Work vehicle, method of controlling work vehicle, and controller for work vehicle

Abstract

To securely prevent an implement tip from being caused to penetrate the ground surface.SOLUTION: A work vehicle comprises: an implement including a joint and an implement tip opposite to the joint; an arm assembly including an arm tip swingably supporting the implement in the joint; a first hydraulic cylinder configured to control an implement direction from the joint toward the implement tip; and a second hydraulic cylinder configured to control an arm height that is a height of the arm tip with respect to a ground contact surface of a traveling device. A controller controls a hydraulic circuit to change an arm height to a reference height, and controls the hydraulic circuit so that during automatic control to change the implement direction and the arm height to a reference direction and the reference height, respectively, the implement direction is changed to the reference direction when the arm height reaches a target height that is the arm height when the implement tip is pointed toward the reference direction, The target height is greater than the reference height.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to a work vehicle, a control method for a work vehicle, and a controller for a work vehicle. [Background technology]

[0002] Patent Document 1 discloses a work vehicle capable of performing automatic implement return control, which changes the position and posture of the implement and arm when a load is dumped to a pre-stored reference position and posture of the implement and arm. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] U.S. Patent No. 7,894,962 Summary of the Invention [Problem to be solved by the invention]

[0004] In the work vehicle of Patent Document 1, the angle of the implement tip is corrected even after the boom is lowered, so there is a risk of the implement tip piercing the ground.

[0005] An object of the technology disclosed in this application is to provide a work vehicle, a control method for a work vehicle, and a controller for a work vehicle that reliably prevents the tip of an implement from sticking into the ground during automatic implement return control. [Means for solving the problem]

[0006] A work vehicle according to a first aspect of the present disclosure includes an implement, an arm assembly, a vehicle body, a traveling device, a first hydraulic cylinder, a second hydraulic cylinder, a hydraulic circuit, an implement attitude detection sensor, an arm attitude detection sensor, a storage device, a controller, and an input device. The implement includes a joint and an implement tip opposite to the joint. The arm assembly includes an arm tip that swingably supports the implement at the joint and an arm base end opposite to the arm tip. The vehicle body swingably supports the arm base end. The traveling device is configured to move the vehicle body. The first hydraulic cylinder is configured to control the implement orientation from the joint toward the implement tip. The second hydraulic cylinder is configured to control an arm height, which is the height of the arm tip relative to the ground surface of the traveling device, in a height direction perpendicular to the traveling direction of the traveling device. The hydraulic circuit is configured to control the first hydraulic cylinder and the second hydraulic cylinder. The implement attitude detection sensor is configured to detect the implement orientation. The arm attitude detection sensor is configured to detect the arm height. The storage device stores first information corresponding to a reference orientation, which is a reference implement orientation, and second information corresponding to a reference height, which is a reference arm height. The controller is configured to control the hydraulic circuit. The input device is configured to receive an instruction to perform automatic control for changing the implement orientation and the arm height to the reference orientation and the reference height, respectively. When the input device receives the instruction, the controller controls the hydraulic circuit so that the arm height becomes the reference height. The controller controls the hydraulic circuit when the arm height changes to a target height, which is the arm height when the tip of the implement is directed to the reference orientation, during the automatic control. The target height is greater than the reference height.

[0007] A control method for a work vehicle according to a second aspect of the present disclosure includes acquiring a reference orientation that is a reference for an implement orientation from a joint that rotatably connects the implement to an arm tip of the work vehicle toward the implement tip. The control method includes acquiring a reference height that is a reference for an arm height that is the height of the arm tip relative to the ground contact surface of the travel device of the work vehicle in a height direction perpendicular to the traveling direction of the travel device of the work vehicle. The control method includes controlling a second hydraulic cylinder so that the arm height becomes the reference height when an instruction to perform automatic control for changing the implement orientation and the arm height to the reference orientation and the reference height, respectively, is received. The control method includes controlling a first hydraulic cylinder so that the implement orientation becomes the reference orientation when the arm height changes to a target height that is greater than the reference height and is the arm height when the implement tip is directed to the reference orientation.

[0008] A controller for a work vehicle according to a third aspect of the present disclosure includes a memory and a processor. The memory is configured to store a first reference value corresponding to a reference orientation serving as a reference for an implement orientation of a first parameter representing an implement orientation from a joint that rotatably connects the implement to an arm tip of the work vehicle toward the implement tip, and a second reference value corresponding to a reference height serving as a reference for an arm height of a second parameter representing an arm height that is the height of the arm tip relative to the ground contact surface of the travel device of the work vehicle in a height direction perpendicular to the traveling direction of the work vehicle. The processor is configured to control the second hydraulic cylinder to set the second parameter to the second reference value when an instruction to perform automatic control for changing the implement orientation and the arm height to the reference orientation and the reference height, respectively, is received, and to control the first hydraulic cylinder to set the first parameter to the first reference value when the arm height changes to a target height that is the arm height when the implement tip is directed to the reference orientation and is greater than the reference height. Effect of the Invention

[0009] According to the technology disclosed in the present application, for example, it is possible to provide a work vehicle, a control method for a work vehicle, and a controller for a work vehicle that reliably prevents the tip of an implement from sticking into the ground during automatic implement return control. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a side view of a work vehicle. [Diagram 2] FIG. 2 is a top view of the work vehicle. [Diagram 3] FIG. 3 is a schematic diagram of a first hydraulic cylinder, a second hydraulic cylinder, and a hydraulic circuit of a work vehicle. [Figure 4] FIG. 4 is a schematic diagram showing an example of the internal configuration of the first control valve and the second control valve. [Diagram 5] FIG. 5 is a view of the first spool and the second spool as viewed from the first direction in FIG. [Figure 6] FIG. 6 is a cross-sectional view of the first control valve and the second control valve taken along line VI-VI in FIG. [Figure 7] FIG. 7 is a cross-sectional view of the first control valve and the second control valve along line VII-VII in FIG. [Figure 8] FIG. 8 is a cross-sectional view of the first control valve and the second control valve along line VIII-VIII in FIG. [Figure 9] FIG. 9 is a schematic diagram showing another example of the internal configuration of the first control valve and the second control valve. [Figure 10] FIG. 10 is a schematic diagram showing yet another example of the internal configuration of the first control valve and the second control valve. [Figure 11] FIG. 11 is a conceptual diagram of automatic implement return control in the case where the implement attitude detection sensor is composed of a first inertial measurement unit and a second inertial measurement unit. [Figure 12] FIG. 12 is a conceptual diagram of automatic implement return control when the implement attitude detection sensor is made of a potentiometer. [Figure 13]FIG. 13 is a diagram showing the relationship between the change in arm height and the change in implement inclination angle in the automatic implement return control. [Figure 14] FIG. 14 is a control block diagram according to the embodiment. [Figure 15] FIG. 15 is a diagram showing the relationship between the change in arm height and the change in joint rotation angle in automatic implement return control. [Figure 16] FIG. 16 is a diagram showing the relationship between the change in arm height and the change in the position of the first hydraulic cylinder in the automatic implement return control. [Figure 17] FIG. 17 is a diagram showing the relationship between the rotation speed of the engine 6 and the first correction coefficient. [Figure 18] FIG. 18 is a diagram showing the concept of cushion control of the first hydraulic cylinder. [Figure 19] FIG. 19 is a diagram showing the concept of cushion control of the second hydraulic cylinder. [Figure 20] FIG. 20 is a flowchart showing a method for controlling a work vehicle. [Figure 21] FIG. 21 shows a modified example of the hydraulic circuit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings, in which like reference numerals indicate corresponding or identical components in each drawing.

[0012] 1 and 2, a work vehicle 1, for example, a compact track loader, includes a vehicle body 2, a pair of travel devices 3, and a working device 4. The vehicle body 2 supports the travel devices 3 and the working device 4. The travel devices 3 are configured to move the vehicle body 2. In the illustrated embodiment, the travel devices 3 are track-type travel devices. Therefore, each of the pair of travel devices 3 includes a driving wheel 31, driven wheels 32 and 33, and a roller 34 driven by a hydraulic motor device 30. However, each of the pair of travel devices 3 is not limited to a track-type travel device. Each of the pair of travel devices 3 may be, for example, a front-wheel / rear-wheel travel device, or a travel device having a front wheel and a rear crawler. The working device 4 includes an implement 41 at a distal end of the working device 4. In FIGS. 1 and 2, a bucket is illustrated as an example of the implement 41. The implement 41 includes a joint 43 and an implement tip 41T opposite to the joint 43. The joint 43 is, for example, a pivot shaft. A proximal end of the working device 4 is attached to the rear of the vehicle body 2. The working device 4 includes a pair of arm assemblies 42 for rotatably supporting the implement 41 via the joint 43. Each of the pair of arm assemblies 42 includes a link mechanism LK including a first link 44, an arm 45, and a second link 59. The arm 45 includes an arm tip 45D that swingably supports the implement 41 at the joint 43, and an arm base end 45P opposite to the arm tip 45D. The arm tip 45D swingably supports the joint 43. The vehicle body 2 swingably supports the arm base end 45P. Specifically, the vehicle body 2 swingably supports the arm base end 45P via the first link 44 and the second link 59. The link mechanism LK connects the vehicle body 2 and the arm tip 45D.

[0013] The first link 44 is rotatable relative to the vehicle body 2 around a fulcrum shaft 46. The second link 59 is rotatable relative to the vehicle body 2 around a fulcrum shaft 59P. The arm 45 is rotatable relative to the first link 44 around a joint shaft 47. The arm 45 is rotatable relative to the second link 59 around a joint shaft 59D. The arm 45 operates with one degree of freedom because it is a link defined by the two free ends (joint shaft 47, joint shaft 59D) of the four-bar link mechanism LK consisting of two fixed ends (fulcrum shaft 46, fulcrum shaft 59P) and two free ends (joint shaft 47, joint shaft 59D). In other words, the rotation angle θ of the fulcrum shaft 59P is J The position of the joint 43 is uniquely determined by this.

[0014] The work vehicle 1 further includes a plurality of second hydraulic cylinders 48. Each of the plurality of second hydraulic cylinders 48 is rotatably connected to the vehicle body 2 and the arm 45, and moves the first link 44, the arm 45, etc., to raise and lower the implement 41. In other words, each of the plurality of second hydraulic cylinders 48 is rotatably connected to the vehicle body 2 and the arm 45, and moves the first link 44, the arm 45, etc., to raise and lower the implement 41. H In this case, the arm height H is the height of the arm tip 45D relative to the ground surface GL of the traveling device 3. A For convenience, the height of the arm tip 45D is the height of the joint 43. That is, the arm height H A is the height direction D between the ground contact surface GL of the traveling device 3 and the joint 43 H The work vehicle 1 detects the position of the arm tip 45D (joint 43) by adjusting the rotation angle θ J The arm position detection sensor 56 is configured to detect the rotation angle θ of the joint (fulcrum shaft 59P) of the link mechanism LK. J 1, for convenience, the rotation angle detection sensor is configured to detect the rotation angle D from the center of the fulcrum shaft 59P in the downward direction of the vehicle. D The angle between the vector pointing to the center of the fulcrum axis 59P and the vector pointing to the center of the joint axis 59D is the rotation angle θ JHowever, other angles may be used. The arm position detection sensor 56 includes, for example, a potentiometer 56r. The arm position detection sensor 56 detects the arm height H A Here, the arm height H A The parameter representing the rotation angle θ is called the second parameter. J is an example of the second parameter.

[0015] The work vehicle 1 further includes at least one first hydraulic cylinder 49. The at least one first hydraulic cylinder 49 is configured to control the implement direction 41D from the joint 43 toward the implement tip 41T. The work vehicle 1 includes an implement attitude detection sensor 57 for detecting the implement direction 41D. As an example, the implement attitude detection sensor 57 includes a first inertial measurement unit (IMU) 57a attached to the implement 41 and a second inertial measurement unit (IMU) 57b attached to the vehicle body 2. The first inertial measurement unit 57a and the second inertial measurement unit 57b each have at least an acceleration sensor and a gyro, and detect the gravity direction D. G That is, the first inertial measurement unit 57a can detect the implement orientation 41D and the gravity orientation D G The second angle θ IG The second inertial measurement unit 57b can detect the vehicle reference direction (for example, the downward direction D of the vehicle). D ) and gravity direction D G The first angle θ VG In FIG. 1, an example is given in which the work vehicle 1 is placed on a horizontal surface, and a downward direction D D is the vehicle reference direction, and the first angle θ VG The work vehicle 1 (controller 15, described later) calculates the first angle θ from the output signal of the second inertial measurement unit 57b. VG and obtains the second angle θ from the output signal of the first inertial measurement unit 57a. IG and obtain the first angle θ VG and the second angle θIG With reference to the vehicle reference direction (e.g., the vehicle downward direction D D ) and the implement inclination angle θ between the implement direction 41D I Here, the parameter representing the implement orientation 41D is called the first parameter. I is an example of a first parameter.

[0016] The arm position detection sensor 56 detects the position P of the second hydraulic cylinder 48 instead of the potentiometer 56r. A The implement attitude detection sensor 57 may be a linear sensor 56p that detects the position P of the first hydraulic cylinder 49 instead of the first inertial measurement unit 57a and the second inertial measurement unit 57b. I An example of such a linear sensor is a stroke detection sensor in a hydraulic cylinder described in the product introduction on pages 75 to 78 of KYB Technical Report No. 54 (April 2017). Also, the implement attitude detection sensor 57 may be a linear sensor 57p that detects the rotation angle θ of the joint 43 instead of the first inertial measurement unit 57a and the second inertial measurement unit 57b or the linear sensor 57p. R The potentiometer 57r may be used to detect the position P of the first hydraulic cylinder 49. I and rotation angle θ R is another example of the first parameter. A is another example of the second parameter.

[0017] The vehicle body 2 includes a cabin 5. The cabin 5 is provided with a front window 51 that can be opened and closed, and its outer shape is defined by a cab frame 53. The front window 51 may be omitted. The work vehicle 1 includes a driver's seat 54 and an operation lever 55 (arm input member 63, implement input member 68) within the cabin 5. As shown in FIG. 2, the cab frame 53 is rotatable around rotational shafts RSL and RSR on the vehicle body 2. In FIGS. 1 and 2, a common pivot A defined by the rotational shafts RSL and RSR is shown. XCThat is, the cab frame 53 is rotatable about a rotation axis A XC It is mounted so as to be rotatable around

[0018] In the embodiment of the present application, FB (Forward direction D F / backward D B ) means the front-rear direction (front direction / rear direction) as seen from the operator seated in the driver's seat 54 of the cabin 5. L , right direction D R , width direction D W The left, right, left and right directions are respectively seen from the operator's point of view. U , downward D D , height direction D H The directions refer to the upward, downward, and height directions as seen from the operator. The forward / backward, left / right (width), and up / down (height) directions of the work vehicle 1 respectively correspond to the forward / backward, left / right (width), and up / down (height) directions as seen from the operator.

[0019] FIG. 1 shows the left side of the work vehicle 1. As shown in FIG. 2, the vehicle body 2 is generally symmetrical with respect to the vehicle body central plane M, and includes a first side surface 2L which is the left side surface, and a second side surface 2R which is the right side surface. Of the pair of traveling devices 3, the traveling device 3 provided on the first side surface 2L is shown as the first traveling device 3L, and the traveling device 3 provided on the second side surface 2R is shown as the second traveling device 3R. Of the pair of arm assemblies 42, the arm assembly 42 provided on the left side with respect to the vehicle body central plane M is shown as the first arm assembly 42L, and the arm assembly 42 provided on the right side with respect to the vehicle body central plane M is shown as the second arm assembly 42R. The first link 44 provided on the left side with respect to the vehicle body central plane M is shown as the first left link 44L. The arm 45 provided on the left side with respect to the vehicle body central plane M is shown as the first arm 45L, and the arm 45 provided on the right side with respect to the vehicle body central plane M is shown as the second arm 45R. The fulcrum shaft 46 provided on the left side with respect to the vehicle body central plane M is shown as the first fulcrum shaft 46L, and the fulcrum shaft 46 provided on the right side with respect to the vehicle body central plane M is shown as the second fulcrum shaft 46R. The joint shaft 47 provided on the left side with respect to the vehicle body central plane M is shown as the first joint shaft 47L, and the joint shaft 47 provided on the right side with respect to the vehicle body central plane M is shown as the second joint shaft 47R. Of the hydraulic motor units 30, the hydraulic motor unit 30 provided on the left side with respect to the vehicle body central plane M is shown as the first hydraulic motor unit 30L, and the hydraulic motor unit 30 provided on the right side with respect to the vehicle body central plane M is shown as the second hydraulic motor unit 30R.

[0020] 1 and 2, the work vehicle 1 further includes an engine 6 provided at the rear of the vehicle body 2, a rotation speed detection sensor 6a, and a plurality of hydraulic pumps 7 including a first traveling hydraulic pump 7L and a second traveling hydraulic pump 7R. The engine 6 is configured to drive the plurality of hydraulic pumps 7. The rotation speed detection sensor 6a is configured to detect the rotation speed of the engine 6. The first traveling hydraulic pump 7L and the second traveling hydraulic pump 7R are configured to discharge hydraulic oil to drive a hydraulic motor device 30 that drives the drive wheels 31, etc. The plurality of hydraulic pumps 7 other than the first traveling hydraulic pump 7L and the second traveling hydraulic pump 7R are configured to discharge hydraulic oil to drive hydraulic actuators (a plurality of second hydraulic cylinders 48, at least one first hydraulic cylinder 49, etc.) connected to the working device 4. The engine 6 is configured to rotate in a direction D of the width of the work vehicle 1. W , and is provided between the pair of arm assemblies 42. The work vehicle 1 further includes a cover 8 for covering the engine 6. The work vehicle 1 further includes a bonnet cover 9 provided at the rear end of the vehicle body 2. The bonnet cover 9 can be opened and closed, allowing a maintenance technician to perform maintenance work on the engine 6, etc. <Hydraulic circuit>

[0021] The work vehicle 1 includes a hydraulic circuit 100 and a controller 15. The hydraulic circuit 100 is configured to control the first hydraulic cylinder 49 and the second hydraulic cylinder 48. FIG. 3 is a schematic configuration diagram of the first hydraulic cylinder 49, the second hydraulic cylinder 48, and the hydraulic circuit 100 of the work vehicle 1. The hydraulic circuit 100 includes a hydraulic pump 11, a pilot pump 12, a first control valve 25, a second control valve 20, a first pilot control valve 65, a second pilot control valve 66, a third pilot control valve 60, a fourth pilot control valve 61, a first oil passage R1, a second oil passage R2, a third oil passage R3, a fourth oil passage R4, a first pilot oil passage PR1, a second pilot oil passage PR2, a bypass oil passage BR1, and a switching mechanism 70. The controller 15 is configured to control the hydraulic circuit 100. In the following embodiments, the first oil passage R1 and the second oil passage R2 may be collectively referred to as the first cylinder hydraulic circuit C1. The third oil passage R3 and the fourth oil passage R4 may be collectively referred to as the second cylinder hydraulic circuit C2. The first cylinder hydraulic circuit C1 connects the first hydraulic cylinder 49 and the hydraulic pump 11. The second cylinder hydraulic circuit C2 connects the second hydraulic cylinder 48 and the hydraulic pump 11.

[0022] The first hydraulic cylinder 49 includes a first chamber CB1 into which the hydraulic oil flows when the implement tip 41T is tilted downward, and a second chamber CB2 into which the hydraulic oil flows when the implement tip 41T is tilted upward. The second hydraulic cylinder 48 includes a third chamber CB3 into which the hydraulic oil flows when the arm tip 45D is raised, and a fourth chamber CB4 into which the hydraulic oil flows when the arm tip 45D is lowered. The hydraulic pump 11 is driven by the engine 6 and configured to supply hydraulic oil stored in the hydraulic oil tank 10 to the first hydraulic cylinder 49 and the second hydraulic cylinder 48. The hydraulic pump 11 is, for example, a variable displacement hydraulic pump. A regulator valve 79, which will be described later, is connected to a port connecting the swash plate of the hydraulic pump 11, and the pressure of the hydraulic oil output from the hydraulic pump 11 is adjusted. The pilot pump 12 is driven by the engine 6 and configured to discharge pilot oil for controlling the second control valve 20 and the first control valve 25. Of the hydraulic oil stored in the hydraulic oil tank 10, the hydraulic oil discharged from the pilot pump 12 and used for control may be referred to as pilot oil, and the pressure of the pilot oil may be referred to as pilot pressure. The pilot pump 12 is, for example, a fixed displacement hydraulic pump.

[0023] The first oil passage R1 connects the hydraulic pump 11 and the first chamber CB1 of the first hydraulic cylinder 49. The first control valve 25 is provided in the first oil passage R1. The first control valve 25 is provided in a first cylinder hydraulic circuit C1 between the hydraulic pump 11 and the first hydraulic cylinder 49. The first control valve 25 has pilot ports 25P1, 25P2, and is configured to control the hydraulic oil supplied to the first chamber CB1 and the second chamber CB2 of the first hydraulic cylinder 49 in accordance with the hydraulic pressure of the pilot oil applied to the pilot ports 25P1, 25P2. The first oil passage R1 includes a partial oil passage R10 common to the third oil passage R3 extending from the hydraulic pump 11 to the joint J11, a partial oil passage R11 extending from the joint J11 to the first control valve 25, a partial oil passage R12 connecting different connection ports of the first control valve 25, and a partial oil passage R13 extending from the first control valve 25 to the first chamber CB1 of the first hydraulic cylinder 49. The second oil passage R2 connects the first control valve 25 and the second chamber CB2 of the first hydraulic cylinder 49. The first oil passage R1 and the second oil passage R2 are branched by being connected to different ports of the first control valve 25.

[0024] FIG. 4 is a schematic diagram showing an example of the internal configuration of the first control valve 25. As shown in FIG. 4, the first control valve 25 has a first spool SPL1 and a first valve housing 25B. FIG. 5 is a diagram showing the first spool SPL1 as seen from the first direction D1 in FIG. 4. With reference to FIGS. 4 and 5, the first spool SPL1 is a rod-shaped member extending in the axial direction Dx. The first direction D1 is perpendicular to the axial direction Dx. The first valve housing 25B supports the first spool SPL1 so as to be slidable in the axial direction Dx. With reference to FIGS. 4 and 5, the first spool SPL1 has a first notch NC1, a second notch NC2, and a third notch NC3. FIG. 6 is a cross-sectional view of the first control valve 25 along the line VI-VI in FIG. 4. FIG. 7 is a cross-sectional view of the first control valve 25 along the line VII-VII in FIG. 4. Fig. 8 is a cross-sectional view of the first control valve 25 taken along line VIII-VIII in Fig. 4. Referring to Fig. 6, the first notch NC1 defines a first axial opening XAP1 in the axial direction Dx. Referring to Fig. 7, the second notch NC2 defines a second axial opening XAP2 in the axial direction Dx. Referring to Fig. 8, the third notch NC3 defines a third axial opening XAP3 in the axial direction Dx.

[0025] Fig. 4 shows the internal configuration of the first control valve 25 in which the position of the first spool SPL1 is switched to the first hydraulic cylinder stationary control position BNP. Fig. 9 shows the internal configuration of the first control valve 25 in which the position of the first spool SPL1 is switched to the first hydraulic cylinder extending control position BEP. Fig. 10 shows the internal configuration of the first control valve 25 in which the position of the first spool SPL1 is switched to the first hydraulic cylinder retracting control position BSP. The first control valve 25 switches the first spool position, which is the position of the first spool SPL1, to the first hydraulic cylinder stationary control position BNP, the first hydraulic cylinder extending control position BEP, or the first hydraulic cylinder retracting control position BSP, depending on the pressure difference between the pilot pressure pp1 applied to the pilot port 25P1 and the pilot pressure pp2 applied to the pilot port 25P2. The first control valve 25 is configured to switch each of the two oil chambers CB1 and CB2 of the first hydraulic cylinder 49 alternatively between a first supplied oil chamber (CB1 or CB2) that supplies hydraulic oil and a first discharged oil chamber (CB2 or CB1) that discharges hydraulic oil by switching the first spool position to a first hydraulic cylinder extension control position BEP or a first hydraulic cylinder contraction control position BSP. Specifically, referring to FIG. 5, when the first spool position is switched to the first hydraulic cylinder extension control position BEP, the first supplied oil chamber is the first chamber CB1 of the first hydraulic cylinder 49, and the first discharged oil chamber is the second chamber CB2 of the first hydraulic cylinder 49. Referring to FIG. 10, when the first spool position is switched to the first hydraulic cylinder contraction control position BSP, the first supplied oil chamber is the second chamber CB2 of the first hydraulic cylinder 49, and the first discharged oil chamber is the first chamber CB1 of the first hydraulic cylinder 49.

[0026] More specifically, the first control valve 25 further includes a first implement control valve port YP1, a second implement control valve port YP2, a third implement control valve port YP3, a fourth implement control valve port YP4, and a fifth implement control valve port YP5. The first implement control valve port YP1 is connected to the hydraulic pump 11 via a first oil passage R1. The second implement control valve port YP2 is connected to the first chamber CB1 of the first hydraulic cylinder 49 via the first oil passage R1. The third implement control valve port YP3 is connected to the second oil passage R2. When the pilot pressure pp1 applied to the pilot port 25P1 is greater than the pilot pressure pp2 applied to the pilot port 25P2 by a predetermined pressure, the first control valve 25 switches the first spool position to a first hydraulic cylinder extension control position BEP that communicates the first implement control valve port YP1 and the second implement control valve port YP2 via the fourth implement control valve port YP4 and communicates the third implement control valve port YP3 with a first drain oil passage DR1 (described later) via the fifth implement control valve port YP5. Referring to FIG. 9, the second implement control valve port YP2 and the second notch NC2 form a first opening SP1. The third implement control valve port YP3 and the first notch NC1 form a third opening SP3. In FIG. 5, the outer shape of the second implement control valve port YP2 at this time is shown by a two-dot chain line, and the first opening SP1 is shown by hatching. The outline of the third implement control valve port YP3 at this time is shown by a two-dot chain line, and the third opening SP3 is shown by hatching. The first opening area AS1, which is the area of ​​the first opening SP1, can be continuously changed by changing the first spool position. The maximum value that the first opening area AS1 can take is sufficiently smaller than the area of ​​the second axial opening XAP2 of the second notch NC2. The third opening area, which is the area of ​​the third opening SP3, can be continuously changed by changing the first spool position. The maximum value that the third opening area can take is sufficiently smaller than the area of ​​the first axial opening XAP1 of the first notch NC1.

[0027] When the pilot pressure pp2 applied to the pilot port 25P2 is greater than the pilot pressure pp1 applied to the pilot port 25P1 by more than the above-mentioned predetermined pressure, the first control valve 25 switches the first spool position to a first hydraulic cylinder contraction control position BSP that communicates the first implement control valve port YP1 and the third implement control valve port YP3 via the fourth implement control valve port YP4 and communicates the second implement control valve port YP2 with DR1 (described later) via the fifth implement control valve port YP5. The first valve housing 25B has a bypass oil passage BYP for connecting the second implement control valve port YP2 and the fifth implement control valve port YP5. The bypass oil passage BYP is also shown in FIG. 6 and FIG. 8. Referring to FIG. 10, the third implement control valve port YP3 and the second notch NC2 form a first opening SP1. The second implement control valve port YP2 and the third notch NC3 form a third opening SP3. In FIG. 5, the outer shape of the third implement control valve port YP3 at this time is shown by a two-dot chain line, and the first opening SP1 is shown by a check pattern. The outer shape of the second implement control valve port YP2 at this time is shown by a two-dot chain line, and the third opening SP3 is shown by a check pattern. The first opening area AS1, which is the area of ​​the first opening SP1, can be continuously changed by changing the first spool position. The maximum value that the first opening area AS1 can have is sufficiently smaller than the area of ​​the second axial opening XAP2 of the second notch NC2. The third opening area, which is the area of ​​the third opening SP3, can be continuously changed by changing the first spool position. The maximum value that the third opening area can have is sufficiently smaller than the area of ​​the third axial opening XAP3 of the third notch NC3.

[0028] When the absolute value of the difference between the pilot pressure pp2 applied to the pilot port 25P2 and the pilot pressure pp1 applied to the pilot port 25P1 is equal to or less than the above-mentioned predetermined pressure, the first control valve 25 switches the first spool position to the first hydraulic cylinder stationary control position BNP which isolates the first implement control valve port YP1, the second implement control valve port YP2, the third implement control valve port YP3, the fourth implement control valve port YP4, and the fifth implement control valve port YP5. Note that in the schematic diagrams of the first control valve 25 shown in Figures 4, 9, and 10, the parts related to the control of the oil passage between the first implement control valve port YP1 and the fourth implement control valve port YP4 are omitted.

[0029] As shown in FIG. 3, the hydraulic circuit 100 further includes a shuttle valve 81 that outputs the higher pressure of the pressure applied to the second implement control valve port YP2 or the third implement control valve port YP3 and the pressure applied to the second arm control valve port XP2 or the third arm control valve port XP3, which will be described later, and a first pressure compensating valve 77 provided in the first cylinder hydraulic circuit C1 between the first control valve 25 and the hydraulic pump 11. The first pressure compensating valve 77 communicates the first implement control valve port YP1 and the fourth implement control valve port YP4 only when the pressure applied to the first implement control valve port YP1 is equal to or higher than the pressure output from the shuttle valve 81 by a fourth threshold pressure. This fourth threshold pressure may be referred to as the first pressure. In other words, the first pressure compensating valve 77 controls the hydraulic pressure of the hydraulic oil output from the first opening SP1 to be lower by the first pressure than the hydraulic pressure of the hydraulic oil input to the first opening SP1.

[0030] The first control valve 25 is configured to change a first opening area AS1, which is the area of ​​a first opening SP1 that communicates an oil passage connecting the first supplied oil chamber (CB1 or CB2) and the first control valve 25 with an oil passage connecting the hydraulic pump 11 and the first control valve 25, according to the first spool position. Since the maximum value that the first opening area AS1 can take is sufficiently smaller than the area of ​​the second axial opening XAP2 of the second notch NC2, if the first opening SP1 is regarded as an orifice, it is known that the flow rate of hydraulic oil passing through the first opening SP1 is proportional to the product of the square root of the pressure difference between the input and output of the first opening SP1 and the first opening area AS1. Since the first pressure compensating valve 77 controls the pressure difference between the input and output of the first opening SP1 to be the first pressure, the first control valve 25 can adjust the supply amount of hydraulic oil per unit time to the first supply oil chamber (CB1 or CB2) by changing the first opening area AS1 at each of the first hydraulic cylinder extension control position BEP and the first hydraulic cylinder contraction control position BSP. The third opening SP3 can be said to be an opening of the first control valve 25 that communicates the oil passage connecting the first discharge oil chamber (CB2 or CB1) and the first control valve 25 with the first drain oil passage DR1 (described later). The area of ​​the third opening SP3 changes depending on the first opening area AS1. In FIG. 9, the first opening SP1 is an opening between the second implement control valve port YP2 and the first spool SPL1, and the third opening SP3 is an opening between the third implement control valve port YP3 and the first spool SPL1. In FIG. 10, the first opening SP1 is an opening between the third implement control valve port YP3 and the first spool SPL1, and the third opening SP3 is an opening between the second implement control valve port YP2 and the first spool SPL1.

[0031] The third oil passage R3 connects the hydraulic pump 11 and the third chamber CB3 of the second hydraulic cylinder 48. The third oil passage R3 includes a partial oil passage R10 common to the first oil passage R1 extending from the hydraulic pump 11 to the joint J11, and a partial oil passage R31 branching from the first oil passage R1 at the joint J11. The second control valve 20 is provided in the third oil passage R3. The second control valve 20 is provided in the second cylinder hydraulic circuit C2 between the hydraulic pump 11 and the second hydraulic cylinder 48. The second control valve 20 has pilot ports 20P1, 20P2, and is configured to control the hydraulic oil supplied to the third chamber CB3 and the fourth chamber CB4 of the second hydraulic cylinder 48 according to the hydraulic pressure of the pilot oil applied to the pilot ports 20P1, 20P2. The third oil passage R3 further includes a partial oil passage R32 that connects different connection ports of the second control valve 20 together, and a partial oil passage R33 that extends to the third chamber CB3 of the second hydraulic cylinder 48. The fourth oil passage R4 connects the second control valve 20 and the fourth chamber CB4 of the second hydraulic cylinder 48. The third oil passage R3 and the fourth oil passage R4 are branched by being connected to different ports of the first control valve 25.

[0032] FIG. 4 is a schematic diagram showing an example of the internal configuration of the second control valve 20. In FIG. 4, the reference numerals of the second control valve 20 are shown in parentheses. As shown in FIG. 4, the second control valve 20 has a second spool SPL2 and a second valve housing 20B. FIG. 5 also shows a view of the second spool SPL2 seen from the first direction D1 in FIG. 4. With reference to FIGS. 4 and 5, the second spool SPL2 is a rod-shaped member extending in the axial direction Dx. The first direction D1 is perpendicular to the axial direction Dx. The second valve housing 20B supports the second spool SPL2 slidably in the axial direction Dx. With reference to FIGS. 4 and 5, the second spool SPL2 has a fourth notch NC4, a fifth notch NC5, and a sixth notch NC6. FIG. 6 is a cross-sectional view of the second control valve 20 along the line VI-VI in FIG. 4. FIG 7 is a cross-sectional view of the second control valve 20 taken along line VII-VII in FIG 4. FIG 8 is a cross-sectional view of the second control valve 20 taken along line VIII-VIII in FIG 4. Referring to FIG 6, the fourth notch NC4 forms a fourth axial opening XAP4 in the axial direction Dx. Referring to FIG 7, the fifth notch NC5 forms a fifth axial opening XAP5 in the axial direction Dx. Referring to FIG 8, the sixth notch NC6 forms a sixth axial opening XAP6 in the axial direction Dx.

[0033] Fig. 4 shows the internal configuration of the second control valve 20 in which the position of the second spool SPL2 is switched to the second hydraulic cylinder stationary control position ANP. Fig. 9 shows the internal configuration of the second control valve 20 in which the position of the second spool SPL2 is switched to the second hydraulic cylinder extension control position AEP. Fig. 10 shows the internal configuration of the second control valve 20 in which the position of the second spool SPL2 is switched to the second hydraulic cylinder retraction control position ASP. The second control valve 20 switches the second spool position, which is the position of the second spool SPL2, to the second hydraulic cylinder stationary control position ANP, the second hydraulic cylinder extension control position AEP, or the second hydraulic cylinder retraction control position ASP, depending on the pressure difference between the pilot pressure pp3 applied to the pilot port 20P1 and the pilot pressure pp4 applied to the pilot port 20P2. The second control valve 20 switches each of the two oil chambers (CB3, CB4) of the second hydraulic cylinder 48 alternatively between a second supplied oil chamber (CB3 or CB4) that supplies hydraulic oil and a second discharged oil chamber (CB3 or CB4) that discharges hydraulic oil by switching the second spool position to a second hydraulic cylinder extension control position AEP or a second hydraulic cylinder contraction control position ASP. Specifically, referring to FIG. 9, when the second spool position is switched to the second hydraulic cylinder extension control position AEP, the second supplied oil chamber is the third chamber CB3 of the second hydraulic cylinder 48, and the first discharged oil chamber is the fourth chamber CB4 of the second hydraulic cylinder 48. Referring to FIG. 10, when the second spool position is switched to the second hydraulic cylinder contraction control position ASP, the second supplied oil chamber is the fourth chamber CB4 of the second hydraulic cylinder 48, and the first discharged oil chamber is the third chamber CB3 of the second hydraulic cylinder 48.

[0034] More specifically, the second control valve 20 further includes a first arm control valve port XP1, a second arm control valve port XP2, a third arm control valve port XP3, a fourth arm control valve port XP4, and a fifth arm control valve port XP5. The first arm control valve port XP1 is connected to the hydraulic pump 11 via a third oil passage R3. The second arm control valve port XP2 is connected to a fourth oil passage R4. The third arm control valve port XP3 is connected to the third chamber CB3 of the second hydraulic cylinder 48 via the third oil passage R3. When the pilot pressure pp3 applied to the pilot port 20P1 is greater than the pilot pressure pp4 applied to the pilot port 20P2 by a predetermined pressure, the second control valve 20 switches the second spool position to a second hydraulic cylinder extension control position AEP that communicates the first arm control valve port XP1 and the third arm control valve port XP3 via the fourth arm control valve port XP4 and communicates the second arm control valve port XP2 with a first drain oil passage DR1 (described later) via the fifth arm control valve port XP5. Referring to FIG. 9, the third arm control valve port XP3 and the fifth notch NC5 form a second opening SP2. The second arm control valve port XP2 and the fourth notch NC4 form a fourth opening SP4. In FIG. 5, the outline of the third arm control valve port XP3 at this time is indicated by a two-dot chain line, and the second opening SP2 is indicated by hatching. The outline of the second arm control valve port XP2 at this time is shown by a two-dot chain line, and the fourth opening SP4 is shown by hatching. The second opening area AS2, which is the area of ​​the second opening SP2, can be continuously changed by changing the second spool position. The maximum value that the second opening area AS2 can take is sufficiently smaller than the area of ​​the fifth axial opening XAP5 of the fifth notch NC5. The fourth opening area, which is the area of ​​the fourth opening SP4, can be continuously changed by changing the second spool position. The maximum value that the fourth opening area can take is sufficiently smaller than the area of ​​the fourth axial opening XAP4 of the fourth notch NC4.

[0035] When the pilot pressure pp4 applied to the pilot port 20P2 is greater than the pilot pressure pp3 applied to the pilot port 20P1 by more than the above-mentioned predetermined pressure, the second control valve 20 switches the second spool position to the second hydraulic cylinder contraction control position ASP, which communicates the first arm control valve port XP1 and the second arm control valve port XP2 via the fourth arm control valve port XP4 and communicates the third arm control valve port XP3 with the first drain oil passage DR1 via the fifth arm control valve port XP5. The second valve housing 20B has a bypass oil passage BYP for connecting the third arm control valve port XP3 and the fifth arm control valve port XP5. The bypass oil passage BYP is also shown in Figures 6 and 8. Referring to Figure 10, the second arm control valve port XP2 and the fifth notch NC5 form a second opening SP2. The third arm control valve port XP3 and the sixth notch NC6 form a fourth opening SP4. In FIG. 5, the outer shape of the second arm control valve port XP2 at this time is shown by a two-dot chain line, and the second opening SP2 is shown by a check pattern. The outer shape of the third arm control valve port XP3 at this time is shown by a two-dot chain line, and the fourth opening SP4 is shown by a check pattern. The second opening area AS2, which is the area of ​​the second opening SP2, can be continuously changed by changing the second spool position. The maximum value that the second opening area AS2 can have is sufficiently smaller than the area of ​​the fifth axial opening XAP5 of the fifth notch NC5. The fourth opening area, which is the area of ​​the fourth opening SP4, can be continuously changed by changing the second spool position. The maximum value that the fourth opening area can have is sufficiently smaller than the area of ​​the sixth axial opening XAP6 of the sixth notch NC6.

[0036] When the absolute value of the difference between the pilot pressure pp4 applied to the pilot port 20P2 and the pilot pressure pp3 applied to the pilot port 20P1 is equal to or less than the predetermined pressure, the second control valve 20 switches the second spool position to the second hydraulic cylinder stationary control position ANP which isolates the first arm control valve port XP1, the second arm control valve port XP2, the third arm control valve port XP3, the fourth arm control valve port XP4, and the fifth arm control valve port XP5. Note that in the schematic diagrams of the first control valve 25 shown in Figures 4, 9, and 10, the parts related to the control of the oil passage between the first arm control valve port XP1 and the fourth arm control valve port XP4 are omitted.

[0037] 3, the hydraulic circuit 100 further includes a shuttle valve 82 that outputs the higher pressure of the pressure applied to the second arm control valve port XP2 or the third arm control valve port XP3 described later and the pressure applied to the second implement control valve port YP2 or the third implement control valve port YP3, and a second pressure compensating valve 76 provided in the second cylinder hydraulic circuit C2 between the second control valve 20 and the hydraulic pump 11. The second pressure compensating valve 76 communicates between the first arm control valve port XP1 and the fourth arm control valve port XP4 only when the pressure applied to the first arm control valve port XP1 is equal to or higher than the pressure output from the shuttle valve 82 by a third threshold pressure. The third threshold pressure is equal to the fourth threshold pressure and may be referred to as the first pressure. The second pressure compensating valve 76 is configured to control the second output hydraulic pressure of the hydraulic oil output from the second control valve 20 to the second supplied oil chamber (CB3 or CB4) to be lower by the first pressure than the second input hydraulic pressure input from the second pressure compensating valve 76 to the second control valve 20. This makes it possible to prevent arm control from being performed unless the hydraulic pressure from the hydraulic pump 11 meets the third threshold pressure.

[0038] The second control valve 20 is configured to change a second opening area AS2, which is the area of ​​a second opening SP2 of the second control valve 20 that communicates an oil passage connecting the second supplied oil chamber (CB3 or CB4) and the second control valve 20 with an oil passage connecting the hydraulic pump 11 and the second control valve 20, according to the second spool position. Since the maximum value that the second opening area AS2 can take is sufficiently smaller than the area of ​​the fifth axial opening XAP5 of the fifth notch NC5, if the second opening SP2 is regarded as an orifice, it is known that the flow rate of hydraulic oil passing through the second opening SP2 is proportional to the product of the square root of the pressure difference between the input and output of the second opening SP2 and the second opening area AS2. Since the second pressure compensating valve 76 controls the pressure difference between the input and output of the second opening SP2 to be the first pressure, the second control valve 20 can adjust the supply amount of hydraulic oil per unit time to the second supplied oil chamber (CB3 or CB4) by changing the second opening area AS2 at each of the second hydraulic cylinder extension control position AEP and the second hydraulic cylinder retraction control position ASP. The fourth opening SP4 can be said to be an opening of the second control valve 20 that communicates the oil passage connecting the second discharged oil chamber (CB3 or CB4) and the second control valve 20 with the first drain oil passage DR1 (described later). The area of ​​the fourth opening SP4 changes depending on the second opening area AS2. In FIG. 9, the second opening SP2 is an opening between the third arm control valve port XP3 and the second spool SPL2, and the fourth opening SP4 is an opening between the second arm control valve port XP2 and the second spool SPL2. In FIG. 10, the second opening SP2 is an opening between the second arm control valve port XP2 and the second spool SPL2, and the fourth opening SP4 is an opening between the third arm control valve port XP3 and the second spool SPL2.

[0039] Since the pressure difference (third threshold pressure) adjusted by the first pressure compensating valve 77 at the input / output of the first opening SP1 and the pressure difference (fourth threshold pressure) adjusted by the second pressure compensating valve 76 at the input / output of the second opening SP2 are set to the same first pressure, the ratio between the flow rate of hydraulic oil per unit time through the first control valve 25 and the flow rate of hydraulic oil per unit time through the second control valve 20 can be adjusted by the ratio between the first opening area AS1 and the second opening area AS2. The second pressure compensating valve 76 and the first pressure compensating valve 77 are collectively referred to as a pressure control mechanism 78.

[0040] The pressure control mechanism 78 further includes a shuttle valve 83 that outputs the higher of the hydraulic pressure applied to the first oil receiving chamber (CB1 or CB2) and the hydraulic pressure applied to the second oil receiving chamber (CB3 or CB4), and a regulator valve 79 for making the pressure of the hydraulic oil output from the hydraulic pump 11 equal to or higher than the first pressure output from the shuttle valve 83. The regulator valve 79 is switched to a first position PV1 when the hydraulic pressure is lower than the higher hydraulic pressure and higher than the first pressure, and is switched to a second position PV2 when the hydraulic pressure is higher than the higher hydraulic pressure by the first pressure or higher. As a result, even if the hydraulic pressure of at least one of the first hydraulic cylinder 49 and the second hydraulic cylinder 48 rises during control, the hydraulic pump 11 can supply a pressure equal to or higher than the first pressure, so that the first hydraulic cylinder 49 and the second hydraulic cylinder 48 can be continuously controlled. When the hydraulic pump 11 is controlled in this manner, the pressure difference between the lower of the hydraulic pressure applied to the first supply oil chamber (CB1 or CB2) and the hydraulic pressure applied to the second supply oil chamber (CB3 or CB4) and the pressure of the hydraulic oil output from the hydraulic pump 11 becomes greater than the first pressure described above. However, the functions of the first pressure compensating valve 77 and the second pressure compensating valve 76 adjust the pressure difference between the input and output of the first opening SP1 and the pressure difference between the input and output of the second opening SP2 to the same first pressure. Note that the pressure control mechanism 78 may use other hydraulic control components to set the first pressure or higher than the higher of the hydraulic pressure applied to the first supply oil chamber (CB1 or CB2) and the hydraulic pressure applied to the second supply oil chamber (CB3 or CB4).

[0041] In this way, the pressure control mechanism 78 can adjust the flow rate of hydraulic oil per unit time through the first control valve 25 by the first opening area AS1, so the first control valve 25 is configured to adjust the amount of hydraulic oil supplied per unit time to the first supplied oil chamber (CB1 or CB2) and the amount of hydraulic oil discharged per unit time from the first discharged oil chamber (CB2 or CB1) in accordance with the first spool position, which is the position of the first spool SPL1. The pressure control mechanism 78 can adjust the flow rate of hydraulic oil per unit time through the second control valve 20 by the second opening area AS2, so the second control valve 20 is configured to adjust the amount of hydraulic oil supplied per unit time to the second supplied oil chamber (CB3 or CB4) and the amount of hydraulic oil discharged per unit time from the second discharged oil chamber (CB4 or CB3) in accordance with the second spool position, which is the position of the second spool SPL2.

[0042] The first pilot oil passage PR1 connects the pilot ports 20P1 and 20P2 to the pilot pump 12. Specifically, the first pilot oil passage PR1 includes a partial oil passage PR10 common to the second pilot oil passage PR2 extending from the pilot pump 12 to the third pilot control valve 60 and the fourth pilot control valve 61, a partial oil passage PR11 extending from the third pilot control valve 60 to the pilot port 20P1, and a partial oil passage PR12 extending from the fourth pilot control valve 61 to the pilot port 20P2. The hydraulic circuit 100 further includes an additional solenoid valve 14 provided in the partial oil passage PR10. That is, the additional solenoid valve 14 is provided in at least one of the first pilot oil passage PR1 between the pilot pump 12 and the third pilot control valve 60 and the fourth pilot control valve 61, and the second pilot oil passage PR2 between the pilot pump 12 and the first pilot control valve 65 and the second pilot control valve 66. The additional solenoid valve 14 is a solenoid valve capable of changing the pressure of the hydraulic oil output from the pilot pump 12. The pressure of this hydraulic oil can be changed under the control of the controller 15.

[0043] The third pilot control valve 60 is an electromagnetic control valve provided in the first pilot oil passage PR1. The third pilot control valve 60 has a solenoid 60s, and controls the hydraulic pressure of the pilot oil applied to the pilot port 20P1 based on a control amount u3 applied to the solenoid 60s. The arm input member 63 is equipped with a rotation detection sensor 18 such as a potentiometer, and the controller 15 obtains an operation amount of the arm input member 63 operated for raising and lowering the arm 45 from the rotation detection sensor 18, and outputs a control amount u3 to be applied to the solenoid 60s based on the operation amount. The fourth pilot control valve 61 is an electromagnetic control valve provided in the first pilot oil passage PR1. The fourth pilot control valve 61 has a solenoid 61s, and controls the hydraulic pressure of the pilot oil applied to the pilot port 20P2 based on a control amount u4 applied to the solenoid 61s. The controller 15 obtains the amount of operation of the arm input member 63 operated to raise and lower the arm 45 from the rotation detection sensor 18, and outputs a control amount u4 to be applied to the solenoid 61s based on the amount of operation. When the arm input member 63 is tilted forward, the controller 15 operates the third pilot control valve 60 to output a pilot pressure pp3 from the third pilot control valve 60 to the partial oil passage PR11. This pilot pressure pp3 acts on the pilot port 20P1 of the second control valve 20. When the arm input member 63 is tilted rearward, the controller 15 operates the fourth pilot control valve 61 to output a pilot pressure pp4 from the pressure control valve 62 to the partial oil passage PR12. This pilot pressure pp4 acts on the pilot port 20P2 of the second control valve 20.

[0044] More specifically, when an operation for raising the arm 45 is performed by the arm input member 63 (an operation for tilting the arm input member 63 rearward), the pilot pressure pp3 applied to the pilot port 20P1 becomes higher than the predetermined pressure than the pilot pressure pp4 applied to the pilot port 20P2. When an operation for lowering the arm 45 is performed by the arm input member 63 (an operation for tilting the arm input member 63 forward), the pilot pressure pp4 applied to the pilot port 20P2 becomes higher than the predetermined pressure than the pilot pressure pp3 applied to the pilot port 20P1. When the operation amount of the arm input member 63 is smaller than a predetermined threshold amount, the absolute value of the difference between the pilot pressure pp4 applied to the pilot port 20P2 and the pilot pressure pp3 applied to the pilot port 20P1 becomes equal to or less than the predetermined pressure.

[0045] The second pilot oil passage PR2 connects the pilot ports 25P1 and 25P2 to the pilot pump 12. Specifically, the second pilot oil passage PR2 includes a partial oil passage PR10 common to the first pilot oil passage PR1 extending from the pilot pump 12 to the first pilot control valve 65 and the second pilot control valve 66, a partial oil passage PR21 extending from the first pilot control valve 65 to the pilot port 25P1, and a partial oil passage PR22 extending from the second pilot control valve 66 to the pilot port 25P2. The first pilot control valve 65 is an electromagnetic control valve provided in the second pilot oil passage PR2. The first pilot control valve 65 has a solenoid 65s, and controls the hydraulic pressure of the pilot oil applied to the pilot port 25P1 based on a control amount u1 applied to the solenoid 65s. The implement input member 68 is equipped with a rotation detection sensor 19 such as a potentiometer, and the controller 15 acquires the tilt angle of the implement input member 68 detected by the rotation detection sensor 18, and outputs a control amount u1 to be applied to the solenoid 65s based on the operation amount. The second pilot control valve 66 is an electromagnetic control valve provided in the second pilot oil passage PR2. The second pilot control valve 66 has a solenoid 66s, and controls the hydraulic pressure of the pilot oil applied to the pilot port 25P2 based on the control amount u2 to be applied to the solenoid 66s. The controller 15 acquires the tilt angle of the implement input member 68 detected by the rotation detection sensor 18, and outputs a control amount u2 to be applied to the solenoid 66s based on the operation amount.

[0046] When the implement input member 68 is tilted to the right, the controller 15 operates the first pilot control valve 65 to output a pilot pressure pp1 from the first pilot control valve 65 to the partial oil passage PR21. This pilot pressure pp1 acts on the pilot port 25P1 of the first control valve 25. When the implement input member 68 is tilted to the left, the controller 15 operates the second pilot control valve 66 to output a pilot pressure pp2 from the second pilot control valve 66 to the partial oil passage PR22. This pilot pressure pp2 acts on the pilot port 25P2 of the first control valve 25.

[0047] More specifically, when an operation for tilting the implement tip 41T downward by the implement input member 68 (an operation for tilting the implement input member 68 to the right) is performed, the pilot pressure pp1 applied to the pilot port 25P1 becomes greater than the above-mentioned predetermined pressure than the pilot pressure pp2 applied to the pilot port 25P2. When an operation for tilting the implement tip 41T upward by the implement input member 68 (an operation for tilting the implement input member 68 to the left) is performed, the pilot pressure pp2 applied to the pilot port 25P2 becomes greater than the above-mentioned predetermined pressure than the pilot pressure pp1 applied to the pilot port 25P1. When the operation amount of the implement input member 68 is smaller than a predetermined threshold amount, the absolute value of the difference between the pilot pressure pp2 applied to the pilot port 25P2 and the pilot pressure pp1 applied to the pilot port 25P1 becomes equal to or less than the above-mentioned predetermined pressure.

[0048] In addition, in Fig. 3, the arm input member 63 and the implement input member 68 are illustrated as separate members, but they may be the same member as represented by the operation lever 55 in Fig. 1. In this case, the rotation detection sensors 18, 19 are disposed around the same member.

[0049] The bypass oil passage BR1 is configured to connect the fourth oil passage R4 and the first oil passage R1. The bypass oil passage BR1 is connected to the fourth oil passage R4 at the first joint J1. The bypass oil passage BR1 is connected to the first oil passage R1 at the third joint J3. The switching mechanism 70 is configured to control the connection and disconnection of the fourth oil passage R4 and the first oil passage R1 by the bypass oil passage BR1. The controller 15 is configured to control the switching mechanism 70 to connect the fourth oil passage R4 and the first oil passage R1 when it is determined that the horizontal control of the implement 41 has been performed. The controller 15 is, for example, a hardware controller such as an ECU. Therefore, the controller 15 includes electronic circuits such as a hardware processor 15P and a memory 15M. The memory 15M may be referred to as a storage device.

[0050] The switching mechanism 70 includes a solenoid valve 71 and a first switching valve 72. The first switching valve 72 is provided in a fourth oil passage R4 between the first joint J1 and the second control valve 20, and has a first pilot port PP1. The first switching valve 72 is configured to cut off the connection between the second control valve 20 and the fourth chamber CB4 of the second hydraulic cylinder 48 via the fourth oil passage R4 when a pilot oil pressure equal to or greater than the first threshold pressure is applied to the first pilot port PP1, and to connect the second control valve 20 and the fourth chamber CB4 via the fourth oil passage R4 when a pilot oil pressure smaller than the first threshold pressure is applied to the first pilot port PP1. The solenoid valve 71 is switchable between a second position VP2 that communicates the first pilot port PP1 with the hydraulic oil tank 10 and a first position VP1 that connects the first pilot port PP1 to an oil passage that can apply a pilot pressure equal to or greater than the first threshold pressure to the first pilot port PP1.

[0051] The controller 15 is connected to a solenoid of the solenoid valve 71. For example, when the controller 15 determines that the horizontal control of the implement 41 has been performed, it transmits an electric signal to the solenoid valve 71 to switch the solenoid valve 71 to the first position VP1.

[0052] Furthermore, the work vehicle 1 further includes an ON / OFF switch 16 connected to the controller 15. When the switch 16 is switched ON, the controller 15 transmits an electrical signal to the solenoid valve 71 to switch the solenoid valve 71 to the first position VP1. This switch 16 is switched ON when performing the above-mentioned horizontal control.

[0053] The work vehicle 1 further includes an additional bypass oil passage BR2 that connects between the fourth oil passage R4 between the first changeover valve 72 and the second control valve 20 and the second oil passage R2. The additional bypass oil passage BR2 connects to the fourth oil passage R4 at the second joint J2 and connects to the second oil passage R2 at the fourth joint J4. The changeover mechanism 70 further includes a second changeover valve 73 provided in the bypass oil passage BR1 and a third changeover valve 74 provided in the additional bypass oil passage BR2. The bypass oil passage BR1 includes a partial oil passage BR10 from the first joint J1 to the second changeover valve 73 and a partial oil passage BR11 from the second changeover valve 73 to the third joint J3. The additional bypass oil passage BR2 includes a partial oil passage BR20 from the second joint J2 to the third changeover valve 74 and a partial oil passage BR21 from the third changeover valve 74 to the fourth joint J4. The work vehicle 1 further includes a first connection path CR1 connecting an additional bypass oil passage BR2 (partial oil passage BR20) between the second joint J2 and the third switching valve 74 and the second switching valve 73, a second connection path CR2 connecting the bypass oil passage BR1 (partial oil passage BR11) between the third joint J3 and the second switching valve 73 and the third switching valve 74, and a third connection path CR3 connecting the bypass oil passage BR1 (partial oil passage BR11) between the second connection path CR2 and the second switching valve 73 and the second switching valve 73.

[0054] The second changeover valve 73 is configured to switch to a first communication position CP1 that communicates the first joint J1 and the third joint J3 when a first hydraulic pressure in a bypass oil passage BR1 (partial oil passage BR10) between the first joint J1 and the second changeover valve 73 is greater than a second hydraulic pressure in the first connection passage CR1, and to switch to a first blocking position BP1 that blocks communication between the first joint J1 and the third joint J3 when the second hydraulic pressure is equal to or less than the first hydraulic pressure. The second changeover valve 73 is configured to connect the partial oil passage BR10 and the first connection passage CR1 when switched to the first blocking position BP1. The second changeover valve 73 is configured to block the partial oil passage BR10 and the first connection passage CR1 when switched to the first communication position CP1.

[0055] The third changeover valve 74 is switched to any one of a second cutoff position BP2, a 21st communication position CP21, and a 22nd communication position CP22 based on a third oil pressure in an additional bypass oil passage BR2 (partial oil passage BR20) between the second joint J2 and the third changeover valve 74 and a fourth oil pressure in the second connection passage CR2. The 21st communication position CP21 and the 22nd communication position CP22 are collectively referred to as the second communication position CP2. Since a check valve CKV is provided between the second connection passage CR2 and the third joint J3, the oil pressure in the first oil passage R1 does not affect the oil pressure in the second connection passage CR2. The third changeover valve 74 is configured to switch to a second communication position CP2 that communicates the second joint J2 and the fourth joint J4 when the third hydraulic pressure is lower than the fourth hydraulic pressure, and to switch to a second blocking position BP2 that blocks communication between the second joint J2 and the fourth joint J4 when the fourth hydraulic pressure is equal to or lower than the third hydraulic pressure. When the difference between the fourth hydraulic pressure and the third hydraulic pressure is lower than a predetermined pressure, the third changeover valve 74 switches to a 21st communication position CP21 to communicate the second joint J2 and the fourth joint J4 and block the connection between the third connection passage CR3 and the partial oil passage BR11. On the other hand, when the third hydraulic pressure is lower than the fourth hydraulic pressure by a predetermined pressure or more, the third changeover valve 74 switches to the 21st communication position CP21 to communicate the second joint J2 and the fourth joint J4 and connect the third connection passage CR3 and the bypass oil passage BR1 (partial oil passage BR11). This makes it possible to prevent the hydraulic pressure in the bypass oil passage BR1 (partial oil passage BR11) from becoming too high.

[0056] Furthermore, the work vehicle 1 further includes a first drain oil passage DR1 that connects the fourth chamber CB4 and the hydraulic oil tank 10 when the second control valve 20 and the fourth chamber CB4 of the second hydraulic cylinder 48 are connected via the fourth oil passage R4 by the first changeover valve 72. The changeover mechanism 70 further includes a first counterbalance valve BV1 provided in the first drain oil passage DR1, a fourth changeover valve 75, a third pilot oil passage PR3 that connects the fourth changeover valve 75 and the first pilot port PP1 of the first changeover valve 72, a fourth pilot oil passage PR4 that connects the first drain oil passage DR1 between the first changeover valve 72 and the first counterbalance valve BV1 and the fourth changeover valve 75, and a second drain oil passage DR2 that connects the fourth changeover valve 75 and the hydraulic oil tank 10. The first counterbalance valve BV1 is a pressure control valve that opens when the pressure at the illustrated joint J8 becomes higher than the pressure at the joint J9 by a predetermined pressure or more, and is configured to allow hydraulic oil to flow from the joint J8 to the joint J9. The first threshold pressure is lower than the predetermined pressure at which the first counterbalance valve BV1 opens. The same counterbalance valves BV2-BV4 are connected to fourth to sixth drain oil passages DR4-DR6 that are connected to the third oil passage R3, the first oil passage R1, and the second oil passage R2, respectively. The fourth to sixth drain oil passages DR4-DR6 are connected to the first drain oil passage DR1.

[0057] The fourth switching valve 75 includes a first connection port ZP1 connected to the third pilot oil passage PR3, a second connection port ZP2 connected to the fourth pilot oil passage PR4, a third connection port ZP3 connected to the second drain oil passage DR2, and a switching valve pilot port 75P to which pilot pressure is applied by the solenoid valve 71. When pilot oil pressure equal to or greater than the second threshold pressure is applied to the switching valve pilot port 75P, the fourth switching valve 75 is switched to a drain position DP that connects the first connection port ZP1, the second connection port ZP2, and the third connection port ZP3. When pilot oil pressure smaller than the second threshold pressure is applied to the switching valve pilot port 75P, the fourth switching valve 75 is switched to a pressure increase position UP that connects the first connection port ZP1 and the second connection port ZP2 and disconnects the third connection port ZP3 from the first connection port ZP1 and the second connection port ZP2.

[0058] When the solenoid valve 71 is switched to the second position VP2 by the controller 15, a pilot oil pressure equal to or greater than the second threshold pressure is applied to the switching valve pilot port 75P. Therefore, the fourth switching valve 75 is switched to the drain position DP, and the pilot pressure applied to the first pilot port PP1 falls below the first threshold pressure. At this time, the first switching valve 72 is opened, and the second control valve 20 and the fourth chamber CB4 are connected via the fourth oil passage R4, and the fourth oil passage R4 is connected to the first drain oil passage DR1 to the first counterbalance valve BV1.

[0059] At this time, when the arm input member 63 is tilted forward, the pilot pressure pp3 applied to the pilot port 20P1 becomes greater than the pilot pressure pp4 applied to the pilot port 20P2 and is greater than the above-mentioned predetermined pressure, so that the second control valve 20 is switched to the second hydraulic cylinder extension control position AEP. Therefore, the hydraulic oil having a pressure exceeding the third threshold pressure from the hydraulic pump 11 is sent to the third chamber CB3 of the second hydraulic cylinder 48 via the second control valve 20. As a result, the hydraulic oil is output from the fourth chamber CB4 of the second hydraulic cylinder 48 to the fourth oil passage R4. Since the first switching valve 72 is open, the hydraulic oil is sent to the second arm control valve port XP2 of the second control valve 20 and discharged to the third drain oil passage DR3 connected to the first drain oil passage DR1.

[0060] In addition, when the arm input member 63 is tilted rearward, the pilot pressure pp4 applied to the pilot port 20P2 becomes greater than the pilot pressure pp3 applied to the pilot port 20P1 and is greater than the above-mentioned predetermined pressure, so that the second control valve 20 is switched to the second hydraulic cylinder contraction control position ASP. Therefore, the hydraulic oil having a pressure exceeding the third threshold pressure from the hydraulic pump 11 is sent to the fourth chamber CB4 of the second hydraulic cylinder 48 via the second control valve 20 and the first switching valve 72. As a result, the hydraulic oil is output from the third chamber CB3 of the second hydraulic cylinder 48 to the third oil passage R3. The hydraulic oil is sent to the third arm control valve port XP3 of the second control valve 20 and discharged to the third drain oil passage DR3 connected to the first drain oil passage DR1.

[0061] When the solenoid valve 71 is switched to the second position VP2 by the controller 15, the control of the implement 41 is performed independently of the control of the arm 45, except for the automatic implement return control described later. In this state, when the implement input member 68 is tilted to the right, the pilot pressure pp1 applied to the pilot port 25P1 becomes greater than the pilot pressure pp2 applied to the pilot port 25P2 and is greater than the above-mentioned predetermined pressure, so that the first control valve 25 is switched to the first hydraulic cylinder extension control position BEP. Therefore, the hydraulic oil having a pressure exceeding the fourth threshold pressure from the hydraulic pump 11 is sent to the first chamber CB1 of the first hydraulic cylinder 49 via the first control valve 25. As a result, the hydraulic oil is output from the second chamber CB2 of the first hydraulic cylinder 49 to the second oil passage R2. The hydraulic oil is sent to the third implement control valve port YP3 of the first control valve 25 and discharged to the seventh drain oil passage DR7 connected to the first drain oil passage DR1.

[0062] In addition, when the implement input member 68 is tilted to the left, the pilot pressure pp2 applied to the pilot port 25P2 becomes greater than the pilot pressure pp1 applied to the pilot port 25P1 and is greater than the above-mentioned predetermined pressure, so that the first control valve 25 is switched to the first hydraulic cylinder contraction control position BSP. Therefore, the hydraulic oil having a pressure exceeding the fourth threshold pressure from the hydraulic pump 11 is sent to the second chamber CB2 of the first hydraulic cylinder 49 via the first control valve 25. As a result, the hydraulic oil is output from the first chamber CB1 of the first hydraulic cylinder 49 to the first oil passage R1. The hydraulic oil is sent to the second implement control valve port YP2 of the first control valve 25 and discharged to the seventh drain oil passage DR7 connected to the first drain oil passage DR1.

[0063] When the solenoid valve 71 is switched to the first position VP1 by the controller 15 after the solenoid valve 71 is switched to the second position VP2 by the controller 15, a pilot oil pressure smaller than the second threshold pressure is applied to the switching valve pilot port 75P, and the fourth switching valve 75 is switched to the pressure increase position UP. At the beginning of the switching, the pilot pressure applied to the first pilot port PP1 is lower than the first threshold pressure, but the pilot pressure is immediately increased by the pressure of the hydraulic oil flowing from the fourth oil passage R4. Since the predetermined pressure at which the first counterbalance valve opens is higher than the first threshold pressure, the pilot pressure exceeds the first threshold pressure, and the first switching valve 72 is closed. As a result, the connection between the second control valve 20 and the fourth chamber CB4 of the second hydraulic cylinder 48 via the fourth oil passage R4 is cut off.

[0064] When the first changeover valve 72 is closed, an operation is performed to lift the arm 45 (an operation to tilt the arm input member 63 rearward) and no operation is performed on the implement 41 (an operation to not tilt the implement input member 68 anywhere), the second control valve 20 is switched to the second hydraulic cylinder extension control position AEP, and the first control valve 25 is switched to the first hydraulic cylinder stationary control position BNP. When the arm input member 63 and the implement input member 68 are the same, this operation refers to an operation in which the same input member is tilted rearward without being tilted left or right.

[0065] At this time, as explained above, the hydraulic oil flows out from the fourth chamber CB4 of the second hydraulic cylinder 48, but because the first switching valve 72 is closed, it flows from the first joint J1 to the second switching valve 73. In addition, because the additional bypass oil passage BR2 and the first connecting passage CR1 connected thereto are connected to the third drain oil passage DR3, the first hydraulic pressure in the bypass oil passage BR1 (partial oil passage BR10) between the first joint J1 and the second switching valve 73 is greater than the second hydraulic pressure in the first connecting passage CR1. As a result, the second switching valve 73 is switched to the first communicating position CP1. At this time, the hydraulic oil is sent from the second switching valve 73 to the first chamber CB1 of the first hydraulic cylinder 49 via the bypass oil passage BR1 (partial oil passage BR11) and the first oil passage R1 (partial oil passage R13). At this time, the hydraulic oil is output from the second chamber CB2 of the first hydraulic cylinder 49 to the second oil passage R2 and the additional bypass oil passage BR2 (partial oil passage BR21). However, since the third changeover valve 74 is initially positioned at the second shutoff position BP2, the hydraulic oil cannot flow, and the hydraulic pressure of the second connection passage CR2 rises. When the difference between the fourth hydraulic pressure of the second connection passage CR2 and the third hydraulic pressure of the additional bypass oil passage BR2 (partial oil passage BR20) exceeds the connection threshold pressure, the second connection passage CR2 is switched to either the 21st communication position CP21 or the 22nd communication position CP22 based on the difference between the third hydraulic pressure of the additional bypass oil passage BR2 (partial oil passage BR20) and the fourth hydraulic pressure of the second connection passage CR2. When the difference between the fourth hydraulic pressure and the third hydraulic pressure is smaller than a predetermined switching threshold, the third changeover valve 74 is switched to the 21st communication position CP21. When the difference between the fourth hydraulic pressure and the third hydraulic pressure is equal to or greater than a predetermined switching threshold, the third changeover valve 74 is switched to the 22nd communication position CP22. When the third changeover valve 74 is switched to the 21st communication position CP21 or the 22nd communication position CP22, the hydraulic oil output from the second chamber CB2 of the first hydraulic cylinder 49 is discharged to the hydraulic oil tank 10 via the additional bypass oil passage BR2 and the third drain oil passage DR3.

[0066] However, when the hydraulic oil flows out of the fourth chamber CB4 of the second hydraulic cylinder 48, the second hydraulic pressure in the first connection passage CR1 rises, and the second switching valve 73 is switched to the first cut-off position BP1. The hydraulic oil flowing out of the fourth chamber CB4 is discharged to the hydraulic oil tank 10 via the first connection passage CR1, the additional bypass oil passage BR2, and the third drain oil passage DR3. Therefore, a part of the amount of oil discharged from the fourth chamber CB4 of the second hydraulic cylinder 48 by flowing into the third chamber CB3 of the second hydraulic cylinder 48 flows into the first chamber CB1 of the first hydraulic cylinder 49, and the remainder is discharged to the hydraulic oil tank 10. The size of the throttle of the first cut-off position BP1 of the second switching valve 73 is empirically adjusted so that the change in the elevation angle of the arm 45 with respect to the vehicle body 2 and the change in the swing angle with respect to the arm 45 per unit amount of hydraulic oil are substantially equal to each other, and the amount discharged to the hydraulic oil tank 10 is adjusted. Therefore, the swing angle of the implement tip 41T relative to the arm 45 is changed in response to the elevation angle of the arm, so that the direction from the joint 43 to the implement tip 41T is controlled to be approximately horizontal. This type of control is called horizontal control.

[0067] When the first switching valve 72 is closed, an operation is performed to lower the arm 45 (an operation to tilt the arm input member 63 forward) and no operation is performed on the implement 41 (an operation to not tilt the implement input member 68 anywhere), the second control valve 20 is switched to the second hydraulic cylinder contraction control position ASP, and the first control valve 25 is switched to the first hydraulic cylinder stationary control position BNP. At this time, hydraulic oil having a pressure exceeding the third threshold pressure from the hydraulic pump 11 is output from the second arm control valve port XP2. Since this third threshold pressure is greater than the above-mentioned first threshold pressure and the threshold pressure for opening the first counterbalance valve BV1, the hydraulic oil is sent to the fourth chamber CB4 of the second hydraulic cylinder 48 through the fourth oil passage R4 by pushing and opening the first switching valve 72. At this time, the hydraulic oil is discharged from the third chamber CB3 of the second hydraulic cylinder 48 through the third oil passage R3 and the third drain oil passage DR3 to the hydraulic oil tank 10. <Automatic implement return control>

[0068] Next, the automatic implement return control will be explained. Fig. 7 is a conceptual diagram of the automatic implement return control in the case where the implement attitude detection sensor 57 is composed of a first inertial measurement unit 57a and a second inertial measurement unit 57b. The automatic implement return control is an automatic control in which, when the input device 17 is turned ON, the position and attitude of the implement 41 and the arm 45 when the load is dumped are changed to a reference position and attitude of the implement 41 and the arm 45 stored in advance in the memory 15M. This input device 17 is, for example, a button or a switch. The position and attitude of the arm 45 is determined by the arm height H A The arm height H when the load is dumped, i.e., when the automatic implement return control starts, is A is the initial height STA_H, and the implement orientation 41D at the start of the automatic implement return control is the initial orientation STA_D. The control target (reference) arm height H A is set as the reference height REF_H, and the control target (reference) implement orientation 41D of the automatic implement return control is set as the reference orientation REF_D. In the automatic implement return control, the arm height H A from STA_H to REF_H, and the implement orientation 41D is changed from the initial orientation STA_D to the reference orientation REF_D. A and to the reference orientation REF_D and the reference height REF_H, respectively.

[0069] FIG. 8 is a conceptual diagram of automatic implement return control in the case where the implement attitude detection sensor 57 is composed of a potentiometer 57r. Referring to FIG. 8, when the arm height H A In order to control the arm position, when the arm position detection sensor 56 is composed of a potentiometer 56r, the memory 15M stores the rotation angle θ J and arm height H AThe hardware processor 15P stores a table representing a third correspondence relationship between the rotation angle θ J From arm height H A Further, the memory 15M is configured to calculate the rotation angle θ of the fulcrum shaft 59P. J and the position P of the second hydraulic cylinder 48 A The hardware processor 15P stores a table in which a second correspondence relationship between the rotation angle θ J to the position P of the second hydraulic cylinder 48 A At this time, the memory 15M is configured to obtain a rotation angle θ of the fulcrum shaft 59P corresponding to the reference height REF_H as a control target corresponding to the reference height REF_H. J REF_θ J , or the position P of the second hydraulic cylinder 48 at that time A The second reference position REF_P A Remember.

[0070] 7 or 8, when the arm position detection sensor 56 is composed of a linear sensor 56p, the memory 15M stores the position P of the second hydraulic cylinder 48. A and arm height H A The hardware processor 15P stores a table showing a fourth correspondence relationship between the position P detected by the linear sensor 56p and the position P based on the fourth correspondence relationship. A From arm height H A At this time, the memory 15M is configured to obtain the position P of the second hydraulic cylinder 48 as a control target corresponding to REF_H. A The second reference position REF_P A Remember.

[0071] Referring to FIG. 7, the arm 45 rotates so that the position P of the first hydraulic cylinder 49 I Even if the arm height H is fixed (even if the relative position of the implement 41 with respect to the arm tip 45D does not change), A When the implement inclination angle θ changes,I is the arm height H A This arm height H A The implement inclination angle θ changes according to I This is the adjustment angle θ A In the following embodiments, the arm height H A Adjustment angle θ when A θ A (H A For this reason, when the implement attitude detection sensor 57 is composed of the first inertial measurement unit 57a and the second inertial measurement unit 57b, the memory 15M stores the arm height H A and adjustment angle θ A (H A ) and a table showing the fifth correspondence relationship with the adjustment angle θ A is the rotation angle θ of the fulcrum axis 59P J In this case, the rotation angle θ of the fulcrum shaft 59P derived from the third correspondence relationship and the fifth correspondence relationship may be determined according to the following equation. J The corresponding adjustment angle θ A is stored in the memory 15M. Furthermore, the adjustment angle θ A is the position P of the second hydraulic cylinder 48 A In this case, the position P of the second hydraulic cylinder 48 derived from the fourth and fifth correspondence relationships may be determined according to the following equation: A The corresponding adjustment angle θ A is stored in the memory 15M. In FIG. 7 and the following embodiments, for the sake of simplicity, θ A (REF_H)=0, but θ A (REF_H) may be a value other than 0. In that case, θ A Adjustment angle θ based on the value of (REF_H) A (H A ) may be changed from the values ​​used in the following explanations.

[0072] In addition, the memory 15M stores the implement inclination angle θ I Arm height H A Adjustment angle θ changes depending on A (H A ) and the position P of the first hydraulic cylinder 49 IWhen the implement orientation detection sensor 57 is composed of the first inertial measurement unit 57a and the second inertial measurement unit 57b, in order to control the implement orientation 41D, the hardware processor 15P stores a table in which a first correspondence relationship between the implement inclination angle θ I With reference to the position P of the first hydraulic cylinder 49, I However, the position P of the first hydraulic cylinder 49 corresponding to the above-mentioned STA_D and REF_D is controlled. I To find the implement inclination angle θ I Adjustment angle θ A (H A The hardware processor 15P calculates the angle by adding the implement inclination angle θ I Adjustment angle θ A (H A ) based on the first correspondence relationship, the position P of the first hydraulic cylinder 49 is calculated. I At this time, the memory 15M stores the implement tilt angle θ I The reference angle REF_θ I +adjustment angle θ A (REF_H) [θ A When (REF_H)=0, the reference angle REF_θ I ] and the position P of the first hydraulic cylinder 49 at that time I The first reference position REF_P I Remember.

[0073] Referring to FIG. 8, when the implement attitude detection sensor 57 is composed of a potentiometer 57r, the adjustment angle θ A (H A ) is unnecessary, and the rotation angle θ of joint 43 is R is detected from the potentiometer 57r. The hardware processor 15P detects the rotation angle θ R However, the position P of the first hydraulic cylinder 49 corresponding to the initial orientation STA_D and the reference orientation REF_D is controlled. IIn order to obtain the rotation angle θ of the joint 43, the memory 15M stores the rotation angle θ R and the position P of the first hydraulic cylinder 49 I The hardware processor 15P stores a table in which the sixth correspondence relationship is stored. The hardware processor 15P refers to the sixth correspondence relationship and calculates the rotation angle θ R to the position P of the first hydraulic cylinder 49 I At this time, the memory 15M stores the rotation angle θ of the joint 43 corresponding to the reference orientation REF_D as a control target corresponding to the reference orientation REF_D. R The reference rotation angle REF_θ is R Or the position P of the first hydraulic cylinder 49 at that time I The first reference position REF_P I Memorize.

[0074] 7 and 8, when the implement attitude detection sensor 57 is composed of a linear sensor 57p, the above-mentioned adjustment angle θ A (H A ) and the rotation angle θ of joint 43 R The concept of is not necessary, and the position P of the first hydraulic cylinder 49 is I is the control variable, and the position P corresponding to STA_D is I Position P corresponding to REF_D I The memory 15M stores the position P of the first hydraulic cylinder 49 corresponding to REF_D as a control target corresponding to REF_D. I The first reference position REF_P I Among the above, REF_θ R , or REF_P I is called the first information corresponding to the reference orientation REF_D. J or REF_P A is called the second information corresponding to the reference height REF_H. The first information is the first parameter (rotation angle θ R , position P I ) first reference value (REF_θ R , or REF_P I ) REF_P IThe second information is also referred to as a first reference position of the first hydraulic cylinder 49. J , position P A ) second reference value (REF_θ J , REF_P A ) REF_P A This may also be referred to as the second reference position of the second hydraulic cylinder 48.

[0075] This automatic implement return control is characterized by the arm height H between the initial height STA_H and the reference height REF_H. A At the target height TAR_H, the first hydraulic cylinder 49 is controlled so that the position of the implement 41 relative to the arm tip 45D is the same as that at the reference height REF_H. Then, the position P of the first hydraulic cylinder 49 is I is not changed, and the second hydraulic cylinder 48 is controlled to change the arm height H A In other words, the controller 15 changes the arm height H of the arm tip 45D when the implement tip 41T is directed to the reference orientation REF_D during the automatic implement return control. A The controller 15 is configured to determine the arm height H A When an instruction to start the automatic implement return control is received from the input device 17, the controller 15 controls the hydraulic circuit 100 so that the arm height H reaches the target height TAR_H during the automatic implement return control. A The hydraulic circuit 100 is controlled so that the implement orientation 41D becomes the reference orientation REF_D when the target height TAR_H is changed. For example, the target height TAR_H is a predetermined offset value H off That is, the target height TAR_H is greater than the reference height REF_H.

[0076] FIG. 9 shows the arm height H in automatic implement return control when the implement attitude detection sensor 57 is composed of a first inertial measurement unit 57a and a second inertial measurement unit 57b. A Change in implement inclination angle θ I 10 is a diagram showing a relationship between the change in the reference orientation REF_D and the change in the reference height REF_H. FIG. 10 is a control block diagram according to the embodiment. A control system 150 according to the embodiment includes a control target calculation module 151. The control target calculation module 151 is realized by a program stored in the memory 15M, for example, and executed by the hardware processor 15P. First, at the time when the reference height REF_H is input (the time when a registration instruction for registering the reference orientation REF_D and the reference height REF_H is input to the additional input device 13 described later), the hardware processor 15P calculates the target height TAR_H by multiplying the registered reference height REF_H by an offset value H. off The hardware processor 15P calculates the target height TAR_H by adding the adjustment angle θ A (TAR_H) is obtained from the fifth correspondence relationship. The hardware processor 15P further obtains the reference tilt angle REF_θ I +adjustment angle θ A (REF_H) [or θ A When (REF_H)=0, the reference angle REF_θ I ] and read the arm height H A The implement inclination angle REF_θ when the target height TAR_H is reached I +θ A (TAR_H) is determined. REF_θ I +θ A (TAR_H) corresponds to the first reference value of the first parameter corresponding to the target height TAR_H. That is, the controller 15 calculates the first reference value REF_θ of the first parameter corresponding to the target height TAR_H. I +θ A For this reason, the first information determines REF_θ (TAR_H) as the first reference value of the first parameter corresponding to the reference orientation REF_D. I +θ A (TAR_H) is included. REF_θ I+θ A (TAR_H) is stored in the memory 15M when it is calculated. I +θ A (TAR_H) is input to the control target calculation module 151.

[0077] The controller 15 performs the following process when executing the control target calculation module 151. At the start of the automatic implement return control, which is the time when an instruction to start the automatic implement return control is received by the input device 17, the controller 15 calculates a second initial rotation angle STA_θ of the fulcrum shaft 59P corresponding to the initial height STA_H obtained from the arm posture detection sensor 56 at that time. J or the second initial position STA_P of the second hydraulic cylinder 48 A The controller 15 detects the arm position by detecting the second initial rotation angle STA_θ J When the position P of the second hydraulic cylinder 48 is obtained based on the second correspondence relationship, A The second initial position STA_P corresponds to the initial height STA_H, A The controller 15 determines the second initial rotation angle STA_θ by using the arm position detection sensor 56 as a potentiometer 56r. J When acquiring the second initial position STA_P, the controller 15 refers to the third correspondence relationship to determine the initial height STA_H. A When obtaining the initial height STA_H, the fourth correspondence relationship is referred to to determine the initial height STA_H.

[0078] Next, the controller 15 calculates the implement inclination angle θ corresponding to the initial orientation STA_D obtained from the implement attitude detection sensor 57. I STA_θ I is obtained from the output of the implement attitude detection sensor 57. I is the position P of the first hydraulic cylinder 49 at the time when the input device 17 receives an instruction to start the automatic implement return control. I The first initial position STA_P IThe controller 15 calculates the adjustment angle θ A (STA_H). The controller calculates STA_θ I +θ A (STA_H) based on the first correspondence relationship, the position P of the first hydraulic cylinder 49 at the time when the instruction to start the automatic implement return control is received by the input device 17 is calculated. I The first initial position STA_P I The controller 15 calculates the implement inclination angle θ I is STA_θ I From REF_θ I +θ A L1 is expressed as changing linearly from the initial height STA_H at the start of the automatic implement return control to the reference height REF_H. A A map M1 is generated that includes the arm height H at the time t and L2, which is expressed as changing linearly. The horizontal axis of this map M1 is the timing t, and A corresponds to the vertical coordinate on the right side of point P on L2, and the implement tilt angle θ I corresponds to the coordinate on the vertical axis on L1 to the left of point Q. The process of the control target calculation module 151 has been described above.

[0079] The controller 15 detects the second parameter (rotation angle θ J , position P A ) Arm height H A The control system 150 performs feedforward control so that the output voltage Vc decreases monotonically like L2 in FIG. v1 In the feedforward control, when an instruction to start the automatic implement return control is received from the input device 17, the controller 15 receives the second parameter (the rotation angle θ J , the position P of the second hydraulic cylinder 48 A ) as the second reference value (REF_θ J, REF_P A The hydraulic circuit 100 (second hydraulic cylinder 48) is controlled so as to achieve the feedforward control of the second hydraulic cylinder 48. Details of the feedforward control of the second hydraulic cylinder 48 will be described later. <Map Generation>

[0080] When the second hydraulic cylinder 48 is controlled in this manner, the arm height H A H A (t), the corresponding implement inclination angle θ I The controller 15 controls the first hydraulic cylinder 49 so that the arm position approaches the target position (t). Specifically, the controller 15 controls the first hydraulic cylinder 49 based on the second parameter (the rotation angle θ J , the position P of the second hydraulic cylinder 48 A ) based on the third or fourth correspondence relationship, the arm height H A The controller 15 calculates the arm height H A The controller 15 calculates the implement tilt angle θ corresponding to the obtained timing t from the map M1. I (t) is obtained from the map M1. As shown in FIG. 9, in the map M1, the arm height H A The first parameter corresponding to point R where the target height TAR_H is the first reference value REF_θ I +θ A (TAR_H). Therefore, the controller 15 determines the arm height H A When the height changes to the target height TAR_H, the first parameter, the implement inclination angle θ I The first reference value REF_θ I +θ A The hydraulic circuit 100 (first hydraulic cylinder 49) is controlled so that the pressure difference (TAR_H) is set to (TAR_H). In this way, the map M1 represents the control target. The control of the first hydraulic cylinder 49 is performed by feedforward control and feedback control when a predetermined condition is satisfied. For this reason, the control system 150 includes a feedforward controller Cf v1and a feedback converter 152 and a feedback controller Cb v1 The control of the first hydraulic cylinder 49 will be described in detail later. In FIG. 9, the position P of the second hydraulic cylinder 48 corresponding to the target height TAR_H is A The second target position TAR_P A The second target position TAR_P is shown as A is used in feedforward processing, which will be discussed later.

[0081] And the first parameter is the implement inclination angle θ I is the first reference value REF_θ I +θ A When the position of the second hydraulic cylinder 48 becomes (TAR_H), A is the second reference position REF_P A During the period until the position P of the first hydraulic cylinder 49 changes to I The hydraulic circuit 100 is controlled so as not to change the position P of the first hydraulic cylinder 49. I As a result of controlling the first hydraulic cylinder 49 so that the implement inclination angle θ I The controller 15 changes the implement inclination angle θ I However, the first hydraulic cylinder 49 is not controlled so as to move along the dotted line L3.

[0082] FIG. 11 shows the arm height H in automatic implement return control when the implement attitude detection sensor 57 is composed of a potentiometer 57r. A and the rotation angle θ of joint 43 R FIG. 11 is a graph showing the relationship between the change in the implement inclination angle θ and the control parameter θ. I from rotation angle θ R Therefore, the control method of FIG. 11 does not necessarily have to be the same as the control method of FIG. 9 in that the posture of the implement 41 is changed to the arm height H A However, the arm height H A9 in that the parameter REF_D is changed to correspond to the reference orientation REF_D when the target height TAR_H is reached. Note that the control of the second hydraulic cylinder 48 in this case is the same as the control shown in the explanation of FIG.

[0083] In this control, when the target height TAR_H is determined, the controller 15 determines the arm height H A The reference rotation angle REF_θ of joint 43 when the target height TAR_H is reached R Determine REF_θ R is the rotation angle θ of the joint 43 corresponding to the reference orientation REF_D. R That is, REF_θ R is the first reference value of the first parameter corresponding to the target height TAR_H. In other words, the controller 15 calculates the first reference value REF_θ of the first parameter corresponding to the target height TAR_H. R Determine REF_θ R is input to the control target calculation module 151.

[0084] The controller 15 performs the following process when executing the control target calculation module 151. When the automatic implement return control is started, the controller 15 calculates the rotation angle θ of the joint 43 corresponding to the initial orientation STA_D obtained from the implement attitude detection sensor 57 at that time. R STA_θ R is obtained from the output of the implement attitude detection sensor 57. R is the position P of the first hydraulic cylinder 49 at the time when the input device 17 receives an instruction to start the automatic implement return control. I The first initial position STA_P I The controller 15 controls the rotation angle θ R is STA_θ R From REF_θ R L1 is expressed as changing linearly from the initial height STA_H at the start of the automatic implement return control to the reference height REF_H. AA map M2 is generated that includes L2, which is expressed so that L changes linearly. The horizontal axis of the map M2 is the timing t, and the arm height H A corresponds to the vertical coordinate of the right side of point P on L2, and the rotation angle θ of joint 43 at time t R corresponds to the coordinate on the vertical axis on L1 to the left of point Q. The process of the control target calculation module 151 has been described above.

[0085] In Fig. 11, the arm height H A H A (t), the corresponding rotation angle θ R The controller 15 controls the first hydraulic cylinder 49 so that the arm position approaches the target position (t). Specifically, the controller 15 controls the first hydraulic cylinder 49 based on the parameter detected by the arm position detection sensor 56 (the rotation angle θ J , the position P of the second hydraulic cylinder 48 A ) based on the third or fourth correspondence relationship, the arm height H A The controller 15 calculates the arm height H A The controller 15 calculates the rotation angle θ corresponding to the calculated timing t from the map M2. R (t) is obtained from map M2. As shown in FIG. 11, in map M2, the arm height H A Since L1 is determined to pass through point R where the arm height H is the target height TAR_H, the controller 15 A When the height TAR changes to the target height TAR_H, the first parameter, the rotation angle θ R The first reference value REF_θ R In other words, the map M2 is the target of the control. The control of the first hydraulic cylinder 49 is performed in the same manner as in the case of FIG. 9, in which the feedforward control and the feedback control are performed when a predetermined condition is satisfied. v2 The feedforward control is performed by the feedback converter 152 and the feedback controller Cb v2The control of the first hydraulic cylinder 49 will be described in detail later.

[0086] And the rotation angle θ of the joint 43 R is REF_θ R In other words, the position P of the first hydraulic cylinder 49 I is the first reference position REF_P I Then, the position P of the second hydraulic cylinder 48 A The controller 15 controls the position P of the first hydraulic cylinder 49 until the position P of the first hydraulic cylinder 49 changes to the second reference position REF_PA. I The hydraulic circuit 100 is controlled so that the position P of the first hydraulic cylinder 49 does not change. I As a result of controlling the first hydraulic cylinder 49 so that the rotation angle θ of the joint 43 does not change, R The controller 15 changes the rotation angle θ R Alternatively, the first hydraulic cylinder 49 may be controlled so that the rotational axis of the first hydraulic cylinder 49 moves along the straight line L3.

[0087] FIG. 12 shows the arm height H in automatic implement return control when the implement posture detection sensor 57 is composed of a linear sensor 57p. A and the position P of the first hydraulic cylinder 49 I FIG. 12 is a diagram showing the relationship between the change in the implement inclination angle θ and the control parameter θ. I , the rotation angle θ of the joint 43 R to the position P of the first hydraulic cylinder 49 I Therefore, the control method of FIG. 12 does not necessarily have to be the same as the control methods of FIG. 9 and FIG. 11 in that the posture of the implement 41 is changed to the arm height H A However, the arm height H A 9 and 11 in that the parameter REF_D is changed to correspond to the reference orientation REF_D when the target height TAR_H is reached. Note that the control of the second hydraulic cylinder 48 in this case is the same as the control shown in the explanation of FIG.

[0088] In this control, when the target height TAR_H is determined, the controller 15 determines the arm height H A The position REF_P of the first hydraulic cylinder 49 when the target height TAR_H is reached I Determine REF_P I is the position P of the first hydraulic cylinder 49 corresponding to the reference direction REF_D. A The first reference position is REF_P I is the first reference value of the first parameter corresponding to the target height TAR_H. In other words, the controller 15 determines the first reference value REF_P of the first parameter corresponding to the target height TAR_H. I Determine REF_P I is input to the control target calculation module 151.

[0089] The controller 15 performs the following process when executing the control target calculation module 151. When the automatic implement return control is started, the controller 15 calculates the first initial position STA_P obtained from the implement attitude detection sensor 57 at that time. I is obtained from the output of the implement attitude detection sensor 57. The controller 15 determines the position P of the first hydraulic cylinder 49. A STA_P I From REF_P I L1 is expressed as changing linearly from the initial height STA_H at the start of the automatic implement return control to the reference height REF_H. A A map M3 is generated that includes L2 and L3, which are expressed so that L changes linearly. The horizontal axis of the map M3 is the timing t, and the arm height H A corresponds to the coordinate of the vertical axis on the right side of point P on L2, and the position P of the first hydraulic cylinder 49 at the timing t A corresponds to the coordinate on the vertical axis on L1 to the left of point Q. The process of the control target calculation module 151 has been described above.

[0090] In FIG. 12, arm height H at time t A H A(t), the position P of the first hydraulic cylinder 49, which corresponds to the position P of the first hydraulic cylinder 49 shown in FIG. I The controller 15 controls the first hydraulic cylinder 49 so that the arm position approaches the target position (t). Specifically, the controller 15 controls the first hydraulic cylinder 49 based on the parameter detected by the arm position detection sensor 56 (the rotation angle θ J , the position P of the second hydraulic cylinder 48 A ) based on the third or fourth correspondence relationship, the arm height H A The controller 15 calculates the arm height H A The controller 15 calculates the position P of the first hydraulic cylinder 49 corresponding to the calculated timing t from the map M3. I (t) is obtained from map M3. As shown in FIG. 12, in map M3, the arm height H A Since L1 is determined to pass through point R where the arm height H is the target height TAR_H, the controller 15 A When the height TAR changes to the target height TAR_H, the position P of the first hydraulic cylinder 49, which is the first parameter, I The first reference position REF_P I The hydraulic circuit 100 is controlled so that the map M3 is set as the target of control. As in the case of FIG. 11, the first hydraulic cylinder 49 is controlled by feedforward control and feedback control when a predetermined condition is satisfied. v2 The feedforward control is performed by the feedback converter 152 and the feedback controller Cb v2 The control of the first hydraulic cylinder 49 will be described in detail later.

[0091] Position P of the first hydraulic cylinder 49 I is the first reference position REF_P I Then, the position P of the second hydraulic cylinder 48 A is the second reference position REF_P A During the period until the position P of the first hydraulic cylinder 49 changes to IThe hydraulic circuit 100 is controlled so that the position P of the first hydraulic cylinder 49 does not change. I 4 shows the result of controlling the first hydraulic cylinder 49 so that the

[0092] 1st reference position REF_P I , second reference position REF_P A , target height TAR_H, and second target position TAR_P A is determined as follows. The work vehicle 1 is further provided with an additional input device 13 that receives a registration instruction for registering the reference orientation REF_D and the reference height REF_H. In the case where the arm posture detection sensor 56 is composed of a potentiometer 56r, when a registration instruction is received by the additional input device 13, the controller 15 determines the rotation angle θ of the fulcrum shaft 59P (joint) at the time when the registration instruction is received based on the second correspondence relationship. J to the position P of the second hydraulic cylinder 48 A The controller 15 calculates the position P A , the second reference position REF_P A The controller 15 determines the rotation angle θ of the fulcrum shaft 59P (joint) at the time when the registration instruction is accepted based on the third correspondence relationship. J The controller 15 calculates the reference height REF_H by adding an offset value H off The controller 15 calculates the second target position TAR_P from the target height TAR_H based on the fourth correspondence relationship. A The second target position TAR_P obtained in this way is A is stored in memory 15M.

[0093] In the case where the arm posture detection sensor 56 is composed of a linear sensor 56p, when a registration instruction is received by the additional input device 13, the controller 15 detects the position P of the second hydraulic cylinder 48 detected by the linear sensor 56p at the time when the registration instruction is received. A The controller 15 calculates the position P A , the second reference position REF_P AThe controller 15 determines the second reference position REF_P based on the fourth correspondence relationship. A The controller 15 calculates the reference height REF_H by adding an offset value H off The controller 15 calculates the second target position TAR_P from the target height TAR_H based on the fourth correspondence relationship. A The second target position TAR_P obtained in this way is A is stored in memory 15M.

[0094] In the case where the implement attitude detection sensor 57 is composed of a first inertial measurement unit 57a and a second inertial measurement unit 57b, when a registration instruction is received by the additional input device 13, the controller 15 calculates the implement inclination angle θ at the time when the registration instruction is received from the output of the first inertial measurement unit 57a and the output of the second inertial measurement unit 57b at the time when the registration instruction is received. I The reference angle REF_θ I Calculate the reference angle REF_θ I The controller 15 stores the second reference position REF_P in the memory 15M based on the fourth correspondence relationship. A The controller calculates the reference height REF_H from the fifth correspondence relationship, and calculates the adjustment angle θA(REF_H) from the reference height REF_H based on the fifth correspondence relationship. I +θA(REF_H) to 1st reference position REF_P I Request.

[0095] In the case where the implement attitude detection sensor 57 is composed of a potentiometer 57r, when a registration instruction is received by the additional input device 13, the controller 15 calculates the rotation angle θ of the joint 43 at the time when the registration instruction is received from the output of the potentiometer 57r at the time when the registration instruction is received. R The reference rotation angle REF_θ is R Calculate the reference rotation angle REF_θ R The controller 15 stores the reference rotation angle REF_θ Rto the first reference position REF_P I In the case where the implement attitude detection sensor 57 is composed of a linear sensor 57p, when a registration instruction is received by the additional input device 13, the controller 15 calculates the first reference position REF_P from the output of the linear sensor 57p at the time when the registration instruction is received. I Request. <Feedforward control>

[0096] Next, the feedforward control of the first hydraulic cylinder 49 and the feedforward control of the second hydraulic cylinder 48 will be described. In the above-mentioned hydraulic circuit 100, the first pressure compensating valve 77 and the second pressure compensating valve 76 make the pressure difference between the input and output of the first control valve 25 equal to the pressure difference between the input and output of the second control valve 20. Therefore, the ratio between the flow rate of the hydraulic oil per unit time through the first control valve 25 and the flow rate of the hydraulic oil per unit time through the second control valve 20 can be adjusted by the ratio between the first opening area AS1 set in the first control valve 25 and the second opening area AS2 set in the second control valve 20. By utilizing this, the start timing T STA and arm height H A The timing T TAR Then, the feedforward control described below is performed.

[0097] First, when an instruction to start the automatic implement return control is received by the input device 17, the controller 15 executing the control target calculation module 151 calculates the position P of the first hydraulic cylinder 49 at the time when the instruction is received. I The first initial position STA_P I and the position P of the second hydraulic cylinder 48 at the time the instruction is received. A The second initial position STA_P A The controller 15 determines the first reference position REF_P I , second reference position REF_P A , and the second target position TAR_P AThe controller 15 acquires the first initial position STA_P from the memory 15M. I and the first reference position REF_P I Therefore, the position P of the first hydraulic cylinder 49 I the first reference position REF_P I In order to achieve this, the controller 15 calculates a first volume V1 of the hydraulic oil to be supplied from the hydraulic pump 11 to the first hydraulic cylinder 49. A and the second target position TAR_P A Therefore, the position P of the second hydraulic cylinder 48 A The second target position TAR_P A In order to achieve this, a second volume V2 of the hydraulic oil supplied from the hydraulic pump 11 to the second hydraulic cylinder 48 is calculated.

[0098] Next, when the input device 17 receives an instruction to start the automatic implement return control, the controller 15 obtains the maximum allowable value SEM of the sum of the first opening area AS1 and the second opening area AS2 from the rotation speed of the engine 6 at the time when the instruction is received. Specifically, the memory 15M stores a table showing the correspondence between the rotation speed of the engine 6 and the maximum allowable value SEM, and the hardware processor 15P acquires the rotation speed of the engine 6 detected by the rotation speed detection sensor 6a and obtains the maximum allowable value SEM by referring to the table from the rotation speed. The controller 15 obtains a limit value SAM which is the sum of the maximum value SMA1 of the first opening area AS1 when the first control valve 25 is switched to the first hydraulic cylinder contraction control position BSP and the maximum value SMA2 of the second opening area AS2 when the second control valve 20 is switched to the second hydraulic cylinder contraction control position ASP. The controller 15 obtains a reference value SFF which is smaller between the maximum allowable value SEM and the limit value SAM. The limit value SAM is known from the specifications of the first control valve 25 and the second control valve 20, and is stored in advance in the memory 15M.

[0099] The controller 15 calculates a reference area SB1 that serves as a reference for the first opening area AS1 based on the following (Equation 1). SB1=SFF×V1 / (V1+V2)...(Formula 1) That is, the reference area SB1 is (the first volume V1 / (the first volume V1+the second volume V2)) times the reference value SFF. I is the first initial position STA_P I to the first reference position REF_P I Until this occurs, the first opening area AS1 of the first control valve 25 is controlled based on the reference area SB1.

[0100] The controller 15 further performs the following process. When the corrected area SB2 obtained by multiplying the reference area SB1 by the first correction coefficient K1 associated with the rotation speed of the engine 6 is equal to or smaller than the maximum value SMA1 of the first opening area AS1, the controller 15 sets the corrected area SB2 as the first target area TS1. Figure 13 is a diagram showing the relationship between the rotation speed of the engine 6 and the first correction coefficient K1. This is because the arm 45 moves in a direction perpendicular to the arm height H due to the influence of gravity. A On the other hand, the implement 41 must raise the implement tip 41T against gravity. Therefore, when the rotation speed of the engine 6 is low, that is, when the discharge amount from the hydraulic pump 11 is small, the arm height H A This is to remove the influence of the fluctuation amount of the implement direction 41D relative to the fluctuation amount of the implement direction 41D, which becomes smaller with respect to the control target. Fig. 13 is a graph showing a first correction coefficient K1 empirically determined to remove the influence. E 0 is the high idle speed of the engine 6. When the corrected area SB2 is larger than the maximum value SMA1 of the first opening area AS1, the controller 15 sets the maximum value SMA1 as the first target area TS1. The controller 15 sets the second opening area AS2 of the second control valve 20 to a value obtained by subtracting the first target area TS1 from the reference value SFF and multiplying the result by SMA1 / SB2 as the second target area TS2. The first target area TS1 is calculated by the feedforward controller Cf v1 The second target area TS2 is input to the feedforward controller Cf v2 is entered into

[0101] The controller 15 determines the position P of the first hydraulic cylinder 49.I is the first initial position STA_P I to the first reference position REF_P I Until the first control valve 25 reaches the first target area TS1, the controller 15 performs feedforward control so that the first opening area AS1 of the first control valve 25 becomes the first target area TS1. v1 In executing this, a feedforward control amount (FF control amount) u1o of the first pilot control valve 65 and a FF control amount u2o of the second pilot control valve 66 are determined so that the first opening area AS1 of the first control valve 25 becomes the first target area TS1, and the FF control amount u1o is output to the solenoid 65s of the first pilot control valve 65, and the FF control amount u2o is output to the solenoid 66s of the second pilot control valve 66.

[0102] The controller 15 determines the position P of the first hydraulic cylinder 49. I is the first initial position STA_P I to the first reference position REF_P I Until the second control valve 20 reaches the reference value SFF, the second opening area AS2 of the second control valve 20 is controlled by the feedforward control so as to be equal to the area obtained by subtracting the first target area TS1 from the reference value SFF. v2 In executing this, the control quantity u3 of the third pilot control valve 60 and the control quantity u4 of the fourth pilot control valve 61 are determined so that the second opening area AS2 of the second control valve 20 becomes the second target area TS2, and the control quantity u3 is output to the solenoid 60s of the third pilot control valve 60, and the control quantity u4 is output to the solenoid 61s of the fourth pilot control valve 61.

[0103] When the correction area SB2 becomes equal to or smaller than the maximum value SMA1 of the first opening area AS1 and the above-mentioned feedforward control is performed, the controller 15 adjusts the position P of the first hydraulic cylinder 49. I is the first initial position STA_P I to the first reference position REF_P I The position P of the first hydraulic cylinder 49 per unit time I The absolute value of the change in the position P of the second hydraulic cylinder 48 per unit time AThe absolute value of the change in the first reference position REF_P I and the first initial position STA_P I Absolute value of difference with the second target position TAR_P A and the second initial position STA_P A The hydraulic circuit 100 is controlled so that the hydraulic pressure Vp is increased by a factor of (the absolute value of the difference between the hydraulic pressure Vp and the ... <Feedback control>

[0104] Next, feedback control will be described. Referring to Fig. 9, Fig. 11, and Fig. 12, the controller 15 that executes the feedback converter 152 receives the arm height H A Calculate the arm height H A The first parameter (implement inclination angle θ I , the rotation angle θ of the joint 43 R , or the position P of the first hydraulic cylinder 49 I ) target value (θ I (t), θ R (t) or P I Specifically, the controller 15 calculates the rotation angle θ of the fulcrum shaft 59P detected by the arm posture detection sensor 56. J Or the position P of the second hydraulic cylinder 48 A From arm height H A Then, refer to maps M1 to M3 to find the arm height H A θ I (t), θ R (t) or P I (t) is obtained as the target value of the first parameter corresponding to the implement orientation 41D.

[0105] The controller 15 then detects the first parameter (θ I * , θ R * , or P I * In the following embodiments, P I* is also referred to as the detected position of the first hydraulic cylinder 49. v1 The controller 15 executes the above-mentioned process by calculating the detected value and the first reference value REF_P I When the absolute value of the difference between the target value and the first reference value is greater than the absolute value of the difference between the target value and the first reference value by at least a first threshold value, feedback control is performed with the first opening area AS1 of the first control valve 25 as the control target so as to bring the detected value closer to the target value.

[0106] In FIG. 9, the detected value θ I * and the first reference value REF_θ I +θ A The absolute value of the difference with (TAR_H) is the target value θ I (t) and the first reference value REF_θ I +θ A The absolute value of the difference with (TAR_H) is the first threshold D1_θ I The range in which the feedback control range FBR1 is larger than θ I (t)―D1_θ I The range is less than D1_θ I It is preferable that the detected value θ is invariant regardless of the timing t. When the implement attitude detection sensor 57 is composed of the first inertial measurement unit 57a and the second inertial measurement unit 57b, I * When the feedback control range FBR1 is satisfied, the feedback control is performed. Specifically, as shown in FIG. v1 The controller 15 executes the I * From θ I The feedback control amount (FB control amount) u1 of the first pilot control valve 65 is calculated according to the difference e obtained by subtracting (t). * The FB control amount u2 of the second pilot control valve 66 is calculated. * The controller 15 calculates the FF control amount u1o and the FB control amount u1 *The controller 15 outputs the control amount u1 obtained by adding the FF control amount u2o to the FB control amount u2. * The control amount u2 obtained by adding the above is output to the solenoid 66s of the second pilot control valve 66. I * When the feedback control range FBR1 does not apply, the feedback controller cb v1 The controller 15 executes the FB control amount u1 * , u2 * Let be 0.

[0107] In FIG. 11, the detected value θ R * and the first reference value REF_θ R The absolute value of the difference between R (t) and the first reference value REF_θ R The absolute value of the difference between the first threshold D1_θ I The range in which the feedback control range FBR2 is larger than θ R (t)―D1_θ R The range is less than D1_θ R It is preferable that the detected value θ is invariant regardless of the timing t. R * When the feedback control range FBR2 is satisfied, the feedback control is performed. Specifically, as shown in FIG. v1 The controller 15 executes the R * From θ I The FB control amount u1 of the first pilot control valve 65 is calculated according to the difference e obtained by subtracting (t). * The FB control amount u2 of the second pilot control valve 66 is calculated. * The controller 15 calculates the FF control amount u1o and the FB control amount u1 * The controller 15 outputs the control amount u1 obtained by adding the FF control amount u2o to the FB control amount u2. *The control amount u2 obtained by adding the above is output to the solenoid 66s of the second pilot control valve 66. R * When the feedback control range FBR2 does not apply, the feedback controller cb v1 The controller 15 executes the FB control amount u1 * , u2 * Let be 0.

[0108] In FIG. 12, the detected value P I * and the first reference value REF_P I The absolute difference between the target value P I (t) and the first reference value REF_P I The absolute value of the difference between I The range in which the feedback control range FBR3 is larger than or equal to P I (t)+D1_P I It is a larger range. D1_P I It is preferable that the detected value P is invariant regardless of the timing t. When the implement posture detection sensor 57 is composed of a linear sensor 57p, I * When the feedback control range FBR3 is satisfied, the feedback control is performed. Specifically, as shown in FIG. v1 The controller 15 that executes I * From P I The FB control amount u1 of the first pilot control valve 65 is calculated according to the difference e obtained by subtracting (t). * The FB control amount u2 of the second pilot control valve 66 is calculated. * The controller 15 calculates the FF control amount u1o and the FB control amount u1 * The controller 15 outputs the control amount u1 obtained by adding the FF control amount u2o to the FB control amount u2. * The control amount u2 obtained by adding the above is output to the solenoid 66s of the second pilot control valve 66. I *When the feedback control range FBR3 does not apply, the feedback controller cb v1 The controller 15 executes the FB control amount u1 * , u2 * Let be 0.

[0109] As described above, by performing feedback control in addition to the feedforward control, the controller 15 can control the position P I is the first initial position STA_P I to the first reference position REF_P I The position P of the first hydraulic cylinder 49 per unit time I The absolute value of the change in the position P of the second hydraulic cylinder 48 per unit time A The absolute value of the change in the first reference position REF_P I and the first initial position STA_P I Absolute value of difference with the second target position TAR_P A and the second initial position STA_P A The hydraulic circuit 100 is controlled so that the hydraulic pressure Vp is increased by a factor of (the absolute value of the difference between the hydraulic pressure Vp and the ...

[0110] After starting feedback control, when the absolute value of the difference between the detected value and the first reference value becomes smaller than the sum of the absolute value of the difference between the target value and the first reference value and a second threshold value smaller than the first threshold value, the controller 15 performs feedforward control such that the first opening area AS1 of the first control valve 25 is equal to the first target area TS1 by dividing the control amount (the larger of u1 and u2) of the first control valve 25 performed in the feedback control immediately before the absolute value of the difference between the target value and the first reference value by the second threshold value, and sets the second correction coefficient K2 to the value obtained by multiplying the first opening area AS1 of the first control valve 25 by the second correction coefficient K2.

[0111] In FIG. 9, after Δt has elapsed from time t, the detected value θ I * and the first reference value REF_θ I +θ A The absolute value of the difference with (TAR_H) is the target value θI (t) and the first reference value REF_θ I +θ A The absolute value of the difference with (TAR_H) is set to the second threshold D2_θ I The feedback end range FER1 is the range where the feedback is smaller than the sum of θ I (t)―D2_θ I The above range. D2_θ I is D1_θ I When the implement attitude detection sensor 57 is composed of the first inertial measurement unit 57a and the second inertial measurement unit 57b, the detected value θ I * falls within the feedback end range FER1, the controller 15 acquires the control amounts u1 and u2 immediately before the feedback control is terminated. The controller 15 uses the larger of the control amounts u1 and u2, umax, to calculate the second correction coefficient K2. Furthermore, the controller 15 acquires the control amounts u1o and u2o of the first control valve 25 when feedforward control is performed so that the first opening area AS1 becomes the first target area TS1. The controller 15 uses the larger of u1o and u2o, umaxo, to calculate the second correction coefficient K2. The controller 15 sets umax / umaxo as the second correction coefficient K2. Note that, due to the nature of this control, when umax is u1, umaxo becomes u1o, and when umax is u2, umaxo becomes u2o.

[0112] In FIG. 11, after Δt has elapsed from time t, the detected value θ R * and the first reference value REF_θ R The absolute value of the difference between R (t) and the first reference value REF_θ R The absolute value of the difference between I The feedback end range FER2 is the range where the feedback is smaller than the value obtained by adding θ R (t)―D2_θ R The above range. D2_θ R is D1_θ RWhen the implement attitude detection sensor 57 is composed of a potentiometer 57r, the detected value θ R * falls within the feedback end range FER2, the controller 15 acquires the control amounts u1 and u2 immediately before the feedback control is terminated. The controller 15 uses the larger of the control amounts u1 and u2, umax, to calculate the second correction coefficient K2. Furthermore, the controller 15 acquires the control amounts u1o and u2o of the first control valve 25 when feedforward control is performed so that the first opening area AS1 becomes the first target area TS1. The controller 15 uses the larger of u1o and u2o, umaxo, to calculate the second correction coefficient K2. The controller 15 sets umax / umaxo as the second correction coefficient K2. Due to the nature of this control, when umax is u1, umaxo becomes u1o, and when umax is u2, umaxo becomes u2o.

[0113] In FIG. 12, after Δt has elapsed from time t, the detected value P I * and the first reference value REF_P I The absolute difference between the target value P I (t) and the first reference value REF_P I The absolute value of the difference between I The feedback end range FER3 is the range where the feedback is smaller than the value obtained by adding P I (t)+D2_P I The range is as follows: D2_P I D1_P I When the implement posture detection sensor 57 is composed of a linear sensor 57p, the detection value P I *falls within the feedback end range FER3, the controller 15 acquires the control amounts u1 and u2 immediately before the feedback control is terminated. The controller 15 uses the larger of the control amounts u1 and u2, umax, to calculate the second correction coefficient K2. Furthermore, the controller 15 acquires the control amounts u1o and u2o of the first control valve 25 when feedforward control is performed so that the first opening area AS1 becomes the first target area TS1. The controller 15 uses the larger of u1o and u2o, umaxo, to calculate the second correction coefficient K2. The controller 15 sets umax / umaxo as the second correction coefficient K2. Due to the nature of this control, when umax is u1, umaxo becomes u1o, and when umax is u2, umaxo becomes u2o. <Cushion control>

[0114] In the above-mentioned control method, the first hydraulic cylinder 49 is controlled so that the implement orientation 41D becomes the reference orientation REF_D as quickly as possible. Therefore, if the movement of the implement 41 is suddenly stopped when the implement orientation 41D becomes the reference orientation REF_D, the implement 41 will vibrate greatly. Similarly, in the above-mentioned control method, the arm height H A In order to control the second hydraulic cylinder 48 so that the arm height H reaches the reference height REF_H as quickly as possible, A If the movement of the arm 45 is suddenly stopped when the arm height H reaches the reference height REF_H, the arm 45 will vibrate greatly. Such large vibrations put a large load on hydraulic equipment such as the first hydraulic cylinder 49 and the second hydraulic cylinder 48, and are therefore undesirable in terms of durability. Therefore, when the implement orientation 41D approaches the reference orientation REF_D, the position change amount (displacement) of the first hydraulic cylinder 49 per unit time is reduced to reduce the arm height H A When the arm height H approaches the reference height REF_H, the position change amount (displacement) of the second hydraulic cylinder 48 per unit time is reduced. As a result, even if the movement of the implement 41 is stopped when the implement orientation 41D becomes the reference orientation REF_D, the vibration of the implement 41 is suppressed, and the arm height H AEven if the movement of the arm 45 is stopped when the arm height reaches the reference height REF_H, the vibration of the arm 45 is suppressed. This type of control is called cushion control.

[0115] 14 is a diagram showing the concept of cushion control of the first hydraulic cylinder 49. The upper part of FIG. 14 shows the position P I The lower part of FIG. 14 shows the change (displacement) per unit time of the position P I In order to realize the cushion control, the memory 15M stores the position P of the first hydraulic cylinder 49. I is the first reference position REF_P I The position P of the first hydraulic cylinder 49 per unit time immediately before I The change in the first approach speed V APP1 and the displacement velocity V of the first hydraulic cylinder 49. EST1 First approach speed V APP1 First deceleration rate D V1 and remember.

[0116] The controller 15 detects the detected position P of the first hydraulic cylinder 49 detected by the implement attitude detection sensor 57. I * When the implement posture detection sensor 57 includes the first inertial measurement unit 57a and the second inertial measurement unit 57b, the rotation angle θ detected by the arm posture detection sensor 56 (potentiometer 56r) is calculated as follows: J * From arm height H A The estimated value of H A * or the detected position P detected by the arm position detection sensor 56 (linear sensor 56p) A * From arm height H A The estimated value of H A * The controller 15 calculates the detected value θ I * and adjustment angle θ A (H A *) based on the first correspondence relationship, I * When the implement attitude detection sensor 57 is a potentiometer 57r, the detected value θ R * Based on the sixth correspondence relationship, the detected position P I * The controller 15 calculates the detection position P I * The detected position P of the first hydraulic cylinder 49 per unit time is calculated from the time change of I * The displacement velocity V of the first hydraulic cylinder 49 is the change in EST1 The controller 15 calculates the adjustment angle θ A (H A * ) is the arm height H A The estimated value of H A * The detected value θ I * The displacement velocity V of the first hydraulic cylinder 49 is determined based only on EST1 You may ask for:

[0117] The controller 15 controls the displacement speed V of the first hydraulic cylinder 49. EST1 and first approach speed V APP1 The difference between this and the first deceleration D V1 The first deceleration time T is calculated by dividing RED1 The controller 15 calculates the displacement velocity V of the first hydraulic cylinder 49. EST1 and the first deceleration time T RED1 and the first reference position REF_P I Based on this, the displacement velocity V of the first hydraulic cylinder 49 is calculated. EST1 Deceleration start position SR_P of the first hydraulic cylinder 49 at which deceleration starts I Specifically, the controller 15 calculates the first reference position REF_P I The displacement velocity V of the first hydraulic cylinder 49 EST1 The first deceleration time T RED1 The value multiplied by this is the deceleration start position SR_P I Let us assume that.

[0118] When the implement attitude detection sensor 57 is the potentiometer 57r, the controller 15 refers to the sixth correspondence relationship to determine the deceleration start position SR_P I The corresponding rotation angle θ R When the first hydraulic cylinder 49 reaches the detection position P I * is the deceleration start position SR_P I When the implement attitude detection sensor 57 includes the first inertial measurement unit 57a and the second inertial measurement unit 57b, the controller 15 determines that the deceleration start position SR_P I (Implement inclination angle θ I +adjustment angle θ A (H A ) is calculated using the detection result of the arm position detection sensor 56, and the calculated implement inclination angle θ I +adjustment angle θ A (H A ), the first hydraulic cylinder 49 reaches the detection position P I * is the deceleration start position SR_P I is determined to have been reached.

[0119] The controller 15 detects the detected position P of the first hydraulic cylinder 49. I * is the deceleration start position SR_P of the first hydraulic cylinder 49. I After reaching (timing T SR1 ), the displacement velocity V of the first hydraulic cylinder 49 EST1 is the first approach speed V APP1 The displacement velocity V of the first hydraulic cylinder 49 EST1 First deceleration D V1 Specifically, the controller 15 controls the first opening area AS1 of the first control valve 25 so as to decelerate based on the timing T SR1 to the first deceleration time T RED1 After that, the first opening area AS1 is V for the first target area TS1 (or K1 × TS1) during feedforward control. APP1 / V EST1 The feedforward controller C fv1The control amounts u1o and u2o of the cushion control are linearly decreased. Note that, during the cushion control, feedback control is not performed.

[0120] As a result, the arm height H set in maps M1 to M3 A The timing T TAR A little later than T FIN1 At the position P of the first hydraulic cylinder 49 I is the first reference position REF_P I When the implement attitude detection sensor 57 is a potentiometer 57r or a linear sensor 57p, the position P of the first hydraulic cylinder 49 is reached even with this time delay. I the first reference position REF_P I However, when the implement attitude detection sensor 57 includes the first inertial measurement unit 57a and the second inertial measurement unit 57b, the timing T FIN1 Arm height H at A The problem is that the implement tilt angle θ obtained from the first inertial measurement unit 57a and the second inertial measurement unit 57b is a height (TAR_H-ΔH) that is slightly lower than the target height TAR_H. I Ideally, REF_θ I +θ A It should be controlled so that it is (TAR_H-ΔH), but since it is difficult to calculate ΔH, the first reference value REF_θ I +θ A (TAR_H). Therefore, the deviation of the adjustment angle θ A (TAR_H)-θ A The implement tip 41T is controlled to face upward by (TAR_H-ΔH) as the target. Therefore, the arm height H A When the reference height REF_H is reached, the position P of the first hydraulic cylinder 49 I are individually controlled and modified.

[0121] 15 is a diagram showing the concept of cushion control of the second hydraulic cylinder 48. The upper part of FIG. 15 shows the position P AThe lower part of FIG. 15 shows the amount of change (displacement) per unit time of the position P of the second hydraulic cylinder 48. A In order to realize the cushion control, the memory 15M stores the position P of the second hydraulic cylinder 48. A is the second reference position REF_P A The position P of the second hydraulic cylinder 48 per unit time immediately before A The change in the second approach speed V APP2 and the displacement velocity V of the second hydraulic cylinder 48. EST2 to second approach speed V APP2 The second deceleration rate D V2 and remember.

[0122] The controller 15 detects the detected position P of the second hydraulic cylinder 48 detected by the arm position detection sensor 56. A * When the arm position detection sensor 56 is a potentiometer 56r, the rotation angle θ detected by the potentiometer 56r is calculated. J * , referring to the second correspondence relationship, the detected position P A * When the arm position detection sensor 56 is a linear sensor 56p, the detected value detected by the linear sensor 56p is calculated as the detected position P A * The controller 15 detects the position P A * The detected position P of the second hydraulic cylinder 48 per unit time is calculated from the time change of A * The displacement velocity V of the second hydraulic cylinder 48 is the change in EST2 Request.

[0123] The controller 15 controls the displacement speed V of the second hydraulic cylinder 48. EST2 and the second approach speed V APP2 The difference between this and the second deceleration D V2 The second deceleration time T is calculated by dividing RED2 The controller 15 calculates the displacement velocity V of the second hydraulic cylinder 48. EST2 and the second deceleration time T RED2and the second reference position REF_P A Based on this, the displacement velocity V of the second hydraulic cylinder 48 is calculated. EST2 The deceleration start position SR_P of the second hydraulic cylinder 48 at which deceleration starts A Specifically, the controller 15 calculates the second reference position REF_P A The displacement velocity V of the second hydraulic cylinder 48 EST2 The second deceleration time T RED2 The value multiplied by this is the deceleration start position SR_P A Let us assume that.

[0124] When the arm posture detection sensor 56 is the potentiometer 56r, the controller 15 refers to the second correspondence relationship to determine the deceleration start position SR_P A The corresponding rotation angle θ J When the second hydraulic cylinder 48 reaches the detection position P A * is the deceleration start position SR_P A When the arm posture detection sensor 56 is a linear sensor 56p, the controller 15 determines that the arm posture detection sensor 56 has reached the detected position P A * is the deceleration start position SR_P A It is determined whether or not the value has been reached.

[0125] The controller 15 detects the detected position P of the second hydraulic cylinder 48. A * is the deceleration start position SR_P A After reaching (timing T SR2 ), the displacement velocity V of the second hydraulic cylinder 48 EST2 is the second approach speed V APP2 The displacement velocity V of the second hydraulic cylinder 48 is EST2 The second deceleration D V2 Specifically, the controller 15 controls the second opening area AS2 of the second control valve 20 so as to decelerate based on the timing T SR2 to the second deceleration time T RED2 After that, the second opening area AS2 is V for the second target area TS2 during feedforward control. APP2 / V EST2The feedforward controller C fv2 As a result, the arm height H A The timing T REF A little later than T FIN2 At this time, the second hydraulic cylinder 48 is at a position P A is the second reference position REF_P A to reach. <Method of controlling a work vehicle>

[0126] Next, a method for controlling the work vehicle 1 according to this embodiment will be described. FIG. 16 is a flowchart showing the method for controlling the work vehicle 1. In step S1, the controller 15 acquires a reference orientation REF_D that serves as a reference for the implement orientation 41D from the joint 43 that rotatably connects the implement 41 to the arm tip 45D of the work vehicle 1 toward the implement tip 41T. Specifically, the hardware processor 15P of the controller 15 acquires a first reference value (REF_θ) of a first parameter that corresponds to the reference orientation REF_D stored in the memory 15M of the controller 15. R , or REF_P I ) to get the

[0127] In step S2, the controller 15 calculates the height direction D perpendicular to the traveling direction of the traveling device 3 of the work vehicle 1. H The arm height H is the height of the arm tip 45D relative to the ground surface GL of the traveling device 3. A Specifically, the hardware processor 15P of the controller 15 obtains a reference height REF_H that is a reference for the reference orientation REF_D stored in the memory 15M of the controller 15. J , REF_P A ) to get the

[0128] In step S3, the controller 15 calculates the arm height H of the arm tip 45D when the implement tip 41T is directed to the reference direction REF_D. AIn response to this, the controller 15 determines a first reference value (REF_θ) of the first parameter corresponding to the reference orientation REF_D stored in the memory 15M of the controller 15. I +θ A (TAR_H)).

[0129] In step S4, the controller 15 determines the implement direction 41D and the arm height H A In step S4, the controller 15 determines whether an instruction to perform automatic control for changing the arm height H to the reference orientation REF_D and the reference height REF_H, respectively, has been received. Specifically, the controller 15 determines whether an instruction has been received by the input device 17. If the instruction has not been received (NO in step S4), step S4 is repeated. If the instruction has been received (YES in step S4), in step S5, the controller 15 A The controller 15 controls the second hydraulic cylinder 48 so that the second hydraulic cylinder 48 has a height equal to the reference height REF_H. Specifically, the controller 15 performs the above-mentioned feedforward control and cushion control on the second hydraulic cylinder 48.

[0130] As a parallel process of step S5, in step S6, the controller 15 A The controller 15 controls the first hydraulic cylinder 49 so that the implement orientation 41D becomes the reference orientation REF_D when the arm height H changes to the target height TAR_H. Specifically, the controller 15 performs the above-mentioned feedforward control, feedback control, and cushion control on the second hydraulic cylinder 48. After step S6 is completed, the process proceeds to step S5. In step S7, the controller 15 controls the arm height H Ahas reached the reference height REF_H. In step S7, since the implement tip 41T has been controlled to face upward as a target in step S6, the controller 15 controls the first hydraulic cylinder 49 to finely adjust the implement orientation 41D to the reference orientation REF_D. Specifically, for example, in the case where the implement attitude detection sensor 57 is composed of the first inertial measurement unit 57a and the second inertial measurement unit 57b, the implement inclination angle θ I is REF_θ I +θ A (REF_H) [θ A When (REF_H)=0, REF_θ I The first hydraulic cylinder 49 is controlled to finely adjust the force so that the following relation holds: <Effects of the embodiment>

[0131] The controller 15 of the work vehicle 1 according to this embodiment controls the arm height H A When the arm height H changes to a target height TAR_H that is greater than the reference height REF_H, the first hydraulic cylinder 49 is controlled so that the implement orientation 41D becomes the reference orientation REF_D. A When the implement tip 41T reaches the reference height REF_H, the implement tip 41T can be reliably prevented from hitting the ground. <Modification>

[0132] In the above embodiment, the hydraulic circuit 100 is a circuit capable of mechanically achieving horizontal control, but a simpler hydraulic circuit may be used. FIG. 17 shows a modified hydraulic circuit 101. In FIG. 17, the same components as those in FIG. 3 are given the same reference numerals, and detailed description is omitted. The hydraulic circuit 101 has a first control valve 25a instead of the first control valve 25 of the hydraulic circuit 100, and has a second control valve 20a instead of the second control valve 20 of the hydraulic circuit 100. The first control valve 25a has a solenoid 25s, and the position of the spool is changed by sending a control signal to the solenoid 25s. The second control valve 20a has a solenoid 20s, and the position of the spool is changed by sending a control signal to the solenoid 20s. In this modified example, instead of the signals sent to solenoids 60s, 61s in the above embodiment, a control signal is sent to solenoid 25s so that the first opening area AS1 becomes the first target area TS1, and a control signal is sent to solenoid 20s so that the second opening area AS2 becomes the second target area TS2.

[0133] In this application, the term "comprises" and its derivatives are open-ended terms that describe the presence of elements and do not exclude the presence of other elements not listed. This also applies to the terms "have", "include" and their derivatives.

[0134] The terms "member," "part," "element," "body," and "structure" may have multiple meanings, such as a single part or multiple parts.

[0135] Ordinal numbers such as "first" and "second" are merely terms used to identify components and do not have any other meaning (such as a particular order). For example, the presence of a "first element" does not imply the presence of a "second element," and the presence of a "second element" does not imply the presence of a "first element."

[0136] Words expressing degree, such as "substantially," "about," and "approximately," may mean a reasonable deviation that does not significantly change the final result, unless otherwise specified in the embodiment. All numerical values ​​described in this application may be interpreted to include words such as "substantially," "about," and "approximately."

[0137] In this application, the phrase "at least one of A and B" should be interpreted as including A only, B only, and both A and B.

[0138] It is apparent that various changes and modifications of the present invention are possible in light of the above disclosure, and therefore, the present invention may be practiced otherwise than as specifically disclosed herein without departing from the spirit and scope of the present invention.

Claims

1. an implement including a joint and an implement tip opposite the joint; an arm assembly including an arm tip that swingably supports the implement at the joint and an arm base end opposite to the arm tip; a vehicle body that supports the base end of the arm so as to be able to swing; A traveling device for moving the vehicle body; A first hydraulic cylinder configured to control an orientation of the implement from the joint toward the tip of the implement; A second hydraulic cylinder configured to control an arm height, which is a height of the arm tip relative to a ground contact surface of the traveling device, in a height direction perpendicular to the traveling direction of the traveling device; a hydraulic circuit configured to control the first hydraulic cylinder and the second hydraulic cylinder; an implement attitude detection sensor for detecting an orientation of the implement; an arm posture detection sensor for detecting the arm height; A storage device that stores first information corresponding to a reference orientation that is a reference implement orientation and second information corresponding to a reference height that is a reference arm height; a controller configured to control the hydraulic circuit; An input device configured to receive an instruction to perform automatic control for changing the implement orientation and the arm height to the reference orientation and the reference height, respectively; Equipped with The controller: When the instruction is received by the input device, the hydraulic circuit is controlled so that the arm height becomes the reference height; The hydraulic circuit is controlled so that the implement orientation becomes the reference orientation when the arm height changes to a target height, which is the arm height when the tip of the implement is directed to the reference orientation during the automatic control. The target height is greater than the reference height. Work vehicle.

2. The first information includes a first reference value corresponding to the reference orientation of a first parameter representing the implement orientation, the second information includes a second reference value of a second parameter representing the arm height, the second reference value corresponding to the reference height, The controller: When the instruction is received by the input device, the hydraulic circuit is controlled so that the second parameter is set to the second reference value; The hydraulic circuit is controlled so that the first parameter is set to the first reference value when the arm height becomes the target height. A work vehicle according to claim 1.

3. The controller: When the instruction is received by the input device, determining a first reference position which is the position of the first hydraulic cylinder corresponding to the reference orientation, a second reference position which is the position of the second hydraulic cylinder corresponding to the reference height, a second target position which is the position of the second hydraulic cylinder corresponding to the target height, a first initial position which is the position of the first hydraulic cylinder at the time when the instruction is accepted, and a second initial position which is the position of the second hydraulic cylinder at the time when the instruction is accepted; the hydraulic circuit is controlled so that, during a period in which the position of the first hydraulic cylinder changes from the first initial position to the first reference position, an absolute value of a change in the position of the first hydraulic cylinder per unit time becomes equal to (an absolute value of a difference between the first reference position and the first initial position / an absolute value of a difference between a second target position and the second initial position) times an absolute value of a change in the position of the second hydraulic cylinder per unit time. The work vehicle according to claim 2.

4. The controller: when the first parameter reaches the first reference value, the hydraulic circuit is controlled so as not to change the position of the first hydraulic cylinder until the position of the second hydraulic cylinder changes to the second reference position; A work vehicle according to claim 3.

5. The hydraulic circuit includes: a hydraulic pump configured to supply hydraulic fluid to the first hydraulic cylinder and the second hydraulic cylinder; a first cylinder hydraulic circuit connecting the first hydraulic cylinder and the hydraulic pump; a second cylinder hydraulic circuit connecting the second hydraulic cylinder and the hydraulic pump; an engine configured to drive the hydraulic pump; a rotation speed detection sensor configured to detect a rotation speed of the engine; a first control valve that is provided in the first cylinder hydraulic circuit between the hydraulic pump and the first hydraulic cylinder, capable of switching a first supplied oil chamber to which the hydraulic oil is supplied, out of two oil chambers of the first hydraulic cylinder, and capable of adjusting the amount of the hydraulic oil supplied to the first supplied oil chamber per unit time by a first opening area; a second control valve that is provided in the second cylinder hydraulic circuit between the hydraulic pump and the second hydraulic cylinder, capable of switching a second supplied oil chamber to which the hydraulic oil is supplied, out of two oil chambers of the second hydraulic cylinder, and capable of adjusting the amount of the hydraulic oil supplied to the second supplied oil chamber per unit time by a second opening area; a pressure control mechanism including a first pressure compensating valve provided in the first cylinder hydraulic circuit between the first control valve and the hydraulic pump, and a second pressure compensating valve provided in the second cylinder hydraulic circuit between the second control valve and the hydraulic pump, configured to control a first output hydraulic pressure of the hydraulic oil output from the first control valve to the first supplied oil chamber to be lower by a first pressure than a first input hydraulic pressure input from the first pressure compensating valve to the first control valve, and to control a second output hydraulic pressure of the hydraulic oil output from the second control valve to the second supplied oil chamber to be lower by the first pressure than a second input hydraulic pressure input from the second pressure compensating valve to the second control valve; Equipped with The controller: When the instruction is received by the input device, determining a maximum allowable value of the sum of the first opening area and the second opening area based on the rotation speed of the engine at the time when the instruction is received; A limit value that is a sum of a maximum value of the first opening area and a maximum value of the second opening area is obtained; determining a reference value that is smaller between the maximum allowable value and the limit value; calculating a first volume of hydraulic oil to be supplied from the hydraulic pump to the first hydraulic cylinder so as to bring the position of the first hydraulic cylinder to the first reference position, based on a first initial position, which is a position of the first hydraulic cylinder at the time the instruction is received, and the first reference position; calculating a second volume of hydraulic oil to be supplied from the hydraulic pump to the second hydraulic cylinder so as to bring the position of the second hydraulic cylinder to the second target position, based on a second initial position, which is a position of the second hydraulic cylinder at the time the instruction is received, and the second target position; while a position of the first hydraulic cylinder changes from the first initial position to the first reference position, the first opening area of ​​the first control valve is controlled based on a reference area that is (first volume / (first volume+second volume)) times the reference value. A work vehicle according to claim 3.

6. The controller: when a corrected area obtained by multiplying the reference area by a first correction coefficient associated with the rotation speed of the engine is equal to or smaller than a maximum value of the first opening area, the corrected area is set to a first target area; When the correction area is greater than the maximum value of the first opening area, the maximum value is set as the first target area; a feedforward control is performed so that the first opening area of ​​the first control valve is set to the first target area while a position of the first hydraulic cylinder changes from the first initial position to the first reference position. A work vehicle according to claim 5.

7. The controller: a feedforward control is performed such that the second opening area of ​​the second control valve is set to a second target area obtained by subtracting the first target area from the reference value, during a period until a position of the first hydraulic cylinder changes from the first initial position to the first reference position. A work vehicle according to claim 6.

8. The controller: determining the arm height detected by the arm posture detection sensor; Calculating a target value of the first parameter corresponding to the arm height based on the target; acquiring a detected value of the first parameter detected by the implement attitude detection sensor; When an absolute value of the difference between the detected value and the first reference value is greater than an absolute value of the difference between the target value and the first reference value by a first threshold value or more, feedback control is performed with the first opening area of ​​the first control valve as a control target so as to bring the detected value closer to the target value. A work vehicle according to any one of claims 3 to 7.

9. The controller: After starting the feedback control, when an absolute value of a difference between the detected value and the first reference value becomes smaller than a value obtained by adding an absolute value of a difference between the target value and the first reference value to a second threshold value smaller than the first threshold value, a control amount of the first control valve performed in the feedback control immediately before the value fell below the second threshold value is divided by a control amount of the first control valve in a case where the feedforward control is performed so that the first opening area becomes the first target area, and a feedforward control is performed so that the first opening area of ​​the first control valve becomes a value obtained by multiplying the first target area by the second correction coefficient during a period from immediately after the value falls below the second threshold value until a position of the first hydraulic cylinder becomes the first reference position. A work vehicle according to claim 8.

10. The storage device includes: a first approach speed that is an amount of change in the position of the first hydraulic cylinder per unit time immediately before the position of the first hydraulic cylinder becomes the first reference position; and a first deceleration for decelerating the displacement speed of the first hydraulic cylinder to the first approach speed; Remember, The controller: A detected position of the first hydraulic cylinder detected by the implement attitude detection sensor is obtained; determining the displacement velocity of the first hydraulic cylinder, which is the amount of change in the detected position of the first hydraulic cylinder per unit time, from the change in the detected position over time; calculating a first deceleration time by dividing a difference between the displacement speed of the first hydraulic cylinder and the first approach speed by the first deceleration; calculating a deceleration start position of the first hydraulic cylinder at which deceleration from the displacement speed of the first hydraulic cylinder starts, based on the displacement speed of the first hydraulic cylinder, the first deceleration time, and the first reference position; controlling the first opening area of ​​the first control valve so as to decelerate the displacement speed of the first hydraulic cylinder based on the first deceleration from when the detected position of the first hydraulic cylinder reaches the deceleration start position of the first hydraulic cylinder until the displacement speed of the first hydraulic cylinder becomes the first approach speed; A work vehicle according to any one of claims 5 to 7.

11. The storage device includes: a second approach speed that is an amount of change in the position of the second hydraulic cylinder per unit time immediately before the position of the second hydraulic cylinder becomes the second reference position; and a second deceleration for decelerating the displacement speed of the second hydraulic cylinder to the second approach speed; The controller: A detected position of the second hydraulic cylinder detected by the arm posture detection sensor is obtained. determining the displacement speed of the second hydraulic cylinder, which is the amount of change in the detected position of the second hydraulic cylinder per unit time, from the change in the detected position over time; calculating a second deceleration time by dividing a difference between the displacement speed and the second approach speed of the second hydraulic cylinder by the second deceleration; calculating a deceleration start position of the second hydraulic cylinder at which deceleration from the displacement speed of the second hydraulic cylinder starts, based on the displacement speed of the second hydraulic cylinder, the second deceleration time, and the second reference position; controlling the second opening area of ​​the second control valve so as to decelerate the displacement speed of the second hydraulic cylinder based on the second deceleration from when the detected position of the second hydraulic cylinder reaches the deceleration start position of the second hydraulic cylinder until the displacement speed of the second hydraulic cylinder becomes the second approach speed; A work vehicle according to claim 10.

12. the arm assembly includes a link mechanism that connects the vehicle body and the arm tip, the arm posture detection sensor is a rotation angle detection sensor configured to detect a rotation angle of a joint of the link mechanism, The implement attitude detection sensor includes: a first inertial measurement unit (IMU) attached to the implement; a second inertial measurement unit (IMU) attached to the vehicle body; Equipped with the storage device stores a first correspondence relationship between a sum of an implement inclination angle formed by a vehicle reference direction and the implement orientation for defining a posture of the vehicle body and an adjustment angle which is the implement inclination angle that changes according to the arm height even if the position of the first hydraulic cylinder does not change, and a position of the first hydraulic cylinder; The controller: obtaining a first angle between a direction of gravity and the vehicle reference direction from an output signal of the second inertial measurement unit; obtaining a second angle between the gravity direction and the implement direction from an output signal of the first inertial measurement unit; The implement inclination angle is determined by referring to the first angle and the second angle; calculating a position of the first hydraulic cylinder from the sum of the implement inclination angle and the adjustment angle based on the first correspondence relationship; A work vehicle according to any one of claims 2 to 7.

13. the arm assembly includes a link mechanism that connects the vehicle body and the arm base end, the arm posture detection sensor is a rotation angle detection sensor configured to detect a rotation angle of a joint of the link mechanism, the storage device stores a second correspondence relationship between the rotation angle and a position of the second hydraulic cylinder, The controller: determining a position of the second hydraulic cylinder from the rotation angle based on the second correspondence relationship; A work vehicle according to any one of claims 2 to 7.

14. an additional input device that receives a registration instruction for registering the reference orientation and the reference height; When the registration instruction is received by the additional input device, the controller determining a position of the second hydraulic cylinder from the rotation angle of the joint at the time when the registration instruction is received; storing the determined position in the storage device as the second reference position; A work vehicle according to claim 12.

15. an additional input device that receives a registration instruction for registering the reference orientation and the reference height; When the registration instruction is received by the additional input device, the controller calculating a position of the second hydraulic cylinder from the rotation angle of the joint at the time when the registration instruction is received; calculating a reference inclination angle, which is the implement inclination angle at the time when the registration instruction is accepted, from an output of the first inertial measurement unit and an output of the second inertial measurement unit at the time when the registration instruction is accepted; storing the calculated reference tilt angle in the storage device; the controller calculates the first reference position from the reference tilt angle by referring to the first correspondence relationship. A work vehicle as claimed in claim 14.

16. A reference orientation that is a reference for the orientation of the implement from a joint that rotatably connects the implement to the arm tip of the work vehicle toward the tip of the implement is obtained; A reference height is obtained as a reference for an arm height, which is the height of the arm tip relative to the ground contact surface of the traveling device in a height direction perpendicular to the traveling direction of the traveling device of the work vehicle; When an instruction to perform automatic control for changing the implement orientation and the arm height to the reference orientation and the reference height, respectively, is received, the second hydraulic cylinder is controlled so that the arm height becomes the reference height; the arm height is a height when the tip end of the implement is directed to the reference orientation, and when the arm height changes to a target height that is greater than the reference height, the first hydraulic cylinder is controlled so that the orientation of the implement becomes the reference orientation. A method for controlling a work vehicle.

17. a memory configured to store a first reference value corresponding to a reference direction serving as a reference for an implement orientation, the first parameter representing an implement orientation from a joint that rotatably connects the implement to the arm tip of a work vehicle toward the implement tip, and a second reference value corresponding to a reference height serving as a reference for an arm height, the arm height being the height of the arm tip relative to the ground contact surface of a travel device of the work vehicle in a height direction perpendicular to the traveling direction of the work vehicle; When an instruction to perform automatic control for changing the implement orientation and the arm height to the reference orientation and the reference height, respectively, is accepted, a second hydraulic cylinder is controlled so that the second parameter becomes the second reference value; a processor configured to control the first hydraulic cylinder so that the first parameter becomes the first reference value when the arm height changes to a target height that is greater than the reference height, the target height being the arm height when the tip of the implement is directed in the reference orientation; Work vehicle controller.

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