Work machine

Abstract

A work machine comprising a work implement comprises a hydraulic pump that discharges working oil, a hydraulic cylinder for operating the work machine, a meter-out opening that controls the flow rate of working oil discharged from a rod chamber of the hydraulic cylinder to a tank, a regeneration flow path that connects the rod chamber of the hydraulic cylinder and a cap chamber of the hydraulic cylinder, and a controller. The controller calculates an external force acting on the hydraulic cylinder, and controls the meter-out opening on the basis of the calculated external force upon receiving an operation signal for operating the work machine so that the hydraulic cylinder extends.

Description

Work machine

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

[0002] In the technical field related to work machines, a control system for a work machine as disclosed in Patent Document 1 is known. The control system disclosed in Patent Document 1 includes a control valve having a regeneration passage for regenerating hydraulic oil from a meter-out passage to a meter-in passage.

[0003] Japanese Unexamined Patent Application Publication No. 2021-148154

[0004] When switching between a regeneration state and a non-regeneration state, the operability of the work machine may deteriorate.

[0005] An object of the present disclosure is to improve the operability of a work machine.

[0006] According to the present disclosure, a work machine including a working machine is provided. The work machine includes a hydraulic pump that discharges hydraulic oil, a hydraulic cylinder that operates the working machine, a meter-out opening that controls the flow rate of the hydraulic oil discharged from the rod chamber of the hydraulic cylinder to the tank, a regeneration passage that connects the rod chamber of the hydraulic cylinder and the cap chamber of the hydraulic cylinder, and a controller. The controller calculates an external force acting on the hydraulic cylinder, and when receiving an operation signal for operating the working machine so that the hydraulic cylinder extends, controls the meter-out opening based on the calculated external force.

[0007] According to the present disclosure, the operability of the work machine is improved.

[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 diagram illustrating the opening characteristics of the regeneration opening and the meter-out opening at the arm cloud position of the spool of the rod-side control valve according to the first embodiment. Figure 4 is a block diagram showing the controller according to the first embodiment. Figure 5 is a diagram illustrating the state of the hydraulic system according to the first embodiment. Figure 6 is a schematic diagram showing the hydraulic system in the regeneration state according to the first embodiment. Figure 7 is a schematic diagram showing the hydraulic system in the first transient state according to the first embodiment. Figure 8 is a schematic diagram showing the hydraulic system in the drain state according to the first embodiment. Figure 9 is a diagram illustrating the method for calculating the regeneration factor according to the first embodiment. Figure 10 is a diagram illustrating the method for calculating the target drain flow rate, target regeneration flow rate, and target pump flow rate according to the first embodiment. Figure 11 is a diagram illustrating the method for calculating the target regeneration opening area according to the first embodiment. Figure 12 is a diagram illustrating the method for calculating the target meter-out opening area according to the first embodiment. Figure 13 is a timing chart showing the control method of the hydraulic system according to the first embodiment. Figure 14 is a timing chart showing the control method of the hydraulic system according to the first embodiment. Figure 15 is a timing chart showing the control method of the hydraulic system according to the first embodiment. Figure 16 is a flowchart showing the control method of the hydraulic system according to the first embodiment. Figure 17 is a schematic diagram showing the hydraulic system according to the second embodiment.

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

[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. In this embodiment, work machine 1 is a hydraulic excavator. Work machine 1 comprises a traveling body 2, a rotating body 3, a work machine 4, a hydraulic cylinder 5, a controller 6, a work machine operating device 7, and a monitor 60.

[0011] The running body 2 supports the rotating body 3. The running body 2 has a pair of tracks 2A. The working 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 supported so as to be rotatable relative to the traveling body 2. The slewing body 3 has a cab. The operator of the work machine 1 sits in the cab. The work machine operating device 7 and the monitor 60 are located in the cab. The work machine operating device 7 outputs operating signals for operating the work machine 4. The work machine operating device 7 is, for example, a lever that can be operated by the operator. The monitor 60 includes a display device and an input device. The monitor 60 provides display data to the operator. The monitor 60 generates input data when operated by the operator. The traveling body 2 and the slewing body 3 constitute the body of the work machine 1.

[0013] The work implement 4 is rotatably connected to the slewing body 3. The work implement 4 includes a boom 8, an arm 9, and a bucket 10. The boom 8 is rotatably connected to the front of the slewing body 3. The arm 9 is rotatably connected to the tip of the boom 8. The bucket 10 is rotatably connected to the tip of the arm 9.

[0014] The hydraulic cylinder 5 operates the work machine 4. The hydraulic cylinder 5 is driven by hydraulic fluid. The hydraulic cylinder 5 includes a boom cylinder 11, an arm cylinder 12, and a bucket cylinder 13.

[0015] The boom cylinder 11 operates the boom 8. The operation of the boom 8 includes raising and lowering movements. The boom 8 is raised when the boom cylinder 11 extends. The boom 8 is lowered when the boom cylinder 11 retracts.

[0016] The arm cylinder 12 moves the arm 9. The movement of the arm 9 includes arm cloud movement and arm dump movement. When the arm cylinder 12 extends, the arm 9 performs arm cloud movement. When the arm cylinder 12 retracts, the arm 9 performs arm dump movement.

[0017] The bucket cylinder 13 operates the bucket 10. The operation of the bucket 10 includes bucket tilting and bucket dumping. When the bucket cylinder 13 extends, the bucket 10 performs bucket tilting. When the bucket cylinder 13 retracts, the bucket 10 performs bucket dumping.

[0018] <Control System> Figure 2 is a schematic diagram showing the control system 14 of the work machine 1 according to the first embodiment. As shown in Figure 2, the control system 14 includes a controller 6, a work machine operating device 7, a power source 15, and a hydraulic system 16. Figure 2 shows the hydraulic system 16 for driving the arm cylinder 12. The power source 15 is, for example, a diesel engine. The power source 15 may also be an electric motor. The controller 6 receives operation signals from the work machine operating device 7. The controller 6 is configured to control the power source 15 and the hydraulic system 16.

[0019] The arm cylinder 12 includes a cylinder tube 121, a piston 122 that is movable inside the cylinder tube 121, and a rod 123 connected to the piston 122. The internal space of the cylinder tube 121 is divided by the piston 122 into a cap chamber 12A and a rod chamber 12B. The rod 123 is located in the rod chamber 12B. The arm cylinder 12 extends when hydraulic fluid is supplied to the cap chamber 12A and discharged from the rod chamber 12B. The arm cylinder 12 retracts when hydraulic fluid is supplied to the rod chamber 12B and discharged from the cap chamber 12A. In this embodiment, the pressure-receiving area of ​​the piston 122 facing the rod chamber 12B is smaller than the pressure-receiving area of ​​the piston 122 facing the cap chamber 12A.

[0020] The hydraulic system 16 includes a hydraulic pump 17, a tank 18, a pump passage 19, a cap-side passage 20, a cap-side control valve 21, a rod-side passage 22, a rod-side control valve 23, a solenoid proportional valve 70, a drain passage 25, a regeneration passage 26, a relief passage 51, a check valve 27, a cap-side pressure sensor 28, a rod-side pressure sensor 29, and a relief valve 50.

[0021] The hydraulic pump 17 is driven by power transmitted from the power source 15. The hydraulic pump 17 discharges hydraulic fluid. The hydraulic pump 17 is a variable displacement hydraulic pump in which the discharge volume changes, for example, by controlling the tilt angle of the swash plate. The discharge volume of the hydraulic pump 17 is controlled by the controller 6. The pump passage 19 is connected to the discharge port of the hydraulic pump 17. The hydraulic pump 17 draws in hydraulic fluid contained in the tank 18 and discharges it into the pump passage 19.

[0022] The cap-side control valve 21 is configured to control the flow rate of hydraulic fluid supplied to or discharged from the cap chamber 12A of the arm cylinder 12. In this embodiment, the cap-side control valve 21 is a hydraulic pilot-operated control valve having a spool. The displacement of the spool of the cap-side control valve 21 is controlled by the pilot pressure acting on the pilot oil chamber. The spool of the cap-side control valve 21 is movable between a neutral position N1, an arm dump position D1, and an arm cloud position C1. The cap-side control valve 21 has a meter-in opening 30 and a meter-out opening 31. By controlling the displacement of the spool of the cap-side control valve 21, the opening areas of the meter-in opening 30 and the meter-out opening 31 change. When the spool of the cap-side control valve 21 is in the arm cloud position C1, the cap-side control valve 21 is configured to function as a meter-in control valve that controls the flow rate of hydraulic fluid supplied from the hydraulic pump 17 to the cap chamber 12A of the arm cylinder 12. Figure 2 shows the state in which the spool of the cap-side control valve 21 is positioned in the neutral position N1.

[0023] The cap-side control valve 21 has a pump port P1, a first cap port P2, a second cap port P3, and a drain port P4. The pump port P1 is connected to the hydraulic pump 17 via a pump passage 19. The first cap port P2 and the second cap port P3 are each connected to the cap chamber 12A of the arm cylinder 12 via a cap-side passage 20. The drain port P4 is connected to the tank 18 via a drain passage 25.

[0024] The rod-side control valve 23 is configured to control the flow rate of hydraulic fluid supplied to or discharged from the rod chamber 12B of the arm cylinder 12. In this embodiment, the rod-side control valve 23 is a hydraulic pilot-operated control valve having a spool. The displacement of the spool of the rod-side control valve 23 is controlled by pilot pressure acting on the pilot oil chamber. The spool of the rod-side control valve 23 is movable between a neutral position N2, an arm dump position D2, and an arm cloud position C2. The rod-side control valve 23 has a meter-out opening 32, a regeneration opening 33, and a meter-out opening 34. By controlling the displacement of the spool of the rod-side control valve 23, the opening areas of the meter-out opening 32, the regeneration opening 33, and the meter-out opening 34 change. When the spool of the rod-side control valve 23 is in the arm cloud position C2, the rod-side control valve 23 is configured to function as a meter-out control valve that controls the flow rate of hydraulic fluid discharged from the rod chamber 12B of the arm cylinder 12 to the tank 18. Furthermore, when the spool of the rod-side control valve 23 is in the arm cloud position C2, the rod-side control valve 23 is configured to function as a regeneration valve that controls the flow rate of hydraulic fluid supplied from the rod chamber 12B of the arm cylinder 12 to the cap chamber 12A via the regeneration passage 26. Figure 2 shows the state in which the spool of the rod-side control valve 23 is positioned in the neutral position N2.

[0025] Figure 3 is a diagram illustrating the opening characteristics of the regeneration opening 33 and the meter-out opening 34 at the arm cloud position C2 of the spool of the rod-side control valve 23 according to the first embodiment.

[0026] In the graph shown in Figure 3, the horizontal axis represents the spool displacement, and the vertical axis represents the opening area of ​​the regeneration opening 33 and the meter-out opening 34, respectively. In Figure 3, line L33 shows the opening area of ​​the regeneration opening 33, and line L34 shows the opening area of ​​the meter-out opening 34. As shown by lines L33 and L34, the opening areas of the regeneration opening 33 and the meter-out opening 34 change as the spool displacement changes.

[0027] The arm cloud position C2 of the spool of the rod-side control valve 23 has a first region AR1 and a second region AR2. The first region AR1 is set to a range where the amount of spool displacement is small. The second region AR2 is set to a range where the amount of spool displacement is larger than that of the first region AR1.

[0028] As shown in Figure 3, in the first region AR1, only the regeneration opening 33 is open. In the first region AR1, the opening area of ​​the regeneration opening 33 is set to increase as the spool displacement increases. In the second region AR2, where the spool displacement is even greater than in the first region AR1, the opening area of ​​the regeneration opening 33 increases further, and the meter-out opening 34 also opens. In the second region AR2, the opening area of ​​the meter-out opening 34 is set to increase as the spool displacement increases. That is, the rod-side control valve 23 is configured to increase or decrease the regeneration flow rate of hydraulic fluid from the rod chamber 12B of the arm cylinder 12 to the cap chamber 12A, and the discharge flow rate of hydraulic fluid from the rod chamber 12B of the arm cylinder 12 to the tank 18, in accordance with the increase or decrease in the opening area of ​​the regeneration opening 33 and the opening area of ​​the meter-out opening 34 at the arm cloud position C2 of the spool.

[0029] The rod-side control valve 23 has a pump port P5, a first rod port P6, a second rod port P7, a drain port P8, and a regeneration port P9. The pump port P5 is connected to the hydraulic pump 17 via a pump passage 19. The first rod port P6 and the second rod port P7 are each connected to the rod chamber 12B of the arm cylinder 12 via a rod-side passage 22. The drain port P8 is connected to the tank 18 via a drain passage 25.

[0030] The electromagnetic proportional valve 70 supplies the hydraulic fluid discharged from the pilot hydraulic pump 71 to the pilot oil chamber of the cap-side control valve 21 and the pilot oil chamber of the rod-side control valve 23. Based on command signals from the controller 6, the electromagnetic proportional valve 70 generates pilot pressure to control the spool displacement of the cap-side control valve 21 and the spool displacement of the rod-side control valve 23, respectively. That is, the controller 6 controls the cap-side control valve 21 and the rod-side control valve 23 by controlling the pilot pressure generated by the electromagnetic proportional valve 70. The electromagnetic proportional valve 70 includes electromagnetic proportional valve 70CC and electromagnetic proportional valve 70CD for controlling the cap-side control valve 21. The electromagnetic proportional valve 70 includes electromagnetic proportional valve 70RC and electromagnetic proportional valve 70RD for controlling the rod-side control valve 23.

[0031] The regeneration passage 26 is configured to connect the rod chamber 12B and the cap chamber 12A of the arm cylinder 12. The regeneration passage 26 is configured to connect the rod-side passage 22 and the cap-side passage 20. In this embodiment, the regeneration passage 26 connects the regeneration port P9 of the rod-side control valve 23 to the cap-side passage 20. The regeneration passage 26 is connected to the rod-side passage 22 via the rod-side control valve 23. The rod-side control valve 23 is configured to function as a regeneration valve that controls the flow rate of hydraulic fluid supplied from the rod chamber 12B to the cap chamber 12A of the arm cylinder 12.

[0032] A check valve 27 is positioned in the regeneration passage 26. The check valve 27 is configured to block the flow of hydraulic fluid from the cap chamber 12A to the rod chamber 12B. In this embodiment, the check valve 27 is configured to block the flow of hydraulic fluid from the cap-side passage 20 to the regeneration port P9 of the rod-side control valve 23.

[0033] The relief passage 51 is connected to the pump passage 19. The relief passage 51 connects the pump passage 19 to the tank 18. The relief valve 50 is located in the relief passage 51. The relief valve 50 suppresses an excessive rise in the pressure of the hydraulic fluid supplied to the arm cylinder 12. The pressure of the hydraulic fluid supplied to the arm cylinder 12 includes the pressure in the pump passage 19. When the pressure in the pump passage 19 falls below a predetermined set pressure (relief pressure), the relief valve 50 closes, and the hydraulic fluid in the pump passage 19 is not discharged to the tank 18 via the relief valve 50. When the pressure in the pump passage 19 reaches the set pressure, the relief valve 50 opens, and at least a portion of the hydraulic fluid in the pump passage 19 is discharged to the tank 18 via the relief valve 50. By discharging at least a portion of the hydraulic fluid in the pump passage 19 to the tank 18 via the relief valve 50, an excessive rise in the pressure of the hydraulic fluid supplied to the arm cylinder 12 is suppressed. In this embodiment, the relief valve 50 is operated by a solenoid valve 52. The solenoid valve 52 is connected to the relief valve 50. The solenoid valve 52 is controlled by a controller 6. The controller 6 can change the set pressure of the relief valve 50 by controlling the solenoid valve 52.

[0034] If the controller 6 does not receive an operation signal from the work equipment operating device 7, the spool of the cap-side control valve 21 is positioned in the neutral position N1, and the spool of the rod-side control valve 23 is positioned in the neutral position N2. When the spool of the cap-side control valve 21 is positioned in the neutral position N1 and the spool of the rod-side control valve 23 is positioned in the neutral position N2, no hydraulic fluid flows through either the cap-side control valve 21 or the rod-side control valve 23. When the spool of the cap-side control valve 21 is positioned in the neutral position N1 and the spool of the rod-side control valve 23 is positioned in the neutral position N2, no hydraulic fluid is supplied to the arm cylinder 12, no hydraulic fluid is discharged from the arm cylinder 12, and the arm cylinder 12 does not drive.

[0035] When the controller 6 receives an operation signal from the work machine operating device 7 to perform an arm dump operation on the arm 9, it controls the cap-side control valve 21 so that the spool of the cap-side control valve 21 is positioned at the arm dump position D1, and controls the rod-side control valve 23 so that the spool of the rod-side control valve 23 is positioned at the arm dump position D2. When the spool of the cap-side control valve 21 is positioned at the arm dump position D1 and the spool of the rod-side control valve 23 is positioned at the arm dump position D2, hydraulic fluid is supplied to the rod chamber 12B via the rod-side control valve 23, and hydraulic fluid is discharged from the cap chamber 12A via the cap-side control valve 21. When the spool of the cap-side control valve 21 is positioned at the arm dump position D1 and the spool of the rod-side control valve 23 is positioned at the arm dump position D2, the arm cylinder 12 retracts, and the arm 9 performs an arm dump operation.

[0036] When the controller 6 receives an operation signal from the work machine operating device 7 to perform arm cloud operation of the arm 9, it controls the cap-side control valve 21 so that the spool of the cap-side control valve 21 is positioned at arm cloud position C1, and controls the rod-side control valve 23 so that the spool of the rod-side control valve 23 is positioned at arm cloud position C2. When the spool of the cap-side control valve 21 is positioned at arm cloud position C1 and the spool of the rod-side control valve 23 is positioned at arm cloud position C2, hydraulic fluid is supplied to the cap chamber 12A via the cap-side control valve 21, and hydraulic fluid is discharged from the rod chamber 12B via the rod-side control valve 23. When the spool of the cap-side control valve 21 is positioned at arm cloud position C1 and the spool of the rod-side control valve 23 is positioned at arm cloud position C2, the arm cylinder 12 extends, and the arm 9 performs arm cloud operation.

[0037] The cap-side pressure sensor 28 is positioned in the cap-side flow path 20. The cap-side pressure sensor 28 detects the pressure of the hydraulic fluid flowing through the cap-side flow path 20. When the arm cylinder 12 extends, the cap-side pressure sensor 28 detects the meter-in pressure, which indicates the pressure of the hydraulic fluid supplied to the cap chamber 12A.

[0038] The rod-side pressure sensor 29 is positioned in the rod-side flow path 22. The rod-side pressure sensor 29 detects the pressure of the hydraulic fluid flowing through the rod-side flow path 22. When the arm cylinder 12 extends, the rod-side pressure sensor 29 detects the meter-out pressure, which indicates the pressure of the hydraulic fluid discharged from the rod chamber 12B.

[0039] <Controller> Figure 4 is a block diagram of the controller 6 according to the first embodiment. The controller 6 includes a processor 34, a storage device 35, and an input / output interface 36.

[0040] The processor 34 includes a CPU (Central Processing Unit). The storage device 35 includes a recording medium on which computer programs and data are recorded in a readable format by the processor 34. The storage device 35 includes system memory such as RAM (Random Access Memory) or ROM (Read Only Memory) and auxiliary storage memory such as semiconductor memory. The controller 6 is connected to the work machine operating device 7, the cap-side pressure sensor 28, the rod-side pressure sensor 29, the electromagnetic proportional valve 70, the solenoid valve 52, the hydraulic pump 17, and the monitor 60 via an input / output interface 36.

[0041] The monitor 60 includes an input device 61. The input device 61 is operated by an operator who is seated in the cab. Examples of input devices 61 include a touch panel, buttons, a computer keyboard, and a mouse.

[0042] The processor 34 includes an estimation unit 37, a determination unit 38, an arithmetic unit 39, and a control unit 40. The storage device 35 includes a storage unit 41.

[0043] The estimation unit 37 calculates an external force acting on the arm cylinder 12. The external force acting on the arm cylinder 12 refers to the force acting on the rod 123 of the arm cylinder 12 from outside the arm cylinder 12. In the embodiment, when the estimation unit 37 receives an operation signal for operating at least the arm cylinder 12 to extend from the work implement operating device 7, the estimation unit 37 calculates an external force acting on the rod 123 with the direction in which the arm cylinder 12 contracts being defined as the positive direction. That is, when the direction of the external force acting on the rod 123 is the direction in which the arm cylinder 12 contracts, the calculated value of the external force is a positive value. On the other hand, when the direction of the external force acting on the rod 123 is the direction in which the arm cylinder 12 extends, the calculated value of the external force is a negative value. In the following description, the external force acting on the arm cylinder 12 calculated by the estimation unit 37 is appropriately referred to as the estimated external force Fd.

[0044] The estimation unit 37 calculates the estimated external force Fd based on the meter-in pressure Pi indicating the pressure of the hydraulic oil supplied to the cap chamber 12A of the arm cylinder 12, the meter-out pressure Po indicating the pressure of the hydraulic oil discharged from the rod chamber 12B, the cap-side pressure receiving area Ac which is the pressure receiving area of the piston 122 facing the cap chamber 12A, and the rod-side pressure receiving area Ar which is the pressure receiving area of the piston 122 facing the rod chamber 12B. The meter-in pressure Pi is detected by the cap-side pressure sensor 28. The meter-out pressure Po is detected by the rod-side pressure sensor 29. The cap-side pressure receiving area Ac refers to the pressure receiving area of the piston 122 facing the cap chamber 12A. The rod-side pressure receiving area Ar refers to the pressure receiving area of the piston 122 facing the rod chamber 12B. The cap-side pressure receiving area Ac and the rod-side pressure receiving area Ar are known data derived from the design data or specifications data of the arm cylinder 12. The cap-side pressure receiving area Ac is larger than the rod-side pressure receiving area Ar. The estimated external force Fd is calculated based on the following formula (1).

[0045] Fd = Pi × Ac - Po × Ar... (1)

[0046] When the arm cylinder 12 extends, the estimated external force, for example, correlates with the magnitude of the resistance force (load) received by the work implement 4 from the outside. In the operation of the work implement 4, when the load applied to the arm 9 is small, the external force acting on the arm cylinder 12 is small, so the estimated external force Fd also becomes small. When the load applied to the arm 9 is large, the external force acting on the arm cylinder 12 is large, so the estimated external force Fd also becomes large. As an operation of the work implement 4 where the load applied to the arm 9 is small, it is exemplified that the arm 9 performs an arm crowding operation with the bucket 10 being separated from the work target. As an operation of the work implement 4 where the load applied to the arm 9 is large, it is exemplified that the arm 9 performs an arm crowding operation with the bucket 10 being inserted into the work target.

[0047] In the following description, the operation where the arm 9 performs an arm crowding operation with the work implement 4 being separated from the work target is appropriately referred to as an aerial operation, the operation where the arm 9 performs an arm crowding operation with the bucket 10 being inserted into the work target is appropriately referred to as an excavation operation, and the operation that transitions from the excavation operation to the aerial operation is appropriately referred to as a transition operation.

[0048] The determination unit 38 determines the state of the hydraulic system 16 based on the estimated external force Fd calculated by the estimation unit 37. The determination unit 38 calculates a regeneration factor Fa based on the estimated external force Fd and an operation signal from the work implement operation device 7. The calculation unit 39 calculates a target regeneration flow rate Qr, a target drain flow rate Qd, a meter-out flow rate Qo, a target meter-in flow rate Qi, a target pump flow rate Qp, a target regeneration opening area At, and a target meter-out opening area Ad based on the operation signal from the work implement operation device 7 and the regeneration factor Fa calculated by the determination unit 38.

[0049] The control unit 40 controls one or both of the discharge flow rate of the hydraulic pump 17 and the spool displacement amount of the cap-side control valve 21 to adjust the discharge flow rate of the hydraulic oil discharged from the hydraulic pump 17 based on the target pump flow rate Qp calculated by the calculation unit 39. The control unit 40 controls the spool displacement amount of the rod-side control valve 23 based on the target regeneration opening area At and the target meter-out opening area Ad calculated by the calculation unit 39.

[0050] <State of Hydraulic System> Figure 5 is a diagram illustrating the state of the hydraulic system 16 according to the first embodiment. As shown in Figure 5, the state of the hydraulic system 16 includes a lever neutral state R0 in which the work implement operating device 7 is positioned in a neutral position without being operated, and a lever operated state in which the work implement operating device 7 is operated from the neutral position in a second direction so that the arm cylinder 12 extends. In the lever neutral state R0, the arm cylinder 12 is not driven. In the lever operated state, the arm cylinder 12 extends. The lever operated state includes a regeneration state R1, a first transient state R2, a drain state R3, and a second transient state R4.

[0051] Regeneration state R1 refers to the state in which the regeneration ratio, which indicates the proportion of hydraulic fluid discharged from the rod chamber 12B of the arm cylinder 12 that is supplied to the cap chamber 12A of the arm cylinder 12 via the regeneration passage 26, is at its maximum. Drain state R3 refers to the state in which the regeneration ratio is at its minimum. First transient state R2 refers to the first transition state from regeneration state R1 (maximum state) to drain state R3 (minimum state). Second transient state R4 refers to the second transition state from drain state R3 (minimum state) to regeneration state R1 (maximum state). The control unit 40 controls the regeneration opening 33 and the meter-out opening 34 using the four states: regeneration state R1, first transient state R2, drain state R3, and second transient state R4.

[0052] The regeneration ratio refers to the ratio of the flow rate of hydraulic fluid supplied to the cap chamber 12A via the regeneration channel 26 to the flow rate of hydraulic fluid discharged from the rod chamber 12B. In this embodiment, the maximum regeneration ratio means that the regeneration ratio is 100%. The minimum regeneration ratio means that the regeneration ratio is 0%. The maximum regeneration ratio may also mean that the regeneration ratio is a value less than 100% by a specified value. The minimum regeneration ratio may also mean that the regeneration ratio is a value greater than 0% by a specified value. The regeneration ratio in the maximum state is greater than the regeneration ratio in the minimum state. The specified value is, for example, 1%. That is, the regeneration ratio may be between 1% and 99%.

[0053] A first threshold Ha and a second threshold Hb for the estimated external force Fd are predetermined and stored in the storage unit 41. The second threshold Hb is a value greater than the first threshold Ha. The determination unit 38 sets the regeneration ratio to the maximum state when the estimated external force Fd is less than the first threshold Ha. That is, when the estimated external force Fd is less than the first threshold Ha, the determination unit 38 determines the state of the hydraulic system 16 to the regeneration state R1. The determination unit 38 sets the regeneration ratio to the minimum state when the estimated external force Fd is greater than the second threshold Hb. That is, when the estimated external force Fd is greater than the second threshold Hb, the determination unit 38 determines the state of the hydraulic system 16 to the drain state R3.

[0054] The determination unit 38 sets the regeneration ratio to an intermediate state corresponding to the estimated external force Fd if the estimated external force Fd is between a first threshold Ha and a second threshold Hb. That is, if the estimated external force Fd is between a first threshold Ha and a second threshold Hb, the determination unit 38 determines the state of the hydraulic system 16 to either a first transient state R2 or a second transient state R4.

[0055] The first threshold Ha and the second threshold Hb are arbitrarily changeable. The operator can change the first threshold Ha and the second threshold Hb by operating the input device 61 of the monitor 60. The input data generated by operating the input device 61 is transmitted to the controller 6. The determination unit 38 receives the input data from the input device 61. The determination unit 38 can change the first threshold Ha and the second threshold Hb based on the input data from the input device 61. The changed first threshold Ha and the second threshold Hb are stored in the storage unit 41. A candidate list for the first threshold Ha and a candidate list for the second threshold Hb may be predetermined. The candidate list for the first threshold Ha and the candidate list for the second threshold Hb may be displayed on the display device of the monitor 60. The operator can select the first threshold Ha and the second threshold Hb from the candidate list by operating the input device 61. The determination unit 38 can change the first threshold Ha and the second threshold Hb based on the first threshold Ha and the second threshold Hb selected by the operator.

[0056] The determination unit 38 may set the first threshold Ha and the second threshold Hb in conjunction with the set pressure of the relief valve 50. The set pressure of the relief valve 50 can be changed in steps. The operator can change the set pressure of the relief valve 50 by operating the input device 61. The control unit 40 changes the set pressure of the relief valve 50 based on the input data from the input device 61. The control unit 40 can change the set pressure of the relief valve 50 by controlling the solenoid valve 52. When the set pressure of the relief valve 50 is changed, the determination unit 38 may change the first threshold Ha and the second threshold Hb in conjunction with the set pressure of the relief valve 50.

[0057] Figures 6 and 7 are diagrams illustrating the operation of the hydraulic system 16 according to the first embodiment. Figures 6 and 7 show the state in which the arm cylinder 12 is extended and the arm 9 is moved in an arm cloud position. As shown in Figures 6 and 7, the spool of the cap-side control valve 21 is positioned at the arm cloud position C1 and the spool of the rod-side control valve 23 is positioned at the arm cloud position C2.

[0058] As shown in Figures 6 and 7, when the spool of the cap-side control valve 21 is positioned at the arm cloud position C1 and the spool of the rod-side control valve 23 is positioned at the arm cloud position C2, the hydraulic fluid discharged from the hydraulic pump 17 flows through the pump passage 19 and then flows into the meter-in opening 30 of the cap-side control valve 21 via the pump port P1. The hydraulic fluid that has flowed through the meter-in opening 30 flows out from the first cap port P2, flows through the cap-side passage 20, and then flows into the cap chamber 12A. As the hydraulic fluid flows into the cap chamber 12A, the arm cylinder 12 extends. As the arm cylinder 12 extends, the hydraulic fluid in the rod chamber 12B is discharged from the rod chamber 12B. The hydraulic fluid discharged from the rod chamber 12B flows through the rod-side passage 22. The hydraulic fluid that has flowed through the rod-side passage 22 flows into the rod-side control valve 23 via the first rod port P6.

[0059] (Regeneration State) Figure 6 is a schematic diagram showing the hydraulic system 16 in the regeneration state R1 according to the first embodiment. As shown in Figures 5 and 6, the regeneration state R1 is a state in which the hydraulic fluid discharged from the rod chamber 12B is supplied to the cap chamber 12A without being discharged to the tank 18. That is, the regeneration state R1 is a state in which all of the hydraulic fluid discharged from the rod chamber 12B is supplied to the cap chamber 12A. The determination unit 38 determines the state of the hydraulic system 16 to the regeneration state R1 when it has not received an operation signal from the work equipment operating device 7 to operate the arm 9 in arm cloud mode, and immediately after receiving an operation signal from the work equipment operating device 7 to operate the arm 9 in arm cloud mode. The control unit 40 controls the rod-side control valve 23 so that the state of the hydraulic system 16 becomes the regeneration state R1 when it has immediately received an operation signal from the work equipment operating device 7 to operate the arm 9 in arm cloud mode. As shown in Figure 3, immediately after receiving an operation signal from the work machine operating device 7 to move the arm 9 into arm cloud mode, the control unit 40 controls the spool displacement amount of the rod-side control valve 23 to open the regeneration opening 33 and close the meter-out opening 34. As shown in Figure 6, the hydraulic fluid discharged from the rod chamber 12B flows into the regeneration opening 33 from the first rod port P6 via the rod-side flow path 22 and flows out to the regeneration flow path 26 via the regeneration port P9. When the spool displacement amount of the rod-side control valve 23 is controlled to open the regeneration opening 33 and close the meter-out opening 34, the meter-out pressure becomes higher than the meter-in pressure, and the check valve 27 does not obstruct the flow of hydraulic fluid. The hydraulic fluid that has passed through the check valve 27 flows into the cap-side flow path 20 and is then supplied to the cap chamber 12A. That is, when the check valve 27 does not obstruct the flow of hydraulic fluid, the hydraulic fluid discharged from the rod chamber 12B is supplied to the cap chamber 12A without being discharged to the tank 18.

[0060] Furthermore, if the estimated external force Fd calculated by the estimation unit 37 is smaller than the first threshold Ha, the determination unit 38 determines the state of the hydraulic system 16 to the regeneration state R1. The control unit 40 controls the rod-side control valve 23 so that the state of the hydraulic system 16 becomes the regeneration state R1 if the estimated external force Fd is smaller than the first threshold Ha. The control unit 40 controls the spool displacement amount of the rod-side control valve 23 so that the regeneration opening 33 opens and the meter-out opening 34 closes to achieve the regeneration state R1. The control unit 40 controls the spool displacement amount of the rod-side control valve 23 so that the meter-out opening 34 is fully closed if the estimated external force Fd is smaller than the first threshold Ha, and recirculates all of the hydraulic fluid discharged from the rod chamber 12B into the cap chamber 12A.

[0061] (First Transient State) Figure 7 is a schematic diagram showing the hydraulic system 16 in the first transient state R2 according to the first embodiment. As shown in Figures 5 and 7, the first transient state R2 is a state in which a portion of the hydraulic fluid discharged from the rod chamber 12B is discharged into the tank 18, and the remaining hydraulic fluid is supplied to the cap chamber 12A. When the decision unit 38 determines that the regeneration state termination condition for terminating the regeneration state R1 is satisfied, it decides to transition the state of the hydraulic system 16 from the regeneration state R1 to the first transient state R2.

[0062] In this embodiment, the regeneration state termination condition includes the estimated external force Fd being equal to or greater than a first threshold Ha in the regeneration state R1, and the estimated external force Fd not fluctuating above a predetermined frequency. That is, if the estimated external force Fd fluctuates above a predetermined frequency, the regeneration state is maintained even if the estimated external force Fd is equal to or greater than the first threshold Ha.

[0063] A state in which the estimated external force Fd fluctuates above a predetermined frequency includes, for example, a state in which the target cylinder speed of the arm cylinder 12 fluctuates periodically in order to rapidly reciprocate the arm 9, or a state in which the amount of the work equipment operating device 7 fluctuates periodically. Furthermore, a state in which the estimated external force Fd fluctuates above a predetermined frequency may also include a state in which the estimated external force Fd vibrates unstably at a high frequency due to the movement of work equipment other than the arm (for example, when the bucket is reciprocated at a high frequency).

[0064] The control unit 40 controls the rod-side control valve 23 so that the state of the hydraulic system 16 becomes the first transient state R2 if, in the regeneration state R1, the estimated external force Fd is greater than or equal to the first threshold Ha, and the estimated external force Fd is not fluctuating at a predetermined frequency or higher. As shown in Figure 3, the control unit 40 controls the spool displacement amount of the rod-side control valve 23 so that the regeneration opening 33 opens and the meter-out opening 34 becomes the target meter-out opening area Ad. The control unit 40 controls the spool displacement amount of the rod-side control valve 23 so that the opening area of ​​the meter-out opening 34 becomes larger than the opening area in the regeneration state R1. When the spool displacement amount of the rod-side control valve 23 is controlled so that the regeneration opening 33 and the meter-out opening 34 open, as shown in Figure 7, the hydraulic fluid discharged from the rod chamber 12B flows into the regeneration opening 33 from the first rod port P6 via the rod-side flow path 22. A portion of the hydraulic fluid that flows into the regeneration opening 33 flows into the meter-out opening 34 and then into the drain channel 25 via the drain port P8, while the remaining hydraulic fluid flows into the regeneration channel 26 via the regeneration port P9.

[0065] If the meter-out pressure is higher than the meter-in pressure, the check valve 27 does not block the flow of hydraulic fluid. That is, the hydraulic fluid that flows into the regeneration passage 26 passes through the check valve 27, flows into the cap-side passage 20, and is then supplied to the cap chamber 12A. When the check valve 27 does not block the flow of hydraulic fluid, a portion of the hydraulic fluid discharged from the rod chamber 12B is discharged into the tank 18, and the remaining hydraulic fluid is supplied to the cap chamber 12A.

[0066] The control unit 40 gradually changes the regeneration ratio from the maximum state to the minimum state in the first transient state R2 based on the estimated external force Fd. The control unit 40 gradually changes the regeneration ratio from the maximum state to the minimum state in the first transient state R2 based on the duration of the first transient state R2 or the time rate of change of a physical quantity related to the control of the meter-out opening 34. Examples of the time rate of change of a physical quantity related to the control of the meter-out opening 34 include the time derivative of the meter-out pressure, the time derivative of the cylinder velocity of the arm cylinder 12, and the time-minute value of the flow rate of the hydraulic fluid passing through the meter-out opening 34. As will be described later, the duration of the first transient state is, for example, 500 msec.

[0067] Switching directly from the regeneration state R1 to the drain state R3 may cause abrupt changes in the hydraulic fluid flow rate and pressure. By providing a first transient state R2 between the regeneration state R1 and the drain state R3, abrupt changes in the hydraulic fluid flow rate and pressure are suppressed.

[0068] (Drain State) Figure 8 is a schematic diagram showing the hydraulic system 16 in the drain state R3 according to the first embodiment. As shown in Figures 5 and 8, the drain state R3 is a state in which the hydraulic fluid discharged from the rod chamber 12B is not supplied to the cap chamber 12A but is discharged to the tank 18. In other words, the drain state R3 is a state in which all of the hydraulic fluid discharged from the rod chamber 12B is discharged to the tank 18. When the decision unit 38 determines that the first transient state termination condition for terminating the first transient state R2 is satisfied, it decides to transition the state of the hydraulic system 16 from the first transient state R2 to the drain state R3.

[0069] In one embodiment, the first transient state termination condition includes the estimated external force Fd being equal to or greater than the second threshold Hb in the first transient state R2. In another embodiment, the first transient state termination condition includes the fact that a predetermined minimum duration Tm of 100 msec has elapsed since the transition from the regeneration state R1 to the first transient state R2, and the estimated external force Fd is equal to or greater than the second threshold Hb. Furthermore, the first transient state termination condition also includes the fact that the duration of the first transient state R2 exceeds a predetermined maximum duration Tu of 500 msec, even if the estimated external force Fd is not equal to or greater than the second threshold Hb. The control unit 40 controls the rod-side control valve 23 so that the state of the hydraulic system 16 becomes the drain state R3 if the estimated external force Fd is equal to or greater than the second threshold Hb in the first transient state R2, or if the duration of the first transient state R2 exceeds the predetermined maximum duration Tu. As shown in Figure 3, the control unit 40 controls the spool displacement of the rod-side control valve 23 to open the regeneration opening 33 and the meter-out opening 34. When the spool displacement of the rod-side control valve 23 is controlled to open the regeneration opening 33 and the meter-out opening 34, as shown in Figure 8, the hydraulic fluid discharged from the rod chamber 12B flows into the regeneration opening 33 from the first rod port P6 via the rod-side flow path 22. A portion of the hydraulic fluid that flows into the regeneration opening 33 flows into the regeneration flow path 26 via the regeneration port P9, and the remaining hydraulic fluid flows into the meter-out opening 34 and into the drain flow path 25 via the drain port P8.

[0070] If the meter-in pressure is higher than the meter-out pressure, the check valve 27 blocks the flow of hydraulic fluid. Since the hydraulic fluid that flows into the regeneration opening 33 cannot pass through the check valve 27, the hydraulic fluid that flows through the rod-side passage 22 flows from the first rod port P6 into the regeneration opening 33 and then flows into the drain port P8 via the meter-out opening 34. The hydraulic fluid that flows into the drain port P8 is discharged into the tank 18 via the drain passage 25. In other words, if the meter-in pressure is higher than the meter-out pressure, the hydraulic fluid discharged from the rod chamber 12B is not supplied to the cap chamber 12A but is discharged into the tank 18.

[0071] (Second Transient State) As shown in Figures 5 and 7, the second transient state R4 is a state in which a portion of the hydraulic fluid discharged from the rod chamber 12B is discharged into the tank 18, and the remaining hydraulic fluid is supplied to the cap chamber 12A. When the decision unit 38 determines that the drain state termination condition for ending the drain state R3 is satisfied, it decides to transition the state of the hydraulic system 16 from the drain state R3 to the second transient state R4.

[0072] In this embodiment, the drain state termination condition includes the estimated external force Fd being less than the third threshold Hc in the drain state R3, and the meter-in pressure Pi, which indicates the pressure of the hydraulic fluid supplied to the cap chamber 12A, being lower than the meter-out pressure Po, which indicates the pressure of the hydraulic fluid discharged from the rod chamber 12B. When the estimated external force Fd is less than the third threshold Hc and the meter-in pressure Pi is lower than the meter-out pressure Po in the drain state R3, the control unit 40 controls the rod-side control valve 23 so that the state of the hydraulic system 16 becomes the second transient state R4. As shown in Figure 3, the control unit 40 controls the regeneration opening 33 and the meter-out opening 34. The third threshold Hc is a value smaller than the first threshold Ha. The third threshold Hc is a predetermined value and is stored in the storage unit 41.

[0073] The control unit 40 gradually changes the regeneration ratio from a minimum to a maximum state in the second transient state R4 based on the estimated external force Fd. The control unit 40 gradually changes the regeneration ratio from a minimum to a maximum state in the second transient state R4 based on the duration of the second transient state R4 or the time rate of change of the physical quantities related to the control of the meter-out opening 34. Examples of the time rate of change of the physical quantities related to the control of the meter-out opening 32 include the time derivative of the meter-out pressure, the time derivative of the cylinder velocity of the arm cylinder 12, and the time-minute value of the flow rate of the hydraulic fluid passing through the meter-out opening 34. As will be described later, the duration of the second transient state is, for example, 200 msec.

[0074] The switch from the drain state R3 to the second transient state R4 suppresses the rapid increase in regeneration flow rate caused by the reversal of the meter-in pressure Pi and the meter-out pressure Po.

[0075] As shown in Figure 5, when the decision unit 38 determines that the second transient state termination condition for ending the second transient state R4 is satisfied, it decides to transition the state of the hydraulic system 16 from the second transient state R4 to the regeneration state R1.

[0076] In one embodiment, the condition for ending the second transient state includes the duration of the second transient state R4 exceeding a predetermined duration Tn of 200 msec. When the duration of the second transient state R4 exceeds the predetermined duration Tn, the control unit 40 controls the rod-side control valve 23 so that the state of the hydraulic system 16 becomes the regeneration state R1. The control unit 40 opens the regeneration opening 33 and closes the meter-out opening 34 to transition from the second transient state R4 to the regeneration state R1.

[0077] (When estimated external force cannot be calculated) As shown in equation (1) above, the meter-in pressure Pi detected by the cap-side pressure sensor 28 and the meter-out pressure Po detected by the rod-side pressure sensor 29 are used in calculating the estimated external force Fd. If at least one of the cap-side pressure sensor 28 and the meter-out pressure Po is abnormal, the estimation unit 37 may not be able to obtain the meter-in pressure Pi and the meter-out pressure Po. That is, if at least one of the cap-side pressure sensor 28 and the meter-out pressure Po is abnormal, the estimation unit 37 may not be able to calculate the estimated external force Fd. If it is determined that the estimated external force Fd cannot be calculated, the control unit 40 opens the regeneration opening 33 and sets the meter-out opening 34 to a predetermined minimum opening area. In this embodiment, the minimum opening area is zero. That is, if it is determined that the estimated external force Fd cannot be calculated, the control unit 40 opens the regeneration opening 33 and completely closes the meter-out opening 34. If it is determined that the estimated external force Fd cannot be calculated, the state of the hydraulic system 16 is fixed to the regeneration state R1, and the regeneration opening 33 and the meter-out opening 34 are controlled based on the amount of operation of the work implement operating device 7. The minimum opening area may be a value greater than zero. That is, the control unit 40 may fix the meter-out opening 34 to a minute opening area. For example, the control unit 40 may control the rod-side control valve 23 so that the meter-out opening 34 becomes a minute opening area. Alternatively, for example, a throttling valve with a minute opening (not shown) may be placed in the flow path connecting the rod-side flow path 22 and the tank 18.

[0078] <Calculation of Regeneration Factor> Figure 9 is a diagram illustrating the method for calculating the regeneration factor according to the first embodiment. The determination unit 38 calculates the regeneration factor Fa. The regeneration factor is a concept that approximates the regeneration ratio described above.

[0079] As shown in Figure 9, in the regeneration state R1, the determination unit 38 sets the regeneration factor to "1". In the drain state R3, the determination unit 38 sets the regeneration factor to "0".

[0080] In the case of the second transient state R4, the determination unit 38 sets the regeneration factor Fa to gradually increase from "0" to "1" over a predetermined duration Tn of 200 msec in the second transient state R4. When an operation signal to stop the arm 9 is received from the work equipment operating device 7, if the pressure of the hydraulic fluid in the arm cylinder 12 is low after the arm 9 is stopped, a rebound may occur. By returning the hydraulic system 16 to the regeneration state R1 before the arm 9 is stopped, the arm 9 can be stopped after the pressure of the hydraulic fluid in the arm cylinder 12 has increased. Furthermore, the regeneration factor Fa is set so that the transition from the second transient state R4 to the regeneration state R1 is quick immediately before the work equipment operating device 7 is stopped, that is, so that the second transient state R4 ends quickly. The period immediately before the work equipment operating device 7 is included immediately before receiving the operation signal to stop the arm 9 from the work equipment operating device 7.

[0081] In the first transient state R2, the determination unit 38 calculates the regeneration factor Fa based on the estimated external force Fd such that the regeneration factor Fa gradually changes from "1" to "0". In the drain state R3, the meter-out pressure Po can be quickly released when the external force applied to the arm cylinder 12 increases rapidly. Therefore, the regeneration factor Fa is calculated based on the estimated external force Fd so that the transition from the first transient state R2 to the drain state R3 is quick, that is, so that the first transient state R2 ends quickly.

[0082] The method for calculating the regeneration factor Fa in the first transient state R2 will be explained below. The determination unit 38 calculates the regeneration drain coefficient Rd (step SA1). If the estimated external force is Fd, the upper limit of the estimated external force Fd is Fu, and the estimated external force immediately after entering the first transient state R2 is Fs, the regeneration drain coefficient Rd is calculated based on the following equation (2).

[0083] Rd=(Fd-Fs) / (Fu-Fs)...(2)

[0084] Furthermore, the determination unit 38 calculates the upper limit of the regeneration drain coefficient at which the regeneration drain coefficient rises from "0" to "1" during the minimum duration Tm of the first transient state R2, which is 100 msec (step SA2), and calculates the lower limit of the regeneration drain coefficient at which the regeneration drain coefficient rises from "0" to "1" during the maximum duration Tu of the first transient state R2, which is 500 msec (step SA3).

[0085] The determination unit 38 selects the upper limit regeneration drain coefficient from the upper limit regeneration drain coefficient and the lower limit regeneration drain coefficient if the condition [Fs ≥ Fu] is satisfied, and selects the lower limit regeneration drain coefficient from the upper limit regeneration drain coefficient and the lower limit regeneration drain coefficient if the condition [Fs ≥ Fu] is not satisfied (step SA4).

[0086] Next, the determination unit 38 selects the larger of the regeneration drain coefficient selected in step SA4 and the regeneration drain coefficient Rd calculated in step SA1 (step SA5), selects the smaller of the regeneration drain coefficient selected in step SA5 and the upper limit regeneration drain coefficient calculated in step SA2 (step SA6), and determines the regeneration drain coefficient selected in step SA6 as the final regeneration drain coefficient.

[0087] A first correlation data set is predetermined, showing the relationship between the regeneration drain coefficient and the regeneration factor Fa. The first correlation data set includes table data for converting the regeneration drain coefficient to the regeneration factor Fa. The determination unit 38 calculates the regeneration factor Fa from the final regeneration drain coefficient based on the first correlation data set (step SA7). As a result, the regeneration factor Fa in the first transient state R2 is calculated.

[0088] <Calculation Processing by the Calculation Unit> (Calculation of Target Flow Rate) Figure 10 is a diagram illustrating the calculation method for the target drain flow rate Qdt, target regeneration flow rate Qr, and target pump flow rate Qp according to the first embodiment. The calculation unit 39 calculates the target cylinder speed of the arm cylinder 12 based on the operation signal indicating the amount of operation of the work equipment operating device 7 (step SB1). The target cylinder speed Vr may be a value proportional to the amount of operation of the work equipment operating device 7. If a second correlation data showing the relationship between the amount of operation of the work equipment operating device 7 and the target cylinder speed Vr is predetermined, the calculation unit 39 may calculate the target cylinder speed Vr by inputting the operation signal indicating the amount of operation of the work equipment operating device 7 into the second correlation data.

[0089] The calculation unit 39 calculates the target meter-in flow rate Qi based on the target cylinder speed Vr (step SB2). The target meter-in flow rate Qi refers to the target flow rate of hydraulic fluid to be supplied to the cap chamber 12A of the arm cylinder 12. The calculation unit 39 calculates the target meter-in flow rate Qi of hydraulic fluid to be supplied to the cap chamber 12A based on the target cylinder speed Vr calculated in step SB1 and the cap-side pressure receiving area Ac.

[0090] Next, the calculation unit 39 calculates the meter-out flow rate Qo, which is the flow rate of hydraulic fluid discharged from the rod chamber 12B, based on the target meter-in flow rate Qi calculated in step SB2 and the pressure-receiving area ratio Ka, which is the ratio of the pressure-receiving area Ac on the cap side to the pressure-receiving area Ar on the rod side (step SB5). [Ka = Ar / Ac]. For example, if the pressure-receiving area Ar on the rod side is 50% of the pressure-receiving area Ac on the cap side, the meter-out flow rate Qo will be 50% of the target meter-in flow rate Qi.

[0091] The determination unit 38 determines the state of the hydraulic system 16 based on the estimated external force Fd calculated by the estimation unit 37 and the operation signal indicating the amount of operation of the work machine operating device 7, and calculates the regeneration factor Fa as explained with reference to Figure 9 (step SB4).

[0092] The calculation unit 39 calculates a target drain flow rate Qdt, which indicates a target value for the flow rate of the hydraulic fluid passing through the meter-out opening 34 (step SB6).

[0093] The calculation unit 39 calculates the target drain flow rate Qdt based on the meter-out flow rate Qo calculated in step SB5 and the regeneration factor Fa calculated in step SB4. The calculation unit 39 calculates the target drain flow rate Qdt based on the calculation formula [Qdt = Qo × (1 - Fa)]. When there is condensation, as mentioned above, Fa = 0, so Qdt = Qo. In other words, when there is condensation, the target drain flow rate means the estimated value of the drain flow rate. In other words, when there is condensation, the meter-out flow rate is used to calculate the estimated value of the drain flow rate.

[0094] The calculation unit 39 calculates the target regeneration flow rate Qr passing through the regeneration channel 26 based on the meter-out flow rate Qo calculated in step SB5 and the target drain flow rate Qd calculated in step SB6 (step SB7). The target regeneration flow rate Qr is calculated by subtracting the target drain flow rate Qd from the meter-out flow rate Qo. That is, the target regeneration flow rate Qr is calculated based on the calculation formula [Qr = Qo - Qdt]. When regeneration is in progress, Fa = 1, so Qdt = 0, and Qr = Qo. That is, when regeneration is in progress, the target regeneration flow rate represents the estimated regeneration flow rate. That is, when regeneration is in progress, the meter-out flow rate is used to calculate the estimated regeneration flow rate.

[0095] The calculation unit 39 calculates the target pump flow rate Qp of the hydraulic fluid to be discharged from the hydraulic pump 17 based on the target meter-in flow rate Qi and the target regeneration flow rate Qr (step SB3). The target pump flow rate Qp is calculated by subtracting the target regeneration flow rate Qr from the target meter-in flow rate Qi. That is, [Qp = Qi - Qr].

[0096] In step SB7, the calculation unit 39 may calculate an estimated drain flow rate Qde, which indicates an estimated flow rate of hydraulic fluid passing through the meter-out opening 34, based on the meter-out pressure Po detected by the rod-side pressure sensor 29 and the target value or estimated value of the meter-out opening 34. The target regeneration flow rate Qr may then be calculated by subtracting the estimated drain flow rate Qde from the meter-out flow rate Qo calculated in step SB5. The target value of the meter-out opening 34 is calculated based on the target drain flow rate Qdt calculated in step SB5. The estimated value of the meter-out opening 34 is calculated based on the spool displacement detected by the spool displacement sensor of the cap-side control valve 21.

[0097] Furthermore, when the meter-out opening 34 is fully closed, the calculation unit 39 may calculate the target regeneration flow rate Qr based on the flow rate of the hydraulic fluid discharged from the hydraulic pump 17 and the pressure-receiving area of ​​the arm cylinder 12.

[0098] (Calculation of Target Opening Area) Figure 11 is a diagram illustrating the method for calculating the target regeneration opening area At according to the first embodiment. The target regeneration opening area At is the target value for the size of the regeneration opening 33. The calculation unit 39 calculates the target opening area for generating meter-out pressure so that the gravitational force acting on the arm 9 and the hydraulic braking force are balanced and the meter-in pressure is kept low. An external force is generated on the arm cylinder 12 by the gravitational force acting on the arm 9, which acts in the direction of extending the arm cylinder 12. The calculation unit 39 calculates the target opening area for generating meter-out pressure so that the external force acting in the direction of extending the arm cylinder 12 is balanced by the hydraulic braking force that suppresses the extension of the arm cylinder 12.

[0099] The calculation unit 39 processes the estimated external force Fd using a low-pass filter (LPF) (step SC1). The cutoff frequency for the LPF processing is, for example, 0.3 Hz. Based on the estimated external force Fd processed with a strong low-pass filter, the calculation unit 39 can calculate the external force acting on the arm cylinder 12 due to gravity acting on the arm 9.

[0100] The calculation unit 39 pre-sets the target meter-in pressure Pit (step SC3). The target meter-in pressure Pit may be a fixed value stored in the storage unit 41. The target meter-in pressure Pit may also be arbitrarily set by the input device 61. The calculation unit 39 calculates the target meter-out pressure Pot based on the LPF-processed estimated external force Fd, the predetermined target meter-in pressure Pit, the cap-side pressure-receiving area Ac, and the rod-side pressure-receiving area Ar (step SC2). The target meter-out pressure Pot is calculated based on the following equation (3).

[0101] Pot=(Pit×Ac−Fd) / Ar…(3)

[0102] The calculation unit 39 can calculate a target meter-out pressure Pot that provides a hydraulic braking force that balances the external force acting on the arm cylinder 12, based on equation (3). When the external force acting on the arm cylinder 12 is constant (estimated external force Fd is constant), increasing the meter-out pressure also increases the meter-in pressure. Therefore, by setting the meter-out pressure so that the meter-in pressure is low, an appropriate hydraulic braking force can be provided.

[0103] Next, the calculation unit 39 calculates the target regeneration opening area At based on the target regeneration flow rate Qr, the target differential pressure of the regeneration opening 33 which indicates the difference between the target meter-in pressure Pit and the target meter-out pressure Pot in the regeneration state R1, and the predetermined minimum differential pressure ΔPr of the regeneration opening 33 (step SC4). The target regeneration opening area At is calculated based on a calculation formula (for example, Bernoulli's theorem). As an example, the target regeneration opening area At is calculated based on the following equation (4). In equation (4), C is a predetermined constant.

[0104] Ar=Qr / [C×√{MAX(Pot-Pit, ΔPr)}]…(4)

[0105] Figure 12 is a diagram illustrating the method for calculating the target meter-out opening area Ad according to the first embodiment. The calculation unit 39 sets the target meter-out pressure change rate ΔPot, which is the rate of change of the target pressure of the meter-out pressure Po, based on the estimated external force Fd (step SD1). The calculation unit 39 sets the target meter-out pressure change rate ΔPot such that the faster the estimated external force Fd rises, the faster the meter-out pressure Po decreases. The calculation unit 39 pre-sets the minimum target meter-out pressure Potm in the drain state (step SD2). The minimum target meter-out pressure Potm may be a fixed value stored in the storage unit 41. The minimum target meter-out pressure Potm may also be arbitrarily set by the input device 61.

[0106] The calculation unit 39 calculates the target meter-out pressure Pot based on the target meter-out pressure change rate ΔPot and the minimum target meter-out pressure Potm (step SD3). The calculation unit 39 calculates the target meter-out pressure Pot starting from the meter-out pressure Po detected by the rod-side pressure sensor 29 at the moment the regeneration factor becomes 0, that is, when the system transitions from the first transient state R2 to the drain state R3, so that the meter-out pressure Pot decreases to the minimum target meter-out pressure Potm according to the target meter-out pressure change rate ΔPot.

[0107] The calculation unit 39 calculates the target meter-out opening area Ad for drain state R3 using a calculation formula (for example, Bernoulli's theorem) based on the target meter-out pressure Pot and the target drain flow rate Qdt (step SD4). The calculation unit 39 calculates the target meter-out opening area Ad for drain state R3 using a calculation formula, for example, [Ad = Qd / [C × √Pot - Pt)]. C is a predetermined constant, and Pt is the pressure of the tank 18 (i.e., 0). Note that the above calculation formula is just one example.

[0108] As a result, the final target opening area of ​​the meter-out opening is set so that the minimum target meter-out pressure is achieved, and the target meter-out opening area Ad gradually increases over time from the meter-out opening area at the time of transition from the first transient state R2 to the drain state R3, up to the final target opening area.

[0109] As described above, the moment when the regeneration factor becomes 0 is determined to be the time when the transition occurs from the first transient state R2 to the drain state R3. The calculation unit 39 calculates the estimated drain flow rate Qde of the hydraulic fluid passing through the meter-out opening 34 based on the meter-out pressure Po detected by the rod-side pressure sensor 29 and the target meter-out opening area Ad or the estimated value of the meter-out opening 34. The time when the estimated drain flow rate Qde of the hydraulic fluid passing through the meter-out opening 34 and the meter-out flow rate Qo of the hydraulic fluid discharged from the rod chamber 12B become equal is determined to be the time when the transition occurs from the first transient state R2 to the drain state R3. The estimated value of the meter-out opening 34 is calculated based on the spool displacement detected by the spool displacement sensor of the cap-side control valve 21.

[0110] The calculation unit 39 may determine that the point at which the meter-out pressure Po detected by the rod-side pressure sensor 29 transitions from a first pressure state, where the meter-out pressure Po is higher than the meter-in pressure Pi detected by the cap-side pressure sensor 28, to a second pressure state, where the meter-out pressure Po is lower than the meter-in pressure Pi, is the point at which the transition occurs from the first transient state R2 to the drain state R3.

[0111] Furthermore, the calculation unit 39 calculates the target meter-out opening area Ad for the first transient state R2 or the second transient state R4 based on the detected meter-out pressure Po and the target drain flow rate Qdt using a calculation formula (for example, Bernoulli's theorem) (step SD5). The calculation unit 39 calculates the target meter-out opening area Ad for the first transient state R2 or the second transient state R4 based on, for example, the calculation formula [Ad = Qdt / [C × √Po - Pt)]. C is a predetermined constant, and Pt is the pressure of the tank 18. Note that the above calculation formula is just one example.

[0112] The calculation unit 39 switches and outputs the target meter-out opening area Ad based on the regeneration factor indicating the state of the hydraulic system 16 (step SD6). That is, if the state of the hydraulic system 16 is the drain state R3, the calculation unit 39 determines the target meter-out opening area Ad calculated in step SD4 as the final target meter-out opening area Ad. If the state of the hydraulic system 16 is the first transient state R2 or the second transient state R4, the calculation unit 39 determines the target meter-out opening area Ad calculated in step SD5 as the final target meter-out opening area Ad. If the state of the hydraulic system 16 is the regeneration state R1, the calculation unit 39 determines zero as the final target meter-out opening area Ad so that the meter-out opening is fully closed.

[0113] <Control of the rod-side control valve> Next, a method for controlling the spool displacement of the rod-side control valve 23 when the hydraulic system 16 is in a first transient state R2, a second transient state R4, or a drain state R3 will be described. The first transient state R2 and the second transient state R4 are states in which a portion of the hydraulic fluid discharged from the rod chamber 12B passes through the meter-out opening 34. The drain state R3 is a state in which all of the hydraulic fluid discharged from the rod chamber 12B passes through the meter-out opening 34.

[0114] As described above, the calculation unit 39 calculates the meter-out flow rate Qo based on the target meter-in flow rate Qi and the pressure-receiving area ratio Ka. When the regeneration factor Fa < 1, that is, when the hydraulic system 16 is in the first transient state R2, the second transient state R4, or the drain state R3, the calculation unit 39 calculates the target meter-out opening area Ad based on the regeneration factor Fa, the meter-out flow rate Qo, the meter-out pressure Po, and the estimated external force Fd.

[0115] In the first transient state R2 or the second transient state R4, the control unit 40 generates a pilot pressure generation command for the electromagnetic proportional valve 70 to control the rod-side control valve 23, based on the target meter-out opening area Ad and third correlation data showing the relationship between the meter-out opening area of ​​the rod-side control valve 23 and the pilot pressure.

[0116] Based on the target meter-out opening area Ad and the third correlation data, the control unit 40 generates a pilot pressure generation command for the electromagnetic proportional valve 70 for controlling the rod-side control valve 23, such that the meter-out opening 32 gradually opens over time from the meter-out opening area at the time of transition from the first transient state R2 to the drain state R3 to the final target opening area reached in the drain state R3. The control unit 40 outputs the pilot pressure generation command to the electromagnetic proportional valve 70 (including at least the electromagnetic proportional valve 70RC) for controlling the rod-side control valve 23.

[0117] Subsequently, the control unit 40 generates a pilot pressure generation command for the electromagnetic proportional valve 70 for controlling the rod-side control valve 23, based on the final target opening area of ​​the drain state R3 and the third correlation data. The control unit 40 outputs the pilot pressure generation command to the electromagnetic proportional valve 70 (including at least the electromagnetic proportional valve 70RC) for controlling the rod-side control valve 23.

[0118] The control unit 40 controls the meter-out opening based on the target meter-out opening area Ad, such that the faster the estimated external force Fd rises, the faster the pressure of the hydraulic fluid discharged from the rod chamber 12B decreases.

[0119] Next, a method for controlling the spool displacement of the rod-side control valve 23 when the hydraulic system 16 is in a regeneration state R1 will be described. The regeneration state R1 is a state in which the hydraulic fluid discharged from the rod chamber 12B is supplied to the cap chamber 12A without passing through the meter-out opening 34.

[0120] As described above, the calculation unit 39 calculates the meter-out flow rate Qo based on the target meter-in flow rate Qi and the pressure-receiving area ratio Ka. When the regeneration factor Fa = 1, the calculation unit 39 determines the target regeneration flow rate Qr to be the meter-out flow rate Qo. That is, when the hydraulic system 16 is in the regeneration state R1, the calculation unit 39 calculates the target regeneration opening area At of the regeneration opening 33 based on the meter-out flow rate Qo and the estimated external force Fd.

[0121] In the regeneration state R1, the control unit 40 generates a pilot pressure generation command for the electromagnetic proportional valve 70 for controlling the rod-side control valve 23, based on the target regeneration opening area At and fourth correlation data showing the relationship between the regeneration opening area of ​​the rod-side control valve 23 and the pilot pressure. The control unit 40 outputs the pilot pressure generation command to the electromagnetic proportional valve 70 (including at least the electromagnetic proportional valve 70RC) for controlling the rod-side control valve 23.

[0122] <Calculation of Meter-Out Flow Rate> As described above, the calculation unit 39 calculates the meter-out flow rate Qo based on the target meter-in flow rate Qi and the pressure-receiving area ratio Ka. The calculation unit 39 may also calculate the meter-out flow rate Qo by the following method.

[0123] The control unit 40 outputs either a discharge flow rate command for the hydraulic pump 17 or a pilot pressure generation command for the electromagnetic proportional valve 70 for controlling the cap-side control valve 21, or both, in order to adjust the discharge flow rate of the hydraulic fluid discharged from the hydraulic pump 17. The calculation unit 39 may calculate the meter-out flow rate Qo based on the discharge flow rate command or the pilot pressure generation command for the electromagnetic proportional valve 70 for controlling the cap-side control valve 21.

[0124] The calculation unit 39 may calculate the discharge flow rate of the hydraulic fluid discharged from the hydraulic pump 17 based on the rotational speed of the hydraulic pump 17 and the capacity of the hydraulic pump 17, and then calculate the meter-out flow rate Qo based on the calculated discharge flow rate.

[0125] If a stroke sensor is provided to detect the cylinder speed of the arm cylinder 12, the calculation unit 39 may calculate the meter-out flow rate Qo based on the cylinder speed detected by the stroke sensor.

[0126] <Control Method> Figures 13, 14, and 15 are timing charts showing the control method of the hydraulic system 16 according to the first embodiment. Figure 13 shows the timing chart when the work machine 4 is operating in the air. Figure 14 shows the timing chart when the work machine 4 is performing an excavation operation. Figure 15 shows the timing chart when the work machine 4 is performing a transition operation. In Figures 13, 14, and 15, time t1 is a time after time 0, time t2 is a time after time t1, time t3 is a time after time t2, time t4 is a time after time t3, time t5 is a time after time t4, and time t6 is a time after time t5. In Figures 14 and 15, time t7 is a time after time t6, and time t8 is a time after time t7. In Figure 15, time t9 is a time after time t8.

[0127] Furthermore, in Figures 13, 14, and 15, line La indicates the amount of operation of the work machine operating device 7. Line Lb indicates the estimated external force Fd calculated by the estimation unit 37. Line Lc indicates the regeneration factor Fa, which is the ratio of the hydraulic fluid discharged from the rod chamber 12B to the hydraulic fluid supplied to the cap chamber 12A. A regeneration factor Fa of 1 means that all of the hydraulic fluid discharged from the rod chamber 12B is supplied to the cap chamber 12A. A regeneration factor Fa of 0 means that all of the hydraulic fluid discharged from the rod chamber 12B is discharged to the tank 18. Line Ld indicates the target regeneration flow rate Qr, which is the target flow rate of the hydraulic fluid flowing through the regeneration opening 33 (check valve 27). Line Le indicates the target drain flow rate Qd, which is the target flow rate of the hydraulic fluid flowing through the meter-out opening 34. Line Lf indicates the meter-out flow rate Qo, which is the flow rate of the hydraulic fluid discharged from the rod chamber 12B. Line Lg indicates the target meter-in flow rate Qi, which is the target flow rate of the hydraulic fluid flowing into the meter-in opening 30. Line Lh indicates the target pump flow rate Qp, which is the target flow rate of the hydraulic fluid discharged from the hydraulic pump 17.

[0128] (Aerial Operation) As shown in Figure 13, the operation of the work implement operating device 7 is started at time t1 so that the arm cylinder 12 extends. The amount of operation of the work implement operating device 7 gradually increases between time t1 and time t2, reaches a maximum value at time t2, maintains the maximum value between time t2 and time t4, gradually decreases between time t4 and time t5, and becomes 0 at time t5. The estimation unit 37 calculates the estimated external force Fd. The calculation unit 39 calculates the regeneration factor Fa, target regeneration flow rate Qr, target drain flow rate Qd, meter-out flow rate Qo, target meter-in flow rate Qi, and target pump flow rate Qp based on the amount of operation of the work implement operating device 7.

[0129] When the load on arm 9 is small, the estimated external force Fd is less than the first threshold Ha between time point t1 and time point t6. The state of the hydraulic system 16 is regenerated state R1 between time point 0 and time point t6. The regeneration factor Fa is 1 between time point 0 and time point t2.

[0130] The target regeneration flow rate Qr gradually increases between time point t1 and time point t3, reaches a first value at time point t3, maintains the first value between time points t3 and t4, gradually decreases between time points t4 and t5, and becomes 0 at time point t6.

[0131] The target drain flow rate Qd is 0 between time point t1 and time point t6.

[0132] The meter-out flow rate Qo gradually increases between time point t1 and time point t3, reaches a first value at time point t3, maintains that first value between time points t3 and t4, gradually decreases between time points t4 and t5, and becomes 0 at time point t6.

[0133] The target meter-in flow rate Qi gradually increases between time point t1 and time point t3, reaches a second value greater than the first value at time point t3, maintains the second value between time point t3 and time point t4, gradually decreases between time point t4 and time point t6, and becomes 0 at time point t6.

[0134] The target pump flow rate Qp gradually increases between time point t1 and time point t3, reaches a first value at time point t3, maintains the first value between time point t3 and time point t4, gradually decreases between time point t4 and time point t6, and becomes 0 at time point t6.

[0135] (Excavation Operation) As shown in Figure 14, the operation of the work equipment operating device 7 is started at time t1 so that the arm cylinder 12 extends. The amount of operation of the work equipment operating device 7 gradually increases between time t1 and time t2, reaches a maximum value at time t2, maintains the maximum value between time t2 and time t6, gradually decreases between time t6 and time t7, and becomes 0 at time t7. The estimation unit 37 calculates the estimated external force Fd. The calculation unit 39 calculates the regeneration factor Fa, target regeneration flow rate Qr, target drain flow rate Qd, meter-out flow rate Qo, target meter-in flow rate Qi, and target pump flow rate Qp based on the amount of operation of the work equipment operating device 7.

[0136] The estimated external force Fd is lower than the first threshold Ha between time point t1 and time point t4, reaches the first threshold Ha at time point t4, reaches the second threshold Hb at time point t5, and maintains a state of exceeding the second threshold from time point t5 to time point t8. The state of the hydraulic system 16 is regenerated state R1 between time point 0 and time point t4, first transient state R2 between time point t4 and time point t5, drained state between time point t5 and time point t7, and regenerated state between time point t7 and time point t8. The regeneration factor is 1 between time point 0 and time point t4, gradually decreases between time point t4 and time point t5, and becomes 0 at time point t5.

[0137] The target regeneration flow rate Qr gradually increases between time point t1 and time point t3, reaches a first value at time point t3, maintains the first value between time point t3 and time point t4, gradually decreases between time point t4 and time point t5, and becomes 0 at time point t5.

[0138] The target drain flow rate Qd is 0 between time point t1 and time point t4, gradually increases between time point t4 and time point t5, reaches a first value at time point t5, maintains the first value between time point t5 and time point t6, gradually decreases between time point t6 and time point t8, and becomes 0 at time point t8.

[0139] The meter-out flow rate Qo gradually increases between time point t1 and time point t3, reaches a first value at time point t3, maintains this first value between time point t3 and time point t6, gradually decreases between time point t6 and time point t8, and becomes 0 at time point t8.

[0140] The target meter-in flow rate Qi gradually increases between time point t1 and time point t3, reaches a second value greater than the first value at time point t3, maintains the second value between time point t3 and time point t6, gradually decreases between time point t6 and time point t8, and becomes 0 at time point t8.

[0141] The target pump flow rate Qp gradually increases between time point t1 and time point t3, reaches a first value at time point t3, maintains the first value between time point t3 and time point t4, gradually increases between time point t4 and time point t5, reaches a second value greater than the first value at time point t5, maintains the second value between time point t5 and time point t6, gradually decreases between time point t6 and time point t8, and becomes 0 at time point t8.

[0142] Between time point t5 and time point t6, the target meter-in flow rate Qi and the target pump flow rate Qp each remain at the second value. Between time point t5 and time point t6, the target drain flow rate Qd increases to the second value, so the target meter-in flow rate Qi and the target pump flow rate Qp each increase by the amount of the increase in the target drain flow rate Qd.

[0143] (Transition Operation) As shown in Figure 15, the operation of the work implement operating device 7 is started at time t1 so that the arm cylinder 12 extends. The amount of operation of the work implement operating device 7 gradually increases between time t1 and time t2, reaches a maximum value at time t2, maintains the maximum value between time t2 and time t8, gradually decreases between time t8 and time t9, and becomes 0 at time t9. The estimation unit 37 calculates the estimated external force Fd. The calculation unit 39 calculates the regeneration factor Fa, target regeneration flow rate Qr, target drain flow rate Qd, meter-out flow rate Qo, target meter-in flow rate Qi, and target pump flow rate Qp based on the amount of operation of the work implement operating device 7.

[0144] The estimated external force Fd is lower than the first threshold Ha between time point t1 and time point t4, reaches the first threshold Ha at time point t4, reaches the second threshold Hb at time point t5, becomes the third threshold Hc at time point t6, and remains below the third threshold Hc from time point t6 to time point t9. The state of the hydraulic system 16 is regenerated state R1 between time point 0 and time point t4, first transient state R2 between time point t4 and time point t5, drain state R3 between time point t5 and time point t6, second transient state R4 between time point t6 and time point t7, and regenerated state between time point t7 and time point t9. The regeneration factor is 1 between time point 0 and time point t4, gradually decreases between time point t4 and time point t5, becomes 0 at time point t5, gradually increases between time point t6 and time point t7, and reaches 1 at time point t7.

[0145] The target regeneration flow rate Qr gradually increases between time point t1 and time point t3, reaches a first value at time point t3, maintains the first value between time point t3 and time point t4, gradually decreases between time point t4 and time point t5, remains at 0 between time point t5 and time point t6, gradually increases between time point t6 and time point t7, maintains the first value between time point t7 and time point t8, and gradually decreases between time point t8 and time point t9.

[0146] The target drain flow rate Qd is 0 between time point t1 and time point t4, gradually increases between time point t4 and time point t5, reaches a first value at time point t5, maintains the first value between time point t5 and time point t6, gradually decreases between time point t6 and time point t7, and becomes 0 at time point t7.

[0147] The meter-out flow rate Qo gradually increases between time point t1 and time point t3, reaches a first value at time point t3, maintains this first value between time point t3 and time point t8, gradually decreases between time point t8 and time point t9, and becomes 0 at time point t9.

[0148] The target meter-in flow rate Qi gradually increases between time point t1 and time point t3, reaches a second value greater than the first value at time point t3, maintains the second value between time point t3 and time point t8, gradually decreases between time point t8 and time point t9, and becomes 0 at time point t9.

[0149] The target pump flow rate Qp gradually increases between time t1 and time t3, reaches a first value at time t3, maintains the first value between time t3 and time t4, gradually increases between time t4 and time t5, reaches a second value greater than the first value at time t5, maintains the second value between time t5 and time t6, gradually decreases between time t6 and time t7, reaches the first value at time t7, maintains the first value between time t7 and time t8, gradually decreases between time t8 and time t9, and becomes 0 at time t9.

[0150] Between time point t5 and time point t6, the target pump flow rate Qp remains at the second value. Between time point t5 and time point t6, the target drain flow rate Qd increases to the first value, so the target pump flow rate Qp increases by the amount of the increase in the target drain flow rate Qd.

[0151] Figure 16 is a flowchart showing the control method of the hydraulic system 16 according to the embodiment. Figure 16 is a flowchart showing the control method of the hydraulic system 16 when the controller 6 receives an operation signal from the work equipment operating device 7 to perform arm cloud operation on the arm 9.

[0152] The estimation unit 37 starts calculating the estimated external force Fd (step S1). If no operation signal is received from the work machine operating device 7, the determination unit 38 determines the state of the hydraulic system 16 to the regeneration state R1. The control unit 40 controls the rod-side control valve 23 to achieve the regeneration state R1 (step S2).

[0153] The decision unit 38 determines whether or not it has received an operation signal from the work implement operating device 7 (step S3). If it determines in step S3 that it has not received an operation signal from the work implement operating device 7 (step S3: No), the process ends. If it determines in step S3 that it has received an operation signal from the work implement operating device 7 (step S3: Yes), the decision unit 38 determines whether or not the regeneration state termination condition is satisfied (step S4). If it determines in step S4 that the regeneration state termination condition is not satisfied (step S4: No), the decision unit 38 decides to maintain the state of the hydraulic system 16 in the regeneration state R1. As explained with reference to Figure 13, the calculation unit 39 calculates the target pump flow rate Qp and the target regeneration opening area At based on the operation signal indicating the amount of operation of the work implement operating device 7 and the estimated external force Fd (step S5). The control unit 40 outputs a control command so that the target flow rate or target opening area calculated by the calculation unit 39 is achieved (step S6).

[0154] In step S4, if it is determined that the conditions for ending the regeneration state are satisfied (step S4: Yes), the decision unit 38 decides to transition the state of the hydraulic system 16 from the regeneration state R1 to the first transient state R2 (step S7).

[0155] The decision unit 38 determines whether or not the first transient state termination condition is satisfied (step S8). If, in step S8, it is determined that the first transient state termination condition is not satisfied (step S8: No), the decision unit 38 decides to maintain the state of the hydraulic system 16 in the first transient state R2. As explained with reference to Figures 14 and 15, the calculation unit 39 calculates the target pump flow rate Qp and the target meter-out opening area Ad based on the operation signal indicating the amount of operation of the work machine operating device 7 and the estimated external force Fd (step S9). The control unit 40 outputs a control command so that the target flow rate or target opening area calculated by the calculation unit 39 is achieved (step S10).

[0156] In step S8, if it is determined that the first transient state termination condition is satisfied (step S8: Yes), the decision unit 38 decides to transition the state of the hydraulic system 16 from the first transient state R2 to the drain state R3 (step S11).

[0157] The decision unit 38 determines whether or not the drain state termination condition is satisfied (step S12). If, in step S12, it is determined that the drain state termination condition is not satisfied (step S12: No), the decision unit 38 decides to maintain the state of the hydraulic system 16 in the drain state R3. As explained with reference to Figures 14 and 15, the calculation unit 39 calculates the target pump flow rate Qp and the target meter-out opening area Ad based on the operation signal indicating the amount of operation of the work machine operating device 7 and the estimated external force Fd (step S13). The control unit 40 outputs a control command so that the target flow rate or target opening area calculated by the calculation unit 39 is achieved (step S14).

[0158] In step S12, if it is determined that the drain state termination condition is satisfied (step S12: Yes), the decision unit 38 decides to transition the state of the hydraulic system 16 from the drain state R3 to the second transient state R4 (step S15).

[0159] The decision unit 38 determines whether or not the second transient state termination condition is satisfied (step S16). If, in step S16, it is determined that the second transient state termination condition is not satisfied (step S16: No), the decision unit 38 decides to maintain the state of the hydraulic system 16 in the second transient state R4. As explained with reference to Figures 14 and 15, the calculation unit 39 calculates the target pump flow rate Qp and the target meter-out opening area Ad based on the operation signal indicating the amount of operation of the work equipment operating device 7 and the estimated external force Fd (step S17). The control unit 40 outputs a control command so that the target flow rate or target opening area calculated by the calculation unit 39 is achieved (step S18).

[0160] In step S16, if it is determined that the second transient state termination condition is satisfied (step S16: Yes), the decision unit 38 decides to transition the state of the hydraulic system 16 from the second transient state R4 to the regeneration state R1 (step S2).

[0161] <Effects> As described above, in this embodiment, the controller 6 calculates the estimated external force acting on the arm cylinder 12, taking the direction in which the arm cylinder 12 retracts as the positive direction. If the estimated external force is smaller than the first threshold Ha, the controller 6 controls the rod-side control valve 23 so that the hydraulic fluid discharged from the rod chamber 12B is supplied to the cap chamber 12A instead of being discharged to the tank 18, resulting in a regeneration state R1. Since the hydraulic fluid discharged from the rod chamber 12B is regenerated in the cap chamber 12A, the energy efficiency of the work machine 1 is improved. In addition, pressure loss is reduced by controlling the regeneration opening 33, and complete regeneration is performed by closing the meter-out opening 34 completely to achieve a regeneration rate of 100%, thereby reducing the flow rate of hydraulic fluid discharged from the hydraulic pump 17. As a result, the energy efficiency of the work machine 1 is improved.

[0162] Furthermore, in this embodiment, the operability of the work machine 1 is improved. When the state of the hydraulic system 16 is switched between a regeneration state R1 and a non-regeneration state (first transient state R2, drain state R3, and second transient state R4), the operability of the work machine 1 may decrease. For example, when the state of the work machine 4 is switched between operating in the air (light load work state) and heavy excavation of the work object (heavy load work state), the hydraulic system 16 is switched between a regeneration state and a non-regeneration state. In situations where the state of the hydraulic system 16 is switched between a regeneration state and a non-regeneration state, even though the amount of operation of the work machine operating device 7 is constant, the operating speed of the work machine 4 may change unexpectedly due to discontinuous and sudden changes in the flow rate and pressure on the hydraulic circuit. If the operating speed of the work machine 4 changes unexpectedly, the work machine 1 may vibrate or be subjected to shocks. If the work machine 1 vibrates or is subjected to shocks, the operability of the work machine 1 may decrease.

[0163] For example, when the state of the hydraulic system 16 is switched from a regenerating state to a non-regenerating state, when the meter-out opening 34 opens, the hydraulic fluid discharged from the rod chamber 12B begins to flow into the tank 18, so the regeneration flow rate decreases and the meter-out pressure drops. The moment the meter-out pressure falls below the meter-in pressure, the check valve 27 closes and no regeneration occurs at all. In addition, the decrease in regeneration flow rate may cause a decrease in the operating speed of the work implement 4.

[0164] On the other hand, in the regeneration state, in order to maintain the cylinder speed of the hydraulic cylinder 5 as much as possible, it is necessary to increase the pump flow rate to compensate for the decrease in regeneration flow rate. However, if the timing of the decrease in regeneration flow rate and the increase in pump flow rate do not coincide with the change in hydraulic fluid flow rate, the cylinder speed of the hydraulic cylinder 5 will decelerate once and then re-accelerate, which may cause the operation of the work machine 4 to change unexpectedly.

[0165] In this embodiment, the controller 6 calculates an estimated external force Fd acting on the hydraulic cylinder 5, and when it receives an operation signal to operate the work machine 4 so that the hydraulic cylinder 5 extends, it controls the opening area of ​​the meter-out opening 34, the opening area of ​​the regeneration opening 33, and the discharge flow rate of the hydraulic pump 17 based on the calculated estimated external force Fd. This suppresses a decrease in the operability of the work machine 1.

[0166] <Modification> In the first embodiment described above, the meter-in opening 30 and the regeneration opening 33 may be omitted. It is sufficient that the check valve 27 is located in the regeneration passage 26 and the meter-out opening 34 is located in the drain passage 25. By controlling the meter-out opening 34 and the hydraulic pump 17 based on the estimated external force Fd, the operability when switching from the regeneration state to the drain state is improved.

[0167] In the first embodiment described above, the regeneration opening 33 may be omitted. It is sufficient that the check valve 27 is located in the regeneration passage 26, the meter-in opening 30 is located in the pump passage 19, and the meter-out opening 32 is located in the drain passage 25. The meter-in opening 30 may be controlled by the cap-side control valve 21, and the meter-out opening 32 may be controlled by the rod-side control valve 23. Furthermore, it is sufficient that a rod-side pressure sensor 29 is provided to detect the meter-out pressure Po, which indicates the pressure of the hydraulic fluid discharged from the rod chamber 12B of the arm cylinder 12, and a cap-side pressure sensor 28 is provided to detect the meter-in pressure Pi, which indicates the pressure of the hydraulic fluid supplied to the cap chamber 12A.

[0168] In the first embodiment described above, the drain passage 25, check valve 27, meter-in opening 30, and meter-out opening 34 may be omitted. It is sufficient that the regeneration opening 33 is located in the regeneration passage 26 and that the regeneration opening 33 is controlled by the rod-side control valve 23. It is also sufficient that a rod-side pressure sensor 29 is provided to detect the meter-out pressure Po, which indicates the pressure of the hydraulic fluid discharged from the rod chamber 12B of the arm cylinder 12, and a cap-side pressure sensor 28 is provided to detect the meter-in pressure Pi, which indicates the pressure of the hydraulic fluid supplied to the cap chamber 12A. The controller 6 calculates the estimated external force Fd and controls the regeneration opening 33 based on the estimated external force Fd and the meter-out flow rate Qo of the hydraulic fluid discharged from the rod chamber 12B. The controller 6 calculates the target regeneration flow rate Qr based on the meter-out flow rate Qo of the hydraulic fluid discharged from the rod chamber 12B. The meter-out flow rate Qo may be the target meter-out flow rate, the actual meter-out flow rate detected by a flow sensor for detecting the meter-out flow rate, or the estimated meter-out flow rate calculated from the cylinder speed. The cylinder speed may be the target cylinder speed, or the actual cylinder speed detected by a stroke sensor for detecting the cylinder speed. Based on the target regeneration flow rate Qr, the controller 6 controls the regeneration opening 33 so that the pressure of the hydraulic fluid supplied to the cap chamber 12A becomes the target meter-in pressure Pit. Based on the estimated external force Fd and the target meter-in pressure Pit, the controller 6 calculates the target meter-out pressure Pot. Based on the target differential pressure, which is the difference between the target meter-in pressure Pit and the target meter-out pressure Pot, and the target regeneration flow rate Qr, the controller 6 calculates the target regeneration opening area At of the regeneration opening 33.

[0169] [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 first embodiment described above will be denoted by the same reference numerals, and the descriptions of those components will be simplified or omitted.

[0170] Figure 17 is a schematic diagram showing a hydraulic system 16 according to the second embodiment. In the above embodiment, the rod-side control valve 23 has the function of both a meter-out control valve and a regeneration valve. As shown in Figure 17, the rod-side control valve 23 and the regeneration valve 72 may be separate valves. The cap-side control valve 21 is connected to the pump passage 19 and the cap-side passage 20, respectively. The rod-side control valve 23 is connected to the rod-side passage 22 and the drain passage 25, respectively. The regeneration passage 26 connects the rod-side passage 22 and the cap-side passage 20. The regeneration valve 72 is located in the regeneration passage 26.

[0171] In the second embodiment, the meter-out pressure Po of the hydraulic fluid discharged from the rod chamber 12B is detected by the rod-side pressure sensor 29. The meter-in pressure Pi of the hydraulic fluid supplied to the cap chamber 12A is detected by the cap-side pressure sensor 28. Based on the pressure difference between the meter-in pressure Pi and the meter-out pressure Po, the controller 6 controls the regeneration valve 72 to completely close the regeneration opening to prevent backflow of hydraulic fluid from the cap chamber 12A to the rod chamber 12B.

[0172] In the second embodiment, the controller 6 adjusts the flow rate of the hydraulic fluid discharged from the hydraulic pump 17 so that the cylinder speed of the arm cylinder 12 does not fluctuate even if the regeneration flow rate of the hydraulic fluid passing through the regeneration channel 26 changes.

[0173] The controller 6 calculates the target regeneration flow rate Qr of the hydraulic fluid passing through the regeneration channel 26, and calculates the target pump flow rate Qp of the hydraulic fluid to be discharged from the hydraulic pump 17 by subtracting the target regeneration flow rate Qr from the target meter-in flow rate Qi of the hydraulic fluid to be supplied to the cap chamber 12A.

[0174] The input device 61 is operated to set the target cylinder speed of the arm cylinder 12. The controller 6 calculates the target meter-in flow rate Qi of the hydraulic fluid to be supplied to the cap chamber 12A based on the target cylinder speed of the arm cylinder 12 and the pressure-receiving area of ​​the arm cylinder 12.

[0175] As a first modification, the controller 6 calculates the target meter-in flow rate Qi of the hydraulic fluid to be supplied to the cap chamber 12A and the meter-out flow rate Qo of the hydraulic fluid discharged from the rod chamber 12B, based on the target cylinder speed of the arm cylinder 12 and the pressure-receiving area of ​​the arm cylinder 12. The controller 6 calculates the flow rate of the hydraulic fluid passing through the meter-out opening 34, based on the meter-out pressure Po detected by the rod-side pressure sensor 29 and the target value or estimated value of the meter-out opening 34. The controller 6 may also calculate the target regeneration flow rate Qr by subtracting the flow rate of the hydraulic fluid passing through the meter-out opening 32 from the meter-out flow rate Qo.

[0176] As a second variation, when the meter-out opening 34 is fully closed, the controller 6 may calculate the target regeneration flow rate Qr based on the flow rate of the hydraulic fluid discharged from the hydraulic pump 17 and the pressure-receiving area of ​​the arm cylinder 12.

[0177] [Other Embodiments] In the above-described embodiment, the estimation unit 37 calculates the estimated external force Fe based on the meter-in pressure Pi detected by the cap-side pressure sensor 28 and the meter-out pressure Po detected by the rod-side pressure sensor 29, but it is not limited to this. For example, in the working machine 1 according to another embodiment, a strain gauge may be attached to the connection between the boom 8 and the slewing body 3, and the estimation unit 37 may calculate the estimated external force Fe based on the measured value of the strain gauge.

[0178] In the above-described embodiment, the controller 6 may calculate the estimated external force Fd based on motion information (velocity, acceleration) of the work machine 4 detected by, for example, an inertial measurement unit (IMU).

[0179] In the above-described embodiment, the controller 6 may determine the state of the hydraulic system 16 without calculating the estimated external force Fd. The controller 6 may determine the state of the hydraulic system 16 based on, for example, the posture of the work machine 4 as captured by a camera. For example, when the bucket 10 is in the air, the state of the hydraulic system 16 may be determined to be the regenerated state R1. When the bucket 10 is embedded in the work object, the state of the hydraulic system 16 may be determined to be the drained state R3. When the bucket 10 is in contact with the work object, the state of the hydraulic system 16 may be determined to be the first transient state R2.

[0180] In the above-described embodiment, the controller 6 calculates the target cylinder speed of the arm cylinder 12 based on an operation signal indicating the amount of operation of the work machine operating device 7, but it is not limited to this. For example, the controller 6 in another embodiment may acquire the target cylinder speed from the input device 61 of the monitor 60. Alternatively, the controller 6 in another embodiment may acquire the target cylinder speed transmitted from a controller different from the controller 6.

[0181] The controller 6 according to the above embodiment may be composed of a single controller, or the configuration of the controller 6 may be divided into multiple controllers, and the multiple controllers may function by cooperating with each other. For example, some of the controllers constituting the input / output interface 36 may be mounted on the work machine 1, while the other controllers constituting the processor 34 and storage device 35 may be provided outside the work machine 1. For example, if the work machine 1 according to another embodiment is remotely operated, the components other than the control unit 40 may be provided in the remote controller.

[0182] In other embodiments, the work machine 1 may be controlled by a remote control system located at a remote location, and the input / output interface 36 may receive operation signals from the remote control system. In this case, the controller 6 may calculate the regeneration factor Fa, the target meter-out opening area Ad, the target meter-in opening area, and the target pump flow rate Qp based on the operation signals received from the remote control system. The control unit 40 may control the cap-side control valve 21, the rod-side control valve 23, and the hydraulic pump 17 based on the operation signals received from the remote control system.

[0183] In other embodiments, the work machine 1 may be operated autonomously. For example, the work machine 1 may be equipped with a measuring device for receiving measurement data regarding the position, orientation, and surrounding terrain of the work machine 1, and the controller 6 may generate operation signals to operate the work machine 4 based on the measurement data and pre-stored design data.

[0184] The work machine 1 according to other embodiments is not limited to a hydraulic excavator, but may be other work machines having work equipment such as a wheel loader.

[0185] 1...Work machine, 2...Traction unit, 2A...Track, 3...Slewing unit, 4...Work machine, 5...Hydraulic cylinder, 6...Controller, 7...Work machine operating device, 8...Boom, 9...Arm, 10...Bucket, 11...Boom cylinder, 12...Arm cylinder, 12A...Cap chamber, 12B...Rod chamber, 13...Bucket cylinder, 14...Control system, 15...Power source, 16...Hydraulic system, 17...Hydraulic pump, 18...Tank, 19...Pump passage, 20...Cap side passage, 21...Cap side control valve (meter-in control valve), 22...Rod side passage, 23...Rod side control valve (meter-out control valve) 25...Drain passage, 26...Regeneration passage, 27...Check valve, 28...Cap-side pressure sensor, 29...Rod-side pressure sensor, 30...Meter-in opening, 31...Meter-out opening, 32...Meter-out opening, 33...Regeneration opening, 34...Meter-out opening, 35...Storage device, 36...Input / output interface, 37...Estimation unit, 38...Determination unit, 39...Calculation unit, 40...Control unit, 41...Storage unit, 50...Relief valve, 51...Relief passage, 52...Solenoid valve, 60...Monitor, 61...Input device, 70...Solenoid proportional valve, 71...Pilot hydraulic pump, 72...Regeneration valve, 12 1...Cylinder tube, 122...Piston, 123...Rod, P1...Pump port, P2...First cap port, P3...Second cap port, P4...Drain port, P5...Pump port, P6...First rod port, P7...Second rod port, P8...Drain port, P9...Regeneration port, R1...Regeneration state, R2...First transient state, R3...Drain state, R4...Second transient state, Ac...Pressure receiving area on cap side, Ar...Pressure receiving area on rod side, At...Target regeneration opening area, Ad...Target meter-out opening area, Fa...Regeneration factor, Fd...Estimated external force, Pi...Meter-in Pressure, Pit...Target meter-in pressure, Po...Meter-out pressure, Pot...Target meter-out pressure, Fs...Estimated external force immediately after the first transient state, Pt...Tank pressure, Potm...Minimum target meter-out pressure, Qr...Target regeneration flow rate, Qd...Target drain flow rate, Qo...Meter-out flow rate, Qi...Target meter-in flow rate, Qp...Target pump flow rate, Tm...Minimum duration, Tn...Determined duration, Tu...Maximum duration, Rd...Regeneration drain coefficient, Fu...Upper limit of estimated external force, Vr...Target cylinder speed, ΔPit...Target meter-in pressure change rate, ΔPot...Target meter-out pressure change rate.

Claims

1. A work machine equipped with a work implement, comprising: a hydraulic pump for discharging hydraulic fluid; a hydraulic cylinder for operating the work implement; a meter-out opening for controlling the flow rate of the hydraulic fluid discharged from the rod chamber of the hydraulic cylinder to a tank; a regeneration passage connecting the rod chamber of the hydraulic cylinder and the cap chamber of the hydraulic cylinder; and a controller, wherein the controller calculates the external force acting on the hydraulic cylinder, and when it receives an operation signal to operate the work implement so that the hydraulic cylinder extends, it controls the meter-out opening based on the calculated external force.

2. The working machine according to claim 1, wherein the controller calculates the external force with the direction in which the hydraulic cylinder contracts as the positive direction, and when the external force is less than a first threshold, the meter-out opening is completely closed to return all of the hydraulic fluid discharged from the rod chamber of the hydraulic cylinder to the cap chamber.

3. The working machine according to claim 1, comprising: a rod-side pressure sensor for detecting the pressure of the hydraulic fluid discharged from the rod chamber; and a cap-side pressure sensor for detecting the pressure of the hydraulic fluid supplied to the cap chamber, wherein the controller calculates the external force based on the meter-in pressure, the meter-out pressure, the pressure-receiving area of ​​the piston facing the cap chamber, and the pressure-receiving area of ​​the piston facing the rod chamber.

4. The work machine according to claim 1, comprising a rod-side pressure sensor for detecting the pressure of the hydraulic fluid discharged from the rod chamber, wherein the controller calculates the external force with the direction of contraction of the hydraulic cylinder as the positive direction, calculates the meter-out flow rate of the hydraulic fluid discharged from the rod chamber, and, if the external force is greater than or equal to a first threshold, determines the opening area of ​​the meter-out opening based on the meter-out flow rate and the pressure detected by the rod-side pressure sensor.

5. The work machine according to claim 4, wherein the controller sets the final target opening area of ​​the meter-out opening so that the pressure detected by the rod-side pressure sensor becomes a predetermined target pressure, and when it is determined that the system has transitioned from a first transient state in which a portion of the hydraulic fluid discharged from the rod chamber passes through the meter-out opening to a drain state in which all of the hydraulic fluid discharged from the rod chamber passes through the meter-out opening, the controller controls the meter-out opening so that the opening area of ​​the meter-out opening gradually opens over time from the opening area of ​​the meter-out opening at the time of the transition from the first transient state to the drain state to the final target opening area.

6. The controller calculates the flow rate of hydraulic fluid passing through the meter-out opening based on the pressure detected by the rod-side pressure sensor and the opening area of ​​the meter-out opening, and determines the time when the flow rate of hydraulic fluid passing through the meter-out opening and the meter-out flow rate of hydraulic fluid discharged from the rod chamber are equal as the time when the machine has transitioned from the first transient state to the drain state, as described in claim 5.

7. The work machine according to claim 1, wherein the controller reduces the opening area of ​​the meter-out opening to a predetermined minimum opening area when the external force is vibrating or when an operation is performed that causes the external force to vibrate.

8. The controller controls the meter-out opening using four states, the regeneration ratio which indicates the proportion of the hydraulic fluid discharged from the rod chamber that is supplied to the cap chamber via the regeneration channel, being the maximum state, the regeneration ratio being the minimum state, a first transition state from the maximum state to the minimum state, and a second transition state from the minimum state to the maximum state, and based on the external force, the controller gradually changes the regeneration ratio from the maximum state to the minimum state in the first transition state, and gradually changes the regeneration ratio from the minimum state to the maximum state in the second transition state, the working machine according to claim 1.

9. The working machine according to claim 8, wherein the controller calculates the external force with the direction in which the hydraulic cylinder contracts as the positive direction, sets the regeneration ratio to the maximum state when the external force is less than a first threshold, sets the regeneration ratio to the minimum state when the external force is greater than a second threshold which is greater than the first threshold, and sets the regeneration ratio to an intermediate state corresponding to the external force when the external force is between the first threshold and the second threshold.

10. The work machine according to claim 9, wherein the controller receives input data from an input device and modifies the first threshold and the second threshold based on the input data.

11. The work machine according to claim 1, wherein the controller determines that the external force cannot be calculated, and sets the opening area of ​​the meter-out opening to a predetermined minimum opening area.

12. The work machine according to claim 1, comprising a meter-in opening for controlling the flow rate of hydraulic fluid supplied from the hydraulic pump to the cap chamber, wherein the cap chamber and the rod chamber with a larger pressure-receiving area are connected to the meter-in opening, and the rod chamber with a smaller pressure-receiving area is connected to the meter-out opening.

13. The work machine according to claim 1, wherein the work machine comprises a boom connected to the body of the work machine and an arm connected to the boom, and the hydraulic cylinder is an arm cylinder for operating the arm.

14. A work machine equipped with a work implement, comprising: a hydraulic pump for discharging hydraulic fluid; a hydraulic cylinder for operating the work implement; a meter-in opening for controlling the flow rate of hydraulic fluid supplied from the hydraulic pump to the cap chamber of the hydraulic cylinder; a meter-out opening for controlling the flow rate of hydraulic fluid discharged from the rod chamber of the hydraulic cylinder to a tank; a regeneration passage connecting the rod chamber of the hydraulic cylinder and the cap chamber of the hydraulic cylinder; and a controller, wherein the controller adjusts the flow rate of hydraulic fluid discharged from the hydraulic pump so that the cylinder speed of the hydraulic cylinder does not fluctuate even if the regeneration flow rate of hydraulic fluid passing through the regeneration passage changes.

15. The working machine according to claim 14, wherein the controller calculates a target regeneration flow rate of the hydraulic fluid passing through the regeneration channel, and calculates a target pump flow rate of the hydraulic fluid to be discharged from the hydraulic pump by subtracting the target regeneration flow rate from a target meter-in flow rate of the hydraulic fluid to be supplied to the cap chamber.

16. The work machine according to claim 15, comprising: an input device for setting a target cylinder speed of the hydraulic cylinder; and a rod-side pressure sensor for detecting the pressure of the hydraulic fluid discharged from the rod chamber, wherein the controller calculates a target meter-in flow rate of hydraulic fluid to be supplied to the cap chamber and a meter-out flow rate of hydraulic fluid discharged from the rod chamber based on the target cylinder speed of the hydraulic cylinder and the pressure-receiving area of ​​the piston facing the cap chamber; calculates the flow rate of hydraulic fluid passing through the meter-out opening based on the pressure detected by the rod-side pressure sensor and the target opening area of ​​the meter-out opening; and calculates the target regeneration flow rate by subtracting the flow rate of hydraulic fluid passing through the meter-out opening from the meter-out flow rate.

17. A work machine equipped with a work implement, comprising: a hydraulic pump for discharging hydraulic fluid; a hydraulic cylinder for operating the work implement; a regeneration opening for controlling the regeneration flow rate of hydraulic fluid supplied from the rod chamber of the hydraulic cylinder to the cap chamber of the hydraulic cylinder; a first control valve for controlling the regeneration opening; and a controller, wherein the controller calculates the external force acting on the hydraulic cylinder, and when it receives an operation signal to operate the work implement so that the hydraulic cylinder extends, it controls the regeneration opening based on the calculated external force and the regeneration flow rate.

18. The working machine according to claim 17, wherein the controller calculates the regeneration flow rate based on the meter-out flow rate of the hydraulic fluid discharged from the rod chamber, sets a target pressure indicating a target value for the pressure of the hydraulic fluid flowing into the cap chamber, and controls the regeneration opening based on the external force, the regeneration flow rate, and the target pressure.

19. The working machine according to claim 18, wherein the controller calculates a target differential pressure indicating a target value of the differential pressure across the regeneration opening based on the external force and the target pressure, and controls the regeneration opening based on the regeneration flow rate and the target differential pressure.

20. The working machine according to claim 17, comprising: a meter-out opening for controlling the flow rate of hydraulic fluid discharged from the rod chamber to a tank; a second control valve for controlling the meter-out opening; a rod-side pressure sensor for detecting the pressure of the hydraulic fluid discharged from the rod chamber; and a cap-side pressure sensor for detecting the pressure of the hydraulic fluid supplied to the cap chamber, wherein the controller controls the regeneration opening to prevent backflow of hydraulic fluid from the rod chamber to the cap chamber based on the pressure difference between the pressure detected by the rod-side pressure sensor and the pressure detected by the cap-side pressure sensor.

Images