JP7805865B2 - Work machinery - Google Patents

Description

The present invention relates to a work machine, such as a hydraulic excavator, equipped with an excavation control system.

For hydraulic excavators, a typical example of a work machine, various excavation control systems have been proposed that smoothly perform excavation operations by performing appropriate actuator operations based on operation information from the operator during the excavation operation. For example, Patent Document 1 proposes a system that calculates the excavation reaction force of the soil acting on the bucket using an excavation reaction force table based on detected boom angle, arm angle, and bucket angle and soil characteristics previously stored in a storage device, and determines whether to modify the excavation operation based on whether the calculated excavation reaction force is greater than a preset upper limit. Patent Document 1 also suggests that it is preferable to notify the operator that the calculated excavation reaction force has exceeded the preset upper limit, or that if the calculated excavation reaction force is greater than the preset upper limit, the boom drive may be controlled to raise the boom and reduce the excavation depth.

Patent No. 5519414

According to Patent Document 1, it is possible to properly determine an overload state due to excavation reaction force during excavation operation, and to correct the excavation operation.

However, because Patent Document 1 focuses only on the magnitude of the excavation reaction force caused by the excavation operation, depending on the direction of the excavation reaction force, the excavation reaction force may be determined to be excessive, and a determination may be made that the excavation operation needs to be corrected, even though the actuator's limit state could be resolved by changing the posture of the boom or arm.

For example, in a state where the excavation reaction force requires more than the maximum linear force that the arm cylinder can generate (hereinafter referred to as an overload state), the arm overload state may be resolved (the linear force of the arm cylinder may be reduced) depending on the attitude of the boom and arm and the direction of movement of the boom and arm. Even in such a case, in Patent Document 1, when the magnitude of the excavation reaction force reaches a predetermined value, the excavation operation is stopped, a notification is given to the operator, and the boom is raised manually or automatically, which means that the excavation operation must be interrupted or the trajectory of the excavation operation must be corrected, reducing excavation efficiency.

The present invention was made in consideration of the above, and its purpose is to provide a work machine that, when an overload condition occurs due to an excavation reaction force during excavation operations by the boom and arm in an excavation control system for the work machine, can eliminate the overload condition without interrupting the excavation operation or correcting the trajectory of the excavation operation, thereby enabling more efficient excavation operations.

In order to achieve the above object, the present invention provides a front working machine including a vehicle body, a boom that rotates vertically relative to the vehicle body, and an arm that rotates vertically relative to the boom, a boom cylinder connected to the vehicle body and the boom and driving the boom vertically relative to the vehicle body, an arm cylinder connected to the boom and the arm and driving the arm vertically relative to the boom, a first operating device that generates an operating signal that commands operation of the boom, a second operating device that generates an operating signal that commands operation of the arm, a first sensor that detects a parameter related to the linear force of the boom cylinder, a second sensor that detects a parameter related to the linear force of the arm cylinder, a third sensor that detects the attitude of the boom, and a fourth sensor that detects the attitude of the arm, wherein the front working machine includes a vehicle body, a boom that rotates vertically relative to the vehicle body, a boom cylinder that is connected to the vehicle body and the boom and drives the boom vertically relative to the vehicle body, an arm cylinder that is connected to the boom and the arm and drives the arm vertically relative to the boom, a first operating device that generates an operating signal that commands operation of the boom, a second operating device that generates an operating signal that commands operation of the arm, a first sensor that detects a parameter related to the linear force of the boom cylinder, a second sensor that detects a parameter related to the linear force of the arm cylinder, a third sensor that detects the attitude of the boom, and a fourth sensor that detects the attitude of the arm, The excavation device further includes a controller that controls the drive of the boom cylinder and the arm cylinder based on the detection signals of the second sensor and the detection signals of the third and fourth sensors, and when the first operating device and the second operating device are operated simultaneously to perform a combined operation in which the boom and the arm are driven simultaneously, the controller calculates the linear forces of the boom cylinder and the arm cylinder based on the detection signals of the first and second sensors, and when either the linear forces of the boom cylinder or the arm cylinder reaches a limit value, the controller calculates the direction in which the linear force that has reached the limit value will decrease based on the detection signals of the third and fourth sensors and the linear forces of the boom cylinder and the arm cylinder, and controls the drive of the boom cylinder and the arm cylinder so that the excavation operating point of the front working machine moves in the direction in which the linear force is decreasing.

In this invention configured as described above, when either the linear force of the boom cylinder or the arm cylinder reaches its limit, the direction in which the linear force that has reached its limit will be reduced is calculated based on the detection signals from the third and fourth sensors and the linear forces of the boom cylinder and the arm cylinder, and the drive of the boom cylinder and the arm cylinder is controlled so that the excavation operating point of the front work implement moves in the direction in which the linear force is reduced. Therefore, even if the magnitude of the excavation reaction force vector (magnitude of the excavation vector) remains unchanged, the proportion of linear force shared by the boom cylinder and the arm cylinder changes, allowing the linear force of the boom cylinder or the arm cylinder to be reduced. As a result, if an overload condition occurs due to the excavation reaction force during excavation operation by the boom and arm, the overload condition can be resolved without interrupting the excavation operation or correcting the trajectory of the excavation operation, making excavation operation more efficient and improving operability.

According to the present invention, if an overload condition occurs due to an excavation reaction force during excavation operations using the boom and arm, the overload condition can be resolved without interrupting the excavation operation or correcting the trajectory of the excavation operation, allowing for more efficient excavation operations.

1 is a perspective view of a hydraulic excavator to which the present invention is applied. 1 is a diagram showing a hydraulic circuit of a hydraulic drive system according to a first embodiment of the present invention. 1 is a diagram showing a control system according to a first embodiment of the present invention; FIG. 10 is a diagram showing the direct force of the boom cylinder, the direct force of the arm cylinder, the boom angle, and the arm angle. 4 is a flowchart illustrating the function of an arithmetic control unit of the controller. FIG. 10 is a diagram illustrating distances J11 and J22 in equation (4). FIG. 10 is a diagram showing torques on the respective axes of the boom rotation fulcrum Pv1 and the arm rotation fulcrum Pv2 generated by the excavation reaction force vector F Dig. FIG. 10 is a diagram showing torques on the respective axes of the boom rotation fulcrum Pv1 and the arm rotation fulcrum Pv2 generated by the boom linear force vector FBoom and the arm linear force vector FArm. FIG. 10 is a diagram showing an example of a direct force reduction direction search map. FIG. 10 is a diagram showing an example of a direct force reduction direction search map. 10A and 10B are diagrams illustrating a form of intervention in a direction of decreasing a direct force in the first embodiment of the present invention. FIG. 10 is a simplified diagram showing a form in which a direct force reduction direction is intervened by a hydraulic circuit. FIG. 10 is a diagram showing a control system according to a second embodiment of the present invention. 4 is a flowchart illustrating the function of an arithmetic control unit of the controller. FIG. 10 is a diagram showing the range of the direction in which the cylinder linear force decreases when it reaches its limit value (linear force decreasing direction range), range 1 that coincides with the extension or retraction direction of the boom cylinder, and range 2 that coincides with the extension or retraction direction of the arm cylinder 3. FIG. 10 is a diagram showing a hydraulic circuit of a hydraulic drive system according to a third embodiment of the present invention. FIG. 4 is a diagram showing pump control characteristics of a regulator. FIG. 10 is a diagram showing a control system according to a third embodiment of the present invention. 10 is a flowchart showing details of the processing contents of a maximum possible pump discharge pressure calculation unit and a direct power limit value calculation unit of the controller. 4 is an explanatory diagram of the calculation principle of the maximum possible pump discharge pressure in the maximum possible pump discharge pressure calculation unit. FIG. FIG. 10 is a perspective view of a hydraulic excavator equipped with a control system according to a fourth embodiment of the present invention. FIG. 10 is a diagram showing a control system according to a fourth embodiment of the present invention. 10 is a flowchart showing a first display process of a control calculation unit of the controller. 10 is a flowchart showing a second display process of a control calculation unit of the controller. 10A and 10B are diagrams showing changes in an image displayed on a display device 70 due to a first display process and a second display process. FIG. 10 is a diagram illustrating an example of a range of a direction in which a linear force is reduced.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings, using a hydraulic excavator as an example of a work machine according to the present invention.

First Embodiment
~Work machinery~
FIG. 1 is a perspective view of a hydraulic excavator to which the present invention is applied.

The hydraulic excavator 100 comprises a lower running body 101, an upper rotating body 103 that is rotatably attached to the lower running body 101 via a rotating device 102 and forms the vehicle body, and a front work machine 104 that is attached to the front of the upper rotating body 103 and forms the work device. The front work machine 104 is composed of a boom 105 attached to the front of the upper rotating body 103 so as to be rotatable in the vertical direction, an arm 106 attached to the tip of the boom 105 so as to be rotatable in the vertical direction, a bucket 107 attached to the tip of the arm 106 so as to be rotatable in the vertical direction, a bucket link 108 rotatably attached to the arm 106 and the bucket 107, a boom cylinder 2 connected to the upper rotating body 103 and the boom 105 and changing the rotation angle between the upper rotating body 103 and the boom 105 by driving the boom 106 up and down relative to the upper rotating body 103, an arm cylinder 3 connected to the boom 105 and the arm 106 and changing the rotation angle between the boom 105 and the arm 106 by driving the arm 106 up and down relative to the boom 105, and a bucket cylinder 4 connected to the arm 106 and the bucket link 108 and changing the rotation angle of the arm 106 and the bucket 107 via the bucket link 108.

The lower traveling structure 101 is equipped with left and right crawler-type traveling devices 109a, 109b (right traveling device 109b is not shown), which are driven by left and right traveling motors 5a, 5b (right traveling motor 5b is not shown), allowing the hydraulic excavator 100 to move to a desired position. The swing device 102 is equipped with a swing motor 6 that changes the rotation angle of the lower traveling structure 101 and the upper swing structure 103.

The upper rotating body 103 is equipped with a cabin 110 that forms the driver's compartment, and a controller 20 that performs the controls described below is located behind the driver's seat 111 within the cabin 110. Furthermore, on the left and right sides in front of the driver's seat 111 within the cabin 110, operation devices 21 and 22 are located that, when operated by the operator, generate operation signals that command the movement (speed and direction) of the boom 105, arm 106, bucket 107, and upper rotating body 103, and operation devices 23a and 23b are located in front of the driver's seat 111, generating operation signals that command the movement (speed and direction) of the left and right traveling devices 109a and 109b.

~Hydraulic drive unit~
2 is a diagram showing the hydraulic circuit of the hydraulic drive system according to this embodiment. For simplicity of illustration, Fig. 2 shows only the parts related to the boom cylinder 2 and the arm cylinder 3 among the boom cylinder 2, arm cylinder 3, bucket cylinder 4, left and right travel motors 5a, 5b, and swing motor 6.

In FIG. 2, the hydraulic drive system of this embodiment includes variable displacement hydraulic pump 10a (first hydraulic pump) and hydraulic pump 10b (second hydraulic pump) driven by a prime mover (e.g., a diesel engine) not shown, an open center type flow control valve 11a (first flow control valve) connected to a center bypass passage 15a (first center bypass passage) connected to a discharge oil passage 13a of hydraulic pump 10a and controlling the flow rate of pressurized oil supplied from hydraulic pump 10a to boom cylinder 2, an open center type flow control valve 12a (second flow control valve) connected in tandem to center bypass passage 15a downstream of flow control valve 11a and controlling the flow rate of pressurized oil supplied from hydraulic pump 10a to arm cylinder 3, and a variable displacement hydraulic pump 10b (first hydraulic pump) driven by a prime mover (e.g., a diesel engine) not shown. It is equipped with an open center type flow control valve 12b (third flow control valve) connected to a center bypass passage 15b (second center bypass passage) connected to the oil outlet passage 13b and controlling the flow rate of pressurized oil supplied from the hydraulic pump 10b to the arm cylinder 3, an open center type fourth flow control valve 11b (fourth flow control valve) connected in tandem to the center bypass passage 15b downstream of the flow control valve 12b and controlling the flow rate of pressurized oil supplied from the hydraulic pump 12b to the boom cylinder 2, a relief valve 14a connected to the discharge oil passage 13a of the hydraulic pump 10a and limiting the maximum value of the discharge pressure of the hydraulic pump 10a, and a relief valve 14b connected to the discharge oil passage 13b of the hydraulic pump 10b and limiting the maximum value of the discharge pressure of the hydraulic pump 10b.

Flow control valves 11a, 12a, 11b, and 12b are electromagnetic switching spool valves, and the spool stroke (opening area) is controlled by a command signal from controller 20.

The hydraulic drive system of this embodiment is configured as an open center system in which the discharge oil passages 13a and 13b of the hydraulic pumps 10a and 10b are connected to the tank T via the center bypass passages 16a and 15b. In this open center system, when the flow control valves 11a, 12a, 11b, and 12b are in the neutral position shown in the figure and the meter-in and meter-out throttles of the flow control valves 11a, 12a, 11b, and 12b are fully closed, the flow control valves 11a, 12a, 11b, and 12b fully open the center bypass passages 15a and 15b, returning the oil discharged from the hydraulic pumps 10a and 10b to the tank T.

When the flow control valves 11a, 11b are operated from the neutral position shown to either the left or right position shown, the meter-in and meter-out throttles of the flow control valves 11a, 11b open and the center bypass passages 15a, 15b are throttled, so that the oil discharged from the hydraulic pump 10a is supplied to the boom cylinder 2 via the flow control valve 11a and the actuator oil passage 16a or 16b, and the oil discharged from the hydraulic pump 10b is also supplied to the boom cylinder 2 via the flow control valve 11b and the actuator oil passage 16c or 16d. At this time, when the flow control valves 11a, 11b are half-operated, the meter-in and meter-out throttles of the flow control valves 11a, 11b open to an opening area corresponding to the amount of operation, and the center bypass passages 15a, 15b are narrowed to an opening area corresponding to the amount of operation, so that pressurized oil at a flow rate corresponding to the amount of operation of the flow control valves 11a, 11b joins and is supplied to the boom cylinder 2, and the boom cylinder 2 is driven at a speed corresponding to the amount of operation of the flow control valves 11a, 11b. Furthermore, when the flow control valves 11a, 11b are fully operated, the meter-in and meter-out throttles of the flow control valves 11a, 11b are fully opened, and the center bypass passages 15a, 15b are fully closed, so that the entire amount of pressurized oil discharged from the hydraulic pumps 10a, 10b is supplied to the boom cylinder 2, and the boom cylinder 2 is driven at high speed.

The same is true when the flow control valves 12a, 12b are operated from the neutral position shown to either the left or right position shown. Oil discharged from hydraulic pump 10b is supplied to arm cylinder 3 via flow control valve 12b and actuator oil line 17a or 17b, and oil discharged from hydraulic pump 10a is supplied to arm cylinder 3 via actuator oil line 17c or 17d. The arm cylinder 3 is driven by the pressurized oil discharged from hydraulic pumps 10a, 10b at a speed corresponding to the amount of operation of flow control valves 12a, 12b.

When both flow control valves 11a, 11b and flow control valves 12a, 12b are half-operated to either the left or right position shown in the figure, the meter-in and meter-out throttles of flow control valves 11a, 11b and flow control valves 12a, 12b open to opening areas corresponding to their respective operation amounts, and center bypass passages 15a, 15b are throttled. Oil discharged from hydraulic pump 10a is supplied preferentially to the upstream flow control valve 11a, with the remaining pressurized oil being supplied to flow control valve 12a. Oil discharged from hydraulic pump 10b is supplied preferentially to the upstream flow control valve 12b, with the remaining pressurized oil being supplied to flow control valve 11b. As a result, the pressurized oil discharged from hydraulic pumps 10a, 10b is combined and supplied to boom cylinder 2 and arm cylinder 3, and boom cylinder 2 and arm cylinder 3 are driven at speeds corresponding to the operation amounts of flow control valves 11a, 11b and flow control valves 12a, 12b.

Furthermore, when both flow control valves 11a, 11b and flow control valves 12a, 12b are fully operated to either the left or right position shown in the figure, the meter-in and meter-out throttles of flow control valves 11a, 11b and flow control valves 12a, 12b are fully opened, center bypass passages 15a, 15b are fully closed, and all of the oil discharged from hydraulic pump 10a is supplied to the upstream flow control valve 11a, and all of the oil discharged from hydraulic pump 10b is supplied to the upstream flow control valve 12b. As a result, the boom cylinder 2 is driven by pressurized oil discharged from hydraulic pump 10a, and the arm cylinder 3 is driven by pressurized oil discharged from hydraulic pump 10b.

~Operating device and sensor~
In FIG. 1 , the operating device 21 functions as an operating device for the boom (first operating device) when the operating lever is operated in the forward/backward direction, and functions as an operating device for the bucket when the operating lever is operated in the left/right direction. The operating device 22 functions as an operating device for swing when the operating lever is operated in the forward/backward direction, and functions as an operating device for the arm (second operating device) when the operating lever is operated in the left/right direction. Hereinafter, the operating device 21 when functioning as an operating device for the boom will be referred to as the operating device 21a (first operating device), and the operating device 22 when functioning as an operating device for the arm will be referred to as the operating device 22a (second operating device). The operating device 21a generates an operating signal that instructs the movement (target speed and direction) of the boom 105, and the operating device 22a generates an operating signal that instructs the movement (target speed and direction) of the arm 106.

In addition, operation devices 21, 22 and operation devices 23a, 23b are electrical operation devices that generate electrical operation signals, and the generated operation signals are transmitted to controller 20.

In Figure 2, pressure sensor 25a, which detects the pressure on the bottom side of boom cylinder 2, and pressure sensor 25b, which detects the pressure on the rod side, are connected to actuator oil line 16a, which is connected to the bottom side of boom cylinder 2, and actuator oil line 16b, which is connected to the rod side. Also, pressure sensor 26a, which detects the pressure on the bottom side of arm cylinder 3, and pressure sensor 26b, which detects the pressure on the rod side, are connected to actuator oil line 17a, which is connected to the bottom side of arm cylinder 3, and actuator oil line 17b, which is connected to the rod side. Pressure sensors 25a and 25b function as first sensors that detect parameters related to the linear force (described below) of boom cylinder 2, and pressure sensors 26a and 26b function as second sensors that detect parameters related to the linear force (described below) of arm cylinder 3.

An IMU 27 that detects the rotation angle of the boom 105 relative to the upper rotating body 103 is provided on the side of the boom 105 shown in Figure 1, and an IMU 28 that detects the rotation angle of the arm 106 relative to the boom 105 is provided on the side of the arm 106. The IMU 27 functions as a third sensor that detects the attitude of the boom 105, and the IMU 28 functions as a fourth sensor that detects the attitude of the arm 106.

Note that IMUs 27 and 28 consist of known inertial measurement units.

~Control System~
FIG. 3 is a diagram showing a control system according to this embodiment.

In FIG. 3, operation signals from operation device 21, which includes operation device 21a (first operation device), and operation device 22, which includes operation device 22a (second operation device), detection signals from pressure sensors 25a, 25b and pressure sensors 26a, 26b, and detection signals from IMUs 27, 28 are input to controller 20, which then performs predetermined calculations and outputs command signals to multiple flow control valves, including flow control valves 11a, 12a, 11b, and 12b.

When the operating device 21a (first operating device) and the operating device 22a (second operating device) are operated simultaneously to perform a combined operation that simultaneously drives the boom 105 and the arm 106, the controller 20 calculates the linear forces of the boom cylinder 2 and the arm cylinder 3 based on the detection signals of the pressure sensors 25a, 25b (first sensors) and the pressure sensors 26a, 26b (second sensors), and if neither the linear forces of the boom cylinder 2 nor the arm cylinder 3 have reached their limit values, the controller 20 calculates the linear forces of the boom cylinder 2 and the arm cylinder 3 based on the operating signals of the operating device 21a and the operating device 22a. When the cylinder 2 and arm cylinder 3 are driven and either the linear force of the boom cylinder 2 or the arm cylinder 3 reaches its limit, the direction in which the linear force that has reached its limit will decrease is calculated based on the detection signals of the IMU 27 (third sensor) and IMU 28 (fourth sensor) and the respective linear forces of the boom cylinder 2 and arm cylinder 3, and the drive of the boom cylinder 2 and arm cylinder 3 is controlled so that the toe of the bucket 107, which is the excavation operating point Pw (see Figure 4) of the front work implement 104, moves in the direction in which this linear force is decreasing.

The functions of the controller 20 are explained in detail below.

As shown in Figure 3, the controller 20 has multiple functional elements, including a linear force calculation unit 20a, an attitude calculation unit 20b, a memory unit 20c, and a control calculation unit 20d.

The linear force calculation unit 20a calculates the linear force of the boom cylinder 2 and the linear force of the arm cylinder 3 based on the detection signals of the pressure sensors 25a and 25b (first sensors) and the detection signals of the pressure sensors 26a and 26b (second sensors).

Figure 4 shows the linear force of the boom cylinder 2 and the linear force of the arm cylinder 3, as well as the boom angle and arm angle described below.

In Figure 4, symbol Fb indicates the linear force of the boom cylinder 2, and symbol Fa indicates the linear force of the arm cylinder 3. The linear force Fb of the boom cylinder 2 refers to the axial thrust (driving force) acting on the piston rod of the boom cylinder 2, and the linear force Fa of the arm cylinder 3 refers to the axial thrust (driving force) acting on the piston rod of the arm cylinder 3.

The linear force calculation unit 20a calculates the linear force Fa of the boom cylinder 2 by subtracting the thrust obtained by multiplying the piston pressure-receiving area on the rod side of the boom cylinder 2 by the pressure detected by pressure sensor 25b from the thrust obtained by multiplying the piston pressure-receiving area on the bottom side of the boom cylinder 2 by the pressure detected by pressure sensor 25a. Similarly, the linear force calculation unit 20a calculates the linear force Fa of the arm cylinder 3 by subtracting the thrust obtained by multiplying the piston pressure-receiving area on the rod side of the arm cylinder 3 by the pressure detected by pressure sensor 26b from the thrust obtained by multiplying the piston pressure-receiving area on the bottom side of the arm cylinder 3 by the pressure detected by pressure sensor 26a.

In the following, the linear force Fb of the boom cylinder 2 may be simply referred to as the boom linear force, and the linear force Fa of the arm cylinder 3 may be simply referred to as the arm linear force.

In Figure 4, the symbol FBoom indicates the linear force vector of the boom cylinder 2, which is the sum of the linear force Fb of the boom cylinder 2 and the directional component of the linear force Fb, and the symbol FArm indicates the linear force vector of the arm cylinder 3, which is the sum of the linear force Fa of the arm cylinder 3 and the directional component of the linear force Fa. Also in Figure 4, the excavation reaction force vector is indicated by the symbol FDig.

The attitude calculation unit 20b calculates the rotation angle (boom angle) θ1 of the boom 105 relative to the upper rotating body 103 and the rotation angle (arm angle) θ2 of the arm 106 relative to the boom 105 based on the detection signals of the IMU 27 (third sensor) and IMU 28 (fourth sensor).

In Figure 4, boom angle θ1 (the rotation angle of the boom 105 relative to the upper rotating body 103) is the angle formed by a line segment BL passing through the rotation fulcrum Pv1 of the boom 105 and the rotation fulcrum (pin) Pv2 of the arm 106, relative to a line segment SL in the fore-and-aft direction parallel to the bottom plate (swivel frame) 103a of the upper rotating body 103, which passes through the rotation fulcrum (pin) Pv1 of the boom 105. Arm angle θ2 (the rotation angle of the arm 106 relative to the boom 105) is the angle formed by a line segment AL passing through the rotation fulcrum Pv2 of the arm 106 and the rotation fulcrum (pin) Pv3 of the bucket 107, relative to the line segment BL.

The memory unit 20c stores various data used in the calculations of the control calculation unit 20d, and in this embodiment, stores limit values for the boom linear force Fb and the arm linear force Fa, as well as a search map (hereinafter sometimes referred to as a linear force reduction direction search map) that searches for the direction in which the linear force decreases when it reaches its limit value.

The limit value of the direct force may be a predetermined value, or may be a value calculated based on the operating information at that time. In this embodiment, the limit value of the direct force is a predetermined value. The predetermined value is, for example, a direct force calculated based on the maximum discharge pressure of the hydraulic pumps 10a and 10b, which is limited by the relief valves 14a and 14b. The direct force reduction direction search map will be described later.

Figure 5 is a flowchart explaining the function of the control calculation unit 20d.

First, the control calculation unit 20d determines whether a combined operation is being performed to simultaneously drive the boom 105 and arm 106, based on the operation signals from the operating devices 21a and 22a (step S100). If this determination indicates that a combined operation is not being performed, the control calculation unit 20d calculates a control command for the flow control valve so that the corresponding actuator is driven in accordance with the operation signal from the operating device 21a or 22a, and outputs a command signal to the flow control valve (step S150). At this time, the boom 105 or arm 106 is driven in accordance with the operation signal from the operating device 21a or 22a.

If it is determined in step S100 that a combined operation is being performed, the control calculation unit 20d further compares the linear forces Fb and Fa of the boom cylinder 2 and arm cylinder 3 calculated by the linear force calculation unit 20a with the linear force limit values stored in the memory unit 20c to determine whether either linear force Fb or Fa has reached its linear force limit value (step S110). If it is determined in step S110 that none of the linear forces have reached their limit values, the control calculation unit 20d calculates control commands for the flow control valves 11a, 11b, 12a, and 12b to drive the boom cylinder 2 and arm cylinder 3 in accordance with the operation signals from the operation devices 21a and 22a, and outputs command signals to the flow control valves 11a, 11b, 12a, and 12b (step S150). At this time, the boom 105 and arm 106 are driven in accordance with the operation signals from the operation devices 21a and 22a.

On the other hand, if step S110 determines that the linear force Fb or Fa of either the boom cylinder 2 or the arm cylinder 3 has reached its limit value, the control calculation unit 20d calculates an excavation reaction force vector FDig indicating the magnitude and direction of the excavation reaction force acting on the excavation operating point Pw (the tip of the bucket 107) of the front work implement 104 according to equation (1) based on the linear forces Fb, Fa of the boom cylinder 2 and the arm cylinder 3 calculated by the linear force calculation unit 20a and the boom angle θ1 (the attitude of the boom 105) and the arm angle θ2 (the attitude of the arm 106) calculated by the attitude calculation unit 20b (step S120).

...(1)

Let us explain equation (1).

In equation (1), the T in the upper right corner of _{J1 and J2} means a transposed matrix. The same applies to the T in the upper right corner of the following matrices. In addition, each variable has the following value.

F Dig: the above-mentioned excavation reaction force vector FCylinder: a cylinder direct force vector obtained by combining the above-mentioned direct force vector FBoom of the boom cylinder 2 and the direct force vector FArm of the arm cylinder 3. The cylinder direct force vector is expressed by the following equation (2).

... (2)

J ₁ : A Jacobian matrix expressed by the following equation (3) having boom angle θ1, arm angle θ2, boom length L1, and arm length L2 as elements.

...(3)

As shown in Figure 7, which will be described later, boom length L1 is the distance between the boom rotation fulcrum (pin) Pv1 and the arm rotation fulcrum (pin) Pv2, and arm length L2 is the distance between the arm rotation fulcrum (pin) Pv2 and the bucket rotation fulcrum (pin) Pv3.

_J2 : A Jacobian matrix expressed by the following equation (4) whose elements are the distance J11 from the boom rotation fulcrum (pin) Pv1 to the central axis of the boom cylinder 2 and the distance J22 from the arm rotation fulcrum (pin) Pv2 to the central axis of the arm cylinder 3.

...(4)

Figure 6 is a diagram explaining the distances j11 and j22 in equation (4). j11 is the length of a perpendicular line hanging down from the boom rotation fulcrum (pin) Pv1 to the central axis of the boom cylinder 2, and can be calculated from the geometric relationship between the boom angle θ1, the distance Cp1 between the boom rotation fulcrum Pv1 and the rotation fulcrum Pv3 at the base end of the boom cylinder 2, and the distance Cm1 between the boom rotation fulcrum Pv1 and the rotation fulcrum Pv4 at the tip of the rod of the boom cylinder 2. j22 is the length of a perpendicular line hanging down from the arm rotation fulcrum (pin) Pv2 to the central axis of the arm cylinder 3, and can be calculated from the geometric relationship between the arm angle θ2, the distance Cp2 between the arm rotation fulcrum Pv2 and the rotation fulcrum Pv5 at the base end of the arm cylinder 3, and the distance Cm2 between the arm rotation fulcrum Pv2 and the rotation fulcrum Pv6 at the tip of the rod of the arm cylinder 3.

The derivation process for equation (1) is explained below.

Equation (1) is derived from the balance between the torque on each axis of the boom rotation fulcrum Pv1 and the arm rotation fulcrum Pv2 generated by the excavation reaction force vector F Dig and the torque on each axis of the boom rotation fulcrum Pv1 and the arm rotation fulcrum Pv2 generated by the direct force vector F Boom of the boom cylinder 2 (hereinafter sometimes referred to as the boom direct force vector) and the direct force vector FArm of the arm cylinder 3 (hereinafter sometimes referred to as the arm direct force vector).

Figure 7 shows the torque on each axis of the boom rotation fulcrum Pv1 and the arm rotation fulcrum Pv2 generated by the excavation reaction force vector FDig.

Figure 8 shows the torques on each axis of the boom rotation fulcrum Pv1 and the arm rotation fulcrum Pv2 generated by the boom linear force vector FBoom and the arm linear force vector FArm.

In Figures 7 and 8, the torques on each axis of the boom rotation fulcrum Pv1 and arm rotation fulcrum Pv2 are indicated by symbols τ1 and τ2.

The relationship between the excavation vector that generates the excavation reaction force vector F Dig and the torques τ1 and τ2 is expressed by the following equation (5).

...(5)
The relationships between the torques τ1, τ2 of the respective axes of the boom rotation fulcrum Pv1 and the arm rotation fulcrum Pv2 generated by the boom linear force vector FBoom and the arm linear force vector FArm and the boom linear force vector FBoom and the arm linear force vector FArm are respectively expressed by the following equations (6A) and (6B).

... (6A)

... (6B)

From equations (5), (6A), and (6B), the following relationship is obtained:

... (7)
Therefore, the following equation (8) is obtained.

...(8)
As shown in the above formula (2),
FCylinder=[FBoom FArm] ^T
Therefore, by transforming equation (8), the above-mentioned equation (1) is obtained.

Returning to Figure 5, the control calculation unit 20d calculates the direction in which the cylinder linear force Fb or Fa, which has reached its limit value, will decrease based on the excavation reaction force vector FDig, boom angle θ1, arm angle θ2 (posture), linear force Fb of the boom cylinder 2, and linear force Fa of the arm cylinder 3 (step S130).

More specifically, when either the linear forces of the boom cylinder 2 or the arm cylinder 3 reach their limit values, the control calculation unit 20d calculates the excavation reaction force vector FDig acting on the excavation operating point Pw (the tip of the bucket 107) of the front work implement 104 based on the detection signals of the IMU 27 (third sensor) and IMU 28 (fourth sensor) and the linear forces of the boom cylinder 2 and the arm cylinder 3, and calculates the direction in which the linear forces of the hydraulic cylinders that have reached the limit values will decrease while maintaining the magnitude of the excavation reaction force vector FDig based on the excavation reaction force vector FDig, the detection signals of the IMU 27 (third sensor) and IMU 28 (fourth sensor), and the linear forces of the boom cylinder 2 and the arm cylinder 3.

Next, the control calculation unit 20d calculates a control command to operate the boom cylinder 2 and arm cylinder 3 so that the excavation operating point Pw (toe of the bucket 107) of the front work implement 104 moves in the direction in which the linear force of the hydraulic cylinder, which has reached its limit value as calculated in step S130, decreases, and outputs a command signal to the flow control valves 11a, 11b, 12a, and 12b (step S140). This controls the boom cylinder 2 and arm cylinder 3 so that the excavation operating point Pw (toe of the bucket 107) of the front work implement 104 moves in the direction in which the linear force calculated in step S103 decreases.

This section explains the calculation method for determining the direction in which the linear force of the hydraulic cylinder decreases after reaching its limit value in step S130 (hereinafter simply referred to as the linear force decrease direction).

Examples of methods for calculating the direction of linear force reduction include:

(a) A method of calculating Jacobian matrices J1 and J2 near the current posture of the front work implement 104 (see FIG. 1) (hereinafter, sometimes simply referred to as the front posture), and repeatedly calculating the direct force vector FCylinder online;
(b) A method in which the Jacobian matrices J1 and J2 are calculated in advance for all front postures within the operating range of the hydraulic cylinder, a map is created for each front posture, and the matrices are calculated using the maps;
(c) A method in which the front posture, excavation reaction force vector FDig, and direct force vector FCylinder are used as a set, and a number of maps (direct force decrease direction search maps) are created with different front posture, excavation reaction force vector FDig, and direct force vector FCylinder (boom direct force, arm direct force), and these maps are used to perform the search.

The calculation method in step S130 can be any method other than the above, as long as it determines the direction in which the cylinder linear force decreases from the current front posture.

Figures 9 and 10 show an example of a direct force reduction direction search map used in the calculation method (c) above.

The direct force reduction direction search map uses black and white shading (contour lines) to show the magnitude of the arm direct force, which is part of the direct force vector FCylinder, for a given excavation reaction force vector FDig. Figures 9 and 10 show lines on the map indicating the boom and arm as the front posture. The black and white shading is a collection of unit blocks in which position information and information on the magnitude of the arm direct force are stored; for example, position information is stored as a value in the XY coordinate system, and the magnitude of the arm direct force is stored as a numerical value (scalar value).

Figures 9 and 10 are maps for arm linear force, but there is also a separate map for boom linear force. Also, Figures 9 and 10 are examples for a certain excavation reaction force vector, and there are maps with different shades of black and white indicating the magnitude of the linear force for each excavation reaction force vector.

For example, when the arm linear force reaches its limit, the control calculation unit 20d selects a map that sets the front posture, excavation reaction force vector, and arm linear force at that time, and selects, from among the unit sections where the arm linear force decreases after reaching its limit, the unit section where the arm linear force decreases the most, using the current position of the excavation operating point Pw of the front work implement 104 as the reference point, and selects the direction in which that unit section is located as the direction of linear force decrease, and changes the front posture so that the excavation operating point Pw moves in that direction.

In Figures 9 and 10, symbol A indicates the position of the excavation operating point Pw when the arm linear force reaches its limit value and a search is made for a direction to reduce the linear force, and symbol B indicates the position of the excavation operating point Pw after the direction to reduce the linear force has been selected and the front posture has been changed. When a search is made for a direction to reduce the linear force, the front posture is in the state shown in Figure 9, and when the front posture is changed so that the excavation operating point Pw moves in the direction of reducing the linear force, the excavation operating point Pw moves from position A to position B, as shown in Figure 10.

By changing the front posture in this way, even if the magnitude of the excavation reaction force vector (magnitude of the excavation vector) does not change, the proportion of direct current force shared by the boom cylinder 2 and arm cylinder 3 changes, making it possible to reduce the direct current force of the arm cylinder 3 when it has reached its limit value.

In step S140, the control calculation unit 20d calculates a control command to move the excavation operating point Pw of the front attachment 104 from position A to position B based on the position information for positions A and B, and outputs a command signal.

The method for calculating the control command in step S140 will now be explained.

In step S140, to move the excavation operating point Pw of the front attachment 104 from position A to position B, the operation signals of the operating devices 21a, 22a input to the controller 20 are corrected so that the excavation operating point Pw moves in the direction in which the linear force calculated in step S130 decreases.

In this embodiment, the controller 20 corrects the operation signals of the operation devices 21a and 22a by incorporating the direction of reduction in linear force calculated in step S130 into the operation signals, thereby generating a command signal. However, the form of intervention is not limited to this, as long as the direction of reduction in linear force calculated in step S130 can be incorporated into the operation signals of the operation devices 21a and 22a.

Figure 11 is a diagram showing how the direct force reduction direction is intervened in this embodiment. Figure 11 shows a simplified version of the hydraulic drive system shown in Figure 2. As described above, the operation signals of the operating devices 21a and 22a are input to the controller 20, which then corrects the operation signals by intervening the direct force reduction direction calculated in step S130 to generate a command signal. This command signal is output directly to the solenoid 11S of the flow control valves 11a, 11b, 12a, and 12b of the hydraulic drive system.

Figure 12 is a simplified diagram showing how the direct force reduction direction calculated in step S130 is applied via a hydraulic circuit.

In Figure 12, the flow control valve 11 is a hydraulic pilot-type switching valve equipped with a hydraulic drive unit 11h to which signal pressure is directed from a hydraulic pilot circuit 66. The hydraulic pilot circuit 66 is equipped with an operating pressure reducing valve 60 that is switched by operating the levers of the operating devices 21a, 22a and generates operating pilot pressure for normal mode, a pilot pump 61 and pilot relief valve 62 that constitute the pilot hydraulic source 67, a solenoid pressure reducing valve 63 that generates control pilot pressure for intervention mode in response to a command signal from the controller 20, and a solenoid switching valve 64 that switches the signal pressure directed to the hydraulic drive unit 11h between operating pilot pressure for normal mode and control pilot pressure for intervention mode.

When neither the boom direct force nor the arm direct force has reached its limit value, the controller 20 is in normal mode, and the solenoid pressure reducing valve 63 and the solenoid switching valve 64 are in the positions shown in the figure.

In this normal mode, the operating pilot pressure generated by the operating devices 21a and 22a is directed to the hydraulic drive unit 11h of the flow control valve 11 via the solenoid switching valve 64, and the boom cylinder 2 and arm cylinder 3 are driven in response to the lever operation of the operating devices 21a and 22a.

When either the boom linear force or the arm linear force reaches its limit, the controller 20 transitions from normal mode to intervention mode. In this intervention mode, the controller 20 calculates control commands to operate the boom cylinder 2 and arm cylinder 3 in a direction that reduces the cylinder linear force, and outputs command signals to the solenoid pressure reducing valve 63 and the solenoid switching valve 64, respectively.

The solenoid pressure reducing valve 63 generates the control pilot pressure for the intervention mode in response to a command signal from the controller, and the solenoid switching valve 64 switches from the position shown in the figure in response to a command signal from the controller.

As a result, the intervention mode control pilot pressure generated by the solenoid pressure reducing valve 63 is directed via the solenoid switching valve 64 to the hydraulic drive unit 11h of the flow control valve 11, and the boom cylinder 2 and arm cylinder 3 are controlled so that the excavation operating point of the front work implement 104 (the tip of the bucket 107) moves in the direction in which the direct force of the arm cylinder 3 is reduced.

~Effects~
According to this embodiment, when either the linear force of the boom cylinder 2 or the arm cylinder 3 reaches its limit, the direction in which the linear force of the boom cylinder 2 or the arm cylinder 3 is reduced is calculated in accordance with the attitude of the boom 105 and the arm 106, and the drive of the boom cylinder 2 and the arm cylinder 3 is controlled so that the excavation operating point Pw (tip of the bucket) of the front work implement 104 moves in that direction, so that even if the magnitude of the excavation reaction force vector (magnitude of the excavation vector) does not change, the proportion of linear force shared by the boom cylinder 2 and the arm cylinder 3 changes, and the linear force of the boom cylinder 2 or the arm cylinder 3 whose linear force has reached its limit can be reduced. As a result, when an overload state occurs due to the excavation reaction force during excavation operation by the boom 105 and the arm 106, the overload state can be resolved without interrupting the excavation operation or discontinuously correcting the trajectory of the excavation operation, making it possible to perform the excavation operation more efficiently and improving operability.

In this embodiment, the controller 20 is located on the upper rotating body 103, but the controller 20 may be located anywhere as long as it is capable of issuing operational commands to the actuators.

In addition, in this embodiment, the structure is a three-link structure consisting of the boom 105, arm 106, and bucket 107, but the number of links and their shape can be any number as long as it has a mechanism of two or more links with a working device at the tip that performs the work. Also, "boom" and "arm" are names of links, and other names may be used as long as the links have equivalent functions.

Furthermore, in this embodiment, the linear force of the hydraulic cylinder was calculated using a pressure sensor, but any type of sensor can be used as long as it can measure the linear force of the hydraulic cylinder. For example, a strain gauge, a strain gauge, or a piezoelectric element may be embedded in the piston rod.

In addition, in this embodiment, IMUs 27 and 28 are used as sensors to detect the posture of the boom 105 and arm 106. However, instead of IMUs 27 and 28, angle sensors may be provided on the rotary joints of the boom 105 and arm 106, and the posture of the boom cylinder 2 and arm cylinder 3 may be measured using the angle sensors.

Second Embodiment
A second embodiment of the present invention will now be described.

Figure 13 shows the control system related to this embodiment.

In this embodiment, the controller 20 of the control system further includes the functional elements of the controller 20 of the first embodiment shown in Figure 3, as well as the functional element of a lever operation direction determination unit 20e.

The controller 20 uses the lever operation direction determination unit 20e to determine whether the lever operation direction of the operation device 21a and the operation device 22a is the extension or retraction direction of the boom cylinder 2 and the arm cylinder 3, respectively, based on the operation signals from the operation device 21a (first operation device) and the operation device 22a (second operation device), and sends the determination result to the control calculation unit 20d.

The control calculation unit 20d determines whether there is a range within the range of directions in which the linear force decreases after reaching its limit value that matches the extension or retraction direction of the boom cylinder 2 and arm cylinder 3. If a matching range exists, it calculates the direction in which the linear force decreases after reaching its limit value within that matching range and controls the drive of the boom cylinder 2 and arm cylinder 3 so that the excavation operating point Pw of the front work implement 104 moves in that direction. If no matching range exists, it stops the drive of the boom cylinder 2 and arm cylinder 3.

Figure 14 is a flowchart explaining the function of the control calculation unit 20d.

After steps S100 to S120, the control calculation unit 20d uses, for example, the linear force reduction direction search map selected by the control calculation unit 20d to calculate in step S130A the range of directions in which the cylinder linear force Fb or Fa, which has reached its limit value, will decrease (hereinafter sometimes referred to as the linear force reduction direction range) based on the excavation reaction force vector FDig, boom angle θ1, arm angle θ2 (posture), linear force Fb of the boom cylinder 2, and linear force Fa of the arm cylinder 3 (step S130A).

Figure 26 is a diagram showing an example of a direct force reduction direction range. The direct force reduction direction range is a predetermined range within which the direct force of the unit section calculated based on the current position of the excavation operating point Pw decreases in the direct force reduction direction search map selected by the control calculation unit 20d. The size and shape of the predetermined range may be determined in advance, or may be calculated as a range including the value (movement distance to the next step) obtained by multiplying the movement speed of the excavation operating point Pw by the calculation interval time of the controller.

Next, the control calculation unit 20d determines whether the linear force reduction direction range includes range 1 (see Figure 15) that matches the extension or retraction direction of the boom cylinder 2 acquired from the lever operation direction determination unit 20e, or range 2 (see Figure 15) that matches the extension or retraction direction of the arm cylinder 3 (S132). If neither range 1 nor range 2 exists within the linear force reduction direction range, the control calculation unit 20d stops the boom cylinder 2 and the arm cylinder 3 (S140D). If range 1 or range 2 exists within the linear force reduction direction range, the control calculation unit 20d further determines whether either range 1 or range 2 exists within the linear force reduction direction range (S134). If either range 1 or range 2 exists within the linear force reduction direction range, the control calculation unit 20d calculates the direction in which the linear force will decrease within range 1 or range 2 that exists within the linear force reduction direction range, calculates a control command to operate the boom cylinder 2 and arm cylinder 3 so that the digging operating point Pw (the tip of the bucket 107) of the front work implement 104 moves in that direction, and operates the boom cylinder 2 and arm cylinder 3 (S140A).

Next, if both range 1 and range 2 exist within the range of the linear force reduction direction and overlap (S136), the control calculation unit 20d calculates the direction in which the linear force will decrease within the overlapping range of range 1 and range 2, calculates a control command to operate the boom cylinder 2 and arm cylinder 3 so that the excavation operating point Pw (the tip of the bucket 107) of the front work implement 104 moves in that direction, and operates the boom cylinder 2 and arm cylinder 3 (S140B).

In step S136, if range 1 and range 2 do not overlap, the control calculation unit 20d selects one of ranges 1 and 2, which is a predetermined range, calculates the direction in which the linear force will decrease within that range, calculates a control command to operate the boom cylinder 2 and arm cylinder 3 so that the excavation operating point Pw (the tip of the bucket 107) of the front work implement 104 moves in that direction, and operates the boom cylinder 2 and arm cylinder 3 (S140C).

Figure 15 shows the range in which the cylinder linear force Fb or Fa decreases after reaching its limit value (linear force decreasing direction range), as well as range 1 which coincides with the extension or retraction direction of the boom cylinder 2 and range 2 which coincides with the extension or retraction direction of the arm cylinder 3.

As mentioned above, the linear force reduction direction range of the boom cylinder 2 and the linear force reduction direction range of the arm cylinder 3 are ranges calculated, for example, using the linear force reduction direction search map selected by the control calculation unit 20d (step S130A in Figure 14), and these ranges are indicated by diagonal lines in Figure 15.

In Figure 15, range 1 coinciding with the extension direction of the boom cylinder 2 is formed on the pivot point Pv2 side of the arm 106 of the movement trajectory Ta of the excavation operating point Pw when the arm 106 is rotated by the arm cylinder 3, and range 1 coinciding with the retraction direction of the boom cylinder 2 is formed on the opposite side of the pivot point Pv2 of the arm 106 of the movement trajectory Ta and on the pivot point Pv1 side of the boom 105 of the movement trajectory Tb of the excavation operating point Pw when the boom 105 is rotated by the boom cylinder 2. Range 2 coinciding with the extension direction of the arm cylinder 3 is formed on the pivot point Pv1 side of the movement trajectory Tb, and range 2 coinciding with the retraction direction of the arm cylinder 3 is formed on the pivot point Pv2 of the movement trajectory Ta and on the opposite side of the pivot point Pv1 of the movement trajectory Ta.

~Effects~
According to this embodiment, when the extension/retraction direction of at least one of the boom cylinder 2 and the arm cylinder 3 matches the extension/retraction direction indicated by the operation signals of the operation device 21a and the operation device 22a, control is performed so that the excavation operating point Pw (tip of the bucket) of the front work implement 104 moves in the direction in which the linear force of the boom cylinder 2 or the arm cylinder 3, calculated according to the attitude of the boom 105 and the arm 106, decreases. Therefore, in addition to the effects of the first embodiment, it is possible to perform operations that better reflect the operation of the operator, further improving operability.

Third Embodiment
A third embodiment of the present invention will now be described.

Figure 16 is a diagram showing the hydraulic circuit of the hydraulic drive system according to this embodiment. Similar to the hydraulic drive system shown in Figure 2, the hydraulic drive system shown in Figure 16 includes variable displacement hydraulic pump 10a (first hydraulic pump) and hydraulic pump 10b (second hydraulic pump), open center type flow control valve 11a (first flow control valve), open center type flow control valve 12a (second flow control valve), open center type flow control valve 12b (third flow control valve), open center type fourth flow control valve 11b (fourth flow control valve), and relief valves 14a and 14b.

The hydraulic drive system of this embodiment also includes a regulator 56a that controls the discharge flow rate of hydraulic pump 10a so that the absorption horsepower of hydraulic pump 10a does not exceed a preset maximum horsepower; a regulator 56b that controls the discharge flow rate of hydraulic pump 10b so that the absorption horsepower of hydraulic pump 10b does not exceed a preset maximum horsepower; a pressure sensor 58a (fifth sensor) that detects the intermediate pressure of pressurized oil flowing through the first center bypass passage 15a between the first flow control valve 11a and the second flow control valve 12a; a pressure sensor 58b (sixth sensor) that detects the intermediate pressure of pressurized oil flowing through the second center bypass passage 15b between the third flow control valve 12b and the fourth flow control valve 11b; a pressure sensor 57a (seventh sensor) that is connected to the discharge oil passage 13a of hydraulic pump 10a and detects the discharge pressure of hydraulic pump 10a; and a pressure sensor 57a (eighth sensor) that is connected to the discharge oil passage 13b of hydraulic pump 10b and detects the discharge pressure of hydraulic pump 10b.

Figure 17 shows the pump control characteristics of regulators 56a and 56b.

In Figure 17, Pmin is the minimum discharge pressure of the hydraulic pumps 10a, 10b when none of the operating devices are operated, Pmax is the maximum discharge pressure of the hydraulic pumps 10a, 10b determined by the set pressure of the relief valves 14a, 14b, qmax is the maximum capacity (maximum tilt angle) determined by the structure of the hydraulic pumps 10a, 10b, and Qmax is the maximum flow rate of the hydraulic pumps 10a, 10b calculated by multiplying qmax by the pump rotation speed. In Figure 17, Qmax is shown assuming that the pump rotation speed is constant.

When the discharge pressure of hydraulic pumps 10a, 10b is between the minimum pressure Pmin and pressure Pa, the maximum capacity of hydraulic pumps 10a, 10b is qmax. When the discharge pressure of hydraulic pumps 10a, 10b is between the minimum pressure Pa and maximum pressure Pmax, the maximum capacity of hydraulic pumps 10a, 10b is limited to the torque characteristic curve CTmax (pump discharge pressure x capacity = constant). As the discharge pressure of hydraulic pumps 10a, 10b increases, the capacity of hydraulic pumps 10a, 10b decreases, and the capacity of hydraulic pumps 10a, 10b is controlled so that the absorption torque of hydraulic pumps 10a, 10b does not exceed the maximum torque Tmax (constant torque control).

Furthermore, as a result of controlling the capacity and torque of hydraulic pumps 10a, 10b as described above, the discharge flow rate and absorption horsepower of hydraulic pumps 10a, 10b are similarly controlled. That is, when the discharge pressure of hydraulic pumps 10a, 10b is between minimum pressure Pmin and pressure Pa, the maximum flow rate of hydraulic pumps 10a, 10b is Qmax. When the discharge pressure of hydraulic pumps 10a, 10b is between minimum pressure Pa and maximum pressure Pmax, the maximum flow rate of hydraulic pumps 10a, 10b is limited to the horsepower characteristic curve CHmax (pump discharge pressure x flow rate = constant). As the discharge pressure of hydraulic pumps 10a, 10b increases, the discharge flow rate of hydraulic pumps 10a, 10b decreases, and the discharge flow rate of hydraulic pumps 10a, 10b is controlled so that the absorption horsepower of hydraulic pumps 10a, 10b does not exceed maximum horsepower Hmax (constant horsepower control).

Figure 18 shows the control system related to this embodiment.

As shown in FIG. 18, the controller 20 further includes the functional elements of a maximum possible pump discharge pressure calculation unit 20f and a direct current power limit value calculation unit 20g in addition to the functional elements of the controller 20 of the first embodiment shown in FIG. 3, and the memory unit 20c stores pump control characteristics including the setting of the maximum horsepower Hmax used in controlling the regulators 56a and 56b, instead of the direct current power limit values (boom direct current power Fb limit value and arm direct current power Fa limit value) stored in the memory unit 20c of the controller 20 of the first embodiment.

In addition to the input signals of the controller 20 of the first embodiment shown in Figure 3 (operation signals from operation devices 21a, 22a, detection signals from pressure sensors 25a, 25b and pressure sensors 26a, 26b, and detection signals from IMUs 27, 28), the controller 20 also receives detection signals from the pressure sensors 58a, 58b described above.Based on these input signals, the controller 20 performs the following calculation processing in addition to the calculation processing of the controller 20 of the first embodiment shown in Figure 3, and outputs command signals to multiple flow control valves including flow control valves 11a, 12a, 11b, and 12b, and to regulators 56a and 56b.

First, the controller 20 calculates, in the control calculation unit 20d, a command value for controlling the discharge flow rate of the hydraulic pump 10a based on the detection signals from the pressure sensors 57a, 57b and the maximum horsepower Hmax of the pump control characteristics stored in the memory unit 20c, so that the absorption horsepower of the hydraulic pumps 10a, 10b does not exceed the maximum horsepower, and outputs a command signal to the regulators 56a, 56b. Based on this command signal, the regulators 56a, 56b perform the constant torque/horsepower control described above.

Regulators 56a, 56b may not be electronically controlled by command signals output from controller 20, but may be hydraulically controlled by directing the discharge pressure of hydraulic pumps 10a, 10b to regulators 56a, 56b to drive capacity change members (e.g., swash plates) of hydraulic pumps 10a, 10b.

In addition, the controller 20 uses the operation signals from the operating devices 21a and 22a, the detection signals from the pressure sensors 58a and 58b, and the maximum horsepower Hmax of the pump control characteristics to calculate the maximum possible discharge pressure of each of the hydraulic pumps 10a and 10b, limited by the maximum horsepower Hmax, assuming that the linear force of either the boom cylinder 2 or the arm cylinder 3 has reached its limit and is in an overloaded state. The maximum possible pump discharge pressure calculation unit 20f calculates the maximum possible linear force of the boom cylinder 2 or the arm cylinder 3 when the drive of the boom cylinder 2 or the arm cylinder 3 has stopped and the pressure on the discharge side of the boom cylinder 2 or the arm cylinder 3 is zero, by multiplying the pressure-receiving area of the piston of each of the boom cylinder 2 and the arm cylinder 3 by the maximum possible discharge pressure. The control calculation unit 20d uses this maximum possible linear force as the limit value of the linear force and calculates the direction in which the linear force of the hydraulic cylinder that has reached its limit will be reduced for each of the boom cylinder 2 and the arm cylinder 3.

Figure 19 is a flowchart showing the details of the processing performed by the maximum possible pump discharge pressure calculation unit 20f and the direct power limit value calculation unit 20g. Figure 20 is an explanatory diagram of the calculation principle for the maximum possible pump discharge pressure in the maximum possible pump discharge pressure calculation unit 20f.

First, assuming that the direct force of either the boom cylinder 2 or the arm cylinder 3 has reached its limit value and is in an overload state in which the drive of the boom cylinder 2 or the arm cylinder 3 has stopped, and the flow rate of pressurized oil supplied to the boom cylinder 2 or the arm cylinder 3 is zero, the maximum possible pump discharge pressure calculation unit 20f determines an arbitrary pump discharge pressure Pi, and calculates the center bypass flow rate Qc using the orifice equation shown in Equation (9) below based on that discharge pressure Pi, the intermediate pressure Pc of the center bypass passages 15a and 15b detected by the pressure sensors 58a and 58b, and the current opening area Ac of the center bypass passage of the flow control valve (step S200).

... (9)

Ac: Center bypass opening area of the upstream flow control valve
If Pc is detected for a certain pressure Pp (Pi), Qc can be calculated from the above orifice formula.
It is derived.

The opening area Ac of the center bypass passage of the flow control valve can be calculated from the operation signal of the operating devices 21a and 22a and the preset opening area characteristics of the flow control valves 11a and 12b (the relationship between the operation signal and the meter-in opening area).

Next, the maximum possible pump discharge pressure calculation unit 20f determines whether the center bypass flow rate Qc in an overload state is equal to the maximum flow rate QHmax of the hydraulic pump 10a or 10b under constant horsepower control, i.e., whether the flow rate Qc is a flow rate that can be discharged by the hydraulic pump 10a or 10b (step S210). If the flow rate Qc cannot be discharged by the hydraulic pump 10a or 10b, processing returns to step S200, where the arbitrary pump discharge pressure Pi is changed and steps S200 and S210 are repeated until the determination in step S210 indicates that discharge is possible, searching for an arbitrary pump discharge pressure Pi at which the flow rate Qc can be discharged by the hydraulic pump 10a or 10b (the flow rate Qc is equal to the maximum flow rate QHmax). If the determination in step S210 indicates that the flow rate Qc can be discharged by the hydraulic pump 10a or 10b, the arbitrary pump discharge pressure Pi at that time is set as the maximum possible discharge pressure (step S220).

Next, the linear force limit value calculation unit 20g assumes that the drive of the boom cylinder 2 and arm cylinder 3 has stopped and the pressure on the discharge side of the boom cylinder 2 or arm cylinder 3 is zero, and calculates the maximum possible linear force of the boom cylinder 2 or arm cylinder 3 by multiplying the pressure-receiving area of the piston of the boom cylinder 2 or arm cylinder 3 by the maximum possible discharge pressure (step S230).

As mentioned above, the control calculation unit 20d uses this maximum possible linear force as the limit value of the linear force, and calculates the direction in which the linear force of the hydraulic cylinders that have reached their limit value, for the boom cylinder 2 and arm cylinder 3, will be reduced.

~Effects~
According to this embodiment, even if the operating levers of the operating devices 21a, 22a are operated finely and the discharge pressure of the hydraulic pumps 10a, 10b does not rise to the set pressure of the relief valves 14a, 14b, the limit value of the direct force can be calculated based on the actual operating state of the hydraulic circuit, so that the limit value of the actuator direct force of the boom cylinder 2 and arm cylinder 3 can be set more accurately, and excavation operations can be performed more efficiently.

<Fourth embodiment>
A fourth embodiment of the present invention will now be described.

Figure 21 is a perspective view of a hydraulic excavator equipped with a control system according to this embodiment.

The control system of this embodiment further includes a display device 70 installed in the cabin 110 of the upper rotating body 103.

Furthermore, the hydraulic circuit of the hydraulic drive system of this embodiment is the same as that of the hydraulic drive system of the third embodiment shown in Figure 16.

Figure 22 shows the control system related to this embodiment.

In Figure 22, the controller 20 has functional elements similar to those of the controller 20 of the third embodiment shown in Figure 18, including a maximum possible pump discharge pressure calculation unit 20f and a control calculation unit 20d.

As described above, the controller 20 uses the maximum possible pump discharge pressure calculation unit 20f to calculate the maximum possible discharge pressure of each of the hydraulic pumps 10a and 10b, limited by the maximum horsepower Hmax, based on the operation signals of the operating devices 21a and 22a, the detection signals of the pressure sensors 58a and 58b, and the maximum horsepower Hmax of the pump control characteristics, assuming that the direct force of either the boom cylinder 2 or the arm cylinder 3 has reached its limit value and is in an overload state.

However, in this embodiment, the maximum possible discharge pressure calculated by the maximum possible pump discharge pressure calculation unit 20f is sent not only to the direct power limit value calculation unit 20g but also to the control calculation unit 20d.

In addition, the control calculation unit 20d performs a first display process using the maximum possible linear forces of the boom cylinder 2 and the arm cylinder 3 calculated by the linear force limit value calculation unit 20g, and performs a second display process using the discharge pressures of the hydraulic pumps 10a and 10b indicated by the detection signals of the pressure sensors 57a and 57b and the maximum possible discharge pressure calculated by the maximum possible pump discharge pressure calculation unit 20f, and outputs a command signal to the display device 70.

Figure 23 is a flowchart showing the first display process of the control and calculation unit 20d.

The control calculation unit 20d determines for each cylinder whether the linear force of the boom cylinder 2 and the arm cylinder 3 has reached its limit (step S300). If the linear force of neither the boom cylinder 2 nor the arm cylinder 3 has reached its limit, the color scheme of the illustrations of the boom cylinder 2 and the arm cylinder 3 remains the default color (standard color) (step S310). On the other hand, when the linear force of either the boom cylinder 2 or the arm cylinder 3 has reached its limit, the control calculation unit 20d outputs a command signal to the display device 70 and changes the color scheme of the illustration of the hydraulic cylinder whose linear force has reached its limit from the default color (step S320).

Figure 24 is a flowchart showing the second display process of the control and calculation unit 20d.

The control calculation unit 20d determines for each hydraulic pump 10a, 10b whether the discharge pressure has approached the maximum possible discharge pressure (step S350). If the discharge pressure of neither hydraulic pump 10a, 10b has approached the maximum possible discharge pressure, the color scheme of the illustration of the hydraulic pump 10a, 10b remains the default color (standard color) (step S360). On the other hand, when the discharge pressure of either hydraulic pump 10a, 10b has approached the maximum possible discharge pressure, the control calculation unit 20d outputs a command signal to the display device 70 and changes the color scheme of the illustration of the hydraulic pump whose discharge pressure has approached the maximum possible discharge pressure from the default color (step S370).

Figure 25 shows the changes in the image displayed on the display device 70 due to the first and second display processes.

When the linear force of either the boom cylinder 2 or arm cylinder 3 (arm cylinder 3 in the illustrated example) reaches its limit, the color of the illustration of the hydraulic cylinder (arm cylinder 3) whose linear force has reached its limit changes, as shown on the right side of Figure 25, allowing the operator to visually identify which hydraulic cylinder has reached its limit.

Similarly, when the discharge pressure of either hydraulic pump 10a or 10b (hydraulic pump 10b in the illustrated example) approaches the maximum possible discharge pressure, the color of the illustration of the hydraulic pump (hydraulic pump 10b in the illustrated example) whose discharge pressure is approaching the maximum possible discharge pressure changes, as shown on the left side of Figure 25, allowing the operator to visually identify which hydraulic pump has its discharge pressure approaching the maximum possible discharge pressure.

In this embodiment, the display device 70 displays both the load state of the hydraulic pumps 10a, 10b and the load state of the boom cylinder 2 and arm cylinder 3 during excavation, but it is also possible to display only one of them.

~Effects~
According to this embodiment, the operator can visually identify hydraulic pumps whose discharge pressure is approaching the maximum possible discharge pressure, or hydraulic cylinders whose direct force has reached its limit value, so that the operator can properly understand the load state of the hydraulic pumps 10a, 10b and/or the boom cylinder 2 and arm cylinder 3 during excavation, thereby further improving operating efficiency.

<Others>
In the above embodiment, when calculating the direction in which the linear forces of the boom cylinder 2 and arm cylinder 3 that have reached their limit values are decreasing, the excavation reaction force vector is calculated using the respective postures of the boom cylinder 2 and arm cylinder 3 detected by the IMUs 27 and 28. However, the excavation reaction force vector may also be calculated using the velocity, acceleration, and equation of motion of the boom cylinder 2 and arm cylinder 3 in addition to the postures.

The speed and acceleration of the boom cylinder 2 and arm cylinder 3 may be detected, for example, by the IMUs 27 and 28 that detect their posture, or independent speed and acceleration sensors may be used. Furthermore, if the posture of the boom cylinder 2 and arm cylinder 3 is measured using an angle sensor on the rotary joint, the angle information from the angle sensor may be differentiated to determine the speed and acceleration.

By calculating the excavation reaction force vector including the speed and acceleration of the boom cylinder 2 and arm cylinder 3, the excavation reaction force vector can be calculated more accurately. As a result, the direction in which the direct forces of the boom cylinder 2 and arm cylinder 3 decrease when they reach their limit values can be calculated more accurately, allowing for more efficient excavation operations.

In addition, in the above embodiment, the working machine was described as a hydraulic excavator, but the working machine may be a working machine other than a hydraulic excavator (for example, a wheeled hydraulic excavator, a hydraulic crane, a wheel loader, etc.) as long as it has a vehicle body and a front working implement equipped with a boom and an arm.

100 Hydraulic excavator 103 Upper rotating body (vehicle body)
104 Front working implement 105 Boom 106 Arm 107 Bucket 2 Boom cylinder 3 Arm cylinder 4 Bucket cylinder 10a, 10b Hydraulic pump (first and second hydraulic pumps)
11a, 12a: flow control valves (first and second flow control valves)
12a, 12b Flow control valves (third and fourth flow control valves)
13a, 13b: Discharge oil passages 14a, 14b: Relief valves 15a, 15b: Center bypass passages (first and second center bypass passages)
20 Controller 20a Direct-acting force calculation unit 20b Attitude calculation unit 20c Memory unit 20d Control calculation unit 20e Lever operation direction determination unit 20f Maximum possible pump discharge pressure calculation unit 20g Direct-acting force limit value calculation unit 21, 22 Operation device 21a Boom operation device 22a Arm operation device 25a, 25b Pressure sensor (first sensor)
26a, 26b Pressure sensors (second sensors)
27, 28 IMU (3rd and 4th sensors)
56a, 56b Regulators (first and second regulators)
57a, 57b Pressure sensors (seventh and eighth sensors)
58a, 58b Pressure sensors (fifth and sixth sensors)
70 Display device

Claims (6)

The car body and
a front working machine including a boom that rotates vertically relative to the vehicle body and an arm that rotates vertically relative to the boom;
a boom cylinder connected to the vehicle body and the boom and driving the boom in the up and down direction relative to the vehicle body;
an arm cylinder connected to the boom and the arm and driving the arm in a vertical direction relative to the boom;
a first operating device that generates an operating signal that instructs operation of the boom;
a second operating device that generates an operating signal that instructs the operation of the arm;
a first sensor for detecting a parameter related to the linear force of the boom cylinder;
a second sensor for detecting a parameter related to the linear force of the arm cylinder;
a third sensor for detecting the attitude of the boom;
a fourth sensor that detects the posture of the arm,
a controller that controls driving of the boom cylinder and the arm cylinder based on operation signals of the first operating device and the second operating device, detection signals of the first sensor and the second sensor, and detection signals of the third sensor and the fourth sensor,
The controller
when the first operating device and the second operating device are simultaneously operated to perform a combined operation in which the boom and the arm are simultaneously driven, a linear force of each of the boom cylinder and the arm cylinder is calculated based on the detection signals of the first sensor and the second sensor,
When either the linear force of the boom cylinder or the arm cylinder reaches a limit value, a direction in which the linear force that has reached the limit value will decrease is calculated based on the detection signals of the third sensor and the fourth sensor and the respective linear forces of the boom cylinder and the arm cylinder, and drive of the boom cylinder and the arm cylinder is controlled so that the excavation operating point of the front work machine moves in the direction in which the linear force is decreased. 2. The work machine according to claim 1,
The controller
When either the linear forces of the boom cylinder or the arm cylinder reach the limit value, an excavation reaction force vector acting on the excavation operating point of the front work machine is calculated based on the detection signals of the third and fourth sensors and the linear forces of the boom cylinder and the arm cylinder, and the direction in which the linear force of the hydraulic cylinder that has reached the limit value will be reduced while maintaining the magnitude of the excavation reaction force vector is calculated based on the excavation reaction force vector, the detection signals of the third and fourth sensors, and the linear force. 3. The work machine according to claim 2,
The controller
determining whether the operation directions of the first operation device and the second operation device are the extension direction or the retraction direction of the boom cylinder and the arm cylinder based on the operation signals of the first operation device and the second operation device,
determining whether or not a range that coincides with the extension direction or retraction direction of the boom cylinder and the arm cylinder exists within a range in which the linear force that has reached the limit value decreases;
If the matching range exists, the direction in which the linear force that has reached the limit value will decrease within the matching range is calculated, and the drive of the boom cylinder and the arm cylinder is controlled so that the excavation operating point of the front work machine moves in the direction in which the linear force will decrease, and if the matching range does not exist, the drive of the boom cylinder and the arm cylinder is stopped. 2. The work machine according to claim 1,
a first hydraulic pump and a second hydraulic pump of a variable displacement type;
a first flow control valve of an open center type connected to a first center bypass passage connected to a discharge oil passage of the first hydraulic pump, and controlling the flow rate of pressure oil supplied from the first hydraulic pump to the boom cylinder;
a second flow control valve of an open center type connected in tandem to the first center bypass passage downstream of the first flow control valve and controlling the flow rate of pressure oil supplied from the first hydraulic pump to the arm cylinder;
a third flow control valve of an open center type connected to a second center bypass passage connected to a discharge oil passage of the second hydraulic pump, and controlling the flow rate of pressure oil supplied from the second hydraulic pump to the arm cylinder;
an open-center type fourth flow control valve connected in tandem to the second center bypass passage downstream of the third flow control valve and controlling the flow rate of pressure oil supplied from the second hydraulic pump to the boom cylinder;
a first regulator that controls the discharge flow rate of the first hydraulic pump so that the absorption horsepower of the first hydraulic pump does not exceed a preset maximum horsepower;
a second regulator that controls the discharge flow rate of the second hydraulic pump so that the absorption horsepower of the second hydraulic pump does not exceed a preset maximum horsepower;
a fifth sensor that detects an intermediate pressure of pressure oil flowing through the first center bypass passage between the first flow control valve and the second flow control valve;
a sixth sensor that detects an intermediate pressure of pressure oil flowing through the second center bypass passage between the third flow control valve and the fourth flow control valve,
The controller
storing pump control characteristics including the setting of the maximum horsepower used in controlling the first regulator and the second regulator;
calculates the maximum possible discharge pressure of each of the first hydraulic pump and the second hydraulic pump, which is limited by the maximum horsepower, based on the detection signals of the first operating device and the second operating device, the detection signals of the fifth sensor and the sixth sensor, and the maximum horsepower of the pump control characteristics, assuming that the direct force of either the boom cylinder or the arm cylinder is in an overload state where it has reached the limit value;
a maximum possible linear force of each of the boom cylinder and the arm cylinder calculated by multiplying the pressure-receiving area of the piston of each of the boom cylinder and the arm cylinder by the maximum possible discharge pressure, and using the maximum possible linear force as a limit value of the linear force, a direction in which the linear force of the hydraulic cylinder that has reached the limit value will decrease is calculated for each of the boom cylinder and the arm cylinder. 2. The work machine according to claim 1,
a display device that displays an illustration of the front working implement including the boom, the arm, the boom cylinder, and the arm cylinder,
The controller
a work machine which determines whether the linear forces of the boom cylinder and the arm cylinder have reached the limit value for each cylinder, and when the linear force of either the boom cylinder or the arm cylinder has reached the limit value, changes the color of an illustration of the corresponding boom cylinder or arm cylinder. 2. The work machine according to claim 1,
a first hydraulic pump and a second hydraulic pump of a variable displacement type;
a first flow control valve of an open center type connected to a first center bypass passage connected to a discharge oil passage of the first hydraulic pump, and controlling the flow rate of pressure oil supplied from the first hydraulic pump to the boom cylinder;
a second flow control valve of an open center type connected in tandem to the first center bypass passage downstream of the first flow control valve and controlling the flow rate of pressure oil supplied from the first hydraulic pump to the arm cylinder;
a third flow control valve of an open center type connected to a second center bypass passage connected to a discharge oil passage of the second hydraulic pump, and controlling the flow rate of pressure oil supplied from the second hydraulic pump to the arm cylinder;
an open-center type fourth flow control valve connected in tandem to the second center bypass passage downstream of the third flow control valve and configured to control the flow rate of pressure oil supplied from the second hydraulic pump to the boom cylinder;
a first regulator that controls the discharge flow rate of the first hydraulic pump so that the absorption horsepower of the first hydraulic pump does not exceed a preset maximum horsepower;
a second regulator that controls the discharge flow rate of the second hydraulic pump so that the absorption horsepower of the second hydraulic pump does not exceed a preset maximum horsepower;
a fifth sensor that detects an intermediate pressure of pressure oil flowing through the first center bypass passage between the first flow control valve and the second flow control valve;
a sixth sensor that detects an intermediate pressure of pressure oil flowing through the second center bypass passage between the third flow control valve and the fourth flow control valve;
a seventh sensor that detects the discharge pressure of the first hydraulic pump;
an eighth sensor that detects the discharge pressure of the second hydraulic pump;
a display device that displays an illustration of the front working implement including the boom, the arm, the boom cylinder, and the arm cylinder,
The controller
storing pump control characteristics including a setting of a maximum horsepower used in controlling the first regulator and the second regulator;
calculates the maximum possible discharge pressure of each of the first hydraulic pump and the second hydraulic pump, which is limited by the maximum horsepower, based on the detection signals of the first operating device and the second operating device, the detection signals of the fifth sensor and the sixth sensor, and the maximum horsepower of the pump control characteristics, when it is assumed that the direct force of either the boom cylinder or the arm cylinder is in an overload state where it has reached the limit value;
a determination is made for each pump as to whether the discharge pressure of the first hydraulic pump detected by the seventh sensor and the discharge pressure of the second hydraulic pump detected by the eighth sensor have approached the maximum possible discharge pressure, and when the discharge pressure of either the first hydraulic pump or the second hydraulic pump approaches the maximum possible discharge pressure, the color of an illustration of the hydraulic pump whose discharge pressure has approached the maximum possible discharge pressure is changed.