Work Machine

Abstract

This work machine comprises: a work device that includes a plurality of hydraulic cylinders which are driven by hydraulic fluid from a pump, and a plurality of driven members which are driven by the hydraulic cylinders; an operation device that outputs operation commands for the hydraulic cylinders; a control device that controls the operation of the work device on the basis of the operation commands from the operation device; and an orientation detection device that detects the orientation of the work device. The control device computes the target pressure and the target speed of each of the hydraulic cylinders on the basis of the operation command, computes the target flow rate of each of the hydraulic cylinders on the basis of the target speed, and computes the actual speed of each of the hydraulic cylinders on the basis of the detection result by the orientation detection device. When the degree of deviation between the target speed and the actual speed of a hydraulic cylinder is greater than a predetermined value, the control device controls the pressure of that hydraulic cylinder and, when the degree of deviation is smaller than the predetermined value, the control device controls the flow rate of that hydraulic cylinder.

Description

[Technical field]

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

[0002] In a work machine such as a hydraulic excavator, a driven member such as a boom or an arm is rotationally driven by a fluid pressure cylinder such as a hydraulic cylinder. Generally, in order to control the trajectory of the work device, it is desirable that the speed of the fluid pressure cylinder is constant when the operation signal is constant.

[0003] However, since the working implement is made of a welded structure made of welded steel plates, it has a large inertial mass. Therefore, when an operation command changes suddenly, the driven member may suddenly accelerate or stop, causing a shock to the entire vehicle body. For this reason, a method is known for reducing the shock by gradually switching a directional control valve that controls the supply and discharge of pressure oil to the hydraulic cylinder for the front working implement (see Patent Document 1).

[0004] In the work machine described in Patent Document 1, when the boom lowering operation time is longer than the set time, the return movement of the spool of the boom pilot switching valve (directional control valve) is delayed by switching the solenoid switching valve provided in the pilot line connected to the boom lowering pilot port from an open oil line position to an oil line position with a throttle section. When the return movement of the spool is delayed, the opening of the meter-out opening of the directional control valve gradually decreases and the brake pressure gradually increases, so that the boom can be stopped gently. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 7-207697 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the work machine described in Patent Document 1, by delaying the return motion of the spool of the directional control valve, the opening of the meter-out opening of the directional control valve gradually decreases, and the opening of the meter-in opening of the directional control valve also gradually decreases. As a result, the balance between the brake pressure generated when the boom cylinder stops and the pushing pressure by the pump is lost, and there is a risk that the actuator cannot be stopped slowly and stably.

[0007] An object of the present invention is to operate a working device at a stable acceleration / deceleration while preventing the working device from suddenly moving. [Means for solving the problem]

[0008] A working machine according to one aspect of the present invention includes a pump that discharges a hydraulic fluid, a working device having a plurality of fluid pressure cylinders driven by the hydraulic fluid discharged from the pump and a plurality of driven members driven by the fluid pressure cylinders, an operation device that outputs an operation command for the fluid pressure cylinder, a control device that controls the operation of the working device based on an operation command from the operation device, and an attitude detection device that detects the attitude of the working device. The control device calculates a target pressure and a target speed of the fluid pressure cylinder based on the operation command from the operation device, and calculates a target flow rate of the fluid pressure cylinder based on the target speed of the fluid pressure cylinder. The control device calculates an actual speed of the fluid pressure cylinder based on a detection result from the attitude detection device, and calculates a degree of deviation between the target speed of the fluid pressure cylinder and the actual speed of the fluid pressure cylinder. When the degree of deviation is greater than a predetermined value, the control device executes pressure control to set the pressure of the fluid pressure cylinder to the target pressure. When the degree of deviation is smaller than a predetermined value, the control device executes flow rate control for setting the flow rate of the fluid pressure cylinder to the target flow rate. Effect of the Invention

[0009] According to the present invention, the working device can be operated at a stable acceleration / deceleration while preventing the working device from suddenly moving. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a side view of a hydraulic excavator according to an embodiment of the present invention. [Diagram 2] FIG. 1 is a diagram showing a hydraulic system mounted on a hydraulic excavator. [Diagram 3] FIG. 2 is a diagram showing the coordinate system (excavator reference coordinate system) in a hydraulic excavator. [Figure 4] FIG. 2 is a functional block diagram of a main controller, showing functions for calculating a meter-in target pressure, a meter-out target pressure, a pump target pressure, and an actuator target speed, and a function for setting a pressure control flag. [Diagram 5] FIG. 2 is a functional block diagram of a main controller, illustrating functions for calculating a meter-in control valve command value, a directional control valve command value, and a pump volume command value for pressure control. [Figure 6] FIG. 2 is a functional block diagram of a main controller, showing functions for calculating a directional control valve command value, a meter-in control valve command value, and a pump volume command value for flow rate control. [Figure 7] FIG. 2 is a functional block diagram of a main controller, showing functions for generating a directional control valve command, a meter-in control valve command, and a pump volume command. [Figure 8] 4 is a diagram showing the contents of the calculation process performed by an inertia moment correction ratio calculation unit C1. FIG. [Figure 9] 4 is a diagram for explaining a method of calculating a measured value Ia of the moment of inertia from the equation of motion. [Figure 10] FIG. 4 is a diagram for explaining a method of calculating a reference value Ib of the moment of inertia. [Figure 11] 4 is a diagram showing the contents of the calculation process performed by a target thrust calculation unit C2. FIG. [Figure 12] FIG. 11 is a diagram showing the contents of the calculation process performed by a target pressure calculation unit C3, and shows the process for calculating a meter-in target pressure and a meter-out target pressure. [Figure 13]FIG. 11 is a diagram showing the contents of the calculation process performed by a target pressure calculation unit C3, and shows the process for calculating a pump target pressure. [Figure 14] FIG. 4 is a diagram showing the contents of the calculation process performed by an actuator target speed calculation unit C4. [Figure 15] FIG. 13 is a diagram showing the contents of the calculation process performed by a pressure control flag setting unit C5. [Figure 16] FIG. 4 is a diagram showing the contents of the calculation process performed by a meter-in pressure calculation unit C6. [Figure 17] FIG. 13 is a diagram showing the contents of the calculation process performed by a pressure control meter-in control valve command calculation unit C7. [Figure 18] FIG. 13 is a diagram showing the contents of the calculation process performed by a pressure control directional control valve command calculation unit C8. [Figure 19] FIG. 13 is a diagram showing the contents of the calculation process performed by a pressure control pump volume command calculation unit C9. [Figure 20] FIG. 4 is a diagram showing the contents of the calculation process performed by a bleed-off valve command generating unit C10. [Figure 21] FIG. 13 is a diagram showing the contents of the calculation process performed by a flow rate control directional control valve command calculation unit C11. [Figure 22] 13 is a diagram showing the contents of the calculation process performed by an actuator target flow rate calculation unit C12. [Figure 23] FIG. 13 is a diagram showing the contents of the calculation process performed by a flow rate control meter-in control valve command calculation unit C13. [Figure 24] 13 is a diagram showing the contents of the calculation process performed by a flow rate control pump volume command calculation unit C14. FIG. [Diagram 25] 4 is a time chart showing an example of an operation when a boom raising operation is performed alone in the hydraulic excavator according to the embodiment. [Figure 26] 5 is a time chart showing an example of an operation when a boom raising operation alone is performed in a hydraulic excavator according to a comparative example of the present embodiment. [Figure 27] 5 is a time chart showing an example of an operation when an arm pulling operation alone is performed in the hydraulic excavator according to the present embodiment. [Figure 28]5 is a time chart showing an example of an operation when an arm pulling operation alone is performed in a hydraulic excavator according to a comparative example of the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] A working machine according to an embodiment of the present invention will be described with reference to the drawings. In this embodiment, an example will be described in which the working machine is a crawler-type hydraulic excavator.

[0012] Fig. 1 is a side view of a hydraulic excavator 1 according to an embodiment of the present invention. For ease of explanation, the front-rear and up-down directions of the hydraulic excavator 1 are defined as shown in Fig. 1. In other words, in this embodiment, unless otherwise specified, the front of the driver's seat (the left direction in the figure) is the front of the hydraulic excavator 1.

[0013] The hydraulic excavator 1 comprises a machine body (vehicle body) 20 and a working device 10 attached to the machine body 20. The machine body 20 comprises a running body 2 and a rotating body 3 mounted on the running body 2 so as to be capable of rotating. The running body 2 has a pair of left and right crawlers and a traveling hydraulic motor 2a which serves as an actuator. The running body 2 travels by driving the crawlers by the traveling hydraulic motor 2a. The rotating body 3 has a rotating hydraulic motor 3a which serves as an actuator. The rotating body 3 rotates relative to the running body 2 by the rotating hydraulic motor 3a.

[0014] The revolving body 3 has a revolving frame 30, a cab 31 provided on the front left side of the revolving frame 30, a counterweight 32 provided at the rear of the revolving frame 30, and an engine room 33 provided on the revolving frame 30 behind the cab 31. The engine room 33 accommodates an engine as a power source and hydraulic equipment such as a hydraulic pump, valves, and accumulators. The working device 10 is rotatably connected to the center of the front of the revolving frame 30.

[0015] The working device 10 is an articulated working device having a plurality of driven members (11, 12, 13) rotatably connected to each other, and a plurality of fluid pressure cylinders (11a, 12a, 13a) for driving the driven members. In this embodiment, three driven members, a boom 11, an arm 12, and a bucket 13, are connected in series. The boom 11 has a base end rotatably connected to the front of the revolving frame 30 by a boom pin 11b (see FIG. 3). The arm 12 has a base end rotatably connected to the tip of the boom 11 by an arm pin 12b (see FIG. 3). The bucket 13 is rotatably connected to the tip of the arm 12 by a bucket pin 13b (see FIG. 3). The boom pin 11b, the arm pin 12b, and the bucket pin 13b are arranged parallel to each other, and the driven members (11, 12, 13) are rotatable relative to each other in the same plane.

[0016] The boom 11 is driven by a hydraulic cylinder (hereinafter also referred to as boom cylinder 11a) which is an actuator, and rotates relative to the revolving frame 30. The arm 12 is driven by a hydraulic cylinder (hereinafter also referred to as arm cylinder 12a) which is an actuator, and rotates relative to the boom 11. The bucket 13 is driven by a hydraulic cylinder (hereinafter also referred to as bucket cylinder 13a) which is an actuator, and rotates relative to the arm 12. These hydraulic cylinders (11a, 12, 13a) are driven by hydraulic oil which serves as a working fluid and is discharged from a pump 81 (see FIG. 2) which will be described later.

[0017] Fig. 2 is a diagram showing a hydraulic system 90 mounted on the hydraulic excavator 1. Note that the hydraulic system 90 is provided with hydraulic equipment for driving a plurality of hydraulic actuators (2a, 3a, 11a, 12a, 13a), but Fig. 2 only shows hydraulic equipment for driving the boom cylinder 11a and the arm cylinder 12a, and does not show hydraulic equipment for driving the other hydraulic actuators (2a, 3a, 13a).

[0018] 2 also illustrates a main controller 100, which is a control device that controls the operation of the work device 10 based on operation commands from the operation devices 23, 24, and devices (23-29) that output signals to the main controller 100. As shown in Fig. 2, the hydraulic excavator 1 includes an operation device (also referred to as a boom operation device) 23 for operating the boom cylinder 11a (boom 11), and an operation device (also referred to as an arm operation device) 24 for operating the arm cylinder 12a (arm 12). The operation devices (23, 24) are provided in the operator's cab 31.

[0019] The boom operation device 23 has an operation lever 23a that can be tilted from a neutral position to the boom-raising side and the boom-lowering side, and an operation sensor that detects the operation direction and operation amount of the operation lever 23a and outputs an operation signal indicating the operation direction and operation amount of the operation lever 23a to the main controller 100 as an operation command for the boom cylinder 11a. The arm operation device 24 has an operation lever 24a that can be tilted from a neutral position to the arm cloud side (arm retract side) and the arm dump side (arm push side), and an operation sensor that detects the operation direction and operation amount of the operation lever 24a and outputs an operation signal indicating the operation direction and operation amount of the operation lever 24a to the main controller 100 as an operation command for the arm cylinder 12a.

[0020] When the operation levers 23a, 24a are tilted from the neutral position to one side (the hydraulic cylinder extension side), the operation devices 23, 24 output an operation signal representing a positive operation amount. 4a When the operating lever 23a, 24a is tilted from the neutral position to the other side (the hydraulic cylinder retraction side), it outputs an operation signal that indicates a negative value of the operation amount. The operation amount (operation angle) of the operating lever 23a, 24a detected by the operation sensor of the operating device 23, 24 is 0[%] (0°) when in the neutral position, and the more it is tilted from the neutral position, the larger the absolute value becomes.

[0021] Although not shown, an engine control dial for setting a target rotation speed of the engine 80 is provided in the cab 31. The main controller 100 determines the target rotation speed based on an operation signal from the engine control dial, and outputs a signal of the determined target rotation speed to the engine controller 108. The engine 80 is provided with an engine rotation speed sensor 80a for detecting an actual rotation speed of the engine 80, and a fuel injection device 80b for adjusting the amount of fuel injected into a cylinder of the engine 80. The engine controller 108 controls the fuel injection device 80b so that the actual rotation speed of the engine 80 detected by the engine rotation speed sensor 80a becomes the target rotation speed output from the main controller 100.

[0022] The hydraulic system 90 comprises a variable displacement pump 81 whose discharge capacity (displacement volume) can be changed, a main circuit HC that supplies hydraulic oil discharged from the pump 81 to the boom cylinder 11a and the arm cylinder 12a, and a bleed-off passage Lb that connects the pump 81 to a tank 19 in which the hydraulic oil is stored.

[0023] The pump 81 is connected to the engine 80 and driven by the engine 80 to suck and discharge hydraulic oil from the tank 19. The pump 81 is a piston-type hydraulic pump (fluid pressure pump) and its discharge capacity changes when the inclination of a swash plate is changed by a regulator 81a. The engine 80 is the power source of the hydraulic excavator 1 and is constituted by an internal combustion engine such as a diesel engine, for example.

[0024] The main circuit HC is provided with a directional control valve (hereinafter also referred to as the boom control valve) 45 that controls the flow of hydraulic oil supplied from the pump 81 to the boom cylinder 11a and the flow of hydraulic oil discharged from the boom cylinder 11a to the tank 19, and a directional control valve (hereinafter also referred to as the arm control valve) 46 that controls the flow of hydraulic oil supplied from the pump 81 to the arm cylinder 12a and the flow of hydraulic oil discharged from the arm cylinder 12a to the tank 19.

[0025] The directional control valves 45 and 46 have pilot pressure receiving portions 45c, 45d, 46c, and 46d, and solenoid valves 45a, 45b, 46a, and 46b that output pilot pressure to the pilot pressure receiving portions 45c, 45d, 46c, and 46d. The solenoid valves 45a, 45b, 46a, and 46b reduce pilot primary pressure from a pilot circuit having a pilot hydraulic source such as a pilot pump (not shown), generate pilot secondary pressure, and output the generated pilot secondary pressure to the pilot pressure receiving portions 45c, 45d, 46c, and 46d of the directional control valves 45 and 46.

[0026] The solenoid valves 45a, 45b, 46a, and 46b are solenoid proportional valves that are driven by a solenoid thrust force generated in response to a control current supplied from the main controller 100 to a solenoid, and generate a pilot secondary pressure in response to the control current.

[0027] The main controller 100 controls the solenoid valves 45a, 45b based on an operation signal output from the boom operation device 23, and controls the solenoid valves 46a, 46b based on an operation signal output from the arm operation device 24.

[0028] When the pilot secondary pressure generated by the solenoid valve 45a acts on the pilot pressure receiving portion 45c of the boom control valve 45, the boom control valve 45 is switched to the extended position. As a result, the hydraulic oil discharged from the pump 81 is guided to the bottom chamber of the boom cylinder 11a and the hydraulic oil is discharged from the rod chamber to the tank 19, and the boom cylinder 11a is extended. As a result, the boom 11 rotates upward (i.e., the boom 11 stands up).

[0029] When the pilot secondary pressure generated by the solenoid valve 45b acts on the pilot pressure receiving portion 45d of the boom control valve 45, the boom control valve 45 is switched to the contracted position. As a result, the hydraulic oil discharged from the pump 81 is guided to the rod chamber of the boom cylinder 11a and the hydraulic oil is discharged from the bottom chamber to the tank 19, causing the boom cylinder 11a to contract. As a result, the boom 11 rotates downward (i.e., the boom 11 is lowered).

[0030] When the pilot secondary pressure generated by the solenoid valve 46a acts on the pilot pressure receiving portion 46c of the arm control valve 46, the arm control valve 46 is switched to the extension position. As a result, the hydraulic oil discharged from the pump 81 is guided to the bottom chamber of the arm cylinder 12a and the hydraulic oil is discharged from the rod chamber to the tank 19, and the arm cylinder 12a is extended. As a result, the arm 12 rotates downward (i.e., the arm 12 performs a crowding operation (arm pulling operation)).

[0031] When the pilot secondary pressure generated by the solenoid valve 46b acts on the pilot pressure receiving portion 46d of the arm control valve 46, the arm control valve 46 is switched to the contracted position. As a result, the hydraulic oil discharged from the pump 81 is guided to the rod chamber of the arm cylinder 12a and the hydraulic oil is discharged from the bottom chamber to the tank 19, and the arm cylinder 12a contracts. As a result, the arm 12 rotates upward (i.e., the arm 12 performs a dumping operation (arm pushing operation)).

[0032] The main circuit HC is provided with a relief valve 47 which determines the maximum pressure of the pump discharge pressure by discharging the hydraulic oil discharged from the pump 81 into the tank 19 when the pump discharge pressure (circuit pressure) exceeds a preset set pressure.

[0033] A meter-in control valve (also referred to as a boom meter-in control valve) 41 that controls the flow of hydraulic oil supplied to the boom cylinder 11a is provided in a passage (upstream passage of the boom control valve 45) connected to the pump port of the boom control valve 45. The meter-in control valve 41 also functions as a check valve for maintaining the load pressure of the boom cylinder 11a, and is fully closed when the pump discharge pressure falls below the cylinder pressure. A meter-in control valve (also referred to as an arm meter-in control valve) 42 that controls the flow of hydraulic oil supplied to the arm cylinder 12a is provided in a passage (upstream passage of the arm control valve 46) connected to the pump port of the arm control valve 46. The meter-in control valve 42 also functions as a check valve for maintaining the load pressure of the arm cylinder 12a, and is fully closed when the pump discharge pressure falls below the cylinder pressure.

[0034] The meter-in control valves 41, 42 are electromagnetic proportional valves that are driven by a solenoid thrust generated in response to a control current supplied from the main controller 100 to an electromagnetic drive unit (solenoid), and whose opening degree (meter-in opening area) is adjusted in response to the control current.

[0035] The bleed-off passage Lb is provided so as to branch off from the pump discharge passage upstream of the meter-in control valves 41, 42. The bleed-off passage Lb is provided with a bleed-off valve 18 that discharges the hydraulic oil discharged from the pump 81 to the tank 19. The bleed-off valve 18 is capable of adjusting the bleed-off flow rate and the pump discharge pressure by changing the opening degree of the bleed-off passage Lb.

[0036] The bleed-off valve 18 is an electromagnetic proportional valve that is driven by a solenoid thrust generated in response to a control current supplied from the main controller 100 to an electromagnetic drive unit (solenoid), and whose opening (bleed-off opening area) is adjusted in response to the control current.

[0037] The main controller 100 is configured as a microcomputer including a CPU (Central Processing Unit) 101 as an operating circuit, a ROM (Read Only Memory) 102 as a storage device, a RAM (Random Access Memory) 103 as a storage device, an input / output interface 104, and other peripheral circuits. The main controller 100 may be configured as one microcomputer or multiple microcomputers. The engine controller 108 has a similar configuration to the main controller 100, is connected to the main controller 100, and exchanges information (data) with the main controller 100.

[0038] The ROM 102 is a non-volatile memory such as an EEPROM, and stores programs capable of executing various calculations. In other words, the ROM 102 is a storage medium capable of reading programs that realize the functions of this embodiment. The RAM 103 is a volatile memory, and is a work memory that directly inputs and outputs data to and from the CPU 101. The RAM 103 temporarily stores necessary data while the CPU 101 is executing the programs. The main controller 100 may further include a storage device such as a flash memory, a hard disk drive, or the like.

[0039] The CPU 101 is a processing device that loads a program stored in the ROM 102 into the RAM 103 and executes the program, and performs a predetermined calculation process on signals received from the input / output interface 104, the ROM 102, and the RAM 103 in accordance with the program. Signals from the operation devices 23, 24, the pressure sensors 25-29, the attitude detection device 15, the engine controller 108, and the like are input to the input / output interface 104. An input section of the input / output interface 104 converts the input signals into data that can be calculated by the CPU 101. An output section of the input / output interface 104 generates an output signal according to the calculation result by the CPU 101, and outputs the signal to the directional control valves 45, 46, the meter-in control valves 41, 42, the bleed-off valve 18, the regulator 81a, and the like.

[0040] The attitude detection device 15 includes IMUs (Inertial Measurement Units) 15a to 15d attached to the boom 11, the arm 12, the bucket 13, and the rotating frame 30, respectively, a rotation angle sensor 15e attached to the machine body 20, and an attitude calculation controller 15f. L (See Figure 1.)

[0041] The IMUs 15a, 15b, 15c, and 15d detect angular velocities and accelerations of three orthogonal axes of members as information related to the attitude of the hydraulic excavator 1, and output the detection results to the attitude calculation controller 15f. The swing angle sensor 15e detects a swing angle, which is a relative angle of the swing body 3 with respect to the traveling body 2 in a plane perpendicular to the swing central axis, as information related to the attitude of the hydraulic excavator 1, and outputs the detection result to the attitude calculation controller 15f. The attitude calculation controller 15f calculates a boom angle α, an arm angle β, a bucket angle γ, a vehicle body inclination angle φ, and a swing angle θ based on the detection results of the IMUs 15a to 15d and the detection result of the swing angle sensor 15e, and outputs the calculation results to the main controller 100. In this way, the attitude detection device 15 has a function of detecting the attitudes of the working device 10 and the machine body 20.

[0042] FIG. 3 is a diagram showing a coordinate system (excavator reference coordinate system) in the hydraulic excavator 1. As shown in FIG. 3, the excavator reference coordinate system is a coordinate system set with respect to the traveling body 2. In the excavator reference coordinate system, the central axis of rotation of the revolving body 3 is set as the Z axis. In the excavator reference coordinate system, in a posture in which the front-rear direction of the revolving body 3 coincides with the front-rear direction of the traveling body 2, an axis that is perpendicular to the Z axis (central axis of rotation) and the boom pin 11b and passes through the central axis of the boom pin 11b is set as the X axis. In other words, an axis extending in the front-rear direction of the traveling body 2 is set as the X axis. In the excavator reference coordinate system, an axis perpendicular to each of the X axis and the Z axis is set as the Y axis, and the intersection of the X axis, the Y axis, and the Z axis is set as the origin O. Boom angle α is the inclination angle of boom 11 with respect to the XY plane, arm angle β is the inclination angle of arm 12 with respect to boom 11, bucket angle γ is the inclination angle of bucket 13 with respect to arm 12, and swing angle θ is the rotation angle of rotating body 3 with respect to running body 2. Also, vehicle body inclination angle φ is the inclination angle of machine body 20 (rotating body 3) with respect to the horizontal plane (reference plane), that is, the angle between the horizontal plane (reference plane) and the X-axis.

[0043] As shown in FIG. 2, the pressure sensor 25 detects the pump discharge pressure (circuit pressure of the main circuit HC) and outputs a signal representing the detection result (pump discharge pressure) to the main controller 100. The pressure sensor 26 detects the pressure in the bottom chamber of the boom cylinder 11a (hereinafter also referred to as bottom pressure or boom bottom pressure) and outputs a signal representing the detection result to the main controller 100. The pressure sensor 27 detects the pressure in the rod chamber of the boom cylinder 11a (hereinafter also referred to as rod pressure or boom rod pressure) and outputs a signal representing the detection result to the main controller 100. The pressure sensor 28 detects the pressure in the bottom chamber of the arm cylinder 12a (hereinafter also referred to as bottom pressure or arm bottom pressure) and outputs a signal representing the detection result to the main controller 100. The pressure sensor 29 detects the pressure in the rod chamber of the arm cylinder 12a (hereinafter also referred to as rod pressure or arm rod pressure) and outputs a signal representing the detection result to the main controller 100.

[0044] The main controller 100 calculates the target pressure and the target speed of the hydraulic cylinders (11a, 12a) based on the operation commands from the operating devices 23, 24, and calculates the target flow rate of the hydraulic cylinders (11a, 12a) based on the target speed of the hydraulic cylinders (11a, 12a). The main controller 100 also calculates the actual speed of the hydraulic cylinders (11a, 12a) based on the detection result of the attitude detection device 15, and calculates a speed deviation ratio as the degree of deviation between the target speed and the actual speed of the hydraulic cylinders (11a, 12a). When the speed deviation ratio is greater than a predetermined value Rw, the main controller 100 executes pressure control for setting the pressure of the hydraulic cylinders (11a, 12a) to the target pressure, thereby preventing the hydraulic cylinders (11a, 12a) from suddenly operating, and thereby operates the hydraulic cylinders (11a, 12a) at a stable acceleration / deceleration speed. In addition, when the speed deviation ratio is smaller than a predetermined value Rw, the main controller 100 executes flow control to set the flow rate of the hydraulic cylinders (11a, 12a) to a target flow rate, thereby operating the hydraulic cylinders (11a, 12a) at a speed intended by the operator.

[0045] Hereinafter, the functions of the main controller 100 will be described in detail with reference to Figs. 4 to 24. Figs. 4 to 7 are functional block diagrams of the main controller 100. Fig. 4 shows a function for calculating a meter-in target pressure, a meter-out target pressure, a pump target pressure, and an actuator target speed, and a function for setting a pressure control flag. Fig. 5 shows a function for calculating a meter-in control valve command value, a directional control valve command value, and a pump volume command value for pressure control. Fig. 6 shows a function for calculating a directional control valve command value, a meter-in control valve command value, and a pump volume command value for flow rate control. Fig. 7 shows a function for generating a directional control valve command, a meter-in control valve command, and a pump volume command. The main controller 100 functions as a calculation unit that performs various calculations by executing a program stored in the ROM 102.

[0046] Specifically, as shown in Fig. 4, the main controller 100 functions as an inertia moment correction ratio calculator C1, a target thrust calculator C2, a target pressure calculator C3, an actuator target speed calculator C4, an actuator actual speed calculator C18, and a pressure control flag setting unit C5. Also, as shown in Fig. 5, the main controller 100 functions as a meter-in pressure calculator C6, a pressure control meter-in control valve command calculator C7, a pressure control directional control valve command calculator C8, and a pressure control pump volume command calculator C9. Also, as shown in Fig. 6, the main controller 100 functions as a bleed-off valve command generator C10, a flow rate control directional control valve command calculator C11, an actuator target flow rate calculator C12, a flow rate control meter-in control valve command calculator C13, and a flow rate control pump volume command calculator C14. Furthermore, as shown in Fig. 7, the main controller 100 functions as a directional control valve command generator C15, a meter-in control valve command generator C16, and a pump volume command generator C17.

[0047] 8 is a diagram showing the contents of the calculation process performed by the inertia moment correction ratio calculation unit C1. The inertia moment correction ratio calculation unit C1 calculates the inertia moment correction ratio Cr based on the cylinder pressures (boom bottom pressure, boom rod pressure, arm bottom pressure, and arm rod pressure) detected by the pressure sensors 26 to 29 and the posture information of the hydraulic excavator 1 detected by the posture detection device 15 (angle information of each member).

[0048] 8, the moment of inertia correction ratio calculation unit C1 functions as a thrust moment calculation unit O1a, a gravitational moment calculation unit O1b, calculation units O1c, O1d, and O1e, a moment of inertia reference value calculation unit O1f, a calculation unit O1g, a determination unit O1h, a selection unit O1i, a low-pass filter processing unit O1j, and a calculation unit O1k. The thrust moment calculation unit O1a, the gravitational moment calculation unit O1b, and the calculation units O1c, O1d, and O1e function as an inertia moment actual measurement value calculation unit O1z that calculates an inertia moment actual measurement value Ia based on cylinder pressure and attitude information and information stored in ROM 102.

[0049] A method for calculating the measured value Ia of the moment of inertia from the equation of motion will be described with reference to Fig. 9. Fig. 9 is a diagram for explaining a method for calculating the measured value Ia of the moment of inertia around the boom pin 11b from the equation of motion.

[0050] The boom cylinder 11a has an end of a rod connected to the boom 11 by a rod-side pin, and an end of a cylinder tube connected to the revolving frame 30 by a bottom-side pin. As shown in Fig. 9, the length of a line segment (OA) that is a straight line connecting a center point Ob of the boom pin 11b and a center point A of the rod-side pin of the boom cylinder 11a is La, the thrust in the axial direction (central axis direction) of the boom cylinder 11a is F, and the angle between an axis perpendicular to the line segment (OA) and the central axis of the boom cylinder 11a is Ψa. In addition, the length of a line segment (OG) that is a straight line connecting a center point Ob of the boom pin 11b and a center G of the center of gravity of the working device 10 supported by the revolving frame 30 via the boom pin 11b is Lg.

[0051] When each dimension is defined as above, the rotational moment (hereinafter also referred to as thrust moment) Mf about the boom pin 11b due to the thrust F of the boom cylinder 11a acting on the working implement 10 is calculated by the following formula (1).

[0052]

number

[0053] The thrust F of the boom cylinder 11a is calculated by the following formula (2), where the piston pressure receiving area in the bottom chamber (pressure receiving area for two cylinders) is Sbot, the piston pressure receiving area on the rod chamber side (pressure receiving area for two cylinders) is Srod, the pressure of hydraulic oil acting on the bottom chamber (bottom pressure) is Pbot, and the pressure of hydraulic oil acting on the rod chamber (rod pressure) is Prod.

[0054]

number

[0055] The rotational moment Mg around the boom pin 11b due to gravity acting on the working implement 10 (hereinafter also referred to as gravity moment) is expressed by the following equation (3), where the mass of the working implement 10 supported by the revolving frame 30 via the boom pin 11b is m, the gravitational acceleration is g, and the angle between the axis perpendicular to the line segment (OG) and the vertical axis (axis in the direction of gravity) is Ψb.

[0056]

number

[0057] For this reason, the equation of motion for rotation about the boom pin 11b is given by the following equation (4), where the moment of inertia about the boom pin 11b is I and the angular acceleration of the boom 11 is α″. It is assumed that no external load is acting on the working implement 10.

[0058]

number

[0059] Therefore, the moment of inertia I is calculated by the following equation (5).

[0060]

number

[0061] The ROM 102 of the main controller 100 stores various dimensional data for calculating the above formulas (1) to (5) in advance.

[0062] The angle Ψa in formula (1) can be calculated based on the boom angle α calculated by the attitude detection device 15 and dimensional data previously stored in ROM 102. The dimensional data stored in ROM 102 includes the length La of the boom pin 11b and the line segment (OA), the length Lb of the line segment (OB) which is a straight line connecting the boom pin 11b and the center point B of the bottom side pin of the boom cylinder 11a, the angle αt between the line segment (OB) and the X-axis, and the angle αu between the line segment (OA) and the straight line connecting the boom pin 11b and the arm pin 12b.

[0063] 8 calculates, for example, the length of the boom cylinder 11a (cylinder length) based on the lengths La, Lb, the angles αt, αu, and the boom angle α detected by the attitude detection device 15, calculates the angle ∠OAB between the line segments (OA) and (AB), and calculates Ψa by subtracting ∠OAB from 90°. The cylinder speed is calculated by differentiating the cylinder length with respect to time.

[0064] The thrust force F in the formula (2) can be calculated based on the bottom pressure Pbot detected by the pressure sensor 26, the rod pressure Prod detected by the pressure sensor 27, and the pressure receiving areas Sbot, Srod stored in the ROM 102 in advance.

[0065] The thrust moment calculation unit O1a calculates the thrust moment Mf by using equations (1) and (2) based on the detection results of the pressure sensors 26 and 27, the detection results of the attitude detection device 15, and various data stored in the ROM 102.

[0066] The length Lb and the angle Ψb in equation (3) (i.e., the center of gravity position G of the composite center of gravity of the driven members) can be calculated based on the angles α, β, γ of each driven member detected by the posture detection device 15, and the center of gravity positions, masses and lengths of the boom 11, arm 12 and bucket 13, which are pre-stored in ROM 102.

[0067] The gravitational moment calculation unit O1b calculates the gravitational moment Mg by using the formula (3) based on the detection results of the attitude detection device 15 and various data stored in the ROM 102.

[0068] The calculation unit O1c adds the gravity moment Mg, which is the result of the calculation in the gravity moment calculation unit O1b, to the thrust moment Mf, which is the result of the calculation in the thrust moment calculation unit O1a. That is, the calculation unit O1c performs calculation based on the formula (4).

[0069] The calculation unit O1d calculates the angular acceleration α" of the boom 11 based on the detection result from the attitude detection device 15. The angular acceleration α" is calculated by differentiating the boom angle α by second order with respect to time. The calculation unit O1d repeatedly obtains the boom angle α detected by the attitude detection device 15 at a predetermined control period. For this reason, the calculation unit O1d calculates the boom angular velocity α' (=(αb-αa) / (tb-ta)), which is the time rate of change of the boom angle α, by dividing the difference (αb-αa) between the previous value αa and the current value αb of the boom angle α, which are repeatedly detected at the predetermined control period, by the time Δt (=tb-ta) from the time ta when the previous value αa was detected to the time tb when the current value αb was detected. Furthermore, the calculation unit O1d similarly calculates the boom angular acceleration α" which is the time rate of change of the boom angular velocity α' from the previous value and the current value of the boom angular velocity α'.

[0070] The calculation unit O1e calculates the actual value of the moment of inertia I (actual measured moment of inertia value Ia) by dividing the calculation result in the calculation unit O1c by the calculation result in the calculation unit O1d. That is, the calculation unit O1e performs calculation based on the formula (5). When the angular acceleration α″ is 0 (zero), the calculation unit O1e takes measures to prevent division by zero, for example, by replacing it with a predetermined minimum value.

[0071] The measured value Ia of the moment of inertia thus obtained will be a different value from the moment of inertia (reference value Ib of the moment of inertia) when the bucket 13 is unloaded, as described below, if it is affected by external loads such as the loading condition inside the bucket 13 or a reaction force from the ground during excavation work.

[0072] The inertia moment reference value calculation unit O1f calculates the inertia moment reference value Ib based on the posture information and the information stored in the ROM 102. The inertia moment reference value Ib is the moment of inertia of the working implement 10 when the bucket 13 is in an empty state and is not moving in a predetermined posture, and is calculated based on the posture of the working implement 10.

[0073] A method for calculating the inertia moment reference value Ib will be described with reference to Fig. 10. Fig. 10 is a diagram for explaining a method for calculating the inertia moment reference value Ib. The inertia moment reference value Ib is expressed by the following formula (6), where the moment around the center point Ob of the boom pin 11b of the boom 11 is I1, the moment around the center point Ob of the boom pin 11b of the arm 12 is I2, and the moment around the center point Ob of the boom pin 11b of the bucket 13 is I3.

[0074]

number

[0075] Moments I1, I2, and I3 are expressed by the following equation (7), where Ig1 is the moment of inertia about the center of gravity of the boom 11, Ig2 is the moment of inertia about the center of gravity of the arm 12, m1 is the mass of the boom 11, m2 is the mass of the arm 12, m3 is the mass of the bucket 13, Lg1 is the distance from the center point Ob of the boom pin 11b to the center of gravity G1 of the boom 11, Lg2 is the distance from the center point Ob of the boom pin 11b to the center of gravity G2 of the arm 12, and Lg3 is the distance from the center point Ob of the boom pin 11b to the center of gravity G3 of the bucket 13.

[0076]

number

[0077] The distances Lg1, Lg2, and Lg3 in equation (7) can be calculated based on the angles α, β, and γ of each driven member detected by the posture detection device 15, as well as the distance from the boom pin 11b to the center of gravity position G1 of the boom 11, the distance from the arm pin 12b to the center of gravity position G2 of the arm 12, and the distance from the bucket pin 13b to the center of gravity position G3 of the bucket 13, which are pre-stored in ROM 102.

[0078] The inertia moment reference value calculation unit O1f calculates the inertia moment reference value Ib based on the detection results from the attitude detection device 15 and various data stored in the ROM 102, by using the equations (6) and (7).

[0079] The calculation unit O1g calculates the absolute value of the angular acceleration α" which is the calculation result of the calculation unit O1d. The judgment unit O1h judges whether the calculation result |α"| of the calculation unit O1g is greater than a preset threshold value Th1. When the judgment unit O1h makes a positive judgment, i.e., when it is judged that the absolute value of the angular acceleration |α"| is greater than the threshold value Th1, the selection unit O1i selects the moment of inertia actual measured value Ia and outputs it to the low-pass filter processing unit O1j. When the judgment unit O1h makes a negative judgment, i.e., when it is judged that the absolute value of the angular acceleration |α"| is equal to or less than the threshold value Th1, the selection unit O1i selects the moment of inertia reference value Ib and outputs it to the low-pass filter processing unit O1j.

[0080] The low-pass filter processing unit O1j performs low-pass filtering on the output from the selection unit O1i and outputs the result as an inertia moment estimated value Ie. The calculation unit O1k calculates an inertia moment correction ratio Cr by dividing the inertia moment estimated value Ie by the inertia moment reference value Ib.

[0081] In this way, the inertia moment correction ratio calculation unit C1 calculates the inertia moment correction ratio Cr based on the cylinder pressure and posture information. Note that, although the calculation of the inertia moment correction ratio Cr about the boom pin 11b has been described as an example, the same calculation is performed for the inertia moment correction ratio Cr about the arm pin 12b and the inertia moment correction ratio Cr about the bucket pin 13b.

[0082] 11 is a diagram showing the contents of the calculation process performed by the target thrust calculation unit C2. The target thrust calculation unit C2 calculates the target thrust of the hydraulic cylinder based on the operation signal, the attitude information, the inertia moment correction ratio Cr calculated by the inertia moment correction ratio calculation unit C1, and the gravitational moment Mg of the working device 10. In the following, a calculation method of the target thrust for the boom cylinder 11a will be described as an example.

[0083] The target thrust calculation unit C2 functions as calculation units O2a, O2b, O2c, O2d, O2e, and O2f, a minimum value selection unit O2g, a calculation unit O2h, a determination unit O2i, a selection unit O2j, a calculation unit O2k, and a thrust component calculation unit O2l. The ROM 102 stores a maximum torque table T2a in which the operation signal corresponds to the maximum torque, and an acceleration torque table T2b in which the operation signal corresponds to the acceleration torque target value.

[0084] The maximum torque table T2a has characteristics such that the absolute value of the maximum torque increases as the absolute value of the operation amount of the operation lever 23a increases. The calculation unit O2a refers to the maximum torque table T2a and calculates the maximum torque based on the operation signal input from the boom operation device 23. The maximum torque is the maximum value of the torque when the working device 10 is stopped during pressing or the like.

[0085] The acceleration torque table T2b has characteristics such that the absolute value of the acceleration torque target value increases as the absolute value of the operation amount of the operation lever 23a increases. The calculation unit O2a refers to the acceleration torque table T2b and calculates the acceleration torque target value based on the operation signal input from the boom operation device 23. The acceleration torque target value is a target value of the acceleration torque when the working device 10 is operated in the air, etc.

[0086] The calculation unit O2c subtracts 1 from the inertia moment correction ratio Cr around the boom pin 11b, and the calculation unit O2d multiplies the calculation result in the calculation unit O2c by a gain Gm. The calculation unit O2e adds 1 to the calculation result in the calculation unit O2d to calculate a torque adjustment gain. The gain Gm is a value from 0 (zero) to 1 (0≦Gm≦1) and is stored in the ROM 102 in advance.

[0087] The calculation unit O2f calculates a corrected acceleration torque target value by multiplying the acceleration torque target value calculated by the calculation unit O2b by the torque adjustment gain calculated by the calculation unit O2e. As a result, when the measured moment of inertia Ia is larger than the reference moment of inertia value Ib, the acceleration torque is corrected to be larger, and when the measured moment of inertia Ia is smaller than the reference moment of inertia value Ib, the acceleration torque is corrected to be smaller. When the measured moment of inertia Ia and the reference moment of inertia value Ib are the same value, the acceleration torque target value is multiplied by 1 to calculate the corrected acceleration torque target value (acceleration torque target value=corrected acceleration torque target value).

[0088] The gain Gm may be changed by an operator's operation on an input device (not shown) such as a touch panel. When the gain Gm is set to 0, the acceleration torque target value is multiplied by 1 even if the measured moment of inertia value Ia and the reference moment of inertia value Ib are different. In other words, the acceleration torque target value is not corrected according to the moment of inertia correction ratio. The larger the gain Gm, the greater the influence of the correction of the acceleration torque target value by the moment of inertia correction ratio. The operator can adjust the magnitude of the actuator acceleration by setting the magnitude of the gain Gm using the input device.

[0089] The minimum value selection unit O2g selects the smaller one of the maximum torque calculated by the calculation unit O2a and the corrected acceleration torque target value (acceleration torque target value×torque adjustment gain) which is the result of calculation by the calculation unit O2f.

[0090] The calculation unit O2h calculates the absolute value of the operation signal of the boom cylinder 11a (the operation amount of the operation lever 23a). The judgment unit O2i judges whether or not the absolute value of the operation signal is greater than a preset threshold value Th2. If the judgment unit O2i makes a positive judgment, i.e., if it is judged that the absolute value of the operation signal is greater than the threshold value Th2, the selection unit O2j selects the minimum value selected by the minimum value selection unit O2g. If the judgment unit O2i makes a negative judgment, i.e., if it is judged that the absolute value of the operation signal is equal to or less than the threshold value Th2, the selection unit O2j selects 0 (zero).

[0091] The calculation unit O2k calculates the boom target torque by subtracting the gravitational moment Mg of the working implement 10 from the value selected by the selection unit O2j. That is, the calculation unit O2k calculates the target torque by adding a torque in a direction that cancels the rotational moment Mg due to gravity acting on the working implement 10 to the value selected by the selection unit O2j. The thrust component calculation unit O2l calculates the axial thrust component of the boom cylinder 11a as the target thrust based on the boom target torque calculated by the calculation unit O2k, the attitude information, and the dimensional data stored in the ROM 102. That is, the thrust component calculation unit O2l calculates the thrust of the boom cylinder 11a required to generate the boom target torque as the target thrust of the boom cylinder 11a.

[0092] In this way, the target thrust calculation unit C2 calculates the target thrust based on the operation signal, the attitude information, the inertia moment correction ratio Cr, and the gravity moment Mg. Note that although the calculation of the target thrust of the boom cylinder 11a has been described as an example, similar calculations are also performed for the target thrust of the arm cylinder 12a and the target thrust of the bucket cylinder 13a.

[0093] Figures 12 and 13 are diagrams showing the contents of the calculation process performed by target pressure calculation unit C3. Figure 12 shows the process for calculating the meter-in target pressure and the meter-out target pressure, and Figure 13 shows the process for calculating the pump target pressure. As shown in Figure 12, target pressure calculation unit C3 calculates the meter-in target pressure and the meter-out target pressure based on the target thrust and operation signal of the hydraulic cylinder. Below, an example of calculating the meter-in target pressure and the meter-out target pressure of boom cylinder 11a based on the target thrust and operation signal of boom cylinder 11a will be representatively described.

[0094] The target pressure calculation section C3 functions as calculation sections O3a and O3b, a determination section O3c, selection sections O3d and O3e, and maximum value selection sections O3f and O3g.

[0095] The calculation unit O3a multiplies the target thrust of the boom cylinder 11a calculated by the target thrust calculation unit C2 by (1 / Sbot) to calculate a bottom side target pressure. The calculation unit O3b multiplies the target thrust of the boom cylinder 11a calculated by the target thrust calculation unit C2 by (-1 / Srod) to calculate a rod side target pressure.

[0096] The determination unit O3c determines whether the boom operation amount is a positive value based on the operation signal of the boom cylinder 11a. The selection unit O3d selects the bottom side target pressure when the boom operation amount is a positive value, and selects the rod side target pressure when the boom operation amount is not a positive value. The selection unit O3e selects the rod side target pressure when the boom operation amount is a positive value, and selects the bottom side target pressure when the boom operation amount is a negative value.

[0097] Maximum value selection unit O3f compares the target pressure selected by selection unit O3d with a predetermined value P1 (e.g., about 1 MPa) previously stored in ROM 102, selects the larger one, and determines the selected value as the meter-in target pressure. Maximum value selection unit O3g compares the target pressure selected by selection unit O3e with 0 (zero), selects the larger one, and determines the selected value as the meter-out target pressure.

[0098] In this way, the target pressure calculation unit C3 calculates the meter-in target pressure and the meter-out target pressure of the hydraulic cylinder based on the operation signal and the target thrust. For example, when the operation lever 23a is operated to the maximum operation position so as to accelerate the boom cylinder 11a in the extension direction, the target thrust calculation unit C2 calculates a positive target thrust, and the judgment unit O3c judges it as positive. Therefore, the selection unit O3d selects the bottom side target pressure obtained by multiplying the positive target thrust by (1 / Sbot). Therefore, the maximum value selection unit O3f selects the bottom side target pressure selected by the selection unit O3d as the meter-in target pressure. Note that the selection unit O3e selects the rod side target pressure obtained by multiplying the positive target thrust by (-1 / Srod), but since the selected value is smaller than 0 (zero), the maximum value selection unit O3g selects 0 (zero) as the meter-out target pressure.

[0099] Although the calculation of the meter-in target pressure and meter-out target pressure of the boom cylinder 11a has been described as an example, similar calculations are performed for the meter-in target pressure and meter-out target pressure of the arm cylinder 12a and the meter-in target pressure and meter-out target pressure of the bucket cylinder 13a.

[0100] 13, the target pressure calculation unit C3 also functions as a maximum value selection unit O3h. The maximum value selection unit O3h selects the largest of the meter-in target pressures of the hydraulic cylinders calculated by the maximum value selection unit O3f, and determines the selected meter-in target pressure as the pump target pressure.

[0101] 14 is a diagram showing the contents of the calculation process performed by the actuator target speed calculation unit C4. The actuator target speed calculation unit C4 calculates the target speed of each actuator based on the operation signal of each actuator. Below, an example of calculating the target speed of the boom cylinder (actuator) 11a based on the operation signal of the boom cylinder (actuator) 11a will be representatively described.

[0102] As shown in Fig. 14, the actuator target speed calculation unit C4 calculates the target speed of the boom cylinder 11a based on the operation signal of the boom cylinder 11a. A table T4 in which the operation signal is associated with the target speed of the boom cylinder 11a is stored in the ROM 102. The table T4 has characteristics in which the absolute value of the target speed increases as the absolute value of the operation amount of the operating lever 23a increases.

[0103] Actuator target speed calculation unit C4 refers to table T4 and calculates the target speed of boom cylinder 11a based on the operation signal input from boom operation device 23. Note that the target speed indicates the target speed in the extension direction of boom cylinder 11a when it is positive, and indicates the target speed in the retraction direction of boom cylinder 11a when it is negative.

[0104] Although not shown, the actuator target speed calculation unit C4 also calculates target speeds for the arm cylinder 12a, the bucket cylinder 13a, the traveling hydraulic motor 2a, and the swing hydraulic motor 3a.

[0105] 15 is a diagram showing the contents of the calculation process performed by the pressure control flag setting unit C5. The pressure control flag setting unit C5 sets the pressure control flag to on or off based on the actuator target speed and actual speed. The following will explain an example of setting the pressure control flag for the boom cylinder (actuator) 11a based on the target speed and actual speed of the boom cylinder (actuator) 11a.

[0106] The actual speed of the boom cylinder 11a is calculated by an actuator actual speed calculation unit C18 shown in Fig. 4. The actuator actual speed calculation unit C18 calculates the actual speeds of the boom cylinder 11a, the arm cylinder 12a, and the bucket cylinder 13a based on the posture information detected by the posture detection device 15. For example, the actuator actual speed calculation unit C18 calculates the actual speed of the boom cylinder 11a based on the length La of the line segment (OA), the length Lb of the line segment (OB), the boom angle α detected by the posture detection device 15, and the formed angles αt and αu shown in Fig. 9.

[0107] As shown in FIG. 15, the pressure control flag setting unit C5 functions as calculation units O5a, O5b, and O5e, a maximum value selection unit O5f, a calculation unit O5g, a determination unit O5h, and a selection unit O5i.

[0108] The calculation unit O5a calculates a cylinder speed difference by subtracting the actual speed from the target speed of the boom cylinder 11a. The calculation unit O5b calculates the absolute value of the cylinder speed difference calculated by the calculation unit O5a. The calculation unit O5e calculates the absolute value of the target speed of the boom cylinder 11a. The maximum value selection unit O5f compares the absolute value of the target speed of the boom cylinder 11a calculated by the calculation unit O5e with the minimum cylinder speed Vmin stored in advance in the ROM 102, and selects the larger one. The minimum cylinder speed Vmin is a speed at which the hydraulic cylinder is considered to be almost stopped, and is set to a value of, for example, about 5 [mm / s].

[0109] The calculation unit O5g calculates a speed deviation ratio by dividing the absolute value of the cylinder speed difference calculated by the calculation unit O5b by the value selected by the maximum value selection unit O5f. The speed deviation ratio is an index that indicates the degree of deviation between the target speed and the actual speed of the boom cylinder 11a, and the larger the value, the greater the deviation between the target speed and the actual speed. The judgment unit O5h judges whether or not the speed deviation ratio is greater than a predetermined value Rw stored in the ROM 102 in advance. The predetermined value Rw is a predetermined threshold value, and is set to, for example, a value of about 0.2. In this case, it can be said that the judgment unit O5h is executing a judgment process that judges whether or not the speed deviation of the actual speed with respect to the target speed of the boom cylinder 11a exceeds 20%.

[0110] When the determination unit O5h makes a positive determination, that is, when it is determined that the speed deviation ratio is greater than the predetermined value Rw, the selection unit O5i sets the pressure control flag to ON. When the determination unit O5h makes a negative determination, that is, when it is determined that the speed deviation ratio is equal to or smaller than the predetermined value Rw, the selection unit O5i sets the pressure control flag to OFF. As will be described later, the pressure control flag is a flag for switching the control method of the hydraulic cylinder between pressure control and flow control. As will be described later, when the pressure control flag is set to ON, the main controller 100 executes pressure control for setting the pressures (meter-in pressure and meter-out pressure) of the hydraulic cylinders (11a, 12a) to target pressures (meter-in target pressure and meter-out target pressure). When the pressure control flag is set to OFF, the main controller 100 executes flow control for setting the flow rate supplied to the hydraulic cylinders (11a, 12a) to the target flow rate.

[0111] 16 is a diagram showing the contents of the calculation process performed by meter-in pressure calculation unit C6. Meter-in pressure calculation unit C6 calculates the actual meter-in pressure of each hydraulic cylinder and the maximum actual meter-in pressure, which is the maximum value among the multiple actual meter-in pressures, based on the cylinder pressure.

[0112] As shown in Fig. 16, the meter-in pressure calculation unit C6 functions as a determination unit O6a, a selection unit O6b, and a maximum value selection unit O6c. The determination unit O6a determines whether or not the boom operation amount is a positive value based on the operation signal of the boom cylinder 11a. If the boom operation amount is a positive value, the selection unit O6b selects the boom bottom pressure detected by the pressure sensor 26 as the actual boom meter-in pressure, and if the boom operation amount is not a positive value, the selection unit O6b selects the boom rod pressure detected by the pressure sensor 27 as the actual boom meter-in pressure. Although not shown in the figure, by a similar process, either the arm bottom pressure detected by the pressure sensor 28 or the arm rod pressure detected by the pressure sensor 29 is selected as the actual arm meter-in pressure, and either the bottom pressure or the rod pressure of the bucket cylinder 13a is selected as the actual bucket meter-in pressure.

[0113] The maximum value selection unit O6c selects the largest one of the actual boom meter-in pressure, the actual arm meter-in pressure, and the actual bucket meter-in pressure, and determines the selected one as the actual meter-in maximum pressure.

[0114] 17 is a diagram showing the contents of the calculation process performed by pressure control meter-in control valve command calculation unit C7. Pressure control meter-in control valve command calculation unit C7 calculates a pressure control meter-in control valve command value based on the actual meter-in pressure and the target meter-in pressure. The following will representatively explain an example in which a pressure control meter-in control valve command value for boom cylinder 11a is calculated based on the actual meter-in pressure and the target meter-in pressure of boom cylinder 11a.

[0115] 17, the pressure control meter-in control valve command calculation unit C7 functions as calculation units O7a, O7b, and O7c. The calculation unit O7a calculates the meter-in pressure deviation by subtracting the target meter-in pressure of the boom cylinder 11a from the actual meter-in pressure of the boom cylinder 11a.

[0116] The calculation unit O7b calculates the target opening area of ​​the meter-in control valve 41 based on the meter-in pressure deviation. A table T7b in which the meter-in pressure deviation and the target opening area of ​​the meter-in control valve 41 are associated with each other is stored in the ROM 102. The table T7b has characteristics such that when the meter-in pressure deviation is equal to or greater than 0 (zero), the target opening area is a minimum value Aimin (>0), and when the meter-in pressure deviation is less than 0 (zero), the target opening area is a maximum value Aimax (>Aimin). The calculation unit O7b refers to the table T7b and calculates the target opening area of ​​the meter-in control valve 41 based on the meter-in pressure deviation.

[0117] The calculation unit O7c refers to a current conversion table T7c stored in ROM 102, and calculates a target value of a control current to be supplied to an electromagnetic drive unit (solenoid) of the meter-in control valve 41 as a pressure control meter-in control valve command value based on the target opening area of ​​the meter-in control valve 41.

[0118] The pressure control meter-in control valve command calculation unit C7 also calculates pressure control meter-in control valve command values ​​for the meter-in control valve 42 of the arm cylinder 12a and the meter-in control valve (not shown) of the bucket cylinder 13a.

[0119] 18 is a diagram showing the contents of the calculation process performed by pressure control directional control valve command calculation unit C8. Pressure control directional control valve command calculation unit C8 calculates a pressure control directional control valve command value based on the cylinder pressure, operation signal, meter-out target pressure calculated by target pressure calculation unit C3, and target thrust calculated by target thrust calculation unit C2. Below, a representative example will be described in which the pressure control directional control valve command value of the boom cylinder 11a is calculated based on the cylinder pressure (rod pressure and bottom pressure) of the boom cylinder 11a, the operation signal, and the meter-out target pressure.

[0120] As shown in FIG. 18, the pressure control directional control valve command calculation unit C8 functions as calculation units O8a, O8b, O8c, and O8d, determination units O8e and O8f, selection units O8g and O8h, and calculation units O8i and O8j.

[0121] The calculation unit O8a calculates the meter-out pressure deviation by subtracting the boom rod pressure from the meter-out target pressure, and the calculation unit O8b calculates the meter-out pressure deviation by subtracting the boom bottom pressure from the meter-out target pressure.

[0122] The calculation units O8c, O8d calculate the target opening area of ​​the directional control valve 45 based on the meter-out pressure deviation. Tables T8c, T8d in which the meter-out pressure deviation and the target opening area of ​​the directional control valve 45 are associated are stored in the ROM 102. The tables T8c, T8d have characteristics such that when the meter-out pressure deviation is 0 (zero) or more, the target opening area is a minimum value Aomin (>0), and when the meter-out pressure deviation is less than 0 (zero), the target opening area is a maximum value Aomax (>Aomin). The calculation units O8c, O8d refer to the tables T8c, T8d and calculate the target opening area of ​​the directional control valve 45 based on the meter-out pressure deviation.

[0123] The determination unit O8e determines whether the boom operation amount is a positive value and the target thrust of the boom cylinder 11a is a positive value. The determination unit O8f determines whether the boom operation amount is a negative value and the target thrust of the boom cylinder 11a is a negative value.

[0124] If the determination unit O8e makes an affirmative decision, i.e., if it is determined that the boom operation amount is a positive value and the target thrust of the boom cylinder 11a is a positive value, the selection unit O8g selects, as the target opening area, the maximum value Aomax pre-stored in the ROM 102. If the determination unit O8e makes a negative decision, i.e., if it is determined that the boom operation amount is not a positive value or the target thrust of the boom cylinder 11a is not a positive value, the selection unit O8g selects the target opening area calculated by the calculation unit O8c.

[0125] If the determination unit O8f makes a positive determination, i.e., if it is determined that the boom operation amount is a negative value and the target thrust of the boom cylinder 11a is a negative value, the selection unit O8h selects, as the target opening area, the maximum value Aomax pre-stored in the ROM 102. If the determination unit O8f makes a negative determination, i.e., if it is determined that the boom operation amount is not a negative value or the target thrust of the boom cylinder 11a is not a negative value, the selection unit O8h selects the target opening area calculated by the calculation unit O8d.

[0126] The calculation unit O8i refers to a current conversion table T8i stored in ROM 102, and calculates a target value of a control current to be supplied to the solenoid of the solenoid valve 45a for driving the directional control valve 45 to the cylinder extension side as a pressure control directional control valve command value based on the target opening area of ​​the directional control valve 45 selected by the selection unit O8g. The calculation unit O8i calculates the control current based on the table T8i only when the boom cylinder 11a is operated to the extension side. When the boom cylinder 11a is operated to the retraction side, the calculation unit O8i does not perform calculation based on the table T8i, and sets the control current to a minimum value (standby current).

[0127] The calculation unit O8j refers to the current conversion table T8j stored in ROM 102, and calculates a target value of the control current to be supplied to the solenoid of the solenoid valve 45b for driving the directional control valve 45 to the cylinder retraction side as a pressure control directional control valve command value based on the target opening area of ​​the directional control valve 45 selected by the selection unit O8h. The calculation unit O8j calculates the control current based on the table T8j only when the boom cylinder 11a is operated to the retraction side. When the boom cylinder 11a is operated to the extension side, the calculation unit O8j does not perform calculation based on the table T8j, and sets the control current to a minimum value (standby current).

[0128] The pressure control directional control valve command calculation unit C8 controls the directional control valve 4 of the arm cylinder 12a. 6 The pressure control directional control valve command value for the directional control valve (not shown) of the bucket cylinder 13a is also calculated.

[0129] 19 is a diagram showing the contents of the calculation process performed by the pressure control pump volume command calculation unit C9. The pressure control pump volume command calculation unit C9 calculates a pressure control pump volume command value based on the pump target pressure and the actual pump discharge pressure.

[0130] 19, the pressure control pump volume command calculation unit C9 functions as calculation units O9a and O9b. The calculation unit O9a calculates the pump pressure deviation by subtracting the actual pump discharge pressure from the pump target pressure.

[0131] The calculation unit O9b calculates the discharge capacity of the pump 81 based on the pump pressure deviation. A table T9b in which the pump pressure deviation and the discharge capacity of the pump 81 are associated with each other is stored in the ROM 102. The table T9b has characteristics in which the discharge capacity is a minimum value qmin (>0) when the pump pressure deviation is less than 0 (zero), and the discharge capacity is a maximum value qmax (>qmin) when the pump pressure deviation is 0 (zero) or more. The calculation unit O9b refers to the table T9b and calculates the discharge capacity of the pump 81 as a pump volume command value for pressure control based on the pump pressure deviation.

[0132] Fig. 20 is a diagram showing the contents of the calculation process performed by the bleed-off valve command generating unit C10. As shown in Fig. 20, the bleed-off valve command generating unit C10 generates a bleed-off valve command for controlling a control current supplied to an electromagnetic driving unit (solenoid) of the bleed-off valve 18 based on an operation signal of an actuator.

[0133] The bleed-off valve command generating unit C10 functions as a calculation unit O10a, a minimum value selection unit O10b, and a calculation unit O10c. The ROM 102 stores tables T10a1 and T10a2 in which the operation signals of the actuators (the operation signal of the boom cylinder 11a, the operation signal of the arm cylinder 12a, etc.) correspond to the operation required opening area of ​​the bleed-off valve 18. The calculation unit O10a calculates the operation required opening area based on the operation signal corresponding to each actuator. Below, an example of calculating the operation required opening area based on the operation signal of the boom cylinder 11a will be representatively described.

[0134] The calculation unit O10a calculates the operation required opening area of ​​the bleed-off valve 18 based on the operation signal of the boom cylinder 11a. The table T10a1 has characteristics such that the operation required opening area decreases as the absolute value of the operation amount of the operating lever 23a increases. In this embodiment, when the operating lever 23a is located in a dead zone including the neutral position, the operation required opening area is set to be the maximum opening area.

[0135] The calculation unit O10a refers to table T10a1 and calculates the operation required opening area based on the operation signal input from the boom operation device 23. The calculation unit O10a also refers to table T10a2 and calculates the operation required opening area based on the operation signal input from the arm operation device 24. Furthermore, although not shown, the calculation unit O10a calculates the operation required opening area based on the operation signal of the bucket cylinder 13a, the operation signal of the traveling hydraulic motor 2a, and the operation signal of the swing hydraulic motor 3a.

[0136] Minimum value selection unit O10b selects the smallest of the multiple operation required opening areas calculated by calculation unit O10a, and sets the selected one as the target opening area At of bleed-off valve 18. Minimum value selection unit O10b outputs the target opening area At of bleed-off valve 18 to calculation unit O10c. Note that minimum value selection unit O10b also outputs the target opening area At of bleed-off valve 18 to flow control pump volume command calculation unit C14 (see FIG. 6 reference).

[0137] The calculation unit O10c refers to a current conversion table T10c stored in ROM 102 and calculates a target value of a control current to be supplied to an electromagnetic drive unit (solenoid) of bleed-off valve 18 based on the target opening area At input from the minimum value selection unit O10b. The calculation unit O10c generates a bleed-off valve command for controlling the control current supplied to the electromagnetic drive unit of bleed-off valve 18 to the target value, and outputs the generated bleed-off valve command to a current control unit (not shown). The current control unit controls the control current supplied to the electromagnetic drive unit of bleed-off valve 18 to the target value based on the bleed-off valve command.

[0138] FIG. 21 is a diagram showing the contents of the calculation process performed by the flow rate control directional control valve command calculation unit C11. As shown in FIG. 21, the flow rate control directional control valve command calculation unit C11 calculates a target value of the control current supplied to the solenoid valves 45a, 45b, 46a, and 46b that drive the directional control valves 45 and 46. The flow rate control directional control valve command calculation unit C11 refers to a table T11a stored in the ROM 102, and calculates a target value of the control current supplied to the solenoid valves 45a and 46a as a flow rate control directional control valve command value based on the operation signal of the actuators (boom cylinder 11a and arm cylinder 12a). The flow rate control directional control valve command calculation unit C11 refers to a table T11b stored in the ROM 102, and calculates a target value of the control current supplied to the solenoid valves 45b and 46b as a flow rate control directional control valve command value based on the operation signal of the actuators (boom cylinder 11a and arm cylinder 12a).

[0139] 22 is a diagram showing the contents of the calculation process performed by the actuator target flow rate calculation unit C12. The actuator target flow rate calculation unit C12 calculates the target flow rate of each actuator based on information (target speed and operation signal) corresponding to each actuator. Below, an example of calculating the target flow rate of the boom cylinder 11a based on the target speed and operation signal of the boom cylinder 11a will be representatively described.

[0140] As shown in FIG. 22, the actuator target flow rate calculation unit C12 functions as multiplication units O12a and O12b, a determination unit O12c, and a selection unit O12d.

[0141] The multiplication unit O12a multiplies the target speed (positive value) of the boom cylinder 11a calculated by the actuator target speed calculation unit C4 by (Sbot) to calculate a bottom side inflow target flow rate. The multiplication unit O12b multiplies the target speed (negative value) of the boom cylinder 11a calculated by the actuator target speed calculation unit C4 by (-Srod) to calculate a rod side inflow target flow rate.

[0142] The determination unit O12c determines whether the boom operation amount is a positive value based on the operation signal of the boom cylinder 11a. If the boom operation amount is a positive value, the determination unit O12c determines the bottom side target inflow flow rate as the target flow rate of the boom cylinder 11a. If the boom operation amount is not a positive value, the determination unit O12c determines the rod side target inflow flow rate as the target flow rate of the boom cylinder 11a.

[0143] The actuator target flow rate calculation unit C12 calculates the respective target flow rates based on the operation signal and target speed of the arm cylinder 12a, the operation signal and target speed of the bucket cylinder 13a, the operation signal and target speed of the traveling hydraulic motor 2a, and the operation signal and target speed of the swing hydraulic motor 3a.

[0144] Fig. 23 is a diagram showing the contents of the calculation process performed by flow rate control meter-in control valve command calculation unit C13. As shown in Fig. 23, flow rate control meter-in control valve command calculation unit C13 calculates a flow rate control meter-in control valve command value based on the target flow rate calculated by actuator target flow rate calculation unit C12, the pump discharge pressure detected by pressure sensor 25, and the actual meter-in pressure and actual meter-in maximum pressure calculated by meter-in pressure calculation unit C6. Below, a representative example will be described in which a flow rate control meter-in control valve command value for meter-in control valve 41 of boom cylinder 11a is calculated based on the target flow rate, actual meter-in pressure, actual meter-in maximum pressure of boom cylinder 11a, and pump discharge pressure.

[0145] The flow rate control meter-in control valve command calculation unit C13 functions as calculation units O13a, O13b, O13c, O13d, and O13e, a determination unit O13f, a selection unit O13g, and a calculation unit O13h.

[0146] Calculation unit O13a subtracts the actual meter-in pressure from the actual meter-in maximum pressure. Calculation unit O13b subtracts the actual meter-in pressure from the pump discharge pressure. Calculation unit O13c takes the square root of the calculation result in calculation unit O13b. Calculation unit O13d multiplies the calculation result in calculation unit O13c by a flow coefficient c stored in ROM 102. Calculation unit O13e divides the calculation result in calculation unit O13d from the target flow rate of boom cylinder 11a to calculate a target opening area of ​​the meter-in control valve 41.

[0147] Determination unit O13f determines whether the difference between the actual meter-in maximum pressure and the actual meter-in pressure, which is the result of calculation by calculation unit O13a, is greater than 0. When determination unit O13f makes a positive determination, i.e., when it is determined that the difference between the actual meter-in maximum pressure and the actual meter-in pressure is greater than 0, selection unit O13g selects the target opening area calculated by calculation unit O13e. When determination unit O13f makes a negative determination, i.e., when it is determined that the difference between the actual meter-in maximum pressure and the actual meter-in pressure is equal to or less than 0, selection unit O13g selects the maximum value Aimax pre-stored in ROM 102 as the target opening area.

[0148] The calculation unit O13h refers to the current conversion table T7c stored in ROM 102, and calculates a target value of the control current to be supplied to the electromagnetic drive unit (solenoid) of the meter-in control valve 41 as a flow rate control meter-in control valve command value based on the target opening area of ​​the meter-in control valve 41 selected by the selection unit O13g.

[0149] The flow rate control meter-in control valve command calculation unit C13 also calculates a flow rate control meter-in control valve command value for the meter-in control valve 42 of the arm cylinder 12a and the meter-in control valve (not shown) of the bucket cylinder 13a.

[0150] Fig. 24 is a diagram showing the contents of the calculation process performed by the flow rate control pump volume command calculation unit C14. As shown in Fig. 24, the flow rate control pump volume command calculation unit C14 generates a pump volume command to be output to a regulator 81a that controls the discharge capacity of the pump 81. The flow rate control pump volume command calculation unit C14 functions as an integrator O14a, a calculator O14b, multipliers O14c and O14d, an adder O14e, and a divider O14f.

[0151] The integrating unit O14a integrates the target flow rates of the actuators (boom cylinder 11a, arm cylinder 12a, etc.) calculated by the actuator target flow rate calculation unit C12 to calculate a target flow rate total value. The calculation unit O14b takes the square root of the pump discharge pressure P detected by the pressure sensor 25. The multiplying unit O14c multiplies the calculation result of the calculation unit O14b (the square root of the pump discharge pressure P) by the target opening area At of the bleed-off valve 18 calculated by the bleed-off valve command generation unit C10. The multiplying unit O14d multiplies the calculation result of the multiplying unit O14c by the flow coefficient c stored in the ROM 102 to calculate the bleed-off flow rate (the flow rate of the hydraulic oil passing through the bleed-off valve 18). The adding unit O14e adds the bleed-off flow rate, which is the calculation result of the multiplying unit O14d, to the target flow rate total value, which is the calculation result of the integrating unit O14a, to calculate the pump target flow rate Qt.

[0152] A division unit O14f divides the pump target flow rate Qt, which is the result of the calculation in the addition unit O14e, by the actual engine speed detected by the engine speed sensor 80a to calculate a target value of the discharge capacity (displacement volume) as a pump capacity command value.

[0153] As shown in Fig. 7, the directional control valve command generating unit C15 judges whether or not the pressure control flag is set to ON. When the pressure control flag is set to ON, the directional control valve command generating unit C15 selects the pressure control directional control valve command value calculated by the pressure control directional control valve command calculating unit C8, generates a directional control valve command for controlling the control current supplied to the solenoid valves 45a, 45b, 46a, and 46b to the pressure control directional control valve command value (target value), and outputs the generated directional control valve command to a current control unit (not shown). When the pressure control flag is set to OFF, the directional control valve command generating unit C15 selects the flow rate control directional control valve command value calculated by the flow rate control directional control valve command calculating unit C11, generates a directional control valve command for controlling the control current supplied to the solenoid valves 45a, 45b, 46a, and 46b to the flow rate control directional control valve command value (target value), and outputs the generated directional control valve command to a current control unit (not shown). The current control unit controls the control current supplied to the solenoids of the solenoid valves 45a, 45b, 46a, and 46b based on the directional control valve command so that the control current becomes a target value.

[0154] The meter-in control valve command generating unit C16 determines whether or not the pressure control flag is set to ON. If the pressure control flag is set to ON, the meter-in control valve command generating unit C16 selects the pressure control meter-in control valve command value calculated by the pressure control meter-in control valve command calculating unit C7, generates a meter-in control valve command for controlling the control current supplied to the electromagnetic driving unit (solenoid) of the meter-in control valves 41, 42 to the pressure control meter-in control valve command value (target value), and outputs the generated meter-in control valve command to a current control unit (not shown). When the pressure control flag is set to off, meter-in control valve command generation unit C16 selects the flow rate control meter-in control valve command value calculated by flow rate control meter-in control valve command calculation unit C13, generates a meter-in control valve command for controlling the control current supplied to the electromagnetic drive unit (solenoid) of the meter-in control valves 41, 42 to the flow rate control meter-in control valve command value (target value), and outputs the generated meter-in control valve command to a current control unit (not shown). The current control unit controls the control current supplied to the electromagnetic drive unit (solenoid) of the meter-in control valves 41, 42 based on the meter-in control valve command so that the control current becomes the target value.

[0155] The pump volume command generating unit C17 compares the pressure control pump volume command value calculated by the pressure control pump volume command calculating unit C9 with the flow rate control pump volume command value calculated by the flow rate control pump volume command calculating unit C14, and selects the larger one. The pump volume command generating unit C17 generates a pump volume command for controlling the discharge capacity of the pump 81 to the selected pump volume command value, and outputs the generated pump volume command to the regulator 81a.

[0156] Next, an example of the operation when an independent boom raising operation is performed in the hydraulic excavator 1 according to this embodiment will be described with reference to Fig. 25. Fig. 25 is a time chart showing changes in the pump target flow rate, actual boom flow rate, pump discharge pressure, and boom bottom pressure when an independent boom raising operation is performed.

[0157] The horizontal axis of Fig. 25 indicates time (hours). The vertical axis of Fig. 25(A) indicates the operation signal (boom raising operation amount) of boom cylinder 11a, the vertical axis of Fig. 25(B) indicates the target speed and actual speed of boom cylinder 11a, the vertical axis of Fig. 25(C) indicates the on / off state of the pressure control flag, the vertical axis of Fig. 25(D) indicates the target thrust of boom cylinder 11a, and the vertical axis of Fig. 25(E) indicates the boom meter-in target pressure and pump target pressure. Note that since this is a time chart for the case of boom raising alone, the boom meter-in target pressure and the pump target pressure are the same. The vertical axis of Figure 25(F) indicates the control valve signal (control current value) of the boom raising side of directional control valve 45, the vertical axis of Figure 25(G) indicates the control valve signal (control current value) of boom meter-in control valve 41, Figure 25(H) indicates the target flow rate (boom target flow rate) and actual flow rate (boom actual flow rate) of boom cylinder 11a and the target flow rate (pump target flow rate) of pump 81, and Figure 25(I) indicates the pump discharge pressure (pump pressure) detected by pressure sensor 25 and the boom bottom pressure detected by pressure sensor 26.

[0158] At time t0, the control lever 23a is held in the neutral position. At time t1, when the control lever 23a is operated toward the maximum operation position, the cylinder target speed increases as the operation amount increases. The actual cylinder speed increases following the cylinder target speed. At time t2, when it is determined that the speed deviation rate is larger than the predetermined value Rw, the pressure control flag is switched from OFF to ON (see FIG. 15).

[0159] When the pressure control flag is set to ON, the pump flow rate is controlled so that the pump discharge pressure is maintained at the pump target pressure. As shown in Fig. 19, the main controller 100 monitors the difference between the pump target pressure and the actual pump discharge pressure, and controls the discharge capacity of the pump 81 so that the actual pump discharge pressure is maintained at the pump target pressure.

[0160] In the case of boom-raising alone, the pump target pressure coincides with the boom meter-in target pressure (see FIG. 13). Therefore, the meter-in control valve 41 is held in the fully open position (opening area=Aimax) (see FIG. 23), and the flow rate of the pump 81 is controlled so that the actual meter-in pressure (actual pump discharge pressure) is held at the meter-in target pressure (pump target pressure). As a result, the flow rate of hydraulic oil supplied to the boom cylinder 11a (actual boom flow rate) gradually increases from time t2 to time t3.

[0161] At time t3, when it is determined that the speed deviation rate between the target speed and the actual speed of the boom cylinder 11a is equal to or less than the predetermined value Rw, the pressure control flag is switched from on to off (see FIG. 15). This transitions the control state from pressure control to normal flow control. As a result, the flow rate of the hydraulic oil supplied to the boom cylinder 11a is controlled so that the extension speed of the boom cylinder 11a is constant.

[0162] FIG. 26 is a time chart showing an example of the operation when boom raising alone is performed in a hydraulic excavator according to a comparative example of this embodiment. In this comparative example, the pressure control described in this embodiment is not executed. In other words, even if the target speed and actual speed of the boom cylinder 11a deviate from each other, the flow rate control is executed. For this reason, for example, when the operation lever 23a is suddenly operated from the neutral position to the maximum operation position on the boom raising side, the pump target flow rate and the boom target flow rate are suddenly increased to the maximum flow rate according to the operation amount of the operation lever 23a. As a result, the actual boom flow rate increases suddenly, and the operation of the boom cylinder 11a may become unstable.

[0163] In contrast, in this embodiment, as shown in Fig. 25, when there is a discrepancy between the target speed and the actual speed of the boom cylinder 11a after a boom-raising operation, the flow rate of hydraulic oil supplied to the boom cylinder 11a is controlled to gradually increase so that the meter-in pressure of the boom cylinder 11a remains constant. Therefore, according to this embodiment, the actual boom flow rate does not increase suddenly, the operation of the boom 11 is prevented from becoming unstable, and the boom 11 can be accelerated at a substantially constant acceleration.

[0164] Although not shown, for example, in the case where a combined operation of boom raising operation and arm dump operation is performed instead of a single boom raising operation, the boom raising operation and arm dump operation can be performed stably in the same manner. Here, when the arm meter-in target pressure is greater than the boom meter-in target pressure, the arm meter-in target pressure is set as the pump target pressure (see FIG. 13).

[0165] In this case, when the pressure control flag is set to on, the arm meter-in control valve 42 is controlled to the fully open position, and the meter-in pressure of the arm cylinder 12a is controlled by the pump flow rate. Meanwhile, the main controller 100 monitors the difference between the meter-in target pressure and the actual meter-in pressure, and controls the opening of the boom meter-in control valve 41 so as to reduce the difference. In other words, the main controller 100 reduces the pump pressure by controlling the opening of the boom meter-in control valve 41, and controls the actual meter-in pressure so that the actual meter-in pressure is maintained at the meter-in target pressure (see FIG. 17).

[0166] This prevents a shock from occurring due to a sudden increase in hydraulic oil supplied to the boom cylinder 11a and the arm cylinder 12a immediately after the start of the combined operation of boom raising and arm dumping, allowing the boom cylinder 11a and the arm cylinder 12a to operate smoothly.

[0167] Next, an example of the operation when an arm pulling operation alone is performed in the hydraulic excavator 1 according to this embodiment will be described with reference to Fig. 27. Fig. 27 is a time chart showing changes in the pump target flow rate, the actual arm flow rate, and the arm rod pressure when an operation to stop the arm pulling operation alone is performed.

[0168] The horizontal axis of Fig. 27 indicates time (hours). The vertical axis of Fig. 27(A) indicates the operation signal (arm crowd operation amount) of the arm cylinder 12a, the vertical axis of Fig. 27(B) indicates the target speed and actual speed of the arm cylinder 12a, the vertical axis of Fig. 27(C) indicates the on / off state of the pressure control flag, the vertical axis of Fig. 27(D) indicates the target thrust of the arm cylinder 12a, and the vertical axis of Fig. 27(E) indicates the arm meter-out target pressure. The vertical axis of Fig. 27(F) indicates the control valve signal (control current value) of the arm pull side of the directional control valve 46, the vertical axis of Fig. 27(G) indicates the control valve signal (control current value) of the arm meter-in control valve 42, Fig. 27(H) indicates the target flow rate (arm target flow rate) and actual flow rate (arm actual flow rate) of the arm cylinder 12a and the target flow rate (pump target flow rate) of the pump 81, and Fig. 27(I) indicates the pump discharge pressure detected by the pressure sensor 25 and the rod pressure of the arm cylinder 12a detected by the pressure sensor 29. Note that since this is a time chart for the case of only arm pull operation, the arm bottom pressure and the pump pressure match.

[0169] At time t4, the control lever 24a is held at the maximum operation position. At time t5, when the control lever 24a is operated toward the neutral position, the cylinder target speed decreases as the operation amount decreases. The actual cylinder speed decreases following the cylinder target speed. At time t6, when it is determined that the speed deviation rate is larger than the predetermined value Rw, the pressure control flag is switched from OFF to ON (see FIG. 15).

[0170] When the pressure control flag is set to on, the directional control valve 46 serving as a meter-out control valve is controlled so that the arm rod pressure is maintained at the arm meter-out target pressure. As shown in Fig. 18, the main controller 100 monitors the difference between the meter-out target pressure and the arm rod pressure, and controls the aperture of the directional control valve 46 so that the arm rod pressure is maintained at the meter-out target pressure. The main controller 100 controls the aperture of the meter-in control valve 42 so that the meter-in pressure is maintained at a predetermined value P1 (for example, about 1 MPa), thereby preventing the occurrence of cavitation.

[0171] FIG. 28 is a time chart showing an example of the operation when the arm retraction alone is performed in a hydraulic excavator according to a comparative example of this embodiment. In this comparative example, the pressure control described in this embodiment is not executed. In other words, even if the target speed and actual speed of the arm cylinder 12a deviate from each other, the flow rate control is executed. For this reason, for example, when the operation lever 24a is suddenly operated from the maximum operation position on the arm retraction side to the neutral position, the pump target flow rate and the arm target flow rate are suddenly reduced to the minimum flow rate according to the operation amount of the operation lever 24a. As a result, the actual arm flow rate is suddenly reduced, and the operation of the arm cylinder 12a may become unstable.

[0172] In contrast to this, in this embodiment, as shown in Fig. 27, when the target speed and actual speed of the arm cylinder 12a deviate from each other after the stopping operation of the arm pulling alone operation, the flow rate of the hydraulic oil supplied to the arm cylinder 12a is controlled to gradually decrease so that the meter-out pressure of the arm cylinder 12a becomes constant. Therefore, according to this embodiment, the actual arm flow rate does not decrease suddenly, the operation of the arm 12 is prevented from becoming unstable, and the arm 12 can be decelerated at a substantially constant deceleration.

[0173] According to the above-described embodiment, the following advantageous effects are obtained.

[0174] (1) A hydraulic excavator (work machine) 1 includes a pump 81 that discharges a hydraulic fluid, a working device 10 having a plurality of fluid pressure cylinders (boom cylinder 11a, arm cylinder 12a, and bucket cylinder 13a) driven by the hydraulic fluid discharged from the pump 81 and a plurality of driven members (boom 11, arm 12, and bucket 13) driven by the fluid pressure cylinders (boom cylinder 11a, arm cylinder 12a, and bucket cylinder 13a), operation devices 23, 24 that output operation signals (operation commands) for the fluid pressure cylinders (boom cylinder 11a, arm cylinder 12a, and bucket cylinder 13a), a main controller (control device) 100 that controls the operation of the working device 10 based on the operation signals from the operation devices 23, 24, and an attitude detection device 15 that detects the attitude of the working device 10.

[0175] The main controller 100 calculates the meter-in target pressure and the meter-out target pressure (see FIG. 12) and the target speed (see FIG. 14) of the boom cylinder (fluid pressure cylinder) 11a and the arm cylinder (fluid pressure cylinder) 12a based on the operation signals from the operation devices 23, 24. The main controller 100 calculates the target flow rate of the hydraulic cylinders (11a, 12a) based on the target speed of the hydraulic cylinders (11a, 12a) (see FIG. 22). The main controller 100 calculates the actual speed of the hydraulic cylinders 11a, 12a based on the detection result of the attitude detection device 15 (see FIG. 4), and calculates a speed deviation rate that indicates the degree of deviation between the target speed and the actual speed of the hydraulic cylinders (11a, 12a) (see FIG. 15).

[0176] When the speed deviation rate is larger than a predetermined value Rw, the main controller 100 executes pressure control to set the pressures (meter-in pressure and meter-out pressure) of the hydraulic cylinders 11a, 12a to target pressures (meter-in target pressure and meter-out target pressure) (see Figs. 7, 15, etc.). When the speed deviation rate is smaller than a predetermined value Rw, the main controller 100 executes flow control to set the flow rates (supply flow rates) of the hydraulic cylinders 11a, 12a to target flow rates (see Figs. 7, 15, etc.).

[0177] In this configuration, when the speed deviation rate (deviation rate) is greater than a predetermined value Rw, pressure control is executed, thereby preventing sudden movement of the working implement 10 and allowing the working implement 10 to operate at a stable acceleration / deceleration rate. When the speed deviation rate (deviation rate) is smaller than the predetermined value Rw, flow control is executed, allowing the working implement 10 to operate at a speed intended by the operator. As a result, the accuracy of work such as excavation and leveling can be improved.

[0178] (2) The hydraulic excavator 1 is equipped with meter-in control valves 41, 42 that control the flow of working fluid supplied to the hydraulic cylinders (11a, 12a). The pump 81 is a variable displacement pump whose discharge capacity can be changed. When the hydraulic cylinders (11a, 12a) are accelerating, the main controller 100 controls the meter-in pressure of the hydraulic cylinders (11a, 12a) by controlling the discharge capacity of the pump 81 and the aperture of the meter-in control valve 41 in pressure control (see FIGS. 12, 13, 17, 19, 25, etc.). This makes it possible to operate the working implement 10 with stable acceleration in pressure control.

[0179] (3) The hydraulic excavator 1 includes directional control valves (meter-out control valves) 45, 46 that control the flow of the working fluid discharged from the hydraulic cylinders (11a, 12a). When the hydraulic cylinders (11a, 12a) are decelerating, the main controller 100 controls the meter-out pressure of the hydraulic cylinders (11a, 12a) by controlling the apertures of the directional control valves (meter-out control valves) 45, 46 in pressure control (see FIGS. 12, 18, 27, etc.). This makes it possible to operate the working implement 10 at a stable deceleration in pressure control.

[0180] (4) In the present embodiment, the meter-out control valves are the directional control valves 45, 46 that control the flow of the working fluid supplied from the pump 81 to the hydraulic cylinders (11a, 12a). In other words, the directional control valves 45, 46 have a function as a meter-out control valve. For this reason, there is no need to provide a dedicated meter-out control valve in addition to the directional control valves 45, 46, and therefore the cost of the hydraulic excavator 1 can be reduced compared to the case where a dedicated meter-out control valve is provided.

[0181] (5) The hydraulic excavator 1 is equipped with pressure sensors 26, 27, 28, 29 which detect the pressure of the hydraulic cylinders (11a, 12a). The main controller 100 calculates the thrust F of the hydraulic cylinders (11a, 12a) based on the detection results of the pressure sensors 26, 27, 28, 29 (see FIG. 8), and calculates the acceleration / deceleration (speed change rate) α″ of the hydraulic cylinders (11a, 12a) based on the detection result of the attitude detection device 15 (see FIG. 8). The main controller 100 determines the target pressure of the hydraulic cylinders (11a, 12a) taking into account the thrust F and acceleration α″ of the hydraulic cylinders (11a, 12a) (see FIGS. 11 and 12).

[0182] In the articulated working apparatus 10, even when the hydraulic cylinders (11a, 12a) are driven at a constant acceleration / deceleration, the acceleration / deceleration of the driven members (11, 12) may change significantly depending on the posture of the working apparatus 10. In this embodiment, the thrust F of the hydraulic cylinders (11a, 12a) and the acceleration / deceleration α″ of the driven members are actually measured, the acceleration torque target value is corrected with a torque adjustment gain, the target torque and target thrust are calculated, and the target pressure is computed based on the calculation results. This makes it possible to prevent the acceleration / deceleration from changing depending on the posture of the working apparatus 10.

[0183] (6) The main controller 100 calculates the rotation moment Mg due to gravity acting on the working device 10 based on the detection result of the attitude detection device 15, and determines the target pressure of the hydraulic cylinders (11a, 12a) so as to cancel the rotation moment Mg due to gravity (see FIGS. 11 and 12). This makes it possible to suppress changes in the acceleration / deceleration of the working device 10 due to the effect of gravity when the attitude of the working device 10 changes. In other words, the working device 10 can be operated at an appropriate acceleration / deceleration regardless of the attitude of the working device 10.

[0184] (7) In this embodiment, the main controller 100 calculates a rotational moment Mf due to the thrust of the hydraulic cylinders (11a, 12a) acting on the working implement 10, based on the detection result of the attitude detection device 15 and the thrust F of the hydraulic cylinders (11a, 12a). The main controller 100 calculates an actual measured value of inertia Ia based on the rotational moment Mg due to the thrust, the rotational moment Mg due to gravity, and the acceleration / deceleration rate α″, and determines a target pressure for the hydraulic cylinders (11a, 12a) by taking the actual measured value of inertia Ia into consideration (see FIGS. 8, 11, 12, etc.). This makes it possible to prevent changes in the acceleration / deceleration rate of the working implement 10 due to the influence of the reaction force acting on the bucket 13 from the natural ground, gravity acting on the excavated material loaded in the bucket 13, and the like during work such as excavation work and ground leveling work.

[0185] As described above, according to this embodiment, it is possible to provide a hydraulic excavator 1 that can prevent the working implement 10 from suddenly accelerating or decelerating when an operation command changes suddenly, and can operate the working implement 10 at an acceleration / deceleration intended by the operator. With such a hydraulic excavator 1, it is possible to easily perform work such as highly accurate excavation and ground leveling along a target surface.

[0186] The following modified examples are also within the scope of the present invention, and it is possible to combine the configurations shown in the modified examples with the configurations described in the above-mentioned embodiments, or to combine the configurations described in the different modified examples below.

[0187] <Variation 1> In the above embodiment, the directional control valves 45, 46 are used as meter-out control valves to adjust the opening of the passage of the hydraulic oil discharged from the hydraulic cylinders (11a, 12a), but the present invention is not limited to this. A meter-out control valve may be provided separately from the directional control valves 45, 46. In this case, adjustment of the opening of the meter-out side passage by the directional control valves 45, 46 becomes unnecessary. Therefore, it is possible to reduce the influence of pressure loss of the working fluid passing through the meter-in side passage of the directional control valves 45, 46 due to adjustment of the meter-out side passage by the directional control valves 45, 46. Furthermore, when a dedicated meter-out control valve specialized in adjusting the opening of the meter-out side passage is provided, the control accuracy can be improved by reducing the size of the meter-out control valve, for example.

[0188] <Variation 2> In the above embodiment, the operating devices 23, 24 are described as an example of an apparatus operated by an operator, but the present invention is not limited to this. The present invention can also be applied to a case where the working apparatus 10 is operated based on an operation command from an automatic pilot device instead of the operating devices 23, 24. Furthermore, in a case where a semi-automatic pilot device is provided that outputs an operation command to assist the operation of the working apparatus 10 by the operator, the present invention can also be applied to a case where the working apparatus 10 is operated based on an operation command from the semi-automatic pilot device.

[0189] <Modification 3> In the above embodiment, an example has been described in which the rotation moment of gravity acting on the working device 10 is calculated each time and reflected in the target pressure, but the present invention is not limited to this. A value equivalent to the rotation moment of gravity acting on the working device 10 in a specified posture may be stored in the ROM 102, and the target pressure may be determined taking this value into consideration.

[0190] <Modification 4> In the above embodiment, the working machine is a crawler type hydraulic excavator 1, but the present invention is not limited to this. The present invention can be applied to various working machines that drive multiple driven members with a fluid pressure cylinder, such as a wheeled hydraulic excavator or a wheel loader.

[0191] <Variation 5> Some or all of the functions of the control device (main controller 100) described in the above embodiment may be realized by hardware (for example, by designing logic for executing each function in an integrated circuit).

[0192] Although the embodiments of the present invention have been described above, the above-mentioned embodiments merely show 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-mentioned embodiments. [Explanation of symbols]

[0193] 1...hydraulic excavator (working machine), 10...working device, 11...boom (driven member), 11a...boom cylinder (fluid pressure cylinder), 12...arm (driven member), 12a...arm cylinder (fluid pressure cylinder), 13...bucket (driven member), 13a...bucket cylinder (fluid pressure cylinder), 15...posture detection device, 18...bleed-off valve, 19...tank, 20...machine body, 23, 24...operation device, 26 to 29...pressure sensor, 41, 42...meter-in control valve, 45, 46...directional control valve (meter-out control valve), 81...pump, 81a...regulator, 100...main controller (control device)

Claims

1. A work machine including a pump that discharges a hydraulic fluid, a working device having a plurality of fluid pressure cylinders driven by the hydraulic fluid discharged from the pump and a plurality of driven members driven by the fluid pressure cylinders, an operating device that outputs an operation command for the fluid pressure cylinders, and a control device that controls an operation of the working device based on the operation command of the operating device, a posture detection device for detecting a posture of the working device, The control device includes: Calculating a target pressure and a target speed of the fluid pressure cylinder based on an operation command from the operating device; Calculating a target flow rate of the fluid pressure cylinder based on a target speed of the fluid pressure cylinder; Calculating an actual speed of the fluid pressure cylinder based on a detection result of the attitude detection device; Calculating a degree of deviation between a target speed of the fluid pressure cylinder and an actual speed of the fluid pressure cylinder; When the degree of deviation is greater than a predetermined value, a pressure control is executed to set the pressure of the fluid pressure cylinder to the target pressure. When the degree of deviation is smaller than a predetermined value, a flow rate control is executed to set the flow rate of the fluid pressure cylinder to the target flow rate. A working machine characterized by:

2. 2. The work machine according to claim 1, a meter-in control valve for controlling a flow of the working fluid supplied to the fluid pressure cylinder, The pump is a variable displacement pump whose discharge capacity is changeable, The control device includes: In the pressure control, the discharge capacity of the pump and the opening degree of the meter-in control valve are controlled to control the meter-in pressure of the fluid pressure cylinder. A working machine characterized by:

3. 2. The work machine according to claim 1, a meter-out control valve for controlling the flow of the working fluid discharged from the fluid pressure cylinder, The control device includes: In the pressure control, the meter-out pressure of the fluid pressure cylinder is controlled by controlling the opening degree of the meter-out control valve. A working machine characterized by:

4. 4. The work machine according to claim 3, The meter-out control valve is a directional control valve that controls the flow of the working fluid supplied from the pump to the fluid pressure cylinder. A working machine characterized by:

5. 2. The work machine according to claim 1, a pressure sensor for detecting a pressure of the fluid pressure cylinder; The control device includes: Calculating a thrust of the fluid pressure cylinder based on a detection result of the pressure sensor; Calculating an acceleration / deceleration of the driven member based on a detection result of the attitude detection device; determining the target pressure of the fluid pressure cylinder in consideration of the thrust of the fluid pressure cylinder and the acceleration / deceleration of the driven member; A working machine characterized by:

6. 2. The work machine according to claim 1, The control device includes: Calculating a rotational moment due to gravity acting on the working device based on a detection result of the attitude detection device; determining the target pressure of the fluid pressure cylinder so as to cancel the rotational moment due to gravity; A working machine characterized by:

7. 2. The work machine according to claim 1, a pressure sensor for detecting a pressure of the fluid pressure cylinder; The control device includes: Calculating a thrust of the fluid pressure cylinder based on a detection result of the pressure sensor; Calculating a rotational moment due to gravity acting on the working device based on a detection result of the attitude detection device; calculating a rotational moment acting on the working device due to the thrust of the fluid pressure cylinder based on a detection result of the attitude detection device and the thrust of the fluid pressure cylinder; Calculating an acceleration / deceleration of the driven member based on a detection result of the attitude detection device; Calculating a moment of inertia based on the rotational moment due to the thrust, the rotational moment due to gravity, and the acceleration / deceleration; determining the target pressure of the fluid pressure cylinder taking the moment of inertia into consideration; A working machine characterized by:

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