along with , The calculation means, when calculating the target opening area of ​​the flow control valve, calculates a differential pressure across the supply valve passage of the directional control valve based on the target supply flow rate and the opening area of ​​the supply valve passage of the directional control valve, further calculates a differential pressure across the flow control valve based on the differential pressure across the supply valve passage of the directional control valve and the target differential pressure, and calculates the target opening area of ​​the flow control valve based on the differential pressure across the flow control valve and the target supply flow rate. The hydraulic control system is characterized by the above. The invention of claim 2 relates to the hydraulic control system of claim 1, which includes first and second hydraulic pumps, a high flow rate hydraulic actuator using both the first and second hydraulic pumps as hydraulic supply sources, a directional control valve having a supply valve path and a discharge valve path for the high flow rate hydraulic actuator and switching the supply and discharge direction, and a main side supply oil path and a sub side supply oil path connecting the first and second hydraulic pumps to a pump port of the directional control valve, respectively, and a flow control valve is disposed in the sub side supply oil path for controlling the supply flow rate from the second hydraulic pump to the directional control valve, and when the operation amount of an operating tool for the high flow rate hydraulic actuator is less than a set value, the flow control valve is closed so that only the supply flow rate from the first hydraulic pump via the main side supply oil path is supplied to the directional control valve, and when the operation amount of an operating tool for the high flow rate hydraulic actuator is equal to or greater than the set value, the flow control valve is opened so that the supply flow rate from the second hydraulic pump via the sub side supply oil path and the supply flow rate from the first hydraulic pump via the main side oil path are joined together and supplied to the directional control valve, a target supply flow rate setting means provided in the control means sets target supply flow rates from the first and second hydraulic pumps to the large flow hydraulic actuator for each hydraulic pump in accordance with the amount of operation of an operating tool for the large flow hydraulic actuator, the directional control valve opening area setting means sets the opening areas of the supply valve path and the discharge valve path of the directional control valve in accordance with the amount of operation of an operating tool for the large flow hydraulic actuator, the target differential pressure setting means sets a target differential pressure between the pump pressure of the second hydraulic pump and the load pressure of the large flow hydraulic actuator, and the calculation means calculates a target opening area of ​​the flow control valve for supplying the target supply flow rate from the second hydraulic pump to the large flow hydraulic actuator based on the set target supply flow rate, the opening area of ​​the directional control valve supply valve path and the target differential pressure. When calculating the target opening area of ​​the flow control valve, the calculation means calculates a differential pressure across the directional control valve supply valve passage based on the target supply flow rates from the first and second hydraulic pumps to the high flow hydraulic actuator and the opening area of ​​the directional control valve supply valve passage, further calculates a differential pressure across the flow control valve based on the differential pressure across the directional control valve supply valve passage and the target differential pressure, and calculates the target opening area of ​​the flow control valve based on the differential pressure across the flow control valve and the target supply flow rate from the second hydraulic pump to the high flow hydraulic actuator. The hydraulic control system is characterized by the above. Effect of the Invention

[0006] By adopting the invention of claim 1, the relationship between the supply flow rate and the discharge flow rate to the hydraulic actuator can be changed, while preventing the directional control valve from becoming large. To, flow This allows the target opening area of ​​the quantity control valve to be calculated with high accuracy, which contributes to improving the accuracy of supply flow rate control. Claim 2 By making the invention, even in a large flow rate hydraulic actuator using the first and second hydraulic pumps as hydraulic supply sources, the relationship between the supply flow rate and the discharge flow rate for the large flow rate hydraulic actuator can be changed in the range where the supply flow rate of pressure oil is large from both hydraulic pumps, while avoiding an increase in the size of the directional control valve. 2, large The target opening area of ​​the flow control valve for the flow hydraulic actuator can be calculated with high accuracy, which contributes to improving the accuracy of supply flow control. [Brief description of the drawings]

[0007] [Figure 1] FIG. 2 is a hydraulic circuit diagram showing the first embodiment. [Diagram 2] FIG. 2 is a block diagram showing inputs and outputs of a controller. [Diagram 3] FIG. 13 is a diagram showing the relationship between the operating tool operation amount when the stick operating tool is operated alone and the target supply flow rates of the first and second hydraulic pumps, the opening area of ​​the stick flow control valve, and the opening area of ​​the stick directional control valve. [Figure 4] FIG. 2 is a diagram showing an assembled state of a stick directional control valve and a stick flow rate control valve. [Diagram 5] FIG. 5 is a hydraulic circuit diagram showing a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. 1 is a hydraulic circuit diagram showing a first embodiment of a hydraulic control system for a hydraulic excavator to which the present invention is applied, in which A and B are variable displacement hydraulic pumps, Aa and Ba are capacity varying means for varying the capacity of the hydraulic pumps A and B based on a control signal from a controller 10 described later, 3 is an oil tank, 4 is a left traveling motor, 5 is a right traveling motor, 6 is a boom cylinder, 7 is a swing motor, 8 is a stick cylinder, and 9 is a bucket cylinder. The left traveling motor 4, right traveling motor 5, boom cylinder 6, swing motor 7, stick cylinder 8, and bucket cylinder 9 are hydraulic actuators that use hydraulic pumps A and B as hydraulic supply sources, but among these hydraulic actuators, the boom cylinder 6 and stick cylinder 8 are hydraulic actuators that use both hydraulic pumps A and B as hydraulic supply sources, and correspond to the large flow rate hydraulic actuators of the present invention. The boom cylinder 6, stick cylinder 8 and bucket cylinder 9 are hydraulic cylinders that extend and retract to swing the boom, stick and bucket (none of which are shown) that make up the front working equipment of the hydraulic excavator, the left traveling motor 4 and the right traveling motor 5 are hydraulic motors that operate to drive the left and right traveling bodies of the hydraulic excavator forward and backward, respectively, and the swing motor 7 is a hydraulic motor that operates to swing the upper swing body of the hydraulic excavator left and right.

[0009] The hydraulic pump A is connected to a pump line C via a straight travel valve 11 in a first position X, which will be described later, and is also connected to a left travel direction change valve 13. On the other hand, the hydraulic pump B is connected to a pump line D, and is also connected to a right travel direction change valve 14 via the straight travel valve 11 in the first position X.

[0010] The straight travel valve 11 is a two-position switching valve that switches between a first position X and a second position Y based on a control signal output from the controller 10. When the straight travel valve 11 is in the first position X, the discharge oil of the hydraulic pump A is supplied to the pump line C and the left travel direction switching valve 13, and the discharge oil of the hydraulic pump B is supplied to the pump line D and the right travel direction switching valve 14. When the straight travel valve 11 is in the second position Y, the discharge oil of the hydraulic pump A is supplied to both the left and right travel direction switching valves 13 and 14, and the discharge oil of the hydraulic pump B is supplied to both pump lines C and D. The controller 10 switches the straight travel valve 11 between the first position X and the second position Y in response to the operation of the left and right travel operating tools (not shown) and other hydraulic actuator operating tools (boom, swing, stick, and bucket operating tools, none of which are shown), thereby making it possible to equalize the supply flow rates to the left and right travel motors 4 and 5 during straight travel. In the following description, a case will be described in which the straight travel valve 11 is located in the first position X, that is, the discharge oil of the hydraulic pump A is supplied to the pump line C and the left travel directional control valve 13, and the discharge oil of the hydraulic pump B is supplied to the pump line D and the right travel directional control valve 14.

[0011] The left and right traveling direction changeover valves 13, 14 are closed center type spool valves that control the supply and exhaust flow rates for the left and right traveling motors 4, 5 and switch the supply and exhaust direction, and are provided with forward and reverse pilot ports 13a, 13b, 14a, 14b that are connected to traveling electromagnetic proportional valves (a forward side electromagnetic proportional valve for left traveling, a reverse side electromagnetic proportional valve for left traveling, a forward side electromagnetic proportional valve for right traveling, and a reverse side electromagnetic proportional valve for right and left traveling, although not shown in the figures) that output pilot pressure based on a control signal output from the controller 10. The left and right travel direction changeover valves 13, 14 are located in a neutral position N where no supply / discharge control is performed for the left and right travel motors 4, 5 when pilot pressure is not input to the forward and reverse pilot ports 13a, 13b, 14a, 14b. However, when pilot pressure is input to the forward pilot ports 13a, 14a, the valves are switched to a forward operating position X, and supply valve paths 13e, 14f supply oil discharged from hydraulic pump A and hydraulic pump B to the forward ports 4a, 5a of the left travel motor 4 and the right travel motor 5. In addition, when pilot pressure is input to the reverse side pilot ports 13b, 14b, the hydraulic control unit 10 switches to the reverse side operating position Y, opening the supply valve paths 13e, 14e that supply oil discharged from the hydraulic pumps A and B to the reverse side ports 4b, 5b of the left traveling motor 4 and the right traveling motor 5, and opening the discharge valve paths 13f, 14f that allow the discharged oil from the forward side ports 4a, 5a to flow into the oil tank 3. The supply flow rate and discharge flow rate for the left traveling motor 4 and the right traveling motor 5 when they are located in the forward operating position X or the reverse operating position Y are controlled by the opening areas of the supply valve paths 13e, 14e and the discharge valve paths 13f, 14f, and the opening areas are increased or decreased according to the spool movement position associated with an increase or decrease in the pilot pressure output from the traveling electromagnetic proportional valve to the forward side or reverse side pilot port 13a, 13b, 14a, 14b.When the left or right traveling operating device is operated, the controller 10 controls the traveling electromagnetic proportional valve so as to output a pilot pressure that increases or decreases according to the amount of operation of the traveling operating device, thereby making it possible to drive the left and right traveling motors 4, 5 at a speed according to the amount of operation of the traveling operating device.

[0012] On the other hand, a boom main side supply oil passage 17, a stick sub side supply oil passage 18, and a bucket supply oil passage 19 are branched off from pump line C connected to hydraulic pump A in a state in parallel with each other, and a boom sub side supply oil passage 20, a swing supply oil passage 21, and a stick main side supply oil passage 22 are branched off from pump line D connected to hydraulic pump B in a state in parallel with each other. The boom main side supply oil passage 17 and the boom sub side supply oil passage 20 are oil passages that connect hydraulic pumps A, B, respectively, to a pump port 23p of a boom direction control valve 23 described later, and the stick main side supply oil passage 22 and the stick sub side supply oil passage 18 are oil passages that connect hydraulic pumps B, A, respectively, to a pump port 25p of a stick direction control valve 25. Furthermore, the swing supply oil passage 21 is an oil passage that connects hydraulic pump B to the pump port 24p of the swing direction control valve 24, and the bucket supply oil passage 19 is an oil passage that connects hydraulic pump A to the pump port 26p of the bucket direction control valve 26.

[0013] A stick flow control valve 28 that controls the supply flow rate from hydraulic pump A to the stick direction change valve 25 is disposed in the stick sub-side supply oil passage 18, and a boom flow control valve 29 that controls the supply flow rate from hydraulic pump B to the boom direction change valve 23 is disposed in the boom sub-side supply oil passage 20. The stick flow control valve 28 and the boom flow control valve 29 are poppet valves that control the flow rate by pilot operation using a stick flow control solenoid proportional valve 45 and a boom flow control solenoid proportional valve 46 (shown in FIG. 2) that operate based on a control signal output from the controller 10, and have a backflow prevention function that allows oil to flow from the hydraulic pumps A and B to the stick direction change valve 25 and the boom direction change valve 23, but prevents backflow.

[0014] On the other hand, no flow control valves such as the stick flow control valve 28 and boom flow control valve 29 are arranged in the boom main supply oil passage 17, bucket supply oil passage 19, swing supply oil passage 21 and stick main supply oil passage 22, and the supply flow rates from hydraulic pump A or hydraulic pump B via the boom main supply oil passage 17, bucket supply oil passage 19, swing supply oil passage 21 and stick main supply oil passage 22 are supplied directly to the boom direction change valve 23, bucket direction change valve 26, swing direction change valve 24 and stick direction change valve 25 without being flow rate controlled. Furthermore, check valves 30 are provided in each of these boom main supply oil passage 17, bucket supply oil passage 19, swing supply oil passage 21, and stick main supply oil passage 22, and allow the flow of oil from hydraulic pumps A, B to the boom direction change valve 23, bucket direction change valve 26, swing direction change valve 24, and stick direction change valve 25, but prevent reverse flow.

[0015] Thus, the pump port 23p of the boom direction switching valve 23 can be supplied with pressurized oil from hydraulic pump A via the boom main side supply oil passage 17 and with pressurized oil from hydraulic pump B via the boom sub side supply oil passage 20, and the pressurized oil from hydraulic pump B is supplied to the boom direction switching valve 23 in a state where the flow rate is controlled (including a shut-off state) by a boom flow control valve 29 disposed in the boom sub side supply oil passage 20. Also, the pump port 25p of the stick direction switching valve 25 can be supplied with pressurized oil from hydraulic pump B via the stick main side supply oil passage 22 and with pressurized oil from hydraulic pump A via the stick sub side supply oil passage 18, and the pressurized oil from hydraulic pump A is supplied to the stick direction switching valve 25 in a state where the flow rate is controlled (including a shut-off state) by a stick flow control valve 28 disposed in the stick sub side supply oil passage 18.

[0016] Next, the directional control valves 23 to 26 for the boom, for turning, for stick and for bucket will be described. First, the direction control valves 24, 26 for swing and bucket to which pressure oil is supplied from either one of the hydraulic pumps A and B will be described. The direction control valve 24 for swing is a closed center type spool valve that controls the supply and discharge flow rate for the swing motor 7 and switches the supply and discharge direction, and includes left and right pilot ports 24a, 24b connected to left and right electromagnetic proportional valves 42a, 42b (shown in FIG. 2) for swing that output pilot pressure based on a control signal output from the controller 10, a pump port 24p connected to the swing supply oil passage 21, a tank port 24t connected to the tank line T leading to the oil tank 3, one actuator port 24c connected to the left swing port 7a of the swing motor 7, and the other actuator port 24d connected to the right swing port 7b of the swing motor 7. When pilot pressure is not input to both the left and right rotation side pilot ports 24a, 24b, the rotation direction change valve 24 is located in a neutral position N in which supply and discharge control for the rotation motor 7 is not performed. However, when pilot pressure is input to the left rotation side pilot port 24a, the rotation direction change valve 24 switches to the left rotation side operating position X to open the supply valve path 24e from the pump port 24p to one actuator port 24c and the discharge valve path 24f from the other actuator port 24d to the tank port 24t. When pilot pressure is input to the right rotation side pilot port 24b, the rotation direction change valve 24 switches to the right rotation side operating position Y to open the supply valve path 24e from the pump port 24p to the other actuator port 24d and the discharge valve path 24f from the one actuator port 24c to the tank port 24t. The supply flow rate and discharge flow rate to the rotation motor 7 when it is located at the left rotation side operating position X or the right rotation side operating position Y are controlled by the opening areas of the supply valve path 24e and the discharge valve path 24f, and the opening areas are increased or decreased according to the spool movement position associated with an increase or decrease in the pilot pressure output from the left rotation side and right rotation side electromagnetic proportional valves 42a, 42b to the left rotation side and right rotation side pilot ports 24a, 24b.

[0017] In addition, the bucket directional control valve 26 is a closed center type spool valve that controls the supply and discharge flow rate for the bucket cylinder 9 and switches the supply and discharge direction, and is provided with extension side and retraction side pilot ports 26a, 26b that are respectively connected to bucket extension side and retraction side electromagnetic proportional valves 44a, 44b (shown in FIG. 2) that output pilot pressure based on a control signal output from the controller 10, a pump port 26p connected to the bucket supply oil passage 19, a tank port 26t connected to the tank line T, one actuator port 26c connected to the head side port 9a of the bucket cylinder 9, and the other actuator port 26d connected to the rod side port 9b of the bucket cylinder 9. The bucket direction control valve 26 has a structure similar to that of the swing direction control valve 24 described above, and is configured to open a supply valve path 26e from the pump port 26p to the actuator port 26c or 26d, and a discharge valve path 26f from the actuator port 26d or 26c to the tank port 26t, by switching from the neutral position N to the extension side operating position X or the retraction side operating position Y. The supply flow rate and discharge flow rate to the bucket cylinder 9 are controlled by the opening areas of the supply valve path 26e and the discharge valve path 26f, and the opening areas are increased and decreased in accordance with the spool movement position associated with increase and decrease in the pilot pressures output from the bucket side extension side and retraction side solenoid proportional valves 44a, 44b.

[0018] Next, the directional control valves 25, 23 for stick and boom to which pressure oil is supplied from both hydraulic pumps A and B will be described. The directional control valve 25 for stick is a closed center type spool valve that controls the supply and discharge flow rate and the regeneration flow rate for the stick cylinder 8 and switches the supply and discharge direction, and includes extension and retraction pilot ports 25a, 25b connected to the stick extension and retraction solenoid proportional valves 43a, 43b (shown in FIG. 2) that output pilot pressure based on a control signal output from the controller 10, a pump port 25p connected to the stick main supply oil passage 22 and the stick sub supply oil passage 18, a tank port 25t connected to the tank line T, one actuator port 25c connected to the head side port 8a of the stick cylinder 8, and the other actuator port 25d connected to the rod side port 8b of the stick cylinder 8. When pilot pressure is not input to both the extension side and retraction side pilot ports 25a, 25b, the stick directional control valve 25 is located in a neutral position N where supply and discharge control for the stick cylinder 8 is not performed. However, when pilot pressure is input to the extension side pilot port 25a, the stick directional control valve 25 switches to the extension side operating position X and opens the supply valve path 25e from the pump port 25p to one actuator port 25c and the discharge valve path 25f from the other actuator port 25d to the tank port 25t, and opens the regeneration valve path 25g that supplies a portion of the oil discharged from the other actuator port 25d to the one actuator port 25c as regenerated oil. When pilot pressure is input to the retraction side pilot port 25b, the stick directional control valve 25 switches to the retraction side operating position Y and opens the supply valve path 25e from the pump port 25p to the other actuator port 25d and the discharge valve path 25f from the one actuator port 25c to the tank port 25t.The opening areas of the supply valve passage 25e, the discharge valve passage 25f, and the regeneration valve passage 25g are controlled to increase or decrease according to the moving position of the spool that moves by the pilot pressure output from the stick extension side and retraction side electromagnetic proportional valves 43a, 43b, and the discharge flow rate and regeneration flow rate from the stick cylinder 8 are controlled by the opening areas of the discharge valve passage 25f and the regeneration valve passage 25g, respectively. Also, the supply flow rate to the stick cylinder 8 is controlled by the opening area of ​​the supply valve passage 25e of the stick directional control valve 25 when the stick flow control valve 28 closes the stick sub-side supply oil passage 18, as described later, while it is controlled by the opening area of ​​the stick flow control valve 28 and the opening area of ​​the supply valve passage 25e of the stick directional control valve 25 when the stick flow control valve 28 opens the stick sub-side supply oil passage 18.

[0019] In addition, the boom directional control valve 23 is a closed center type spool valve that performs supply and discharge flow rate control and regeneration flow rate control for the boom cylinder 6 and switches the supply and discharge direction, and is provided with extension side and retraction side pilot ports 23a, 23b that are respectively connected to boom extension side and retraction side solenoid proportional valves 41a, 41b (shown in FIG. 2) that output pilot pressure based on a control signal output from the controller 10, a pump port 23p that is connected to the boom main side supply oil passage 17 and the boom sub-side supply oil passage 20, a tank port 23t that is connected to the tank line T, one actuator port 23c that is connected to the head side port 6a of the boom cylinder 6, and the other actuator port 23d that is connected to the rod side port 6b of the boom cylinder 6. The boom direction control valve 23 has the same structure as the stick direction control valve 25 described above, and is configured to open the supply valve passage 23e from the pump port 23p to the actuator port 23c or 23d and the discharge valve passage 24f from the actuator port 23d or 23c to the tank port 23t by switching from the neutral position N to the extension side operating position X and the retraction side operating position Y, and further open the regeneration valve passage 23g that supplies a part of the discharged oil from one actuator port 23c to the other actuator port 23d as regenerated oil in the retraction side operating position Y. The opening areas of the supply valve passage 23e, the discharge valve passage 23f, and the regeneration valve passage 23g are controlled to increase or decrease according to the moving position of the spool that moves by the pilot pressure output from the boom extension side and retraction side electromagnetic proportional valves 41a and 41b, and the discharge flow rate and the regeneration flow rate from the boom cylinder 6 are controlled by the opening areas of the discharge valve passage 23f and the regeneration valve passage 23g, respectively. In addition, the supply flow rate to the boom cylinder 6 is controlled by the opening area of ​​the supply valve path 23e of the boom direction change valve 23 when the boom flow control valve 29 closes the boom sub-side supply oil path 20, and on the other hand, when the boom flow control valve 29 opens the boom sub-side supply oil path 20, the supply flow rate to the boom cylinder 6 is controlled by the opening area of ​​the boom flow control valve 29 and the opening area of ​​the supply valve path 23e of the boom direction change valve 23.

[0020] 1, E and F are bleed lines that branch off from the upstream positions of all the directional control valves 13, 14, 23-26 connected to the pump lines C and D and reach the tank line T, and bleed valves 31 and 32 are provided in the bleed lines E and F. These bleed valves 31 and 32 are operated by pilot pressures output from bleed electromagnetic proportional valves 47a and 47b (shown in FIG. 2) to increase and decrease the bleed flow rate that flows from the hydraulic pumps A and B to the oil tank 3 via the bleed lines E and F, and the bleed electromagnetic proportional valves 47a and 47b are adapted to increase and decrease the output pilot pressure to the bleed valves 31 and 32 based on a control signal output from the controller 10.

[0021] On the other hand, as shown in the block diagram of FIG. 2, the controller 10 (corresponding to the control means of the present invention) includes boom operation detection means 50 for detecting the operation direction and operation amount of a boom operating tool, swing operation detection means 51 for detecting the operation direction and operation amount of a swing operating tool, stick operation detection means 52 for detecting the operation direction and operation amount of a stick operating tool, bucket operation detection means 53 for detecting the operation direction and operation amount of a bucket operating tool, pump A pressure sensor 54a for detecting the pump pressure of hydraulic pump A, pump pressure sensor 54b for detecting the pump pressure of hydraulic pump B, and a control means 55 for detecting the operation direction and operation amount of a control means for ... and pump B pressure sensor 54b for detecting the load pressure on the head side and rod side of boom cylinder 6, boom pressure sensors 55a, 55b for detecting the load pressure on the head side and rod side of boom cylinder 6, swing pressure sensors 56a, 56b for detecting the load pressure on the left swing side and right swing side of swing motor 7, stick pressure sensors 57a, 57b for detecting the load pressure on the head side and rod side of stick cylinder 8, bucket pressure sensors 58a, 58b for detecting the load pressure on the head side and rod side of bucket cylinder 9, and the like are input, and based on these input signals, Based on the above, there are provided boom extension and retraction side solenoid proportional valves 41a, 41b, left and right retraction side solenoid proportional valves 42a, 42b, stick extension and retraction side solenoid proportional valves 43a, 43b, bucket extension and retraction side solenoid proportional valves 44a, 44b, which output pilot pressure to pilot ports 23a, 23b to 26a, 26b of the boom, retraction, stick and bucket directional control valves 23 to 26, respectively, and a stick flow control valve 28 for outputting pilot pressure to the stick flow control valve 28 disposed in the stick sub-side supply oil passage 18. The boom flow control solenoid proportional valve 45 outputs a pilot pressure to the boom flow control valve 29 disposed in the boom sub-side supply oil passage 20, the bleed solenoid proportional valves 47a, 47b output pilot pressure to the bleed valves 31, 32, and the capacity varying means Aa, Ba of the hydraulic pumps A, B. In this way, the boom flow control solenoid proportional valve 45 outputs a pilot pressure to the boom flow control valve 29 disposed in the boom sub-side supply oil passage 20, the boom flow control ...The controller 10 also controls the switching of the straight travel valve 11 and oil supply and discharge control for the left and right travel motors 4, 5, but a description of these controls will be omitted here.

[0022] Next, the control performed by the controller 10 will be described. When detection signals are input from the operation detection means 50-53 for the boom, swing, stick, and bucket, the controller 10 determines a target discharge flow rate based on these detection signals to increase the discharge flow rate of the hydraulic pumps A and B in response to an increase in the amount of operation of the operating tool, and outputs control signals to the capacity varying means Aa and Ba of the hydraulic pumps A and B so as to obtain the target discharge flow rate. In this case, the discharge flow rates of the hydraulic pumps A and B are individually controlled in accordance with the hydraulic pumps A and B that serve as the hydraulic supply sources for the hydraulic actuators being operated.

[0023] Furthermore, when detection signals are input from the respective operation detection means 50-53 for the boom, swing, stick, and bucket, the controller 10 outputs control signals to the bleed solenoid proportional valves 47a, 47b to control the bleed valves 31, 32 in order to reduce (including zero bleed flow rate) the bleed flow rate flowing from the hydraulic pumps A, B to the oil tank 3 in response to an increase in the amount of operation of the operating tool based on these detection signals. In this case, the bleed flow rates of the bleed lines E, F are individually controlled in response to the hydraulic pumps A, B which serve as the hydraulic supply sources for the operated hydraulic actuators.

[0024] Furthermore, when detection signals are input from the respective operation detection means 50-53 for the boom, swing, stick, and bucket, the controller 10 determines a target supply flow rate Qs for the boom cylinder 6, swing motor 7, stick cylinder 8, and bucket cylinder 9 in accordance with the operation amount of each operating tool. In this case, a target operating speed of each hydraulic actuator corresponding to the operating tool operation amount is set in advance, and a target supply flow rate Qs corresponding to the operating tool operation amount is set based on the target operating speed, but for the boom cylinder 6 and stick cylinder 8 which use both hydraulic pumps A and B as hydraulic supply sources, target supply flow rates Qa, Qb (Qa+Qb=Qs) from hydraulic pumps A and B are set for each hydraulic pump, respectively. In setting the target supply flow rates Qa, Qb for the boom cylinder 6 and the stick cylinder 8, the controller 10 sets the total flow rate of the target supply flow rate Qs to the boom cylinder 6 and the stick cylinder 8 from hydraulic pump A or hydraulic pump B to which the boom and stick main supply oil passages 17, 22 are connected when the operating tool operation amount is less than a preset set value L (set value L is set individually for the boom operating tool and the stick operating tool), that is, in the case of the boom cylinder 6, the total flow rate of the target supply flow rate Qs is supplied from hydraulic pump A and not from hydraulic pump B (Qs=Qa, Qb=0), and in the case of the stick cylinder 8, the total flow rate of the target supply flow rate Qs is supplied from hydraulic pump B and not from hydraulic pump A (Qs=Qb, Qa=0). On the other hand, when the operating tool operation amount is equal to or greater than the set value L, the controller 10 sets the total flow rate of the target supply flow rate Qs to be supplied from both hydraulic pumps A and B (Qs=Qa+Qb, Qa≠0, Qb≠0). The controller 10 is equipped with a target supply flow rate setting unit 60 (corresponding to the target supply flow rate setting means of the present invention) that sets the target supply flow rates Qs, Qa, Qb in accordance with the operating tool operation amount. The target supply flow rate setting unit 60 has data such as a map showing the relationship between the operating tool operation amount and the target supply flow rates Qs, Qa, Qb, and sets the target supply flow rates Qs, Qa, Qb using this data. Such data is incorporated into the target supply flow rate setting unit 60 as a control parameter, and it is possible to change the value of the target supply flow rate corresponding to the operating tool operation amount in accordance with, for example, the work content performed by the hydraulic excavator.

[0025] Then, the controller 10 outputs a control signal for pilot pressure output to the electromagnetic proportional valves 41a, 41b-44a, 44b, 45, 46 for the corresponding hydraulic actuators so that the target supply flow rate Qs is supplied to the boom cylinder 6, the swing motor 7, the stick cylinder 8, and the bucket cylinder 9, thereby controlling the directional control valves 23-26 and the flow control valves 28, 29. In this case, for the swing motor 7 and the bucket cylinder 9 which use either one of the hydraulic pumps A and B as the hydraulic supply source, a control signal is output to the swing left and right swing side electromagnetic proportional valves 42a, 42b and the bucket extension and retraction side electromagnetic proportional valves 44a, 44b so that the supply valve passages 24e, 26e of the swing direction control valve 24 and the bucket direction control valve 26 have opening areas corresponding to the operating amount of the operating tool. Thus, supply flow rate control for the swing motor 7 and the bucket cylinder 9 is performed by the opening areas of the supply valve passages 24e, 26e of the swing direction control valve 24 and the bucket direction control valve 26, while discharge flow rate control is also performed by the opening area of ​​the discharge valve passages 24f, 26f at the spool movement positions corresponding to the opening areas of the supply valve passages 24e, 26e.

[0026] On the other hand, for the boom cylinder 6 and the stick cylinder 8 which use both hydraulic pumps A and B as hydraulic supply sources, control signals are output to the boom extension side and retraction side solenoid proportional valves 41a, 41b and the stick extension side and retraction side solenoid proportional valves 43a, 43b so that the supply valve passages 23e, 25e of the boom directional control valve 23 and the stick directional control valve 25 have opening areas corresponding to the operating tool operation amount. Furthermore, when the operating tool operation amount is less than the set value L, the controller 10 outputs control signals to the boom flow rate control solenoid proportional valve 46 and the stick flow rate control solenoid proportional valve 45 to close the boom flow rate control valve 29 disposed in the boom sub-side supply oil passage 20 and the stick flow rate control valve 28 disposed in the stick sub-side supply oil passage 18, whereas when the operating tool operation amount is equal to or greater than the set value L, the controller 10 outputs control signals to the boom flow rate control solenoid proportional valve 46 and the stick flow rate control solenoid proportional valve 45 to open the boom flow rate control valve 29 and the stick flow rate control valve 28. As a result, when the operating amount of the operating tool is less than the set value L, only the supply flow rate from hydraulic pump A or B connected to boom main supply oil passage 17 and stick main supply oil passage 22 is supplied to boom cylinder 6 and stick cylinder 8, and the supply flow rate control to boom cylinder 6 and stick cylinder 8 is performed by the opening area of ​​supply valve passages 23e, 25e (boom direction control valve supply valve passage 23e, stick direction control valve supply valve passage 25e) of boom direction control valve 23 and stick direction control valve 25. Also, the discharge flow rate control and regeneration flow rate control in this case are performed by the opening area of ​​discharge valve passages 23f, 25f and regeneration valve passages 23g, 25g at the spool movement positions corresponding to the opening areas of the supply valve passages 23e, 25e of boom direction control valve 23 and stick direction control valve 25, respectively. On the other hand, when the operating amount of the operating tool is equal to or greater than the set value L, the total flow rate from both hydraulic pumps A and B is supplied to the boom cylinder 6 and the stick cylinder 8, and the supply flow rate control to the boom cylinder and the stick cylinder 8 is performed by the opening areas of the boom direction control valve supply valve passage 23e and the stick direction control valve supply valve passage 25e and the opening areas of the boom flow control valve 29 and the stick flow control valve 28. Even in this case, the discharge flow rate control and the regeneration flow rate control are performed by the opening areas of the discharge valve passages 23f, 25f and the regeneration valve passages 23g, 25g at the spool movement positions corresponding to the opening areas of the supply valve passages 23e, 25e of the boom direction control valve 23 and the stick direction control valve 25, respectively. The controller 10 is provided with a directional control valve opening area setting unit (corresponding to the directional control valve opening area setting means of the present invention) 61 which sets the opening areas of the supply valve passages 23e-26e and the discharge valve passages 23f-26f of the directional control valves 23-26 in accordance with the operating tool operation amount. The directional control valve opening area setting unit 61 is provided with data such as a map showing the relationship between the operating tool operation amount and the opening areas (or spool movement positions) of the supply valve passages 23e-26e and the discharge valve passages 23f-26f of the directional control valves 23-26 and sets the opening areas using the data. Such data is incorporated into the directional control valve opening area setting unit 61 as control parameters, and it is possible to change the values ​​of the opening areas of the supply valve passages 23e-26e and the discharge valve passages 23f-26f of the directional control valves 23-26 which correspond to the operating tool operation amount in accordance with the work content performed by the hydraulic excavator, for example. Incidentally, the relationship between the opening area of ​​the supply valve passages 23e to 26e and the opening area of ​​the discharge valve passages 23f to 26f of each of the directional control valves 23 to 26 is uniquely determined by the spool movement position and cannot be changed. Furthermore, in this embodiment, the boom cylinder 6 and the stick cylinder 8 are hydraulic actuators equivalent to the high flow hydraulic actuator of the present invention as described above, and both the first and second hydraulic pumps of the present invention are used as hydraulic supply sources, but the first hydraulic pump of the present invention is a hydraulic pump to which a main supply oil passage is connected, and the second hydraulic pump is a hydraulic pump to which a sub supply oil passage is connected, so that when the boom cylinder 6 is used as the high flow hydraulic actuator of the present invention, hydraulic pump A becomes the first hydraulic pump and hydraulic pump B becomes the second hydraulic pump, and when the stick cylinder 8 is used as the high flow hydraulic actuator of the present invention, hydraulic pump B becomes the first hydraulic pump and hydraulic pump A becomes the second hydraulic pump.

[0027] As described above, when the operating amount of the operating tool is equal to or greater than the set value L, supply flow control to the boom cylinder 6 and the stick cylinder 8 is performed by the opening areas of the boom direction control valve supply valve path 23e and the stick direction control valve supply valve path 25e and the opening areas of the boom flow control valve 29 and the stick flow control valve 28, and the opening areas of the boom direction control valve supply valve path 23e and the stick direction control valve supply valve path 25e are controlled to become opening areas corresponding to the operating amount of the operating tool, while the opening areas of the boom flow control valve 29 and the stick flow control valve 28 are controlled to become target opening area Af calculated by a calculation unit (corresponding to the calculation means of the present invention) 62 provided in the controller 10. In this case, the calculation unit 62 calculates the target opening area Af so that the flow rates passing through the boom flow control valve 29 and the stick flow control valve 28 become the target supply flow rates Qb, Qa of the hydraulic pumps B, A connected to the boom sub-side supply oil passage 20 and stick sub-side supply oil passage 18 in which the boom flow control valve 29 and stick flow control valve 28 are arranged, and the calculation procedure will be explained below, but since the method of determining the target opening area Af of the boom flow control valve 29 and the stick flow control valve 28 is similar, the following will explain the stick flow control valve 28 as an example. The calculation unit 62 first calculates a differential pressure ΔPs across the supply valve passage 25e for the stick direction control valve when the target supply flow rate Qs passes through, using the following formula (1) based on a target supply flow rate Qs (Qs=Qa+Qb) from both hydraulic pumps A and B to the stick cylinder 8 and an opening area As of the supply valve passage 25e for the stick direction control valve. Furthermore, based on the calculated differential pressure ΔPs across the supply valve passage 25e for the stick direction control valve and a target differential pressure ΔPc that is set in advance as a target differential pressure between the pump pressure of the hydraulic pump A and the load pressure of the stick cylinder 8, the calculation unit 62 calculates a differential pressure ΔPf across the flow control valve for stick 28 using the following formula (2). Furthermore, based on the calculated differential pressure ΔPf before and after the stick flow control valve 28 and the target supply flow rate Qa from the hydraulic pump A to which the stick sub-side supply oil passage 18 is connected, the target opening area Af of the stick flow control valve 28 when the target supply flow rate Qa from the hydraulic pump A passes through the stick flow control valve 28 is calculated using the following equation (3). ΔPs={Qs / (C·As)} 2 (1) ΔPf = ΔPc - ΔPs (2) Af = Qa / (C √ΔPf) (3) In addition, in equations (1), (2), and (3), Qs is the target supply flow rate from both hydraulic pumps, the first and second hydraulic pumps A and B, Qa is the target supply flow rate from hydraulic pump A, As is the opening area of ​​the supply valve passage 25e for the stick directional control valve, Af is the target opening area of ​​the stick flow control valve 28, ΔPc is the target differential pressure between the pump pressure of hydraulic pump A and the load pressure of the stick cylinder 8, ΔPs is the differential pressure before and after the supply valve passage 25e for the stick directional control valve, ΔPf is the differential pressure before and after the stick flow control valve 28, and C is a coefficient. Moreover, the above formulas (1) and (3) are used to calculate the flow rate of an orifice as shown in the following formula (4). Q = C A √ΔP (4) In equation (4), Q is the flow rate through the orifice, A is the opening area of ​​the orifice, ΔP is the differential pressure before and after the orifice, and C is a coefficient. Furthermore, as described above, the target differential pressure ΔPc is a value that is set in advance as a target differential pressure between the pump pressure of the hydraulic pump A and the load pressure of the stick cylinder 8, and the relationship between the pump flow rate relative to the operating tool operation amount and the opening area of ​​the stick directional control valve supply valve passage 25e is designed and adjusted in advance so that the target differential pressure ΔPc is maintained. Note that the target differential pressure ΔPc may be a fixed value or a value given by a map relative to the operating tool operation amount, and is set by a target differential pressure setting unit (corresponding to the target differential pressure setting means of the present invention) 63 provided in the controller 10.

[0028] By controlling the opening area of ​​the stick flow control valve 28 to the target opening area Af calculated in this manner, the flow rate passing through the stick flow control valve 28 is controlled to the target supply flow rate Qa from the hydraulic pump A to the stick cylinder 8, and further, the flow rate passing through the stick directional control valve supply valve path 25e is controlled to the target supply flow rate Qs from both the first and second hydraulic pumps A, B to the stick cylinder 8. Thus, even if the opening area As of the stick directional control valve supply valve path 25e is set according to the operating amount of the operating tool, the supply flow rate to the stick cylinder 8 can be increased or decreased by increasing or decreasing the opening area of ​​the stick flow control valve 28, and the discharge flow rate and regeneration flow rate from the stick cylinder 8 are controlled by the opening areas of the discharge valve path 25f and regeneration valve path 25g of the stick directional control valve 25. Therefore, by increasing or decreasing the opening area of ​​the stick flow control valve 28, the relationship between the supply flow rate and the discharge flow rate and regeneration flow rate for the stick cylinder 8 can be changed.

[0029] Next, the control of the stick directional control valve 25 and the stick flow control valve 28 by the controller 10 when the stick operating tool is operated alone to the extension side (stick-in side) will be specifically described. First, when the stick operating tool is operated independently to the extension side, the controller 10 sets the target supply flow rates Qa, Qb from the hydraulic pumps A, B to the stick cylinder 8 in accordance with the operating tool operation amount, and in this case, when the operating tool operation amount is less than a preset value L, the target supply flow rate Qb of the hydraulic pump B connected to the stick main side supply oil passage 22 is set to increase in accordance with an increase in the operating tool operation amount, while the target supply flow rate Qa of the hydraulic pump A connected to the stick sub side supply oil passage 18 is set to "zero". When the operating tool operation amount becomes equal to or greater than the set value L, the target supply flow rate Qb of the hydraulic pump B is further increased to the maximum flow rate, while the target supply flow rate Qa of the hydraulic pump A is set to increase in accordance with an increase in the operating tool operation amount (see FIG. 3). Furthermore, when the stick operating tool is operated independently to the extension side, the controller 10 sets the opening area As of the supply valve passage 25e of the stick directional control valve 25 in accordance with the operating amount of the operating tool. In this case, the opening areas of the discharge valve passage 25f and the regeneration valve passage 25g are also set according to the spool movement position corresponding to the opening area As of the supply valve passage 25e. Furthermore, when the operating amount of the operating tool is equal to or greater than the set value L, the controller 10 calculates the target opening area Af by using the above-mentioned formulas (1), (2), and (3) to set the passing flow rate of the stick flow control valve 28 disposed in the stick sub-side supply oil passage 18 to the target supply flow rate Qa of the hydraulic pump A. The controller 10 then outputs a control signal to the stick extension side electromagnetic proportional valve 43a to switch the stick directional control valve 25 to the extension side operating position X, and controls the opening area of ​​the supply valve path 25e in the extension side operating position X to be the set opening area As. Furthermore, the controller 10 outputs a control signal to the stick flow rate control electromagnetic proportional valve 45 to control the supply flow rate from the stick flow rate control valve 28 to the stick directional control valve 25, and in this case, when the operating amount of the operating tool is less than the set value L, the controller 10 controls the stick flow rate control valve 28 to close, whereas when the operating amount of the operating tool is equal to or greater than the set value L, the controller 10 controls the stick flow rate control valve 28 to be the calculated target opening area Af. As a result, when the operating amount of the operating tool is less than the set value L, pressure oil is supplied to the stick cylinder 8 only from hydraulic pump B, and the supply flow rate is controlled by the opening area As of the supply valve path 25e of the stick directional control valve 25, while when the operating amount is equal to or greater than the set value L, pressure oil is supplied from both hydraulic pumps A and B, and the supply flow rate is controlled by the opening area As of the supply valve path 25e of the stick directional control valve 25 and the opening area Af of the stick flow control valve 28. In addition, the discharge flow rate and regeneration flow rate of the stick cylinder 8 are controlled by the opening areas of the discharge valve path 25f and regeneration valve path 25g of the stick directional control valve 25, respectively.

[0030] In the present embodiment configured as described above, the hydraulic control system of the hydraulic excavator includes hydraulic pumps A and B, a boom cylinder 6 and a stick cylinder 8 using both of these hydraulic pumps A and B as hydraulic supply sources, and a swing motor 7 and a bucket cylinder 9 using one of the hydraulic pumps A and B as a hydraulic supply source. Taking the stick cylinder 8 as an example, the supply and discharge flow rate control for the boom cylinder 6 and the stick cylinder 8 using both of the hydraulic pumps A and B as hydraulic supply sources is the same control. A stick direction switching valve 25 having a supply valve path 25e and a discharge valve path 25f and switching the supply and discharge direction, a stick main side supply oil path 22 and a stick sub side supply oil path 18 connecting hydraulic pumps B and A to a pump port 25p of the stick direction switching valve 25, a stick flow control valve 28 arranged in the stick sub side supply oil path 18 and controlling the supply flow rate from the hydraulic pump A to the stick direction switching valve 25, and a controller for controlling the operation of the stick direction switching valve 25 and the stick flow control valve 28. When the operation amount of the stick operating tool is less than the set value L, the stick flow control valve 28 is closed so that only the supply flow rate from the hydraulic pump B via the stick main side supply oil passage 22 is supplied to the stick directional control valve 25, and when the operation amount of the stick operating tool is equal to or greater than the set value L, the stick flow control valve 28 is opened so that the supply flow rate from the hydraulic pump A via the stick sub side supply oil passage 18 and the supply flow rate from the hydraulic pump B via the stick main side oil passage 22 are joined together to supply the stick directional control valve 25. On the other hand, the discharge flow rate control for the stick cylinder 8 is performed based on the opening area of ​​the discharge valve path 25f of the stick direction control valve 25, and the supply flow rate control is performed based on the opening area of ​​the supply valve path 25e of the stick direction control valve 25 when the stick flow control valve 28 is closed, and based on the opening area of ​​the stick flow control valve 28 and the opening area of ​​the supply valve path 25e of the stick direction control valve 25 when the stick flow control valve 28 is open.The controller 10 includes a target supply flow rate setting unit 60 that sets target supply flow rates Qa, Qb from the hydraulic pumps A, B to the stick cylinder 8 for each hydraulic pump in accordance with the amount of operation of the stick oil operating tool, a directional control valve opening area setting unit 61 that sets the opening area of ​​the supply valve path 25e and the discharge valve path 25f of the stick directional control valve 25 in accordance with the amount of operation of the stick operating tool, a target differential pressure setting unit 63 that sets a target differential pressure ΔPc between the pump pressure of the hydraulic pump A and the load pressure of the stick cylinder 8, and a calculation unit 62 that calculates a target opening area Af of the stick flow rate control valve 28 for supplying the target supply flow rate Qa from the hydraulic pump A to the stick cylinder 8 based on the set target supply flow rates Qa, Qb, the opening area As of the stick directional control valve supply valve path 25e, and the target differential pressure ΔPc, and controls the operation of the stick flow rate control valve 28 to achieve the target opening area Af calculated by the calculation unit 62.

[0031] Thus, the boom cylinder 6 and the stick cylinder 8, which have both hydraulic pumps A and B as their hydraulic supply sources, are supplied with pressurized oil only from one of the hydraulic pumps A or B when the operating tool operation amount is less than the set value L, and are supplied with pressurized oil from both hydraulic pumps A and B when the operating tool operation amount is equal to or greater than the set value L. In addition, when pressurized oil is supplied from both hydraulic pumps A and B, the supply flow rate control is performed based on the opening area of ​​the boom and stick flow control valves 29 and 28 disposed in the boom and stick sub-side supply oil passages 20 and 18 connected to the other hydraulic pump B or A, and the boom and stick directional switches 30 and 31. While control is based on the opening area of ​​the supply valve passages 23e, 25e of the switching valves 23, 25, discharge flow rate control is based on the opening area of ​​the discharge valve passages 23f, 25f of the boom and stick directional control valves 23, 25. As a result, even if the relationship in the opening area between the supply valve passages 23e, 25e and the discharge valve passages 23f, 25f in the boom and stick directional control valves 23, 25 is unique, by increasing or decreasing the opening area of ​​the boom and stick flow control valves 29, 28, it is possible to change the relationship between the supply flow rates and discharge flow rates for the boom cylinder 6 and the stick cylinder 8. In this way, in the range where the supply flow rate of pressurized oil is high from both hydraulic pumps A, B (the operating amount of the operating tool is equal to or greater than the set value L), the relationship between the supply flow rate and the discharge flow rate can be changed, thereby improving operability and work efficiency. However, in the range where the supply flow rate is low where pressurized oil is supplied only from one of the hydraulic pumps A or B (the operating amount of the operating tool is less than the set value L), the supply flow rate can be controlled only by the boom and stick directional control valves 23, 25, which makes it possible to omit the flow control valve for the main supply oil passage to which one of the hydraulic pumps A or B is connected and the solenoid proportional valve that pilots the flow control valve, thereby contributing to a reduction in the number of parts, a simplification of the circuit, and cost reduction.

[0032] As described above, in this embodiment, by arranging the boom and stick flow control valves 29, 28 in the boom and stick sub-side supply oil passages 20, 18, it is possible to change the relationship between the supply flow rate and the discharge flow rate in the range where pressure oil is supplied from both hydraulic pumps A, B. In this configuration, control of the supply flow rate to the boom cylinder 6 and stick cylinder 8 when pressure oil is supplied from both hydraulic pumps A, B is performed by the opening area of ​​the boom and stick flow control valves 29, 28 and the opening area of ​​the supply valve passages 23e, 25e of the boom and stick directional control valves 23, 25. Therefore, it is not necessary to design the opening area of ​​the supply valve passages 23e, 25e of the boom and stick directional control valves 23, 25 to be so large that no pressure difference occurs before and after the supply valve passages 23e, 25e, and it is possible to avoid increasing the size of the boom and stick directional control valves 23, 25. Moreover, when controlling the supply flow rates to the boom cylinder 6 and the stick cylinder 8 by the opening areas of the boom and stick flow control valves 29 and 28 and the opening areas of the supply valve passages 23e and 25e of the boom and stick directional control valves 23 and 25, the controller 10 sets target supply flow rates Qa and Qb from the hydraulic pumps A and B to the boom cylinder 6 and the stick cylinder 8, the opening areas As of the supply valve passages 23e and 25e of the boom and stick directional control valves 23 and 25, and the pump pressures A and B of the hydraulic pumps B and A which supply pressure oil to the boom and stick flow control valves 29 and 28. and the target pressure difference ΔPc between the load pressure of the boom cylinder 6 and the stick cylinder 8, the opening area of ​​the boom and stick flow control valves 29, 28 can be controlled to an opening area according to the target supply flow rates Qa, Qb, the opening area As of the boom and stick directional control valve supply valve passages 23e, 25e, and the target pressure difference ΔPc between the pump pressure of the hydraulic pumps B, A and the load pressure of the boom cylinder 6 and stick cylinder 8, allowing for highly accurate supply flow rate control.

[0033] Furthermore, when calculating the target opening area Af of the boom and stick flow control valves 29, 28, the calculation unit 62 calculates a front-to-rear differential pressure ΔPs of the boom and stick directional control valve supply valve passages 23e, 25e based on the target supply flow rates Qa, Qb from the hydraulic pumps A, B to the boom cylinder 6 and the stick cylinder 8 and the opening area As of the boom and stick directional control valve supply valve passages 23e, 25e, and further calculates the boom and stick flow control valves 29, 29 based on the calculated front-to-rear differential pressure ΔPs of the boom and stick directional control valve supply valve passages 23e, 25e and the target differential pressure ΔPc. , 28 is calculated, and a target opening area Af of the boom and stick flow control valves 29, 28 is calculated based on the calculated front-to-rear differential pressure ΔPf of the boom and stick flow control valves 29, 28 and the target supply flow rates Qb, Qa of the hydraulic pumps B, A that supply pressure oil to the boom and stick flow control valves 29, 28. This makes it possible to accurately calculate the target opening area Af of the boom and stick flow control valves 29, 28 for supplying the target supply flow rates Qb, Qa to the boom cylinder 6 and stick cylinder 8, which contributes to improving the accuracy of supply flow rate control.

[0034] Next, a second embodiment of the present invention will be described with reference to FIG. 5. The second embodiment differs from the first embodiment in the oil supply / drainage control for the bucket cylinder 9, but other parts are similar to those of the first embodiment, and the same reference numerals are used for parts similar to those of the first embodiment, and the description thereof will be omitted. In the first embodiment, the present invention is embodied in the oil supply / drainage control of a large flow rate actuator (boom cylinder 6 and stick cylinder 8 in the first embodiment) that uses both the first and second hydraulic pumps as hydraulic supply sources, but in the second embodiment, the present invention is embodied in the oil supply / drainage control of a hydraulic actuator (bucket cylinder 9 is exemplified in the second embodiment) that uses one hydraulic pump as a hydraulic supply source. Also, FIG. 2 is shared with the first embodiment.

[0035] In the second embodiment, a bucket flow control valve 65 that controls the supply flow rate from the hydraulic pump A to the bucket direction control valve 26 is disposed in bucket supply oil passage 19 leading from the hydraulic pump A to the pump port 26p of the bucket direction control valve 26. The bucket flow control valve 65 is a poppet valve that performs flow control by being pilot operated by a bucket flow control solenoid proportional valve (not shown) that operates based on a control signal from the controller 10, and has a similar structure to the stick flow control valve 28 and the boom flow control valve 29 of the first embodiment.

[0036] Moreover, the bucket directional control valve 26 has a structure similar to that of the first embodiment and includes extension side and retraction side pilot ports 26a, 26b, a pump port 26p, a tank port 26t, one actuator port 26c, and the other actuator port 26d, and is configured to switch from a neutral position N to an extension side operating position X or a retraction side operating position Y by pilot pressures output from the bucket extension side and retraction side solenoid proportional valves 44a, 44b, and to open a supply valve path 26e extending from the pump port 26p to the actuator port 26c or 26d, and a discharge valve path 26f extending from the actuator port 26d or 26c to the tank port 26t. The opening areas of the supply valve path 26e and the discharge valve path 26f are controlled to be increased or decreased in accordance with the movement position of the spool, which is moved by the pilot pressures output from the bucket extension side and retraction side electromagnetic proportional valves 44a, 44b, and the discharge flow rate from the bucket cylinder 9 is controlled by the opening area of ​​the discharge valve path 26f, while the supply flow rate to the bucket cylinder 9 is controlled by the opening area of ​​the supply valve path 26e of the bucket directional control valve 26 and the opening area of ​​the bucket flow control valve 65 located upstream of the bucket directional control valve 26.

[0037] Then, when a detection signal is input from bucket operation detection means 53, controller 10 sets a target supply flow rate Qs for bucket cylinder 9 in accordance with the amount of operation of the operating tool in target supply flow rate setting unit 60. Furthermore, directional control valve opening area setting unit 61 sets the opening area As of supply valve path 26e of bucket direction control valve 26 in accordance with the amount of operation of the operating tool, and controls bucket direction control valve 26 to achieve the set opening area As. In this case, the opening area of ​​discharge valve path 26f is also set by the spool movement position corresponding to the opening area As of supply valve path 26e. Furthermore, controller 10 calculates in calculation unit 62 a target opening area Af for setting the flow rate passing through bucket flow control valve 65 to the target supply flow rate Qs, and controls bucket flow control valve 65 to achieve the calculated target opening area Af.

[0038] When calculating the target opening area Af of the bucket flow rate control valve 65, the calculation unit 62 calculates a differential pressure ΔPs across the bucket direction control valve supply valve path 26e when the target supply flow rate Qs passes, using the following equation (5) based on the target supply flow rate Qs to the bucket cylinder 9 and the opening area As of the bucket direction control valve supply valve path 26e. Furthermore, based on the calculated differential pressure ΔPs across the bucket direction control valve supply valve path 26e and a target differential pressure ΔPc that is set in advance as a target differential pressure between the pump pressure of the hydraulic pump A and the load pressure of the bucket cylinder 9, the calculation unit 62 calculates a differential pressure ΔPf across the bucket flow rate control valve 65, using the following equation (6). Furthermore, based on the calculated differential pressure ΔPf before and after the bucket flow control valve 65 and the target supply flow rate Qs to the bucket cylinder 9, the target opening area Af of the bucket flow control valve 65 at the time when the target supply flow rate Qs passes through the bucket flow control valve 65 is calculated using the following equation (7). ΔPs={Qs / (C·As)} 2 (5) ΔPf = ΔPc - ΔPs (6) Af = Qs / (C √ΔPf) (7) In addition, in equations (5), (6), and (7), Qs is the target supply flow rate for bucket cylinder 9, As is the opening area of ​​bucket directional control valve supply valve passage 26e, Af is the target opening area of ​​bucket flow control valve 65, ΔPc is the target differential pressure between the pump pressure of hydraulic pump A and the load pressure of bucket cylinder 9, ΔPs is the differential pressure before and after bucket directional control valve supply valve passage 26e, ΔPf is the differential pressure before and after bucket flow control valve 65, and C is a coefficient.

[0039] Then, by controlling the opening area of ​​the bucket flow control valve 65 to become the target opening area Af calculated in this manner, the flow rate passing through the bucket flow control valve 65 and the bucket direction control valve supply valve path 26e is controlled to become the target supply flow rate Qs to the bucket cylinder 8. Thus, even if the opening area As of the bucket direction control valve supply valve path 26e is set in accordance with the amount of operation of the operating tool, the supply flow rate to the bucket cylinder 9 can be controlled to increase or decrease by increasing or decreasing the opening area of ​​the bucket flow control valve 65, and the discharge flow rate from the bucket cylinder 9 is controlled by the opening area of ​​the discharge valve path 26f of the bucket direction control valve 26, so that by increasing or decreasing the opening area of ​​the bucket flow control valve 65, the relationship between the supply flow rate and the discharge flow rate to the bucket cylinder 9 can be changed.

[0040] In the second embodiment configured as described above, a bucket flow control valve 65 for controlling the supply flow rate from the hydraulic pump A to the bucket direction switching valve 26 is provided upstream of the bucket direction switching valve 26 which has a supply valve path 26e and a discharge valve path 26f for the bucket cylinder 9 and switches the supply and discharge direction. The discharge flow rate control for the bucket cylinder 9 is performed based on the opening area of ​​the discharge valve path 26f of the bucket direction switching valve 26, and the supply flow rate control is performed based on the opening area of ​​the supply valve path 26e of the bucket direction switching valve 26 and the opening area of ​​the bucket flow control valve 65. The controller 10 is configured to include a target supply flow rate setting unit 60 for setting a target supply flow rate Qs from the hydraulic pump A to the bucket cylinder 9 in accordance with the operation amount of the bucket operating tool, and a target supply flow rate setting unit 62 for setting the supply valve path 26e and the discharge valve path 26f of the bucket direction switching valve 26 in accordance with the operation amount of the bucket operating tool. a target differential pressure setting unit 63 that sets a target pressure difference ΔPc between the pump pressure of hydraulic pump A and the load pressure of bucket cylinder 9, and a calculation unit 62 that calculates a target opening area Af of a bucket flow control valve 65 for supplying the target supply flow rate Qs to the bucket cylinder 9, based on the set target supply flow rate Qs, the opening area As of the bucket directional control valve supply valve path 26e and the target differential pressure ΔPc, and operation of the bucket flow control valve 65 is controlled to achieve the target opening area Af calculated by the calculation unit 62.

[0041] Thus, control of the supply flow rate to the bucket cylinder 9 is performed based on the opening area of ​​the supply valve path 26e of the bucket direction control valve 26 and the opening area of ​​the bucket flow control valve 65. As a result, even if the relationship in the opening area between the supply valve path 26e and the discharge valve path 26f in the bucket direction control valve 26 is unique, by increasing or decreasing the opening area of ​​the bucket flow control valve 65, it is possible to change the relationship between the supply flow rate and discharge flow rate to the bucket cylinder 9.

[0042] As described above, in the second embodiment, by arranging the bucket flow rate control valve 65 upstream of the bucket direction control valve 26, it is possible to change the relationship between the supply flow rate and the discharge flow rate to the bucket cylinder 9. In this configuration, the supply flow rate to the bucket cylinder 9 is controlled by the opening area of ​​the supply valve path 26e of the bucket direction control valve 26 and the opening area of ​​the bucket flow control valve 65. Therefore, there is no need to design the opening area of ​​the supply valve path 26e of the bucket direction control valve 26 to be so large that no pressure difference occurs before and after the supply valve path 26e, and it is possible to avoid an increase in the size of the bucket direction control valve 26. Moreover, when controlling the supply flow rate to the bucket cylinder 9 using the opening area of ​​the supply valve path 26e of the bucket directional control valve 26 and the opening area of ​​the bucket flow control valve 65, the controller 10 is configured to calculate the target opening area Af of the bucket flow control valve 65 based on the target supply flow rate Qs from hydraulic pump A to the bucket cylinder 9, the opening area As of the supply valve path 26e of the bucket directional control valve 26, and the target differential pressure ΔPc between the pump pressure of hydraulic pump A and the load pressure of the bucket cylinder 9, so that the opening area of ​​the bucket flow control valve 65 can be controlled to an opening area according to the target supply flow rate Qs, the opening area As of the supply valve path 26e of the bucket directional control valve, and the target differential pressure ΔPc between the pump pressure and the load pressure of the bucket cylinder 9, thereby enabling highly accurate supply flow rate control.

[0043] Furthermore, in calculating the target opening area Af of the bucket flow control valve 65, the calculation unit 62 calculates a front-to-back pressure differential ΔPs of the bucket direction control valve supply valve path 26e based on the target supply flow rate Qs from the hydraulic pump A to the bucket cylinder 9 and the opening area As of the bucket direction control valve supply valve path 26e, further calculates a front-to-back pressure differential ΔPf of the bucket flow control valve 65 based on the calculated front-to-back pressure differential ΔPs of the bucket direction control valve supply valve path 26e and the target pressure differential ΔPc, and calculates the target opening area Af of the bucket flow control valve 65 based on the calculated front-to-back pressure differential ΔPf of the bucket flow control valve 65 and the target supply flow rate Qs. This makes it possible to accurately calculate the target opening area Af of the bucket flow control valve 65 for supplying the target supply flow rate Qs to the bucket cylinder 9, which contributes to improving the accuracy of supply flow rate control.

[0044] Of course, the present invention is not limited to the first and second embodiments. For example, a flow control valve having a structure similar to that of the flow control valve arranged in the sub-side supply oil passage may be arranged in the main-side supply oil passage (in the first embodiment, the main-side supply oil passages 17 and 22 for the boom and stick) that connects the first hydraulic pump to the directional control valve for the large flow rate hydraulic actuator. In this case, the flow control valve arranged in the main-side supply oil passage is set to open over the entire operation range of the operating tool, and its opening area is controlled in the same way as the opening area of ​​the flow control valve arranged in the sub-side supply oil passage, thereby making it possible to change the relationship between the supply flow rate and the discharge flow rate for the large flow rate hydraulic actuator over the entire operation range. Furthermore, in carrying out the present invention, the opening area of ​​the flow control valve calculated by the calculation means can be corrected based on the detection values ​​of pressure sensors that measure the pump pressure of the hydraulic pump, the load pressure of the hydraulic actuator, etc., and by configuring in this way, even more accurate supply flow rate control can be achieved. Furthermore, the present invention is not limited to hydraulic excavators, but can of course be applied to various types of work machines provided with hydraulic actuators. [Industrial Applicability]

[0045] The present invention can be used in a hydraulic control system for a work machine such as a hydraulic excavator. [Explanation of symbols]

[0046] 6 Boom cylinder 8 Stick Cylinder 9 Bucket Cylinder 10 Controller 17 Main oil supply line for boom 18 Sub-side oil supply passage for stick 19. Bucket oil supply line 20 Boom sub-side oil supply line 22 Main oil supply passage for stick 23 Boom directional control valve 23e Boom directional control valve supply passage 23f Boom directional control valve discharge passage 25 Stick directional control valve 25e Stick directional control valve supply passage 25f Stick directional control valve exhaust valve passage 26 Bucket directional control valve 26e Bucket directional control valve supply passage 26f Bucket directional control valve discharge passage 28 Flow control valve for sticks 29 Boom flow control valve 60 Target supply flow rate setting section 61 Directional control valve opening area setting unit 62 Arithmetic section 63 Target differential pressure setting unit 65 Bucket flow control valve A, B hydraulic pump

Claims

1. A hydraulic control system including a hydraulic pump and a hydraulic actuator using the hydraulic pump as a hydraulic supply source, a directional control valve having a supply valve path and a discharge valve path for the hydraulic actuator and switching the supply and discharge direction, a flow control valve arranged upstream of the directional control valve and controlling the supply flow rate from the hydraulic pump to the directional control valve, and control means for controlling the operation of the directional control valve and the flow control valve, The discharge flow rate control for the hydraulic actuator is performed based on the opening area of ​​the discharge valve passage of the directional control valve, and the supply flow rate control is performed based on the opening area of ​​the supply valve passage of the directional control valve and the opening area of ​​the flow control valve, The control means includes target supply flow rate setting means for setting a target supply flow rate from the hydraulic pump to the hydraulic actuator in accordance with the amount of operation of the hydraulic actuator operating tool, directional control valve opening area setting means for setting the opening areas of the supply valve path and the discharge valve path of the directional control valve in accordance with the amount of operation of the hydraulic actuator operating tool, target differential pressure setting means for setting in advance a target differential pressure between the pump pressure of the hydraulic pump and the load pressure of the hydraulic actuator, and calculation means for calculating a target opening area of ​​a flow control valve for supplying the target supply flow rate to the hydraulic actuator based on the set target supply flow rate, the opening area of ​​the directional control valve supply valve path and the target differential pressure, and controls operation of the flow control valve so as to achieve the target opening area calculated by the calculation means, and a hydraulic control system characterized in that, when calculating the target opening area of ​​the flow control valve, the calculation means calculates a differential pressure across the supply valve passage of the directional control valve based on the target supply flow rate and the opening area of ​​the supply valve passage of the directional control valve, further calculates a differential pressure across the flow control valve based on the differential pressure across the supply valve passage of the directional control valve and the target differential pressure, and calculates the target opening area of ​​the flow control valve based on the differential pressure across the flow control valve and the target supply flow rate.

2. According to claim 1, the hydraulic control system includes first and second hydraulic pumps, a high flow rate hydraulic actuator using both the first and second hydraulic pumps as hydraulic supply sources, a directional control valve having a supply valve path and a discharge valve path for the high flow rate hydraulic actuator and switching the supply and discharge direction, a main side supply oil passage and a sub side supply oil passage connecting the first and second hydraulic pumps to pump ports of the directional control valve, respectively, and a flow control valve is disposed in the sub side supply oil passage for controlling the supply flow rate from the second hydraulic pump to the directional control valve, When the operation amount of the operating tool for the large flow rate hydraulic actuator is less than a set value, the flow control valve is closed so that only the supply flow rate from the first hydraulic pump via the main side supply oil passage is supplied to the directional control valve, and when the operation amount of the operating tool for the large flow rate hydraulic actuator is equal to or greater than the set value, the flow control valve is opened so that the supply flow rate from the second hydraulic pump via the sub side supply oil passage and the supply flow rate from the first hydraulic pump via the main side oil passage are joined together and supplied to the directional control valve, The discharge flow rate control for the large flow rate hydraulic actuator is performed based on the opening area of ​​the discharge valve passage of the directional control valve, and the supply flow rate control is performed based on the opening area of ​​the supply valve passage of the directional control valve when the flow control valve is closed, and based on the opening area of ​​the flow control valve and the opening area of ​​the supply valve passage of the directional control valve when the flow control valve is open; the target supply flow rate setting means provided in the control means sets target supply flow rates from the first and second hydraulic pumps to the high flow hydraulic actuator for each hydraulic pump in accordance with the amount of operation of the operating tool for the high flow hydraulic actuator, the directional control valve opening area setting means sets the opening areas of the supply valve path and the discharge valve path of the directional control valve in accordance with the amount of operation of the operating tool for the high flow hydraulic actuator, the target differential pressure setting means sets a target differential pressure between the pump pressure of the second hydraulic pump and the load pressure of the high flow hydraulic actuator, and the calculation means calculates a target opening area of ​​the flow control valve for supplying the target supply flow rate from the second hydraulic pump to the high flow hydraulic actuator based on the set target supply flow rate, the opening area of ​​the directional control valve supply valve path and the target differential pressure; a hydraulic control system characterized in that, when calculating the target opening area of ​​the flow control valve, the calculation means calculates a differential pressure across the directional control valve supply valve passage based on the target supply flow rates from the first and second hydraulic pumps to the high flow hydraulic actuator and the opening area of ​​the directional control valve supply valve passage, further calculates a differential pressure across the flow control valve based on the differential pressure across the directional control valve supply valve passage and the target differential pressure, and calculates the target opening area of ​​the flow control valve based on the differential pressure across the flow control valve and the target supply flow rate from the second hydraulic pump to the high flow hydraulic actuator.

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