Hydraulic drive device for work machine

Abstract

Provided is a hydraulic drive device for a work machine, the hydraulic drive device comprising an actuator (30), an unload valve (43), and a controller (70). The controller (70) calculates an actuator target flow rate Qat on the basis of an actuator operation amount and controls the unload flow rate Qu in the unload valve (43) on the basis of the actuator target flow rate Qat. The controller (70) changes an unload full closure flow rate Qac in accordance with a condition relating to the usage status of a work machine (10), and the unload full closure flow rate Qac is the minimum value of the actuator target flow rate Qat for fully closing the unload valve (43).

Description

Hydraulic drive device for a working machine

[0001] The present invention relates to a device for hydraulically driving a working machine.

[0002] Patent Document 1 discloses an excavator including an actuator and a bleed valve. The bleed valve is an unloading valve that enables control of the flow rate of hydraulic oil returning to the tank without passing through the actuator, and has an opening area that changes according to the operation amount for the actuator. Patent Document 1 further discloses changing the characteristic of the opening area of the bleed valve with respect to the operation amount according to the acceleration / deceleration state of the actuator (see the summary of Patent Document 1, FIG. 4, etc.).

[0003] Japanese Patent Application Laid-Open No. 2021-156082

[0004] The present invention is a device for hydraulically driving a working machine, which includes an unloading valve and can set the characteristics of the unloading valve to appropriate characteristics according to the usage situation of the working machine according to the usage situation of the working machine. The purpose is to provide such a device.

[0005] The provided device is for hydraulically driving a work machine, and the device comprises a tank for storing hydraulic fluid, a pump for discharging the hydraulic fluid stored in the tank, an actuator, an unload valve, and a controller. The actuator is driven by the supply of hydraulic fluid discharged by the pump, thereby moving the work machine. The unload valve operates to change the unload flow rate, which is the flow rate of hydraulic fluid discharged by the pump and returned to the tank through the unload valve without passing through the actuator. The controller calculates an actuator target flow rate, which is a target value for the flow rate of hydraulic fluid into the actuator, based on the actuator operation amount, which is the magnitude of the operation to drive the actuator, and controls the unload flow rate based on the actuator target flow rate. The controller is configured to change the unload full-close flow rate according to set conditions regarding the usage status of the work machine. The unload full-close flow rate is the minimum value of the actuator target flow rate that fully closes the unload valve.

[0006] This is a side view of a work machine according to an embodiment of the present invention. This is a diagram showing the elements of a hydraulic drive system mounted on the work machine. This is a graph showing the relationship between the flow rate of the hydraulic fluid in the pump, actuator, and unload valve included in the hydraulic drive system, and the target flow rate of the actuator. This is a block diagram showing the unload control process performed by the controller included in the hydraulic drive system. This is a flowchart showing the calculation process for the target flow rate, etc., performed by the controller. This is a flowchart showing the pump control process, control valve control, and unload valve control process performed by the controller.

[0007] Embodiments of the present invention will be described with reference to Figures 1 to 6.

[0008] Figure 1 shows a work machine 10 according to the embodiment described above. The work machine 10 illustrated in Figure 1 is an excavator. The work machine 10 can be any machine used for performing work, and may be a construction machine other than a hydraulic excavator, or a material handling machine used for material handling. Examples of the construction machine include, in addition to the excavator, a crane, a bulldozer, and a wheel loader. The work machine 10 illustrated in Figure 1 operates in response to operations given by an operator.

[0009] The aforementioned work machine 10 comprises a machine body 10a, an attachment 15, and a hydraulic drive device 100 shown in Figure 2.

[0010] The machine body 10a is the main body portion of the work machine 10. The machine body 10a includes a lower body 11 and an upper rotating body 13.

[0011] The lower body 11 supports the upper rotating body 13 so that it can rotate. The lower body 11 illustrated in Figure 1 is a lower traveling body that can travel on a traveling surface such as the ground, and includes a traveling device. The traveling device includes a pair of left and right crawlers. The traveling device may also include a plurality of wheels.

[0012] The upper rotating body 13 is rotatably mounted on the lower body 11. The upper rotating body 13 includes a driver's cab 13c. An operating device is located in the driver's cab 13c, which allows an operator to control the work machine 10, and the work machine 10 can be operated (ridden operation) by an operator sitting in the driver's cab 13c. The work machine 10 may also be remotely operated by an operation given to a remote control device located outside the work machine 10, or it may be capable of automatic operation.

[0013] The attachment 15 is attached to the upper slewing body 13 of the machine body 10a and is capable of performing work operations. The attachment 15 illustrated in Figure 1 includes a boom 15a, an arm 15b, and a tip attachment 15c.

[0014] The boom 15a is connected to and attached to the upper slewing body 13 so that it can be raised and lowered, specifically so that it can rotate in the vertical direction. The arm 15b is connected to the boom 15a so that it can rotate in the vertical direction.

[0015] The tip attachment 15c constitutes the tip of the attachment 15. The tip attachment 15c is connected to the arm 15b so as to be rotatable in the vertical direction. The tip attachment 15c illustrated in Figure 1 is a bucket capable of scooping up and excavating objects. The tip attachment 15c may also include any of the following: a device for gripping objects (grapple, nibbler, rotating fork, etc.), a device for crushing objects (breaker, etc.), or a magnet for attracting metal objects.

[0016] The hydraulic drive device 100 is a device for moving the work machine 10 by hydraulic pressure. The hydraulic drive device 100 includes a plurality of elements shown in Figure 2, which include a hydraulic circuit 20, a plurality of actuators 30, a detection unit 50, an input unit 60, a controller 70, and an output unit 80.

[0017] The plurality of actuators 30 are driven by the supply of hydraulic fluid from the hydraulic circuit 20, thereby moving each of the plurality of movable parts of the work machine 10 by hydraulic pressure. That is, the hydraulic circuit 20 is a circuit for driving each of the plurality of actuators 30 by hydraulic pressure, and enables the driving of each of the plurality of actuators 30 to be controlled by the controller 70. The hydraulic drive device according to the present invention may include only a single actuator.

[0018] The hydraulic circuit 20 includes a tank 25, a pump 21, a pump capacity actuator 23, a plurality of control valves 41, and an unload valve 43.

[0019] Tank 25 is a container for storing hydraulic fluid. The hydraulic fluid is the fluid used to operate the plurality of actuators 30, that is, the fluid used to move the work machine 10 by hydraulic pressure.

[0020] The pump 21 is a hydraulic pump that discharges the hydraulic fluid stored in the tank 25. The pump 21 is driven by a drive source (not shown), which draws in the hydraulic fluid from the tank 25 and supplies it to the actuator 30. The pump 21 includes a rotor that is rotated by the drive source. The drive source may be an engine or an electric motor. The hydraulic circuit 20 may include only a single pump 21 or may include multiple pumps 21. The pump 21 illustrated in Figure 2 is a variable displacement hydraulic pump having a variable capacity.

[0021] The pump capacity controller 23 changes the pump capacity of the pump 21 in accordance with the pump capacity command input from the controller 70. The pump capacity controller 23 changes the pump capacity by, for example, changing the tilt angle of the pump 21. The flow rate of the hydraulic fluid discharged by the pump 21, i.e., the pump discharge flow rate Qp, is proportional to the rotational speed of the pump 21 and the pump capacity, respectively. Therefore, by changing the pump capacity in accordance with the pump capacity command from the controller 70, the pump capacity controller 23 enables the controller 70 to control the pump discharge flow rate Qp. The pump capacity command may be an electrical signal or a pilot hydraulic pressure. The pilot hydraulic pressure is, for example, a hydraulic pressure signal converted from an electrical signal output from the controller 70.

[0022] Each of the actuators 30 is a hydraulic actuator that is moved by hydraulic pressure. The plurality of actuators 30 can be connected to the pump 21 via oil passages included in the hydraulic circuit 20.

[0023] The plurality of actuators 30 include a plurality of hydraulic actuators shown in Figure 1, namely a pair of travel motors 31, a slewing motor 33, a boom cylinder 35a, an arm cylinder 35b, and a tip attachment cylinder 35c.

[0024] Each of the pair of travel motors 31 is a hydraulic motor that causes the lower body 11 to perform a travel motion. Specifically, each of the pair of travel motors 31 moves the left and right crawlers that constitute the travel device of the lower body 11.

[0025] The aforementioned slewing motor 33 is a hydraulic motor that rotates the upper slewing body 13 relative to the lower body 11.

[0026] The boom cylinder 35a, the arm cylinder 35b, and the tip attachment cylinder 35c are extendable and retractable hydraulic cylinders for moving the attachment 15. The boom cylinder 35a extends and retracts to raise and lower the boom 15a relative to the upper slewing body 13. The arm cylinder 35b extends and retracts to rotate the arm 15b relative to the boom 15a. The tip attachment cylinder 35c extends and retracts to rotate the tip attachment 15c relative to the arm 15b. If the tip attachment 15c includes a plurality of working members that move relative to each other, for example, for gripping objects, the plurality of actuators 30 may include actuators for moving the plurality of working members relative to each other.

[0027] The plurality of control valves 41 are each positioned between the pump 21 and the plurality of actuators 30, and operate to change the movement of the plurality of actuators 30. Each of the control valves 41 functions as a directional control valve (direction switching valve) that switches the direction of movement of the actuator 30 (for example, rotational direction or extension direction) by switching the direction of the flow of hydraulic fluid from the pump 21 to the actuator 30. Each of the control valves 41 also functions as a flow control valve that changes the speed of movement of the actuator 30 by changing the flow rate of hydraulic fluid flowing into (supplied to) the actuator 30 through the control valve 41. The control valves 41 open and close in response to a control valve command (opening command) input to the control valve 41 to change the opening area (opening degree), thereby changing the flow rate of hydraulic fluid supplied to the actuator 30 through the control valve 41. The control valve command may be, for example, a pilot hydraulic pressure or an electrical signal. In Figure 2, only one actuator (hydraulic cylinder) 30 and one corresponding control valve 41 are shown as representative examples from the plurality of actuators 30.

[0028] The unload valve 43 is a bleed-off valve provided in the bleed-off line 24. The bleed-off line 24 is an oil passage that branches off from the pump line 22 connected to the discharge port of the pump 21 and returns the oil discharged from the pump 21 to the tank 25 without passing through the actuator 30. The unload valve 43 opens and closes to change the unload flow rate Qu, which is the flow rate of the hydraulic oil discharged from the pump 21 that flows into the tank 25 through the unload valve 43 without passing through the actuator 30. The unload valve 43 opens and closes to change the opening area in the unload valve 43 in response to an unload command (opening command) input to the unload valve 43, thereby changing the unload flow rate Qu. The unload valve 43 is, for example, an electromagnetic proportional valve, and the electromagnetic proportional valve is, for example, an electromagnetic proportional pressure reducing valve.

[0029] The detection unit 50 detects the state of the work machine 10. The detection unit 50 includes a plurality of detectors, each of which may be mounted on the work machine 10 or located outside the work machine 10. The state of the work machine 10 may be the state of the work machine 10 itself or the state of the outside of the work machine 10.

[0030] The detection unit 50 illustrated in Figure 2 includes a plurality of actuator speed detectors 51 and an imaging device 53.

[0031] The plurality of actuator speed detectors 51 each detect the actuator speed, which is the operating speed of each of the plurality of actuators 30. For example, each of the actuator speed detectors 51 detects the extension / retraction speed of a hydraulic cylinder or the rotational speed of a hydraulic motor. The actuator speed detectors 51 may detect the actuator speed itself, or they may detect a speed corresponding to the actuator speed, for example, the speed of movement of a movable part of the work machine 10 that is moved by the actuator 30. For example, the actuator speed detector 51 may detect the rotational speed of the boom 15a relative to the upper slewing body 13 shown in Figure 1, i.e., the speed of the luffing motion, and thereby detect the extension / retraction speed of the boom cylinder 35a. The actuator speed detectors 51 output, for example, a signal (speed detection signal) indicating the measured speed.

[0032] The imaging device 53 captures an object to be imaged, that is, it generates an image of the object to be imaged. The imaging device 53 may image the outside of the work machine 10, the surface of the work machine 10, or the inside of the work machine 10. For example, the imaging device 53 may be a cab camera that images the inside of the cab 13c, or a cockpit camera that images the area around the cockpit inside the cab 13c. The imaging device 53 may be a camera that detects two-dimensional images, or it may be a camera that detects three-dimensional images (distance images) that include depth information. The imaging device 53 generates and outputs an image signal that includes the information of the generated image.

[0033] The input unit 60 receives an operation from an operator to input information to the controller 70 and inputs a signal corresponding to the operation to the controller 70. The information is used in processing performed by the controller 70. The input unit 60 may include a touch panel, mouse, keyboard, and switch. The input unit 60 may include a tablet, smartphone, and personal computer. The input unit 60 may be provided on the work machine 10, for example, in the operator's cab 13c. The input unit 60 may be located outside the work machine 10. For example, the input unit 60 may be located in a device for remotely operating the work machine 10, or it may be included in the output unit 80.

[0034] The input unit 60 illustrated in Figure 2 includes an operating device 61, a receiver 63, a remote operation response device 65, and an operation mode designation unit 67.

[0035] The operating device 61 is configured such that an operator can input commands to the operating device 61 to move the work machine 10. The operating device 61 may be located in the operator's cab 13c or may be included in a device for remotely operating the work machine 10. The operating device 61 includes an operating member to which the commands are input. The operating member may be a lever or a pedal.

[0036] The operation given to the operating device 61, that is, the operation for moving the work machine 10, is an actuator operation for driving the actuator 30, and the actuator operation may be any of the following: travel operation, slewing operation, or attachment operation. The travel operation is an operation for causing the lower body 11 to perform a travel motion. The slewing operation is an operation for causing the upper slewing body 13 to slewing relative to the lower body 11. The attachment operation is an operation for moving the attachment 15, and may be any of the following: boom operation for raising and lowering the boom 15a relative to the upper slewing body 13, arm operation for rotating the arm 15b relative to the boom 15a, or tip attachment operation for rotating the tip attachment 15c relative to the arm 15b.

[0037] The operating device 61 generates and outputs an operation signal (command signal) which is a signal corresponding to the actuator operation input to the operating device 61. The operation signal is input to the controller 70, thereby providing the controller 70 with the designation of the actuator 30 to be operated from among the plurality of actuators 30, and the speed (amount of operation) of the actuator 30 to be operated.

[0038] The operating device 61 illustrated in Figure 2 includes a plurality of in-cabin operating devices 61a and a plurality of remote operating devices 61b.

[0039] The plurality of in-cabin controls 61a are arranged inside the driver's cab 13c. Each of the in-cabin controls 61a generates and outputs an onboard operation signal, which is an operation signal corresponding to an operation given to the in-cabin control 61a. The onboard operation signal is, for example, an electrical signal. The plurality of in-cabin controls 61a may include, for example, an electric lever or an electric pedal. In this case, the in-cabin controls 61a may include an angle sensor (for example, a variable resistor) that detects the angle of the lever or pedal. The operation signal output by the in-cabin controls 61a may be pilot hydraulic pressure. For example, the plurality of in-cabin controls 61a may include a hydraulic remote control valve. The pilot hydraulic pressure may be detected by a hydraulic sensor, and the electrical signal (pilot pressure detection signal) output by the hydraulic sensor may be input to the controller 70.

[0040] The plurality of remote control devices 61b are located outside the work machine 10. Each of the remote control devices 61b generates and outputs a remote operation signal, which is an operation signal corresponding to the operation given to the remote control device 61b. The remote operation signal is, for example, an electrical signal.

[0041] The receiver 63 receives various types of information. The receiver 63 is attached to the work machine 10 and receives signals arriving from outside the work machine 10.

[0042] The receiver 63 may receive information used for remote operation. The information received by the receiver 63 may include information indicating that remote operation is to be performed, and specifically may include the remote operation signal transmitted from the remote control 61b. The information received by the receiver 63 is information used for remote operation and may also include signals output from elements other than the remote control 61b (for example, switches) among the elements included in the input unit 60.

[0043] The receiver 63 may receive information used for automatic driving. The receiver 63 may receive information used for automatic driving from a device (such as a tablet, a personal computer, etc.) arranged outside the working machine 10 among the devices constituting the input unit 60. The information received by the receiver 63 may include information indicating that automatic driving is to be performed. The information received by the receiver 63 may include information about the content of automatic driving, and this information may be, for example, information about the content of work, or information about an attachment target trajectory that is the target of the trajectory of the attachment 15. The information received by the receiver 63 may include an automatic driving operation signal that is an operation signal for operating the attachment 15 in automatic driving.

[0044] The remote operation response device 65 enables an operation to be given to the in-cab operator 61a from outside the working machine 10. The remote operation response device 65 is a so-called retrofit device attached to the in-cab operator 61a. The remote operation response device 65 gives the same operation to the in-cab operator 61a as the operation given to the remote operator 61b. Specifically, the receiver 63 receives the remote operation signal output from the remote operator 61b according to the operation given to the remote operator 61b, and the remote operation response device 65 performs an operation according to the received remote operation signal, whereby the same operation as the operation given to the remote operator 61b is given to the in-cab operator 61a, that is, the in-cab operator 61a is moved.

[0045] The operation mode specifying unit 67 includes an operation mode specifying operation unit capable of receiving an operation mode specifying operation by an operator, and sets the operation mode specified by the operation mode specifying operation as the operation mode to be executed from among a plurality of prepared operation modes. The mode specifying operation unit is, for example, a switch for switching the operation mode. The operation mode is a mode related to the operation method of the working machine 10, and specifically, is information related to the method of operating to drive the actuator 30. That is, in the plurality of operation modes, the operation methods for moving the working machine are different from each other.

[0046] Specifically, the operation of the work machine 10 includes on-vehicle manual operation, remote operation, and automatic control operation. The on-vehicle manual operation is an operation manually performed by an operator in the cab 13c. The remote operation is an operation by an operator outside the work machine 10, and is performed, for example, using the remote controller 61b. The automatic control operation includes assist operation and automatic operation. The assist operation is also called machine control (MC; Machine Control system) or semi-automatic operation. The assist operation is performed as follows. A work plan, which is a plan of work to be performed by the work machine 10, is stored in the controller 70. The operator only performs an operation (on-vehicle operation or remote operation) on an operation target element (for example, the arm 15b) among a plurality of elements included in the attachment 15, and the controller 70 automatically controls the operations of elements other than the operation target element (for example, the boom 15a and the tip attachment 15c) so that the work machine 10 operates according to the work plan corresponding to the operation. Therefore, the assist operation corresponds to an on-vehicle operation together with the on-vehicle manual operation when the operation is performed in the cab 13a. In the automatic operation, the controller 70 controls the movements of the plurality of actuators 30 so that the work machine 10 automatically moves according to the work plan without an operation by the operator.

[0047] As shown in FIG. 2, the operation mode specifying unit 67 includes a remote operation mode specifying unit 67a, an automatic operation mode specifying unit 67b, and an assist operation mode specifying unit 67c. The remote operation mode specifying unit 67a specifies an operation mode in which the remote operation mode should be executed. The automatic operation mode specifying unit 67b specifies an operation mode in which the automatic operation mode should be executed. The assist operation mode specifying unit 67c includes, for example, an assist operation switch or an MC switch, and specifies an operation mode in which the assist operation mode should be executed. The operation mode specifying unit 67 may further include an on-vehicle manual operation mode specifying unit that specifies an operation mode in which the on-vehicle manual operation mode in which the on-vehicle manual operation is performed should be executed.

[0048] The controller 70 includes a computer that performs signal input / output, calculations (processing), and information storage. The controller 70 includes a storage unit 70b for storing a program and an calculation unit 70a capable of executing the program, and the functions of the controller 70 are realized by the execution of the program. The controller 70 may communicate with other devices, and the communication may be either wireless or wired. If the controller 70 includes multiple components, the components may be connected to each other by wireless or wired communication. Examples of means for performing the communication include mobile phone lines, optical lines, wireless LANs (Local Area Networks), and wired LANs. For example, the controller 70 receives information output from the detection unit 50 and the input unit 60, respectively. For example, the controller 70 generates a signal (command) to move the work machine 10 and inputs it to the hydraulic circuit 20. The controller 70 inputs information to the output unit 80 and causes the output unit 80 to output the information. The controller 70 may be mounted on the work machine 10, or it may be located outside the work machine 10. The controller 70 may include multiple elements that are distributed, that is, it may constitute a distributed system.

[0049] The controller 70 includes a plurality of functional elements, the plurality of functional elements including a hydraulic circuit control unit 71 and an automatic control unit 73.

[0050] The hydraulic circuit control unit 71 controls the hydraulic circuit 20. The hydraulic circuit control unit 71 includes a pump control unit 71b, an unload valve control unit 71c, a control valve control unit 71d, and an actuator target flow rate setting unit 71a shown in Figure 4.

[0051] The actuator target flow rate setting unit 71a sets the actuator target flow rate Qat, which is the target value of the actuator flow rate Qa. The actuator flow rate Qa is the sum of the flow rates of the hydraulic fluid flowing into each of the actuators 30, and the sum of the actuator flow rate Qa and the unload flow rate Qu corresponds to the pump discharge flow rate Qp.

[0052] The pump control unit 71b controls the capacity of the pump 21. Specifically, the pump control unit 71b inputs the pump capacity command to the pump capacity operator 23, thereby controlling the capacity of the pump 21 and controlling the pump discharge flow rate Qp, which is the flow rate of hydraulic fluid discharged from the pump 21.

[0053] The unload valve control unit 71c changes the unload opening area Au, which is the opening area of ​​the unload valve 43, thereby controlling the unload flow rate Qu, that is, the flow rate of hydraulic fluid that returns from the pump 21 to the tank 25 without passing through the actuator 30. Specifically, the unload valve control unit 71c controls the unload flow rate Qu by inputting the unload command to the unload valve 43 and opening the unload valve 43 to an opening degree (opening area) corresponding to the unload command.

[0054] As shown in Figure 4, the unload valve control unit 71c includes an unload full-close flow rate setting unit 71c1, an unload flow rate calculation unit 71c2, and an unload command generation unit 71c3. The unload full-close flow rate setting unit 71c1 sets the unload full-close flow rate Qac, which is the minimum value of the actuator target flow rate Qat that closes the unload valve 43, as will be described in detail later. The unload flow rate calculation unit 71c2 calculates the unload flow rate Qu or a corresponding physical quantity, such as the opening degree or opening area of ​​the unload valve 43, according to the actuator target flow rate Qat. The unload command generation unit 71c3 generates the unload command to be input to the unload valve 43.

[0055] The control valve control unit 71d controls the actuator-specific flow rate corresponding to the opening degree of each of the plurality of control valves 41, thereby controlling the movement (driving direction and driving speed) of each of the plurality of actuators 30. Specifically, the control valve control unit 71d inputs the control valve command to each of the control valves 41 to change the opening area (opening degree) of the control valve 41, thereby controlling the movement of the actuator 30 corresponding to the control valve 41.

[0056] The automatic control unit 73 performs automatic control of the work machine 10 so that it moves according to the work plan. The automatic control may be control for automatic operation or control for assisted operation. Specifically, the automatic control unit 73 generates commands to move the work machine 10 according to the work plan and inputs them to the hydraulic circuit 20. The automatic control unit 73 performs the automatic control based on the state (position, posture, etc.) of the work machine 10 detected by the detection unit 50.

[0057] The output unit 80 outputs information based on signals input from the controller 70. The output of the information may be in the form of light (such as a display), sound (such as voice), or vibration. For example, the output unit 80 includes a device (monitor) for displaying the information. The output unit 80 may be a tablet, smartphone, or personal computer. The output unit 80 may also be a device installed in the operator's cab 13c, such as a cluster gauge. The output unit 80 may also be an external output device located outside the work machine 10. The output unit 80 may be included in a device for remotely controlling the work machine 10.

[0058] Next, the calculation and control operations performed by the controller 70 and the associated operations of the hydraulic drive device 100 will be described.

[0059] The hydraulic circuit control unit 71 of the controller 70 controls the hydraulic circuit 20 as follows: The controller 70 acquires the actuator operation amount. The actuator operation amount is the magnitude of the actuator operation given to each of the actuators 30, that is, the operation to drive the actuator 30. In the onboard manual operation, the actuator operation amount is the operation amount (e.g., lever angle, pedal angle) given to the in-cabin control unit 61a. In the remote operation, the actuator operation amount is the operation amount given to the remote control unit 61b. In the automatic operation, the actuator operation amount is the operation amount calculated by the controller 70 to automatically move the actuator 30. In the assisted operation, the actuator operation amount includes both the operation amount given to the control device 61 by the operator to move the target element and the operation amount calculated by the controller 70.

[0060] The controller 70 controls the pump discharge flow rate Qp, the actuator flow rate Qa, and the unload flow rate Qu based on the actuator operation amount. More specifically, the controller 70 calculates the actuator target flow rate Qat based on the actuator operation amount. More specifically, the controller 70 calculates the actuator target flow rate, which is the target flow rate for each of the plurality of actuators 30, based on the actuator-specific operation amount, which is the operation amount for each of the plurality of actuators 30, and calculates the sum of the actuator-specific target flow rates as the actuator target flow rate Qat. The controller 70 operates the capacity of the pump 21, the opening of the unload valve 43, and the openings of the plurality of control valves 41 so that the total flow rate of hydraulic fluid flowing into the plurality of actuators 30 becomes the actuator target flow rate Qat.

[0061] As shown in Figure 4, the unload flow rate calculation unit 71c2 of the unload valve control unit 71c of the controller 70 calculates the unload flow rate Qu or a corresponding value based on the actuator target flow rate Qat. A feature of the controller 70 is that the unload full-close flow rate setting unit 71c1 of the controller 70 changes the characteristic (timing) of fully closing the unload valve 43 according to the unload full-close flow rate change condition. Specifically, the unload full-close flow rate setting unit 71c1 sets the unload full-close flow rate Qac according to the unload full-close flow rate change condition. As shown in Figure 3, the unload full-close flow rate Qac set by the unload full-close flow rate setting unit 71c1 is the minimum value of the actuator target flow rate Qat that causes the unload valve 43 to be fully closed. Therefore, the controller 70 fully closes the unload valve 43 when the actuator target flow rate Qat is equal to or greater than the unload full-close flow rate Qac.

[0062] The decrease in the unload valve closing flow rate Qac (for example, the change in the unload valve closing flow rate Qac from flow rate Qat-1 to flow rate Qat-2 shown in Figure 3) is a decrease in the minimum value of the actuator target flow rate Qat that causes the unload valve 43 to close completely. Therefore, as the actuator target flow rate Qat gradually increases with increasing actuator operation, the smaller the unload valve closing flow rate Qac, the earlier the unload valve 43 closes (at a smaller actuator target flow rate Qat). The complete closure of the unload valve 43 allows virtually all of the hydraulic fluid discharged from the pump 21 (except for a small leak) to be supplied to the actuator 30. Thus, suppressing the unload valve closing flow rate Qac reduces the loss of hydraulic energy from the hydraulic fluid discharged from the pump 21, thereby improving the fuel efficiency of the work machine 10.

[0063] Conversely, an increase in the unloading fully closed flow rate Qac (for example, the change in the unloading fully closed flow rate Qac from flow rate Qat-1 to flow rate Qat-3 shown in Figure 3) is an increase in the minimum value of the actuator target flow rate Qat that fully closes the unloading valve 43. Therefore, when the actuator target flow rate Qat gradually increases due to an increase in the actuator operation amount, the larger the unloading fully closed flow rate Qac, the later the unloading valve 43 will close (at a larger actuator target flow rate Qat). This suppresses the change in the speed of the actuator 30 accompanying the change in the actuator operation amount, thereby improving the fine control performance of the actuator 30. For example, the operating feel of the control device 61 is improved when the operator operates the work machine 10 (either on-board operation or remote operation). Also, the accuracy of the operation of the actuator 30 is improved regardless of the operating mode. For example, the accuracy of positioning the attachment 15 is improved, and the accuracy of work performed by the attachment 15 (e.g., construction) is improved.

[0064] The unload closing flow rate Qac may be continuously changeable or stepwise changeable, for example, selectable from a plurality of closing flow rate candidates. The number of closing flow rate candidates and corresponding unload characteristics is not limited. The unload characteristic is a characteristic of the unload flow rate Qu with respect to the actuator target flow rate Qat. For example, the candidates for the unload characteristic may include an operability-priority characteristic and an energy-saving-priority characteristic. The unload closing flow rate Qac in the energy-saving-priority characteristic is smaller than the unload closing flow rate Qac in the operability-priority characteristic. The candidates for the unload characteristic may also include unload characteristics other than the operability-priority characteristic and the energy-saving-priority characteristic. For example, an unload characteristic (e.g., a standard characteristic or an intermediate characteristic) corresponding to the unload closing flow rate Qac between the unload closing flow rate Qac in the energy-saving-priority characteristic and the unload closing flow rate Qac in the operability-priority characteristic may be included.

[0065] The graph shown in Figure 3 illustrates the characteristics of the unload opening area Au, the actual actuator flow rate Qar, and the actual pump discharge flow rate Qpr, which are controlled by the controller 70 according to the actuator target flow rate Qat, using dashed, dashed, and solid lines, respectively. The actual pump discharge flow rate Qpr is the actual flow rate of the hydraulic fluid discharged from the pump 21, i.e., the measured value of the pump discharge flow rate Qp. The actual actuator flow rate Qar is the actual flow rate of the hydraulic fluid flowing into the actuator 30, i.e., the measured value of the actuator flow rate Qa. The unload flow rate Qu corresponds to the difference between the actual pump discharge flow rate Qpr and the actual actuator flow rate Qar.

[0066] In the characteristics shown in Figure 3, when the actuator target flow rate Qat is 0, the controller 70 minimizes the capacity of the pump 21 to make the actual pump discharge flow rate Qpr equal to the minimum pump discharge flow rate Qpmin. On the other hand, when the actuator target flow rate Qat is 0, the controller 70 maximizes the unload opening area Au, that is, fully opens the unload valve 43.

[0067] When the actuator operation is not being applied to the operating device 61 (for example, when the lever is in the neutral position or the pedal is not pressed), the actuator operation amount input to the controller 70 is substantially zero, and the operation signal is off, until the actual operation amount reaches a predetermined minimum effective operation amount. Therefore, the actuator target flow rate Qat is zero, and the controller 70 does not operate the actuator 30. In contrast, when the actual operation amount exceeds the minimum effective operation amount, the actuator operation amount becomes greater than zero, and the operation signal turns on. As a result, the actuator target flow rate Qat becomes greater than zero, and the controller 70 operates the actuator 30 according to the operation amount.

[0068] In the range where the actuator target flow rate Qat is from 0 to the flow rate Qat-1 set as the unload fully closed flow rate Qac, the controller 70 increases the actual pump discharge flow rate Qpr while decreasing the unload opening area Au as the actuator target flow rate Qat increases. For example, the unload opening area Au decreases from an initial value Auo, for example, about 80 mm, as the actuator target flow rate Qat increases. ２ , and can be gradually reduced.

[0069] When the actuator target flow rate Qat is the unloading fully closed flow rate Qac (in the example where the unloading opening area Au is shown by the dashed line in Figure 3, this is the flow rate Qat-1), the controller 70 minimizes the unloading opening area Au, that is, it fully closes the unloading valve 43. On the other hand, in this example, the controller 70 sets the actual pump discharge flow rate Qpr to half of the maximum pump discharge flow rate Qpmax (= Qpmax / 2).

[0070] In the range where the actuator target flow rate Qat is greater than the flow rate Qat-1, the controller 70 keeps the unload valve 43 fully closed, while increasing the actual pump discharge flow rate Qpr as the actuator target flow rate Qat increases.

[0071] When the actuator target flow rate Qat is at its maximum, that is, when the actuator operation amount is at its maximum, the controller 70 sets the actual pump discharge flow rate Qpr to the maximum pump discharge flow rate Qpmax. Specifically, the controller 70 maximizes the capacity of the pump 21.

[0072] If the unload closing flow rate Qac is reduced, for example, if the unload closing flow rate Qac is changed to a flow rate Qat-2 which is smaller than the flow rate Qat-1 but greater than 0, the controller 70 minimizes the unload opening area Au when the actuator target flow rate Qat gradually increases from 0 to reach the flow rate Qat-2 (before the time when the actuator target flow rate Qat reaches the flow rate Qat-1), as shown by the dashed line in Figure 3. That is, in the example shown in Figure 3, the controller 70 completely closes the unload valve 43 before the time when the actual pump discharge flow rate Qpr reaches half of the maximum pump discharge flow rate Qpmax. As is clear from comparing the dashed line and the dashed line showing the actual actuator flow rate Qar in Figure 3, the reduction in the unload closing flow rate Qac increases the ratio of the change in the actual actuator flow rate Qar to the change in the actuator target flow rate Qat, which is the slope of the straight line showing the actual actuator flow rate Qar in Figure 3.

[0073] Conversely, if the unloading fully closed flow rate Qac is increased, for example, if the unloading fully closed flow rate Qac is increased to a flow rate Qat-3 (≤ Qpmax) which is greater than the flow rate Qat-1, the controller 70 fully closes the unloading valve 43 when the actuator target flow rate Qat gradually increases from 0 to reach the flow rate Qat-3, that is, after the time when the actuator target flow rate Qat becomes the flow rate Qat-1. Specifically, the controller 70 gradually decreases the unloading opening area Au as the actuator operation amount gradually increases from 0. In the example shown in Figure 3, the controller 70 fully closes the unloading valve 43 after the time when the actual pump discharge flow rate Qpr becomes half of the maximum pump discharge flow rate Qpmax. As is clear from comparing the dashed line and the dotted line representing the actual actuator flow rate Qar in Figure 3, increasing the unloaded fully closed flow rate Qac reduces the rate of change in the actual actuator flow rate Qar with respect to the change in the actuator target flow rate Qat, i.e., the slope of the straight line representing the actual actuator flow rate Qar, in other words, it makes the change in the actual actuator flow rate Qar gentler. This makes it possible to reduce the change in the speed of the actuator 30 with respect to the change in the actuator operating amount, thereby improving fine operability.

[0074] The controller 70 stores the unload total closing flow rate change conditions and changes the unload total closing flow rate Qac according to the unload total closing flow rate change conditions. The unload total closing flow rate change conditions are conditions related to the usage status of the work machine 10. The unload total closing flow rate change conditions can be set in various ways. Specifically, the unload total closing flow rate change conditions may include conditions related to the operating mode, conditions related to the work content, and other conditions, or they may be a combination of multiple conditions.

[0075] The unload total closed flow rate change condition may include an operability priority condition, which is a condition set to determine that the usage situation should prioritize operability. In this case, it is preferable that the controller 70 is configured to increase the unload total closed flow rate Qac when the operability priority condition is met, for example, to set the unload characteristics to the operability priority characteristics. Conversely, it is preferable that the controller 70 is configured to decrease the unload total closed flow rate Qac when the operability priority condition is not met, for example, to set the unload characteristics to the energy saving priority characteristics.

[0076] Furthermore, the unload total closing flow rate change condition may include an energy saving priority condition, which is a condition for determining that the usage situation should prioritize the suppression of hydraulic energy (energy saving). Preferably, the controller 70 is configured to reduce the unload total closing flow rate Qac when the energy saving priority condition is met, for example, by setting the unload characteristics to the energy saving priority characteristics. Preferably, the controller 70 is configured to increase the unload total closing flow rate Qac when the energy saving priority condition is not met, for example, by setting the unload characteristics to the operability priority characteristics.

[0077] The unload full-close flow rate change conditions may include conditions for the operating mode. The controller 70 may change the unload full-close flow rate Qac according to the operating mode being performed. For example, the controller 70 may change the unload full-close flow rate Qac depending on whether the operating mode being performed is a manual onboard driving mode, a remote driving mode, an assisted driving mode, or an automatic driving mode.

[0078] Specific examples of the correspondence (assignment) between the operating mode and the unload fully closed flow rate Qac are as follows: In operating modes in which the operator manually operates the work machine 10 (specifically, the onboard manual operation mode and the remote operation mode), the need to prioritize the operability of the operating device 61 is higher than when the work machine 10 is automatically controlled, so the controller 70 may set the unload fully closed flow rate Qac larger than in other operating modes (for example, the unload characteristic may be set to the operability priority characteristic). Also, in operating modes in which the controller 70 automatically controls the work machine 10 (specifically, the assist operation mode and the automatic operation mode), the need to prioritize the operability of the operating device 61 is lower than in onboard operation and remote operation, so the controller 70 may set the unload fully closed flow rate Qac smaller than in other operating modes (for example, the unload characteristic may be set to the energy saving priority characteristic). However, as described later, even in the assist operation or automatic operation, it may be preferable to set the unload fully closed flow rate Qac larger depending on the work content of the work machine 10. Conversely, even with the aforementioned onboard manual operation or remote operation, the unloading fully closed flow rate Qac may be reduced depending on the work content of the work machine 10.

[0079] The operating mode to be executed may be manually specified by the operator, for example, by an operating mode specification operation given to the operating mode specification unit 67 shown in Figure 2. Alternatively, the operating mode to be executed may be automatically determined by the controller 70. That is, the controller 70 may perform an operating mode determination process. The determination of the operating mode may be an automatic determination based on an operation signal, an automatic determination using the imaging device 53, or an automatic determination combining these.

[0080] The controller 70 may specify the operating mode to be executed in response to the operating mode specification operation manually given to the operating mode specification unit 67. For example, the operating mode specification unit 67 inputs an operating mode specification signal to the controller 70, which is a signal for specifying the operating mode to be executed in response to a specification operation given by the operator. The controller 70 determines (sets) the operating mode to be executed based on the operating mode specification signal and sets the unload fully closed flow rate Qac according to the determined operating mode.

[0081] The controller 70 may determine the operating mode to be performed based on the operation signal corresponding to the actuator operation for driving the actuator 30. For example, if the controller 70 receives the onboard driving operation signal from the driver's cab control unit 61a, it determines that the operating mode to be performed is the onboard manual driving mode. If the controller 70 receives the remote driving operation signal from the remote control unit 61b through the receiver 63, it determines that the operating mode to be performed is the remote driving mode. If the automatic control unit 73 of the controller 70 generates an assist driving operation signal, which is an operation signal for the assist driving mode, the controller 70 determines that the operating mode to be performed is the assist driving mode. If the automatic control unit 73 of the controller 70 generates an automatic driving operation signal, which is an operation signal for the automatic driving mode, the controller 70 determines that the operating mode to be performed is the automatic driving mode.

[0082] The controller 70 may determine the operating mode to be performed based on the image of the interior of the driver's cab 13c generated by the imaging device 53. For example, the controller 70 may determine the operating mode to be performed by performing image recognition (image detection) on the captured image.

[0083] For example, the controller 70 may determine whether the operating mode to be executed is the remote operation mode based on whether the remote operation response device 65 is visible in the captured image. The controller 70 may determine that the operating mode to be executed is the remote operation mode when the remote operation response device 65 is visible in the captured image, that is, when the remote operation response device 65 is located inside the driver's cab 13c. Alternatively, the controller 70 may determine whether the operating mode to be executed is the remote operation mode based on whether the remote operation response device 65 is operating (giving operation to) the in-cab operator 61a. The controller 70 may determine that the operating mode to be executed is the remote operation mode when the remote operation response device 65 is operating the in-cab operator 61a.

[0084] The controller 70 may determine whether the driving mode to be executed is the onboard driving mode based on whether or not the operator is visible in the captured image. The onboard driving mode includes the onboard manual driving mode and the assisted driving mode, respectively. The controller 70 may determine that the mode to be executed is the onboard driving mode if the operator is visible in the captured image. The controller 70 may also determine whether or not the driving mode to be executed is the onboard driving mode based on whether or not the operator is operating the in-cabin control unit 61a. The controller 70 may determine that the driving mode to be executed is the onboard driving mode if the operator is operating the in-cabin control unit 61a.

[0085] The controller 70 may determine the operating mode based on multiple types of information. For example, the controller 70 may determine the operating mode to be executed based on two or more types of information selected from information about manual operation, information about operation signals, and information about captured images.

[0086] The unload full-close flow rate change conditions may include conditions relating to the work content, more specifically, the work performed by the work machine 10. The controller 70 may change the unload full-close flow rate Qac according to the work content. For example, the work content may be set in the controller 70 in the automatic operation mode or the assist operation mode. Alternatively, the work content may be set in the controller 70 in the onboard operation mode or the remote operation mode. In either case, the controller 70 may change the unload full-close flow rate Qac according to the set work content.

[0087] Specific examples of the correspondence (assignment) between the work content and the unload fully closed flow rate Qac are as follows: For work where the accuracy of the position of the attachment 15 is important, such as work to shape terrain (embankment, etc.) (shaping work, finishing work), or work that requires the precise movement of the work object, it is necessary to prioritize the operability of the actuator 30. In such work, the controller 70 increases the unload fully closed flow rate Qac compared to work where it is not necessary to prioritize operability. For example, the controller 70 sets the unload characteristics to the operability priority characteristics. In work where it is not necessary to prioritize the operability of the actuator 30, the controller 70 decreases the unload fully closed flow rate Qac compared to work where it is not necessary to prioritize operability. For example, the controller 70 sets the unload characteristics to the energy saving priority characteristics.

[0088] The identification of the work content (for example, determining whether or not it is a work content where ease of operation is a major priority) may be input to the controller 70 through the input unit 60, or it may be performed automatically by the controller 70 based on information about the work plan, etc.

[0089] The unload total closed flow rate change conditions may include conditions relating to the operating mode and the work content. The controller 70 may change the unload total closed flow rate Qac according to the conditions relating to the operating mode and the work content. The unload total closed flow rate change conditions may include conditions other than the operating mode or the work content. For example, the controller 70 may change the unload total closed flow rate Qac according to an operation given to a switch other than the operating mode specification operation unit included in the operating mode specification unit 67.

[0090] The relationship (assignment) between the unload full-close flow rate change condition and the unload full-close flow rate Qac (see Figure 3) can be set in various ways. The assignment may be set manually by the operator using the input unit 60, or it may be stored in the controller 70 in advance. Alternatively, the controller 70 may automatically set and change the assignment depending on the conditions.

[0091] For example, the controller 70 may set the initial unloading characteristic (default) to the operability priority characteristic, and the conditions for changing the unloading characteristic from the operability priority characteristic to the energy saving priority characteristic may be set by an operation given to the input unit 60 by the operator.

[0092] Furthermore, the controller 70 may, for example, set the unloading characteristics to the operability priority characteristics when the driving mode is the onboard manual driving mode or the remote driving mode. The controller 70 may also set the unloading characteristics to the operability priority characteristics when the driving mode is the assist driving mode or the automatic driving mode and the work content requires a high degree of priority on operability. The controller 70 may also set the unloading characteristics to the energy saving priority characteristics when the driving mode is the assist driving mode or the automatic driving mode and the work content requires little priority on operability.

[0093] The process of changing the unloading fully closed flow rate Qac, and the process of determining the unloading opening area Au based on the changed unloading fully closed flow rate Qac, may be carried out in various ways. Examples of such methods will be explained below with reference to Figure 4.

[0094] The unload fully closed flow rate setting unit 71c1 of the controller 70 stores the relationship (assignment) between the unload fully closed flow rate change condition and the unload fully closed flow rate Qac. The controller 70 acquires information (for example, operating mode, work content, etc.) to determine whether the unload fully closed flow rate change condition is met, and the unload fully closed flow rate setting unit 71c1 determines the unload fully closed flow rate Qac (for example, 50 L / min) based on the acquired information and the information about the assignment.

[0095] The unload flow rate calculation unit 71c2 of the controller 70 sets an unload flow rate map Mu, as illustrated in Figure 4, based on the unload fully closed flow rate Qac (for example, 50 L / min) set by the unload fully closed flow rate setting unit 71c1. The unload flow rate map Mu specifies the relationship between the actuator target flow rate Qat and the unload flow rate Qu or a physical quantity of the unload valve 43 that enables the identification of the unload flow rate Qu. The unload flow rate map Mu illustrated in Figure 4 specifies the relationship between the actuator target flow rate Qat and the value of the unload flow rate Qu itself. Alternatively, the unload flow rate map Mu may specify the relationship between the actuator target flow rate Qat and the opening area of ​​the unload valve 43 (unload opening area Au), as shown in the graph in Figure 3.

[0096] In the unload flow rate map Mu shown in Figure 4, in the range where the actuator target flow rate Qat is less than the unload fully closed flow rate Qac, the unload flow rate Qu decreases from its maximum value as the actuator target flow rate Qat increases from 0, and in the range where the actuator target flow rate Qat is greater than or equal to the unload fully closed flow rate Qac, the unload flow rate Qu is 0. On the other hand, in the unload flow rate map corresponding to the graph shown in Figure 3, i.e., the unload opening map, in the range where the actuator target flow rate Qat is less than the unload fully closed flow rate Qac, the unload opening area Au decreases from the initial value Auo (for example, 80 mm) as the actuator target flow rate Qat increases from 0. ２ ) decreases. In the unload opening map, the unload opening area Au becomes 0, that is, the unload valve 43 is fully closed, in the range where the actuator target flow rate Qat is equal to or greater than the unload fully closed flow rate Qac.

[0097] For example, the controller 70 may store a plurality of unload flow rate maps Mu corresponding to different unload fully closed flow rates Qac, and the unload flow rate calculation unit 71c2 may be configured to select an unload flow rate map Mu from the plurality of unload flow rate maps Mu that corresponds to the unload fully closed flow rate Qac (for example, 50 L / min) set by the unload fully closed flow rate setting unit 71c1.

[0098] The unload flow rate calculation unit 71c2 of the controller 70 may be configured to modify a pre-stored unload flow rate map Mu according to the unload fully closed flow rate Qac. For example, the controller 70 may store information about the shape of a line in the unload flow rate map Mu that shows the relationship between the actuator target flow rate Qat and the unload flow rate Qu or information relating thereto, and may be configured to change the scale of the actuator target flow rate Qat in the unload flow rate map Mu according to the unload fully closed flow rate Qac while maintaining the shape. Specifically, the controller 70 may be configured to change the scale such that the unload flow rate Qu becomes greater than 0 when the actuator target flow rate Qat is less than the unload fully closed flow rate Qac, and the unload flow rate Qu becomes 0 when the actuator target flow rate Qat is equal to or greater than the unload fully closed flow rate Qac.

[0099] The scale can be changed, for example, as follows: The controller 70 sets the unit flow rate to a value obtained by dividing the unload fully closed flow rate Qac (e.g., 50 L / min) by the number of map divisions. The number of map divisions corresponds to the resolution (level of detail, scale coarseness or fineness) of the unload flow rate map Mu, and the unit flow rate corresponds to one division, one segment, or one step on the horizontal axis of the unload flow rate map Mu. For example, if the unload fully closed flow rate Qac is 50 L / min and the number of map divisions is 5, the unit flow rate is 10 L / min. Based on the unit flow rate, it is possible to set up a map in which the unload flow rate Qu is set (plotted) for each unit flow rate (e.g., 10 L / min). The value of the unload flow rate Qu corresponding to the actuator target flow rate Qat other than an integer multiple of the unit flow rate can be calculated by interpolation (e.g., linear interpolation) based on the value of the unload flow rate Qu set corresponding to the actuator target flow rate Qat which is an integer multiple of the unit flow rate.

[0100] The controller 70 can obtain multiple flow rate values ​​for the unload flow rate Qu by multiplying the unit flow rate (e.g., 10 L / min) by a plurality of multipliers. The plurality of multipliers are integers from 0 to N, and the maximum multiplier N is set to an integer greater than the number of map divisions (e.g., 5), which is 7 in the example shown in Figure 4. The maximum multiplier N may be variable. For example, when the unit flow rate is 10 L / min, the plurality of flow rate values ​​for the unload flow rate Qu are 0, 10, 20, ... 10 × (N-1), 10N, and these constitute the scale of the actuator target flow rate Qat in the unload flow rate map Mu. In this way, the unload flow rate map Mu is formed to calculate an unload flow rate Qu greater than 0 when the actuator target flow rate Qat is less than the unload fully closed flow rate Qac, and to set the unload flow rate Qu to 0 when it is greater than or equal to the unload fully closed flow rate Qac.

[0101] The actuator target flow rate setting unit 71a of the controller 70 calculates the actuator target flow rate Qat based on the actuator operation amount. The unload flow rate calculation unit 71c2 of the controller 70 determines the unload flow rate Qu or a corresponding value (for example, unload opening area Au) corresponding to the calculated actuator target flow rate Qat, based on the unload flow rate map M set as described above. For example, the unload flow rate calculation unit 71c2 of the controller 70 determines a target value for the unload flow rate Qu corresponding to the actuator target flow rate Qat based on the unload flow rate map Mu. Alternatively, the controller 70 may determine a target value for the unload opening area Au corresponding to the actuator target flow rate Qat based on an unload opening map corresponding to the graph shown in Figure 3.

[0102] The unload command generation unit 71c3 of the controller 70 generates (calculates) an unload command to be input to the unload valve 43 according to a target value of the unload flow rate Qu or a corresponding value calculated by the unload flow rate calculation unit 71c2. The unload command is, for example, a current value. The controller 70 stores information about the relationship between the unload flow rate Qu or a corresponding value (for example, the unload opening area Au) and the unload command, for example, an unload command map, and the unload command generation unit 71c3 generates an unload command corresponding to the target value calculated by the unload flow rate calculation unit 71c2 based on the unload command map. The controller 70 inputs the unload command thus generated to the unload valve 43.

[0103] The controller 70 causes the output unit 80 to output information about the unload total closed flow rate Qac. The controller 70 may also cause the output unit 80 to output at least one of a display and / or sound. The information to be output may be the value of the unload total closed flow rate Qac (for example, 50 L / min). The information about the unload total closed flow rate Qac may also be the set unload characteristics (for example, the energy saving priority characteristic or the operability priority characteristic). Outputting the information allows the operator to understand the unload total closed flow rate Qac or the status related thereto. For example, the output allows the operator to understand whether an appropriate unload total closed flow rate Qac is set according to the operating mode, work content, etc.

[0104] Next, specific examples of the processing performed by the controller 70 will be explained with reference to the flowcharts shown in Figures 5 and 6. Figure 5 shows the process for calculating the target value of the unload flow rate Qu, and Figure 6 shows the process for controlling the actuator flow rate Qa based on the calculated value.

[0105] In the initial state, specifically when the work machine 10 is idling and none of the actuators 30 are moving, the controller 70 sets the assignment of unload characteristics (step S11 in Figure 5). The assignment is the relationship between the unload total closing flow rate change conditions (e.g., operating mode, work content) and the unload characteristics (e.g., the energy saving priority characteristic, the operability priority characteristic). As described above, the assignment may be set by a manual operation given to the input unit 60 by the operator, may be stored in advance in the controller 70, or may be set automatically by the controller 70.

[0106] Next, the controller 70 determines the operating mode that is the condition for changing the unload fully closed flow rate. In Figure 5, the controller 70 determines the operating mode based on the operation signal input to the controller 70 and the designation by the operating mode designation unit 67 (steps S12 to S14, S12y, S13y, S14y, S14n). Specifically, the controller 70 determines that the operating mode to be executed is the remote operation mode if the remote operation signal is input from the remote control unit 61b (the remote operation signal is ON) (YES in step S12) (step S12y). The controller 70 determines that the operating mode to be executed is the automatic operation mode if the automatic control unit 73 is generating an automatic operation signal (the automatic operation signal is ON) (YES in step S13) (step S13y). The controller 70 determines that the driving mode to be executed is the assist driving mode if the assist driving mode is specified by the assist driving mode specification unit 67c (the MC switch in the example shown in Figure 5) (YES in step S14) (step S14y). The controller 70 determines that the driving mode to be executed is the manual onboard driving mode if none of the above cases apply (NO in step S14) (step S14n).

[0107] Next, the controller 70 determines whether the operation signal is ON, that is, whether the actuator operation amount has reached the minimum effective operation amount, which is an effective operation amount sufficient to move the actuator 30 (step S21). If the controller 70 determines that the operation signal is ON, that is, that the actuator operation amount is equal to or greater than the minimum effective operation amount (YES in step S21), it performs the processing from step S22 onwards. In this embodiment, since hydraulic fluid can be supplied to the plurality of actuators 30 from one pump 21, the controller 70 performs the processing from step S22 onwards when the operation signal for at least one of the plurality of actuators 30 is ON, that is, when the actuator operation amount is equal to or greater than the minimum effective operation amount.

[0108] In step S22, the controller 70 calculates the target flow rate for each actuator 30, which is the target value of the flow rate of hydraulic fluid flowing into the actuator 30, based on the actuator operating amount (e.g., lever angle) for each actuator 30. The controller 70 may also calculate the target speed of each actuator 30 as a parameter substantially equivalent to the target flow rate for each actuator 30. The speed of the actuator 30 and the actuator flow rate Qa are mutually interchangeable.

[0109] Furthermore, the controller 70 calculates the actuator target flow rate Qat, which is the sum of the target flow rates for each actuator (step S23).

[0110] On the other hand, the controller 70 determines whether to set the unload characteristics to the energy-saving priority characteristics or the operability priority characteristics based on the unload total closed flow rate change conditions. Specifically, the controller 70 determines whether the conditions for setting the unload characteristics to the energy-saving priority characteristics (unload total closed flow rate change conditions) are met (step S31). If it is determined that the conditions are met (YES in step S31), the unload characteristics are set to the energy-saving priority characteristics, and the unload total closed flow rate Qac is made smaller than the unload total closed flow rate Qac in the operability priority mode (step S32). Conversely, if it is determined that the conditions are not met (NO in step S31), the controller 70 sets the unload characteristics to the operability priority characteristics, and the unload total closed flow rate Qac is made larger than the unload total closed flow rate Qac in the energy-saving priority characteristics (step S33).

[0111] In either case, the unload flow rate calculation unit 71c2 of the controller 70 sets the unload flow rate map Mu corresponding to the unload characteristics (for example, by modifying the basic map) as shown in Figure 4 (step S34).

[0112] Based on the unload flow rate map Mu set in this manner, the unload flow rate calculation unit 71c2 of the controller 70 calculates a target value for the unload flow rate Qu, which corresponds to the actuator target flow rate Qat calculated in step S23, or a corresponding physical quantity (for example, unload opening area Au) (step S35).

[0113] The controller 70 acquires the actual flow rate for each of the actuators 30 (step S41 in Figure 6). Specifically, the controller 70 acquires the actuator drive speed detected by the actuator speed detector 51 and converts this drive speed into the actual flow rate for each actuator, which is the flow rate of the hydraulic fluid flowing into the actuator 30. The actual flow rate for each actuator may also be directly detected by a flow sensor and acquired by the controller 70.

[0114] The controller 70 executes a plurality of control processes shown in Figure 4, namely, pump control processes (steps S51 to S54), control valve control processes (steps S62 to S64), and unload valve control processes (steps S73, S74), so that the hydraulic fluid discharged from the pump 21 flows into the plurality of actuators 30 at the target flow rate Qat of the actuators.

[0115] In the pump control process described above, the pump control unit 71b of the controller 70 controls the pump discharge flow rate Qp based on the actuator target flow rate Qat.

[0116] First, the controller 70 calculates the actual pump discharge flow rate Qpr, which is the actual flow rate of the hydraulic fluid discharged by the pump 21, based on the capacity of the pump 21. The actual pump discharge flow rate Qpr corresponds to the sum of the actuator actual flow rate Qar, which is the total value of the actual flow rates for each actuator obtained in step S41, and the unload flow rate Qu. The actual pump discharge flow rate Qpr may be detected by a flow sensor and obtained by the controller 70.

[0117] Based on the actual pump discharge flow rate Qpr, the controller 70 performs feedback control of the pump discharge flow rate Qp. Specifically, the controller 70 calculates the target pump discharge flow rate Qpt, which is the target value of the pump discharge flow rate Qp, i.e., the sum of the actuator target flow rate Qat and the unload flow rate Qu, and adjusts the capacity of the pump 21 to reduce the deviation of the actual pump discharge flow rate Qpr from the target pump discharge flow rate Qpt. Specifically, the controller 70 calculates the capacity command signal to make the actual capacity of the pump 21 a target capacity corresponding to the target pump discharge flow rate Qpt (step S53), and outputs the capacity command signal and inputs it to the pump capacity actuator 23 (step S54). The capacity command signal is, for example, a current value (command current).

[0118] When the actual flow rate Qar of the actuator 30 does not reach the target flow rate Qat of the actuator (i.e., the speed of the actuator 30 does not reach the target speed) during acceleration of the actuator 30's operation, the actual flow rate Qpr of the pump discharge is smaller than the target flow rate Qpt of the pump discharge. Therefore, the controller 70 controls the system to increase the target flow rate Qpt by increasing the target flow rate Qpt in accordance with the deviation of the actual flow rate Qpr of the pump discharge. Conversely, when the actual flow rate Qar of the actuator 30 exceeds the target flow rate Qat (i.e., the speed of the actuator 30 exceeds the target speed) during deceleration of the actuator 30, the actual flow rate Qpr of the pump discharge is larger than the target flow rate Qpt. Therefore, the controller 70 controls the system to decrease the target flow rate Qpt by decreasing the target flow rate Qpt in accordance with the deviation of the actual flow rate Qpr of the pump discharge. Furthermore, if the actual pump discharge flow rate Qpr deviates from the target pump discharge flow rate Qpt (an error occurs) due to variations in the equipment characteristics of the pump 21, the controller 70 modifies the target pump discharge flow rate Qpt to reduce the deviation of the actual pump discharge flow rate Qpr from the target pump discharge flow rate Qpt.

[0119] In the control valve control process described above, the control valve control unit 71d of the controller 70 provides feedback control of the flow rate from the control valve 41 to the actuator 30 by adjusting the opening area of ​​each control valve 41 based on the actuator target flow rate Qat (step S62). Specifically, the controller 70 adjusts the opening area of ​​the control valve 41 to reduce the deviation between the actuator-specific target flow rate obtained in step S22 and the actuator-specific actual flow rate obtained in step S41. In this way, the controller 70 compensates for the target flow rate of each actuator 30 (target flow rate of the control valve 41). Specifically, the controller 70 calculates a control valve command to set the actual opening area of ​​the control valve 41 to the target value of the opening area calculated in step S62 (step S63), and outputs the control valve command to input to the control valve 41 (step S64). The control valve command is, for example, a current value (command current). In this embodiment, the controller 70 calculates and outputs control valve commands for each of the control valves 41 that correspond to each of the actuators 30.

[0120] In the unload valve control process described above, the unload valve control unit 71c of the controller 70 controls the unload flow rate Qu based on the actuator target flow rate Qat (feedforward control).

[0121] Specifically, the unload command generation unit 71c3 of the controller 70 calculates (generates) the unload command (step S73), outputs the unload command, and inputs it to the unload valve 43 (step S74). More specifically, the controller 70 calculates a target value for the unload flow rate Qu corresponding to the actuator target flow rate Qat based on the unload flow rate map Mu set in step S35, and calculates an unload command corresponding to the target value for the unload flow rate Qu calculated in step S35 shown in Figure 5, based on the unload command map shown in Figure 4.

[0122] The controller 70 repeatedly executes the processes shown in Figures 5 and 6, as described above.

[0123] As described above, the hydraulic drive device 100 allows the controller 70 to perform hydraulic drive control according to the usage conditions of the work machine 10 by changing the unload full-close flow rate Qac. Specifically, by increasing the unload full-close flow rate Qac, the controller 70 can suppress the rapid decrease in the unload opening area Au of the unload valve 43 that occurs with changes in the actuator operation amount, that is, it can make the change in unload flow rate Qu more gradual, thereby improving the operability of the actuator 30, for example. On the other hand, by decreasing the unload full-close flow rate Qac, the controller 70 can enable the unload valve 43 to close with a relatively small actuator operation amount, thereby reducing the loss of hydraulic energy output by the pump 21 and improving the fuel efficiency of the work machine 10, for example. Therefore, by changing the unload full-close flow rate Qac according to the unload full-close flow rate change conditions, which are conditions related to the usage conditions of the work machine 10, the controller 70 can make the characteristic of fully closing the unload valve 43 an appropriate characteristic according to the usage conditions of the work machine 10.

[0124] Specifically, the controller 70 according to the above embodiment can set an appropriate unload fully closed flow rate Qac according to the operating mode by changing the unload fully closed flow rate Qac according to the operating mode.

[0125] Furthermore, the controller 70 can appropriately determine the operating mode based on the image of the inside of the operator's cab 13c generated by the imaging device 53, thereby enabling it to set an appropriate unload fully closed flow rate Qac according to the operating mode.

[0126] Furthermore, the controller 70 can appropriately determine whether the operating mode is the remote operation mode based on whether the remote operation response device 65 is visible in the captured image, thereby appropriately changing the unload fully closed flow rate Qac.

[0127] Furthermore, the controller 70 can provide an unload fully closed flow rate Qac suitable for the operating mode specified by the operator by changing the unload fully closed flow rate Qac according to the operating mode specified by the operating mode specification unit 67.

[0128] The controller 70 outputs information about the unloaded fully closed flow rate Qac to the output unit 80, thereby enabling the operator to grasp this information.

[0129] (Modifications) The above embodiments (including modifications within the embodiments (hereinafter the same)) may be modified in various ways. For example, the number of components in the above embodiments may be changed, and some components may not be provided. For example, the arrangement of components may be changed. For example, the connections between components shown in Figure 2 may be changed. For example, the inclusion relationships of components may be changed in various ways. For example, a component described as a subordinate component included in a higher-level component may not be included in this higher-level component, but may be included in other components. For example, a group of elements described as distinct from each other may be treated as a single element. For example, a single element may be divided into a group of distinct elements. For example, each component may have only a part of each characteristic (function, arrangement, shape, operation, etc.).

[0130] For example, the order of steps in the flowcharts shown in Figures 5 and 6 may be changed, and some steps may be omitted. For example, various types of information (values, ranges, etc.) may be pre-set in the controller 70 shown in Figure 2, or they may be set by being read into the controller 70 from an external storage device. Various types of information may be set in the controller 70 based on information set by manual operation of the input unit 60 by an operator. Various types of information may be set in the controller 70 based on information detected by the detection unit 50. For example, various types of information may not be changed, may be changed by manual operation, or may be automatically changed by the controller 70 according to some condition. For example, the controller 70 may perform substantially the same processing as the processing (calculation, judgment, etc.) of the above embodiment. For example, the mathematical formulas, processing procedures, and information used in the processing can be changed in various ways. For example, the controller 70 may perform processing using information that can be converted into the various types of information used in the above embodiment. The processing performed by the controller 70 may be combined in various ways.

[0131] A control program may be set to cause the controller 70 (computer) to perform the above-described process, or a control method may be performed to execute the above-described process. Each of the above operations may be referred to as a "step" in the control program and control method described above. For example, changing the unload fully closed flow rate Qac (see Figure 3) may be referred to as the "unload fully closed flow rate change step".

[0132] As described above, a device for driving a work machine by hydraulics is provided. The device comprises a tank for storing hydraulic fluid, a pump for discharging the hydraulic fluid stored in the tank, an actuator, an unload valve, and a controller. The actuator is driven by the supply of hydraulic fluid discharged by the pump, thereby moving the work machine. The unload valve operates to change the unload flow rate, which is the flow rate of hydraulic fluid discharged by the pump and returned to the tank through the unload valve without passing through the actuator. The controller calculates an actuator target flow rate, which is a target value for the flow rate of hydraulic fluid flowing into the actuator, based on the actuator operation amount, which is the magnitude of the operation to drive the actuator, and controls the unload flow rate based on the actuator target flow rate. The controller is configured to change the unload full-close flow rate according to conditions set for the usage status of the work machine. The unload full-close flow rate is the minimum value of the actuator target flow rate that fully closes the unload valve.

[0133] If the work machine can be operated in multiple operating modes, each of which has a different method of operation for moving the work machine, the controller is preferably configured to change the unload full-close flow rate according to the operating mode being performed among the multiple operating modes.

[0134] The hydraulic drive system may further include an imaging device that generates an image, which is an image of the inside of the operator's cab of the work machine. In this case, the controller is preferably configured to determine the operating mode to be performed based on the image generated by the imaging device.

[0135] The hydraulic drive system may further include an in-cab operating device located inside the operator's cab that provides an operation for driving the actuator. In this case, the controller is preferably configured to determine whether the operating mode being performed is a remote operation mode based on whether a remote operation response device that provides the operation to the in-cab operating device in response to a command from outside the work machine is visible in the captured image, and to change the unload full-close flow rate according to whether the operating mode is a remote operation mode.

[0136] The hydraulic drive device may further include an operating mode designation unit that designates an operating mode to be executed from among the plurality of operating modes based on a designated operation given by the operator. In this case, the controller is preferably configured to change the unload full-close flow rate according to the operating mode designated by the operating mode designation unit.

[0137] The hydraulic drive device may further include an output unit that outputs information. In this case, the controller is preferably configured to cause the output unit to output information about the unloaded total closed flow rate.

Claims

1. A hydraulic drive device for driving a work machine, comprising: a tank for storing hydraulic fluid; a pump for discharging the hydraulic fluid stored in the tank; an actuator that moves the work machine by being driven by the supply of hydraulic fluid discharged by the pump; an unload valve for changing the unload flow rate, wherein the unload flow rate is the flow rate of hydraulic fluid discharged by the pump and flowing into the tank through the unload valve without passing through the actuator; and a controller that calculates an actuator target flow rate, which is a target value for the flow rate of hydraulic fluid flowing into the actuator, based on an actuator operation amount, which is the magnitude of the operation to drive the actuator, and controls the unload flow rate based on the actuator target flow rate, wherein the controller is configured to change the unload fully closed flow rate, which is the minimum value of the actuator target flow rate that completely closes the unload valve, according to conditions relating to the usage status of the work machine.

2. A hydraulic drive system according to claim 1, wherein the work machine is capable of being operated in a plurality of operating modes, each of which has a different method of operation for moving the work machine, and the controller is configured to change the unload fully closed flow rate according to the operating mode being performed among the plurality of operating modes.

3. A hydraulic drive system according to claim 2, further comprising an imaging device that generates an image which is an image of the inside of the operator's cab of the work machine, wherein the controller determines the operating mode to be performed based on the image generated by the imaging device.

4. A hydraulic drive system according to claim 3, further comprising an in-cabin operating device disposed inside the operator's cab and for which an operation to drive the actuator is given, wherein the controller is configured to determine whether the operating mode to be performed is a remote operation mode based on whether or not a remote operation response device that gives the operation to the in-cabin operating device in response to a command from outside the work machine is visible in the captured image, and to change the unload total closed flow rate according to whether or not the operating mode is a remote operation mode.

5. A hydraulic drive device according to claim 2, further comprising an operating mode designation unit that designates an operating mode to be executed from among the plurality of operating modes based on a designated operation given by an operator, wherein the controller is configured to change the unload total closed flow rate according to the operating mode designated by the operating mode designation unit.

6. A hydraulic drive device according to claim 1, further comprising an output unit for outputting information, wherein the controller is configured to cause the output unit to output information regarding the unloaded fully closed flow rate.

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