Hydraulic system of hydraulic excavator, hydraulic excavator, and control method of hydraulic excavator

Abstract

The hydraulic system of the hydraulic excavator includes an operating state determination unit and a valve control unit. When the operating state of the working machine is determined to be a heavy excavation state, the valve control unit controls the first boom operating valve, the first arm operating valve, the first bucket operating valve, the second boom operating valve, the second arm operating valve, and the second bucket operating valve so that the flow of hydraulic oil from the first hydraulic pump to the boom cylinder is restricted, hydraulic oil is supplied from the second hydraulic pump to the boom cylinder, hydraulic oil is supplied from both the first and second hydraulic pumps to the arm cylinder, and hydraulic oil is supplied from one or both of the first and second hydraulic pumps to the bucket cylinder.

Description

Technical Field

[0001] The present disclosure relates to a hydraulic system of a hydraulic excavator, a hydraulic excavator, and a control method of the hydraulic excavator. Background Art

[0002] In the technical field related to hydraulic excavators, a hydraulic excavator as disclosed in Patent Document 1 is known.

[0003] Patent Document 1: Japanese Patent Application Publication No. 2019-052465 Summary of the Invention

[0004] A hydraulic excavator has three hydraulic cylinders: a boom cylinder, an arm cylinder, and a bucket cylinder. In a hydraulic system that distributes hydraulic oil discharged from two hydraulic pumps to the three hydraulic cylinders, the hydraulic oil may not be properly distributed to the hydraulic cylinders depending on the working state of the work machine.

[0005] An object of the present disclosure is to appropriately distribute hydraulic oil discharged from two hydraulic pumps to three hydraulic cylinders.

[0006] According to the present disclosure, a hydraulic system of a hydraulic excavator is provided, which comprises: a first hydraulic pump; a second hydraulic pump; a boom cylinder for moving the boom of the working machine; an arm cylinder for moving the arm of the working machine; a bucket cylinder for moving the bucket of the working machine; a first boom operating valve for controlling the flow of hydraulic oil from the first hydraulic pump toward the boom cylinder; a first arm operating valve for controlling the flow of hydraulic oil from the first hydraulic pump toward the arm cylinder; a first bucket operating valve for controlling the flow of hydraulic oil from the first hydraulic pump toward the bucket cylinder; a second boom operating valve for controlling the flow of hydraulic oil from the second hydraulic pump toward the boom cylinder; and a second arm an operating valve for controlling the flow of hydraulic oil from the second hydraulic pump to the boom cylinder; a second bucket operating valve for controlling the flow of hydraulic oil from the second hydraulic pump to the bucket cylinder; an arm check valve for inhibiting the hydraulic oil from flowing back from the boom cylinder to the second hydraulic pump via the second arm operating valve; a bucket check valve for inhibiting the hydraulic oil from flowing back from the bucket cylinder to the second hydraulic pump via the second bucket operating valve; an operating device for operating at least one of the boom cylinder, the boom cylinder, and the bucket cylinder; an operating state judgment unit based on the operating state of the operating device, the boom cylinder bottom pressure indicating the pressure of the cylinder bottom chamber of the boom cylinder, the boom cylinder bottom pressure indicating the pressure of the cylinder bottom chamber of the boom cylinder, and the bucket cylinder bottom pressure indicating the pressure of the cylinder bottom chamber of the bucket cylinder to judge the working state of the working machine; and a valve control unit, which controls at least one of the first boom operating valve, the first dipper arm operating valve, the first bucket operating valve, the second boom operating valve, the second dipper arm operating valve, and the second bucket operating valve based on the working state of the working machine judged by the working state judging unit, the working state judging unit judges that the working state of the working machine is a normal state when the dipper arm excavation operation amount of the operating device is above the first threshold value or the bucket excavation operation amount of the operating device is above the second threshold value, and when the boom cylinder bottom pressure is higher than the higher value of the boom cylinder bottom pressure and the bucket cylinder bottom pressure, and When the higher of the cylinder bottom pressure and the bucket cylinder bottom pressure is higher than the boom cylinder bottom pressure, it is determined that the working state of the work machine is the heavy excavation state. When it is determined that the working state of the work machine is the heavy excavation state, the valve control unit controls the first boom operating valve, the first arm operating valve, the first bucket operating valve, the second boom operating valve, the second arm operating valve, and the second bucket operating valve in a manner such that the flow of hydraulic oil from the first hydraulic pump to the boom cylinder is restricted, and hydraulic oil is supplied from the second hydraulic pump to the boom cylinder, and hydraulic oil is supplied from both the first hydraulic pump and the second hydraulic pump to the arm cylinder, and hydraulic oil is supplied from one or both of the first hydraulic pump and the second hydraulic pump to the bucket cylinder.

[0007] According to the present disclosure, the hydraulic oil discharged from the two hydraulic pumps is appropriately distributed to the three hydraulic cylinders. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 It is a perspective view showing a hydraulic excavator according to the embodiment.

[0009] Figure 2 It is a schematic diagram for explaining the operation of the working machine according to the embodiment.

[0010] Figure 3 It is a schematic diagram showing a hydraulic system of a hydraulic excavator according to an embodiment.

[0011] Figure 4 This is a functional block diagram showing a control device for a hydraulic excavator according to an embodiment.

[0012] Figure 5 It is a schematic diagram showing a determination method of the work status determination unit according to the embodiment.

[0013] Figure 6 This is a schematic diagram showing the hydraulic system when it is determined that the working state of the working machine according to the embodiment is a normal state.

[0014] Figure 7 This is a schematic diagram showing the hydraulic system when determining that the working state of the working machine according to the embodiment is the heavy excavation state.

[0015] Figure 8 This is a flowchart showing a method for controlling a hydraulic excavator according to an embodiment.

[0016] Figure 9 This is a timing chart showing a method for controlling a hydraulic excavator according to the embodiment.

[0017] Figure 10 This is a block diagram showing a computer system according to an embodiment. DETAILED DESCRIPTION

[0018] Hereinafter, the embodiments of the present disclosure will be described with reference to the accompanying drawings, but the present disclosure is not limited to the embodiments. The constituent elements of the embodiments described below can be combined as appropriate. In addition, some constituent elements may not be used.

[0019] hydraulic excavator

[0020] Figure 1 1 is a perspective view showing a hydraulic excavator 1 according to an embodiment. Figure 1 As shown, the hydraulic excavator 1 includes a revolving body 2 , a traveling body 3 , an operating device 4 , a working machine 10 , a boom cylinder 21 , an arm cylinder 22 , and a bucket cylinder 23 .

[0021] The revolving structure 2 supports the working machine 10. The revolving structure 2 includes a cab 2A. The operator of the hydraulic excavator 1 rides in the cab 2A. An operator's seat 2B, on which the operator sits, is provided in the cab 2A.

[0022] The traveling body 3 supports the revolving body 2. The traveling body 3 includes a pair of crawler tracks 3A. The hydraulic excavator 1 travels by the rotation of the crawler tracks 3A. The traveling body 3 may also include tires mounted on the axles.

[0023] The operating device 4 is operated by the operator of the hydraulic excavator 1. The operating device 4 is operated to operate the working machine 10. The operating device 4 is arranged in the operator's cab 2A.

[0024] The working machine 10 includes a boom 11, an arm 12, and a bucket 13. The boom 11 is rotatably connected to the revolving unit 2. The arm 12 is rotatably connected to the boom 11. The bucket 13 is rotatably connected to the arm 12.

[0025] The boom cylinder 21, the arm cylinder 22, and the bucket cylinder 23 are all hydraulic cylinders. The boom cylinder 21 is used to operate the boom 11. The arm cylinder 22 is used to operate the arm 12. The bucket cylinder 23 is used to operate the bucket 13.

[0026] Operation of the work machine

[0027] Figure 2 Schematic diagram for explaining the operation of the working machine 10 according to the embodiment. When the operating device 4 is operated, at least one of the boom cylinder 21, the arm cylinder 22, and the bucket cylinder 23 is operated.

[0028] The boom cylinder 21 is used to raise or lower the boom 11. When the boom raising operation is performed on the operating device 4, the boom cylinder 21 is extended, and the boom 11 is raised. When the boom lowering operation is performed on the operating device 4, the boom cylinder 21 is retracted, and the boom 11 is lowered.

[0029] The arm cylinder 22 causes the arm 12 to perform digging or bucket-dumping operations. By operating the operating device 4 to dig with the arm, the arm cylinder 22 extends, causing the arm 12 to dig. By operating the operating device 4 to dump with the arm, the arm cylinder 22 retracts, causing the arm 12 to dump.

[0030] The bucket cylinder 23 is used to make the bucket 13 perform digging or dumping. When the bucket digging operation is performed on the operating device 4, the bucket cylinder 23 is extended, and the bucket 13 performs digging. When the bucket dumping operation is performed on the operating device 4, the bucket cylinder 23 is shortened, and the bucket 13 performs dumping.

[0031] hydraulic system

[0032] Figure 3 Schematic diagram showing the hydraulic system 5 of the hydraulic excavator 1 according to the embodiment. Figure 3 As shown, the hydraulic system 5 includes: an engine 6, a first hydraulic pump 31, a second hydraulic pump 32, a boom cylinder 21, an arm cylinder 22, a bucket cylinder 23, an operating device 4, a first boom operating valve 41L, a first arm operating valve 42L, a first bucket operating valve 43L, a second boom operating valve 41R, a second arm operating valve 42R, a second bucket operating valve 43R, and an oil tank 7.

[0033] The engine 6 is a power source of the hydraulic excavator 1. As an example of the engine 6, a diesel engine can be shown.

[0034] The first hydraulic pump 31 and the second hydraulic pump 32 each discharge hydraulic oil. The first hydraulic pump 31 and the second hydraulic pump 32 are each driven by power generated by the engine 6. In the embodiment, both the first hydraulic pump 31 and the second hydraulic pump 32 are variable capacity hydraulic pumps. The first hydraulic pump 31 includes a swash plate 31A that is driven to change the capacity of the first hydraulic pump 31. The second hydraulic pump 32 includes a swash plate 32A that is driven to change the capacity of the second hydraulic pump 32.

[0035] The boom cylinder 21 includes a cylinder bottom chamber 21A and a rod chamber 21B. The boom cylinder 21 is extended by supplying hydraulic oil to the cylinder bottom chamber 21A, and is retracted by supplying hydraulic oil to the rod chamber 21B.

[0036] The arm cylinder 22 includes a cylinder bottom chamber 22A and a rod chamber 22B. The arm cylinder 22 is extended by supplying hydraulic oil to the cylinder bottom chamber 22A, and is retracted by supplying hydraulic oil to the rod chamber 22B.

[0037] The bucket cylinder 23 includes a cylinder bottom chamber 23A and a rod chamber 23B. The bucket cylinder 23 is extended by supplying hydraulic oil to the cylinder bottom chamber 23A, and is contracted by supplying hydraulic oil to the rod chamber 23B.

[0038] The operating device 4 is operated by the operator to operate at least one of the boom cylinder 21, the arm cylinder 22, and the bucket cylinder 23. Figure 3 In the example shown, the operating device 4 includes a boom operating lever 401 that is operated to operate the boom cylinder 21, an arm operating lever 402 that is operated to operate the arm cylinder 22, and a bucket operating lever 403 that is operated to operate the bucket cylinder 23. Figure 3The operating device 4 shown is an example. The operating device 4 may also include two working levers. Specifically, one of the working levers may be operated in the front-to-back direction to actuate the boom cylinder 21, while the bucket cylinder 23 may be operated in the left-to-right direction. Furthermore, the other working lever may be operated in the left-to-right direction to actuate the arm cylinder 22.

[0039] The first boom operating valve 41L is connected to the first hydraulic pump 31. The first boom operating valve 41L controls the flow of hydraulic oil from the first hydraulic pump 31 to the boom cylinder 21. The first boom operating valve 41L controls the flow rate and direction of the hydraulic oil supplied from the first hydraulic pump 31 to the boom cylinder 21.

[0040] The first arm operating valve 42L is connected to the first hydraulic pump 31. The first arm operating valve 42L controls the flow of hydraulic oil from the first hydraulic pump 31 to the arm cylinder 22. The first arm operating valve 42L controls the flow rate and flow direction of the hydraulic oil supplied from the first hydraulic pump 31 to the arm cylinder 22.

[0041] The first bucket operating valve 43L is connected to the first hydraulic pump 31. The first bucket operating valve 43L controls the flow of hydraulic oil from the first hydraulic pump 31 to the bucket cylinder 23. The first bucket operating valve 43L controls the flow rate and direction of the hydraulic oil supplied from the first hydraulic pump 31 to the bucket cylinder 23.

[0042] The second boom operating valve 41R is connected to the second hydraulic pump 32. The second boom operating valve 41R controls the flow of hydraulic oil from the second hydraulic pump 32 to the boom cylinder 21. The second boom operating valve 41R controls the flow rate and flow direction of the hydraulic oil supplied from the second hydraulic pump 32 to the boom cylinder 21.

[0043] The second arm operating valve 42R is connected to the second hydraulic pump 32. The second arm operating valve 42R controls the flow of hydraulic oil from the second hydraulic pump 32 to the arm cylinder 22. The second arm operating valve 42R controls the flow rate and flow direction of the hydraulic oil supplied from the second hydraulic pump 32 to the arm cylinder 22.

[0044] The second bucket operating valve 43R is connected to the second hydraulic pump 32. The second bucket operating valve 43R controls the flow of hydraulic oil from the second hydraulic pump 32 to the bucket cylinder 23. The second bucket operating valve 43R controls the flow rate and direction of the hydraulic oil supplied from the second hydraulic pump 32 to the bucket cylinder 23.

[0045] The first boom operating valve 41L and the second boom operating valve 41R are both sliding spool-type valves that control the flow rate and direction of the hydraulic oil supplied to the boom cylinder 21 by moving a rod-shaped valve core. Axial movement of the valve core switches the supply of hydraulic oil to the cylinder bottom chamber 21A and the rod chamber 21B of the boom cylinder 21. Furthermore, the flow rate of the hydraulic oil supplied to the boom cylinder 21 is adjusted based on the amount of valve core movement.

[0046] The first arm operating valve 42L and the second arm operating valve 42R are both sliding spool-type flow control valves. Axial movement of the spool switches the supply of hydraulic oil to the cylinder bottom chamber 22A and the rod chamber 22B of the arm cylinder 22. Furthermore, the flow rate of hydraulic oil supplied to the arm cylinder 22 is adjusted based on the amount of spool movement.

[0047] The first bucket operating valve 43L and the second bucket operating valve 43R are both sliding spool-type flow-control valves. By axially moving the spools, the supply of hydraulic oil to the cylinder bottom chamber 23A and the supply of hydraulic oil to the rod chamber 23B of the bucket cylinder 23 are switched. Furthermore, the flow rate of the hydraulic oil supplied to the bucket cylinder 23 is adjusted based on the amount of spool movement.

[0048] The first boom operating valve 41L, the first arm operating valve 42L, and the first bucket operating valve 43L constitute a first operating valve group 40L connected to the first hydraulic pump 31 .

[0049] The second boom operating valve 41R, the second arm operating valve 42R, and the second bucket operating valve 43R constitute a second operating valve group 40R connected to the second hydraulic pump 32 .

[0050] The first boom operating valve 41L is connected to the first hydraulic pump 31 via the discharge flow path 50L and the supply flow path 51L. The first dipper arm operating valve 42L is connected to the first hydraulic pump 31 via the discharge flow path 50L and the supply flow path 52L. The first bucket operating valve 43L is connected to the first hydraulic pump 31 via the discharge flow path 50L and the supply flow path 53L. The discharge flow path 50L is connected to the discharge port of the first hydraulic pump 31. The supply flow path 51L, the supply flow path 52L, and the supply flow path 53L are connected in parallel to the discharge flow path 50L.

[0051] The second boom operating valve 41R is connected to the second hydraulic pump 32 via the discharge flow path 50R and the supply flow path 51R. The second arm operating valve 42R is connected to the second hydraulic pump 32 via the discharge flow path 50R and the supply flow path 52R. The second bucket operating valve 43R is connected to the second hydraulic pump 32 via the discharge flow path 50R and the supply flow path 53R. The discharge flow path 50R is connected to the discharge port of the second hydraulic pump 32. The supply flow path 51R, the supply flow path 52R and the supply flow path 53R are connected in parallel to the discharge flow path 50R.

[0052] The first boom operating valve 41L is connected to the cylinder bottom chamber 21A of the boom cylinder 21 via the cylinder bottom flow path 54 and the cylinder bottom flow path 54L. The second boom operating valve 41R is connected to the cylinder bottom chamber 21A of the boom cylinder 21 via the cylinder bottom flow path 54 and the cylinder bottom flow path 54R. The cylinder bottom flow path 54 is connected to the cylinder bottom chamber 21A. The cylinder bottom flow path 54L is connected to the first boom operating valve 41L. The cylinder bottom flow path 54R is connected to the second boom operating valve 41R.

[0053] The first boom operating valve 42L is connected to the cylinder bottom chamber 22A of the boom cylinder 22 via the cylinder bottom flow path 55 and the cylinder bottom flow path 55L. The second boom operating valve 42R is connected to the cylinder bottom chamber 22A of the boom cylinder 22 via the cylinder bottom flow path 55 and the cylinder bottom flow path 55R. The cylinder bottom flow path 55 is connected to the cylinder bottom chamber 22A. The cylinder bottom flow path 55L is connected to the first boom operating valve 42L. The cylinder bottom flow path 55R is connected to the second boom operating valve 42R.

[0054] The first bucket operating valve 43L is connected to the cylinder bottom chamber 23A of the bucket cylinder 23 via the cylinder bottom flow passage 56 and the cylinder bottom flow passage 56L. The second bucket operating valve 43R is connected to the cylinder bottom chamber 23A of the bucket cylinder 23 via the cylinder bottom flow passage 56 and the cylinder bottom flow passage 56R. The cylinder bottom flow passage 56 is connected to the cylinder bottom chamber 23A. The cylinder bottom flow passage 56L is connected to the first bucket operating valve 43L. The cylinder bottom flow passage 56R is connected to the second bucket operating valve 43R.

[0055] The first boom operating valve 41L is connected to the rod chamber 21B of the boom cylinder 21 via the rod chamber flow path 57 and the rod chamber flow path 57L. The second boom operating valve 41R is connected to the rod chamber 21B of the boom cylinder 21 via the rod chamber flow path 57 and the rod chamber flow path 57R. The rod chamber flow path 57 is connected to the rod chamber 21B. The rod chamber flow path 57L is connected to the first boom operating valve 41L. The rod chamber flow path 57R is connected to the second boom operating valve 41R.

[0056] The first boom operating valve 42L is connected to the rod chamber 22B of the boom cylinder 22 via the rod chamber flow path 58 and the rod chamber flow path 58L. The second boom operating valve 42R is connected to the rod chamber 22B of the boom cylinder 22 via the rod chamber flow path 58 and the rod chamber flow path 58R. The rod chamber flow path 58 is connected to the rod chamber 22B. The rod chamber flow path 58L is connected to the first boom operating valve 42L. The rod chamber flow path 58R is connected to the second boom operating valve 42R.

[0057] The first bucket operating valve 43L is connected to the rod chamber 23B of the bucket cylinder 23 via the rod chamber flow path 59 and the rod chamber flow path 59L. The second bucket operating valve 43R is connected to the rod chamber 23B of the bucket cylinder 23 via the rod chamber flow path 59 and the rod chamber flow path 59R. The rod chamber flow path 59 is connected to the rod chamber 23B. The rod chamber flow path 59L is connected to the first bucket operating valve 43L. The rod chamber flow path 59R is connected to the second bucket operating valve 43R.

[0058] The valve core of the first boom operating valve 41L and the valve core of the second boom operating valve 41R move between the cylinder bottom chamber supply position, the rod chamber supply position, and the neutral position. The cylinder bottom chamber supply position is a position where the hydraulic oil supplied to the cylinder bottom chamber 21A of the boom cylinder 21 flows; the rod chamber supply position is a position where the hydraulic oil supplied to the rod chamber 21B of the boom cylinder 21 flows; and the neutral position is a position where the hydraulic oil is not allowed to flow. Figure 3 In the illustrated example, the valve body of the first boom operating valve 41L and the valve body of the second boom operating valve 41R are arranged in the neutral position.

[0059] The valve core of the first boom operating valve 42L and the valve core of the second boom operating valve 42R move between the cylinder bottom chamber supply position, the rod chamber supply position, and the neutral position. The cylinder bottom chamber supply position is a position where the hydraulic oil supplied to the cylinder bottom chamber 22A of the boom cylinder 22 flows; the rod chamber supply position is a position where the hydraulic oil supplied to the rod chamber 22B of the boom cylinder 22 flows; the neutral position is a position where the hydraulic oil is not allowed to flow. Figure 3 In the illustrated example, the valve body of the first arm operation valve 42L and the valve body of the second arm operation valve 42R are arranged in the neutral position.

[0060] The valve core of the first bucket operating valve 43L and the valve core of the second bucket operating valve 43R move between the cylinder bottom chamber supply position, the rod chamber supply position, and the neutral position. The cylinder bottom chamber supply position is a position where the hydraulic oil supplied to the cylinder bottom chamber 23A of the bucket cylinder 23 flows; the rod chamber supply position is a position where the hydraulic oil supplied to the rod chamber 23B of the bucket cylinder 23 flows; and the neutral position is a position where the hydraulic oil is not allowed to flow. Figure 3 In the illustrated example, the valve body of the first bucket operating valve 43L and the valve body of the second bucket operating valve 43R are arranged in the neutral position.

[0061] The first boom operating valve 41L is connected to the oil tank 7 via a discharge flow path 61L. The hydraulic oil supplied from the boom cylinder 21 to the first boom operating valve 41L is supplied to the oil tank 7 via the discharge flow path 61L. The second boom operating valve 41R is connected to the oil tank 7 via a discharge flow path 61R. The hydraulic oil supplied from the boom cylinder 21 to the second boom operating valve 41R is supplied to the oil tank 7 via the discharge flow path 61R.

[0062] The first boom operating valve 42L is connected to the oil tank 7 via the discharge flow path 62L. The hydraulic oil supplied from the boom cylinder 22 to the first boom operating valve 42L is supplied to the oil tank 7 via the discharge flow path 62L. The second boom operating valve 42R is connected to the oil tank 7 via the discharge flow path 62R. The hydraulic oil supplied from the boom cylinder 22 to the second boom operating valve 42R is supplied to the oil tank 7 via the discharge flow path 62R.

[0063] The first bucket operating valve 43L is connected to the oil tank 7 via a discharge flow path 63L. The hydraulic oil supplied from the bucket cylinder 23 to the first bucket operating valve 43L is supplied to the oil tank 7 via the discharge flow path 63L. The second bucket operating valve 43R is connected to the oil tank 7 via a discharge flow path 63R. The hydraulic oil supplied from the bucket cylinder 23 to the second bucket operating valve 43R is supplied to the oil tank 7 via the discharge flow path 63R.

[0064] The first hydraulic pump 31, the first boom operating valve 41L, the first arm operating valve 42L, and the first bucket operating valve 43L are connected via a neutral flow path 64L. The neutral flow path 64L is connected to the oil tank 7 via a negative control mechanism 65L that negatively controls the capacity of the first hydraulic pump 31. When the valve spools of the first boom operating valve 41L, the first arm operating valve 42L, and the first bucket operating valve 43L are all in their neutral positions, hydraulic oil discharged from the first hydraulic pump 31 is supplied to the oil tank 7 via the first boom operating valve 41L, the first arm operating valve 42L, the first bucket operating valve 43L, and the neutral flow path 64L.

[0065] The second hydraulic pump 32, the second boom operating valve 41R, the second arm operating valve 42R, and the second bucket operating valve 43R are connected via a neutral flow path 64R. The neutral flow path 64R is connected to the oil tank 7 via a negative control mechanism 65R that negatively controls the capacity of the second hydraulic pump 32. When the valve spools of the second boom operating valve 41R, the second arm operating valve 42R, and the second bucket operating valve 43R are all in their neutral positions, the hydraulic oil discharged from the second hydraulic pump 32 is supplied to the oil tank 7 via the second boom operating valve 41R, the second arm operating valve 42R, the second bucket operating valve 43R, and the neutral flow path 64R.

[0066] In addition, Figure 3 In the figure, there are multiple fuel tanks 7, but there can also be only one fuel tank 7.

[0067] The boom check valve 44L is disposed in the supply flow path 51L. The arm check valve 45L is disposed in the supply flow path 52L. The bucket check valve 46L is disposed in the supply flow path 53L.

[0068] The boom check valve 44L is used to prevent hydraulic oil from flowing back from the boom cylinder 21 to the first hydraulic pump 31 via the first boom operating valve 41L. The arm check valve 45L is used to prevent hydraulic oil from flowing back from the arm cylinder 22 to the first hydraulic pump 31 via the first arm operating valve 42L. The bucket check valve 46L is used to prevent hydraulic oil from flowing back from the bucket cylinder 23 to the first hydraulic pump 31 via the first bucket operating valve 43L.

[0069] The boom check valve 44R is disposed in the supply flow path 51R. The arm check valve 45R is disposed in the supply flow path 52R. The bucket check valve 46R is disposed in the supply flow path 53R.

[0070] The boom check valve 44R is used to prevent hydraulic oil from flowing back from the boom cylinder 21 to the second hydraulic pump 32 via the second boom operating valve 41R. The arm check valve 45R is used to prevent hydraulic oil from flowing back from the arm cylinder 22 to the second hydraulic pump 32 via the second arm operating valve 42R. The bucket check valve 46R is used to prevent hydraulic oil from flowing back from the bucket cylinder 23 to the second hydraulic pump 32 via the second bucket operating valve 43R.

[0071] In addition, the hydraulic system 5 has: a first discharge pressure sensor 71, a second discharge pressure sensor 72, a boom cylinder bottom pressure sensor 73, a boom rod pressure sensor 74, an arm cylinder bottom pressure sensor 75, an arm rod pressure sensor 76, a bucket cylinder bottom pressure sensor 77, and a bucket rod pressure sensor 78.

[0072] The first discharge pressure sensor 71 is for detecting a first discharge pressure indicating the pressure of the hydraulic oil discharged from the first hydraulic pump 31. The first discharge pressure sensor 71 is disposed at a discharge port of the first hydraulic pump 31.

[0073] The second discharge pressure sensor 72 is for detecting a second discharge pressure indicating the pressure of the hydraulic oil discharged from the second hydraulic pump 32. The second discharge pressure sensor 72 is disposed at a discharge port of the second hydraulic pump 32.

[0074] The boom cylinder bottom pressure sensor 73 detects the boom cylinder bottom pressure indicating the pressure of the cylinder bottom chamber 21A of the boom cylinder 21. The boom cylinder bottom pressure sensor 73 is disposed in the cylinder bottom flow path 54.

[0075] The boom rod pressure sensor 74 detects a boom rod pressure indicating the pressure in the rod chamber 21B of the boom cylinder 21. The boom rod pressure sensor 74 is disposed in the rod chamber flow path 57.

[0076] The arm cylinder bottom pressure sensor 75 detects the arm cylinder bottom pressure indicating the pressure of the cylinder bottom chamber 22A of the arm cylinder 22. The arm cylinder bottom pressure sensor 75 is disposed in the cylinder bottom flow path 55.

[0077] The arm rod pressure sensor 76 detects the arm rod pressure indicating the pressure of the rod chamber 22B of the arm cylinder 22. The arm rod pressure sensor 76 is arranged in the rod chamber flow path 58.

[0078] The bucket cylinder bottom pressure sensor 77 detects a bucket cylinder bottom pressure indicating the pressure of the cylinder bottom chamber 23A of the bucket cylinder 23 . The bucket cylinder bottom pressure sensor 77 is disposed in the cylinder bottom flow path 56 .

[0079] The bucket rod pressure sensor 78 detects the bucket rod pressure indicating the pressure of the rod chamber 23B of the bucket cylinder 23 . The bucket rod pressure sensor 78 is arranged in the rod chamber flow path 59 .

[0080] Furthermore, the hydraulic system 5 includes a boom operation amount sensor 81 , an arm operation amount sensor 82 , and a bucket operation amount sensor 83 .

[0081] The boom operation amount sensor 81 is used to detect the boom operation amount representing the operation amount of the operating device 4 that operates the boom cylinder 21. In the embodiment, the boom operating lever 401 is provided with a PPC (Proportional Pressure Control) valve. The PPC valve generates a pilot pressure based on the operation angle of the boom operating lever 401. The boom operation amount sensor 81 is a pressure sensor for detecting the PPC pressure as the boom operation amount, and the PPC pressure represents the pilot pressure generated by the PPC valve based on the operation angle of the boom operating lever 401. Two boom operation amount sensors 81 are provided. One of the boom operation amount sensors 81 is used to detect the boom raising operation amount, and the boom raising operation amount represents the boom operation amount when the boom raising operation is performed. The other boom operation amount sensor 81 is used to detect the boom lowering operation amount, and the boom lowering operation amount represents the boom operation amount when the boom lowering operation is performed.

[0082] The arm operation amount sensor 82 is used to detect the arm operation amount, which represents the operation amount of the operating device 4 that operates the arm cylinder 22. Like the boom operating lever 401, the arm operating lever 402 is provided with a PPC valve. The arm operation amount sensor 82 is a pressure sensor for detecting the PPC pressure as the arm operation amount, which represents the pilot pressure generated by the PPC valve based on the operating angle of the arm operating lever 402. Two arm operation amount sensors 82 are provided. One of the arm operation amount sensors 82 is used to detect the arm excavation operation amount, which represents the arm operation amount when the arm excavation operation is performed. The other arm operation amount sensor 82 is used to detect the arm dumping operation amount, which represents the arm operation amount when the arm dumping operation is performed.

[0083] The bucket operation amount sensor 83 detects the bucket operation amount, which represents the amount of operation of the operating device 4 operating the bucket cylinder 23. Like the boom operating lever 401 and the arm operating lever 402, the bucket operating lever 403 is equipped with a PPC valve. The bucket operation amount sensor 83 is a pressure sensor that detects the PPC pressure, which represents the pilot pressure generated by the PPC valve based on the operating angle of the bucket operating lever 403, serving as the bucket operation amount. Two bucket operation amount sensors 83 are provided. One bucket operation amount sensor 83 detects the bucket excavation operation amount, which represents the amount of bucket operation during bucket excavation. The other bucket operation amount sensor 83 detects the bucket dumping operation amount, which represents the amount of bucket operation during bucket dumping.

[0084] Alternatively, the boom operation amount sensor 81 may be an angle sensor for detecting the operation angle of the boom operating lever 401 as the boom operation amount. The arm operation amount sensor 82 may be an angle sensor for detecting the operation angle of the arm operating lever 402 as the arm operation amount. The bucket operation amount sensor 83 may be an angle sensor for detecting the operation angle of the bucket operating lever 403 as the bucket operation amount.

[0085] Control device

[0086] Figure 4 1 is a functional block diagram showing a control device 9 of the hydraulic excavator 1 according to the embodiment. The control device 9 is mounted on the hydraulic excavator 1. The control device 9 controls the hydraulic system 5. The control device 9 includes a computer system.

[0087] The control device 9 is connected to the first discharge pressure sensor 71, the second discharge pressure sensor 72, the boom cylinder bottom pressure sensor 73, the boom rod pressure sensor 74, the arm cylinder bottom pressure sensor 75, the arm rod pressure sensor 76, the bucket cylinder bottom pressure sensor 77, the bucket rod pressure sensor 78, the boom operation amount sensor 81, the arm operation amount sensor 82, and the bucket operation amount sensor 83 via a communication line. Furthermore, the control device 9 is connected to the first hydraulic pump 31, the second hydraulic pump 32, the first boom operating valve 41L, the second boom operating valve 41R, the first arm operating valve 42L, the second arm operating valve 42R, the first bucket operating valve 43L, and the second bucket operating valve 43R via control lines.

[0088] The control device 9 includes a detection data acquisition unit 91 , an operation state determination unit 92 , a valve control unit 93 , a pump control unit 94 , and a storage unit 95 .

[0089] The detection data acquisition unit 91 is used to acquire: the detection data of the first discharge pressure sensor 71, the detection data of the second discharge pressure sensor 72, the detection data of the boom cylinder bottom pressure sensor 73, the detection data of the boom rod pressure sensor 74, the detection data of the dipper cylinder bottom pressure sensor 75, the detection data of the dipper rod pressure sensor 76, the detection data of the bucket cylinder bottom pressure sensor 77, the detection data of the bucket rod pressure sensor 78, the detection data of the boom operation amount sensor 81, the detection data of the dipper rod operation amount sensor 82, and the detection data of the bucket operation amount sensor 83.

[0090] The working state determination unit 92 determines the working state of the working machine 10. The working state of the working machine 10 includes a normal state and a heavy excavation state.

[0091] The normal state refers to a state in which the bucket 13 is excavating the object to be excavated at an excavation load less than a predetermined excavation load, or a state in which the work machine 10 is not excavating the object to be excavated. In the normal state, the excavation reaction force acting on the work machine 10 is less than the gravity acting on the work machine 10. In the normal state, the boom cylinder bottom pressure is higher than the arm cylinder bottom pressure and the bucket cylinder bottom pressure.

[0092] The heavy excavation state refers to a state in which the bucket 13 is excavating the excavation object at an excavation load higher than a predetermined excavation load. In the heavy excavation state, a large excavation reaction force acts on the work machine 10. In the heavy excavation state, the boom cylinder bottom pressure is lower than the arm cylinder bottom pressure and the bucket cylinder bottom pressure.

[0093] For example, during excavation, there are alternately a normal state where the boom cylinder bottom pressure is greater than the arm cylinder bottom pressure and the bucket cylinder bottom pressure, and a heavy excavation state where the boom cylinder bottom pressure is lower than the arm cylinder bottom pressure and the bucket cylinder bottom pressure.

[0094] The working state determination unit 92 can determine the working state of the working machine 10 based on the operating state of the operating device 4, the boom cylinder bottom pressure, the arm cylinder bottom pressure, and the bucket cylinder bottom pressure. The working state determination unit 92 can determine the working state of the working machine 10 based on the detection data of the arm operation amount sensor 82, the detection data of the bucket operation amount sensor 83, the detection data of the arm cylinder bottom pressure sensor 75, and the detection data of the bucket cylinder bottom pressure sensor 77.

[0095] In the embodiment, the normal state refers to an operating state in which the arm excavation operation amount of the operating device 4 is greater than the first threshold R1 or the bucket excavation operation amount is greater than the second threshold R2, and the boom cylinder bottom pressure is higher than the higher value of the arm cylinder bottom pressure and the bucket cylinder bottom pressure.

[0096] In the embodiment, the heavy excavation state refers to an operating state in which the arm excavation operation amount of the operating device 4 is greater than the first threshold R1 or the bucket excavation operation amount is greater than the second threshold R2, and the higher value of the arm cylinder bottom pressure and the bucket cylinder bottom pressure is higher than the boom cylinder bottom pressure.

[0097] Figure 5 : is a schematic diagram showing the judgment method of the working state judgment unit 92 involved in the embodiment. The working state judgment unit 92 can judge whether the boom excavation operation is performed based on the detection data of the boom operation amount sensor 82. In addition, the working state judgment unit 92 can obtain the boom excavation operation amount based on the detection data of the boom operation amount sensor 82, and the boom excavation operation amount represents the boom operation amount when the boom excavation operation of the operating device 4 is performed. In addition, the working state judgment unit 92 can judge whether the bucket excavation operation is performed based on the detection data of the bucket operation amount sensor 83. In addition, the working state judgment unit 92 can obtain the bucket excavation operation amount based on the detection data of the bucket operation amount sensor 83, and the bucket excavation operation amount represents the bucket operation amount when the bucket excavation operation of the operating device 4 is performed.

[0098] The working state determination unit 92 determines that the working state of the working machine 10 is the heavy excavation state when the heavy excavation determination conditions are met: the arm excavation operation amount is greater than or equal to a first threshold value R1, or the bucket excavation operation amount is greater than or equal to a second threshold value R2, and the higher of the arm cylinder bottom pressure and the bucket cylinder bottom pressure is greater than the boom cylinder bottom pressure. The first threshold value R1 and the second threshold value R2 are preset values and stored in the storage unit 95.

[0099] The first threshold value R1 is a threshold value for the PPC pressure of the arm working lever 402. The second threshold value R2 is a threshold value for the PPC pressure of the bucket working lever 403. As an example, the first threshold value R1 and the second threshold value R2 are both 5 kg / cm 2 . The first threshold value R1 and the second threshold value R2 are both relatively low values. After the operation of the boom working lever 402 is just started, the boom excavation operation amount exceeds the first threshold value R1. After the operation of the bucket working lever 403 is just started, the bucket excavation operation amount exceeds the second threshold value R2. The working state judgment unit 92 can determine that the boom excavation operation has started when the boom excavation operation amount becomes greater than the first threshold value R1. The working state judgment unit 92 can determine that the bucket excavation operation has started when the bucket excavation operation amount becomes greater than the second threshold value R2.

[0100] When determining that the heavy excavation determination condition is not satisfied, the working state determination unit 92 determines that the working state of the working machine 10 is the normal state.

[0101] The valve control unit 93 controls at least one of the first boom operating valve 41L, the first arm operating valve 42L, the first bucket operating valve 43L, the second boom operating valve 41R, the second arm operating valve 42R, and the second bucket operating valve 43R based on the operating state of the work machine 10 determined by the operating state determination unit 92. If the operating state of the work machine 10 is determined to be the normal state, the valve control unit 93 performs valve control to place the hydraulic system 5 in a first hydraulic oil supply state. If the operating state of the work machine 10 is determined to be the heavy excavation state, the valve control unit 93 performs valve control to place the hydraulic system 5 in a second hydraulic oil supply state different from the first hydraulic oil supply state.

[0102] The pump control unit 94 controls the first hydraulic pump 31 and the second hydraulic pump 32 based on the operating state of the work machine 10 determined by the operating state determination unit 92. In the embodiment, the pump control unit 94 controls the absorption torque of the first hydraulic pump 31 and the absorption torque of the second hydraulic pump 32 based on the operating state of the work machine 10 and the operating state of the operating device 4.

[0103] If the working state of the work machine 10 is determined to be the normal state, the pump control unit 94 sets the upper limit value of the absorption torque of the first hydraulic pump 31 to be equal to the upper limit value of the absorption torque of the second hydraulic pump 32. If the working state of the work machine 10 is determined to be the heavy excavation state and the boom raising operation amount is greater than or equal to the third threshold value R3, the pump control unit 94 sets the upper limit value of the absorption torque of the first hydraulic pump 31 to be higher than the upper limit value of the absorption torque of the second hydraulic pump 32. The third threshold value R3 is a preset value and is stored in the storage unit 95.

[0104] The third threshold value R3 is a threshold value for the PPC pressure of the boom working lever 401. As an example, the third threshold value R3 is 5 kg / cm 2 The third threshold value R3 is a relatively low value. Immediately after the boom operating lever 401 is operated, the boom raising operation amount exceeds the third threshold value R3. The working state determination unit 92 can determine that the boom raising operation has started when the boom raising operation amount is equal to or greater than the third threshold value R3.

[0105] In a heavy excavation state, where the excavation load applied to the work machine 10 increases, the operator often performs a boom-up operation to reduce the excavation load applied to the bucket 13 and arm 12. When the working state of the work machine 10 is determined to be a heavy excavation state and the boom-up operation amount is greater than or equal to the third threshold value R3, the pump control unit 94 drives at least one of the swash plate 31A and the swash plate 32A so that the upper limit value of the absorption torque of the first hydraulic pump 31 is greater than the upper limit value of the absorption torque of the second hydraulic pump 32.

[0106] The working state determination unit 92 can determine whether the boom raising operation amount is greater than or equal to the third threshold value R3 based on the detection data of the boom operation amount sensor 81. Figure 5 As shown, when it is determined that the heavy excavation determination condition is met and the boom raising operation amount is greater than the third threshold value R3, the pump control unit 94 performs absorption torque control so that the upper limit value of the absorption torque of the first hydraulic pump 31 is higher than the upper limit value of the absorption torque of the second hydraulic pump 32.

[0107] Generally speaking, the absorption torque Tp [kgm] of a hydraulic pump can be expressed by the following equation (1).

[0108] Tp=q×P / (200×π) / ηt…(1)

[0109] In formula (1), Tp is the absorption torque of the hydraulic pump [kgm], q is the capacity of the hydraulic pump [cc / rev], and P is the discharge pressure of the hydraulic oil discharged from the hydraulic pump [kg / cm 2 ], ηt is the torque efficiency of the hydraulic pump.

[0110] The capacity q of the first hydraulic pump 31 can be adjusted by changing the angle of the swash plate 31A of the first hydraulic pump 31. The capacity q of the second hydraulic pump 32 can be adjusted by changing the angle of the swash plate 32A of the second hydraulic pump 32. A first discharge pressure, representing the discharge pressure P of the first hydraulic pump 31, is detected by a first discharge pressure sensor 71. A second discharge pressure, representing the discharge pressure P of the second hydraulic pump 32, is detected by a second discharge pressure sensor 72. The torque efficiency ηt is a known value, inherent to each of the first and second hydraulic pumps 31 and 32.

[0111] Therefore, assuming that the absorption torque Tp of the first hydraulic pump 31 is absorption torque Tp1 and the absorption torque Tp of the second hydraulic pump 32 is absorption torque Tp2, the pump control unit 94 can adjust the angle of the swash plate 31A based on the detection data of the first discharge pressure sensor 71, thereby controlling the absorption torque Tp1 of the first hydraulic pump 31. The pump control unit 94 can also adjust the angle of the swash plate 32A based on the detection data of the second discharge pressure sensor 72, thereby controlling the absorption torque Tp2 of the second hydraulic pump 32.

[0112] When the working state of the work machine 10 is determined to be the normal state, the pump control unit 94 adjusts the angle of at least one of the swash plates 31A and 32A based on the detection data from the first and second discharge pressure sensors 71 and 72 so that the upper limit value of the absorption torque Tp1 of the first hydraulic pump 31 and the upper limit value of the absorption torque Tp2 of the second hydraulic pump 32 are equal. Specifically, the pump control unit 94 adjusts the displacement q of the first and second hydraulic pumps 31 and 32 so that the ratio of the upper limit value of the absorption torque Tp1 to the upper limit value of the absorption torque Tp2 is "Tp1:Tp2=50:50."

[0113] When the working state of the work machine 10 is determined to be the heavy excavation state and the boom raising operation amount is greater than or equal to the third threshold value R3, the pump control unit 94 adjusts the angle of at least one of the swash plates 31A and 32A based on the detection data from the first and second discharge pressure sensors 71 and 72 so that the upper limit value of the absorption torque Tp1 of the first hydraulic pump 31 is higher than the upper limit value of the absorption torque Tp2 of the second hydraulic pump 32. In the embodiment, the pump control unit 94 adjusts the displacement q of the first and second hydraulic pumps 31 and 32 so that the ratio of the upper limit value of the absorption torque Tp1 to the upper limit value of the absorption torque Tp2 is, for example, "Tp1:Tp2=90:10."

[0114] In the embodiment, the pump control unit 94 performs absorption torque control in consideration of not only the boom raising operation amount but also the arm excavation operation amount and the bucket excavation operation amount. Figure 5 As shown, when the working state of the work machine 10 is the heavy excavation state, if it is determined that the boom raising operation amount is greater than or equal to the third threshold value R3, the arm excavation operation amount is greater than or equal to the fourth threshold value R4, and the bucket excavation operation amount is greater than or equal to the fifth threshold value R5, the pump control unit 94 sets the upper limit of the absorption torque of the first hydraulic pump 31 to be higher than the upper limit of the absorption torque of the second hydraulic pump 32. The working state determination unit 92 can determine whether the arm excavation operation amount is greater than or equal to the fourth threshold value R4 based on the detection data of the arm excavation operation amount sensor 82. The working state determination unit 92 can determine whether the bucket excavation operation amount is greater than or equal to the fifth threshold value R5 based on the detection data of the bucket excavation operation amount sensor 83.

[0115] The fourth threshold value R4 is a threshold value for the PPC pressure of the arm working lever 402. The fifth threshold value R5 is a threshold value for the PPC pressure of the bucket working lever 403. The fourth threshold value R4 is higher than the first threshold value R1. The fifth threshold value R5 is higher than the second threshold value R2. As an example, the fourth threshold value R4 is 15 kg / cm 2 The fifth threshold R5 is 10kg / cm 2. After the boom working lever 402 is operated to a certain extent, the boom excavation operation amount exceeds the fourth threshold value R4. For example, after the boom working lever 402 is operated from the neutral position to more than 50% of the movable range of the boom working lever 402, the boom excavation operation amount exceeds the fourth threshold value R4. The working status judgment unit 92 can determine that the boom excavation operation is fully performed when the boom excavation operation amount is above the fourth threshold value R4. Similarly, after the bucket working lever 403 is operated to a certain extent, the bucket excavation operation amount exceeds the fifth threshold value R5. The working status judgment unit 92 can determine that the bucket excavation operation is fully performed when the bucket excavation operation amount becomes above the fifth threshold value R5.

[0116] Figure 6 Schematic diagram showing the hydraulic system 5 when determining that the working state of the working machine 10 according to the embodiment is the normal state. Figure 6 The state shown is where the hydraulic system 5 is set to the first hydraulic oil supply state.

[0117] like Figure 6 As shown, when the working state of the work machine 10 is determined to be normal, the valve control unit 93 controls the first boom operating valve 41L and the second boom operating valve 41R so that hydraulic oil is supplied from both the first hydraulic pump 31 and the second hydraulic pump 32 to the cylinder bottom chamber 21A of the boom cylinder 21. Furthermore, when the working state of the work machine 10 is determined to be normal, the valve control unit 93 controls the first arm operating valve 42L and the second arm operating valve 42R so that hydraulic oil is supplied from both the first hydraulic pump 31 and the second hydraulic pump 32 to the cylinder bottom chamber 22A of the arm cylinder 22. Furthermore, when the working state of the work machine 10 is determined to be normal, the valve control unit 93 controls the first bucket operating valve 43L and the second bucket operating valve 43R so that hydraulic oil is supplied from both the first hydraulic pump 31 and the second hydraulic pump 32 to the cylinder bottom chamber 23A of the bucket cylinder 23.

[0118] That is, when the working state of the working machine 10 is normal, the valve control unit 93 arranges the respective valve cores of the first boom operating valve 41L, the second boom operating valve 41R, the first dipper arm operating valve 42L, the second dipper arm operating valve 42R, the first bucket operating valve 43L, and the second bucket operating valve 43R at the cylinder bottom chamber supply position.

[0119] A portion of the hydraulic oil discharged from the first hydraulic pump 31 flows through the first boom operating valve 41L and is then supplied to the cylinder bottom flowpath 54. A portion of the hydraulic oil discharged from the second hydraulic pump 32 flows through the second boom operating valve 41R and is then supplied to the cylinder bottom flowpath 54. The hydraulic oil discharged from the first hydraulic pump 31 and the hydraulic oil discharged from the second hydraulic pump 32 merge in the cylinder bottom flowpath 54 and are then supplied to the cylinder bottom chamber 21A of the boom cylinder 21.

[0120] A portion of the hydraulic oil discharged from the first hydraulic pump 31 flows through the first boom operating valve 42L and is then supplied to the cylinder bottom flowpath 55. A portion of the hydraulic oil discharged from the second hydraulic pump 32 flows through the second boom operating valve 42R and is then supplied to the cylinder bottom flowpath 55. The hydraulic oil discharged from the first hydraulic pump 31 and the hydraulic oil discharged from the second hydraulic pump 32 merge in the cylinder bottom flowpath 55 and are then supplied to the cylinder bottom chamber 22A of the boom cylinder 22.

[0121] A portion of the hydraulic oil discharged from the first hydraulic pump 31 flows through the first bucket operating valve 43L and is then supplied to the cylinder bottom flowpath 56. A portion of the hydraulic oil discharged from the second hydraulic pump 32 flows through the second bucket operating valve 43R and is then supplied to the cylinder bottom flowpath 56. The hydraulic oil discharged from the first hydraulic pump 31 and the hydraulic oil discharged from the second hydraulic pump 32 merge in the cylinder bottom flowpath 56 and are then supplied to the cylinder bottom chamber 23A of the arm cylinder 23.

[0122] In addition, when it is determined that the working state of the working machine 10 is normal, the valve control unit 93 can also control the first bucket operating valve 43L and the second bucket operating valve 43R in such a way that hydraulic oil is supplied from one of the first hydraulic pump 31 and the second hydraulic pump 32 to the cylinder bottom chamber 23A of the bucket cylinder 23.

[0123] Figure 7 Schematic diagram showing the hydraulic system 5 when determining that the working state of the working machine 10 according to the embodiment is the heavy excavation state. Figure 7 The state shown is where the hydraulic system 5 is set to the second hydraulic oil supply state.

[0124] After determining that the working state of the working machine 10 has changed from Figure 6 When the normal state shown is changed to the heavy excavation state, the valve control unit 93 performs valve control so that the hydraulic system 5 changes from the first hydraulic oil supply state to the second hydraulic oil supply state.

[0125] like Figure 7 As shown, when it is determined that the working state of the work machine 10 has changed from the normal state to the heavy excavation state, the valve control unit 93 controls the first boom operating valve 41L so as to restrict the flow of hydraulic oil from the first hydraulic pump 31 to the boom cylinder 21.

[0126] When it is determined that the working state of the working machine 10 is the heavy excavation state, the valve control unit 93 controls the first boom operating valve 41L, the first arm operating valve 42L, the first bucket operating valve 43L, the second boom operating valve 41R, the second arm operating valve 42R, and the second bucket operating valve 43R in such a manner that the flow of hydraulic oil from the first hydraulic pump 31 to the boom cylinder 21 is restricted, and hydraulic oil is supplied from the second hydraulic pump 32 to the boom cylinder 21, and hydraulic oil is supplied from both the first hydraulic pump 31 and the second hydraulic pump 32 to the boom cylinder 22, and hydraulic oil is supplied from one or both of the first hydraulic pump 31 and the second hydraulic pump 32 to the bucket cylinder 23.

[0127] exist Figure 7 In the example shown, the valve element of the first boom operating valve 41L is in the neutral position. Specifically, upon determining that the state has shifted from the normal state to the heavy excavation state, the valve control unit 93 moves the valve element of the first boom operating valve 41L from the cylinder bottom chamber supply position to the neutral position, thereby restricting the flow of hydraulic oil from the first hydraulic pump 31 to the boom cylinder 21.

[0128] In the heavy excavation state, the valve element of the first boom operating valve 41L is in the neutral position. Therefore, the first boom operating valve 41L blocks the flow of hydraulic oil. The hydraulic oil discharged from the first hydraulic pump 31 is not supplied to the boom cylinder 21 .

[0129] In the heavy excavation state, the valve cores of the first arm operating valve 42L and the first bucket operating valve 43L are both in the cylinder bottom chamber supply position. Therefore, a portion of the hydraulic oil discharged from the first hydraulic pump 31 flows through the first arm operating valve 42L and is then supplied to the cylinder bottom chamber 22A of the arm cylinder 22. A portion of the hydraulic oil discharged from the first hydraulic pump 31 flows through the first bucket operating valve 43L and is then supplied to the cylinder bottom chamber 23A of the bucket cylinder 23.

[0130] In the heavy excavation state, the valve element of the second boom operating valve 41R is located at the cylinder bottom chamber supply position. Therefore, the hydraulic oil discharged from the second hydraulic pump 32 flows through the second boom operating valve 41R and is supplied to the cylinder bottom chamber 21A of the boom cylinder 21 .

[0131] In the heavy excavation state, the valve core of the second arm operating valve 42R and the valve core of the second bucket operating valve 43R are both arranged at the cylinder bottom chamber supply position. In the embodiment, the arm check valve 45R is arranged in the supply flow path 52R. Figure 7In the example shown, at least a portion of the hydraulic oil discharged from the first hydraulic pump 31 is supplied to the cylinder bottom flow path 55R and the second arm operating valve 42R. The absorption torque of the first hydraulic pump 31 is higher than the absorption torque of the second hydraulic pump 32. The pressure in the cylinder bottom flow path 55R between the arm cylinder 22 and the arm check valve 45R is higher than the pressure in the supply flow path 52R between the second hydraulic pump 32 and the arm check valve 45R. The hydraulic oil discharged from the second hydraulic pump 32 cannot flow through the arm check valve 45R. The arm check valve 45R blocks the flow of hydraulic oil discharged from the second hydraulic pump 32. Consequently, hydraulic oil cannot be supplied from the second hydraulic pump 32 to the arm cylinder 22. Furthermore, a bucket check valve 46R is disposed in the supply flow path 53R. Similar to the arm check valve 45R, the bucket check valve 46R blocks the flow of hydraulic oil discharged from the second hydraulic pump 32. Consequently, hydraulic oil cannot be supplied from the second hydraulic pump 32 to the bucket cylinder 23.

[0132] Thus, in a normal state, the hydraulic oil discharged from the first hydraulic pump 31 is distributed to the cylinder bottom chamber 21A of the boom cylinder 21, the cylinder bottom chamber 22A of the arm cylinder 22, and the cylinder bottom chamber 23A of the bucket cylinder 23. Furthermore, in a normal state, the hydraulic oil discharged from the second hydraulic pump 32 is distributed to the cylinder bottom chamber 21A of the boom cylinder 21, the cylinder bottom chamber 22A of the arm cylinder 22, and the cylinder bottom chamber 23A of the bucket cylinder 23.

[0133] In the heavy excavation state, the hydraulic oil discharged from the first hydraulic pump 31 is supplied to the cylinder bottom chamber 22A of the arm cylinder 22 and the cylinder bottom chamber 23A of the bucket cylinder 23, but is not supplied to the boom cylinder 21. The hydraulic oil discharged from the second hydraulic pump 32 is supplied to the cylinder bottom chamber 21A of the boom cylinder 21, but is not supplied to the arm cylinder 22 and the bucket cylinder 23.

[0134] In addition, if Figure 6 As shown, in the normal state, the valve spools of the first boom operating valve 41L, the second boom operating valve 41R, the first arm operating valve 42L, the second arm operating valve 42R, the first bucket operating valve 43L, and the second bucket operating valve 43R are each located at the cylinder bottom chamber supply position. When it is determined that the normal state has shifted to the heavy excavation state, the valve control unit 93 moves only the valve spool of the first boom operating valve 41L from the cylinder bottom chamber supply position to the neutral position so as to restrict the flow of hydraulic oil from the first hydraulic pump 31 to the boom cylinder 21.

[0135] Furthermore, in the heavy excavation state, the first boom operating valve 41L does not necessarily block the flow of hydraulic oil from the first hydraulic pump 31 to the boom cylinder 21. In the heavy excavation state, the first boom operating valve 41L may also supply hydraulic oil to the boom cylinder 21 at a flow rate lower than the flow rate of hydraulic oil supplied from the first hydraulic pump 31 to the boom cylinder 21 in the normal state. For example, upon determining that the heavy excavation state has shifted from the normal state, in which the valve spools of the first boom operating valve 41L, the second boom operating valve 41R, the first arm operating valve 42L, the second arm operating valve 42R, the first bucket operating valve 43L, and the second bucket operating valve 43R are positioned at the cylinder bottom chamber supply position, the valve control unit 93 may move only the valve spool of the first boom operating valve 41L to reduce the flow rate of hydraulic oil supplied from the first hydraulic pump 31 to the boom cylinder 21.

[0136] Furthermore, the arm check valve 45R and bucket check valve 46R may be omitted. If the working state of the work machine 10 is determined to be the heavy excavation state, the valve control unit 93 may move the valve element of the first boom operating valve 41L to the neutral position and place the valve element of the second boom operating valve 41R in the cylinder bottom chamber supply position to supply hydraulic oil from the second hydraulic pump 32 to the boom cylinder 21 while preventing hydraulic oil from being supplied from the first hydraulic pump 31 to the boom cylinder 21. Furthermore, if the working state of the work machine 10 is determined to be the heavy excavation state, the valve control unit 93 may move the valve element of the first arm operating valve 42L to the cylinder bottom chamber supply position and move the valve element of the second arm operating valve 42R to the neutral position to supply hydraulic oil from the first hydraulic pump 31 to the boom cylinder 22 while preventing hydraulic oil from being supplied from the second hydraulic pump 32 to the boom cylinder 22. In addition, when it is determined that the working state of the working machine 10 is a heavy excavation state, the valve control unit 93 can also configure the valve core of the first bucket operating valve 43L to the cylinder bottom chamber supply position, and configure the valve core of the second bucket operating valve 43R to the neutral position, so as to supply hydraulic oil from the first hydraulic pump 31 to the bucket cylinder 23 and not supply hydraulic oil from the second hydraulic pump 32 to the bucket cylinder 23.

[0137] Control method of hydraulic excavator

[0138] Figure 8 Flowchart 1 is a flowchart showing a method for controlling the hydraulic excavator 1 according to the embodiment. The hydraulic excavator 1 starts operating. The working state determination unit 92 determines whether the working state of the working machine 10 has changed from the normal state to the heavy excavation state (step S1).

[0139] That is, as reference Figure 5As described, the working status judgment unit 92 judges whether the working state is in the following state, that is, the boom excavation amount is greater than the first threshold value R1 or the bucket excavation operation amount is greater than the second threshold value R2, and the higher value of the boom cylinder bottom pressure and the bucket cylinder bottom pressure is higher than the boom cylinder bottom pressure.

[0140] In step S1, when it is determined that the working state of the working machine 10 has not changed from the normal state to the heavy excavation state (step S1: No), the pump control unit 94 makes the hydraulic system 5 a reference Figure 6 The valve control is performed in the manner of the first hydraulic oil supply state described above (step S2).

[0141] The pump control unit 94 performs absorption torque control so that the ratio of the upper limit value of the absorption torque Tp1 of the first hydraulic pump 31 and the upper limit value of the absorption torque Tp2 of the second hydraulic pump 32 become equal (step S3 ).

[0142] In step S1, when it is determined that the working state of the working machine 10 has changed from the normal state to the heavy excavation state (step S1: Yes), the pump control unit 94 makes the hydraulic system 5 a reference state. Figure 7 The valve control is performed in the manner of the second hydraulic oil supply state described above (step S4).

[0143] The working state determination unit 92 determines whether the boom raising operation amount in the heavy excavation state is greater than or equal to the third threshold R3, the arm excavation operation amount is greater than or equal to the fourth threshold R4, and the bucket excavation operation amount is greater than or equal to the fifth threshold R5 (step S5).

[0144] In step S5, when it is determined that the boom raising operation amount is greater than the third threshold value R3, the arm excavation operation amount is greater than the fourth threshold value R4, and the bucket excavation operation amount is greater than the fifth threshold value R5 when the heavy excavation state is not in progress (step S5: No), the pump control unit 94 performs absorption torque control in such a manner that the ratio of the upper limit value of the absorption torque Tp1 of the first hydraulic pump 31 to the upper limit value of the absorption torque Tp2 of the second hydraulic pump 32 is equal (step S3).

[0145] In step S5, if it is determined that the boom raising operation amount is greater than or equal to the third threshold R3, the arm excavation operation amount is greater than or equal to the fourth threshold R4, and the bucket excavation operation amount is greater than or equal to the fifth threshold R5 in the heavy excavation state (step S5: Yes), the pump control unit 94 performs absorption torque control so that the ratio of the upper limit value of the absorption torque Tp1 of the first hydraulic pump 31 to the upper limit value of the absorption torque Tp2 of the second hydraulic pump 32 is different. The pump control unit 94 performs absorption torque control so that the upper limit value of the absorption torque Tp1 of the first hydraulic pump 31 is greater than the upper limit value of the absorption torque Tp2 of the second hydraulic pump 32 (step S6).

[0146] Figure 9 This is a time chart illustrating a control method for a hydraulic excavator 1 according to an embodiment. At time ta, an arm excavation operation is performed on the operating device 4, and a bucket excavation operation is performed. At time tb, after time ta, if the arm excavation operation amount exceeds a first threshold value R1, the bucket excavation operation amount exceeds a second threshold value R2, and the higher of the arm cylinder bottom pressure and the bucket cylinder bottom pressure exceeds the boom cylinder bottom pressure, a heavy excavation state is determined. In the heavy excavation state, both the arm cylinder bottom pressure and the bucket cylinder bottom pressure are high. Meanwhile, the boom cylinder bottom pressure is low.

[0147] When it is determined that the working state of the working machine 10 is the heavy excavation state, the valve control unit 93 moves the valve core of the first boom operating valve 41L from the initial position to the initial position at time tc after time tb. Figure 6 The cylinder bottom cavity supply position shown is moved to Figure 7 The movement of the valve body of the first boom operating valve 41L may be started at time tb or at a time between time tb and time tc.

[0148] The hydraulic oil discharged from the first hydraulic pump 31 is supplied to the cylinder bottom chamber 22A of the arm cylinder 22 and the cylinder bottom chamber 23A of the bucket cylinder 23. The hydraulic oil discharged from the second hydraulic pump 32 is supplied to the cylinder bottom chamber 21A of the boom cylinder 21.

[0149] In a heavy excavation state where the excavation load applied to the work machine 10 becomes high, the operator performs a boom raising operation in order to reduce the excavation load applied to the bucket 13 and the arm 12. Figure 9 In the example shown, the boom raising operation starts at time tc. As the boom raising operation is performed, the boom cylinder bottom pressure increases.

[0150] After the boom raising operation begins, at time td after time tc, the pump control unit 94 begins absorption torque control, which changes the ratio of the upper limit value of the absorption torque Tp1 of the first hydraulic pump 31 to the upper limit value of the absorption torque Tp2 of the second hydraulic pump 32 so that the upper limit value of the absorption torque Tp1 of the first hydraulic pump 31 is higher than the upper limit value of the absorption torque Tp2 of the second hydraulic pump 32. As the upper limit value of the absorption torque Tp1 of the first hydraulic pump 31 increases, hydraulic oil is smoothly supplied from the first hydraulic pump 31 to the arm cylinder 22 and bucket cylinder 23, respectively.

[0151] At time te after time td, when the arm excavation operation is completed, the working state determination unit 92 determines that the working state of the working machine 10 has become the normal state.

[0152] Computer system

[0153] Figure 10 : is a block diagram showing a computer system 1000 involved in an embodiment. The above-mentioned control device 9 includes a computer system 1000. The computer system 1000 has: a processor 1001, such as a CPU (Central Processing Unit); a main memory 1002, which includes a non-volatile memory such as a ROM (Read Only Memory) and a volatile memory such as a RAM (Random Access Memory); a memory 1003; and an interface 1004, which includes an input and output circuit. The functions of the control device 9 are stored in the memory 1003 as a computer program. The processor 1001 reads the computer program from the memory 1003 and loads it into the main memory 1002, and performs the above-mentioned processing according to the computer program. In addition, the computer program can also be transmitted to the computer system 1000 via a network.

[0154] Effect

[0155] As described above, according to the embodiment, when the working state of the work machine 10 is determined to be the normal state, hydraulic oil is supplied from both the first hydraulic pump 31 and the second hydraulic pump 32 to the cylinder bottom chamber 21A of the boom cylinder 21, hydraulic oil is supplied from both the first hydraulic pump 31 and the second hydraulic pump 32 to the cylinder bottom chamber 22A of the arm cylinder 22, and hydraulic oil is supplied from one or both of the first hydraulic pump 31 and the second hydraulic pump 32 to the cylinder bottom chamber 23A of the bucket cylinder 23. Thus, when the working state of the work machine 10 is the normal state, the hydraulic oil discharged from the first hydraulic pump 31 and the second hydraulic pump 32 is appropriately distributed to the cylinder bottom chamber 21A of the boom cylinder 21, the cylinder bottom chamber 22A of the arm cylinder 22, and the cylinder bottom chamber 23A of the bucket cylinder 23, respectively.

[0156] If the working state of the work machine 10 is determined to be the heavy excavation state, hydraulic oil is supplied from the second hydraulic pump 32 to the cylinder bottom chamber 21A of the boom cylinder 21, and the supply of hydraulic oil from the first hydraulic pump 31 to the boom cylinder 21 is blocked. Furthermore, if the working state of the work machine 10 is determined to be the heavy excavation state, hydraulic oil is supplied from the first hydraulic pump 31 to the cylinder bottom chamber 22A of the arm cylinder 22 and the cylinder bottom chamber 23A of the bucket cylinder 23, and the supply of hydraulic oil from the second hydraulic pump 32 to the arm cylinder 22 and the bucket cylinder 23 is blocked.

[0157] In the heavy excavation state, the arm cylinder 22 and the bucket cylinder 23 are each subjected to the excavation reaction force that causes them to retract. Therefore, the arm cylinder bottom pressure and the bucket cylinder bottom pressure each increase. On the other hand, the weight of the work machine 10 applied to the boom cylinder 21 is reduced by the excavation reaction force. Therefore, the boom cylinder bottom pressure is lower than the arm cylinder bottom pressure and the bucket cylinder bottom pressure. In the heavy excavation state, if the supply of hydraulic oil from the first hydraulic pump 31 to the cylinder bottom chamber 21A of the boom cylinder 21 is not blocked, the hydraulic oil discharged from the first hydraulic pump 31 is supplied to the boom cylinder 21, resulting in an increased possibility of insufficient pressure of the hydraulic oil supplied to the cylinder bottom chamber 22A of the arm cylinder 22 and the hydraulic oil supplied to the cylinder bottom chamber 23A of the bucket cylinder 23. As a result, the excavation force of the work machine 10 may be reduced.

[0158] In the embodiment, in the heavy excavation state, the supply of hydraulic oil from the first hydraulic pump 31 to the cylinder bottom chamber 21A of the boom cylinder 21 is blocked. Therefore, the pressure of the hydraulic oil supplied to the cylinder bottom chamber 22A of the arm cylinder 22 and the pressure of the hydraulic oil supplied to the cylinder bottom chamber 23A of the bucket cylinder 23 are suppressed. The boom cylinder 21 can operate based on the hydraulic oil supplied from the second hydraulic pump 32. Therefore, when the working state of the work machine 10 is the heavy excavation state, the hydraulic oil discharged from the first hydraulic pump 31 and the second hydraulic pump 32 are also appropriately distributed to the cylinder bottom chamber 21A of the boom cylinder 21, the cylinder bottom chamber 22A of the arm cylinder 22, and the cylinder bottom chamber 23A of the bucket cylinder 23.

[0159] In the heavy excavation state, where the excavation load applied to the work machine 10 increases, the operator often performs a boom-up operation to reduce the excavation load applied to the bucket 13 and arm 12. When the work machine 10 is determined to be in the heavy excavation state and the boom-up operation is performed, the pump control unit 94 increases the absorption torque of the first hydraulic pump 31 to be higher than the absorption torque of the second hydraulic pump 32. In the heavy excavation state, the first hydraulic pump 31 supplies hydraulic oil to both the arm cylinder 22 and the bucket cylinder 23, while the second hydraulic pump 32 supplies hydraulic oil to the arm cylinder 21. Therefore, in the heavy excavation state, by increasing the absorption torque of the first hydraulic pump 31, insufficient hydraulic oil supplied to the arm cylinder 22 and the bucket cylinder 23 is prevented.

[0160] Explanation of symbols

[0161] 1…Hydraulic excavator; 2…Slewing unit; 2A…Operating cab; 2B…Operating seat; 3…Traveling unit; 3A…Crawler tracks; 4…Operating device; 5…Hydraulic system; 6…Engine; 7…Fuel tank; 9…Control device; 10…Working machine; 11…Boom; 12…Arm; 13…Bucket; 21…Boom cylinder; 21A…Cylinder bottom chamber; 21B…Rod chamber; 22…Arm cylinder; 22A…Cylinder bottom chamber; 22B…Rod chamber; 23…Bucket cylinder; 23A…Cylinder bottom chamber; 23B…Rod chamber; 31…First hydraulic pump; 31A…Swash plate; 32…Second hydraulic pump; 32A…Swash plate; 40L…First operating valve group; 40R…Second operating valve group 41L…First boom operating valve; 41R…Second boom operating valve; 42L…First arm operating valve; 42R…Second arm operating valve; 43L…First bucket operating valve; 43R…Second bucket operating valve; 44L…Boom check valve; 44R…Boom check valve; 45L…Arm check valve; 45R…Arm check valve; 46L…Bucket check valve; 46R…Bucket check valve; 50L…Discharge flow path; 50R…Discharge flow path; 51L…Supply flow path; 51R…Supply flow path; 52L…Supply flow path; 52R…Supply flow path; 53L…Supply flow path; 53R…Supply flow path; 54…Cylinder bottom flow path; 54L…Cylinder bottom flow path Path; 54R…cylinder bottom flow path; 55…cylinder bottom flow path; 55L…cylinder bottom flow path; 55R…cylinder bottom flow path; 56…cylinder bottom flow path; 56L…cylinder bottom flow path; 56R…cylinder bottom flow path; 57…rod chamber flow path; 57L…rod chamber flow path; 57R…rod chamber flow path; 58…rod chamber flow path; 58L…rod chamber flow path; 58R…rod chamber flow path; 59…rod chamber flow path; 59L…rod chamber flow path; 59R…rod chamber flow path; 61L…discharge flow path; 61R…discharge flow path; 62L…discharge flow path; 62R…discharge flow path; 63L…discharge flow path; 63R…discharge flow path; 64L…neutral flow path; 64R…neutral flow path; 65L…negative Control mechanism; 65R…Negative control mechanism; 71…First discharge pressure sensor; 72…Second discharge pressure sensor; 73…Boom cylinder bottom pressure sensor; 74…Boom rod pressure sensor; 75…Boom cylinder bottom pressure sensor; 76…Boom rod pressure sensor; 77…Bucket cylinder bottom pressure sensor; 78…Bucket rod pressure sensor; 81…Boom operation amount sensor; 82…Boom operation amount sensor; 83…Bucket operation amount sensor; 91…Detection data acquisition unit; 92…Working status judgment unit; 93…Valve control unit; 94…Pump control unit; 95…Storage unit; 401…Boom operating lever; 402…Boom operating lever; 403…Bucket operating lever.

Claims

1. A hydraulic system for a hydraulic excavator, characterized in that: have: First hydraulic pump; a second hydraulic pump; A boom cylinder, which is used to move the boom of the working machine; A boom cylinder, used to move the boom of the working machine; a bucket cylinder for actuating the bucket of the working machine; a first boom operating valve for controlling the flow of hydraulic oil from the first hydraulic pump toward the boom cylinder; a first boom operating valve for controlling the flow of hydraulic oil from the first hydraulic pump toward the boom cylinder; a first bucket operating valve for controlling the flow of hydraulic oil from the first hydraulic pump toward the bucket cylinder; a second boom operating valve for controlling the flow of hydraulic oil from the second hydraulic pump toward the boom cylinder; a second boom operating valve for controlling the flow of hydraulic oil from the second hydraulic pump toward the boom cylinder; a second bucket operating valve for controlling the flow of hydraulic oil from the second hydraulic pump toward the bucket cylinder; an arm check valve for inhibiting hydraulic oil from flowing back from the arm cylinder to the second hydraulic pump via the second arm operating valve; a bucket check valve for inhibiting hydraulic oil from flowing back from the bucket cylinder to the second hydraulic pump via the second bucket operating valve; an operating device that is operated to actuate at least one of the boom cylinder, the arm cylinder, and the bucket cylinder; a working state determining unit for determining the working state of the working machine based on the operating state of the operating device, a boom cylinder bottom pressure indicating the pressure of the cylinder bottom chamber of the boom cylinder, an arm cylinder bottom pressure indicating the pressure of the cylinder bottom chamber of the arm cylinder, and a bucket cylinder bottom pressure indicating the pressure of the cylinder bottom chamber of the bucket cylinder; as well as a valve control unit that controls at least one of the first boom operating valve, the first arm operating valve, the first bucket operating valve, the second boom operating valve, the second arm operating valve, and the second bucket operating valve based on the operating state of the work machine determined by the operating state determination unit; The working state judgment unit determines that the working state of the working machine is a normal state when the arm excavation operation amount of the operating device is greater than a first threshold value or the bucket excavation operation amount of the operating device is greater than a second threshold value, and the boom cylinder bottom pressure is higher than the higher value of the arm cylinder bottom pressure and the bucket cylinder bottom pressure, and determines that the working state of the working machine is a heavy excavation state when the higher value of the arm cylinder bottom pressure and the bucket cylinder bottom pressure is higher than the boom cylinder bottom pressure. When it is determined that the working state of the working machine is a heavy excavation state, The valve control unit controls the first boom operating valve, the first arm operating valve, the first bucket operating valve, the second boom operating valve, the second arm operating valve, and the second bucket operating valve in such a manner that the flow of hydraulic oil from the first hydraulic pump to the boom cylinder is restricted, hydraulic oil is supplied from the second hydraulic pump to the boom cylinder, hydraulic oil is supplied from both the first hydraulic pump and the second hydraulic pump to the arm cylinder, and hydraulic oil is supplied from one or both of the first hydraulic pump and the second hydraulic pump to the bucket cylinder.

2. The hydraulic system of a hydraulic excavator according to claim 1, characterized in that: When it is determined that the working state of the working machine is a normal state, The valve control unit controls the first boom operating valve, the first arm operating valve, the first bucket operating valve, the second boom operating valve, the second arm operating valve, and the second bucket operating valve in such a manner that hydraulic oil is supplied to the boom cylinder from both the first hydraulic pump and the second hydraulic pump, and hydraulic oil is supplied to the arm cylinder from both the first hydraulic pump and the second hydraulic pump, and hydraulic oil is supplied to the bucket cylinder from one or both of the first hydraulic pump and the second hydraulic pump.

3. The hydraulic system of a hydraulic excavator according to claim 2, characterized in that: In the normal state, the valve cores of the first boom operating valve, the second boom operating valve, the first arm operating valve, the second arm operating valve, the first bucket operating valve, and the second bucket operating valve are arranged at cylinder bottom chamber supply positions; When it is determined that the state has changed from the normal state to the heavy excavation state, the valve control unit moves only the valve body of the first boom operating valve so as to restrict the flow of hydraulic oil from the first hydraulic pump to the boom cylinder.

4. The hydraulic system of a hydraulic excavator according to any one of claims 1 to 3, characterized in that: have: A bucket arm operation amount sensor, which is used to detect the bucket arm operation amount of the operating device; a bucket operation amount sensor for detecting the bucket operation amount of the operating device; A boom cylinder bottom pressure sensor, used to detect the boom cylinder bottom pressure; and Bucket cylinder bottom pressure sensor, which is used to detect the bucket cylinder bottom pressure, The working state determination unit determines the working state based on detection data of the arm operation amount sensor, detection data of the bucket operation amount sensor, detection data of the arm cylinder bottom pressure sensor, and detection data of the bucket cylinder bottom pressure sensor.

5. The hydraulic system of a hydraulic excavator according to any one of claims 1 to 3, characterized in that: have: The pump control unit is configured to make an upper limit value of the absorption torque of the first hydraulic pump higher than an upper limit value of the absorption torque of the second hydraulic pump when it is determined that the boom raising operation amount in the heavy excavation state is equal to or greater than a third threshold value.

6. The hydraulic system of a hydraulic excavator according to claim 5, characterized in that: have: a boom operation amount sensor for detecting the boom operation amount of the operating device; The working state determination unit determines whether the boom raising operation amount is equal to or greater than the third threshold value based on detection data of the boom operation amount sensor.

7. The hydraulic system of a hydraulic excavator according to claim 5, characterized in that: When it is determined that the arm excavation operation amount is equal to or greater than a fourth threshold value and the bucket excavation operation amount is equal to or greater than a fifth threshold value in the heavy excavation state, the pump control unit sets an upper limit value of the absorption torque of the first hydraulic pump higher than an upper limit value of the absorption torque of the second hydraulic pump.

8. A hydraulic excavator, characterized in that: have: A hydraulic system for a hydraulic excavator according to any one of claims 1 to 7.

9. A method for controlling a hydraulic excavator, the hydraulic excavator comprising: First hydraulic pump; a second hydraulic pump; A boom cylinder, which is used to move the boom of the working machine; A boom cylinder, used to move the boom of the working machine; a bucket cylinder for actuating the bucket of the working machine; a first boom operating valve for controlling the flow of hydraulic oil from the first hydraulic pump toward the boom cylinder; a first boom operating valve for controlling the flow of hydraulic oil from the first hydraulic pump toward the boom cylinder; a first bucket operating valve for controlling the flow of hydraulic oil from the first hydraulic pump toward the bucket cylinder; a second boom operating valve for controlling the flow of hydraulic oil from the second hydraulic pump toward the boom cylinder; a second boom operating valve for controlling the flow of hydraulic oil from the second hydraulic pump toward the boom cylinder; a second bucket operating valve for controlling the flow of hydraulic oil from the second hydraulic pump toward the bucket cylinder; an arm check valve for inhibiting hydraulic oil from flowing back from the arm cylinder to the second hydraulic pump via the second arm operating valve; a bucket check valve for inhibiting hydraulic oil from flowing back from the bucket cylinder to the second hydraulic pump via the second bucket operating valve; and An operating device is operated to actuate at least one of the boom cylinder, the arm cylinder, and the bucket cylinder, wherein the control method for the hydraulic excavator is characterized in that: determining an operating state of the work machine based on an operating state of the operating device, a boom cylinder bottom pressure indicating a pressure in a cylinder bottom chamber of the boom cylinder, an arm cylinder bottom pressure indicating a pressure in a cylinder bottom chamber of the arm cylinder, and a bucket cylinder bottom pressure indicating a pressure in a cylinder bottom chamber of the bucket cylinder; When the arm excavation operation amount of the operating device is greater than a first threshold value or the bucket excavation operation amount of the operating device is greater than a second threshold value, and the boom cylinder bottom pressure is higher than the higher value of the arm cylinder bottom pressure and the bucket cylinder bottom pressure, the operating state of the working machine is determined to be a normal state, and when the higher value of the arm cylinder bottom pressure and the bucket cylinder bottom pressure is higher than the boom cylinder bottom pressure, the operating state of the working machine is determined to be a heavy excavation state. When it is determined that the working state of the working machine is a heavy excavation state, The first boom operating valve, the first arm operating valve, the first bucket operating valve, the second boom operating valve, the second arm operating valve, and the second bucket operating valve are controlled in such a manner that the flow of hydraulic oil from the first hydraulic pump toward the boom cylinder is restricted, hydraulic oil is supplied to the boom cylinder from the second hydraulic pump, hydraulic oil is supplied to the arm cylinder from both the first hydraulic pump and the second hydraulic pump, and hydraulic oil is supplied to the bucket cylinder from one or both of the first hydraulic pump and the second hydraulic pump.

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