Control system for work machine

Abstract

This control system for a work machine comprises: a pump that discharges hydraulic oil; a meter-in valve that controls a flow rate of the hydraulic oil supplied from the pump to an actuator; a valve circuit that connects the pump and the meter-in valve; a bleed circuit that branches from the valve circuit and is connected to a tank; a bleed valve that is disposed in the bleed circuit and controls the flow rate of the hydraulic oil discharged from the valve circuit to the tank by changing a valve opening; and a controller. The controller: calculates a valve circuit target flow rate indicating a target flow rate of the hydraulic oil supplied to the valve circuit; calculates a valve circuit target pressure indicating a target pressure of the hydraulic oil supplied to the valve circuit; calculates a leakage flow rate indicating an estimated flow rate of the hydraulic oil leaking from the valve circuit; calculates, on the basis of the valve circuit target flow rate, the valve circuit target pressure, and the leakage flow rate, a target opening area of the bleed valve when the hydraulic oil is discharged from the valve circuit to the tank via the bleed valve; and controls the bleed valve on the basis of the target opening area.

Description

Work machine control system

[0001] The present disclosure relates to a control system for a work machine.

[0002] In the technical field related to work machines, there is known a hydraulic circuit as disclosed in Patent Document 1. In Patent Document 1, the hydraulic circuit includes a discharge passage connected to a hydraulic pump, a bypass circuit connected to the discharge passage, and a bleed-off valve disposed in the bypass circuit.

[0003] Japanese Patent Application Publication No. 04-136504

[0004] The hydraulic oil discharged from the hydraulic pump is supplied to the hydraulic actuator via a meter-in valve. It is necessary to supply the hydraulic oil at an appropriate pressure and flow rate to the meter-in valve so that the hydraulic actuator operates properly.

[0005] An object of the present disclosure is to supply hydraulic oil at an appropriate pressure and flow rate to a meter-in valve.

[0006] According to the present disclosure, there is provided a control system for a work machine including a pump that discharges hydraulic oil, a meter-in valve that controls the flow rate of hydraulic oil supplied from the pump to an actuator, a valve circuit that connects the pump and the meter-in valve, a bleed circuit that branches off from the valve circuit and is connected to a tank, a bleed valve that is disposed in the bleed circuit and controls the flow rate of hydraulic oil discharged from the valve circuit to the tank by changing a valve opening, and a controller. The controller calculates a valve circuit target flow rate that indicates a target flow rate of hydraulic oil to be supplied to the valve circuit, calculates a valve circuit target pressure that indicates a target pressure of hydraulic oil to be supplied to the valve circuit, calculates a leakage flow rate that indicates an estimated flow rate of hydraulic oil leaking from the valve circuit, and calculates a target opening area of ​​the bleed valve when hydraulic oil is discharged from the valve circuit to the tank via the bleed valve based on the valve circuit target flow rate, the valve circuit target pressure, and the leakage flow rate, and controls the bleed valve based on the target opening area.

[0007] According to the present disclosure, hydraulic oil at an appropriate pressure and flow rate is supplied to the meter-in valve.

[0008] FIG. 1 is a side view showing a work machine according to a first embodiment. FIG. 2 is a hardware configuration diagram showing a controller according to the first embodiment. FIG. 3 is a diagram schematically showing a control system for a work machine according to the first embodiment. FIG. 4 is a flowchart showing a control method for a work machine according to the first embodiment. FIG. 5 is a diagram for explaining a method for calculating an actuator target flow rate and a valve circuit target flow rate according to the first embodiment. FIG. 6 is a diagram for explaining a method for calculating an actuator target pressure and a valve circuit target pressure according to the first embodiment. FIG. 7 is a flowchart showing a method for calculating a leakage flow rate according to the first embodiment. FIG. 8 is a diagram for explaining the relationship between the flow rate of hydraulic oil and the opening area of ​​a bleed valve according to the first embodiment. FIG. 9 is a diagram for explaining the relationship between the flow rate of hydraulic oil and the opening area of ​​a bleed valve according to a comparative example. FIG. 10 is a diagram for explaining the relationship between the flow rate of hydraulic oil and the opening area of ​​a bleed valve according to a modification of the first embodiment. FIG. 11 is a diagram schematically showing a control system for a work machine according to a second embodiment. FIG. 12 is a flowchart showing a control method for a work machine according to the second embodiment. FIG. 13 is a diagram for explaining a method for calculating the opening area of ​​a meter-in valve and an estimated valve circuit flow rate according to the second embodiment. Fig. 14 is a flowchart showing a method for calculating a leakage flow rate according to the second embodiment. Fig. 15 is a flowchart showing a method for controlling a work machine according to the third embodiment. Fig. 16 is a diagram for explaining a method for calculating a valve circuit target flow rate according to the third embodiment. Fig. 17 is a diagram showing the relationship between a lever operation amount, a valve circuit target flow rate, and a valve target pressure according to the third embodiment. Fig. 18 is a diagram showing the relationship between a lever operation amount, a pump target flow rate, and a valve target pressure according to the third embodiment.

[0009] First Embodiment A first embodiment will be described.

[0010] <Working Machine> Figure 1 is a side view showing a working machine 1 according to the first embodiment. The working machine 1 operates at a work site. Examples of the working machine 1 include a hydraulic excavator, a wheel loader, and a bulldozer. In this embodiment, the working machine 1 is a hydraulic excavator. The working machine 1 includes a traveling body 2, a rotating body 3, a working implement 4, a swing motor 5, a working implement cylinder 6, a controller 7, an operating device 8, and a monitor 9.

[0011] The running body 2 supports the rotating body 3. The running body 2 has a pair of tracks 2A. The work machine 1 travels as the tracks 2A rotate.

[0012] The rotating body 3 is disposed above the running body 2. The rotating body 3 is rotatably supported on the running body 2. The rotating body 3 has a cab. An operator of the work machine 1 sits in the cab. An operation device 8 and a monitor 9 are disposed in the cab. The operation device 8 is operated by the operator. The operation device 8 is operated to rotate the rotating body 3. The operation device 8 is operated to operate the work implement 4. The operation device 8 includes a plurality of levers. The monitor 9 includes a display device and an input device. The display device provides display data to the operator sitting in the cab. The input device is operated by the operator sitting in the cab. Examples of the display device include a flat panel display such as a liquid crystal display or an organic EL display. Examples of the input device include a touch panel, a button, a computer keyboard, and a mouse.

[0013] The work implement 4 is rotatably attached to the revolving unit 3. The work implement 4 includes a boom 4A, an arm 4B, and a bucket 4C. The boom 4A is rotatably connected to the front portion of the revolving unit 3. The arm 4B is rotatably connected to the tip of the boom 4A. The bucket 4C is rotatably connected to the tip of the arm 4B.

[0014] The swing motor 5 swings the swing body 3 supported by the traveling body 2. The swing motor 5 is a hydraulic motor driven by hydraulic oil.

[0015] The work implement cylinder 6 operates the work implement 4 attached to the revolving body 3. The work implement cylinder 6 is a hydraulic cylinder driven by hydraulic oil. The work implement cylinder 6 has a cylinder tube, a piston that is movable inside the cylinder tube, and a rod that is fixed to the piston. The piston divides the interior of the cylinder tube into a head chamber and a bottom chamber. The work implement cylinder 6 contracts as hydraulic oil flows into the head chamber and out of the bottom chamber. The work implement cylinder 6 extends as hydraulic oil flows into the bottom chamber and out of the head chamber. The work implement cylinder 6 includes a boom cylinder 6A, an arm cylinder 6B, and a bucket cylinder 6C.

[0016] The boom cylinder 6A operates the boom 4A. The base end of the cylinder tube of the boom cylinder 6A is connected to the revolving unit 3, and the tip end of the rod of the boom cylinder 6A is connected to the boom 4A. The operation of the boom 4A includes a raising operation and a lowering operation. The boom 4A is raised when hydraulic oil flows into the bottom chamber of the boom cylinder 6A and the boom cylinder 6A extends. The boom 4A is lowered when hydraulic oil flows into the head chamber of the boom cylinder 6A and the boom cylinder 6A retracts.

[0017] The arm cylinder 6B operates the arm 4B. The base end of the cylinder tube of the arm cylinder 6B is connected to the boom 4A, and the tip end of the rod of the arm cylinder 6B is connected to the arm 4B. The operations of the arm 4B include an excavation operation and a dumping operation. When hydraulic oil flows into the bottom chamber of the arm cylinder 6B and the arm cylinder 6B extends, the arm 4B performs an excavation operation. When hydraulic oil flows into the head chamber of the arm cylinder 6B and the arm cylinder 6B retracts, the arm 4B performs a dumping operation.

[0018] The bucket cylinder 6C operates the bucket 4C. The base end of the cylinder tube of the bucket cylinder 6C is connected to the arm 4B, and the tip end of the rod of the bucket cylinder 6C is connected to the bucket 4C via a link mechanism. The operations of the bucket 4C include an excavation operation and a dumping operation. The bucket 4C performs an excavation operation when hydraulic oil flows into the bottom chamber of the bucket cylinder 6C and the bucket cylinder 6C extends. The bucket 4C performs a dumping operation when hydraulic oil flows into the head chamber of the bucket cylinder 6C and the bucket cylinder 6C contracts.

[0019] <Controller> FIG. 2 is a hardware configuration diagram showing the controller 7 according to the first embodiment. The controller 7 includes a computer 10. The computer 10 includes a processor 10A such as a CPU (Central Processing Unit), a main memory 10B including a nonvolatile memory such as a ROM (Read Only Memory) and a volatile memory such as a RAM (Random Access Memory), a storage 10C, an input / output interface 10D including an input / output circuit, and a communication interface 10E including a communication circuit. The functions of the controller 7 are stored in the storage 10C as a computer program 10F. The processor 10A reads the computer program 10F from the storage 10C, loads it into the main memory 10B, and executes processing in accordance with the computer program 10F. The computer program 10F may be distributed to the computer 10 via a network.

[0020] <Control System> Figure 3 is a diagram that schematically shows a control system 11A of the work machine 1 according to the first embodiment. The control system 11A includes a hydraulic system (hydraulic circuit) that operates based on hydraulic oil. As shown in Figure 3, the control system 11A has a controller 7, an operating device 8, a pump 12, a meter-in valve 13, a bleed valve 14, a servo valve 15, a tank 16, a valve circuit 17, an actuator circuit 18, a tank circuit 25, a bleed circuit 19, a valve circuit pressure sensor 20, an actuator circuit pressure sensor 21, a rotation speed sensor 22, and a hydraulic oil temperature sensor 23.

[0021] The pump 12 is a hydraulic pump that discharges hydraulic oil. The pump 12 has a discharge port 12A. The pump 12 discharges hydraulic oil from the discharge port 12A. The valve circuit 17 is connected to the discharge port 12A. The discharge port 12A discharges hydraulic oil to the valve circuit 17.

[0022] The meter-in valve 13 includes a directional control valve that controls the flow rate and direction of hydraulic oil supplied from the pump 12 to the actuators of the work machine 1. The actuators are hydraulic actuators included in the work machine 1. The actuators are driven based on the hydraulic oil supplied from the pump 12. Examples of the actuators included in the work machine 1 include a work implement cylinder 6 for operating the work implement 4, a swing motor 5 for rotating the swing unit 3, and a travel motor, which is a hydraulic motor, for operating the travel unit 2. FIG. 3 shows, as an example, a boom cylinder 6A and an arm cylinder 6B as actuators to which hydraulic oil is supplied. Note that the actuators may also include a bucket cylinder 6C.

[0023] The operating device 8 is operated to operate the actuator of the work machine 1. The operating device 8 includes a plurality of levers. When the operating device 8 is operated, an operating signal (electrical signal) for operating the hydraulic actuator of the work machine 1 is generated. The operating signal of the operating device 8 is transmitted to the controller 7. The operating signal of the operating device 8 includes an operating amount of the operating device 8. The operating amount indicates the value of the operating signal. The operating amount may be considered as the signal strength of the operating signal. The operating amount may be considered as the operating angle (tilting angle) of the lever. The controller 7 controls the hydraulic actuator based on the operating amount of the operating device 8. In the following description, the operating amount of the operating device 8 will be referred to as the lever operating amount, as appropriate.

[0024] In the embodiment, the operation signal (operation amount) is generated by operating the operation device 8, but the operation signal may also be generated by, for example, the controller 7. The controller 7 may automatically generate the operation signal without the operator operating the operation device 8. The operation signal may also be generated by a controller separate from the controller 7. The separate controller may be located outside the work machine 1. The operation signal may be transmitted from a controller located outside the work machine 1 to the controller 7 mounted on the work machine 1. The operation device 8 may also be located outside the work machine 1. The work machine 1 may be remotely operated by a remote operation device located outside the work machine 1. When the work machine 1 is remotely operated by the remote operation device, a remote controller connected to the remote operation device may generate the operation signal. The operation signal generated by the remote controller may be transmitted to the controller 7 mounted on the work machine 1.

[0025] The valve circuit 17 connects the pump 12 and the meter-in valve 13. The pump 12 and the meter-in valve 13 are connected via the valve circuit 17. A plurality of meter-in valves 13 are provided. In the example shown in FIG. 3 , the meter-in valves 13 include a first meter-in valve 13A and a second meter-in valve 13B. The meter-in valves 13 operate based on a control command from the controller 7. The valve circuit 17 distributes the hydraulic oil discharged from the pump 12 to the first meter-in valve 13A and the second meter-in valve 13B.

[0026] The actuator circuit 18 connects the meter-in valve 13 and the actuator of the work machine 1. The meter-in valve 13 and the actuator of the work machine 1 are connected via the actuator circuit 18. Hydraulic oil flowing into the actuator of the work machine 1 flows through the actuator circuit 18. Hydraulic oil is supplied to the actuator of the work machine 1 via the actuator circuit 18. In the example shown in Fig. 3, the actuator circuit 18 includes a first actuator circuit 18A that connects the first meter-in valve 13A and the boom cylinder 6A, and a second actuator circuit 18B that connects the second meter-in valve 13B and the arm cylinder 6B.

[0027] The tank circuit 25 connects the actuators of the work machine 1 to the tank 16. Hydraulic oil flowing out from the actuators of the work machine 1 flows through the tank circuit 25. The hydraulic oil is discharged from the actuators of the work machine 1 to the tank 16 via the tank circuit 25. In the example shown in Fig. 3, the tank circuit 25 includes a first tank circuit 25A that connects the boom cylinder 6A to the tank 16, and a second tank circuit 25B that connects the arm cylinder 6B to the tank 16. A meter-out valve that controls the flow rate of hydraulic oil discharged from the actuators to the tank 16 may be arranged in the tank circuit 25.

[0028] Fig. 3 is a simplified diagram of a hydraulic system. In the example shown in Fig. 3, actuator circuits 18 (18A, 18B) are connected to the bottom chambers of the work machine cylinders 6 (6A, 6B). Tank circuits 25 (25A, 25B) are connected to the head chambers of the work machine cylinders 6 (6A, 6B).

[0029] The bleed circuit 19 is provided so as to branch off from the valve circuit 17. The bleed circuit 19 is connected to the tank 16. The bleed circuit 19 connects the valve circuit 17 and the tank 16.

[0030] The bleed valve 14 operates to discharge at least a portion of the hydraulic oil discharged from the pump 12 to the valve circuit 17 into the tank 16. The bleed valve 14 is disposed in the bleed circuit 19. The bleed valve 14 controls the flow rate of the hydraulic oil discharged from the valve circuit 17 to the tank 16 via the bleed circuit 19. When the opening of the bleed valve 14 is opened, at least a portion of the hydraulic oil in the valve circuit 17 is discharged into the tank 16 via the bleed circuit 19 and the bleed valve 14. When the opening of the bleed valve 14 is closed, the hydraulic oil in the valve circuit 17 is not discharged into the tank 16 via the bleed circuit 19 and the bleed valve 14. The bleed valve 14 operates based on a control command from the controller 7. By changing the valve opening of the bleed valve 14, the flow rate of the hydraulic oil discharged from the valve circuit 17 to the tank 16 is controlled. The valve opening area of ​​the bleed valve 14 changes based on the control command from the controller 7.

[0031] The servo valve 15 drives the swash plate of the pump 12. The servo valve 15 operates based on a control command from the controller 7.

[0032] The valve circuit pressure sensor 20 detects the pressure of the hydraulic oil in the valve circuit 17. The pressure of the hydraulic oil in the valve circuit 17 is equal to the discharge pressure of the hydraulic oil discharged from the pump 12. The detection data of the valve circuit pressure sensor 20 is sent to the controller 7.

[0033] The actuator circuit pressure sensor 21 detects the pressure of the hydraulic oil in the actuator circuit 18. The pressure of the hydraulic oil in the actuator circuit 18 is equal to the load pressure acting on the work machine cylinder 6. The detection data of the actuator circuit pressure sensor 21 is sent to the controller 7.

[0034] The rotation speed sensor 22 detects the rotation speed of the pump 12. The detection data of the rotation speed sensor 22 is transmitted to the controller 7. The hydraulic oil temperature sensor 23 detects the temperature of the hydraulic oil. In the embodiment, the hydraulic oil temperature sensor 23 detects the temperature of the hydraulic oil contained in the tank 16. The detection data of the hydraulic oil temperature sensor 23 is transmitted to the controller 7.

[0035] The controller 7 has multiple functional units. The functions of the functional units of the controller 7 are performed by a processor 10A. The functional units of the controller 7 include a meter-in valve command unit 7A that outputs a control command to the meter-in valve 13, a bleed valve command unit 7B that outputs a control command to the bleed valve 14, a pump swash plate command unit 7C that outputs a control command to the servo valve 15, a lever operation amount acquisition unit 7D that receives an operation signal from the operating device 8, a valve circuit pressure acquisition unit 7E that acquires detection data from the valve circuit pressure sensor 20, an actuator circuit pressure acquisition unit 7F that acquires detection data from the actuator circuit pressure sensor 21, a rotation speed acquisition unit 7G that acquires detection data from the rotation speed sensor 22, a hydraulic oil temperature acquisition unit 7H that acquires detection data from the hydraulic oil temperature sensor 23, and a calculation unit 7P.

[0036] <Bleed Valve> The bleed valve 14 operates to discharge excess hydraulic oil discharged from the pump 12 to the valve circuit 17 into the tank 16. For example, due to insufficient responsiveness of the pump 12 to a change in capacity or insufficient control accuracy of the discharge flow rate, the discharge flow rate of hydraulic oil from the pump 12 may exceed the target flow rate of hydraulic oil supplied to the meter-in valve 13. When the discharge flow rate of the pump 12 exceeds the target flow rate of the meter-in valve 13, the bleed valve 14 opens, and the excess hydraulic oil discharged from the pump 12 is discharged into the tank 16 via the bleed circuit 19. Furthermore, due to, for example, the hardware characteristics of the pump 12, the pump 12 has a minimum pump flow rate Q_p_min that indicates a minimum value of the discharge flow rate. Note that the minimum pump flow rate Q_p_min may be a preset value. The minimum pump flow rate Q_p_min may be a flow rate that is lower than the flow rate of hydraulic oil discharged from the pump 12, and may be a fixed value or a variable value corresponding to a target opening area. On the other hand, the target flow rate of the meter-in valve 13 may be zero or a very small flow rate. When the target flow rate of the meter-in valve 13 is lower than the pump minimum flow rate Q_p_min, the bleed valve 14 opens and excess hydraulic oil discharged from the pump 12 is discharged to the tank 16 via the bleed circuit 19.

[0037] When excessive hydraulic oil is discharged to the tank 16 via the bleed circuit 19, if the opening of the bleed valve 14 is not properly controlled and, for example, an excessive amount of hydraulic oil is discharged to the tank 16, there is a possibility that the target flow rate of hydraulic oil will not be supplied to the meter-in valve 13. If the target flow rate of hydraulic oil is not supplied to the meter-in valve 13 and the pressure in the valve circuit 17 drops, it may become difficult to operate the work machine cylinder 6 (actuator) at the target operating speed. Therefore, it is necessary to control the flow rate of hydraulic oil discharged to the tank 16 via the bleed valve 14 so that the pressure in the valve circuit 17 (the pressure of hydraulic oil supplied to the meter-in valve 13) is maintained at an appropriate value.

[0038] In this embodiment, the controller 7 controls the bleed valve 14 so that hydraulic oil at a target flow rate and target pressure is supplied to the meter-in valve 13 .

[0039] <Leakage Flow Rate> Hydraulic oil may leak from at least a portion of the valve circuit 17. For example, hydraulic oil may leak from a small gap in the valve circuit 17. If hydraulic oil leaks from the valve circuit 17, hydraulic oil will be supplied to the meter-in valve 13 at a flow rate less than the discharge flow rate of the pump 12. If the flow rate of hydraulic oil discharged from the pump 12 is defined as the pump discharge flow rate, the flow rate of hydraulic oil supplied to the meter-in valve 13 is defined as the valve supply flow rate, and the flow rate of hydraulic oil discharged to the tank 16 via the bleed valve 14 is defined as the bleed flow rate, then the relationship [Leakage Flow Rate] = [Pump Discharge Flow Rate] - ([Valve Supply Flow Rate] + [Bleed Flow Rate]) holds. Therefore, when controlling the bleed valve 14 so that hydraulic oil is supplied to the meter-in valve 13 at a target flow rate, the leakage flow rate Q_leak must be taken into consideration.

[0040] In the embodiment, the controller 7 controls the bleed valve 14 taking into account the leakage flow rate Q_leak of the valve circuit 17 .

[0041] It should be noted that hydraulic oil may leak not only from the valve circuit 17 but also from, for example, the pump 12 and the bleed circuit 19. The leakage flow rate Q_leak may be a concept that includes not only the flow rate of hydraulic oil leaking from the valve circuit 17 but also the flow rate of hydraulic oil leaking from the pump 12 and the flow rate of hydraulic oil leaking from the bleed circuit 19. Hydraulic oil may leak from components of the hydraulic system other than the valve circuit 17, the pump 12, and the bleed circuit 19. The leakage flow rate Q_leak may be a concept that includes the flow rate of hydraulic oil leaking from various components of the hydraulic system.

[0042] <Control Method> Figure 4 is a flowchart showing a control method for the work machine 1 according to the first embodiment. The actuator circuit pressure sensor 21 detects the pressure of the hydraulic oil in the actuator circuit 18. The actuator circuit pressure acquisition unit 7F acquires the detection data of the actuator circuit pressure sensor 21. As described above, the pressure of the hydraulic oil in the actuator circuit 18 is equal to the load pressure applied to the actuators of the work machine 1. The actuator circuit pressure acquisition unit 7F calculates an actuator load pressure P_act indicating the load pressure applied to each of the multiple actuators (actuator circuits 18) based on the detection data of the actuator circuit pressure sensor 21. The actuator circuit pressure acquisition unit 7F acquires the detection data of the actuator circuit pressure sensor 21 to acquire the actuator load pressure P_act (step SA1).

[0043] The valve circuit pressure sensor 20 detects the pressure of the hydraulic oil in the valve circuit 17. The valve circuit pressure acquisition unit 7E acquires detection data from the valve circuit pressure sensor 20. The detection data from the valve circuit pressure sensor 20 indicates a valve circuit detected pressure P_p that indicates the pressure of the hydraulic oil in the valve circuit 17 detected by the valve circuit pressure sensor 20. The valve circuit pressure acquisition unit 7E acquires the detection data from the valve circuit pressure sensor 20 to acquire the valve circuit detected pressure P_p (step SA2).

[0044] The lever operation amount acquisition unit 7D acquires an operation signal generated by operating the operation device 8. The operation signal includes the operation amount of the operation device 8. The lever operation amount acquisition unit 7D acquires a lever operation amount indicating the operation amount of the operation device 8 by acquiring the operation signal from the operation device 8. As described above, there are multiple actuators in the work machine 1. The lever operation amount acquisition unit 7D acquires multiple lever operation amounts for operating each of the multiple actuators (step SA3).

[0045] The calculation unit 7P calculates an actuator target flow rate Q_tgt indicating a target flow rate of hydraulic oil to be supplied to each of the plurality of actuator circuits 18 (actuators) based on the lever operation amount acquired in step SA3 (step SA4).The calculation unit 7P calculates a valve circuit target flow rate Q_valve indicating a target flow rate of hydraulic oil to be supplied from the pump 12 to the valve circuit 17 based on the actuator target flow rate Q_tgt calculated in step SA4 (step SA5).

[0046] Fig. 5 is a diagram for explaining a method for calculating the actuator target flow rate Q_tgt and the valve circuit target flow rate Q_valve according to the first embodiment. Fig. 5 shows an example in which the lever operation amount acquisition unit 7D acquires the operation amount of lever A, which is operated to operate actuator A, the operation amount of lever B, which is operated to operate actuator B, and the operation amount of lever C, which is operated to operate actuator C. As shown in Fig. 5, first correlation data indicating the relationship between the lever operation amount and the actuator target flow rate Q_tgt is determined in advance. The calculation unit 7P calculates the actuator target flow rate Q_tgt based on the lever operation amount and the first correlation data.

[0047] 5 , the first correlation data for actuator A indicates the relationship between the operation amount of lever A and an actuator target flow rate Q_tgt_A indicating a target flow rate of hydraulic oil to be supplied to actuator A. The first correlation data for actuator B indicates the relationship between the operation amount of lever B and an actuator target flow rate Q_tgt_B indicating a target flow rate of hydraulic oil to be supplied to actuator B. The first correlation data for actuator C indicates the relationship between the operation amount of lever C and an actuator target flow rate Q_tgt_C indicating a target flow rate of hydraulic oil to be supplied to actuator C.

[0048] The calculation unit 7P calculates an actuator target flow rate Q_tgt_A indicating a target flow rate of hydraulic oil to be supplied to actuator A, based on the operation amount of lever A and the first correlation data for actuator A. The calculation unit 7P calculates an actuator target flow rate Q_tgt_B indicating a target flow rate of hydraulic oil to be supplied to actuator B, based on the operation amount of lever B and the first correlation data for actuator B. The calculation unit 7P calculates an actuator target flow rate Q_tgt_C indicating a target flow rate of hydraulic oil to be supplied to actuator C, based on the operation amount of lever C and the first correlation data for actuator C.

[0049] As described above, the operation amount is not limited to the operation amount of the operation device 8, but may be the value of an operation signal automatically generated by the controller 7, the value of an operation signal generated by a controller other than the controller 7, the operation amount of a remote operation device, or the value of an operation signal generated by a remote controller.

[0050] The calculation unit 7P calculates the valve circuit target flow rate Q_valve by calculating the sum of a plurality of actuator target flow rates Q_tgt. In the example shown in Fig. 5, the valve circuit target flow rate Q_valve is the sum of the actuator target flow rates Q_tgt_A, Q_tgt_B, and Q_tgt_C (Q_valve = Q_tgt_A + Q_tgt_B + Q_tgt_C).

[0051] The calculation unit 7P calculates an actuator target pressure P_tgt indicating a target pressure of hydraulic oil to be supplied to each of the plurality of actuator circuits 18 (actuators) based on the lever operation amount acquired in step SA3 (step SA6).The calculation unit 7P calculates a valve circuit target pressure P_valve indicating a target pressure of hydraulic oil to be supplied from the pump 12 to the valve circuit 17 based on the actuator target pressure P_tgt calculated in step SA6 (step SA7).

[0052] FIG. 6 is a diagram for explaining a method for calculating the actuator target pressure P_tgt and the valve circuit target pressure P_valve according to the first embodiment. FIG. 6 shows an example in which the lever operation amount acquisition unit 7D acquires the operation amount of lever A, which is operated to operate actuator A, the operation amount of lever B, which is operated to operate actuator B, and the operation amount of lever C, which is operated to operate actuator C. As shown in FIG. 6 , second correlation data indicating the relationship between the lever operation amount and the actuator target pressure P_tgt is determined in advance. The calculation unit 7P calculates the actuator target pressure P_tgt based on the lever operation amount and the second correlation data. The calculation unit 7P calculates the actuator target pressure P_tgt corresponding to the actuator target flow rate Q_tgt.

[0053] 6 , the second correlation data for actuator A indicates the relationship between the operation amount of lever A and an actuator target pressure P_tgt_A indicating the target pressure of hydraulic oil supplied to actuator A. The second correlation data for actuator B indicates the relationship between the operation amount of lever B and an actuator target pressure P_tgt_B indicating the target pressure of hydraulic oil supplied to actuator B. The second correlation data for actuator C indicates the relationship between the operation amount of lever C and an actuator target pressure P_tgt_C indicating the target pressure of hydraulic oil supplied to actuator C.

[0054] The calculation unit 7P calculates an actuator target pressure P_tgt_A indicating a target pressure of hydraulic oil to be supplied to actuator A, based on the operation amount of lever A and the second correlation data for actuator A. The calculation unit 7P calculates an actuator target pressure P_tgt_B indicating a target pressure of hydraulic oil to be supplied to actuator B, based on the operation amount of lever B and the second correlation data for actuator B. The calculation unit 7P calculates an actuator target pressure P_tgt_C indicating a target pressure of hydraulic oil to be supplied to actuator C, based on the operation amount of lever C and the second correlation data for actuator C.

[0055] As described above, the operation amount is not limited to the operation amount of the operation device 8, but may be the value of an operation signal automatically generated by the controller 7, the value of an operation signal generated by a controller other than the controller 7, the operation amount of a remote operation device, or the value of an operation signal generated by a remote controller.

[0056] The calculation unit 7P calculates the actuator target pressure P_tgt corresponding to the actuator target flow rate Q_tgt. The calculation unit 7P calculates the valve circuit target pressure P_valve based on the actuator target pressure P_tgt calculated in step SA6 and the multiple actuator load pressures P_act acquired in step SA1. In this embodiment, the calculation unit 7P determines the actuator target pressure P_tgt corresponding to the actuator with the maximum actuator load pressure P_act as the valve circuit target pressure P_valve. For example, if an actuator load pressure P_act_A applied to actuator A, an actuator load pressure P_actB applied to actuator B, and an actuator load pressure P_act_C applied to actuator C are acquired and the actuator load pressure P_act_A is the maximum, the calculation unit 7P determines the actuator target pressure P_tgt_A corresponding to actuator A as the valve circuit target pressure P_valve.

[0057] The calculation unit 7P calculates the leakage flow rate Q_leak, which indicates the estimated flow rate of hydraulic oil leaking from the valve circuit 17. The calculation unit 7P calculates the leakage flow rate Q_leak based on the valve circuit target flow rate Q_valve, the valve circuit detected pressure P_p, and the valve circuit target pressure P_valve. In this embodiment, the calculation unit 7P calculates the leakage flow rate Q_leak based on the valve circuit detected pressure P_p, which indicates the pressure detected by the valve circuit pressure sensor 20 when the valve circuit target flow rate Q_valve is zero, and the valve circuit target pressure P_valve calculated when the valve circuit target flow rate Q_valve is zero (step SA8).

[0058] 7 is a flowchart showing a method for calculating the leakage flow rate Q_leak according to the first embodiment. The calculation unit 7P determines whether the valve circuit target flow rate Q_valve calculated in step SA5 is zero (step SB1). If the valve circuit target flow rate Q_valve is zero, this means that the operating device 8 (lever A, lever B, lever C) is not being operated.

[0059] If it is determined in step SB1 that the valve circuit target flow rate Q_valve is not zero (step SB1: No), the calculation unit 7P does not calculate the leakage flow rate Q_leak (step SB2).

[0060] If it is determined in step SB1 that the valve circuit target flow rate Q_valve is zero (step SB1: Yes), the calculation unit 7P starts calculating the leakage flow rate Q_leak. The calculation unit 7P calculates the leakage flow rate Q_leak based on the valve circuit detected pressure P_p detected by the valve circuit pressure sensor 20 when the valve circuit target flow rate Q_valve is zero and the valve circuit target pressure P_valve calculated when the valve circuit target flow rate Q_valve is zero. When calculation of the leakage flow rate Q_leak is started, an arbitrary initial value for the leakage flow rate Q_leak is set.

[0061] The calculation unit 7P determines whether the valve circuit detected pressure P_p detected by the valve circuit pressure sensor 20 when the valve circuit target flow rate Q_valve is zero is higher than the valve circuit target pressure P_valve calculated in step SA7 (step SB3).

[0062] If it is determined in step SB3 that the valve circuit detected pressure P_p is higher than the valve circuit target pressure P_valve (step SB3: Yes), the calculation unit 7P decreases the initial value for the leakage flow rate Q_leak (step SB4).

[0063] If it is determined in step SB3 that the valve circuit detected pressure P_p is equal to or lower than the valve circuit target pressure P_valve (step SB3: No), the calculation unit 7P increases the initial value for the leakage flow rate Q_leak (step SB5).

[0064] The calculation unit 7P updates the leakage flow rate Q_leak calculated in the process of step SB4 or the process of step SB5 (step SB6).

[0065] The following equation (1) is an arithmetic equation for calculating the target opening area A_bleed of the bleed valve 14. Equation (1) is a physical equation that expresses the relationship between the flow rate of hydraulic oil passing through the bleed valve 14 and the passing pressure loss, taking into account the leakage flow rate Q_leak. In equation (1), Q_p is the pump target flow rate that indicates the target flow rate of hydraulic oil discharged from the pump 12. As shown in equation (2), the pump target flow rate Q_p is the sum of the valve circuit target flow rate Q_valve and the leakage flow rate Q_leak. In equation (1), C is a flow coefficient, and P_ofst is a preset boost pressure.

[0066]

[0067]

[0068] When the valve circuit target flow rate Q_valve is zero, the pump target flow rate Q_p in equation (1) is the pump minimum flow rate Q_p_min, and the numerator of equation (1) is [max(Q_p_min-Q_leak, 0)]. The boost pressure P_ofst is a value equal to or greater than 0. When [P_p=P_valve], the valve circuit target pressure P_valve is selected in the denominator of equation (1).

[0069] If the leakage flow rate Q_leak is reduced in step SB4 when the valve circuit detected pressure P_p is higher than the valve circuit target pressure P_valve, the numerator of equation (1) becomes larger, and the target opening area A_bleed of the bleed valve 14 becomes larger. If the target opening area A_bleed of the bleed valve 14 becomes larger, the valve circuit detected pressure P_p becomes lower, approaching the valve circuit target pressure P_valve. If the valve circuit detected pressure P_p is equal to or lower than the valve circuit target pressure P_valve, and the leakage flow rate Q_leak is increased in step SB5, the numerator of equation (1) becomes smaller, and the target opening area A_bleed of the bleed valve 14 becomes smaller. If the target opening area A_bleed of the bleed valve 14 becomes smaller, the valve circuit detected pressure P_p becomes higher, and approaching the valve circuit target pressure P_valve.

[0070] The calculation unit 7P adjusts the target opening area A_bleed of the bleed valve 14 so that the valve circuit detected pressure P_p matches the valve circuit target pressure P_valve, and calculates the leakage flow rate Q_leak. The calculation unit 7P repeats the processes of steps SB3 to SB6 based on equation (1) until the valve circuit detected pressure P_p matches the valve circuit target pressure P_valve. The calculation unit 7P determines the leakage flow rate Q_leak obtained when the target opening area A_bleed of the bleed valve 14 is adjusted so that the valve circuit detected pressure P_p matches the valve circuit target pressure P_valve, as the calculated leakage flow rate Q_leak.

[0071] The calculation unit 7P may determine whether or not to start calculating the leakage flow rate Q_leak based on detection data from the rotation speed sensor 22. The controller 7 does not calculate the leakage flow rate Q_leak when the rotation speed of the pump 12 detected by the rotation speed sensor 22 is equal to or lower than a predetermined rotation speed threshold. The leakage flow rate Q_leak may vary depending on the rotation speed of the pump 12. In order to accurately calculate the leakage flow rate Q_leak, the calculation unit 7P calculates the leakage flow rate Q_leak when the rotation speed of the pump 12 satisfies a predetermined rotation speed condition.

[0072] The calculation unit 7P may calculate and store the leakage flow rate Q_leak, which changes depending on the rotation speed of the pump 12. That is, the leakage flow rate Q_leak may be calculated for each different rotation speed of the pump 12. The calculation unit 7P may use the stored leakage flow rate Q_leak to calculate the target opening area A_bleed of the bleed valve 14. That is, the calculation unit 7P may calculate the target opening area A_bleed of the bleed valve 14 using the leakage flow rate Q_leak corresponding to the rotation speed of the pump 12.

[0073] The calculation unit 7P may determine whether to start calculating the leakage flow rate Q_leak based on detection data from the hydraulic oil temperature sensor 23. The controller 7 does not calculate the leakage flow rate Q_leak when the temperature of the hydraulic oil detected by the hydraulic oil temperature sensor 23 is equal to or lower than a predetermined temperature threshold. The viscosity of the hydraulic oil changes depending on the temperature of the hydraulic oil, which may change the leakage flow rate Q_leak. In order to accurately calculate the leakage flow rate Q_leak, the calculation unit 7P calculates the leakage flow rate Q_leak when the temperature of the hydraulic oil satisfies predetermined temperature conditions.

[0074] The calculation unit 7P may calculate and store the leakage flow rate Q_leak, which varies depending on the temperature of the hydraulic oil. That is, the leakage flow rate Q_leak may be calculated for each different temperature of the hydraulic oil. The calculation unit 7P may use the stored leakage flow rate Q_leak to calculate the target opening area A_bleed of the bleed valve 14. That is, the calculation unit 7P may calculate the target opening area A_bleed of the bleed valve 14 using the leakage flow rate Q_leak according to the temperature of the hydraulic oil.

[0075] The calculation unit 7P calculates (step SA9) a pump target flow rate Q_p indicating a target flow rate of hydraulic oil to be discharged from the pump 12, based on the valve circuit target flow rate Q_valve calculated in step SA5 and the leakage flow rate Q_leak calculated in step SA8. As shown in equation (2), the pump target flow rate Q_p is the sum of the valve circuit target flow rate Q_valve and the leakage flow rate Q_leak.

[0076] Calculation unit 7P calculates a target opening area A_bleed of the bleed valve 14 based on the valve circuit target flow rate Q_valve calculated in step SA5, the valve circuit target pressure P_valve calculated in step SA7, and the leakage flow rate Q_leak calculated in step SA8. In this embodiment, calculation unit 7P calculates the target opening area A_bleed of the bleed valve 14 based on the valve circuit detected pressure P_p acquired in step SA2, the valve circuit target flow rate Q_valve calculated in step SA5, the valve circuit target pressure P_valve calculated in step SA7, the leakage flow rate Q_leak calculated in step SA8, and the pump target flow rate Q_p calculated in step SA9. Calculation unit 7P calculates the target opening area A_bleed of the bleed valve 14 based on equation (1) (step SA10).

[0077] As described above, the boost pressure P_ofst in equation (1) is a preset pressure value. The calculation unit 7P adds the valve circuit detected pressure P_p and the preset boost pressure P_ofst. If the valve circuit target pressure P_valve calculated based on the actuator target pressure P_tgt is set as the first valve circuit target pressure, and the sum of the valve circuit detected pressure P_p and the boost pressure P_ofst, [P_p + P_ofst], is set as the second valve circuit target pressure, then, as shown in the denominator of equation (1), the calculation unit 7P calculates the target opening area A_bleed of the bleed valve 14 based on the smaller of the first valve circuit target pressure and the second valve circuit target pressure.

[0078] The bleed valve command unit 7B calculates a bleed valve command value for adjusting the opening area of ​​the bleed valve 14 based on the target opening area A_bleed of the bleed valve 14 calculated in step SA10 (step SA11). The bleed valve command unit 7B outputs a bleed valve command, which is a control command for controlling the bleed valve 14, based on the target opening area A_bleed of the bleed valve 14. The bleed valve command unit 7B outputs the bleed valve command so that the opening area of ​​the bleed valve 14 becomes the target opening area A_bleed of the bleed valve 14 (step SA12).

[0079] The pump swash plate command unit 7C calculates a pump swash plate command value for adjusting the displacement of the pump 12 based on the target pump flow rate Q_p calculated in step SA9 (step SA13). The pump swash plate command unit 7C outputs a pump swash plate command, which is a control command for controlling the displacement of the pump 12 based on the target pump flow rate Q_p. The pump swash plate command unit 7C outputs a pump swash plate command such that hydraulic oil is discharged from the pump 12 at the target pump flow rate Q_p (step SA14).

[0080] The meter-in valve command unit 7A calculates a meter-in valve command value for adjusting the opening area A_tgt of the meter-in valve 13 based on the actuator target flow rate Q_tgt calculated in step SA4 (step SA15).

[0081] The meter-in valve command unit 7A calculates the opening area A_tgt (target opening area) of the meter-in valve 13 based on the valve circuit detected pressure P_p and the actuator load pressure P_act. The meter-in valve command unit 7A calculates the opening area A_tgt of the meter-in valve 13 based on the following equation (3): In equation (3), C is a flow rate constant.

[0082]

[0083] A first conversion table is determined in advance, taking into consideration the opening characteristics of the spool of the meter-in valve 13. The first conversion table is a conversion table for converting the opening area A_tgt of the meter-in valve 13 into a target spool stroke of the meter-in valve 13. The meter-in valve command unit 7A inputs the opening area A_tgt of the meter-in valve 13 calculated based on equation (3) into the first conversion table to calculate the target spool stroke of the meter-in valve 13. In addition, a second conversion table is determined in advance for converting the target spool stroke of the meter-in valve 13 into a meter-in valve command value. The meter-in valve command unit 7A can calculate the meter-in valve command value for adjusting the opening area A_tgt of the meter-in valve 13 by inputting the target spool stroke of the meter-in valve 13 into the second conversion table.

[0084] The meter-in valve command unit 7A outputs a meter-in valve command, which is a control command for controlling the opening area of ​​the meter-in valve 13, so that hydraulic oil is supplied to the actuator at the actuator target flow rate Q_tgt (step SA16).

[0085] As described above, the pump 12 has a pump minimum flow rate Q_p_min that indicates the minimum value of the discharge flow rate. In this embodiment, when the target opening area A_bleed of the bleed valve 14 exceeds a predetermined value, the pump swash plate command unit 7C controls the pump 12 so that hydraulic oil is discharged from the pump 12 at the pump minimum flow rate Q_p_min. When the target opening area A_bleed of the bleed valve 14 is equal to or smaller than the predetermined value, the pump swash plate command unit 7C controls the pump 12 so that hydraulic oil is discharged from the pump 12 at the pump target flow rate Q_p based on the valve circuit target flow rate Q_valve. The predetermined value is zero or a very small value greater than zero.

[0086] If the capacity of the pump 12 and the opening area of ​​the bleed valve 14 are changed simultaneously, the flow rate of hydraulic oil supplied from the pump 12 to the valve circuit 17 and the flow rate of hydraulic oil discharged to the tank 16 via the bleed valve 14 will change simultaneously. If the flow rate of hydraulic oil supplied from the pump 12 to the valve circuit 17 and the flow rate of hydraulic oil discharged to the tank 16 via the bleed valve 14 change simultaneously, the pressure of the hydraulic oil in the valve circuit 17 may become unstable. In the embodiment, when the target opening area A_bleed of the bleed valve 14 is greater than zero, that is, when the opening of the bleed valve 14 is open, the pump swash plate command unit 7C controls the pump 12 so that hydraulic oil is discharged from the pump 12 at the minimum pump flow rate Q_p_min. When the target opening area A_bleed of the bleed valve 14 is zero, i.e., when the opening of the bleed valve 14 is closed, the pump swash plate command unit 7C causes the pump 12 to discharge hydraulic oil at the pump target flow rate Q_p so that hydraulic oil is supplied to the valve circuit 17 at the valve circuit target flow rate Q_valve. That is, when the opening of the bleed valve 14 is open, the pump swash plate command unit 7C keeps the displacement of the pump 12 constant. After the opening of the bleed valve 14 is closed, the pump swash plate command unit 7C increases the displacement of the pump 12 based on the valve circuit target flow rate Q_valve. By not simultaneously changing the flow rate of hydraulic oil supplied from the pump 12 to the valve circuit 17 and the flow rate of hydraulic oil discharged to the tank 16 via the bleed valve 14, the pressure of hydraulic oil in the valve circuit 17 is stabilized.

[0087] In the embodiment, the capacity of the pump 12 is increased by considering the state in which the valve opening of the bleed valve 14 is closed as the stable state of the valve circuit 17, but the state in which the valve opening of the bleed valve 14 is closed is an example of the stable state. As long as the flow rate of hydraulic oil discharged from the valve circuit 17 is sufficiently suppressed and the pressure in the valve circuit 17 is stable, the valve opening of the bleed valve 14 does not need to be closed, and the valve opening may be small. Furthermore, whether the valve circuit 17 is in a stable state may be determined based on the state of the valve opening of the bleed valve 14, or may be determined based on fluctuations in the pressure in the valve circuit 17, a rate of change in the opening command of the bleed valve 14, etc.

[0088] <Effects> As described above, the controller 7 calculates the valve circuit target flow rate Q_valve indicating the target flow rate of hydraulic oil to be supplied to the valve circuit 17, calculates the valve circuit target pressure P_valve (or P_p+P_ofst) indicating the target pressure of hydraulic oil to be supplied to the valve circuit 17, calculates the leakage flow rate Q_leak indicating the estimated flow rate of hydraulic oil leaking from the valve circuit 17, calculates the target opening area A_bleed of the bleed valve 14 based on the valve circuit target flow rate Q_valve, the valve circuit target pressure P_valve (or P_p+P_ofst), and the leakage flow rate Q_leak, and controls the bleed valve 14 based on the target opening area A_bleed of the bleed valve 14.

[0089] According to the above configuration, hydraulic oil at an appropriate pressure and flow rate is supplied to the meter-in valve 13. As described above, the relationship [leakage flow rate] = [pump discharge flow rate] - ([valve supply flow rate] + [bleed flow rate]) holds. Therefore, when controlling the bleed valve 14 so that hydraulic oil is supplied to the meter-in valve 13 at a target flow rate, it is necessary to take the leakage flow rate Q_leak into consideration. In the embodiment, the controller 7 controls the bleed valve 14 in consideration of the leakage flow rate Q_leak of the valve circuit 17. Furthermore, the target opening area A_bleed of the bleed valve 14 is calculated based on the valve circuit target flow rate Q_valve, the valve circuit target pressure P_valve (or P_p + P_ofst), and the leakage flow rate Q_leak. The target opening area A_bleed of the bleed valve 14 is calculated in consideration of not only the leakage flow rate Q_leak, but also the valve circuit target flow rate Q_valve and the valve circuit target pressure P_valve (or P_p + P_ofst). Since the bleed valve 14 is controlled taking into consideration the valve circuit target flow rate Q_valve and the valve circuit target pressure P_valve (or P_p+P_ofst), hydraulic oil is supplied to the meter-in valve 13 at the target flow rate and target pressure.

[0090] Furthermore, the controller 7 takes into consideration the leakage flow rate Q_leak and controls the bleed valve 14 so that hydraulic oil is supplied to the valve circuit 17 at the valve circuit target flow rate Q_valve and the valve circuit target pressure P_valve (or P_p+P_ofst). Because the controller 7 controls the flow rate and pressure, improving the degree of control freedom, the flow rate and pressure loss of the hydraulic oil discharged from the bleed valve 14 to the tank 16 are reduced, and a hydraulic system with less loss is constructed.

[0091] The controller 7 calculates the leakage flow rate Q_leak based on the valve circuit detected pressure P_p, which indicates the pressure detected by the valve circuit pressure sensor 20 when the valve circuit target flow rate Q_valve is zero, and the valve circuit target pressure P_valve. The controller 7 calculates the leakage flow rate Q_leak by adjusting the target opening area A_bleed of the bleed valve 14 so that the valve circuit detected pressure P_p and the valve circuit target pressure P_valve coincide.

[0092] According to the above configuration, the leakage flow rate Q_leak on the control model is calculated so that the valve circuit detected pressure P_p and the valve circuit target pressure P_valve coincide with each other, and therefore hydraulic oil at an appropriate pressure and flow rate is supplied to the meter-in valve 13.

[0093] The controller 7 calculates an actuator target pressure P_tgt indicating a target pressure of hydraulic oil to be supplied to each of the plurality of actuator circuits 18, based on the amount of operation of the operating device 8, and calculates a valve circuit target pressure P_valve based on the actuator target pressure P_tgt. The controller 7 calculates an actuator load pressure P_act indicating the load pressure applied to each of the plurality of actuators, based on the detection data of the actuator circuit pressure sensors 21, and determines the actuator target pressure P_tgt corresponding to the actuator with the maximum actuator load pressure P_act as the valve circuit target pressure P_valve.

[0094] With the above configuration, hydraulic oil at an appropriate pressure is supplied to the meter-in valve 13, and good acceleration and stability can be obtained, for example, when an actuator starts to operate. Furthermore, in a combined operation in which multiple actuators operate simultaneously, the actuator with the highest load pressure is the most difficult to operate. By setting the maximum actuator load pressure P_act among the actuator load pressures P_act applied to each of the multiple actuators as the valve circuit target pressure P_valve, each of the multiple actuators can operate with sufficient acceleration.

[0095] As described with reference to Fig. 7, the valve circuit target pressure P_valve (actuator target pressure P_tgt) is calculated based on the lever operation amount and the second correlation data. By adjusting the second correlation data, the pressure characteristics of the hydraulic oil corresponding to the lever operation amount (so-called throttling characteristics) can be adjusted as desired.

[0096] A first valve circuit target pressure P_valve and a second valve circuit target pressure [P_p+P_ofst] are calculated as the valve circuit target pressures. As shown in the denominator of equation (1), the target opening area A_bleed of the bleed valve 14 is calculated based on the smaller of the first valve circuit target pressure and the second valve circuit target pressure.

[0097] The above configuration prevents an excessive flow rate of hydraulic oil from being supplied to the valve circuit 17. The load pressure of the actuator circuit 18 changes depending on the magnitude of the load applied to the actuator. For example, when the work implement 4 is operated in the gravity direction, the load pressure applied to the actuator does not increase even if the flow rate of hydraulic oil from the pump 12 is increased. If control is performed to increase the pressure of the hydraulic oil in the valve circuit 17 to the target pressure when the work implement 4 is operated in the gravity direction, this means that hydraulic oil that generates an acceleration higher than the acceleration when the work implement 4 is operated due to the action of gravity is supplied to the valve circuit 17. Therefore, there is a possibility that the work implement 4 will operate with excessive acceleration. According to the embodiment, the actual pressure in the valve circuit 17 does not increase above the predetermined boost pressure P_ofst, thereby preventing an excessive flow rate of hydraulic oil from being supplied to the valve circuit 17.

[0098] The controller 7 calculates the valve circuit target flow rate Q_valve based on the operation amount of the operating device 8. The controller 7 calculates the actuator target flow rate Q_tgt indicating the target flow rate of hydraulic oil to be supplied to the actuator circuit 18 based on the operation amount of the operating device 8, and calculates the valve circuit target flow rate Q_valve based on the actuator target flow rate Q_tgt.

[0099] In the above configuration, the meter-in valve 13 is controlled based on the target flow rates Q_tgt of the multiple actuators, and the pump 12 and bleed valve 14 are controlled based on the total value of the target flow rates Q_tgt of the multiple actuators, so that the flow rate of hydraulic oil supplied to each actuator and the flow rate of hydraulic oil discharged to the tank 16 via the bleed valve 14 are controlled in an appropriate balance. As a result, the hydraulic oil in the valve circuit 17 is maintained at an appropriate pressure.

[0100] The controller 7 calculates a pump target flow rate Q_p indicating a target flow rate of hydraulic oil to be discharged from the pump 12 based on the valve circuit target flow rate Q_valve and the leakage flow rate Q_leak, and controls the capacity of the pump 12 based on the pump target flow rate Q_p.

[0101] In the above configuration, the pump target flow rate Q_p is the sum of the valve circuit target flow rate Q_valve and the leakage flow rate Q_leak, so the flow rate of hydraulic oil actually supplied to the meter-in valve 13 is controlled to a flow rate equivalent to the valve circuit target flow rate Q_valve. If the leakage flow rate Q_leak were not taken into account in the pump target flow rate Q_p, the flow rate of hydraulic oil actually supplied to the meter-in valve 13 would be a flow rate that is less than the valve circuit target flow rate Q_valve by the leakage flow rate Q_leak. As a result, there is a possibility that the timing at which the actuator starts to move will be delayed. With the above configuration, an appropriate flow rate of hydraulic oil is supplied to the meter-in valve 13.

[0102] Fig. 8 is a diagram for explaining the relationship between the flow rate of hydraulic oil and the opening area of ​​the bleed valve 14 according to the first embodiment. Fig. 9 is a diagram for explaining the relationship between the flow rate of hydraulic oil and the opening area of ​​the bleed valve 14 according to a comparative example. In each of the graphs in Fig. 8 and Fig. 9, the horizontal axis represents time, and the vertical axis represents the flow rate of hydraulic oil.

[0103] FIG. 8 shows the relationship between the hydraulic oil and the flow rate when the leakage flow rate Q_leak is taken into consideration and Q_p = Q_valve + Q_leak as shown in equation (2). At time t1, the opening area of ​​the bleed valve 14 starts to decrease, and at time t2, the opening area of ​​the bleed valve 14 becomes zero. At time t1, the flow rate of hydraulic oil actually supplied to the meter-in valve 13 and the valve circuit target flow rate Q_valve start to increase. At time t2, the pump target flow rate Q_p starts to increase. As shown in FIG. 8, by taking the leakage flow rate Q_leak into consideration, the flow rate of hydraulic oil actually supplied to the meter-in valve 13 coincides with the valve circuit target flow rate Q_valve.

[0104] FIG. 9 shows the relationship between the hydraulic oil and the flow rate when the leakage flow rate Q_leak is not taken into account and Q_p = Q_valve. At time t1, the valve circuit target flow rate Q_valve starts to increase, and at time t2, the flow rate of hydraulic oil actually supplied to the meter-in valve 13 starts to increase. At time t2, the opening area of ​​the bleed valve 14 starts to decrease, and at time t3, the opening area of ​​the bleed valve 14 becomes zero. At time t3, the pump target flow rate Q_p starts to increase. As shown in FIG. 9, if the leakage flow rate Q_leak is not taken into account, the flow rate of hydraulic oil actually supplied to the meter-in valve 13 and the valve circuit target flow rate Q_valve do not match. As a result, the timing at which the actuator starts to move is delayed.

[0105] <Modification> The calculation unit 7P may calculate the pump target flow rate Q_p based on the following equation (4). In equation (4), Q_strtn is a set value for gradually changing the value of the pump target flow rate Q_p from a value that takes the leakage flow rate Q_leak into consideration to a value that does not. By calculating the pump target flow rate Q_p using equation (4), when the valve circuit target flow rate Q_valve is zero, the calculation yields "Q_p = Q_valve + Q_leak." However, as the valve circuit target flow rate Q_valve approaches the set value Q_strtn, the influence of the leakage flow rate Q_leak becomes smaller, and when the valve circuit target flow rate Q_valve is greater than the set value Q_strtn, the calculation yields "Q_p = Q_valve."

[0106]

[0107] The calculation unit 7P calculates a pump target flow rate Q_p indicating a target flow rate of hydraulic oil to be discharged from the pump 12, based on the valve circuit target flow rate Q_valve and the corrected leakage flow rate [Q_leak×(1−Q_valve / Q_strtn)]. The bleed valve command unit 7B controls the target opening area A_bleed of the bleed valve 14, based on the target opening area A_bleed of the bleed valve 14 calculated based on the pump target flow rate Q_p. The pump swash plate command unit 7C controls the displacement of the pump 12 based on the pump target flow rate Q_p.

[0108] FIG. 10 is a diagram illustrating the relationship between the flow rate of hydraulic oil and the opening area of ​​the bleed valve 14 according to a modification of the first embodiment. In the graph of FIG. 10, the horizontal axis represents time, and the vertical axis represents the flow rate of hydraulic oil. At time t1, the opening area of ​​the bleed valve 14 starts to decrease, and at time t2, the opening area of ​​the bleed valve 14 becomes zero. At time t1, the flow rate of hydraulic oil actually supplied to the meter-in valve 13 and the valve circuit target flow rate Q_valve start to increase. The rate of increase in the flow rate of hydraulic oil actually supplied to the meter-in valve 13 is smaller than the rate of increase in the valve circuit target flow rate Q_valve. At time t2, the pump target flow rate Q_p starts to increase. At time t4, the pump target flow rate Q_p and the valve circuit target flow rate Q_valve become equal.

[0109] The calculation of the leakage flow rate Q_leak may contain errors due to its calculation logic, and if that value is used as is to calculate the pump target flow rate Q_p, the deviation between the expected flow rate actually supplied to the actuator and the actual flow rate may conversely become larger than when the leakage flow rate Q_leak is not taken into account. The main purpose of calculating the pump target flow rate Q_p taking the leakage flow rate Q_leak into account is to avoid delaying the timing of starting the supply of flow rate to the actuator in response to operation, so by calculating the pump target flow rate Q_p as in the embodiment, the timing of starting the supply of flow rate to the actuator is not delayed, and by reducing the influence of the leakage flow rate Q_leak on the pump target flow rate Q_p in the range where the target flow rate is large, it is possible to mitigate the adverse effects of calculation errors in the leakage flow rate Q_leak.

[0110] Second Embodiment A second embodiment will be described below. In the following description, the same or equivalent components as those in the above-described embodiment will be denoted by the same reference numerals, and the description of those components will be simplified or omitted.

[0111] 11 is a diagram schematically showing a control system 11B of a working machine 1 according to the second embodiment. The second embodiment differs from the first embodiment in that a spool stroke sensor 24 is provided to detect the spool stroke of the meter-in valve 13, and that the controller 7 has a spool stroke acquisition unit 7J that acquires detection data from the spool stroke sensor 24. The spool stroke sensor 24 includes a first spool stroke sensor 24A that detects the spool stroke of the first meter-in valve 13A, and a second spool stroke sensor 24B that detects the spool stroke of the second meter-in valve 13B.

[0112] 12 is a flowchart showing a control method for a work machine 1 according to the second embodiment. The actuator circuit pressure acquisition unit 7F acquires a plurality of actuator load pressures P_act (step SD1). The spool stroke acquisition unit 7J acquires detection data from each of the plurality of spool stroke sensors 24 (step SD2). The valve circuit pressure acquisition unit 7E acquires a valve circuit detected pressure P_p (step SD3). The lever operation amount acquisition unit 7D acquires the lever operation amount (step SD4).

[0113] As in the first embodiment described above, the calculation unit 7P calculates a plurality of actuator target flow rates Q_tgt based on the lever operation amounts (step SD5). The calculation unit 7P calculates a valve circuit target flow rate Q_valve based on the plurality of actuator target flow rates Q_tgt (step SD6). The calculation unit 7P calculates a plurality of actuator target pressures P_tgt based on the lever operation amounts (step SD9). The calculation unit 7P calculates a valve circuit target pressure P_valve based on the plurality of actuator target pressures P_tgt (step SD10).

[0114] The calculation unit 7P calculates the opening area A_act of the meter-in valve 13 based on the spool stroke detected by the spool stroke sensor 24 (step SD7). The calculation unit 7P calculates a meter-in valve estimated flow rate Q_act indicating an estimated flow rate of hydraulic oil passing through each of the multiple meter-in valves 13 based on the opening area A_act of the meter-in valve 13. The calculation unit 7P calculates a valve circuit estimated flow rate Q_v_est indicating an estimated flow rate of hydraulic oil supplied to the valve circuit 17 based on the meter-in valve estimated flow rates Q_act of each of the multiple meter-in valves 13 (step SD8).

[0115] Fig. 13 is a diagram for explaining a method for calculating the opening area A_act of the meter-in valve 13 and the valve circuit estimated flow rate Q_v_est according to the second embodiment. Fig. 13 shows an example in which the spool stroke obtaining unit 7J obtains the spool stroke of the meter-in valve 13 that controls the hydraulic oil supplied to actuator A, the spool stroke of the meter-in valve 13 that controls the hydraulic oil supplied to actuator B, and the spool stroke of the meter-in valve 13 that controls the hydraulic oil supplied to actuator C. As shown in Fig. 13 , third correlation data indicating the relationship between the spool stroke and the opening area A_act of the meter-in valve 13 is determined in advance. The calculation unit 7P calculates the opening area A_act of the meter-in valve 13 based on the spool stroke and the third correlation data.

[0116] 13 , the third correlation data for the meter-in valve 13 of actuator A indicates the relationship between the spool stroke of the meter-in valve 13 of actuator A and the opening area A_act_A of the meter-in valve 13 of actuator A. The third correlation data for the meter-in valve 13 of actuator B indicates the relationship between the spool stroke of the meter-in valve 13 of actuator B and the opening area A_act_B of the meter-in valve 13 of actuator B. The third correlation data for the meter-in valve 13 of actuator C indicates the relationship between the spool stroke of the meter-in valve 13 of actuator C and the opening area A_act_C of the meter-in valve 13 of actuator C.

[0117] The calculation unit 7P calculates a meter-in valve estimated flow rate Q_act indicating an estimated flow rate of hydraulic oil passing through the meter-in valve 13, based on the opening area A_act of the meter-in valve 13, the valve circuit detected pressure P_p, and the actuator load pressure P_act. The calculation unit 7P calculates the meter-in valve estimated flow rate Q_act_A of the meter-in valve 13 of actuator A, based on the valve circuit detected pressure P_p, the actuator load pressure P_act_A of actuator A, and the opening area A_act_A of the meter-in valve 13 of actuator A. The calculation unit 7P calculates the meter-in valve estimated flow rate Q_act_B of the meter-in valve 13 of actuator B, based on the valve circuit detected pressure P_p, the actuator load pressure P_act_B of actuator B, and the opening area A_act_B of the meter-in valve 13 of actuator B. The calculation unit 7P calculates the meter-in valve estimated flow rate Q_act_C of the meter-in valve 13 of actuator C based on the valve circuit detected pressure P_p, the actuator load pressure P_act_C of actuator C, and the opening area A_act_C of the meter-in valve 13 of actuator C.

[0118] The calculation unit 7P adds up the multiple meter-in valve estimated flow rates Q_act to calculate the valve circuit estimated flow rate Q_v_est. In the example shown in Fig. 13, the valve circuit estimated flow rate Q_v_est is the sum of the meter-in valve estimated flow rate Q_act_A, the meter-in valve estimated flow rate Q_act_B, and the meter-in valve estimated flow rate Q_act_C (Q_v_est = Q_act_A + Q_act_B + Q_act_C).

[0119] The calculation unit 7P calculates the leakage flow rate Q_leak based on the valve circuit detected pressure P_p acquired in step SD3, the valve circuit target pressure P_valve calculated in step SD10, and the valve circuit estimated flow rate Q_v_est calculated in step SD8 (step SD11).

[0120] 14 is a flowchart showing a method for calculating the leakage flow rate Q_leak according to the second embodiment. A calculation unit 7P calculates the leakage flow rate Q_leak based on the valve circuit estimated flow rate Q_v_est, the valve circuit target pressure P_valve, and the valve circuit detected pressure P_p.

[0121] The calculation unit 7P determines whether the valve circuit estimated flow rate Q_v_est is lower than a preset value Q_est_lim (step SC1).

[0122] If it is determined in step SC1 that the valve circuit estimated flow rate Q_v_est does not fall below the set value Q_est_lim (step SC1: No), the calculation unit 7P does not calculate the leakage flow rate Q_leak (step SC2).

[0123] If it is determined in step SC1 that the valve circuit estimated flow rate Q_v_est is lower than the set value Q_est_lim (step SC1: Yes), the calculation unit 7P starts calculating the leakage flow rate Q_leak. The calculation unit 7P calculates the leakage flow rate Q_leak based on the valve circuit detected pressure P_p and the valve circuit target pressure P_valve. When calculation of the leakage flow rate Q_leak is started, an arbitrary initial value for the leakage flow rate Q_leak is set.

[0124] The calculation unit 7P determines whether the valve circuit detected pressure P_p is higher than the valve circuit target pressure P_valve (step SC3).

[0125] If it is determined in step SC3 that the valve circuit detected pressure P_p is higher than the valve circuit target pressure P_valve (step SC3: Yes), the calculation unit 7P decreases the initial value for the leakage flow rate Q_leak (step SC4).

[0126] If it is determined in step SC3 that the valve circuit detected pressure P_p is equal to or lower than the valve circuit target pressure P_valve (step SC3: No), the calculation unit 7P increases the initial value for the leakage flow rate Q_leak (step SC5).

[0127] The calculation unit 7P updates the leakage flow rate Q_leak calculated in the process of step SC4 or the process of step SC5 (step SC6).

[0128] The following equation (5) is an arithmetic equation for calculating the target opening area A_bleed of the bleed valve 14. Equation (5) is a physical equation that expresses the relationship between the flow rate and the passing pressure loss of the hydraulic oil passing through the bleed valve 14, taking into account the leakage flow rate Q_leak. As with equation (1), in equation (5), C is a flow coefficient, and P_ofst is a preset boost pressure.

[0129]

[0130] The boosting pressure P_ofst is a value equal to or greater than 0. When [P_p=P_valve], the valve circuit target pressure P_valve is selected in the denominator of equation (1).

[0131] If the leakage flow rate Q_leak is reduced in step SC4 when the valve circuit detected pressure P_p is higher than the valve circuit target pressure P_valve, the numerator of equation (5) becomes larger, and the target opening area A_bleed of the bleed valve 14 becomes larger. If the target opening area A_bleed of the bleed valve 14 becomes larger, the valve circuit detected pressure P_p decreases, approaching the valve circuit target pressure P_valve. If the valve circuit detected pressure P_p is equal to or lower than the valve circuit target pressure P_valve, and the leakage flow rate Q_leak is increased in step SC5, the numerator of equation (5) becomes smaller, and the target opening area A_bleed of the bleed valve 14 becomes smaller. If the target opening area A_bleed of the bleed valve 14 becomes smaller, the valve circuit detected pressure P_p increases, and approaches the valve circuit target pressure P_valve.

[0132] The calculation unit 7P calculates the leakage flow rate Q_leak by adjusting the target opening area A_bleed of the bleed valve 14 so that the valve circuit detected pressure P_p matches the valve circuit target pressure P_valve. The calculation unit 7P repeats the processes of steps SC3 to SC6 based on equation (5) until the valve circuit detected pressure P_p matches the valve circuit target pressure P_valve. The calculation unit 7P determines the leakage flow rate Q_leak obtained when the target opening area A_bleed of the bleed valve 14 is adjusted so that the valve circuit detected pressure P_p matches the valve circuit target pressure P_valve as the calculated leakage flow rate Q_leak.

[0133] In this embodiment, by using equation (5), the value of the leakage flow rate Q_leak continues to be updated until the valve circuit estimated flow rate Q_v_est exceeds a preset value Q_est_lim, and therefore even after a certain amount of flow is flowing to the actuator, the actuator load pressure is controlled to a pressure close to the targeted valve circuit target pressure P_valve, thereby improving the accuracy of force control according to the target flow rate.On the other hand, as the supply flow rate to the actuator increases, disturbance factors due to increased pressure fluctuations become stronger, making it difficult to stabilize control, and therefore calculation of the leakage flow rate Q_leak ends at a flow rate equal to or greater than the set value Q_est_lim.

[0134] The calculation unit 7P may determine whether or not to start calculating the leakage flow rate Q_leak based on detection data from the rotation speed sensor 22. The controller 7 does not calculate the leakage flow rate Q_leak when the rotation speed of the pump 12 detected by the rotation speed sensor 22 is equal to or lower than a predetermined rotation speed threshold. The leakage flow rate Q_leak may vary depending on the rotation speed of the pump 12. In order to accurately calculate the leakage flow rate Q_leak, the calculation unit 7P calculates the leakage flow rate Q_leak when the rotation speed of the pump 12 satisfies a predetermined rotation speed condition.

[0135] The calculation unit 7P may calculate and store the leakage flow rate Q_leak, which changes depending on the rotation speed of the pump 12. That is, the leakage flow rate Q_leak may be calculated for each different rotation speed of the pump 12. The calculation unit 7P may use the stored leakage flow rate Q_leak to calculate the target opening area A_bleed of the bleed valve 14. That is, the calculation unit 7P may calculate the target opening area A_bleed of the bleed valve 14 using the leakage flow rate Q_leak corresponding to the rotation speed of the pump 12.

[0136] The calculation unit 7P may determine whether to start calculating the leakage flow rate Q_leak based on detection data from the hydraulic oil temperature sensor 23. The controller 7 does not calculate the leakage flow rate Q_leak when the temperature of the hydraulic oil detected by the hydraulic oil temperature sensor 23 is equal to or lower than a predetermined temperature threshold. The viscosity of the hydraulic oil changes depending on the temperature of the hydraulic oil, which may change the leakage flow rate Q_leak. In order to accurately calculate the leakage flow rate Q_leak, the calculation unit 7P calculates the leakage flow rate Q_leak when the temperature of the hydraulic oil satisfies predetermined temperature conditions.

[0137] The calculation unit 7P may calculate and store the leakage flow rate Q_leak, which varies depending on the temperature of the hydraulic oil. That is, the leakage flow rate Q_leak may be calculated for each different temperature of the hydraulic oil. The calculation unit 7P may use the stored leakage flow rate Q_leak to calculate the target opening area A_bleed of the bleed valve 14. That is, the calculation unit 7P may calculate the target opening area A_bleed of the bleed valve 14 using the leakage flow rate Q_leak according to the temperature of the hydraulic oil.

[0138] The calculation unit 7P calculates the pump target flow rate Q_p, which indicates the target flow rate of hydraulic oil discharged from the pump 12, based on the valve circuit target flow rate Q_valve calculated in step SD6 and the leakage flow rate Q_leak calculated in step SD11 (step SD12).

[0139] The calculation unit 7P calculates the target opening area A_bleed of the bleed valve 14 based on the valve circuit target flow rate Q_valve calculated in step SD6, the valve circuit target pressure P_valve calculated in step SD10, and the leakage flow rate Q_leak calculated in step SD11. In this embodiment, the calculation unit 7P calculates the target opening area A_bleed of the bleed valve 14 based on the valve circuit detected pressure P_p acquired in step SD3, the valve circuit target flow rate Q_valve calculated in step SD6, the valve circuit estimated flow rate Q_v_est calculated in step SD8, the valve circuit target pressure P_valve calculated in step SD10, the leakage flow rate Q_leak calculated in step SD11, and the pump target flow rate Q_p calculated in step SD12. The calculation unit 7P calculates the target opening area A_bleed of the bleed valve 14 based on equation (5) (step SD13).

[0140] As described above, the boost pressure P_ofst in equation (5) is a preset pressure value. The calculation unit 7P adds the valve circuit detected pressure P_p and the preset boost pressure P_ofst. If the valve circuit target pressure P_valve calculated based on the actuator target pressure P_tgt is set as the first valve circuit target pressure, and the value [P_p + P_ofst] obtained by adding the valve circuit detected pressure P_p and the boost pressure P_ofst is set as the second valve circuit target pressure, then, as shown in the denominator of equation (1), the calculation unit 7P calculates the target opening area A_bleed of the bleed valve 14 based on the smaller of the first valve circuit target pressure and the second valve circuit target pressure.

[0141] When the valve circuit target flow rate Q_valve calculated based on the operation amount of the operating device 8 is set to the first valve target flow rate and the valve circuit estimated flow rate Q_v_est is set to the second valve target flow rate, as shown in the numerator of equation (5), the calculation unit 7P calculates the target opening area A_bleed of the bleed valve 14 based on the smaller of the first valve circuit target flow rate and the second valve circuit target flow rate.

[0142] The bleed valve command unit 7B calculates a bleed valve command value for adjusting the opening area of ​​the bleed valve 14 based on the target opening area A_bleed of the bleed valve 14 calculated in step SD13 (step SD14). The bleed valve command unit 7B outputs a bleed valve command, which is a control command for controlling the bleed valve 14, based on the target opening area A_bleed of the bleed valve 14. The bleed valve command unit 7B outputs a bleed valve command such that the opening area of ​​the bleed valve 14 becomes the target opening area A_bleed of the bleed valve 14 (step SD15).

[0143] The pump swash plate command unit 7C calculates a pump swash plate command value for adjusting the displacement of the pump 12 based on the pump target flow rate Q_p calculated in step SD12 (step SD16). The pump swash plate command unit 7C outputs a pump swash plate command, which is a control command for controlling the displacement of the pump 12 based on the pump target flow rate Q_p. The pump swash plate command unit 7C outputs a pump swash plate command such that hydraulic oil is discharged from the pump 12 at the pump target flow rate Q_p (step SD17).

[0144] The meter-in valve command unit 7A calculates a meter-in valve command value for adjusting the opening area of ​​the meter-in valve 13 based on the actuator target flow rate Q_tgt calculated in step SD5 (step SD18).

[0145] The meter-in valve command unit 7A calculates the opening area A_tgt (target opening area) of the meter-in valve 13 based on the valve circuit detected pressure P_p and the actuator load pressure P_act. The meter-in valve command unit 7A calculates the opening area A_tgt of the meter-in valve 13 based on the above-mentioned equation (3).

[0146] A first conversion table is determined in advance, taking into consideration the opening characteristics of the spool of the meter-in valve 13. The first conversion table is a conversion table for converting the opening area A_tgt of the meter-in valve 13 into a target spool stroke of the meter-in valve 13. The meter-in valve command unit 7A inputs the opening area A_tgt of the meter-in valve 13 calculated based on equation (3) into the first conversion table to calculate the target spool stroke of the meter-in valve 13. In addition, a second conversion table is determined in advance for converting the target spool stroke of the meter-in valve 13 into a meter-in valve command value. The meter-in valve command unit 7A can calculate the meter-in valve command value for adjusting the opening area A_tgt of the meter-in valve 13 by inputting the target spool stroke of the meter-in valve 13 into the second conversion table.

[0147] The meter-in valve command unit 7A outputs a meter-in valve command, which is a control command for controlling the opening area of ​​the meter-in valve 13, so that hydraulic oil is supplied to the actuator at the actuator target flow rate Q_tgt (step SD19).

[0148] As described above, the controller 7 calculates the opening area A_act of the meter-in valve 13, calculates the meter-in valve estimated flow rate Q_act indicating the estimated flow rate of hydraulic oil passing through the meter-in valve 13 based on the opening area A_act of the meter-in valve 13, and adds up the multiple meter-in valve estimated flow rates Q_act to calculate the valve circuit estimated flow rate Q_v_est indicating the estimated flow rate of hydraulic oil to be supplied to the valve circuit 17.

[0149] According to the above configuration, even if there is a possibility that the flow rate actually supplied to each actuator may deviate from the target flow rate, the opening area A_act of the meter-in valve 13 is calculated, and the flow rate supplied to each actuator is accurately calculated based on the opening area A_act of the meter-in valve 13, thereby controlling the flow rate of hydraulic oil supplied to each actuator and the flow rate of hydraulic oil discharged to the tank 16 via the bleed valve 14 to maintain an appropriate balance. As a result, the hydraulic oil in the valve circuit 17 is maintained at the target pressure.

[0150] The controller 7 defines the valve circuit target flow rate Q_valve calculated based on the operation amount of the operating device 8 as the first valve target flow rate and the valve circuit estimated flow rate Q_v_est as the second valve target flow rate, and calculates the target opening area A_bleed of the bleed valve 14 based on the smaller of the first valve circuit target flow rate and the second valve circuit target flow rate.

[0151] With the above-described configuration, hydraulic oil at an appropriate pressure is supplied to the actuator. If the opening area A_act of the meter-in valve 13 is smaller than the target opening area, there is a possibility that the pressure in the valve circuit 17 will increase excessively. With the above-described configuration, the pressure in the valve circuit 17 is prevented from increasing excessively.

[0152] Third Embodiment A third embodiment will be described below. In the following description, the same or equivalent components as those in the above-described embodiment will be denoted by the same reference numerals, and the description of those components will be simplified or omitted.

[0153] 15 is a flowchart showing a control method for a work machine 1 according to the third embodiment. The control system used in this embodiment is the same as the control system 11A described in the first embodiment above.

[0154] As in the first embodiment described above, the actuator circuit pressure acquisition unit 7F acquires a plurality of actuator load pressures P_act (step SE1), the valve circuit pressure acquisition unit 7E acquires a valve circuit detected pressure P_p (step SE2), and the lever operation amount acquisition unit 7D acquires a lever operation amount (step SE3).

[0155] As in the first embodiment described above, the calculation unit 7P calculates a plurality of actuator target flow rates Q_tgt based on the lever operation amount (step SE4). The calculation unit 7P calculates a plurality of actuator target pressures P_tgt based on the lever operation amount (step SE5). The calculation unit 7P calculates a valve circuit target pressure P_valve based on the plurality of actuator target pressures P_tgt (step SE6).

[0156] In the embodiment, the calculation unit 7P calculates the valve circuit target flow rate Q_valve, which indicates the target flow rate of hydraulic oil to be supplied to the valve circuit 17, based on the lever operation amount, the actuator load pressure P_act, and the valve circuit target pressure P_valve (step SE7).

[0157] 16 is a diagram for explaining a method of calculating the valve circuit target flow rate Q_valve according to the third embodiment. As in the first embodiment described above, first correlation data indicating the relationship between the lever operation amount and the actuator target flow rate Q_tgt is determined in advance. The calculation unit 7P calculates the actuator target flow rate Q_tgt based on the lever operation amount and the first correlation data.

[0158] The calculation unit 7P calculates an actuator target flow rate Q_tgt_A indicating a target flow rate of hydraulic oil to be supplied to actuator A, based on the operation amount of lever A and the first correlation data for actuator A. The calculation unit 7P calculates an actuator target flow rate Q_tgt_B indicating a target flow rate of hydraulic oil to be supplied to actuator B, based on the operation amount of lever B and the first correlation data for actuator B. The calculation unit 7P calculates an actuator target flow rate Q_tgt_C indicating a target flow rate of hydraulic oil to be supplied to actuator C, based on the operation amount of lever C and the first correlation data for actuator C.

[0159] The calculation unit 7P calculates the sum of the actuator target flow rate Q_tgt_A, the actuator target flow rate Q_tgt_B, and the actuator target flow rate Q_tgt_C.

[0160] The calculation unit 7P selects the maximum actuator load pressure P_act from the multiple actuator load pressures P_act. For example, when the actuator load pressure P_act_A applied to actuator A, the actuator load pressure P_act_B applied to actuator B, and the actuator load pressure P_act_C applied to actuator C are acquired and the actuator load pressure P_act_A is the maximum, the calculation unit 7P selects the actuator target pressure P_tgt_A corresponding to actuator A.

[0161] The calculation unit 7P calculates an arithmetic expression in which the larger of the sum of the boost pressure P_ofst and the valve circuit target pressure P_valve minus the maximum value of the actuator load pressure P_act and 0 is used as the numerator, and the boost pressure P_ofst is used as the denominator. The calculation unit 7P multiplies the smaller of the calculated value and 1 by the sum of the actuator target flow rates Q_tgt, and sets the value as the valve circuit target flow rate Q_valve.

[0162] The calculation unit 7P calculates the leakage flow rate Q_leak based on the valve circuit detected pressure P_p and the valve circuit target flow rate Q_valve (step SE8). The calculation unit 7P calculates the leakage flow rate Q_leak based on, for example, the method described with reference to FIG. 7.

[0163] The calculation unit 7P calculates the pump target flow rate Q_p, which indicates the target flow rate of hydraulic oil discharged from the pump 12, based on the valve circuit target flow rate Q_valve calculated in step SE7 and the leakage flow rate Q_leak calculated in step SE8 (step SE9).

[0164] The calculation unit 7P calculates the target opening area A_bleed of the bleed valve 14 based on the valve circuit detected pressure P_p acquired in step SE2, the valve circuit target flow rate Q_valve calculated in step SE7, the valve circuit target pressure P_valve calculated in step SE6, the leakage flow rate Q_leak calculated in step SE8, and the pump target flow rate Q_p calculated in step SE9. The calculation unit 7P calculates the target opening area A_bleed of the bleed valve 14 based on equation (1) (step SE10).

[0165] The bleed valve command unit 7B calculates a bleed valve command value for adjusting the opening area of ​​the bleed valve 14 based on the target opening area A_bleed of the bleed valve 14 calculated in step SE10 (step SE11). The bleed valve command unit 7B outputs a bleed valve command, which is a control command for controlling the bleed valve 14, based on the target opening area A_bleed of the bleed valve 14. The bleed valve command unit 7B outputs the bleed valve command so that the opening area of ​​the bleed valve 14 becomes the target opening area A_bleed of the bleed valve 14 (step SE12).

[0166] The pump swash plate command unit 7C calculates a pump swash plate command value for adjusting the displacement of the pump 12 based on the pump target flow rate Q_p calculated in step SE9 (step SE13). The pump swash plate command unit 7C outputs a pump swash plate command, which is a control command for controlling the displacement of the pump 12 based on the pump target flow rate Q_p. The pump swash plate command unit 7C outputs a pump swash plate command so that hydraulic oil is discharged from the pump 12 at the pump target flow rate Q_p (step SE14).

[0167] The meter-in valve command unit 7A calculates a meter-in valve command value for adjusting the opening area of ​​the meter-in valve 13 based on the actuator target flow rate Q_tgt calculated in step SE4 (step SE15).

[0168] The meter-in valve command unit 7A calculates the opening area A_tgt (target opening area) of the meter-in valve 13 based on the valve circuit detected pressure P_p and the actuator load pressure P_act. The meter-in valve command unit 7A calculates the opening area A_tgt of the meter-in valve 13 based on the above-mentioned equation (3).

[0169] A first conversion table is determined in advance, taking into consideration the opening characteristics of the spool of the meter-in valve 13. The first conversion table is a conversion table for converting the opening area A_tgt of the meter-in valve 13 into a target spool stroke of the meter-in valve 13. The meter-in valve command unit 7A inputs the opening area A_tgt of the meter-in valve 13 calculated based on equation (3) into the first conversion table to calculate the target spool stroke of the meter-in valve 13. In addition, a second conversion table is determined in advance for converting the target spool stroke of the meter-in valve 13 into a meter-in valve command value. The meter-in valve command unit 7A can calculate the meter-in valve command value for adjusting the opening area A_tgt of the meter-in valve 13 by inputting the target spool stroke of the meter-in valve 13 into the second conversion table.

[0170] The meter-in valve command unit 7A outputs a meter-in valve command, which is a control command for controlling the opening area of ​​the meter-in valve 13, so that hydraulic oil is supplied to the actuator at the actuator target flow rate Q_tgt (step SE16).

[0171] As described above, the pump 12 has a pump minimum flow rate Q_p_min that indicates the minimum value of the discharge flow rate. In this embodiment, when the valve circuit detected pressure P_p, which indicates the pressure detected by the valve circuit pressure sensor 20, exceeds the valve circuit target pressure P_valve or a pressure close thereto, the pump swash plate command unit 7C controls the pump 12 so that hydraulic oil is discharged from the pump 12 at the pump minimum flow rate Q_p_min. When the valve circuit detected pressure P_p is equal to or lower than the valve circuit target pressure P_valve or a pressure close thereto, the pump swash plate command unit 7C controls the pump 12 so that hydraulic oil is discharged from the pump 12 at the pump target flow rate Q_p, based on the valve circuit target flow rate Q_valve.

[0172] In the embodiment, the discharge flow rate of the hydraulic oil discharged from the pump 12 is set to the pump minimum flow rate Q_p_min, but when the valve circuit detected pressure P_p exceeds the valve circuit target pressure P_valve, as long as the discharge flow rate of the pump 12 can be reduced to below the pump target flow rate Q_p, the discharge flow rate of the pump 12 is not limited to the pump minimum flow rate value Q_p_min and may be set to a flow rate reduced below the pump target flow rate Q_p. Furthermore, the discharge flow rate of the pump 12 may be a fixed value or a variable value corresponding to the valve circuit target pressure P_valve.

[0173] Fig. 17 is a diagram showing the relationship between the lever operation amount, the valve circuit target flow rate Q_valve, and the valve target pressure P_valve according to the third embodiment. Fig. 18 is a diagram showing the relationship between the lever operation amount, the pump target flow rate Q_p, and the valve target pressure P_valve according to the third embodiment.

[0174] As shown in Figures 17 and 18, for example, if the multiple actuator load pressures P_act are 0 MPa, 10 MPa, and 20 MPa, respectively, when calculating the valve circuit target flow rate Q_valve, as described with reference to Figure 16, an actuator load pressure P_act of 20 MPa is selected. As the actuator load pressure P_act increases, the timing at which the valve circuit target flow rate Q_valve begins to increase becomes later relative to the lever operation amount. That is, as shown in Figure 18, the timing at which the pump target flow rate Q_p begins to increase from the minimum pump flow rate Q_p_min also becomes later. If the pump target flow rate Q_p does not increase, the pressure in the valve circuit 17 will not increase any further, and so the pressure in the valve circuit 17 will be suppressed at the valve target pressure P_valve or a pressure close to it.

[0175] As described above, in the third embodiment, the change in the flow rate of hydraulic oil supplied to the actuator according to the actuator load pressure P_act (so-called throttling characteristics) can be made to occur over a wider range relative to the lever operation amount. This reduces the sudden start of movement of the work implement cylinder 6 when lifting a heavy object with the work implement 4, thereby achieving stable operation. While this effect can also be obtained in the first and second embodiments described above, in the third embodiment, the sudden start of movement of the work implement cylinder 6 is more effectively suppressed.

[0176] 1...working machine, 2...traveling body, 2A...track, 3...swivel body, 4...working implement, 4A...boom, 4B...arm, 4C...bucket, 5...swivel motor, 6...working implement cylinder, 6A...boom cylinder, 6B...arm cylinder, 6C...bucket cylinder, 7...controller, 7A...meter-in valve command unit, 7B...bleed valve command unit, 7C...pump swash plate command unit, 7D...lever operation amount acquisition unit, 7E...valve circuit pressure acquisition unit, 7F...actuator circuit pressure acquisition unit, 7G...rotation speed acquisition unit, 7H...hydraulic oil temperature acquisition unit, 7J...spool Stroke acquisition unit, 7P...calculation unit, 8...operation device, 9...monitor, 10...computer, 10A...processor, 10B...main memory, 10C...storage, 10D...input / output interface, 10E...communication interface, 10F...computer program, 11A...control system, 11B...control system, 12...pump, 12A...discharge port, 13...meter-in valve, 13A...first meter-in valve, 13B...second meter-in valve, 14...bleed valve, 15...servo valve, 16...tank, 17...valve circuit, 18 ...actuator circuit, 18A...first actuator circuit, 18B...second actuator circuit, 19...bleed circuit, 20...valve circuit pressure sensor, 21...actuator circuit pressure sensor, 22...rotational speed sensor, 23...hydraulic oil temperature sensor, 24...spool stroke sensor, 24A...first spool stroke sensor, 24B...second spool stroke sensor, 25...tank circuit, 25A...first tank circuit, 25B...second tank circuit, A_act...opening area of ​​meter-in valve, A_bleed...bleed valve target opening area of ​​the valve, P_act...actuator load pressure, P_ofst...boosting pressure, P_p...valve circuit detected pressure, P_tgt...actuator target pressure, P_valve...valve circuit target pressure, Q_act...meter-in valve estimated flow rate, Q_est_lim...set value, Q_leak...leakage flow rate, Q_p...pump target flow rate, Q_p_min...pump minimum flow rate, Q_strtn...set value, Q_tgt...actuator target flow rate, Q_valve...valve circuit target flow rate, Q_v_est...valve circuit estimated flow rate.

Claims

1. A control system for a work machine comprising: a pump that discharges hydraulic oil; a meter-in valve that controls the flow rate of hydraulic oil supplied from the pump to an actuator; a valve circuit that connects the pump and the meter-in valve; a bleed circuit that branches off from the valve circuit and is connected to a tank; a bleed valve that is disposed in the bleed circuit and controls the flow rate of hydraulic oil discharged from the valve circuit to the tank by changing a valve opening; and a controller, wherein the controller calculates a valve circuit target flow rate that indicates a target flow rate of hydraulic oil to be supplied to the valve circuit; calculates a valve circuit target pressure that indicates a target pressure of hydraulic oil to be supplied to the valve circuit; calculates a leakage flow rate that indicates an estimated flow rate of hydraulic oil leaking from the valve circuit; calculates a target opening area of ​​the bleed valve when hydraulic oil is discharged from the valve circuit to the tank via the bleed valve based on the valve circuit target flow rate, the valve circuit target pressure, and the leakage flow rate; and controls the bleed valve based on the target opening area.

2. A control system for a work machine according to claim 1, further comprising a valve circuit pressure sensor that detects the pressure of hydraulic oil in the valve circuit, and wherein the controller calculates the leakage flow rate based on the valve circuit target pressure and a valve circuit detected pressure that indicates the pressure detected by the valve circuit pressure sensor when the valve circuit target flow rate is zero.

3. A control system for a work machine according to claim 2, wherein the controller calculates the leakage flow rate by adjusting the target opening area of ​​the bleed valve so that the valve circuit detected pressure and the valve circuit target pressure coincide with each other.

4. A control system for a working machine as set forth in claim 1, comprising: an actuator circuit connecting the meter-in valve and the actuator; a spool stroke sensor detecting a spool stroke of the meter-in valve; a valve circuit pressure sensor detecting the pressure of hydraulic oil in the valve circuit; and an actuator circuit pressure sensor detecting the pressure of the actuator circuit, wherein the controller acquires a valve circuit detected pressure indicating the pressure detected by the valve circuit pressure sensor; calculates an actuator load pressure indicating the load pressure on the actuator based on detection data from the actuator circuit pressure sensor; calculates a valve circuit estimated flow rate indicating an estimated flow rate of hydraulic oil supplied to the valve circuit based on the spool stroke, the valve circuit detected pressure, and the actuator load pressure; and calculates the leakage flow rate based on the valve circuit detected pressure, the valve circuit target pressure, and the valve circuit estimated flow rate.

5. A control system for a work machine according to claim 4, wherein, when the valve circuit estimated flow rate is lower than a set value, the controller adjusts the target opening area of ​​the bleed valve so that the valve circuit target pressure and the valve circuit detected pressure coincide with each other, and calculates the leakage flow rate.

6. A work machine control system according to claim 2 or claim 4, wherein the controller does not calculate the leakage flow rate when the rotation speed of the pump is equal to or lower than a rotation speed threshold value.

7. A work machine control system according to claim 2 or claim 4, wherein the controller calculates and stores the leakage flow rate which varies depending on the rotation speed of the pump, and calculates a target opening area of ​​the bleed valve using the stored leakage flow rate.

8. A work machine control system according to claim 2 or claim 4, wherein the controller does not calculate the leakage flow rate when the temperature of the hydraulic oil is equal to or lower than a temperature threshold value.

9. A control system for a work machine according to claim 2 or claim 4, wherein the controller calculates and stores the leakage flow rate which varies depending on the temperature of the hydraulic oil, and calculates a target opening area of ​​the bleed valve using the stored leakage flow rate.

10. A control system for a work machine as set forth in claim 1, comprising an actuator circuit connecting the meter-in valve and the actuator, wherein the controller calculates an actuator target pressure indicating a target pressure of hydraulic oil to be supplied to each of the plurality of actuator circuits based on an operation amount indicating a value of an operation signal for operating the actuator, and calculates the valve circuit target pressure based on the actuator target pressure.

11. A control system for a work machine according to claim 10, further comprising an actuator circuit pressure sensor that detects the pressure in the actuator circuit, wherein the controller calculates an actuator load pressure that indicates the load pressure applied to each of the plurality of actuators based on the detection data of the actuator circuit pressure sensor, and determines the actuator target pressure corresponding to the actuator with the maximum actuator load pressure as the valve circuit target pressure.

12. A control system for a work machine as claimed in claim 10 or claim 11, further comprising a valve circuit pressure sensor that detects the pressure of hydraulic oil in the valve circuit, wherein the controller acquires a valve circuit detected pressure indicating the pressure detected by the valve circuit pressure sensor, and calculates the target opening area based on the smaller of the first valve circuit target pressure and the second valve circuit target pressure, where the valve circuit target pressure calculated based on the actuator target pressure is set to a first valve circuit target pressure and the value obtained by adding the valve circuit detected pressure and a preset boost pressure is set to a second valve circuit target pressure.

13. A control system for a work machine according to claim 1, wherein the controller calculates the valve circuit target flow rate based on an operation amount indicating a value of an operation signal for operating the actuator.

14. A control system for a work machine as set forth in claim 13, further comprising an actuator circuit connecting the meter-in valve and the actuator, wherein the controller calculates an actuator target flow rate indicating a target flow rate of hydraulic oil to be supplied to the actuator circuit based on an operation amount indicating a value of an operation signal for operating the actuator, and calculates the valve circuit target flow rate based on the actuator target flow rate.

15. A control system for a work machine as set forth in claim 1, further comprising an actuator circuit connecting the meter-in valve and the actuator, wherein the controller calculates the opening area of ​​the meter-in valve, calculates a meter-in valve estimated flow rate indicating an estimated flow rate of hydraulic oil passing through the meter-in valve based on the opening area of ​​the meter-in valve, and calculates a valve circuit estimated flow rate indicating an estimated flow rate of hydraulic oil supplied to the valve circuit by adding up a plurality of the meter-in valve estimated flow rates.

16. A control system for a work machine as set forth in claim 13 or claim 15, wherein the controller calculates the target opening area based on the smaller of the first valve circuit target flow rate and the second valve circuit target flow rate, where a valve target circuit flow rate calculated based on an operation amount indicating the value of an operation signal for operating the actuator is set as a first valve target flow rate, and an estimated valve circuit flow rate indicating an estimated flow rate of hydraulic oil to be supplied to the valve circuit is set as a second valve target flow rate.

17. A work machine control system according to claim 1, wherein the controller calculates a pump target flow rate indicating a target flow rate of hydraulic oil to be discharged from the pump based on the valve circuit target flow rate and the leakage flow rate, and controls the displacement of the pump based on the pump target flow rate.

18. A control system for a work machine as set forth in claim 17, wherein the controller: calculates a corrected leakage flow rate by correcting the leakage flow rate so that it decreases as the valve circuit target flow rate increases; calculates a pump target flow rate indicating a target flow rate of hydraulic oil to be discharged from the pump based on the valve circuit target flow rate and the corrected leakage flow rate; and controls the capacity of the pump based on the pump target flow rate.

19. A control system for a work machine comprising: a pump that discharges hydraulic oil; a meter-in valve that controls the flow rate of hydraulic oil supplied from the pump to an actuator; a valve circuit that connects the pump and the meter-in valve; a bleed circuit that branches off from the valve circuit and is connected to a tank; a bleed valve that is disposed in the bleed circuit and controls the flow rate of hydraulic oil discharged from the valve circuit to the tank by changing a valve opening; and a controller, wherein the controller calculates a valve circuit target flow rate that indicates a target flow rate of hydraulic oil to be supplied to the valve circuit; calculates a pump target flow rate that indicates a target flow rate of hydraulic oil to be discharged from the pump based on the valve circuit target flow rate; calculates a target opening area of ​​the bleed valve that discharges hydraulic oil from the valve circuit to the tank via the bleed valve based on the pump target flow rate; controls the bleed valve based on the target opening area; and if the valve circuit becomes unstable due to control of the bleed valve, controls the pump so that the flow rate of hydraulic oil discharged from the pump is reduced to below the pump target flow rate.

20. A control system for a work machine comprising: a pump that discharges hydraulic oil; a meter-in valve that controls the flow rate of hydraulic oil supplied from the pump to an actuator; a valve circuit that connects the pump and the meter-in valve; a bleed circuit that branches off from the valve circuit and is connected to a tank; a bleed valve that is arranged in the bleed circuit and controls the flow rate of hydraulic oil discharged from the valve circuit to the tank by changing a valve opening; a valve circuit pressure sensor that detects the pressure of the valve circuit; and a controller, wherein the controller calculates a valve circuit target flow rate that indicates a target flow rate of hydraulic oil to be supplied to the valve circuit; calculates a valve circuit target pressure that indicates a target pressure of hydraulic oil to be supplied to the valve circuit; calculates a pump target flow rate that indicates a target flow rate of hydraulic oil to be discharged from the pump based on the valve circuit target flow rate; and when the valve circuit detected pressure, which indicates the pressure detected by the valve circuit pressure sensor, exceeds the valve circuit target pressure, controls the pump so that the flow rate of hydraulic oil discharged from the pump is reduced below the pump target flow rate.

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