Construction machinery

Abstract

To provide a construction machine capable of suppressing deterioration of a closed circuit pump.SOLUTION: A construction machine includes a work device having a hydraulic actuator and performing excavation work, a posture detecting device for detecting a posture of the work device, an operation device for operating the work device, a closed circuit pump connected to the hydraulic actuator by a closed circuit, an opened circuit pump connected to the hydraulic actuator by an opened circuit, a charge pump, a charge flow channel for guiding working fluid discharged from the charge pump to the closed circuit, a surplus oil discharge device for discharging the surplus working fluid in the closed circuit to the charge flow channel, and a controller for controlling discharge capacity of the closed circuit pump and the opened circuit pump. The controller determines whether or not the excavation work is performed on the basis of a signal from the posture detecting device and the operation device, and when a transition is made from a state in which the excavation work is not performed to a state in which the excavation work is performed, the controller increases the discharge capacity of the opened circuit pump and decreases the discharge capacity of the closed circuit pump.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to a construction machine. [Background technology]

[0002] There is known a construction machine (working machine) equipped with a hydraulic oil flow path that forms a closed circuit between a hydraulic pump and a hydraulic cylinder, and a charge circuit connected to the hydraulic oil flow path to make up for a shortage of hydraulic oil in the closed circuit due to a difference in the pressure-receiving area between the rod-side oil chamber and the bottom-side oil chamber of the hydraulic cylinder (see Patent Document 1).The charge circuit described in Patent Document 1 has a charge flow path connected to the hydraulic oil flow path and a charge pump that discharges hydraulic oil into the charge flow path, and replenishes hydraulic oil to the hydraulic oil flow path when the pressure in the hydraulic oil flow path becomes lower than the pressure in the charge flow path. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-174325 Summary of the Invention [Problem to be solved by the invention]

[0004] In the construction machine described in Patent Document 1, if the bucket hits hard soil or the like during excavation, restricting the operation of the hydraulic cylinder, the return oil from the hydraulic cylinder decreases, causing a drop in pressure in the hydraulic oil passage. When the pressure in the hydraulic oil passage becomes lower than the pressure in the charge passage, hydraulic oil is replenished from the charge circuit to the hydraulic oil passage. However, there is a possibility that the amount of oil replenished may momentarily fall short of the required flow rate to be supplied to the closed-circuit pump. In this case, negative pressure is created in the charge passage and the hydraulic oil passage, making cavitation more likely to occur. Furthermore, if this occurs repeatedly, it may accelerate the deterioration of the closed-circuit pump over time.

[0005] An object of the present invention is to provide a construction machine that can suppress deterioration of a closed circuit pump. [Means for solving the problem]

[0006] A construction machine according to one aspect of the present invention includes an articulated working device having a plurality of hydraulic actuators for performing excavation work, an attitude detection device for detecting the attitude of the working device, an operating device for operating the working device, a closed-circuit pump connected to the hydraulic actuators by a closed circuit for supplying and discharging hydraulic oil to the hydraulic actuators, an open-circuit pump connected to the hydraulic actuators by an open circuit for supplying hydraulic oil to the hydraulic actuators, a charge pump, a charge flow path for directing hydraulic oil discharged from the charge pump to the closed circuit, an excess oil discharge device for discharging excess hydraulic oil from the closed circuit to the charge flow path, and a controller for controlling the discharge capacities of the closed-circuit pump and the open-circuit pump. The controller determines whether the working device is performing excavation work based on a signal from the attitude detection device and a signal from the operating device, and when the working device transitions from a state in which excavation work is not being performed to a state in which excavation work is being performed, the controller increases the discharge capacity of the open-circuit pump and decreases the discharge capacity of the closed-circuit pump. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a construction machine that can suppress deterioration of a closed circuit pump. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a side view of a hydraulic excavator shown as an example of a construction machine according to an embodiment of the present invention. [Figure 2] FIG. 2 is a diagram showing a hydraulic system mounted on a hydraulic excavator. [Figure 3] FIG. 3 is a hardware configuration diagram of the controller. [Figure 4] FIG. 4 is a functional block diagram of the controller. [Figure 5]FIG. 5 is a diagram showing a first discharge flow rate table and a second discharge flow rate table stored in the nonvolatile memory. [Figure 6] FIG. 6 is a diagram illustrating an example of the calculation process for the attitude of the working device. [Figure 7] FIG. 7 is a flowchart showing an example of an excavation determination process executed by the controller. [Figure 8] FIG. 8 is a flowchart showing an example of flow rate control executed by the controller. DETAILED DESCRIPTION OF THE INVENTION

[0009] A construction machine according to an embodiment of the present invention will be described with reference to the drawings.

[0010] Fig. 1 is a side view of a hydraulic excavator 100 shown as an example of a construction machine according to an embodiment of the present invention. As shown in Fig. 1, the hydraulic excavator 100 comprises a crawler-type running body 30, a revolving body (car body) 40 that is rotatably provided relative to the running body 30, and a front working mechanism (hereinafter referred to as the working mechanism) 20 that is attached to the revolving body 40 and performs excavation work. In addition to the hydraulic excavator 100, the present invention is applicable to various other working machines that perform excavation work at construction sites, mining sites, etc. using working mechanisms, including construction machines such as wheel loaders.

[0011] The traveling body 30 is provided with a pair of left and right hydraulic motors for traveling (hereinafter referred to as traveling motors) 31. The left and right traveling motors 31 independently rotate and drive the left and right crawlers, thereby causing the traveling body 30 to travel forward or backward.

[0012] The rotating body 40 is provided with an operating cab 41 in which operating devices for performing various operations of the hydraulic excavator 100 and a driver's seat where an operator sits are located. The operating devices include an operating device for operating the work implement 20, an operating device for operating the traveling body 30, and an operating device for operating the rotating body 40.

[0013] The revolving unit 40 is equipped with a prime mover such as an engine, a hydraulic pump driven by the engine, and a hydraulic motor for revolving (hereinafter referred to as a revolving motor) 42. The revolving unit 40 is revolved to the right or left relative to the traveling unit 30 by the revolving motor 42.

[0014] The working device 20 is an articulated working device attached to the revolving unit 40, and has a plurality of hydraulic actuators (hydraulic cylinders) and a plurality of (three in this embodiment) driven members that are driven by the plurality of hydraulic actuators. The driven members are the boom 24, arm 23, and bucket 22, which are connected in series. The base end of the boom 24 is rotatably connected to the front of the revolving unit 40 via a boom pin. The base end of the arm 23 is rotatably connected to the tip of the boom 24 via an arm pin. The bucket 22 is rotatably connected to the tip of the arm 23 via a bucket pin.

[0015] The boom 24 is rotationally driven by the extension and retraction of a boom cylinder 27, which is a hydraulic cylinder. The arm 23 is rotationally driven by the extension and retraction of an arm cylinder 26, which is a hydraulic cylinder. The bucket 22 is rotationally driven by the extension and retraction of a bucket cylinder 25, which is a hydraulic cylinder. One end of the boom cylinder 27 is connected to the boom 24, and the other end is connected to the frame of the revolving unit 40. One end of the arm cylinder 26 is connected to the arm 23, and the other end is connected to the boom 24. One end of the bucket cylinder 25 is connected to the bucket 22 via a bucket link, and the other end is connected to the arm 23.

[0016] 2 is a diagram showing a hydraulic system 60 mounted on the hydraulic excavator 100. The hydraulic system 60 includes a plurality of hydraulic circuits for driving a plurality of hydraulic actuators (25 to 27, 31, 42).

[0017] 2 shows only the hydraulic circuit that drives the arm cylinder 26, and does not show the hydraulic circuits that drive the other hydraulic actuators (25, 27, 31, 42).

[0018] The arm cylinder 26 includes a cylindrical cylinder tube with one end closed and a bottom, a head cover that closes the opening at the other end of the cylinder tube, a cylinder rod 26r that penetrates the head cover and is inserted into the cylinder tube, and a piston 26p that is provided at the tip of the cylinder rod 26r and divides the inside of the cylinder tube into a rod-side oil chamber 26b and a bottom-side oil chamber 26a.

[0019] As shown in Fig. 2, the hydraulic system 60 includes a closed circuit pump 1 connected to the arm cylinder 26 by a closed circuit Cc to supply and discharge hydraulic oil to the arm cylinder 26, an open circuit pump 3 connected to the arm cylinder 26 by an open circuit Oc to supply hydraulic oil to the arm cylinder 26, and a controller 7 that controls the discharge capacity (displacement volume) of the closed circuit pump 1 and the open circuit pump 3. The discharge capacity is the amount of discharge per rotation of the pump. The closed circuit Cc is a circuit that returns return oil from the hydraulic actuator to the pump. The open circuit Oc is a circuit that does not return return oil from the hydraulic actuator to the pump, and is configured, for example, so that return oil from the hydraulic actuator returns to a tank (not shown).

[0020] The hydraulic system 60 also includes an arm operating device 8A that instructs the operation of the arm cylinder 26, a boom operating device 8B that instructs the operation of the boom cylinder 27, an arm angle sensor 23S that detects the rotation angle of the arm 23, and a boom angle sensor 24S that detects the rotation angle of the boom 24.

[0021] The arm operating device 8A has a tiltable arm operating lever 8Ab and an arm operation amount sensor 8Aa that detects the operation amount (tilt angle) of the arm operating lever 8Ab. The boom operating device 8B has a tiltable boom operating lever 8Bb and a boom operation amount sensor 8Ba that detects the operation amount (tilt angle) of the boom operating lever 8Bb.

[0022] The arm operation amount sensor 8Aa and the boom operation amount sensor 8Ba are electrically connected to the controller 7. The arm operation amount sensor 8Aa detects the operation amount of the arm operation lever 8Ab, and outputs a signal representing the detection result to the controller 7. The boom operation amount sensor 8Ba detects the operation amount of the boom operation lever 8Bb, and outputs a signal representing the detection result to the controller 7.

[0023] The arm operating device 8A that operates the arm 23 and the boom operating device 8B that operates the boom 24 constitute an operating device 8 that operates the working device 20.

[0024] The arm angle sensor 23S and the boom angle sensor 24S are electrically connected to the controller 7. The arm angle sensor 23S detects the rotation angle of the arm 23 and outputs a signal representing the detection result to the controller 7. The boom angle sensor 24S detects the rotation angle of the boom 24 and outputs a signal representing the detection result to the controller 7.

[0025] The arm angle sensor 23S and the boom angle sensor 24S are, for example, potentiometers that acquire the rotation angle of the member to be driven and output a signal (voltage) corresponding to the acquired angle to the controller 7. The arm angle sensor 23S and the boom angle sensor 24S may be ground angle sensors. Furthermore, the attitude sensor constituting the attitude detection device 10 may be an IMU (Inertial Measurement Unit).

[0026] The arm angle sensor 23S is a posture sensor that detects the posture of the arm 23, and the boom angle sensor 24S is a posture sensor that detects the posture of the boom 24. In other words, the arm angle sensor 23S and the boom angle sensor 24S constitute a posture detection device 10 that detects the posture of the work implement 20.

[0027] Furthermore, the hydraulic system 60 includes a first switching valve 15a, a second switching valve 15b, a first relief valve 19a, a second relief valve 19b, a flushing valve 16, a charge circuit 63, a tank 17, and an engine 5.

[0028] The closed circuit pump 1 and the open circuit pump 3 are rotationally driven by an engine 5 and discharge hydraulic oil. The engine 5 is a power source for the hydraulic excavator 100 and is configured by an internal combustion engine such as a diesel engine. The hydraulic oil is stored in a tank 17.

[0029] The closed circuit pump 1 is a variable displacement hydraulic pump whose discharge capacity (displacement volume) is variable. The closed circuit pump 1 is, for example, a swash plate type hydraulic pump or a bent axis type hydraulic pump.

[0030] The discharge capacity of the closed circuit pump 1 is controlled by a regulator for the closed circuit pump (hereinafter referred to as the first regulator) 2. The first regulator 2 controls the tilt angle of the swash plate or bevel axis of the closed circuit pump 1 based on a control signal from a controller 7, thereby controlling the discharge capacity of the closed circuit pump 1. The discharge flow rate of the closed circuit pump 1 is determined according to the discharge capacity of the closed circuit pump 1 and the rotation speed of the engine 5.

[0031] The closed circuit pump 1 is a bi-directional hydraulic pump that can discharge hydraulic oil in two directions. The closed circuit pump 1 has a first pump port 1a and a second pump port 1b. The closed circuit pump 1 can be switched between a first discharge state and a second discharge state. In the first discharge state, the closed circuit pump 1 draws hydraulic oil from the second pump port 1b and discharges it from the first pump port 1a. In the second discharge state, the closed circuit pump 1 draws hydraulic oil from the first pump port 1a and discharges it from the second pump port 1b.

[0032] The first pump port 1a of the closed circuit pump 1 and the bottom-side oil chamber 26a of the arm cylinder 26 are connected by a first flow path 61. The second pump port 1b of the closed circuit pump 1 and the rod-side oil chamber 26b of the arm cylinder 26 are connected by a second flow path 62. In this embodiment, the closed circuit pump 1 and the arm cylinder 26 are connected by the first flow path 61 and the second flow path 62, thereby forming a closed circuit Cc.

[0033] The open circuit pump 3 is a variable displacement hydraulic pump whose discharge capacity (displacement volume) is changeable. The open circuit pump 3 is, for example, a swash plate type hydraulic pump or a bent axis type hydraulic pump.

[0034] The discharge capacity of the open circuit pump 3 is controlled by a regulator for the open circuit pump (hereinafter referred to as the second regulator) 4. The second regulator 4 controls the tilt angle of the swash plate or the beveled axis of the open circuit pump 3 based on a control signal from a controller 7, thereby controlling the discharge capacity of the open circuit pump 3. The discharge flow rate of the open circuit pump 3 is determined according to the discharge capacity of the open circuit pump 3 and the rotation speed of the engine 5.

[0035] The open circuit pump 3 is a one-way tilting hydraulic pump that can discharge hydraulic oil in one direction. The open circuit pump 3 has a pump port 3a and a suction port 3b. The open circuit pump 3 draws hydraulic oil from the tank 17 through the suction port 3b and discharges it from the pump port 3a.

[0036] The pump port 3a of the open circuit pump 3 is connected to the first flow path 61 via a first switching valve 15a. The pump port 3a of the open circuit pump 3 is connected to the second flow path 62 via a second switching valve 15b.

[0037] The first switching valve 15a and the second switching valve 15b are, for example, two-port, two-position electromagnetic switching valves. The first switching valve 15a and the second switching valve 15b are switched to an open position or a closed position based on a control signal from the controller 7. When not energized, the first switching valve 15a and the second switching valve 15b are switched to the closed position by the biasing force of a spring.

[0038] When the first switching valve 15a is switched to the open position, the discharge flow path of the open circuit pump 3 communicates with the first flow path 61 via the first switching valve 15a. When the first switching valve 15a is switched to the closed position, the communication between the discharge flow path of the open circuit pump 3 and the first flow path 61 is blocked by the first switching valve 15a.

[0039] When the second switching valve 15b is switched to the open position, the discharge flow path of the open circuit pump 3 communicates with the second flow path 62 via the second switching valve 15b. When the second switching valve 15b is switched to the closed position, the communication between the discharge flow path of the open circuit pump 3 and the second flow path 62 is blocked by the second switching valve 15b.

[0040] The first relief valve 19a is connected to the first flow path 61 and determines the maximum pressure of the first flow path 61. The second relief valve 19b is connected to the second flow path 62 and determines the maximum pressure of the second flow path 62.

[0041] The charge circuit 63 includes a charge pump 9, a charge flow path 11 that guides hydraulic oil discharged from the charge pump 9 to the closed circuit Cc through a first makeup valve 66a or a second makeup valve 66b, and a charge relief valve 65 that determines the maximum pressure of the charge flow path 11.

[0042] The charge pump 9 is a fixed displacement hydraulic pump with a constant discharge capacity. The charge pump 9 is, for example, a gear pump. The charge pump 9 is driven by the engine 5 and draws in and discharges hydraulic oil from the tank 17.

[0043] The set pressure of charge relief valve 65 is set to, for example, about 2 MPa. Charge relief valve 65 discharges excess hydraulic oil discharged from charge pump 9 to tank 17, and maintains the pressure in charge flow path 11 at 2 MPa.

[0044] The pump port 9 a of the charge pump 9 is connected to the charge flow path 11 , and the suction port 9 b of the charge pump 9 is connected to the tank 17 .

[0045] Charge passage 11 is connected to first passage 61 via first makeup valve 66a. First makeup valve 66a is a check valve that allows hydraulic oil to flow from charge passage 11 to first passage 61 and prohibits hydraulic oil from flowing from first passage 61 to charge passage 11.

[0046] Additionally, charge passage 11 is connected to second passage 62 via second makeup valve 66b. Second makeup valve 66b is a check valve that allows hydraulic oil to flow from charge passage 11 to second passage 62 and prohibits hydraulic oil from flowing from second passage 62 to charge passage 11.

[0047] Charge pump 9 draws hydraulic oil from tank 17 and discharges it into charge passage 11. The hydraulic oil discharged from charge pump 9 into charge passage 11 is replenished into closed circuit Cc via first makeup valve 66a or second makeup valve 66b.

[0048] The flushing valve 16 is connected to the first flow path 61, the second flow path 62, and the charge flow path 11, and is an excess oil discharge device that discharges excess hydraulic oil (hereinafter also referred to as excess oil) in the closed circuit Cc into the charge flow path 11.

[0049] The flushing valve 16 connects the higher-pressure one of the first and second flow paths 61 and 62 to the charge flow path 11. When the pressure in the first flow path 61 is higher than the pressure in the second flow path 62, the flushing valve 16 moves in a first direction D1, and the first flow path 61 and the charge flow path 11 communicate via the flushing valve 16. When the pressure in the second flow path 62 is higher than the pressure in the first flow path 61, the flushing valve 16 moves in a second direction D2, and the second flow path 62 and the charge flow path 11 communicate via the flushing valve 16.

[0050] The first regulator 2, the second regulator 4, the first switching valve 15a, and the second switching valve 15b are electrically connected to the controller 7. Based on signals from the operation device 8 and the attitude detection device 10, the controller 7 outputs control signals to the first regulator 2, the second regulator 4, the first switching valve 15a, and the second switching valve 15b.

[0051] FIG. 3 is a hardware configuration diagram of the controller 7. As shown in FIG. 3, the controller 7 is composed of a computer including a processing device 71 such as a CPU (Central Processing Unit), MPU (Micro Processing Unit), or DSP (Digital Signal Processor), a non-volatile memory 72 such as a ROM (Read Only Memory), flash memory, or hard disk drive, a volatile memory 73 called RAM (Random Access Memory), an input interface 74, an output interface 75, and other peripheral circuits. The controller 7 may be composed of one computer or multiple computers. The processing device 71 may be an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), or the like.

[0052] Programs capable of executing various calculations are stored in the nonvolatile memory 72. In other words, the nonvolatile memory 72 is a storage medium from which programs that realize the functions of this embodiment can be read.

[0053] The processing unit 71 loads a program stored in the nonvolatile memory 72 into the volatile memory 73 and executes the program. The processing unit 71 performs predetermined arithmetic processing on signals received from the input interface 74, the nonvolatile memory 72, and the volatile memory 73 in accordance with the program.

[0054] The input interface 74 converts signals input from various devices (such as the operating device 8 and the attitude detection device 10) into data that can be calculated by the processing device 71. The output interface 75 generates an output signal according to the calculation result in the processing device 71, and outputs the signal to various devices (such as the first switching valve 15a, the second switching valve 15b, the first regulator 2, the second regulator 4).

[0055] Fig. 4 is a functional block diagram of the controller 7. As shown in Fig. 4, the controller 7 executes a program stored in the nonvolatile memory 72 to function as a target supply flow rate calculation unit 101, a target discharge flow rate calculation unit 102, a valve control unit 103, a determination unit 104, a correction unit 105, a pump control unit 106, and an attitude calculation unit 107.

[0056] For convenience of explanation, the following description will be given assuming that the rotation speed of the engine 5 is constant. As described above, the discharge flow rates of the closed circuit pump 1 and the open circuit pump 3 are determined by the discharge capacity and the rotation speed of the engine 5. The controller 7 controls the discharge capacity of the closed circuit pump 1 and the open circuit pump 3, thereby controlling the discharge flow rates of the closed circuit pump 1 and the open circuit pump 3.

[0057] The target supply flow rate calculation unit 101 calculates a target value of the flow rate of hydraulic oil to be supplied to the arm cylinder 26 (hereinafter referred to as the target supply flow rate) based on the operation amount of the arm operation lever 8Ab detected by the arm operation amount sensor 8Aa.

[0058] A supply flow rate table that defines the relationship between the manipulated variable and the target supply flow rate is stored in the nonvolatile memory 72. The supply flow rate table defines a supply flow rate characteristic in which the target supply flow rate increases as the manipulated variable increases.

[0059] The target supply flow rate calculation unit 101 refers to a supply flow rate table stored in the nonvolatile memory 72, and calculates a target supply flow rate based on the operation amount detected by the arm operation amount sensor 8Aa.

[0060] The target discharge flow rate calculation unit 102 calculates a target flow rate Q1, which is the target value of the discharge flow rate of the closed circuit pump 1, and a target flow rate Q2, which is the target value of the discharge flow rate of the open circuit pump 3, based on the target supply flow rate calculated by the target supply flow rate calculation unit 101.

[0061] The nonvolatile memory 72 stores a first discharge flow rate table and a second discharge flow rate table shown in Fig. 5. The first discharge flow rate table defines the relationship between the target supply flow rate and the target flow rate Q1. The second discharge flow rate table defines the relationship between the target supply flow rate and the target flow rate Q2.

[0062] The first discharge flow rate table defines a discharge flow rate characteristic in which the target flow rate Q1 increases as the target supply flow rate increases within a range from 0 to a predetermined value Ft. The second discharge flow rate table defines a discharge flow rate characteristic in which the target flow rate Q2 is 0 when the target supply flow rate is less than the predetermined value Ft, and the target flow rate Q2 increases as the target supply flow rate increases when the target supply flow rate is equal to or greater than the predetermined value Ft. That is, when the target supply flow rate is within a range from 0 to the predetermined value Ft, the arm cylinder 26 (the actuator to be operated) is driven by hydraulic oil discharged from the closed circuit pump 1. On the other hand, when the target supply flow rate is equal to or greater than the predetermined value Ft, the arm cylinder 26 is driven by hydraulic oil (total flow rate) discharged from both the closed circuit pump 1 and the open circuit pump 3.

[0063] The target discharge flow rate calculation unit 102 refers to the first discharge flow rate table stored in the nonvolatile memory 72 and calculates the target flow rate Q1 of the closed circuit pump 1 based on the target supply flow rate calculated by the target supply flow rate calculation unit 101. The target discharge flow rate calculation unit 102 refers to the second discharge flow rate table stored in the nonvolatile memory 72 and calculates the target flow rate Q2 of the open circuit pump 3 based on the target supply flow rate calculated by the target supply flow rate calculation unit 101.

[0064] As shown in FIG. 4, the valve control section 103 determines the operation direction of the arm operation lever 8Ab based on the detection result of the arm operation amount sensor 8Aa.

[0065] When the operation direction of the arm operating lever 8Ab is the arm crowding direction, the valve control unit 103 outputs an ON signal to the first switching valve 15a and an OFF signal to the second switching valve 15b, so that the first switching valve 15a is in the open position and the second switching valve 15b is in the closed position.

[0066] When the operation direction of the arm operating lever 8Ab is the arm dump direction, the valve control unit 103 outputs an ON signal to the second switching valve 15b and an OFF signal to the first switching valve 15a, thereby positioning the second switching valve 15b in the open position and the first switching valve 15a in the closed position.

[0067] The ON signal corresponds to a control signal (control current) for exciting the solenoids of the first switching valve 15a and the second switching valve 15b to switch them to the open position, and the OFF signal corresponds to a control signal (control current) that corresponds to a standby current.

[0068] The attitude calculation unit 107 calculates the attitude of the working device 20 based on a signal from the attitude detection device 10. An example of calculation processing of the attitude of the working device 20 by the attitude calculation unit 107 will be described with reference to FIG. 6. As shown in FIG. 6, the attitude calculation unit 107 calculates a rotation angle θ1 of the boom 24 from a first reference plane R1 (hereinafter also referred to as the boom angle) based on a signal from the boom angle sensor 24S. The attitude calculation unit 107 calculates a rotation angle θ2 of the arm 23 from a second reference plane R2 (hereinafter also referred to as the arm angle) based on a signal from the arm angle sensor 23S.

[0069] The first reference plane R1 is, for example, a horizontal plane. In this case, the second reference plane R2 is a vertical plane perpendicular to the first reference plane (horizontal plane) R1. The second reference plane R2 may also be, for example, a plane parallel to the central axis Ca of rotation of the rotating unit 40 (see FIG. 1). In this case, the second reference plane R2 is a plane perpendicular to the first reference plane R1, i.e., a plane parallel to the traveling direction of the traveling unit 30.

[0070] The posture calculation unit 107 calculates the height Ha of the tip position of the arm 23 from the ground (hereinafter also referred to as the arm tip height) based on the boom angle θ1, the arm angle θ2, and the dimensions L1, L2 of the work device 1A stored in the non-volatile memory 72.

[0071] The attitude calculation unit 107 calculates the distance H1 in the vertical direction from the center position of the boom pin (also called a foot pin) 24p to the center position of the arm pin 23p based on the following equation (1). H1=L1×sinθ1 (1) Here, L1 is the dimension (boom length) of the line segment connecting the center position of boom pin 24p and the center position of arm pin 23p. The center position of boom pin 24p is the rotation center of boom 24, and the center position of arm pin 23p is the rotation center of arm 23.

[0072] The attitude calculation unit 107 calculates the distance H2 in the vertical direction from the center position of the bucket pin 22p to the center position of the arm pin 23p based on the following equation (2). H2=L2×cosθ2 (2) Here, L2 is the dimension (arm length) of the line segment connecting the center position of the bucket pin 22p and the center position of the arm pin 23p. The center position of the bucket pin 22p is the rotation center of the bucket 22.

[0073] The posture calculation unit 107 calculates the arm tip height Ha, which is the distance in the vertical axis direction from the ground to the center position of the arm pin 23p, based on the following equation (3). Ha = Hb - H3 (3) H3 is calculated by the following equation (4). H3 = H2 - H1 (4) Here, Hb is the distance in the vertical axis direction from the ground to the center position of the boom pin 24p (hereinafter also referred to as the boom foot height), and is stored in the nonvolatile memory 72 in advance.

[0074] The hydraulic excavator 100 may excavate the ground on a deck installed on the ground. In this case, the boom foot height Hb is determined taking into account the height of the deck from the ground. Since deck heights vary depending on the work site, it is preferable to allow the operator to change the boom foot height Ha0. For example, when the operator operates an input device provided in the operator's cab 41, the controller 7 changes the height threshold Ha0 stored in the non-volatile memory 72 based on information input from the input device. The input device may be, for example, a touch panel monitor, a switch box having multiple switches, or the like.

[0075] 4 determines whether or not excavation work is being performed by the working implement 20 based on the calculation results of the attitude calculation unit 107 and the signals from the arm operation amount sensor 8Aa and the boom operation amount sensor 8Ba. An example of this determination method will be described in detail below.

[0076] The determination unit 104 determines whether the tip of the working implement 20 (tip of the bucket 22) is located below the ground surface based on the distance H1, distance H2, and arm tip height Ha calculated by the posture calculation unit 107.

[0077] The determination unit 104 determines whether the arm tip height Ha is equal to or less than the distance H3 (= H2 - H1). If the arm tip height Ha is equal to or less than the distance H3, the determination unit 104 determines that the tip of the working device 20 is located below the ground. If the arm tip height Ha is greater than the distance H3, the determination unit 104 determines that the tip of the working device 20 is located above the ground.

[0078] The posture of the working device 20 when the tip of the working device 20 is positioned below the ground surface is the posture when digging the ground surface. Therefore, the determination unit 104 functions as a posture determination unit that determines whether the posture of the working device 20 is the posture when digging the ground surface, based on the calculation result of the posture calculation unit 107.

[0079] The determination unit 104 determines whether or not an excavation operation is being performed based on a signal from the operation device 8. This will be explained in detail below.

[0080] The determination unit 104 determines whether a boom-raising operation is being performed based on a signal from the boom operation amount sensor 8Ba. The determination unit 104 determines that a boom-raising operation is being performed if the operation amount in the boom-raising direction is equal to or greater than the raising operation amount threshold. The determination unit 104 determines that a boom-raising operation is not being performed if the operation amount in the boom-raising direction is less than the raising operation amount threshold. The raising operation amount threshold is stored in the non-volatile memory 72.

[0081] The determination unit 104 determines whether or not an arm crowding operation is being performed based on a signal from the arm operation amount sensor 8Aa. The determination unit 104 determines that an arm crowding operation is being performed when the operation amount in the arm crowding direction is equal to or greater than the crowd operation amount threshold. The determination unit 104 determines that an arm crowding operation is not being performed when the operation amount in the arm crowding direction is less than the crowd operation amount threshold. The crowd operation amount threshold is stored in the nonvolatile memory 72.

[0082] When the determination unit 104 determines that at least one of a boom raising operation and an arm crowding operation is being performed, it determines that an excavation operation is being performed by the operating device 8. In other words, when any of a boom raising operation alone, an arm crowding operation alone, or a combined operation of boom raising and arm crowding is being performed, the determination unit 104 determines that an excavation operation is being performed by the operating device 8. When the determination unit 104 determines that neither a boom raising operation nor an arm crowding operation is being performed, it determines that an excavation operation is not being performed by the operating device 8.

[0083] When the determination unit 104 determines that the tip of the working device 20 is located below the ground surface and that an excavation operation is being performed, it determines that the working device 20 is performing excavation work (hereinafter also referred to as the excavation state) and sets the excavation flag to on.

[0084] When the determination unit 104 determines that the tip of the working device 20 is located above the ground, it determines that the working device 20 is not performing excavation work (hereinafter also referred to as a non-excavation state) and sets the excavation flag to off. When the determination unit 104 determines that an excavation operation is not being performed, it determines that the working device 20 is not performing excavation work and sets the excavation flag to off.

[0085] The determination unit 104 repeatedly executes the excavation flag setting process at a predetermined control cycle. That is, the determination unit 104 has a function of monitoring whether or not the excavation state is being performed, and detecting the transition of the state between the non-excavation state and the excavation state.

[0086] When the determination unit 104 determines that the hydraulic excavator 100 is in an excavation state, the correction unit 105 calculates a corrected target flow rate Q1c of the closed circuit pump 1 and a corrected target flow rate Q2c of the open circuit pump 3 based on the target flow rate Q1 of the closed circuit pump 1, the target flow rate Q2 of the open circuit pump 3, and the discharge flow rate Q3 of the charge pump 9.

[0087] The correction unit 105 calculates the adjusted flow rate Qa based on the target flow rate Q1, the target flow rate Q2, and the discharge flow rate Q3 of the charge pump 9. The adjusted flow rate Qa is calculated by the following equation (5). Qa = [Q1 - (Q2 + Q3)] / 2 (5) Q1 is the target flow rate of the closed circuit pump 1 calculated by the target discharge flow rate calculation unit 102, Q2 is the target flow rate of the open circuit pump 3 calculated by the target discharge flow rate calculation unit 102, and Q3 is the discharge flow rate of the charge pump 9. The discharge flow rate Q3 of the charge pump 9 is stored in the nonvolatile memory 72.

[0088] The correction unit 105 calculates a corrected target flow rate Q1c based on the target flow rate Q1 and the adjusted flow rate Qa. The corrected target flow rate Q1c is calculated using the following equation (6). Q1c=Q1-Qa (6) The correction unit 105 calculates a corrected target flow rate Q2c based on the target flow rate Q2 and the adjusted flow rate Qa. The corrected target flow rate Q2c is calculated using the following equation (7). Q2c=Q2+Qa (7) Qa is a value obtained by halving the shortage of return oil to the closed circuit pump 1, as expressed by equation (5).

[0089] When the determining unit 104 determines that the hydraulic excavator 100 is in a non-excavation state, the pump control unit 106 outputs a control signal to the first regulator 2 to set the discharge flow rate of the closed circuit pump 1 to the target flow rate Q1 calculated by the target discharge flow rate calculation unit 102. In other words, the pump control unit 106 controls the discharge capacity of the closed circuit pump 1 via the first regulator 2 so that the discharge flow rate of the closed circuit pump 1 becomes the target flow rate Q1.

[0090] When the determining unit 104 determines that the hydraulic excavator 100 is in a non-excavation state, the pump control unit 106 outputs a control signal to the second regulator 4 to set the discharge flow rate of the open circuit pump 3 to the target flow rate Q2 calculated by the target discharge flow rate calculation unit 102. In other words, the pump control unit 106 controls the discharge capacity of the open circuit pump 3 via the second regulator 4 so that the discharge flow rate of the open circuit pump 3 becomes the target flow rate Q2.

[0091] When the determining unit 104 determines that the hydraulic excavator 100 is in an excavation state, the pump control unit 106 outputs a control signal to the first regulator 2 to set the discharge flow rate of the closed circuit pump 1 to the corrected target flow rate Q1c calculated by the correcting unit 105. In other words, the pump control unit 106 controls the discharge capacity of the closed circuit pump 1 via the first regulator 2 so that the discharge flow rate of the closed circuit pump 1 becomes the corrected target flow rate Q1c.

[0092] When the determination unit 104 determines that the hydraulic excavator 100 is in an excavation state, the pump control unit 106 outputs a control signal to the second regulator 4 to set the discharge flow rate of the open circuit pump 3 to the corrected target flow rate Q2c calculated by the correction unit 105. In other words, the pump control unit 106 controls the discharge capacity of the open circuit pump 3 via the second regulator 4 so that the discharge flow rate of the open circuit pump 3 becomes the corrected target flow rate Q2c.

[0093] Therefore, when the non-digging state transitions to the excavating state, the pump control unit 106 increases the discharge capacity of the open circuit pump 3 and decreases the discharge capacity of the closed circuit pump 1 compared to when the state was non-digging. As a result, the discharge flow rate of the open circuit pump 3 increases and the discharge flow rate of the closed circuit pump 1 decreases.

[0094] When the excavation state transitions to the non-excavation state, the pump control unit 106 reduces the discharge capacity of the open circuit pump 3 and increases the discharge capacity of the closed circuit pump 1 compared to when the excavation state is in effect. This reduces the discharge flow rate of the open circuit pump 3 and increases the discharge flow rate of the closed circuit pump.

[0095] An example of the excavation determination process executed by the controller 7 will be described with reference to Fig. 7. The process shown in the flowchart of Fig. 7 is started when an ignition switch (not shown) is turned on, and after initial setting (not shown) is performed, it is repeatedly executed at a predetermined control cycle.

[0096] 7, in step S110, the attitude calculation unit 107 calculates the boom angle θ1 based on the detection result of the boom angle sensor 24S. The attitude calculation unit 107 calculates the distance H1 based on the calculated boom angle θ1 and the boom length L1 stored in the nonvolatile memory 72, and then proceeds to step S115.

[0097] In step S115, the posture calculation unit 107 calculates the arm angle θ2 based on the detection result of the arm angle sensor 23S. The posture calculation unit 107 calculates the distance H2 based on the calculated arm angle θ2 and the arm length L2 stored in the nonvolatile memory 72, and proceeds to step S120.

[0098] In step S120, the posture calculation unit 107 calculates the arm tip height Ha based on the distances H1 and H2 calculated in steps S110 and S115 and the boom foot height Hb stored in the non-volatile memory 72, and proceeds to step S130.

[0099] In step S130, the determination unit 104 determines whether or not the tip of the work implement 20 is positioned below the ground, that is, whether or not the posture of the work implement 20 is such that it is digging the ground, based on the calculation results in steps S110 to S120.

[0100] In step S130, if the arm tip height Ha is equal to or less than the judgment distance H3 (= H2 - H1), the judgment unit 104 judges that the tip of the working device 20 is located below the ground, that is, the posture of the working device 20 is such that it is digging the ground, and proceeds to step S135.

[0101] In step S130, if the arm tip height Ha is greater than the judgment distance H3 (= H2 - H1), the judgment unit 104 judges that the tip of the working device 20 is not positioned below the ground, i.e., the posture of the working device 20 is not a posture for digging the ground, and proceeds to step S145.

[0102] In step S135, the determination unit 104 determines whether or not an excavation operation has been performed based on a signal from the operation device 8. The determination unit 104 determines whether or not a boom raising operation has been performed based on a signal from the boom operation amount sensor 8Ba. The determination unit 104 determines whether or not an arm crowding operation has been performed based on a signal from the arm operation amount sensor 8Aa.

[0103] In step S135, if the determining unit 104 determines that at least one of the boom raising operation and the arm crowding operation is being performed, it determines that the operation device 8 is performing an excavation operation.

[0104] In step S135, if the determining unit 104 determines that neither the boom raising operation nor the arm crowding operation is being performed, it determines that the operation device 8 is not performing an excavation operation.

[0105] If it is determined in step S135 that an excavation operation is being performed, the process proceeds to step S140, and if it is determined that an excavation operation is not being performed, the process proceeds to step S145.

[0106] In step S140, the determination unit 104 determines that the working implement 20 is performing excavation work (excavation state), and sets the excavation flag to ON.

[0107] In step S145, the determining unit 104 determines that the working implement 20 is not performing excavation work (non-excavation state), and sets the excavation flag to OFF.

[0108] When the excavation flag setting process (steps S140, S145) is completed, the process shown in the flowchart of Fig. 7 for this control cycle is completed. In other words, when the processes of steps S140, S145 are completed, the process of step S110 for the next control cycle is executed.

[0109] An example of flow rate control executed by the controller 7 will be described with reference to Fig. 8. The process shown in the flowchart of Fig. 8 is started when an ignition switch (not shown) is turned on, and after initial setting (not shown) is performed, it is repeatedly executed at a predetermined control period.

[0110] As shown in FIG. 8, in step S210, the target supply flow rate calculation unit 101 calculates the target supply flow rate to the arm cylinder 26 based on the operation amount detected by the arm operation amount sensor 8Aa, and identifies the operation direction of the arm operation lever 8Ab, and then proceeds to step S215.

[0111] In step S215, the target discharge flow rate calculation unit 102 calculates the target flow rate Q1 of the closed circuit pump 1 and the target flow rate Q2 of the open circuit pump 3 based on the target supply flow rate calculated in step S210, and then the process proceeds to step S220.

[0112] In step S220, the determination unit 104 determines whether the digging flag is set to on. If it is determined in step S220 that the digging flag is set to on, the process proceeds to step S233, and if it is determined that the digging flag is not set to on, the process proceeds to step S223.

[0113] In step S223, the pump control unit 106 outputs a control signal corresponding to the target flow rate Q1 calculated in step S215 to the first regulator 2 of the closed circuit pump 1, and the process proceeds to step S226.

[0114] In step S226, the pump control unit 106 outputs a control signal to the second regulator 4 of the open circuit pump 3 according to the target flow rate Q2 calculated in step S215.

[0115] Furthermore, although not shown, in step S226, the valve control section 103 outputs control signals according to the operation direction identified in step S210 to the first switching valve 15a and the second switching valve 15b.

[0116] When the process of step S226 is completed, the controller 7 ends the process of this control cycle shown in the flowchart of Fig. 8. That is, when the process of step S226 is completed, the process of step S210 of the next control cycle is executed.

[0117] In step S233, the corrector 105 calculates an adjusted flow rate Qa based on the target flow rates Q1 and Q2 calculated in step S215 and the discharge flow rate Q3 of the charge pump 9, and then the process proceeds to step S236.

[0118] In step S236, the corrector 105 calculates a corrected target flow rate Q1c based on the target flow rate Q1 calculated in step S215 and the adjusted flow rate Qa calculated in step S233, and the process proceeds to step S239.

[0119] In step S239, the corrector 105 calculates a corrected target flow rate Q2c based on the target flow rate Q2 calculated in step S215 and the adjusted flow rate Qa calculated in step S233, and the process proceeds to step S243.

[0120] In step S243, the pump control unit 106 outputs a control signal corresponding to the corrected target flow rate Q1c calculated in step S236 to the first regulator 2 of the closed circuit pump 1, and the process proceeds to step S246.

[0121] In step S246, the pump control unit 106 outputs a control signal to the second regulator 4 of the open circuit pump 3 according to the corrected target flow rate Q2c calculated in step S239.

[0122] Furthermore, although not shown, in step S246, the valve control unit 103 outputs control signals corresponding to the operation direction identified in step S210 to the first switching valve 15a and the second switching valve 15b. After completing the process of step S246, the controller 7 ends the process shown in the flowchart of Fig. 8 for this control cycle.

[0123] In this manner, in this embodiment, when the excavation state is in progress, control is executed to increase the discharge capacity (tilting angle) of the open circuit pump 3 and decrease the discharge capacity (tilting angle) of the closed circuit pump 1 compared to when the excavation state is in progress (hereinafter also referred to as flow rate adjustment control).

[0124] An example of the operation of the hydraulic excavator 100 according to this embodiment will be described. For the sake of convenience, specific numerical values ​​will be used, but these numerical values ​​are merely an example. The discharge flow rate of the charge pump 9 is 30 [L / min], the pressure-receiving area ratio of the bottom-side oil chamber 26a to the rod-side oil chamber 26b of the arm cylinder 26 is 1:0.7, and the set pressure of the charge relief valve 65 is 2.0 [MPa].

[0125] When the operator operates the arm operating lever 8Ab to the arm crowd side, the controller 7 calculates the target supply flow rate.

[0126] Based on the target supply flow rates, the controller 7 calculates a target flow rate Q1 for the closed circuit pump 1 and a target flow rate Q2 for the open circuit pump 3. The controller 7 outputs control signals to the first regulator 2 and the second regulator 4 according to the calculation results.

[0127] The controller 7 also outputs an ON signal to the first selector valve 15a to switch the first selector valve 15a to the open position, and outputs an OFF signal to the second selector valve 15b to keep the second selector valve 15b in the closed position.

[0128] Here, for example, a case will be described in which the target supply flow rate is 100 [L / min], the target flow rate Q1 of the closed circuit pump 1 is 80 [L / min], and the target flow rate Q2 of the open circuit pump 3 is 20 [L / min]. In a non-excavation state, the controller 7 controls the first regulator 2 and the second regulator 4 so that the discharge flow rate of the closed circuit pump 1 is 80 [L / min] and the discharge flow rate of the open circuit pump 3 is 20 [L / min].

[0129] When the flow rate of hydraulic oil supplied to the bottom-side oil chamber 26a of the arm cylinder 26 is 100 [L / min], the flow rate of hydraulic oil discharged from the rod-side oil chamber 26b is 70 [L / min] due to the difference in pressure-receiving area between the bottom-side oil chamber 26a and the rod-side oil chamber 26b. Note that the flow rate of hydraulic oil supplied from the closed circuit Cc to the charge flow path 11 through the flushing valve 16 is 0 [L / min].

[0130] The required flow rate of hydraulic oil returning to closed circuit pump 1 is 80 [L / min], the same as the discharge flow rate. Therefore, of the hydraulic oil discharged from charge pump 9, 10 [L / min] is replenished from charge flow path 11 to second flow path 62 through second makeup valve 66b. The remaining 20 [L / min] of hydraulic oil discharged from charge pump 9 that is not replenished to second flow path 62 is discharged from charge relief valve 65 to tank 17.

[0131] Hydraulic oil is supplied to the bottom-side oil chamber 26a of the arm cylinder 26 and discharged from the rod-side oil chamber 26b, causing the arm cylinder 26 to extend. The extension speed of the arm cylinder 26 is determined by the flow rate of hydraulic oil supplied to the bottom-side oil chamber 26a and the pressure-receiving area of ​​the bottom-side oil chamber 26a. As the arm cylinder 26 extends, the arm 23 moves toward the arm crowding side.

[0132] On the other hand, when excavation work is being performed, an event may occur in which the bucket 22 comes into contact with hard soil. If the bucket 22 comes into contact with hard soil during excavation, the crowding movement of the arm 23 is restricted. For example, the crowding movement of the arm 23 may slow down or stop. When the extension movement of the arm cylinder 26 is restricted, the flow rate of hydraulic oil discharged from the rod-side oil chamber 26b to the second flow path 62 decreases.

[0133] For example, when the crowding operation of the arm 23 stops, the flow rate of the hydraulic oil discharged from the rod-side oil chamber 26b to the second flow path 62 becomes 0 [L / min]. The discharge flow rate of the charge pump 9 is 30 [L / min].

[0134] In this embodiment, the hydraulic oil discharged from the open circuit pump 3 to the first flow path 61 is guided to the charge flow path 11 through the flushing valve 16. However, if we assume that flow rate adjustment control is not performed, the return flow rate of the oil to the closed circuit pump 1 will be 50 [L / min], which is the sum of the discharge flow rate of 30 [L / min] of the charge pump 9 and the discharge flow rate of 20 [L / min] of the open circuit pump 3, and this is less than the required return flow rate of 80 [L / min] of the oil to the closed circuit pump 1.

[0135] If there is a shortage of return oil to the closed circuit pump 1, the return side of the closed circuit pump 1 may temporarily become negative pressure, causing cavitation and possibly deteriorating the closed circuit pump 1. Also, if there is a shortage of return oil to the closed circuit pump 1, there is a risk that the flow rate required to lubricate the gears, bearings, and other moving parts of the closed circuit pump 1 may temporarily become insufficient. As a result, there is a risk that the moving parts may become worn and deteriorate.

[0136] When the pressure in the charge passage 11 and the second passage 62 drops due to a lack of oil returning to the closed circuit pump 1, the pressure difference between the bottom-side oil chamber 26a and the rod-side oil chamber 26b of the arm cylinder 26 increases. As a result, the cylinder thrust of the arm cylinder 26 increases, causing a change in the operating feel.

[0137] Furthermore, as the cylinder thrust increases, so does the load acting on the connecting parts between the driven members of the working device 20. This increases the stress generated in the welds and other parts of the connecting parts between the driven members of the working device 20, which may shorten the life of the connecting parts.

[0138] Therefore, to prevent these problems from occurring, the controller 7 according to this embodiment increases the discharge flow rate of the open circuit pump 3 and decreases the discharge flow rate of the closed circuit pump 1 when the excavation state is compared to when the excavation state is not being performed. This makes it possible to ensure the required flow rate of return oil to the closed circuit pump 1 when the operation of the arm cylinder 26 is restricted.

[0139] When the bucket 22 comes into contact with hard soil and the operation of the arm cylinder 26 is forcibly stopped, the flushing valve 16 is switched to the first direction D1 due to the difference in pressure between the bottom-side oil chamber 26a and the rod-side oil chamber 26b. This causes the first flow path 61 to communicate with the charge flow path 11 via the flushing valve 16. Therefore, the hydraulic oil discharged from the open circuit pump 3 is guided as excess oil through the flushing valve 16 to the charge flow path 11.

[0140] The controller 7 calculates, as the adjusted flow rate Qa, half of the flow rate of hydraulic oil that is insufficient due to the restriction on the operation of the arm cylinder 26. Assuming that flow rate adjustment control is not executed, the flow rate of hydraulic oil that is insufficient is as follows:

[0141] The flow rate of hydraulic oil guided from charge flow path 11 to second flow path 62 through second makeup valve 66b is 50 [L / min], which is the sum of the discharge flow rate of 30 [L / min] of charge pump 9 and the discharge flow rate of 20 [L / min] of open circuit pump 3. Therefore, the shortage of return oil to closed circuit pump 1 is 30 [L / min] (= 80 [L / min] - 50 [L / min]).

[0142] The controller 7 according to this embodiment executes flow rate adjustment control in the excavation state to equalize the discharge rate and suction rate of the closed circuit pump 1, even when the operation of the arm cylinder 26 is restricted. In the flow rate adjustment control, the controller 7 increases the discharge rate of the open circuit pump 3 by 15 [L / min] (= 30 [L / min] / 2) and decreases the discharge rate of the closed circuit pump 1 by 15 [L / min] (= 30 [L / min] / 2) compared to when the excavation state is not being performed.

[0143] Specifically, the controller 7 calculates half of the shortage of hydraulic oil, 30 [L / min], as the adjusted flow rate Qa. The controller 7 calculates a value obtained by adding the adjusted flow rate Qa = 15 [L / min] to the target flow rate of 20 [L / min] of the open circuit pump 3, as a corrected target flow rate Q2c = 35 [L / min]. The controller 7 also calculates a value obtained by subtracting the adjusted flow rate Qa = 15 [L / min] from the target flow rate of 80 [L / min] of the closed circuit pump 1, as a corrected target flow rate Q1c = 65 [L / min].

[0144] The controller 7 controls the first regulator 2 so that the discharge flow rate of the closed circuit pump 1 becomes a corrected target flow rate Q1c=65 [L / min]. The controller 7 controls the second regulator 4 so that the discharge flow rate of the open circuit pump 3 becomes a corrected target flow rate Q2c=35 [L / min].

[0145] During excavation, when the operation of the arm cylinder 26 is not restricted, the flow rate of hydraulic oil supplied to the bottom-side oil chamber 26a of the arm cylinder 26 is 100 [L / min], which is the sum of the discharge flow rate of 65 [L / min] of the closed circuit pump 1 and the discharge flow rate of 35 [L / min] of the open circuit pump 3. The flow rate of return oil from the closed circuit pump 1 is 100 [L / min], which is the sum of the flow rate of hydraulic oil discharged from the rod-side oil chamber 26b of the arm cylinder 26 and the discharge flow rate of 30 [L / min] of the charge pump 9.

[0146] During excavation, when bucket 22 contacts hard soil and arm cylinder 26 is stopped, the flow rate of hydraulic oil discharged from rod-side oil chamber 26b of arm cylinder 26 is 0 [L / min]. However, the flow rate of hydraulic oil guided from charge flow path 11 to second flow path 62 through second makeup valve 66b is 65 [L / min], which is the sum of the discharge flow rate of 30 [L / min] of charge pump 9 and the discharge flow rate of 35 [L / min] of open circuit pump 3. Because the discharge flow rate of closed circuit pump 1 is 65 [L / min], the required flow rate of return oil from closed circuit pump 1 is ensured.

[0147] According to the above-described embodiment, the following advantageous effects are achieved.

[0148] (1) A hydraulic excavator (construction machine) 100 includes an articulated working device 20 having multiple hydraulic actuators (a boom cylinder 27, an arm cylinder 26, and a bucket cylinder 25) for performing excavation work, an attitude detection device 10 for detecting the attitude of the working device 20, an operating device 8 for operating the working device 20, a closed circuit pump 1 connected to the arm cylinder 26 by a closed circuit Cc for supplying and discharging hydraulic oil to the arm cylinder 26, an open circuit pump 3 connected to the arm cylinder 26 by an open circuit Oc for supplying hydraulic oil to the arm cylinder 26, a charge pump 9, a charge flow path 11 for guiding hydraulic oil discharged from the charge pump 9 to the closed circuit Cc, a flushing valve (excess oil discharge device) 16 for discharging excess hydraulic oil from the closed circuit Cc into the charge flow path 11, and a controller 7 for controlling the discharge capacities of the closed circuit pump 1 and the open circuit pump 3.

[0149] The controller 7 determines whether or not excavation work is being performed by the working device 20, based on signals from the attitude detection device 10 and signals from the operation device 8. When the state transitions from a state in which excavation work is not being performed by the working device 20 to a state in which excavation work is being performed, the controller 7 increases the discharge capacity of the open circuit pump 3 and decreases the discharge capacity of the closed circuit pump 1 compared to before the transition. In the excavation state, the flow rate of hydraulic oil discharged from the open circuit pump 3 increases and the flow rate of hydraulic oil discharged from the closed circuit pump 1 decreases compared to the non-excavation state.

[0150] With this configuration, even if the operation of the arm cylinder 26 is restricted due to the bucket 22 coming into contact with hard soil during excavation, it is possible to prevent a shortage of return oil in the closed circuit pump 1. As a result, it is possible to prevent cavitation and galling caused by a shortage of return oil in the closed circuit pump 1.

[0151] Therefore, according to this embodiment, it is possible to provide a hydraulic excavator (construction machine) 100 that can suppress deterioration of the closed circuit pump 1 due to cavitation and galling.

[0152] (2) Furthermore, according to this embodiment, it is possible to prevent a change in the cylinder thrust of the arm cylinder 26 due to a lack of return oil in the closed circuit pump 1. As a result, it is possible to prevent a change in the operational feeling.

[0153] (3) Furthermore, according to this embodiment, it is possible to prevent an increase in the cylinder thrust of the arm cylinder 26 due to a lack of return oil from the closed circuit pump 1, thereby suppressing an increase in the load on the connecting portions between the driven members of the working device 20. As a result, it is possible to suppress a decrease in the lifespan of the working device 20.

[0154] (4) The controller 7 determines whether an excavation operation is being performed based on a signal from the operation device 8, and determines whether the tip of the bucket 22 (tip of the work implement 20) is located below the ground level based on a signal from the attitude detection device 10. The controller 7 determines that the work implement 20 is performing excavation work when the tip of the bucket 22 is located below the ground level and an excavation operation is being performed. The controller 7 determines that the work implement 20 is not performing excavation work when the tip of the bucket 22 is located above the ground level. Furthermore, the controller 7 determines that the work implement 20 is not performing excavation work when an excavation operation is not being performed.

[0155] With this configuration, the flow rate adjustment control is executed while the lower part of the ground is being excavated, thereby preventing a shortage of return oil from the closed circuit pump 1 even if the bucket 22 comes into contact with hard soil during excavation and the operation of the arm cylinder 26 is restricted.

[0156] (5) When the state transitions from one in which excavation work is not being performed by the work implement 20 to one in which excavation work is being performed, the controller 7 increases the discharge capacity of the open circuit pump 3 and decreases the discharge capacity of the closed circuit pump 1 so that the sum of the discharge flow rates of the closed circuit pump 1 and the open circuit pump 3 is maintained (steps S233, S236, S239, S243, and S246 in Figure 8).

[0157] With this configuration, the sum (100 [L / min]) of the discharge flow rate (80 [L / min]) of the closed circuit pump 1 and the discharge flow rate (20 [L / min]) of the open circuit pump 3 in the non-digging state is the same as the sum (100 [L / min]) of the discharge flow rate (65 [L / min]) of the closed circuit pump 1 and the discharge flow rate (35 [L / min]) of the open circuit pump 3 in the excavating state. This allows the working implement 20 to operate at the speed intended by the operator in both the excavating state and the non-digging state.

[0158] (6) Furthermore, the flow rate of return oil from closed circuit pump 1 is the same when bucket 22 comes into contact with hard soil and the movement of arm 23 is restricted, and after bucket 22 has excavated the hard soil. This prevents shocks from occurring in the operation of work implement 20 after excavating hard soil.

[0159] A modification of this embodiment will now be described.

[0160] <Variation 1> In the above embodiment, an example has been described in which the increase in the target flow rate of the open circuit pump 3 and the decrease in the target flow rate of the closed circuit pump 1 when transitioning from the non-digging state to the drilling state are the same, but the present invention is not limited to this. The increase in the target flow rate of the open circuit pump 3 and the decrease in the target flow rate of the closed circuit pump 1 do not have to be the same as long as deterioration due to a lack of return oil in the closed circuit pump 1 is unlikely to occur.

[0161] <Variation 2> In the above embodiment, an example was described in which the controller 7 determines that the tip of the working device 20 is located below the ground when the arm tip height Ha is equal to or less than the distance H3, but the present invention is not limited to this.

[0162] <Variation 2-1> For example, the controller 7 may determine that the tip of the bucket 22 is located below the ground surface when the arm tip height Ha is equal to or smaller than the height threshold Ha0. In this example, the controller 7 determines that the tip of the bucket 22 is located above the ground surface when the arm tip height Ha is greater than the height threshold Ha0. The height threshold Ha0 is stored in advance in the non-volatile memory 72.

[0163] As described above, the hydraulic excavator 100 may excavate the ground on a deck installed on the ground. In this case, the height threshold Ha0 is determined taking into consideration the height of the deck from the ground. Since deck heights vary depending on the work site, it is preferable to allow the operator to change the height threshold Ha0. For example, when the operator operates an input device provided in the operator's cab 41, the controller 7 changes the height threshold Ha0 stored in the non-volatile memory 72 based on information input from the input device.

[0164] <Variation 2-2> Furthermore, the controller 7 may calculate the height of the tip of the bucket 22 based on the signal from the attitude detection device 10, and determine that the tip of the bucket 22 is located below the ground if the calculation result is a negative value. In this case, the attitude detection device 10 includes an attitude sensor (angle sensor) that detects the rotation angle of the bucket 22.

[0165] <Variation 3> In the above embodiment, an example was described in which it is determined that excavation work is being performed by the work implement 20 when the tip of the bucket 22 is positioned below the ground surface and an excavation operation is being performed, but the present invention is not limited to this.

[0166] For example, the controller 7 may determine whether or not scraping work, which is an excavation work on a wall surface, is being performed by the working device 20. The controller 7 determines that scraping work is being performed by the working device 20 when the working device 20 is in a posture for performing scraping work and an operation for performing scraping is being performed.

[0167] The controller 7 determines whether the posture of the working device 20 is for performing scraping work based on the signal from the posture detection device 10. For example, the controller 7 determines that the posture of the working device 20 is for performing scraping work when the tip of the bucket 22 is at least a predetermined distance away from the swing center axis Ca.

[0168] Furthermore, the controller 7 determines whether an operation for scraping off, i.e., an excavation operation on a wall surface, is being performed based on signals from the boom operation amount sensor 8Ba and the arm operation amount sensor 8Aa. For example, when at least one of a boom lowering operation and an arm crowding operation is being performed, the controller 7 determines that an excavation operation on a wall surface is being performed by the operation device 8. When neither a boom lowering operation nor an arm crowding operation is being performed, the controller 7 determines that an excavation operation on a wall surface is being performed by the operation device 8.

[0169] With this configuration, the flow rate adjustment control is executed while the deep side of the wall is being excavated, which prevents a shortage of return oil from the closed circuit pump 1 even if the bucket 22 comes into contact with hard soil during excavation at the deep side of the wall and restricts the operation of the arm cylinder 26.

[0170] <Variation 4> In the above embodiment, an example has been described in which the correction unit 105 calculates the corrected target flow rates Q1c and Q2c when the excavation flag is set to on, but the present invention is not limited to this. For example, the processes of steps S233, S236, and S239 in Fig. 8 may be executed between steps S215 and S220. In other words, the correction unit 105 may always calculate the corrected target flow rates Q1c and Q2c.

[0171] <Variation 5> In the above embodiment, an example has been described in which the first switching valve 15a and the second switching valve 15b are electromagnetic switching valves, but the present invention is not limited to this. Instead of the first switching valve 15a and the second switching valve 15b, the hydraulic system 60 may include a first electromagnetic proportional valve and a second electromagnetic proportional valve that can adjust the flow rate of hydraulic oil discharged from the open circuit pump 3 and guide the hydraulic oil to the closed circuit Cc.

[0172] <Variation 6> In the above embodiment, an example in which the first selector valve 15a and the second selector valve 15b are provided separately has been described, but the present invention is not limited to this. Instead of the first selector valve 15a and the second selector valve 15b, the hydraulic system 60 may be provided with a single spool valve that has the functions of the first selector valve 15a and the second selector valve 15b.

[0173] <Variation 7> In the above embodiment, the flow rate control when the operation of the arm cylinder 26 is restricted has been described, but the present invention is not limited to this. The hydraulic circuits of the boom cylinder 27 and the bucket cylinder 25 may be configured similarly to the hydraulic circuit of the arm cylinder 26, and the controller 7 may execute the same flow rate control as in the above embodiment in the hydraulic circuits of the boom cylinder 27 and the bucket cylinder 25. Furthermore, the hydraulic actuator is not limited to a hydraulic cylinder.

[0174] Although the embodiments of the present invention have been described above, the above embodiments merely illustrate some of the application examples of the present invention, and it is not intended that the technical scope of the present invention be limited to the specific configurations of the above embodiments.

[0175] The above-described embodiments and modifications are provided as examples to facilitate understanding of the present invention, and are not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment or modification with the configuration of another modification, and it is also possible to add the configuration of another modification to the configuration of one embodiment or modification. Note that the control lines and information lines shown in the figures are those considered necessary for explanation, and do not necessarily represent all control lines and information lines required in the product. In reality, it can be assumed that almost all configurations are interconnected. [Explanation of symbols]

[0176] 1...Closed circuit pump, 2...First regulator, 3...Open circuit pump, 4...Second regulator, 5...Engine, 7...Controller, 8...Operation device, 8A...Arm operation device, 8Aa...Arm operation amount sensor, 8Ab...Arm operation lever, 8B...Boom operation device, 8Ba...Boom operation amount sensor, 8Bb...Boom operation lever, 9...Charge pump, 10...Posture detection device, 11...Charge flow path, 15a...First switching valve, 15b...Second switching valve, 16...Flushing valve (excess oil discharge device), 17...Tank, 20...Work device, 22...Bucket, 23...Arm, 24...Boom, 25...Bucket cylinder (hydraulic actuator), 26...Arm cylinder (hydraulic actuator), 26a...Bottom side oil chamber, 26b...Rod side oil chamber, 2 7...Boom cylinder (hydraulic actuator), 30...Traveling body, 31...Travel motor (hydraulic actuator), 40...Swinging body (vehicle body), 42...Swing motor (hydraulic actuator), 60...Hydraulic system, 61...First flow path, 62...Second flow path, 63...Charge circuit, 65...Charge relief valve, 66a...First makeup valve, 66b...Second makeup valve, 71...Processing device, 72...Non-volatile memory, 73...Volatile memory, 74...Input interface, 75...Output interface, 100...Hydraulic excavator (construction machine), 101...Target supply flow rate calculation unit, 102...Target discharge flow rate calculation unit, 103...Valve control unit, 104...Determination unit, 105...Correction unit, 106...Pump control unit, 107...Attitude calculation unit, Cc...Closed circuit, Oc...Open circuit

Claims

1. A construction machine comprising: a multi-joint working device having a plurality of hydraulic actuators for performing excavation work; an attitude detection device for detecting the attitude of the working device; an operating device for operating the working device; a closed circuit pump connected to the hydraulic actuators by a closed circuit for supplying and discharging hydraulic oil to the hydraulic actuators; an open circuit pump connected to the hydraulic actuators by an open circuit for supplying hydraulic oil to the hydraulic actuators; a charge pump; a charge flow path for guiding hydraulic oil discharged from the charge pump to the closed circuit; and a controller for controlling the discharge capacities of the closed circuit pump and the open circuit pump, An excess oil discharge device is provided that discharges excess hydraulic oil from the closed circuit into the charge flow path, The controller determining whether or not excavation work is being performed by the work device based on a signal from the attitude detection device and a signal from the operation device; When the state transitions from a state in which excavation work is not being performed by the work device to a state in which excavation work is being performed, Increasing the discharge capacity of the open circuit pump and decreasing the discharge capacity of the closed circuit pump Construction machinery characterized by:

2. The construction machine according to claim 1, The controller Determine whether an excavation operation is being performed based on a signal from the operation device; determining whether or not the tip of the working implement is positioned below the ground based on a signal from the attitude detection device; When the tip of the working device is located below the ground surface and the excavation operation is being performed, it is determined that the excavation operation is being performed by the working device. Construction machinery characterized by:

3. The construction machine according to claim 1, When a transition occurs from a state in which excavation work is not being performed by the work device to a state in which excavation work is being performed, the controller increases the discharge capacity of the open circuit pump and decreases the discharge capacity of the closed circuit pump so that the sum of the discharge flow rate of the closed circuit pump and the discharge flow rate of the open circuit pump is maintained. Construction machinery characterized by:

4. The construction machine according to claim 1, The controller Determine whether an excavation operation is being performed based on a signal from the operation device; determining whether the posture of the working implement is an excavation posture based on a signal from the posture detection device; When the posture of the working device is a posture for excavating and the excavation operation is being performed, it is determined that the working device is in a state where excavation work is being performed. Construction machinery characterized by:

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