Work machine control system and work machine control method

Abstract

This work machine control system comprises: a hydraulic pump that discharges hydraulic oil; a hydraulic actuator to which the hydraulic oil discharged from the hydraulic pump is supplied; a meter-in valve that adjusts a flow rate of the hydraulic oil flowing into the hydraulic actuator; a meter-out valve that adjusts a flow rate of the hydraulic oil flowing out from the hydraulic actuator; a meter-out pressure sensor that detects a meter-out pressure indicating the pressure of the hydraulic oil flowing out from the hydraulic actuator; and a controller. The controller calculates a target meter-in flow rate indicating a target value of the flow rate of the hydraulic oil flowing into the hydraulic actuator, and a target meter-out flow rate indicating a target value of the flow rate of the hydraulic oil flowing out of the hydraulic actuator, on the basis of a target operation speed of the hydraulic actuator. The controller controls at least one of the hydraulic pump, the meter-in valve, and the meter-out valve to eliminate a state in which the pressure of the hydraulic oil flowing out from the hydraulic actuator is high between the hydraulic actuator and the meter-out valve, on the basis of the meter-out pressure and at least one of the target meter-in flow rate and the target meter-out flow rate.

Description

Control System and Control Method of Working Machine

[0001] The present disclosure relates to a control system and a control method of a working machine.

[0002] In the technical field related to working machines, a hydraulic circuit of a construction machine as disclosed in Patent Document 1 is known. In Patent Document 1, when the hydraulic pressure in the supply path is in a high-pressure state, for the purpose of suppressing a sudden hydraulic pressure fluctuation when the working machine lever is switched to the neutral position, when the operating position of the direction control valve is switched from the communication position to the neutral position, a technique is disclosed in which the flow rate of the pressure oil discharged from the unloading valve increases.

[0003] Japanese Patent Application Laid-Open No. 2011-149509

[0004] The working machine has a hydraulic cylinder that operates the working machine. The hydraulic cylinder operates when the operating device is operated by an operator of the working machine. For example, when the operating device is operated in the first direction so that the hydraulic cylinder extends, hydraulic oil is supplied to the bottom chamber of the hydraulic cylinder. Even after the piston of the hydraulic cylinder reaches the end of the movable range (stroke end), the operating device may continue to be operated in the first direction. If the operating device continues to be operated in the first direction, hydraulic oil will continue to be supplied to the bottom chamber while the piston has reached the stroke end. As a result, the bottom chamber becomes high-pressure. When the operating device is operated in the second direction so that the hydraulic cylinder contracts while the bottom chamber is in a high-pressure state, the operation of the hydraulic cylinder may become unstable due to the high-pressure bottom chamber.

[0005] The present disclosure aims to suppress the occurrence of malfunction in the operation of a hydraulic actuator.

[0006] A control system for a work machine is provided, comprising: a hydraulic pump for discharging hydraulic fluid; a hydraulic actuator to which the hydraulic fluid discharged from the hydraulic pump is supplied; a meter-in valve for adjusting the flow rate of hydraulic fluid flowing into the hydraulic actuator; a meter-out valve for adjusting the flow rate of hydraulic fluid flowing out of the hydraulic actuator; a meter-out pressure sensor for detecting the meter-out pressure indicating the pressure of the hydraulic fluid flowing out of the hydraulic actuator; and a controller. The controller calculates a target meter-in flow rate, which indicates a target value for the flow rate of hydraulic fluid flowing into the hydraulic actuator, and a target meter-out flow rate, which indicates a target value for the flow rate of hydraulic fluid flowing out of the hydraulic actuator, based on the target operating speed of the hydraulic actuator. Based on at least one of the target meter-in flow rate and the target meter-out flow rate and the meter-out pressure, the controller controls the hydraulic pump, the meter-in valve, and at least one of the meter-out valve to eliminate a condition in which the pressure of the hydraulic fluid flowing out of the hydraulic actuator is high between the hydraulic actuator and the meter-out valve.

[0007] According to this disclosure, the occurrence of malfunctions in hydraulic actuators is suppressed.

[0008] Figure 1 is a side view showing a work machine according to the first embodiment. Figure 2 is a schematic diagram showing the control system of the work machine according to the first embodiment. Figure 3 is a hardware configuration diagram showing the controller according to the first embodiment. Figure 4 is a functional block diagram showing the controller according to the first embodiment. Figure 5 is a diagram showing correlation data showing the relationship between the meter-out pressure and the corrected meter-in flow rate according to the first embodiment. Figure 6 is a diagram illustrating an example of the operation of the work machine according to the first embodiment. Figure 7 is a flowchart showing the control method of the work machine according to the first embodiment. Figure 8 is a timing chart showing the control method of the work machine according to the first embodiment. Figure 9 is a flowchart showing the control method of the work machine when the meter-out pressure sensor according to the first embodiment is abnormal. Figure 10 is a functional block diagram showing the controller according to the second embodiment. Figure 11 is a flowchart showing the control method of the work machine according to the second embodiment. Figure 12 is a timing chart showing the control method of the work machine according to the second embodiment.

[0009] [First Embodiment] The first embodiment will now be described.

[0010] <Work Machinery> Figure 1 is a side view showing work machine 1 according to the first embodiment. Work machine 1 operates at the work site. Examples of work machine 1 include a hydraulic excavator, a wheel loader, and a bulldozer. In this embodiment, work machine 1 is a hydraulic excavator. Work machine 1 comprises a traveling body 2, a slewing body 3, a work machine 4, a traveling motor 9, a slewing motor 5, a work machine cylinder 6, a controller 7, and an operating device 8.

[0011] The running body 2 supports the rotating body 3. The running body 2 has a pair of tracks 2A. One track 2A is positioned on the left side of the running body 2. The other track 2A is positioned on the right side of the running body 2. The work machine 1 moves as the tracks 2A rotate.

[0012] The slewing body 3 is positioned above the traveling body 2. The slewing body 3 is rotatably supported by the traveling body 2. The slewing body 3 has a cab. The operator of the work machine 1 is seated in the cab.

[0013] The work implement 4 is rotatably mounted on the slewing body 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 of the slewing body 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 travel motor 9 moves the travel body 2 that supports the slewing body 3. The travel motor 9 rotates the tracks 2A of the travel body 2. The travel motor 9 includes a left travel motor that rotates the left track 2A and a right travel motor that rotates the right track 2A. The travel body 2 moves as the tracks 2A rotate. The travel motor 9 is a hydraulic motor driven by hydraulic fluid. The travel motor 9 is an example of a hydraulic actuator driven by hydraulic fluid.

[0015] The slewing motor 5 rotates the slewing body 3, which is supported by the traveling body 2. The slewing motor 5 is connected to the slewing body 3. The slewing motor 5 is a hydraulic motor driven by hydraulic fluid. The slewing motor 5 is an example of a hydraulic actuator driven by hydraulic fluid.

[0016] The work implement cylinder 6 operates the work implement 4 attached to the slewing body 3. The work implement cylinder 6 is a hydraulic cylinder driven by hydraulic fluid. The work implement cylinder 6 is an example of a hydraulic actuator driven by hydraulic fluid. The work implement cylinder 6 has a cylinder tube 61, a piston 62 that is movable inside the cylinder tube 61, and a rod 63 fixed to the piston 62 (see Figure 2). The work implement cylinder 6 includes a boom cylinder 6A, an arm cylinder 6B, and a bucket cylinder 6C.

[0017] The boom cylinder 6A operates the boom 4A. The base end of the cylinder tube of the boom cylinder 6A is connected to the slewing body 3, and the tip of the rod of the boom cylinder 6A is connected to the boom 4A. The operation of the boom 4A includes raising and lowering movements. When hydraulic fluid flows into the bottom chamber of the boom cylinder 6A and the boom cylinder 6A extends, the boom 4A is raised. When hydraulic fluid flows into the head chamber of the boom cylinder 6A and the boom cylinder 6A retracts, the boom 4A is lowered.

[0018] 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 of the rod of the arm cylinder 6B is connected to the arm 4B. The operation of the arm 4B includes digging and dumping operations. When hydraulic fluid flows into the bottom chamber of the arm cylinder 6B and the arm cylinder 6B extends, the arm 4B performs the digging operation. When hydraulic fluid flows into the head chamber of the arm cylinder 6B and the arm cylinder 6B retracts, the arm 4B performs the dumping operation.

[0019] 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 of the rod of the bucket cylinder 6C is connected to the bucket 4C via a link mechanism. The operation of the bucket 4C includes digging and dumping operations. When hydraulic fluid flows into the bottom chamber of the bucket cylinder 6C and the bucket cylinder 6C extends, the bucket 4C performs the digging operation. When hydraulic fluid flows into the head chamber of the bucket cylinder 6C and the bucket cylinder 6C retracts, the bucket 4C performs the dumping operation.

[0020] The operating device 8 is located in the cab of the slewing body 3. The operating device 8 is operated by an operator seated in the cab. The operator can operate the operating device 8 while seated in the driver's seat located in the cab. The operating device 8 includes a plurality of levers. The operating device 8 is operated to operate the hydraulic actuator of the work machine 1. The operating device 8 is operated to operate at least one of the traveling body 2, the slewing body 3, and the work machine 4.

[0021] When the operating device 8 is operated, an operating signal (electrical signal) is generated to operate the hydraulic actuator of the work machine 1. The operating signal from the operating device 8 is transmitted to the controller 7. The operating signal from the operating device 8 includes the amount of operation of the operating device 8. The amount of operation may be considered as the signal strength of the operating signal. If the operating device 8 includes a lever, the amount of operation may be considered as the operating angle (tilting angle) of the lever. The controller 7 controls the hydraulic actuator based on the amount of operation of the operating device 8.

[0022] In this embodiment, the operation signal (operated quantity) is generated by operating the operating device 8, but the operation signal may be generated by, for example, the controller 7. The controller 7 may automatically generate the operation signal without the operator operating the operating device 8. The operation signal may be generated by a controller other than the controller 7. The other controller may be located outside the work machine 1. The operation signal may be transmitted from the controller located outside the work machine 1 to the controller 7 mounted on the work machine 1. The operating device 8 may be located outside the work machine 1. The work machine 1 may be remotely controlled by a remote control device located outside the work machine 1. When the work machine 1 is remotely controlled by a remote control device, a remote controller connected to the remote control 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.

[0023] <Control System> Figure 2 is a schematic diagram showing the control system 10 of the work machine 1 according to the first embodiment. The control system 10 includes a hydraulic circuit (hydraulic system) that operates using hydraulic fluid. Hereinafter, the hydraulic actuator will be described as the work machine cylinder 6.

[0024] As shown in Figure 2, the control system 10 includes a work machine cylinder 6, a controller 7, an operating device 8, a power source 11, a hydraulic pump 12, a tank 13, a head-side valve 14, a bottom-side valve 15, a head-side pressure sensor 26, a bottom-side pressure sensor 16, a suction passage 18, a pump passage 19, a head-side passage 20, a bottom-side passage 21, a drain passage 27, a regeneration passage 23, and a check valve 24.

[0025] The work machine cylinder 6 is a hydraulic cylinder. The work machine cylinder 6 has a cylinder tube 61, a piston 62, and a rod 63. The piston 62 is movable inside the cylinder tube 61. The rod 63 is fixed to one end face of the piston 62 and moves together with the piston 62. The piston 62 divides the internal space of the cylinder tube 61 into a head chamber 64 and a bottom chamber 65. When the work machine cylinder 6 is retracted, the volume of the head chamber 64 increases. When the work machine cylinder 6 is extended, the volume of the bottom chamber 65 increases. The work machine cylinder 6 is retracted as hydraulic fluid flows into the head chamber 64 and hydraulic fluid flows out of the bottom chamber 65. The work machine cylinder 6 is extended as hydraulic fluid flows into the bottom chamber 65 and hydraulic fluid flows out of the head chamber 64.

[0026] The power source 11 is the power source for the work machine 1. A diesel engine is given as an example of the power source 11. However, the power source 11 may also be an electric motor. The power source 11 is connected to the hydraulic pump 12. The power source 11 drives the hydraulic pump 12.

[0027] The suction passage 18 connects the tank 13 and the hydraulic pump 12. The pump passage 19 connects the hydraulic pump 12 to the head valve 14 and the bottom valve 15. The head passage 20 functions as a meter-in passage when the work cylinder 6 is retracted and as a meter-out passage when the work cylinder 6 is extended. The head passage 20 connects the head valve 14 to the head chamber 64 of the work cylinder 6. The bottom passage 21 functions as a meter-out passage when the work cylinder 6 is retracted and as a meter-in passage when the work cylinder 6 is extended. The bottom passage 21 connects the bottom chamber 65 of the work cylinder 6 to the bottom valve 15. The drain passage 27 connects the bottom valve 15 to the tank 13.

[0028] The hydraulic pump 12 discharges hydraulic fluid. The hydraulic fluid discharged from the hydraulic pump 12 is supplied to the work machine cylinder 6. The hydraulic pump 12 is a swashplate type variable displacement pump. The capacity [cc / rev] of the hydraulic pump 12 is changed by changing the angle of the swashplate of the hydraulic pump 12. The hydraulic pump 12 draws in hydraulic fluid contained in the tank 13 through the suction passage 18. The hydraulic pump 12 discharges the hydraulic fluid drawn in from the tank 13 into the pump passage 19.

[0029] The head-side valve 14 adjusts the flow rate of hydraulic fluid flowing into the inlet of the work machine cylinder 6. In this embodiment, the head-side valve 14 controls the flow rate of hydraulic fluid flowing from the head-side passage 20 into the head chamber 64 of the work machine cylinder 6, or the flow rate of hydraulic fluid flowing from the head chamber 64 into the head-side passage 20. By adjusting the opening area of ​​the head-side valve 14, the flow rate of hydraulic fluid flowing into the work machine cylinder 6 is adjusted. By controlling the flow rate of hydraulic fluid flowing into the work machine cylinder 6, the operating speed (cylinder speed) of the work machine cylinder 6 is controlled. The head-side valve 14 is, for example, an electromagnetic proportional control valve. The spool of the head-side valve 14 is movable between a neutral position N2, a first position U2, and a second position D2. When the spool of the head-side valve 14 is in the first position U2, that is, when the work machine cylinder 6 is retracted, the head-side valve 14 functions as a meter-in valve that controls the flow rate of hydraulic fluid supplied from the hydraulic pump 12 to the head chamber 64 of the work machine cylinder 6. When the spool of the head-side valve 14 is in the second position D2, that is, when the work machine cylinder 6 is extended, the head-side valve 14 functions as a regeneration valve that controls the flow rate of hydraulic fluid supplied from the head chamber 64 of the work machine cylinder 6 to the bottom chamber 65 of the work machine cylinder 6. Figure 2 shows the state in which the spool of the head-side valve 14 is positioned in the neutral position N2.

[0030] The head-side valve 14 has a pump port P5, a first head port P7, a second head port P6, and a regeneration port P8. The pump port P5 is connected to the hydraulic pump 12 via a pump passage 19. The first head port P7 and the second head port P6 are each connected to the head chamber 64 of the work machine cylinder 6 via a head-side passage 20. The regeneration port P8 is connected to the bottom-side valve 15 via a regeneration passage 23.

[0031] The controller 7 determines whether to make the head-side valve 14 function as a meter-in valve or a regeneration valve based on the extension and retraction of the work implement cylinder 6. If the controller 7 determines that the work implement cylinder 6 is retracting and that the head-side valve 14 should function as a meter-in valve, it adjusts the opening area of ​​the meter-in valve (meter-in opening area). If the controller 7 determines that the work implement cylinder 6 is extending and that the head-side valve 14 should function as a regeneration valve, it adjusts the opening area of ​​the regeneration valve (regeneration opening area).

[0032] The bottom valve 15 adjusts the flow rate of hydraulic fluid flowing out of the outlet of the work machine cylinder 6. In this embodiment, the bottom valve 15 controls the flow rate of hydraulic fluid flowing out of the bottom chamber 65 of the work machine cylinder 6 into the bottom passage 21 or the flow rate of hydraulic fluid flowing in from the bottom passage 21 into the bottom chamber 65. By adjusting the opening area of ​​the bottom valve 15, the flow rate of hydraulic fluid flowing out of the work machine cylinder 6 is adjusted. By controlling the flow rate of hydraulic fluid flowing out of the work machine cylinder 6, the operating speed (cylinder speed) of the work machine cylinder 6 is controlled. The bottom valve 15 is, for example, an electromagnetic proportional control valve. The spool of the bottom valve 15 is movable between a neutral position N1, a first position U1, and a second position D1. When the spool of the bottom valve 15 is in the first position U1, that is, when the work machine cylinder 6 is retracted, the bottom valve 15 functions as a meter-out valve that controls the flow rate of hydraulic fluid discharged from the bottom chamber 65 of the work machine cylinder 6 to the tank 13. When the spool of the bottom valve 15 is in the second position D1, that is, when the work machine cylinder 6 is extended, the bottom valve 15 functions as a meter-in valve that controls the flow rate of hydraulic fluid supplied from the hydraulic pump 12 to the bottom chamber 65 of the work machine cylinder 6. Figure 2 shows the state in which the spool of the bottom valve 15 is positioned in the neutral position N1.

[0033] The bottom valve 15 has a pump port P1, a first bottom port P2, a second bottom port P3, and a drain port P4. The pump port P1 is connected to the hydraulic pump 12 via a pump passage 19. The first bottom port P2 and the second bottom port P3 are each connected to the bottom chamber 65 of the work machine cylinder 6 via a bottom passage 21. The drain port P4 is connected to the tank 13 via a drain passage 27.

[0034] The controller 7 determines whether to make the bottom valve 15 function as a meter-out valve or a meter-in valve based on the extension and retraction of the work equipment cylinder 6. If the controller 7 determines that the work equipment cylinder 6 is retracting and that the bottom valve 15 should function as a meter-out valve, it adjusts the opening area of ​​the meter-out valve (meter-out opening area). If the controller 7 determines that the work equipment cylinder 6 is extending and that the bottom valve 15 should function as a meter-in valve, it adjusts the opening area of ​​the meter-in valve (meter-in opening area).

[0035] The regeneration passage 23 connects the head chamber 64 of the work machine cylinder 6 to the head-side passage 20. The regeneration passage 23 also connects the bottom-side passage 21 to the head-side passage 20. In this embodiment, the regeneration passage 23 connects the regeneration port P8 of the head-side valve 14 to the bottom-side passage 21. A check valve 24 is located in the regeneration passage 23. The check valve 24 blocks the flow of hydraulic fluid from the bottom-side passage 21 to the regeneration port P8 of the head-side valve 14.

[0036] The head-side valve 14 functions as a regeneration valve that adjusts the flow rate of hydraulic fluid supplied from the head chamber 64 of the work machine cylinder 6 to the bottom chamber 65 of the work machine cylinder 6 via the head-side passage 20 and the regeneration passage 23. When the spool of the head-side valve 14 is in the second position D2, the hydraulic fluid that has flowed out of the head chamber 64 of the work machine cylinder 6 is regenerated into the bottom chamber 65. The head-side valve 14 functions as a regeneration valve that controls the flow rate of hydraulic fluid supplied from the head chamber 64 to the bottom chamber 65.

[0037] The head-side pressure sensor 26 detects the pressure in the head-side flow path 20 between the work machine cylinder 6 and the head-side valve 14. The head-side pressure sensor 26 functions as a meter-in pressure sensor that detects the meter-in pressure, which indicates the pressure of the hydraulic fluid flowing into the head chamber 64 of the work machine cylinder 6 when the work machine cylinder 6 is retracted. The head-side pressure sensor 26 also functions as a meter-out pressure sensor that detects the meter-out pressure, which indicates the pressure of the hydraulic fluid flowing out of the head chamber 64 of the work machine cylinder 6 when the work machine cylinder 6 is extended. The detection data from the head-side pressure sensor 26 is transmitted to the controller 7.

[0038] The bottom-side pressure sensor 16 detects the pressure in the bottom-side passage 21 between the work machine cylinder 6 and the bottom-side valve 15. The bottom-side pressure sensor 16 functions as a meter-out pressure sensor that detects the meter-out pressure, which indicates the pressure of the hydraulic fluid flowing out of the bottom chamber 65 of the work machine cylinder 6 when the work machine cylinder 6 is retracted. The bottom-side pressure sensor 16 also functions as a meter-in pressure sensor that detects the meter-in pressure, which indicates the pressure of the hydraulic fluid flowing into the bottom chamber 65 of the work machine cylinder 6 when the work machine cylinder 6 is extended. The detection data from the bottom-side pressure sensor 16 is transmitted to the controller 7.

[0039] <Controller> Figure 3 is a hardware configuration diagram showing a controller 7 according to the first embodiment. The controller 7 includes a computer 25. The computer 25 has a processor 25A such as a CPU (Central Processing Unit), a main memory 25B including non-volatile memory such as ROM (Read Only Memory) and volatile memory such as RAM (Random Access Memory), a storage 25C, an input / output interface 25D including input / output circuits, and a communication interface 25E including communication circuits. The functions of the controller 7 are stored in the storage 25C as a computer program 25F. The processor 25A reads the computer program 25F from the storage 25C, loads it into the main memory 25B, and executes processing according to the computer program 25F. The computer program 25F may be distributed to the computer 25 via a network.

[0040] Figure 4 is a functional block diagram showing a controller 7 according to the first embodiment. The controller 7 outputs control commands to control the hydraulic pump 12, the head-side valve 14, and the bottom-side valve 15. The controller 7 has a plurality of functional units. The functions of the functional units of the controller 7 are performed by the processor 25A. The functional units of the controller 7 include a target operating speed calculation unit 71, a target meter-in flow rate calculation unit 72, a target meter-out flow rate calculation unit 73, a corrected meter-in flow rate calculation unit 74, a corrected meter-out flow rate calculation unit 75, a control unit 76, and a threshold storage unit 77.

[0041] The target operating speed calculation unit 71 calculates the target operating speed (target cylinder speed) of the work machine cylinder 6. The target operating speed calculation unit 71 calculates the target operating speed of the work machine cylinder 6 based on the manipulated variable, which indicates the value of the operation signal for operating the work machine cylinder 6. The operation signal is generated when the operating device 8 is operated by the operator. The target operating speed calculation unit 71 calculates the target operating speed of the work machine cylinder 6 based on the manipulated variable of the operating device 8. The target operating speed may be a value proportional to the manipulated variable of the operating device 8. If a first correlation data showing the relationship between the manipulated variable of the operating device 8 and the target operating speed is predetermined, the target operating speed calculation unit 71 may determine the target operating speed by inputting the manipulated variable of the operating device 8 into the first correlation data.

[0042] The target meter-in flow rate calculation unit 72 calculates a target meter-in flow rate, which indicates the target flow rate of the hydraulic fluid flowing into the work machine cylinder 6, based on the target operating speed of the work machine cylinder 6 calculated by the target operating speed calculation unit 71. There is a one-to-one correspondence between the target operating speed of the work machine cylinder 6 and the target meter-in flow rate. The higher the target operating speed, the higher the target meter-in flow rate. The target meter-in flow rate may also be a value proportional to the target operating speed. If a second correlation data showing the relationship between the target operating speed and the target meter-in flow rate is predetermined, the target meter-in flow rate calculation unit 72 may determine the target meter-in flow rate by inputting the target operating speed into the second correlation data. The target meter-in flow rate calculation unit 72 may also calculate the target meter-in flow rate based on the operating amount of the operating device 8.

[0043] As described above, when the work implement cylinder 6 contracts, the head side valve 14 functions as a meter-in valve that controls the flow rate of the hydraulic oil flowing from the hydraulic pump 12 into the head chamber 64 of the work implement cylinder 6. When the work implement cylinder 6 extends, the bottom side valve 15 functions as a meter-in valve that controls the flow rate of the hydraulic oil flowing from the hydraulic pump 12 into the bottom chamber 65 of the work implement cylinder 6. Based on the operation direction (operation amount) of the operation device 8, the work implement cylinder 6 expands and contracts. The target meter-in flow rate calculation unit 72 determines whether to make the head side valve 14 function as a meter-in valve or to make the bottom side valve 15 function as a meter-in valve based on the operation direction of the operation device 8.

[0044] For example, when the head side valve 14 functions as a meter-in valve, the meter-in flow rate is determined by at least one of the flow rate of the hydraulic oil discharged from the hydraulic pump 12 and the opening area of the head side valve 14. Calculating the target meter-in flow rate includes calculating a target pump flow rate indicating a target value of the flow rate of the hydraulic oil discharged from the hydraulic pump 12. Calculating the target meter-in flow rate includes calculating a target meter-in opening indicating a target value of the opening area of the head side valve 14. The target meter-in flow rate and the target pump flow rate correspond one-to-one. The greater the target meter-in flow rate, the greater the target pump flow rate. The target meter-in flow rate and the target meter-in opening correspond one-to-one. The greater the target meter-in flow rate, the larger the target meter-in opening. The same applies when the bottom side valve 15 functions as a meter-in valve.

[0045] The target meter-out flow rate calculation unit 73 calculates a target meter-out flow rate, which indicates the target value of the flow rate of hydraulic fluid flowing out of the work machine cylinder 6, based on the target operating speed of the work machine cylinder 6 calculated by the target operating speed calculation unit 71. There is a one-to-one correspondence between the target operating speed of the work machine cylinder 6 and the target meter-out flow rate. The higher the target operating speed, the higher the target meter-out flow rate. The target meter-out flow rate may also be a value proportional to the target operating speed. If a third correlation data showing the relationship between the target operating speed and the target meter-in flow rate is predetermined, the target meter-out flow rate calculation unit 73 may determine the target meter-out flow rate by inputting the target operating speed into the third correlation data. The target meter-out flow rate calculation unit 73 may also calculate the target meter-out flow rate based on the operating amount of the operating device 8. The target meter-out flow rate calculation unit 73 may also calculate the target meter-in flow rate based on the target meter-in flow rate calculated by the target meter-in flow rate calculation unit 72. The target meter-out flow rate calculation unit 73 may determine the target meter-out flow rate to be the same value as the target meter-in flow rate.

[0046] As described above, the bottom valve 15 functions as a meter-out valve that controls the flow rate of hydraulic fluid flowing out of the bottom chamber 65 of the work machine cylinder 6 when the work machine cylinder 6 is retracted. The work machine cylinder 6 extends and retracts based on the operating direction (amount of operation) of the operating device 8. The target meter-out flow rate calculation unit 73 determines whether to make the bottom valve 15 function as a meter-in valve or a meter-out valve based on the operating direction of the operating device 8.

[0047] For example, when the bottom valve 15 functions as a meter-out valve, the meter-out flow rate is determined by the opening area of ​​the bottom valve 15. Calculating the target meter-out flow rate includes calculating a target meter-out opening that indicates a target value for the opening area of ​​the bottom valve 15.

[0048] After the operation direction of the operation device 8 is switched and it is determined that either the head side valve 14 or the bottom side valve 15 functions as the meter-in valve, the correction meter-in flow rate calculation unit 74 determines whether pressure relief control described later is necessary. For example, when the operation device 8 is operated so that the meter-in valve switches from the bottom side valve 15 to the head side valve 14 (when the operation amount in FIG. 8 described later reverses to positive), the correction meter-in flow rate calculation unit 74 determines whether pressure relief control for discharging the pressure trapped in the bottom chamber 65 and the bottom side flow path 21 is necessary.

[0049] For example, when the head side valve 14 functions as the meter-out valve, if the meter-out pressure detected by the bottom side pressure sensor 16 is equal to or higher than a predetermined threshold value Sh, the correction meter-in flow rate calculation unit 74 calculates a correction meter-in flow rate that is less than the target meter-in flow rate. The threshold value Sh is stored in advance in the threshold value storage unit 77.

[0050] The threshold value Sh includes a first threshold value Sh1 and a second threshold value Sh2 that is smaller than the first threshold value Sh1. When the meter-out pressure is equal to or higher than the first threshold value Sh1, the correction meter-in flow rate calculation unit 74 determines the correction meter-in flow rate to be zero. Note that the correction meter-in flow rate calculation unit 74 may determine the correction meter-in flow rate to be substantially zero. The correction meter-in flow rate calculation unit 74 may also determine the correction meter-in flow rate to be a value greater than zero and smaller than the specified value. When the meter-out pressure is equal to or higher than the second threshold value Sh2 and less than the first threshold value Sh1, the correction meter-in flow rate calculation unit 74 determines the correction meter-in flow rate such that the lower the meter-out pressure, the greater the correction meter-in flow rate. When the meter-out pressure is less than the second threshold value Sh2, the correction meter-in flow rate calculation unit 74 determines the correction meter-in flow rate to be the target meter-in flow rate.

[0051] Figure 5 is a diagram showing correlation data (fourth correlation data) indicating the relationship between the meter-out pressure and the corrected meter-in flow rate according to the first embodiment. The corrected meter-in flow rate calculation unit 74 calculates the corrected meter-in flow rate based on the table data shown in Figure 5. As shown in Figure 5, in the fourth correlation data, if the meter-out pressure is greater than or equal to the first threshold Sh1, the corrected meter-in flow rate is determined to be zero. If the meter-out pressure is greater than or equal to the second threshold Sh2 and less than the first threshold Sh1, the corrected meter-in flow rate is determined to be higher as the meter-out pressure decreases. If the meter-out pressure is greater than or equal to the second threshold Sh2 and less than the first threshold Sh1, the corrected meter-in flow rate is determined to be proportional to the meter-out pressure. If the meter-out pressure is less than the second threshold Sh2, the corrected meter-in flow rate is determined to be the target meter-in flow rate. The corrected meter-in flow rate calculation unit 74 determines the corrected meter-in flow rate by inputting the meter-out pressure detected by the bottom-side pressure sensor 16 into the fourth correlation data.

[0052] As described above, for example, when the head-side valve 14 functions as a meter-in valve, the meter-in flow rate is determined by at least one of the flow rate of the hydraulic fluid discharged from the hydraulic pump 12 and the opening area of ​​the head-side valve 14. Calculating the corrected meter-in flow rate includes calculating the corrected pump flow rate of the hydraulic pump 12, which has a pump flow rate less than the target pump flow rate. Calculating the corrected meter-in flow rate also includes calculating the corrected meter-in opening of the head-side valve 14, which has an opening area smaller than the target meter-in opening. There is a one-to-one correspondence between the corrected meter-in flow rate and the corrected pump flow rate. The greater the corrected meter-in flow rate, the greater the corrected pump flow rate. There is a one-to-one correspondence between the corrected meter-in flow rate and the corrected meter-in opening. The greater the corrected meter-in flow rate, the larger the corrected meter-in opening.

[0053] The corrected meter-out flow rate calculation unit 75 calculates a corrected meter-out flow rate that is greater than the target meter-out flow rate if the meter-out pressure detected by the bottom-side pressure sensor 16 is greater than or equal to a predetermined threshold Sh.

[0054] In this embodiment, the corrected meter-out flow rate calculation unit 75 calculates the corrected meter-out flow rate based on the corrected meter-in flow rate calculated by the corrected meter-in flow rate calculation unit 74. The corrected meter-out flow rate calculation unit 75 calculates the corrected meter-out flow rate based on the difference between the target meter-in flow rate and the corrected meter-in flow rate. The corrected meter-out flow rate calculation unit 75 adds the difference between the target meter-in flow rate and the corrected meter-in flow rate to the target meter-out flow rate to calculate the corrected meter-out flow rate.

[0055] When the target meter-in flow rate is Qir, the corrected meter-in flow rate is Qic, the target meter-out flow rate is Qor, and the corrected meter-out flow rate is Qoc, the corrected meter-out flow rate calculation unit 75 calculates the corrected meter-out flow rate Qoc based on the following equation (1).

[0056] Qoc=Qor+(Qir-Qic)...(1)

[0057] As explained with reference to Figure 5, when the meter-out pressure is greater than or equal to the first threshold Sh1, the corrected meter-in flow rate Qic is determined to be zero, so the corrected meter-out flow rate Qoc is the sum of the target meter-in flow rate Qir and the target meter-out flow rate Qor (Qoc = Qor + Qir). When the meter-out pressure is greater than or equal to the second threshold Sh2 and less than the first threshold Sh1, the corrected meter-out flow rate Qoc becomes smaller as the meter-out pressure decreases. When the meter-out pressure is less than the second threshold Sh2, the corrected meter-in flow rate Qic is determined to be the target meter-in flow rate Qir, so the corrected meter-out flow rate Qoc is determined to be the target meter-out flow rate Qor (Qoc = Qor).

[0058] The corrected meter-out flow rate calculation unit 75 may calculate the corrected meter-out flow rate Qoc by adding a correction value proportional to the difference between the target meter-in flow rate Qir and the corrected meter-in flow rate Qic to the target meter-out flow rate Qor. For example, the corrected meter-out flow rate calculation unit 75 may calculate a correction value by multiplying the difference between the target meter-in flow rate Qir and the corrected meter-in flow rate Qic by the ratio of the pressure-receiving area on the bottom chamber 65 side and the pressure-receiving area on the head chamber 64 side of the piston 62 of the work machine cylinder 6, and then add the calculated correction value to the target meter-out flow rate Qor to calculate the corrected meter-out flow rate Qoc.

[0059] As described above, for example, when the head-side valve 14 functions as a meter-in valve, the meter-out flow rate is determined by the opening area of ​​the bottom-side valve 15. Calculating the corrected meter-out flow rate includes calculating the corrected meter-out opening of the bottom-side valve 15, which has a larger opening area than the target meter-out opening. There is a one-to-one correspondence between the corrected meter-out flow rate and the corrected meter-out opening. The larger the corrected meter-out flow rate, the larger the corrected meter-out opening. The corrected meter-out flow rate calculation unit 75 calculates the corrected meter-out opening based on the difference between the target meter-in opening and the corrected meter-in opening. The corrected meter-out flow rate calculation unit 75 adds the difference between the target meter-in opening and the corrected meter-in opening to the target meter-out opening to calculate the corrected meter-out opening.

[0060] When the target meter-in opening is Air, the corrected meter-in opening is Aic, the target meter-out opening is Aor, and the corrected meter-out opening is Aoc, the corrected meter-out flow rate calculation unit 75 calculates the corrected meter-out opening Aoc based on the following equation (2).

[0061] Aoc=Aor+(Air-Aic)...(2)

[0062] If the meter-out pressure is greater than or equal to the first threshold Sh1, the corrected meter-in opening Aic is determined to be zero, and the corrected meter-out opening Aoc is the sum of the target meter-in opening Air and the target meter-out opening Aor (Aoc = Aor + Air). If the meter-out pressure is greater than or equal to the second threshold Sh2 and less than the first threshold Sh1, the corrected meter-out opening Aoc becomes smaller as the meter-out pressure decreases. If the meter-out pressure is less than the second threshold Sh2, the corrected meter-in opening Aic is determined to be the target meter-in opening Air, and the corrected meter-out opening Aoc is determined to be the target meter-out opening Aor (Aoc = Aor).

[0063] The control unit 76 outputs a control command to control at least one of the hydraulic pump 12, the head-side valve 14, and the bottom-side valve 15. If the meter-out pressure detected by the bottom-side pressure sensor 16 is greater than or equal to a threshold Sh, the control unit 76 controls at least one of the hydraulic pump 12 and the head-side valve 14 so that a corrected meter-in flow rate of hydraulic fluid, less than the target meter-in flow rate, flows into the work machine cylinder 6. If the meter-out pressure detected by the bottom-side pressure sensor 16 is greater than or equal to a threshold Sh, the control unit 76 controls the bottom-side valve 15 so that a corrected meter-out flow rate of hydraulic fluid, greater than the target meter-out flow rate, flows out of the work machine cylinder 6.

[0064] The control unit 76 controls the hydraulic pump 12 so that, if the meter-out pressure is greater than or equal to a threshold Sh, a corrected pump flow rate of hydraulic fluid less than the target pump flow rate is discharged from the hydraulic pump 12. The control unit 76 can change the target pump flow rate to a corrected pump flow rate by controlling the swash plate of the hydraulic pump 12 and changing the capacity of the hydraulic pump 12. The control unit 76 controls the head-side valve 14 so that the corrected meter-in opening has a smaller opening area than the target meter-in opening when the meter-out pressure is greater than or equal to a threshold Sh. The control unit 76 controls the bottom-side valve 15 so that the corrected meter-out opening has a larger opening area than the target meter-out opening when the meter-out pressure is greater than or equal to a threshold Sh.

[0065] As described above, if the meter-out pressure is greater than or equal to the first threshold Sh1, the corrected meter-in flow rate is determined to be zero. If the meter-out pressure is greater than or equal to the first threshold Sh1, the control unit 76 controls at least one of the hydraulic pump 12 and the head-side valve 14 so that the meter-in flow rate becomes zero. For example, the control unit 76 controls the swash plate of the hydraulic pump 12 so that the capacity of the hydraulic pump 12 becomes zero, or controls the head-side valve 14 so that the opening area of ​​the head-side valve 14 becomes zero. If the meter-out pressure is greater than or equal to the second threshold Sh2 and less than the first threshold Sh1, the corrected meter-in flow rate is determined to be greater as the meter-out pressure decreases. If the meter-out pressure is greater than or equal to the second threshold Sh2 and less than the first threshold Sh1, the control unit 76 controls at least one of the hydraulic pump 12 and the head-side valve 14 so that the meter-in flow rate increases as the meter-out pressure decreases. The control unit 76 controls the swash plate of the hydraulic pump 12, for example, so that the capacity of the hydraulic pump 12 increases as the meter-out pressure decreases, or controls the head-side valve 14 so that the opening area of ​​the head-side valve 14 increases. When the meter-out pressure is less than the second threshold Sh2, the control unit 76 controls the hydraulic pump 12 and the head-side valve 14 so that the target meter-in flow rate of hydraulic fluid flows into the work machine cylinder 6. In other words, when the meter-out pressure is less than the second threshold Sh2, the corrected meter-in flow rate is not used. The control unit 76 controls the hydraulic pump 12 and the head-side valve 14 based on the target meter-in flow rate.

[0066] <Pressure Relief Control> Figure 6 is a diagram illustrating an example of the operation of the work machine 1 according to the embodiment. Figure 6 shows the state in which the arm 4B transitions from digging operation to dumping operation. If the operating device 8 includes a lever, the operator of the work machine 1 operates the lever of the operating device 8 in a first direction in order to make the arm 4B dig. When the operating device 8 is operated in the first direction, hydraulic fluid is supplied to the bottom chamber 65 and the arm cylinder 6B extends. If the operating device 8 continues to be operated in the first direction, the piston 62 of the arm cylinder 6B reaches the stroke end. The stroke end refers to the position of the end of the movable range of the piston 62 (rod 63) of the work machine cylinder 6. Even after the arm cylinder 6B is fully extended and the piston 62 has reached the stroke end, the operator may continue to operate the operating device 8 in the first direction without stopping. If the operating device 8 continues to be operated in the first direction, hydraulic fluid will continue to be supplied to the bottom chamber 65 while the piston 62 of the arm cylinder 6B has reached the stroke end. As a result, the bottom chamber 65 may become excessively high pressure. If the lever of the operating device is operated in the second direction to dump the arm 4B while the bottom chamber 65 is under high pressure, that is, if the operating device 8 is operated in the second direction to retract the arm cylinder 6B, the operation of the arm cylinder 6B may become unstable due to the high pressure in the bottom chamber 65. Due to the high pressure in the bottom chamber 65, the operation of the arm cylinder 6B may become unstable, for example, making it difficult for the arm cylinder 6B to retract smoothly, or causing the arm cylinder 6B to operate at an operating speed not intended by the operator.

[0067] In this embodiment, the controller 7 controls at least one of the hydraulic pump 12, the head valve 14, and the bottom valve 15 based on at least one of the target meter-in flow rate and the target meter-out flow rate and the meter-out pressure, so that the pressure of the hydraulic fluid flowing out of the work machine cylinder 6 does not become trapped in the bottom chamber 65 of the arm cylinder 6B or in the bottom-side passage 21 between the work machine cylinder 6 and the bottom-side valve 15. The controller 7 controls at least one of the hydraulic pump 12, the head valve 14, and the bottom-side valve 15 to eliminate the condition where the pressure of the hydraulic fluid flowing out of the work machine cylinder 6 is high between the work machine cylinder 6 and the bottom-side valve 15.

[0068] In this embodiment, when the operating device 8 is operated to operate the work machine cylinder 6 when the piston 62 of the work machine cylinder 6 has reached the stroke end and the bottom chamber 65 is under excessive pressure, the controller 7 performs pressure relief control by increasing the meter-out flow rate so as to suppress the rise in meter-out pressure. In this embodiment, when the operating device 8 is operated to operate the work machine cylinder 6 when the meter-out pressure is above a threshold Sh, the controller 7 controls the bottom-side valve 15 so that the opening area of ​​the bottom-side valve 15 becomes a corrected meter-out opening that is larger than the target meter-out opening. As the meter-out opening becomes larger and the meter-out flow rate increases, the high-pressure state in the bottom chamber 65 is relieved. That is, as the hydraulic fluid flows out of the bottom chamber 65 at a corrected meter-out flow rate that is greater than the target meter-out flow rate, pressure buildup in the bottom chamber 65 and the bottom-side flow path 21 is relieved.

[0069] Furthermore, when the operating device 8 is operated so that the work machine cylinder 6 operates while the meter-out pressure is above a threshold Sh, the controller 7 controls at least one of the hydraulic pump 12 and the head-side valve 14 so that the meter-in flow rate is reduced. The controller 7 controls the hydraulic pump 12 so that the pump flow rate of the hydraulic pump 12 is a corrected pump flow rate that is less than the target pump flow rate, or controls the head-side valve 14 so that the opening area of ​​the head-side valve 14 is a corrected meter-in opening that is smaller than the target meter-in opening. By reducing the meter-in flow rate, the high-pressure condition in the bottom chamber 65 is eliminated.

[0070] When the meter-out pressure is greater than or equal to a threshold Sh, the controller 7 controls at least one of the hydraulic pump 12 and the head-side valve 14 so that a meter-in flow rate of hydraulic fluid less than the target meter-in flow rate flows into the work machine cylinder 6, and controls the bottom-side valve 15 so that a corrected meter-out flow rate of hydraulic fluid greater than the target meter-out flow rate flows out of the work machine cylinder 6.

[0071] The same applies when the head chamber 64 is under high pressure. When the operating device 8 is operated to operate the work machine cylinder 6 while the piston 62 of the work machine cylinder 6 has moved to the stroke end and the head chamber 64 is under excessively high pressure, the controller 7 implements pressure relief control by increasing the meter-out flow rate so as to suppress the rise in meter-out pressure.

[0072] <Control Method> Figure 7 is a flowchart showing the control method for the work machine 1 according to the first embodiment. In the following description, the head-side valve 14 functions as a meter-in valve, and the bottom-side valve 15 functions as a meter-out valve. The bottom-side pressure sensor 16 also functions as a meter-out pressure sensor. The target operating speed calculation unit 71 calculates the target operating speed of the work machine cylinder 6 based on the amount of operation of the operating device 8 (step SA1).

[0073] The target meter-in flow rate calculation unit 72 calculates the target meter-in flow rate of the work machine cylinder 6 based on the target operating speed of the work machine cylinder 6 calculated by the target operating speed calculation unit 71. The target meter-in flow rate calculation unit 72 calculates the target pump flow rate and target meter-in opening based on the target operating speed of the work machine cylinder 6. The target meter-out flow rate calculation unit 73 calculates the target meter-out flow rate of the work machine cylinder 6 based on the target operating speed of the work machine cylinder 6 calculated by the target operating speed calculation unit 71. The target meter-out flow rate calculation unit 73 calculates the target meter-out opening based on the target operating speed of the work machine cylinder 6 (step SA2).

[0074] The corrected meter-in flow rate calculation unit 74 determines whether or not pressure relief control is necessary to release the pressure trapped in the bottom chamber 65 and the bottom-side flow path 21 (step SA3).

[0075] If it is determined in step SA3 that pressure relief control is not necessary (step SA3: No), the process returns to step SA1.

[0076] If it is determined in step SA3 that pressure relief control is necessary (step SA3: Yes), the corrected meter-in flow rate calculation unit 74 determines whether the meter-out pressure detected by the bottom-side pressure sensor 16 is equal to or greater than the second threshold Sh2 (step SA4).

[0077] In step SA4, if it is determined that the meter-out pressure is equal to or greater than the second threshold Sh2 (step SA4: Yes), the corrected meter-in flow rate calculation unit 74 determines whether the meter-out pressure detected by the bottom-side pressure sensor 16 is equal to or greater than the first threshold Sh1 (step SA5).

[0078] In step SA5, if it is determined that the meter-out pressure is greater than or equal to the first threshold Sh1 (step SA5: Yes), the corrected meter-in flow rate calculation unit 74 determines the corrected meter-in flow rate to be zero. The corrected meter-in flow rate calculation unit 74 calculates the corrected pump flow rate and the corrected meter-in opening. The corrected pump flow rate is zero, and the corrected meter-in opening is zero. The control unit 76 controls one or both of the hydraulic pump 12 and the head-side valve 14 (meter-in valve) so that the meter-in flow rate becomes zero (step SA6).

[0079] The corrected meter-out flow rate calculation unit 75 calculates the corrected meter-out opening by adding the difference between the target meter-in opening and the corrected meter-in opening to the target meter-out opening. As described above, if the meter-out pressure is greater than or equal to the first threshold Sh1, the corrected meter-in opening Aic is determined to be zero, and the corrected meter-out opening Aoc becomes the sum of the target meter-in opening Air and the target meter-out opening Aor (Aoc = Aor + Air). The control unit 76 controls the bottom-side valve (meter-out valve) 15 so that the opening area of ​​the bottom-side valve 15 (meter-out valve) becomes the corrected meter-out opening Aoc (step SA7).

[0080] In step SA5, if it is determined that the meter-out pressure is not equal to or greater than the first threshold Sh1 (step SA5: No), the corrected meter-in flow rate calculation unit 74 determines the corrected meter-in flow rate such that the lower the meter-out pressure, the greater the corrected meter-in flow rate. The corrected meter-in flow rate calculation unit 74 calculates the corrected pump flow rate and the corrected meter-in opening. The control unit 76 controls one or both of the hydraulic pump 12 and the head-side valve 14 (meter-in valve) such that the lower the meter-out pressure, the greater the meter-in flow rate (step SA8).

[0081] The corrected meter-out flow rate calculation unit 75 calculates the corrected meter-out opening by adding the difference between the target meter-in opening and the corrected meter-in opening to the target meter-out opening. As described above, when the meter-out pressure is greater than or equal to the second threshold Sh2 and less than the first threshold Sh1, the corrected meter-out opening Aoc is determined to become smaller as the meter-out pressure decreases. The control unit 76 controls the bottom-side valve 15 (meter-out valve) so that the opening area of ​​the bottom-side valve 15 (meter-out valve) becomes the corrected meter-out opening Aoc (step SA9).

[0082] In step SA4, if it is determined that the meter-out pressure is not equal to or greater than the second threshold Sh2 (step SA4: No), the control unit 76 controls one or both of the hydraulic pump 12 and the head-side valve 14 (meter-in valve) based on the target meter-in flow rate. The control unit 76 controls the hydraulic pump 12 so that the hydraulic fluid at the target pump flow rate calculated by the target meter-in flow rate calculation unit 72 is discharged, and controls the head-side valve 14 (meter-in valve) so that it opens to the target meter-in opening calculated by the target meter-in flow rate calculation unit 72 (step SA10).

[0083] The control unit 76 controls the bottom valve 15 (meter-out valve) based on the target meter-out flow rate. As described above, if the meter-out pressure is less than the second threshold Sh2, the corrected meter-in opening Aic is determined to be the target meter-in opening Air, and the corrected meter-out opening Aoc is determined to be the target meter-out opening Aor (Aoc = Aor). The control unit 76 controls the bottom valve 15 (meter-out valve) so that its opening area becomes the target meter-out opening calculated by the target meter-out flow rate calculation unit 73 (step SA11).

[0084] Figure 8 is a timing chart showing the control method of the work machine 1 according to the first embodiment. Figure 8 is a timing chart for when the piston 62 of the arm cylinder 6B, which has been operating to extend as described with reference to Figure 6, reaches the stroke end and then the arm cylinder 6B operates to retract. In the multiple graphs shown in Figure 8, the horizontal axis is time, and the vertical axes are the operating amount of the operating device 8, the hydraulic fluid pressure, the pump flow rate, the opening area of ​​the head-side valve 14, and the opening area of ​​the bottom-side valve 15, respectively.

[0085] In Figure 8, time t1 arrives after time 0, time t2 arrives after time t1, and time t3 arrives after time t2.

[0086] Line La indicates the amount of operation of the operating device 8. Line Lb indicates the meter-out pressure, which is the pressure of the hydraulic fluid flowing out of the arm cylinder 6B. Line Lc indicates the meter-in pressure, which is the pressure of the hydraulic fluid flowing into the arm cylinder 6B. Line Ld indicates the meter-out pressure according to the comparative example. The meter-out pressure according to the comparative example is the meter-out pressure when pressure relief control is not performed even if the bottom chamber 65 exceeds the threshold Sh. In other words, the meter-out pressure according to the comparative example is the meter-out pressure when the opening area of ​​the bottom-side valve 15 is controlled to the target meter-out opening even if the bottom chamber 65 is in a high-pressure state.

[0087] Line Le indicates the target pump flow rate. Line Lf indicates the corrected pump flow rate. Line Lg indicates the target meter-in opening. Line Lh indicates the corrected meter-in opening. Line Li indicates the target meter-out opening. Line Lj indicates the corrected meter-out opening.

[0088] The target meter-in flow rate calculation unit 72 calculates the target pump flow rate and target meter-in opening based on the target operating speed of the work machine cylinder 6. The target meter-out flow rate calculation unit 73 calculates the target meter-out opening based on the target operating speed of the work machine cylinder 6.

[0089] At time 0, the piston 62 reaches the stroke end. If the operating device 8 continues to be operated with the piston 62 at the stroke end, the hydraulic fluid supplied to the bottom chamber 65 will cause the bottom chamber 65 to become high-pressure. From time t1, the operating direction of the lever of the operating device 8 is switched, and the controller 7 operates the work machine cylinder 6 in a direction that moves the piston 62 away from the stroke end. At time t1, the meter-out pressure is greater than or equal to the first threshold Sh1, so the controller 7 starts pressure relief control.

[0090] The corrected meter-in flow rate calculation unit 74 calculates the corrected pump flow rate and the corrected meter-in opening. If the meter-out pressure is greater than or equal to the first threshold Sh1, the corrected pump flow rate and the corrected meter-in opening are determined to be zero. The corrected meter-out flow rate calculation unit 75 calculates the corrected meter-out opening by adding the difference between the target meter-in opening and the corrected meter-in opening to the target meter-out opening. Alternatively, the corrected meter-out flow rate calculation unit 75 may calculate the corrected meter-out opening by adding a correction value proportional to the difference between the target meter-in opening and the corrected meter-in opening to the target meter-out opening. The corrected meter-out flow rate calculation unit 75 may add the difference value, or it may calculate a correction value based on correlation data between the correction value and the difference value and add the correction value. Regardless of the difference value, the meter-out opening does not need to be corrected. That is, the meter-out opening correction value may always be zero.

[0091] As shown in Figure 8, between time point t1 and time point t2, both the corrected pump flow rate and the corrected meter-in opening are maintained at zero. Between time point t1 and time point t2, the corrected meter-out opening is larger than the target meter-out opening. Between time point t1 and time point t2, the meter-out flow rate increases and the meter-in flow rate becomes zero, so the meter-out pressure decreases as shown by line Lb. The meter-out pressure in this embodiment is lower than the meter-out pressure in the comparative example.

[0092] The meter-out pressure gradually decreases due to the pressure relief control. At time t2, the meter-out pressure decreases to the first threshold Sh1. When the meter-out pressure falls below the first threshold Sh1, the corrected pump flow rate is determined to increase as the meter-out pressure decreases, and the meter-in opening is determined to increase as the meter-out pressure decreases. When the meter-out pressure falls below the first threshold Sh1, the meter-out opening is determined to decrease as the meter-out pressure decreases. Between time t2 and time t3, the corrected meter-out opening is larger than the target meter-out opening.

[0093] At time t3, the meter-out pressure drops to the second threshold Sh2. When the meter-out pressure falls below the second threshold Sh2, the hydraulic pump 12 is controlled to discharge hydraulic fluid at the target pump flow rate, and the head-side valve 14 is controlled to open to the target meter-in position. When the meter-out pressure falls below the second threshold Sh2, the bottom-side valve 15 is controlled to open to the target meter-out position.

[0094] <Control when the bottom pressure sensor is abnormal> As described above, in the embodiment, when the bottom pressure sensor 16 functions as a meter-out pressure sensor, if the meter-out pressure detected by the bottom pressure sensor 16 is greater than or equal to the threshold Sh, pressure relief control is performed. That is, when the meter-out pressure detected by the bottom pressure sensor 16 is greater than or equal to the threshold Sh, the corrected meter-in flow rate (corrected pump flow rate and corrected meter-in opening) and the corrected meter-out flow rate (corrected meter-out opening) are calculated. The control method for the work machine 1 when the bottom pressure sensor 16 (meter-out pressure sensor) is abnormal will be described below.

[0095] Figure 9 is a flowchart showing the control method for the work machine 1 when the bottom-side pressure sensor 16 is abnormal according to the first embodiment. When the bottom-side pressure sensor 16 (meter-out pressure sensor) is abnormal, the controller 7 cannot calculate the corrected meter-in flow rate (corrected pump flow rate and corrected meter-in opening) and the corrected meter-out flow rate (corrected meter-out opening). When the bottom-side pressure sensor 16 is abnormal, the controller 7 controls the hydraulic pump 12 and the head-side valve 14 (meter-in valve) so that the hydraulic fluid at the target meter-in flow rate flows into the work machine cylinder 6, and controls the bottom-side valve 15 so that the hydraulic fluid at the target meter-out flow rate flows out of the work machine cylinder 6, so that even if a malfunction of the work machine cylinder 6 occurs due to pressure buildup in the bottom chamber 65 or the bottom-side flow path 21, the work machine cylinder 6 can operate to the minimum extent possible according to the target operating speed of the work machine cylinder 6.

[0096] The corrected meter-in flow rate calculation unit 74 detects an abnormality in the bottom-side pressure sensor 16 (meter-out pressure sensor) (step SB1).

[0097] If the bottom pressure sensor 16 is malfunctioning, the detected data value from the bottom pressure sensor 16 may become excessively low or excessively high. The corrected meter-in flow rate calculation unit 74 can determine that the bottom pressure sensor 16 is malfunctioning if the detected data value from the bottom pressure sensor 16 is below a predetermined third threshold, or if the detected data value from the bottom pressure sensor 16 is above a predetermined fourth threshold. The fourth threshold is a value greater than the third threshold.

[0098] If the bottom-side pressure sensor 16 is abnormal, the corrected meter-in flow rate calculation unit 74 does not calculate the corrected meter-in flow rate (corrected pump flow rate and corrected meter-in opening). The control unit 76 controls the hydraulic pump 12 and the head-side valve 14 (meter-in valve) based on the target meter-in flow rate. That is, if the bottom-side pressure sensor 16 is abnormal, the control unit 76 controls the hydraulic pump 12 and the head-side valve 14 (meter-in valve) so that even if the meter-out pressure is above the threshold Sh, the hydraulic pump 12 discharges hydraulic fluid at the target pump flow rate and the opening area of ​​the head-side valve 14 (meter-in valve) becomes the target meter-in opening (step SB2).

[0099] Furthermore, the control unit 76 controls the bottom valve 15 (meter-out valve) based on the target meter-out flow rate. The control unit 76 controls the bottom valve 15 so that its opening area becomes the target meter-out opening (step SB3).

[0100] <Effects> As described above, when the hydraulic fluid in the chamber from which the hydraulic fluid of the work machine cylinder 6 flows becomes high pressure, pressure relief control is performed. In this embodiment, when the pressure of the hydraulic fluid in the chamber from which the hydraulic fluid of the work machine cylinder 6 flows exceeds a threshold Sh, the bottom-side valve 15, which functions as a meter-out valve, is controlled so that its opening area becomes a corrected meter-out opening that is larger than the target meter-out opening. When the pressure of the hydraulic fluid in the chamber from which the hydraulic fluid of the work machine cylinder 6 flows exceeds a threshold Sh, either the flow rate of the hydraulic fluid discharged from the hydraulic pump 12 or the opening area of ​​the head-side valve 14, which functions as a meter-in valve, or both are controlled so that the meter-in flow rate of the work machine cylinder 6 becomes less than the target meter-in flow rate. Since excessive pressure inside the work machine cylinder 6 is suppressed, instability in the operation of the work machine cylinder 6 is suppressed, and the occurrence of malfunctions of the work machine cylinder 6 is suppressed.

[0101] [Second Embodiment] A second embodiment will now be described. In the following description, components that are the same as or equivalent to those in the above-described embodiment will be denoted by the same reference numerals, and the descriptions of those components will be simplified or omitted.

[0102] In the second embodiment, pressure relief control when the hydraulic circuit includes a regeneration circuit will be described. That is, pressure relief control when the hydraulic fluid is regenerated from the head-side passage 20 to the bottom-side passage 21 will be described. In the second embodiment, pressure relief control will be described when it is a complete regeneration circuit in which all of the hydraulic fluid that flows out from the head chamber 64 of the work machine cylinder 6 is supplied to the bottom-side passage 21.

[0103] In the second embodiment, an example will be described in which, as shown in Figure 2, hydraulic fluid flows out from the head chamber 64 and all of the hydraulic fluid that flows out from the head chamber 64 is supplied to the head-side flow path 20. In the example shown in Figure 2, the spool of the bottom-side valve 15 is positioned at the second position D1, and the bottom-side valve 15 functions as a meter-in valve that adjusts the flow rate of hydraulic fluid flowing from the bottom-side flow path 21 into the bottom chamber 65 of the work machine cylinder 6. The spool of the head-side valve 14 is positioned at the second position D2, and the head-side valve 14 functions as a regeneration valve that adjusts the flow rate of hydraulic fluid supplied from the head chamber 64 to the bottom chamber 65. The bottom-side pressure sensor 16 functions as a meter-in pressure sensor that detects the meter-in pressure, which indicates the pressure of the hydraulic fluid flowing into the bottom chamber 65 of the work machine cylinder 6. The head-side pressure sensor 26 functions as a meter-out pressure sensor that detects the meter-out pressure, which indicates the pressure of the hydraulic fluid flowing out from the head chamber 64 of the work machine cylinder 6.

[0104] <Controller> Figure 10 is a functional block diagram showing a controller 7 according to the second embodiment. The controller 7 outputs control commands to control the hydraulic pump 12, the head-side valve 14, and the bottom-side valve 15. The functional parts of the controller 7 include a target operating speed calculation unit 71, a target meter-in flow rate calculation unit 72, a target regeneration flow rate calculation unit 81, a corrected meter-in flow rate calculation unit 74, a corrected regeneration flow rate calculation unit 82, a drive pressure calculation unit 83, a control unit 76, and a threshold storage unit 77.

[0105] The target operating speed calculation unit 71 calculates the target operating speed (target cylinder speed) of the work machine cylinder 6 based on the amount of operation of the operating device 8.

[0106] The target meter-in flow rate calculation unit 72 calculates the target meter-in flow rate based on the target operating speed of the work machine cylinder 6. Calculating the target meter-in flow rate includes calculating the target pump flow rate and calculating the target meter-in opening.

[0107] The target regeneration flow rate calculation unit 81 calculates a target regeneration flow rate, which indicates the target value of the flow rate of hydraulic fluid supplied from the head chamber 64 to the head-side flow path 20 of the work machine cylinder 6, based on the target operating speed of the work machine cylinder 6 calculated by the target operating speed calculation unit 71. There is a one-to-one correspondence between the target operating speed of the work machine cylinder 6 and the target regeneration flow rate. The higher the target operating speed, the higher the target regeneration flow rate. The target regeneration flow rate may also be a value proportional to the target operating speed. If a fifth correlation data showing the relationship between the target operating speed and the target regeneration flow rate is predetermined, the target regeneration flow rate calculation unit 81 may determine the target regeneration flow rate by inputting the target operating speed into the fifth correlation data. The target regeneration flow rate calculation unit 81 may also calculate the target regeneration flow rate based on the operating amount of the operating device 8. The target regeneration flow rate calculation unit 81 may also calculate the target regeneration flow rate based on the target meter-in flow rate calculated by the target meter-in flow rate calculation unit 72. The target regeneration flow rate calculation unit 81 may determine the target regeneration flow rate to be the same value as the target meter-in flow rate.

[0108] The regeneration flow rate is determined by the opening area of ​​the head-side valve 14 (regeneration valve). Calculating the target regeneration flow rate includes calculating a target regeneration opening that indicates a target value for the opening area of ​​the head-side valve 14 (regeneration valve).

[0109] The corrected meter-in flow rate calculation unit 74 calculates a corrected meter-in flow rate that is less than the target meter-in flow rate if the meter-out pressure detected by the head-side pressure sensor 26 is greater than or equal to the threshold Sh. Calculating the corrected meter-in flow rate includes calculating a corrected pump flow rate for the hydraulic pump 12 that is less than the target pump flow rate, and calculating a corrected meter-in opening for the bottom-side valve 15 that has a smaller opening area than the target meter-in opening.

[0110] The corrected regeneration flow rate calculation unit 82 calculates a corrected regeneration flow rate that is greater than the target regeneration flow rate when the meter-out pressure detected by the head-side pressure sensor 26 is greater than or equal to a predetermined threshold Sh.

[0111] The corrected regeneration flow rate calculation unit 82 calculates the corrected regeneration flow rate based on the corrected meter-in flow rate calculated by the corrected meter-in flow rate calculation unit 74. The corrected regeneration flow rate calculation unit 82 calculates the corrected regeneration flow rate based on the difference between the target meter-in flow rate and the corrected meter-in flow rate. The corrected regeneration flow rate calculation unit 82 adds the difference between the target meter-in flow rate and the corrected meter-in flow rate to the target regeneration flow rate to calculate the corrected regeneration flow rate.

[0112] When the target meter-in flow rate is Qir, the corrected meter-in flow rate is Qic, the target regeneration flow rate is Qrr, and the corrected regeneration flow rate is Qrc, the corrected regeneration flow rate calculation unit 82 calculates the corrected regeneration flow rate Qrc based on the following equation (3).

[0113] Qrc=Qrr+(Qir-Qic)...(3)

[0114] As explained with reference to Figure 5, when the meter-out pressure is greater than or equal to the first threshold Sh1, the corrected meter-in flow rate Qic is determined to be zero, and the corrected regeneration flow rate Qrc is the sum of the target meter-in flow rate Qir and the target regeneration flow rate Qrr (Qrc = Qrr + Qir). When the meter-out pressure is greater than or equal to the second threshold Sh2 and less than the first threshold Sh1, the corrected regeneration flow rate Qrc becomes smaller as the meter-out pressure decreases. When the meter-out pressure is less than the second threshold Sh2, the corrected meter-in flow rate Qic is determined to be the target meter-in flow rate Qir, and therefore the corrected regeneration flow rate Qrc is determined to be the target regeneration flow rate Qrr (Qrc = Qrr).

[0115] As described above, the regeneration flow rate is determined by the opening area of ​​the head-side valve 14 (regeneration valve). Calculating the corrected regeneration flow rate includes calculating the corrected regeneration opening of the head-side valve 14 (regeneration valve), which has a larger opening area than the target regeneration opening. There is a one-to-one correspondence between the corrected regeneration flow rate and the corrected regeneration opening. The larger the corrected regeneration flow rate, the larger the corrected regeneration opening. The corrected regeneration flow rate calculation unit 82 calculates the corrected regeneration opening based on the difference between the target meter-in opening and the corrected meter-in opening. The corrected regeneration flow rate calculation unit 82 adds the difference between the target meter-in opening and the corrected meter-in opening to the target regeneration opening to calculate the corrected regeneration opening.

[0116] When the target meter-in opening is Air, the corrected meter-in opening is Aic, the target regeneration opening is Arr, and the corrected regeneration opening is Arc, the corrected regeneration flow rate calculation unit 82 calculates the corrected regeneration opening Arc based on the following equation (4).

[0117] Arc=Arr+(Air-Aic)...(4)

[0118] If the meter-out pressure is greater than or equal to the first threshold Sh1, the corrected meter-in opening Aic is determined to be zero, and the corrected regeneration opening Arc is the sum of the target meter-in opening Air and the target meter-out opening Aor (Arc = Aor + Air). If the meter-out pressure is greater than or equal to the second threshold Sh2 and less than the first threshold Sh1, the corrected regeneration opening Arc becomes smaller as the meter-out pressure decreases. If the meter-out pressure is less than the second threshold Sh2, the corrected meter-in opening Aic is determined to be the target meter-in opening Air, and the corrected regeneration opening Arc is determined to be the target regeneration opening Arr (Arc = Arr).

[0119] The drive pressure calculation unit 83 calculates the drive pressure applied to the work machine cylinder 6. The drive pressure applied to the work machine cylinder 6 refers to the pressure of the hydraulic fluid when the work machine cylinder 6 is driven. The drive pressure calculation unit 83 calculates the drive pressure when the work machine cylinder 6 extends or when the work machine cylinder 6 retracts.

[0120] The drive pressure calculation unit 83 calculates the drive pressure applied to the piston 62 of the work machine cylinder 6 based on the meter-in pressure detected by the bottom-side pressure sensor 16, the meter-out pressure detected by the head-side pressure sensor 26, and the pressure-receiving area of ​​the work machine cylinder 6. For example, if Pi is the meter-in pressure indicating the pressure of the hydraulic fluid flowing into the bottom chamber 65 when the work machine cylinder 6 extends, Po is the meter-out pressure indicating the pressure of the hydraulic fluid flowing out from the head chamber 64, Ab is the bottom pressure-receiving area of ​​the bottom chamber 65, and Ah is the head pressure-receiving area of ​​the head chamber 64, then the drive pressure Pd is calculated based on the following equation (5). The bottom pressure-receiving area Ab refers to the pressure-receiving area of ​​the piston 62 facing the bottom chamber 65. The head pressure-receiving area Ah refers to the pressure-receiving area of ​​the piston 62 facing the head chamber 64. The bottom pressure receiving area Ab and the head pressure receiving area Ah are known data derived from the design data or specifications data of the work machine cylinder 6.

[0121] Pd=Pi-Po×(Ah÷Ab)…(5)

[0122] The control unit 76 outputs a control command to control at least one of the hydraulic pump 12, the bottom valve 15, and the head valve 14. If the meter-out pressure detected by the head pressure sensor 26 is greater than or equal to a threshold Sh, the control unit 76 controls at least one of the hydraulic pump 12 and the bottom valve 15 (meter-in valve) so that a corrected meter-in flow rate of hydraulic fluid, less than the target meter-in flow rate, flows into the work machine cylinder 6. If the meter-out pressure detected by the head pressure sensor 26 is greater than or equal to a threshold Sh, the control unit 76 controls the head valve 14 (regeneration valve) so that a corrected regeneration flow rate of hydraulic fluid, greater than the target regeneration flow rate, is supplied from the outlet of the work machine cylinder 6 to the head flow path 20.

[0123] The control unit 76 controls the hydraulic pump 12 so that if the meter-out pressure is greater than or equal to a threshold Sh, a corrected pump flow rate of hydraulic fluid less than the target pump flow rate is discharged from the hydraulic pump 12. The control unit 76 controls the bottom-side valve 15 (meter-in valve) so that the corrected meter-in opening has a smaller opening area than the target meter-in opening, if the meter-out pressure is greater than or equal to a threshold Sh. The control unit 76 controls the head-side valve 14 (regeneration valve) so that the corrected regeneration opening has a larger opening area than the target regeneration opening, if the meter-out pressure is greater than or equal to a threshold Sh.

[0124] As described above, if the meter-out pressure is greater than or equal to the first threshold Sh1, the corrected meter-in flow rate is determined to be zero. If the meter-out pressure is greater than or equal to the first threshold Sh1, the control unit 76 controls at least one of the hydraulic pump 12 and the bottom valve 15 (meter-in valve) so that the meter-in flow rate becomes zero. If the meter-out pressure is greater than or equal to the second threshold Sh2 and less than the first threshold Sh1, the corrected meter-in flow rate is determined to increase as the meter-out pressure decreases. If the meter-out pressure is greater than or equal to the second threshold Sh2 and less than the first threshold Sh1, the control unit 76 controls at least one of the hydraulic pump 12 and the bottom valve 15 (meter-in valve) so that the meter-in flow rate increases as the meter-out pressure decreases. If the meter-out pressure is less than the second threshold Sh2, the control unit 76 controls the hydraulic pump 12 and the bottom valve 15 (meter-in valve) so that the target meter-in flow rate of hydraulic fluid flows into the work machine cylinder 6. The control unit 76 controls the hydraulic pump 12 and the bottom valve 15 (meter-in valve) based on the target meter-in flow rate.

[0125] <Pressure Relief Control> As described above, if the operating device 8 continues to be operated even after the arm cylinder 6B has fully retracted and the piston 62 has reached the stroke end, the head chamber 64 may become excessively high pressure. If the operating device 8 is operated to extend the arm cylinder 6B while the head chamber 64 is under high pressure, the operation of the arm cylinder 6B may become unstable due to the high pressure in the head chamber 64.

[0126] In this embodiment, the controller 7 controls at least one of the hydraulic pump 12, the head valve 14, and the bottom valve 15 based on the target meter-in flow rate and the target regeneration flow rate and the meter-out pressure, so that the pressure of the hydraulic fluid flowing out of the head chamber 64 of the work machine cylinder 6 does not become trapped in the head chamber 64 of the arm cylinder 6B, or in the bottom-side passage 21 or the regeneration passage 23 between the work machine cylinder 6 and the bottom-side valve 15.

[0127] In this embodiment, when the operating device 8 is operated to operate the work machine cylinder 6 when the piston 62 of the work machine cylinder 6 has reached the stroke end and the head chamber 64 is under excessive pressure, the controller 7 performs pressure relief control to increase the regeneration flow rate so as to suppress the rise in meter-out pressure. In this embodiment, when the operating device 8 is operated to operate the work machine cylinder 6 when the meter-out pressure is above a threshold Sh, the controller 7 controls the head-side valve 14 (regeneration valve) so that the opening area of ​​the head-side valve 14 (regeneration valve) becomes a corrected regeneration opening that is larger than the target regeneration opening. As the regeneration opening becomes larger and the regeneration flow rate increases, the high-pressure state in the head chamber 64 is relieved. That is, as the hydraulic fluid flows out of the head chamber 64 at a corrected regeneration flow rate that is greater than the target regeneration flow rate, pressure buildup in the head chamber 64, bottom-side flow path 21, and regeneration flow path 23 is relieved.

[0128] Furthermore, when the operating device 8 is operated so that the work machine cylinder 6 operates while the meter-out pressure is above a threshold Sh, the controller 7 controls at least one of the hydraulic pump 12 and the bottom valve 15 (meter-in valve) so that the meter-in flow rate is reduced. The controller 7 controls the hydraulic pump 12 so that the pump flow rate of the hydraulic pump 12 becomes a corrected pump flow rate that is less than the target pump flow rate, or controls the bottom valve 15 (meter-in valve) so that the opening area of ​​the bottom valve 15 (meter-in valve) becomes a corrected meter-in opening that is smaller than the target meter-in opening. By reducing the meter-in flow rate, the high-pressure condition in the head chamber 64 is eliminated.

[0129] In this embodiment, the controller 7 determines, based on the drive pressure Pd applied to the work implement cylinder 6, whether the piston 62 of the work implement cylinder 6 is performing a predetermined operation in which it starts moving from the stroke end. If the controller 7 determines that the operation of the work implement cylinder 6 is a predetermined operation and the meter-out pressure is greater than or equal to a threshold Sh, it controls at least one of the hydraulic pump 12 and the bottom-side valve 15 (meter-in valve) so that a corrected meter-in flow rate of hydraulic fluid, which is less than the target meter-in flow rate, flows into the work implement cylinder 6, and controls the head-side valve 14 (regeneration valve) so that a corrected regeneration flow rate of hydraulic fluid, which is greater than the target regeneration flow rate, is supplied from the outlet of the work implement cylinder 6 to the regeneration passage 23.

[0130] Furthermore, the determination of whether the piston 62 of the work machine cylinder 6 has started moving from the stroke end in a predetermined operation may be performed based on the detection data of an inertial measurement unit (IMU) attached to the work machine 4. Since the inertial sensor can detect the acceleration of the work machine cylinder 6 (work machine 4), the determination of whether or not it is a predetermined operation can be made based on the detection data of the inertial sensor. In addition, if the stroke length of the work machine cylinder 6 can be detected by an encoder, for example, the determination of whether or not it is a predetermined operation may be made based on the detection data of the encoder. Alternatively, image data of the work machine 4 or work machine cylinder 6 may be acquired by a camera attached to the slewing body 3, and the determination of whether or not it is a predetermined operation may be made by image processing the image data.

[0131] The controller 7 does not perform pressure relief control if it determines that the operation of the work machine cylinder 6 is not a predetermined operation, even if the meter-out pressure is above the threshold Sh. In other words, if the controller 7 determines that the operation of the work machine cylinder 6 is not a predetermined operation, even if the meter-out pressure is above the threshold Sh, it controls at least one of the hydraulic pump 12 and the bottom-side valve 15 (meter-in valve) so that the target meter-in flow rate of hydraulic fluid flows into the work machine cylinder 6, and controls the head-side valve 14 (regeneration valve) so that the target regeneration flow rate of hydraulic fluid is supplied from the outlet of the work machine cylinder 6 to the regeneration passage 23.

[0132] For example, when the work implement 4 performs high-load work such as excavating a hard material, the meter-out pressure may exceed the threshold Sh. If pressure relief control is implemented while the work implement 4 is performing high-load work, it becomes difficult for the work implement 4 to perform high-load work.

[0133] In this embodiment, the controller 7 determines whether the operation of the work implement cylinder 6 is a predetermined operation based on the drive pressure Pd. If the operation of the work implement cylinder 6 is a predetermined operation (when the piston 62 starts moving from the stroke end), the drive pressure Pd will not be high even if the meter-out pressure is high. If the operation of the work implement cylinder 6 is not a predetermined operation (when the work implement 4 is performing high-load work), both the meter-out pressure and the drive pressure Pd will be high.

[0134] The controller 7 determines that the operation of the work implement cylinder 6 is a predetermined operation if the drive pressure Pd is less than or equal to a predetermined value. The controller 7 determines that the operation of the work implement cylinder 6 is not a predetermined operation if the drive pressure Pd exceeds the predetermined value.

[0135] The controller 7 performs pressure relief control when the drive pressure Pd is below a specified value and the meter-out pressure is above a threshold Sh. That is, when the controller 7 determines that the operation of the work machine cylinder 6 is a predetermined operation and the meter-out pressure is above a threshold Sh, it controls the head-side valve 14 (regeneration valve) so that a corrected regeneration flow rate of hydraulic fluid greater than the target regeneration flow rate is supplied from the outlet of the work machine cylinder 6 to the regeneration passage 23.

[0136] The controller 7 does not perform pressure relief control if the drive pressure Pd exceeds a specified value even if the meter-out pressure is above the threshold Sh. In other words, if the controller 7 determines that the operation of the work machine cylinder 6 is not the predetermined operation even if the meter-out pressure is above the threshold Sh, it controls the head-side valve 14 (regeneration valve) so that the target regeneration flow rate of hydraulic fluid is supplied from the outlet of the work machine cylinder 6 to the regeneration passage 23. If the controller 7 determines that the work machine 4 is performing high-load work even if the meter-out pressure is above the threshold Sh, it determines that the work machine 4 is performing high-load work. If the controller 7 determines that the work machine 4 is performing high-load work, it does not perform pressure relief control.

[0137] In other words, in this embodiment, when the controller 7 determines that the operation of the work machine cylinder 6 is a predetermined operation, it controls at least one of the hydraulic pump 12, the head valve 14, and the bottom valve 15 based on the target meter-in flow rate and the target regeneration flow rate and the meter-out pressure, so that the pressure of the hydraulic fluid flowing out from the outlet of the work machine cylinder 6 does not get trapped in the head chamber 64 of the arm cylinder 6B or in the bottom-side passage 21 or the regeneration passage 23 between the work machine cylinder 6 and the bottom-side valve 15 (meter-in valve).

[0138] <Control Method> Figure 11 is a flowchart showing the control method for the work machine 1 according to the second embodiment. In the following description, the bottom-side valve 15 functions as a meter-in valve, and the head-side valve 14 functions as a regeneration valve. The target operating speed calculation unit 71 calculates the target operating speed of the work machine cylinder 6 based on the amount of operation of the operating device 8 (step SC1).

[0139] The target meter-in flow rate calculation unit 72 calculates the target meter-in flow rate based on the target operating speed of the work machine cylinder 6. The target meter-in flow rate calculation unit 72 calculates the target pump flow rate and target meter-in opening based on the target operating speed of the work machine cylinder 6. The target regeneration flow rate calculation unit 81 calculates the target regeneration flow rate based on the target operating speed of the work machine cylinder 6. The target regeneration flow rate calculation unit 81 calculates the target regeneration opening based on the target operating speed of the work machine cylinder 6 (step SC2).

[0140] The corrected meter-in flow rate calculation unit 74 determines whether the meter-out pressure detected by the head-side pressure sensor 26 is equal to or greater than the second threshold Sh2 (step SC3).

[0141] The drive pressure calculation unit 83 calculates the drive pressure Pd applied to the work machine cylinder 6 based on equation (5) described above. If, in step SC3, it is determined that the meter-out pressure is equal to or greater than the second threshold Sh2 (step SC3: Yes), the drive pressure calculation unit 83 determines, based on the drive pressure Pd, whether the operation of the work machine cylinder 6 is a predetermined operation (step SC4).

[0142] The drive pressure calculation unit 83 determines that the operation of the work machine cylinder 6 is a predetermined operation if the drive pressure Pd is less than or equal to a predetermined value. The drive pressure calculation unit 83 determines that the operation of the work machine cylinder 6 is not a predetermined operation if the drive pressure Pd exceeds the predetermined value.

[0143] In step SC4, if it is determined that the operation of the work machine cylinder 6 is a predetermined operation (step SC4: Yes), the corrected meter-in flow rate calculation unit 74 determines whether the meter-out pressure detected by the head-side pressure sensor 26 is equal to or greater than the first threshold Sh1 (step SC5).

[0144] In step SC5, if it is determined that the meter-out pressure is equal to or greater than the first threshold Sh1 (step SC5: Yes), the corrected meter-in flow rate calculation unit 74 determines the corrected meter-in flow rate to be zero. The control unit 76 controls one or both of the hydraulic pump 12 and the bottom valve 15 (meter-in valve) so that the meter-in flow rate becomes zero (step SC6).

[0145] The corrected regeneration flow rate calculation unit 82 calculates the corrected regeneration opening by adding the difference between the target meter-in opening and the corrected meter-in opening to the target regeneration opening. As described above, if the meter-out pressure is greater than or equal to the first threshold Sh1, the corrected meter-in opening Aic is determined to be zero, and the corrected regeneration opening Arc becomes the sum of the target meter-in opening Air and the target regeneration opening Arr (Arc = Arr + Air). The control unit 76 controls the head-side valve 14 (regeneration valve) so that the opening area of ​​the head-side valve 14 (regeneration valve) becomes the corrected regeneration opening Arc (step SC7).

[0146] In step SC5, if it is determined that the meter-out pressure is not equal to or greater than the first threshold Sh1 (step SC5: No), the corrected meter-in flow rate calculation unit 74 determines the corrected meter-in flow rate such that the lower the meter-out pressure, the greater the corrected meter-in flow rate. The control unit 76 controls one or both of the hydraulic pump 12 and the bottom-side valve 15 (meter-in valve) such that the lower the meter-out pressure, the greater the meter-in flow rate (step SC8).

[0147] The corrected regeneration flow rate calculation unit 82 calculates the corrected regeneration opening by adding the difference between the target meter-in opening and the corrected meter-in opening to the target regeneration opening. As described above, when the meter-out pressure is greater than or equal to the second threshold Sh2 and less than the first threshold Sh1, the corrected regeneration opening Arc is determined to become smaller as the meter-out pressure decreases. The control unit 76 controls the head-side valve 14 (regeneration valve) so that the opening area of ​​the head-side valve 14 (regeneration valve) becomes the corrected regeneration opening Arc (step SC9).

[0148] In step SC3, if it is determined that the meter-out pressure is not equal to or greater than the second threshold Sh2 (step SC3: No), and in step SC4, if it is determined that the operation of the work machine cylinder 6 is not a predetermined operation (step SC4: No), the control unit 76 controls one or both of the hydraulic pump 12 and the bottom valve 15 (meter-in valve) based on the target meter-in flow rate. The control unit 76 controls the hydraulic pump 12 so that the hydraulic fluid at the target pump flow rate calculated by the target meter-in flow rate calculation unit 72 is discharged, and controls the bottom valve 15 (meter-in valve) so that the target meter-in opening is calculated by the target meter-in flow rate calculation unit 72 (step SC10).

[0149] The control unit 76 controls the head-side valve 14 (regeneration valve) based on the target regeneration flow rate. As described above, if the meter-out pressure is less than the second threshold Sh2, the corrected meter-in opening Aic is determined to be the target meter-in opening Air, and the corrected regeneration opening Arc is determined to be the target regeneration opening Arr (Arc = Arr). The control unit 76 controls the head-side valve 14 (regeneration valve) so that its opening area becomes the target regeneration opening calculated by the target regeneration flow rate calculation unit 81 (step SC11).

[0150] Figure 12 is a timing chart showing the control method of the work machine 1 according to the second embodiment. Figure 12 is a timing chart for when the piston 62 of the arm cylinder 6B, which has been operating to retract, reaches the stroke end and then operates to extend the arm cylinder 6B. In the multiple graphs shown in Figure 12, the horizontal axis is time, and the vertical axes are the operating amount of the operating device 8, the hydraulic fluid pressure, the pump flow rate, the opening area of ​​the bottom valve 15, and the opening area of ​​the head valve 14, respectively.

[0151] In Figure 12, time t1 arrives after time 0, time t2 arrives after time t1, and time t3 arrives after time t2.

[0152] Line La indicates the amount of operation of the operating device 8. Line Lb indicates the meter-out pressure, which is the pressure of the hydraulic fluid flowing out of the arm cylinder 6B. Line Lc indicates the meter-in pressure, which is the pressure of the hydraulic fluid flowing into the arm cylinder 6B. Line Lk indicates the drive pressure Pd. In the example shown in Figure 12, the drive pressure Pd is a low value, and it is determined that the operation of the work machine cylinder 6 is a predetermined operation.

[0153] Line Le indicates the target pump flow rate. Line Lf indicates the corrected pump flow rate. Line Lg indicates the target meter-in opening. Line Lh indicates the corrected meter-in opening. Line Lm indicates the target regeneration opening. Line Ln indicates the corrected regeneration opening.

[0154] The target meter-in flow rate calculation unit 72 calculates the target pump flow rate and target meter-in opening based on the target operating speed of the work machine cylinder 6. The target regeneration flow rate calculation unit 81 calculates the target regeneration opening based on the target operating speed of the work machine cylinder 6.

[0155] At time 0, the piston 62 reaches the stroke end. If the operating device 8 continues to be operated with the piston 62 at the stroke end, the hydraulic fluid supplied to the head chamber 64 will cause the head chamber 64 to become high-pressure. From time t1, the operating direction of the lever of the operating device 8 is switched, and the controller 7 operates the work machine cylinder 6 in a direction that moves the piston 62 away from the stroke end. At time t1, since the meter-out pressure is greater than or equal to the first threshold Sh1, the controller 7 starts pressure relief control. The corrected meter-in flow rate calculation unit 74 calculates the corrected pump flow rate and the corrected meter-in opening. If the meter-out pressure is greater than or equal to the first threshold Sh1, the corrected pump flow rate and the corrected meter-in opening are set to zero. The corrected regeneration flow rate calculation unit 82 adds the difference between the target meter-in opening and the corrected meter-in opening to the target regeneration opening to calculate the corrected regeneration opening.

[0156] The corrected regeneration flow rate calculation unit 82 may calculate the corrected regeneration opening by adding a correction value proportional to the difference between the target meter-in opening and the corrected meter-in opening to the target regeneration opening. The corrected regeneration flow rate calculation unit 82 may add the difference value, or it may calculate the correction value based on correlation data between the correction value and the difference value and add the correction value. Regardless of the difference value, the regeneration opening does not need to be corrected. That is, the correction value added to the target regeneration opening may always be zero.

[0157] As shown in Figure 12, between time point t1 and time point t2, both the corrected pump flow rate and the corrected meter-in opening are maintained at zero. Between time point t1 and time point t2, the corrected regeneration opening is larger than the target regeneration opening. Between time point t1 and time point t2, the regeneration flow rate increases and the meter-in flow rate becomes zero, so the meter-out pressure decreases as shown by line Lb.

[0158] The meter-out pressure gradually decreases due to the pressure relief control. At time t2, the meter-out pressure decreases to the first threshold Sh1. When the meter-out pressure falls below the first threshold Sh1, the corrective pump flow rate is determined to increase as the meter-out pressure decreases, and the meter-in opening is determined to increase as the meter-out pressure decreases. When the meter-out pressure falls below the first threshold Sh1, the regeneration opening is determined to decrease as the meter-out pressure decreases. Between time t2 and time t3, the corrective regeneration opening is larger than the target regeneration opening.

[0159] At time t3, the meter-out pressure drops to the second threshold Sh2. When the meter-out pressure falls below the second threshold Sh2, the hydraulic pump 12 is controlled to discharge hydraulic fluid at the target pump flow rate, and the head-side valve 14 is controlled to open to the target meter-in position. When the meter-out pressure falls below the second threshold Sh2, the head-side valve 14 (regeneration valve) is controlled to open to the target regeneration position.

[0160] <Control when the head-side pressure sensor is abnormal> As described above, in the embodiment, when the operation of the work machine cylinder 6 is a predetermined operation and the meter-out pressure detected by the head-side pressure sensor 26 is greater than or equal to the threshold Sh, pressure relief control is performed. If the head-side pressure sensor 26 is abnormal, the controller 7 cannot calculate the corrected meter-in flow rate (corrected pump flow rate and corrected meter-in opening) and the corrected regeneration flow rate (corrected regeneration opening). If the head-side pressure sensor 26 is abnormal, the controller 7 controls the hydraulic pump 12 and the bottom-side valve 15 so that the hydraulic fluid at the target meter-in flow rate flows into the work machine cylinder 6, and controls the head-side valve 14 (regeneration valve) so that the hydraulic fluid at the target regeneration flow rate is supplied from the outlet of the work machine cylinder 6 to the regeneration flow path.

[0161] <Effects> As described above, in the second embodiment as well, pressure relief control is performed when the inside of the work machine cylinder 6 becomes high pressure. In this embodiment, when the inside of the work machine cylinder 6 exceeds a threshold Sh, the head-side valve 14 (regeneration valve) is controlled so that the opening area of ​​the head-side valve 14 (regeneration valve) becomes a corrected regeneration opening that is larger than the target regeneration opening. Since excessive high pressure inside the work machine cylinder 6 is suppressed, instability in the operation of the work machine cylinder 6 is suppressed, and the occurrence of malfunctions of the work machine cylinder 6 is suppressed.

[0162] In this embodiment, the operation of the work implement cylinder 6 is determined based on the drive pressure Pd to determine whether it is performing a predetermined operation. If the meter-out pressure is above the threshold Sh but the drive pressure Pd exceeds a specified value, it is determined that the work implement 4 is performing high-load work, and pressure relief control is not performed. Since pressure relief control is not performed when the meter-out pressure is above the threshold Sh but the drive pressure Pd exceeds a specified value, high-load work is performed smoothly.

[0163] <Other Embodiments> In the embodiments described above, the pressure relief control of the arm cylinder 6B was explained. The boom cylinder 6A and the bucket cylinder 6C can also be controlled for pressure relief according to the embodiments described above.

[0164] 1...Work machine, 2...Traction unit, 2A...Track, 3...Slewing unit, 4...Work machine, 4A...Boom, 4B...Arm, 4C...Bucket, 5...Slewing motor, 6...Work machine cylinder, 6A...Boom cylinder, 6B...Arm cylinder, 6C...Bucket cylinder, 7...Controller, 8...Operating device, 9...Traction motor, 10...Control system, 11...Power source, 12...Hydraulic pump, 13...Tank, 14...Head side valve (meter-in valve, regeneration valve), 15...Bottom side valve (meter-out valve, meter-in valve), 16...Bottom side pressure sensor, 18...Suction passage, 19...Pump passage, 20...Head side passage, 21...Bottom side passage, 23...Regeneration passage, 24...Check valve, 25...C Computer, 25A...Processor, 25B...Main memory, 25C...Storage, 25D...Input / Output interface, 25E...Communication interface, 25F...Computer program, 26...Head-side pressure sensor, 27...Drain passage, 61...Cylinder tube, 62...Piston, 63...Rod, 64...Head chamber, 65...Bottom chamber, 71...Target operating speed calculation unit, 72...Target meter-in flow rate calculation unit, 73...Target meter-out flow rate calculation unit, 74...Corrected meter-in flow rate calculation unit, 75...Corrected meter-out flow rate calculation unit, 76...Control unit, 77...Threshold storage unit, 81...Target regeneration flow rate calculation unit, 82...Corrected regeneration flow rate calculation unit, 83...Drive pressure calculation unit.

Claims

1. A control system for a work machine comprising: a hydraulic pump for discharging hydraulic fluid; a hydraulic actuator to which the hydraulic fluid discharged from the hydraulic pump is supplied; a meter-in valve for adjusting the flow rate of hydraulic fluid flowing into the hydraulic actuator; a meter-out valve for adjusting the flow rate of hydraulic fluid flowing out of the hydraulic actuator; a meter-out pressure sensor for detecting the meter-out pressure indicating the pressure of the hydraulic fluid flowing out of the hydraulic actuator; and a controller, wherein the controller calculates a target meter-in flow rate indicating a target value for the flow rate of hydraulic fluid flowing into the hydraulic actuator and a target meter-out flow rate indicating a target value for the flow rate of hydraulic fluid flowing out of the hydraulic actuator based on the target operating speed of the hydraulic actuator, and controls at least one of the hydraulic pump, the meter-in valve, and the meter-out valve to resolve a state in which the pressure of the hydraulic fluid flowing out of the hydraulic actuator is high between the hydraulic actuator and the meter-out valve.

2. The control system for a work machine according to claim 1, wherein the controller controls at least one of the hydraulic pump and the meter-in valve so that when the meter-out pressure is greater than or equal to a predetermined threshold, a meter-in flow rate of hydraulic fluid less than the target meter-in flow rate flows into the hydraulic actuator, and controls the meter-out valve so that a meter-out flow rate of hydraulic fluid greater than the target meter-out flow rate flows out from the hydraulic actuator.

3. The threshold includes a first threshold and a second threshold smaller than the first threshold, wherein the controller controls at least one of the hydraulic pump and the meter-in valve so that the meter-in flow rate becomes zero when the meter-out pressure is greater than or equal to the first threshold, controls at least one of the hydraulic pump and the meter-in valve so that the meter-in flow rate increases as the meter-out pressure decreases when the meter-out pressure is greater than or equal to the second threshold and less than the first threshold, and controls the hydraulic pump and the meter-in valve so that the hydraulic fluid at the target meter-in flow rate flows into the hydraulic actuator when the meter-out pressure is less than the second threshold, according to claim 2.

4. The controller calculates, based on the target operating speed, a target pump flow rate indicating a target value for the flow rate of hydraulic fluid discharged from the hydraulic pump, a target meter-in opening indicating a target value for the opening area of ​​the meter-in valve, and a target meter-out opening indicating a target value for the opening area of ​​the meter-out valve; and, if the meter-out pressure is greater than or equal to the threshold, the hydraulic pump is controlled so that a pump flow rate of hydraulic fluid less than the target pump flow rate is discharged from the hydraulic pump, the meter-in valve is controlled so that the corrected meter-in opening has an opening area smaller than the target meter-in opening, and the meter-out valve is controlled so that the corrected meter-out opening has an opening area larger than the target meter-out opening, the control system for a working machine according to claim 2.

5. The control system for a work machine according to claim 4, wherein the controller calculates the corrected meter-out opening based on the difference between the target meter-in opening and the corrected meter-in opening.

6. The control system for a work machine according to claim 5, wherein the controller calculates the corrected meter-out opening by adding a correction value proportional to the difference between the target meter-in opening and the corrected meter-in opening to the target meter-out opening.

7. The control system for a work machine according to claim 2, wherein the controller calculates the target operating speed based on an operating quantity indicating the value of an operating signal for operating the hydraulic actuator.

8. The control system for a work machine according to claim 1, wherein the hydraulic actuator is an arm cylinder that operates an arm included in the work machine of the work machine, and the controller controls at least one of the hydraulic pump and the meter-in valve so that when the operating direction of the arm cylinder is switched and the meter-out pressure is above a predetermined threshold, the hydraulic pump controls the meter-out valve so that a meter-in flow rate of hydraulic fluid less than the target meter-in flow rate flows into the hydraulic actuator, and controls the meter-out valve so that a meter-out flow rate of hydraulic fluid more than the target meter-out flow rate flows out from the arm cylinder.

9. The control system for a work machine according to claim 1, wherein the controller controls the hydraulic pump and the meter-in valve so that the target meter-in flow rate of hydraulic fluid flows into the hydraulic actuator when the meter-out pressure sensor is abnormal, and controls the meter-out valve so that the target meter-out flow rate of hydraulic fluid flows out of the hydraulic actuator.

10. A hydraulic pump that discharges hydraulic fluid; a hydraulic actuator to which the hydraulic fluid discharged from the hydraulic pump is supplied; a meter-in passage connecting the hydraulic pump and the inlet of the hydraulic actuator; a regeneration passage connecting the outlet of the hydraulic actuator and the meter-in passage; a meter-in valve disposed in the meter-in passage for adjusting the flow rate of hydraulic fluid flowing into the inlet of the hydraulic actuator; a regeneration valve disposed in the regeneration passage for adjusting the flow rate of hydraulic fluid supplied from the outlet of the hydraulic actuator to the meter-in passage; a meter-out pressure sensor for detecting a meter-out pressure indicating the pressure of hydraulic fluid flowing out from the outlet of the hydraulic actuator; and a controller, which calculates a target meter-in flow rate indicating a target value for the flow rate of hydraulic fluid flowing into the inlet of the hydraulic actuator and a target regeneration flow rate indicating a target value for the flow rate of hydraulic fluid supplied from the outlet of the hydraulic actuator to the meter-in passage based on the target operating speed of the hydraulic actuator; and determines whether the operation of the hydraulic actuator is a predetermined operation that starts from the end of the movable range of the hydraulic actuator. A control system for a working machine, which, when it is determined that the predetermined operation has occurred, controls the hydraulic pump, the meter-in valve, and at least one of the regeneration valve based on the target meter-in flow rate and the target regeneration flow rate and the meter-out pressure, in order to eliminate the condition in which the pressure of the hydraulic fluid flowing out of the hydraulic actuator is high between the hydraulic actuator and the regeneration valve.

11. The control system for a work machine according to claim 10, wherein the controller determines that the predetermined operation has occurred and the meter-out pressure is equal to or greater than a predetermined threshold, controls at least one of the hydraulic pump and the meter-in valve so that a meter-in flow rate of hydraulic fluid less than the target meter-in flow rate flows into the hydraulic actuator, and controls the regeneration valve so that a regeneration flow rate of hydraulic fluid greater than the target regeneration flow rate is supplied from the outlet to the regeneration channel.

12. The control system for a work machine according to claim 11, wherein the threshold includes a first threshold and a second threshold smaller than the first threshold, and the controller controls at least one of the hydraulic pump and the meter-in valve so that the meter-in flow rate becomes zero when the meter-out pressure is greater than or equal to the first threshold, the hydraulic pump and the meter-in valve so that the meter-in flow rate increases as the meter-out pressure decreases when the meter-out pressure is greater than or equal to the second threshold and less than the first threshold, and the hydraulic pump and the meter-in valve so that the hydraulic fluid at the target meter-in flow rate flows into the hydraulic actuator when the meter-out pressure is less than the second threshold.

13. The controller calculates, based on the target operating speed, a target pump flow rate indicating a target value for the flow rate of hydraulic fluid discharged from the hydraulic pump, a target meter-in opening indicating a target value for the opening area of ​​the meter-in valve, and a target regeneration opening indicating a target value for the opening area of ​​the regeneration valve; and, if the meter-out pressure is greater than or equal to the threshold, the hydraulic pump is controlled so that a pump flow rate of hydraulic fluid less than the target pump flow rate is discharged from the hydraulic pump, the meter-in valve is controlled so that it becomes a corrected meter-in opening with an opening area smaller than the target meter-in opening, and the regeneration valve is controlled so that it becomes a corrected regeneration opening with an opening area larger than the target regeneration opening, the control system for a working machine according to claim 11.

14. The control system for a work machine according to claim 13, wherein the controller calculates the corrected regenerated aperture based on the difference between the target meter-in aperture and the corrected meter-in aperture.

15. The control system for a work machine according to claim 14, wherein the controller calculates the corrected regenerated opening by adding a correction value proportional to the difference between the target meter-in opening and the corrected meter-in opening to the target regenerated opening.

16. The control system for a work machine according to claim 11, wherein the controller calculates the target operating speed based on an operating quantity indicating the value of an operating signal for operating the hydraulic actuator.

17. A control system for a work machine according to claim 10, comprising a meter-in pressure sensor for detecting a meter-in pressure indicating the pressure of the hydraulic fluid flowing into the inlet of the hydraulic actuator, wherein the controller calculates the drive pressure applied to the hydraulic actuator based on the meter-in pressure, the meter-out pressure, and the pressure-receiving area of ​​the hydraulic actuator, and determines that the operation of the hydraulic actuator is the predetermined operation if the drive pressure is less than or equal to a predetermined value.

18. The control system for a work machine according to claim 10, wherein the hydraulic actuator is a hydraulic cylinder that operates the work machine of the work machine, and the controller determines that the operation of the hydraulic cylinder is the predetermined operation, and when the meter-out pressure is above a predetermined threshold, it controls at least one of the hydraulic pump and the meter-in valve so that a meter-in flow rate of hydraulic fluid less than the target meter-in flow rate flows into the hydraulic actuator, and controls the regeneration valve so that a regeneration flow rate of hydraulic fluid greater than the target regeneration flow rate is supplied from the outlet to the regeneration path.

19. The control system for a work machine according to claim 11, wherein the controller controls the hydraulic pump and the meter-in valve so that when the meter-out pressure sensor is abnormal, the hydraulic fluid at the target meter-in flow rate flows into the hydraulic actuator, and controls the regeneration valve so that the hydraulic fluid at the target regeneration flow rate is supplied from the outlet to the regeneration path.

20. A control method for a work machine comprising: a hydraulic pump that discharges hydraulic fluid; a hydraulic actuator to which the hydraulic fluid discharged from the hydraulic pump is supplied; a meter-in passage connecting the hydraulic pump and the inlet of the hydraulic actuator; a regeneration passage connecting the outlet of the hydraulic actuator and the meter-in passage; a meter-in valve disposed in the meter-in passage for adjusting the flow rate of hydraulic fluid flowing into the inlet of the hydraulic actuator; a regeneration valve disposed in the regeneration passage for adjusting the flow rate of hydraulic fluid supplied from the outlet of the hydraulic actuator to the meter-in passage; a meter-out pressure sensor for detecting a meter-out pressure indicating the pressure of hydraulic fluid flowing out from the outlet of the hydraulic actuator; and a controller, wherein the method calculates a target meter-in flow rate indicating a target value for the flow rate of hydraulic fluid flowing into the inlet of the hydraulic actuator and a target regeneration flow rate indicating a target value for the flow rate of hydraulic fluid supplied from the outlet of the hydraulic actuator to the meter-in passage, based on the target operating speed of the hydraulic actuator; and determines whether the operation of the hydraulic actuator is a predetermined operation that starts from the end of the movable range of the hydraulic actuator. A control method for a working machine, which, when it is determined that the predetermined operation has occurred, controls at least one of the hydraulic pump, the meter-in valve, and the regeneration valve based on at least one of the target meter-in flow rate and the target regeneration flow rate and the meter-out pressure, in order to eliminate the condition in which the pressure of the hydraulic fluid flowing out of the hydraulic actuator is high between the hydraulic actuator and the regeneration valve.

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