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

Abstract

To electrically achieve a horizontal control similar to that performed by a hydraulic circuit when an implement is raised.SOLUTION: A work vehicle comprises a processor acquiring a first reference parameter that is a second posture parameter associated with a first posture parameter representing a start arm height in a first correspondence relation. The processor: obtains a measurement value of an arm height from an output of an arm posture detection sensor; and acquires a second reference parameter that is a second posture parameter associated with the first posture parameter representing a measurement value in the first correspondence relation. The processor: determines a target direction such that a difference between the second posture parameter representing a target direction that is a target of an implement direction when the arm height is the measurement value and the second posture parameter representing a start implement direction is equal to a difference between the second reference parameter and the first reference parameter; and controls a first spool position such that the implement direction approaches the target direction.SELECTED DRAWING: Figure 8

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 bucket horizontal control that prevents the bucket's attitude relative to the ground from changing even if the bucket's position is changed by the arm in response to a bucket or arm attitude change command input electrically by a joystick. Patent Document 2 describes a work vehicle that realizes the above-mentioned horizontal control by controlling a hydraulic circuit to send part of the hydraulic oil discharged from the arm cylinder to the bucket cylinder in response to a bucket or arm attitude change command input by an operating valve. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 94 / 26,988 [Patent Document 2] U.S. Patent No. 11,655,615 Summary of the Invention [Problem to be solved by the invention]

[0004] The work vehicle disclosed in Patent Document 1 controls valves that supply hydraulic oil to the bucket and arm cylinders only with electrical signals. The work vehicle disclosed in Patent Document 2 achieves horizontal control by a hydraulic circuit for the bucket lifting operation, but is unable to perform horizontal control for the bucket lowering operation.

[0005] The technology disclosed in the present application provides a work vehicle, a control method for a work vehicle, and a controller for a work vehicle that can achieve horizontal control by a hydraulic circuit when raising the bucket, and by other means when lowering the bucket. [Means for solving the problem]

[0006] A work vehicle according to a first aspect of the present disclosure includes an implement, an arm, a vehicle body, a traveling device, a first hydraulic cylinder, a second hydraulic cylinder, a hydraulic pump, an engine, a rotational speed detection sensor, a first control valve, an arm attitude detection sensor, an implement attitude detection sensor, a storage device, a processor, a first input device, and a second input device. The implement includes a joint and an implement tip opposite the joint. The arm includes a joint and an arm tip that swingably supports the implement and an arm base end opposite 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 pump is configured to supply hydraulic oil to the first hydraulic cylinder and the second hydraulic cylinder. The engine is configured to rotate the hydraulic pump. The rotational speed detection sensor is configured to detect a detected rotational speed of the engine. The first control valve has a first spool, and is configured to alternatively switch each of two oil chambers of the first hydraulic cylinder between a first supplied oil chamber that supplies hydraulic oil and a first discharged oil chamber that discharges hydraulic oil according to a first spool position that is a position of the first spool, and to adjust the supply amount of hydraulic oil per unit time to the first supplied oil chamber and the discharge amount of hydraulic oil per unit time from the first discharged oil chamber according to the first spool position. The arm attitude detection sensor is configured to detect an arm height. The implement attitude detection sensor is configured to detect an implement orientation. The storage device is configured to store a first correspondence relationship in which a first attitude parameter representing the arm height and a second attitude parameter representing the implement orientation are associated with each other. The processor is configured to control the hydraulic pump, the engine, and the first control valve. The first input device is configured to receive a first instruction for performing an implement attitude electric control that controls the implement orientation. The second input device is configured to accept a second instruction to change the arm height.The processor calculates a first attitude parameter representing a starting arm height, which is an arm height at the time when the second instruction is received, from the output of the arm attitude detection sensor after the first instruction is received. The processor calculates a second attitude parameter representing a starting implement orientation, which is an implement orientation at the time when the second instruction is received, from the output of the implement attitude detection sensor after the first instruction is received. The processor acquires a first reference parameter, which is a second attitude parameter associated with the first attitude parameter representing the starting arm height in the first correspondence relationship. The processor controls the second hydraulic cylinder according to the second instruction. The processor obtains a measured value of the arm height from the output of the arm attitude detection sensor. The processor acquires a second reference parameter, which is a second attitude parameter associated with the first attitude parameter representing the measured value in the first correspondence relationship. The processor determines the target orientation such that a difference between the second attitude parameter representing a target orientation, which is a target of the implement orientation when the arm height becomes the measured value, and the second attitude parameter representing the starting implement orientation is equal to a difference between the second reference parameter and the first reference parameter. The processor controls the first spool position so that the implement orientation approaches the target orientation.

[0007] A control method for a work vehicle according to a second aspect of the present disclosure includes receiving a first instruction for performing implement attitude electrical control that controls an implement orientation based on a first correspondence relationship that associates a first attitude parameter that represents an arm height, which is a height of a travel device of the work vehicle relative to a ground contact surface, with a second attitude parameter that represents an implement orientation in which a tip of the implement faces from a joint of the implement, and receiving a second instruction for changing the arm height. The control method includes calculating a first attitude parameter that represents a starting arm height, which is the arm height at the time when the second instruction is accepted after the first instruction is accepted, from an output of an arm attitude detection sensor configured to detect the arm height, and calculating a second attitude parameter that represents a starting implement orientation, which is the implement orientation at the time when the second instruction is accepted after the first instruction is accepted, from an output of an implement attitude detection sensor configured to detect the implement orientation. The control method includes acquiring a first reference parameter which is a second attitude parameter associated in a first correspondence relationship with a first attitude parameter representing a starting arm height, controlling a second hydraulic cylinder configured to control the arm height according to a second instruction, determining a measured value of the arm height from an output of an arm attitude detection sensor for detecting the arm height, and acquiring a second reference parameter which is the second attitude parameter associated in the first correspondence relationship with the first attitude parameter representing the measured value. The control method includes determining a target orientation such that a difference between a second attitude parameter which is a target for an implement orientation when the arm height becomes the measured value and the second attitude parameter which represents a starting implement orientation is equal to a difference between the second reference parameter and the first reference parameter.The control method includes controlling a first spool position of a first control valve which has a first spool and is configured to alternatively switch each of two oil chambers of a first hydraulic cylinder between a first supplied oil chamber that supplies hydraulic oil and a first discharged oil chamber that discharges hydraulic oil depending on a first spool position, which is the position of the first spool, and to adjust the amount of hydraulic oil supplied per unit time to the first supplied oil chamber and the amount of hydraulic oil discharged per unit time from the first discharged oil chamber depending on the first spool position, so that the implement orientation approaches a target orientation.

[0008] A controller for a work vehicle according to a third aspect of the present disclosure includes a storage device and a processor. The storage device is configured to store a first correspondence relationship in which a first attitude parameter representing an arm height, which is a height of a travel device of the work vehicle relative to a ground contact surface, and a second attitude parameter representing an implement orientation in which a tip of the implement faces from a joint of the implement are associated with each other. The processor is configured to receive a first instruction for performing implement attitude electrical control for controlling the implement orientation based on the first correspondence relationship from a first input device, and to receive a second instruction for changing the arm height from a second input device. The processor is configured to calculate a first attitude parameter representing a starting arm height, which is the arm height at the time when the second instruction is accepted after the first instruction is accepted, from an output of an arm attitude detection sensor configured to detect the arm height, and to calculate a second attitude parameter representing a starting implement orientation, which is the implement orientation at the time when the second instruction is accepted after the first instruction is accepted, from an output of an implement attitude detection sensor configured to detect the implement orientation. The processor is configured to obtain a first reference parameter which is a second posture parameter associated with the first posture parameter representing a starting arm height in the first correspondence relationship, control a second hydraulic cylinder configured to control the arm height according to a second instruction, receive an output of an arm posture detection sensor for detecting the arm height, obtain a measured value of the arm height, and obtain a second reference parameter which is the second posture parameter associated with the first posture parameter representing the measured value in the first correspondence relationship. The processor is configured to determine a target orientation such that a difference between the second posture parameter representing a target orientation that is a target for an implement orientation when the arm height becomes the measured value and the second posture parameter representing a starting implement orientation is equal to a difference between the second reference parameter and the first reference parameter.The processor is configured to control the first spool position of a first control valve which has a first spool and is configured to alternatively switch each of the two oil chambers of the first hydraulic cylinder between a first supplied oil chamber that supplies hydraulic oil and a first discharged oil chamber that discharges hydraulic oil depending on a first spool position, which is the position of the first spool, and to adjust the amount of hydraulic oil supplied per unit time to the first supplied oil chamber and the amount of hydraulic oil discharged per unit time from the first discharged oil chamber depending on the first spool position, so that the implement orientation approaches the target orientation. Effect of the Invention

[0009] According to the technology disclosed in the present application, it is possible to provide a work vehicle, a control method for a work vehicle, and a controller for a work vehicle, which can achieve horizontal control by a hydraulic circuit for the operation of raising the bucket, and by other means for the operation of lowering the bucket. [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 implement attitude electrical control / implement attitude mechanical control in a case where the implement attitude detection sensor is composed of a first inertial measurement unit and a second inertial measurement unit, and the arm attitude detection sensor is composed of a potentiometer. [Figure 12] FIG. 12 is a diagram showing the relationship between the change in arm height and the change in the implement inclination angle in electrical control of the implement attitude. [Figure 13] FIG. 13 is a conceptual diagram of implement attitude electrical control / implement attitude mechanical control in the case where the implement attitude detection sensor is composed of a potentiometer or a linear sensor, and the arm attitude detection sensor is composed of a linear sensor. [Figure 14] FIG. 14 is a diagram showing the relationship between the change in arm height and the change in joint rotation angle in electrical control of the implement attitude. [Figure 15] FIG. 15 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 electric control of the implement attitude. [Figure 16] FIG. 16 is a control block diagram according to the embodiment. [Figure 17] FIG. 17 is a diagram showing the relationship between the rotation speed of the engine 6 and the correction gain. [Figure 18] FIG. 18 is an example of the correspondence relationship between the amount of operation of the operating lever (the movement of the arm input member in the front-rear direction) and the second opening area according to the embodiment. [Figure 19] FIG. 19 is a flowchart showing a method for controlling a work vehicle. [Figure 20] FIG. 20 is a diagram for explaining the reference correspondence relationship. 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 That is, the arm position detection sensor 56 is a rotation angle detection sensor configured to detect a rotation angle θ J1, for convenience, the rotation angle detection sensor is configured to detect the rotation angle D 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 J However, 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 first attitude parameter. J is an example of the first attitude parameter. The first attitude parameter is a rotation angle θ J Arm height H converted from A The first attitude parameter may be a parameter representing a rotation angle θ J It may be the same thing.

[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 θVG 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 θ IG 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 second attitude parameter. I is an example of a second attitude 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 second attitude parameter. A is another example of the first posture parameter.

[0017] The vehicle body 2 includes a cabin 5. The cabin 5 is provided with a windshield 51 that can be opened and closed, and its outer shape is defined by a cab frame 53. The windshield 51 may be omitted. The cab frame 53 is rotatable around rotational shafts RSL and RSR on the vehicle body 2, as shown in FIG. 2. In FIG. 1 and FIG. 2, a common pivot A defined by the rotational shafts RSL and RSR is a common pivot A. XC That 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 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] The work vehicle 1 includes a driver's seat 54 and an operation lever 55 (arm input member 63, implement input member 68) in the cabin 5. The arm input member 63 has an arm height H A In the following embodiments, this instruction is referred to as a second instruction. Also, the arm input member 63 is referred to as a second input device. That is, the second input device is configured to receive an instruction to change the arm height H A Increase the rise command and arm height H AThe operation lever 55 is configured to receive a second instruction to move the implement 41D upward and a lowering instruction to reduce the implement 41D downward. The implement input member 68 is configured to receive an instruction to change the implement direction 41D. In the following embodiments, this instruction is referred to as a third instruction. The implement input member 68 is also referred to as a third input device. The operation lever 55 shown in FIG. 1 is configured to receive a second instruction by the forward and backward movement of the operation lever 55, and receive a third instruction by the left and right movement of the operation lever 55. Therefore, the operation lever 55 is formed by integrating the second input device and the third input device. However, as shown later in FIG. 3, the arm input member 63 and the implement input member 68 may be separate members.

[0020] 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.

[0021] 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 detects a detected rotation speed N EThe first traveling hydraulic pump 7L and the second traveling hydraulic pump 7R are configured to discharge hydraulic oil to drive hydraulic actuators (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 detect the rotational speed of the work vehicle 1 in the width direction D. 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>

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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. 9, 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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 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 position of the second spool SPL2 to a second hydraulic cylinder extension control position AEP or a second hydraulic cylinder retraction control position ASP. Specifically, referring to Fig. 9, when the position of the second spool SPL2 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 Figure 10, when the position of the second spool SPL2 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.

[0035] 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, which is the position of the second spool SPL2, 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.

[0036] 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, which is the position of the second spool SPL2, 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.

[0037] 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 above-mentioned predetermined pressure, the second control valve 20 switches the position of the second spool SPL2 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.

[0038] 3, the hydraulic circuit 100 further includes a shuttle valve 82 that outputs the higher 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 output from the shuttle valve 82 is equal to or higher than a third threshold pressure. The third threshold pressure is equal to the fourth threshold pressure and may be referred to as the first pressure. In other words, the second pressure compensating valve 76 is configured to control the oil 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 a first pressure than the oil pressure of the hydraulic oil input from the second pressure compensating valve 76 to the second control valve 20.

[0039] 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.

[0040] 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 via the first control valve 25 and the flow rate of hydraulic oil per unit time via 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.

[0041] 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 is switched to a second position PV2 when the hydraulic pressure is equal to or higher than the first pressure. 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).

[0042] 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.

[0043] 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.

[0044] 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 φ 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 u3 to be applied to the solenoid 60s based on the operation amount φ. 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 operation amount φ 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 u4 to be applied to the solenoid 61s based on the operation amount φ. This operation amount φ corresponds to the second command. 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.

[0045] 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.

[0046] 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 19, 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 19, and outputs a control amount u2 to be applied to the solenoid 66s based on the operation amount.

[0047] 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.

[0048] 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.

[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 work vehicle 1 includes a controller 15 configured to control the hydraulic pump 11, the engine 6, and the first control valve 25. The controller 15 is, for example, a hardware controller such as an ECU. Thus, 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. The hardware processor 15P is configured to control the hydraulic pump 11, the engine 6, and the first control valve 25. 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 performing implement attitude machine control for controlling the implement orientation 41D by changing the connection relationship of the hydraulic circuit 100. That is, the controller 15 (hardware processor 15P) is configured to control the switching mechanism 70 to connect the fourth oil passage R4 and the first oil passage R1 when the third instruction is received and the arm height H AWhen a second instruction to increase the oil pressure is received, the control unit 10 controls the switching mechanism 70 to connect the fourth oil passage R4 and the first oil passage R1 to each other.

[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] A controller 15 is connected to the solenoid of the solenoid valve 71. The work vehicle 1 further includes a first input device 16 configured to receive an instruction for performing implement attitude machine control by changing the connection relationship of the hydraulic circuit 100. In this embodiment, this instruction is referred to as a third instruction. When the third instruction is received, the controller 15, for example, A When a second instruction to increase the pressure is received, an electrical signal is sent to the solenoid valve 71 to switch the solenoid valve 71 to the first position VP1.

[0052] Specifically, the first input device 16 includes an ON / OFF changeover switch 16SW for turning on / off the implement attitude machine control, which is electrically connected to the hardware processor 15P. When the switch 16SW is switched on, the controller 15 transmits an electric signal to the solenoid valve 71 to switch the solenoid valve 71 to the first position VP1. This switch 16SW is switched on when performing the above-mentioned implement attitude machine control. When the implement attitude machine control is turned on by the switch 16SW and an ascending command is received by the second input device (arm input member 63), the hardware processor 15P switches the solenoid valve 71 to the first position VP1. When the implement attitude machine control is turned off by the switch 16SW, the hardware processor 15P switches the solenoid valve 71 to the second position VP2 regardless of the operation of the second input device (arm input member 63).

[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 CKV3 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 implement attitude mechanical control and the implement attitude electric 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. In this way, the ratio of the amount of hydraulic oil flowing into the first chamber CB1 of the first hydraulic cylinder 49 to the amount of hydraulic oil flowing out of the fourth chamber CB4 of the second hydraulic cylinder 48 is adjusted by the size of the throttle of the first cut-off position BP1 of the second switching valve 73. This is called the first hydraulic cylinder = second hydraulic cylinder oil amount fluctuation ratio K0. The second switching valve 73 is controlled to switch between the first communication position CP1 and the first cut-off position BP1 so that the amount of hydraulic oil output per unit time from the second control valve 20 to the second supplied oil chamber (CB3 or CB4) multiplied by the first hydraulic cylinder = second hydraulic cylinder oil amount fluctuation ratio K0 is output from the first control valve 25 to the first supplied oil chamber (CB1 or CB2) per unit time. In this way, the swing angle of the implement tip 41T with respect to the arm 45 is changed in response to the elevation angle of the arm 45, and the direction from the joint 43 toward the implement tip 41T is controlled to be approximately horizontal. Such control is the implement attitude machine control described above.

[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. <Electric implement attitude control>

[0068] Next, the electric control of the implement attitude will be described. Fig. 11 is a conceptual diagram of electric control of the implement attitude / mechanical control of the implement attitude when the implement attitude detection sensor 57 is composed of a first inertial measurement unit 57a and a second inertial measurement unit 57b, and the arm attitude detection sensor 56 is composed of a potentiometer 56r. Electric control of the implement attitude means that, similar to the mechanical control of the implement attitude, the swing angle of the implement tip 41T with respect to the arm 45 is changed in response to the elevation angle of the arm 45 by only operating the arm input member 63 (only by operating the operation lever 55 in the forward and backward directions), thereby electrically controlling the implement orientation 41D so that the direction from the joint 43 to the implement tip 41T is approximately horizontal. The position and orientation of the arm 45 is determined by the arm height H A The arm height H at the start of the electric control of the implement attitude can be defined as A The initial height H A * (0), and the implement orientation 41D at the start of the implement attitude electrical control is defined as the initial orientation D(0).

[0069] With automatic implement return control, the arm height H can be set to any value. A For arm height H A STA_H to H A The change in the second attitude parameter when changing to the arm height H A STA_H to H A The implement orientation 41D is electrically controlled so that the amount of change in the second attitude parameter is the same as the amount of change in the arm height H A is calculated from the output value of the potentiometer 56r, the memory 15M stores the rotation angle θ J and arm height H A Based on this correspondence, the hardware processor 15P calculates the rotation angle θ detected by the potentiometer 56r. J From arm height H A The method is configured to determine:

[0070] In order to realize the electric control of the implement attitude, the memory 15M stores a first correspondence relationship in which a first attitude parameter and a second attitude parameter that change in the mechanical control of the implement attitude are associated with each other. Specifically, the first correspondence relationship is A The arm height H is the reference height A is set by the second input device (arm input member 63), and the implement orientation 41D is set to a reference implement orientation that is a reference for the implement orientation 41D by the third input device (implement input member 68), and then the arm height H A The reference height is the initial height H A * (0). The reference implement orientation is the initial orientation D(0). In the first correspondence relationship, the rotation speed N E is rotated at a first rotation speed, the first attitude parameter and the second attitude parameter are associated with each other.

[0071] The memory 15M stores at least one second correspondence relationship in which the first attitude parameter and the second attitude parameter are associated with each other when the implement attitude electric control is performed in a state in which the engine 6 is driven at at least one rotation speed different from the first rotation speed. Specifically, the at least one second correspondence relationship is a relationship in which the arm height H A The arm height H is the reference height A is set by the second input device (arm input member 63), and the implement orientation 41D is set to a reference implement orientation that is a reference for the implement orientation 41D by the third input device (implement input member 68), and then the arm height H A and implement orientation 41D.

[0072] FIG. 12 shows the second attitude parameter as a function of the implement inclination angle θ I FIG. 12 shows a map M1 representing the first and second correspondence relationships when the arm height H A The corresponding implement inclination angle θ I , arm height H A Implement inclination angle θ when is equal to H_MIN I θ I (H_MIN) is expressed as 0. H_MIN is the minimum arm height H at which the bottom end of the implement 41 coincides with the ground contact surface GL of the traveling device 3. A In FIG. 12, as an example, the rotation speed N E is fast (N EH ) is referred to as a first correspondence relationship between the first attitude parameter and the second attitude parameter, and E is slow (N EL The relationship between the first attitude parameter and the second attitude parameter in the case where the rotation speed N E is slow (N EL), the relationship between the first attitude parameter and the second attitude parameter when the rotation speed N E is fast (N EH The relationship between the first attitude parameter and the second attitude parameter in the case where the rotation speed N of the engine 6 is N 1 may be referred to as a first correspondence relationship. E When the engine 6 is rotating at a low idle speed, the engine 6 is rotating at a low idle speed. E The case where the rotation speed N of the engine 6 is high refers to, for example, the case where the engine 6 is rotating at a high idle speed. E The above mentioned high speed (N EH ), low speed (N EL In this case, there are multiple second correspondence relationships. Ideally, the arm height H A Regardless of implement inclination angle θ I It is desirable for the arm height H to change to 0. However, since the implement attitude machine control is realized by the degree of throttling of the first shutoff position BP1 of the second switching valve 73, it is necessary to change the arm height H A When H_MID, implement inclination angle θ I The implement inclination angle θ is set so that I By controlling in this way, when the implement attitude mechanical control and the implement attitude electrical control are repeated, the implement inclination angle θ I This can prevent errors from accumulating.

[0073] Furthermore, the first input device 16 is configured to receive an instruction to perform implement attitude electric control that controls the implement orientation 41D based on the first correspondence relationship. In the following embodiments, this instruction is referred to as a first instruction. The switch 16SW is configured to set both the implement attitude electric control and the implement attitude mechanical control to OFF, and to set both the implement attitude electric control and the implement attitude mechanical control to ON. In other words, the switch 16SW is also a switch for turning the implement attitude electric control ON / OFF.

[0074] When the switch 16SW is turned ON, the second instruction which is a lift instruction is received by the second input device (arm input member 63), and the first instruction which is a dump instruction (direction to direct the implement orientation 41D downward) is received, the hardware processor 15P controls the implement orientation 41D based on the first instruction in addition to the implement attitude machine control. When the switch 16SW is turned ON, the second instruction which is a lowering instruction is received by the second input device (arm input member 63), and the first instruction which is a scooping instruction (direction to direct the implement orientation 41D upward) is received, the hardware processor 15P disables the implement attitude machine control by switching the solenoid valve 71 to the second position PV2, and controls the implement orientation 41D based on the first instruction.

[0075] When the switch 16SW is turned ON, a second instruction which is a lowering instruction is received by the second input device (arm input member 63), and a first instruction which is a dumping instruction (to point the implement orientation 41D downward) is received, the hardware processor 15P disables the implement attitude machine control by switching the solenoid valve 71 to the second position PV2, and controls the implement orientation 41D based on the first instruction. When the switch 16SW is turned on and the second instruction, which is a lowering instruction, is received by the second input device (arm input member 63), and when the first instruction, which is a scooping instruction (to turn the implement orientation 41D upward), is received, the hardware processor 15P switches the solenoid valve 71 to the second position PV2 to disable the implement orientation mechanical control, and controls the implement orientation 41D based on the larger control amount of the control amount of the implement orientation 41D based on the first instruction and the control amount of the implement orientation 41D by the implement orientation electrical control based on the second instruction. This control amount will be described later.

[0076] In FIG. 12, at least one second correspondence does not exist (the above-mentioned fast (N EH) exists), the hardware processor 15P calculates the arm height H A The first posture parameter H A * (0) is the output θ of the arm position detection sensor 56 (potentiometer 56r) J * The hardware processor 15P calculates the second orientation parameter θ 1 , which represents the initial implement orientation 41D at the time when the second instruction is received after the first instruction is received. I * (0) is calculated from the output of the implement posture detection sensor 57. The hardware processor 15P calculates the first posture parameter H A * The first reference parameter θ, which is the second attitude parameter associated with (0) I (H A * After that, the hardware processor 15P obtains the output θ (0) of the arm posture detection sensor 56 (potentiometer 56r) when the time t has elapsed by controlling the second hydraulic cylinder 48 according to the second instruction (see FIG. 12). J * The hardware processor 15P receives the output θ J * (t) to arm height H A The measured value of H A * The hardware processor 15P calculates the first attitude parameter H A * The second reference parameter θ, which is the second attitude parameter associated with (t) I (H A * (t)) (see FIG. 12). The hardware processor 15P acquires the arm height H A is the measured value H A * A second attitude parameter θ representing a target orientation that is a target of the implement orientation 41D when (t) is reached.I (t) and the second attitude parameter θ representing the starting implement orientation I * The difference between (0) and the second reference parameter θ I (H A * (t)) and the first reference parameter θ I (H A * (0)) and Δθ I (t) is equal to (θ I (t)=θ I * (0)+Δθ I The hardware processor 15P determines the target orientation 41D (observation value θ I * (t) is the target orientation (θ I The first spool position is controlled so as to approach the direction indicated by (t).

[0077] The hardware processor 15P is configured to select a first rotation speed and at least one other rotation speed (in the example of FIG. 12, a high speed N EH Correspondence of low speed N EL Among the correspondence relationships, the detected rotation speed N of the engine 6 E The correspondence relationship corresponding to the rotation speed closest to the low speed N is determined as the reference correspondence relationship from among the first correspondence relationship and at least one of the second correspondence relationships. EL The correspondence relationship between the first posture parameter H A * The third reference parameter θ', which is the second attitude parameter associated with (0) I (H A * The hardware processor 15P acquires the first attitude parameter H A * The fourth reference parameter θ', which is the second attitude parameter associated with (t) I (H A *The hardware processor 15P acquires a second attitude parameter θ I (t) and the second attitude parameter θ representing the starting implement orientation I * The difference between (0) is the fourth reference parameter θ' I (H A * (t)) and the third reference parameter θ' I (H A * (0)) and Δθ' I (t) is equal to (θ I (t)=θ I * (0)+Δθ' I (t)) so that the target orientation (θ I The first spool position is controlled to determine the orientation (t) of the rotational axis.

[0078] 13 is a conceptual diagram of electric control of the implement attitude / mechanical control of the implement attitude when the implement attitude detection sensor 57 is composed of a potentiometer 57r or a linear sensor 57p and the arm attitude detection sensor 56 is composed of a linear sensor 56p. A In this case, the scale 15M indicates the position P of the second hydraulic cylinder 48. A and arm height H A Based on this correspondence, the hardware processor 15P calculates the position P of the second hydraulic cylinder 48 detected by the linear sensor 56p. A From arm height H A The method is configured to determine:

[0079] FIG. 14 shows the second posture parameter as a function of the rotation angle θ R FIG. 14 shows a map M2 representing the first and second correspondence relationships when the arm height H A The corresponding rotation angle θ R , arm height H A The rotation angle θ when is equal to the maximum possible height H_MAXR θ R In FIG. 14, as an example, the rotation speed N E The relationship between the first attitude parameter and the second attitude parameter when the rotation speed N of the engine 6 is high is called a first correspondence relationship. E The relationship between the first attitude parameter and the second attitude parameter when the rotation speed N of the engine 6 is low may be referred to as a second correspondence relationship. E The relationship between the first attitude parameter and the second attitude parameter when the rotation speed N of the engine 6 is low is called a second correspondence relationship. E The relationship between the first attitude parameter and the second attitude parameter when the rotation speed N of the engine 6 is high may be referred to as a first correspondence relationship. E The meaning of low speed / high speed is the same as that explained in FIG. 12. In FIG. 14, the rotation speed N E may include speeds other than the high speed and low speed described above. In this case, there will be a plurality of second correspondence relationships.

[0080] Thereafter, the first attitude parameter is calculated based on the position P of the second hydraulic cylinder 48, which is the output from the linear sensor 57p. A The second attitude parameter is calculated based on the rotation angle θ R 12. The hardware processor 15P receives the arm height H A The first posture parameter H A * (0) is the output P of the arm position detection sensor 56 (linear sensor 56p) A * The hardware processor 15P calculates the second orientation parameter θ 1 , which represents the initial implement orientation 41D at the time when the second instruction is received after the first instruction is received. R *(0) is calculated from the output of the implement posture detection sensor 57. The hardware processor 15P calculates the first posture parameter H A * The first reference parameter θ, which is the second attitude parameter associated with (0) R (H A * After that, the hardware processor 15P controls the second hydraulic cylinder 48 according to the second instruction and obtains the output of the arm posture detection sensor 56 (linear sensor 56p) when the time t has elapsed as P A * The hardware processor 15P receives the output P A * (t) to arm height H A The measured value of H A * The hardware processor 15P calculates the first attitude parameter H A * The second reference parameter θ, which is the second attitude parameter associated with (t) R (H A * (t)) (see FIG. 14). The hardware processor 15P acquires the arm height H A is the measured value H A * A second attitude parameter θ representing a target orientation that is a target of the implement orientation 41D when (t) is reached. R (t) and the second attitude parameter θ representing the starting implement orientation R * The difference between (0) and the second reference parameter θ R (H A * (t)) and the first reference parameter θ R (H A * (0)) and Δθ R (t) is equal to (θ R (t)=θ R * (0)+Δθ RThe hardware processor 15P determines the target orientation 41D (observation value θ R * (t) is the target orientation (θ R The first spool position is controlled so as to approach the direction indicated by (t).

[0081] FIG. 15 shows the second attitude parameter when the position P I FIG. 15 shows a map M3 representing the first and second correspondence relationships when the arm height H A Position P corresponding to I , arm height H A The position P when is equal to the minimum height H_MIN I P I In FIG. 15, as an example, the rotation speed N E The relationship between the first attitude parameter and the second attitude parameter when the rotation speed N of the engine 6 is high is called a first correspondence relationship. E The relationship between the first attitude parameter and the second attitude parameter when the rotation speed N of the engine 6 is low may be referred to as a second correspondence relationship. E The relationship between the first attitude parameter and the second attitude parameter when the rotation speed N of the engine 6 is low is called a second correspondence relationship. E The relationship between the first attitude parameter and the second attitude parameter when the rotation speed N of the engine 6 is high may be referred to as a first correspondence relationship. E The meaning of low speed / high speed is the same as that explained in FIG. 12. In FIG. 15, the rotation speed N E may include speeds other than the high speed and low speed described above. In this case, there will be a plurality of second correspondence relationships.

[0082] Thereafter, the first attitude parameter is calculated based on the position P of the second hydraulic cylinder 48, which is the output from the linear sensor 57p. A The second attitude parameter is calculated based on the position P of the first hydraulic cylinder 49. I14. The hardware processor 15P calculates a second attitude parameter P I * (0) is calculated from the output of the implement posture detection sensor 57. The hardware processor 15P calculates the first posture parameter H A * The first reference parameter P, which is the second attitude parameter associated with (0) I (H A * After that, the hardware processor 15P controls the second hydraulic cylinder 48 according to the second instruction to obtain the arm height H A The measured value of H A * The hardware processor 15P calculates the first attitude parameter H A * A second reference parameter P, which is a second attitude parameter associated with (t) I (H A * (t)) (see FIG. 15). The hardware processor 15P acquires the arm height H A is the measured value H A * A second attitude parameter P representing a target orientation that is a target of the implement orientation 41D when (t) is reached. I (t) and the second attitude parameter P I * The difference between (0) and the second reference parameter P I (H A * (t)) and the first reference parameter P I (H A * (0)) ΔP I (t) is equal to (P I (t)=P I * (0) + ΔP IThe hardware processor 15P determines the target orientation 41D (observation value P I * (t) is the target orientation (P I The first spool position is controlled so as to approach the direction indicated by (t).

[0083] 16 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 and executed by the hardware processor 15P, for example. First, the control target calculation module 151 calculates the rotation speed N of the engine 6 at an arbitrary time t. E (t) is obtained from the rotation speed detection sensor 6a, the operation amount φ(t) of the arm input member 63 (the movement of the operation lever 55 in the front-rear direction) at time t is obtained from the rotation detection sensor 18, and a first attitude parameter H A * (0) is obtained from the arm posture detection sensor 56, and a second posture parameter θ I * (0), θ R * (0), P I * (0) from the implement attitude detection sensor 57. That is, the hardware processor 15P acquires the detected rotation speed N E (t) is obtained. Parameter H A * (0), θ I * (0), θ R * (0), P I * (0) is processed by the feedback converter 152, which will be described later. <Feedforward control>

[0084] The control target calculation module 151 calculates the rotation speed N EBased on this, feedforward control is executed for the first hydraulic cylinder 49 and the second hydraulic cylinder 48. In the above-described 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, so that 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. In the implement posture electrical control, the control target calculation module 151 calculates the ratio between the second opening area AS2 and the first opening area AS1 so that the ratio of the amount of hydraulic oil flowing out of the first chamber CB1 of the first hydraulic cylinder 49 to the amount of hydraulic oil flowing into the fourth chamber CB4 of the second hydraulic cylinder 48 becomes the same as the above-mentioned first hydraulic cylinder = second hydraulic cylinder oil amount fluctuation ratio K0.

[0085] The control target calculation module 151 determines the second opening area AS2 based on the operation amount φ(t) of the operating lever 55 (the movement of the arm input member 63 in the front-rear direction). FIG. 18 shows an example of the correspondence relationship between the operation amount φ(t) of the operating lever 55 (the movement of the arm input member 63 in the front-rear direction) determined by the control target calculation module 151 and the second opening area AS2. Referring to FIG. 18, when the operation amount φ(t) is in the range of 0 to φ 1TH corresponds to the play when not operated, so the second opening area AS2 is determined to be 0. MAX -φ 2TH )~φ MAX If the second spool is operated between ATH1 and SAM2, it can be considered that the operation is fully performed taking into account the play, and the second opening area AS2 is determined to be the maximum value SAM2. When the operation amount φ(t) changes in the range of φ1TH to (φMAX-φ2TH), the second opening area AS2 is exponentially changed from ATH1 to SAM2 according to the magnitude of the operation amount φ(t). In this way, the hardware processor 15P is configured to determine the second spool position according to the second instruction (operation amount φ(t)) and obtain the second opening area AS2 based on the determined second spool position.

[0086] The second opening area AS2 is determined by the feedforward controller Cf v2 The hardware processor 15P controls the feedforward controller Cf v2 In executing the above, the hardware processor 15P determines a control amount u3 of the third pilot control valve 60 and a control amount u4 of the fourth pilot control valve 61 so that the second opening area of ​​the second control valve 20 becomes the above-mentioned value AS2, and outputs the control amount u3 to the solenoid 60s of the third pilot control valve 60 and outputs the control amount u4 to the solenoid 61s of the fourth pilot control valve 61. In this way, the hardware processor 15P is configured to control the second spool SPL2 so that the position of the second spool SPL2 becomes the second spool position determined in accordance with the second instruction (operation amount φ(t)).

[0087] The hardware processor 15P is configured to determine the first opening area AS1 to be a first reference area REF1 obtained by multiplying the second opening area AS2 by a predetermined ratio (first hydraulic cylinder=second hydraulic cylinder oil amount fluctuation ratio K0). Note that the first hydraulic cylinder=second hydraulic cylinder oil amount fluctuation ratio K0 is determined by the rotation speed N E This is because the arm 45 changes in accordance with the arm height H A On the other hand, the implement 41 must raise the implement tip 41T against gravity, so the rotation speed N E is small, that is, when the discharge amount from the hydraulic pump 11 is small, the arm height H A This is because the amount of fluctuation in the implement orientation 41D relative to the amount of fluctuation in the oil amount fluctuation ratio K0 of the first hydraulic cylinder=second hydraulic cylinder becomes smaller with respect to the control target. To take this effect into consideration, the control target calculation module 151 determines the first opening area AS1 from the second opening area AS2 so that AS1 / AS2 is equal to the value obtained by multiplying the correction gain K1 in Fig. 17 by the oil amount fluctuation ratio K0 of the first hydraulic cylinder=second hydraulic cylinder. The memory 15M stores the rotation speed N of the engine 6 as shown in Fig. 17. Eand the correction gain K1. The hardware processor 15P stores a third correspondence relationship between the detected rotation speed N E The correction gain K1 in FIG. 17 corresponds to 1 at the engine rotation speed N E 0 is the high idle speed of engine 6.

[0088] The hardware processor 15P determines the first opening area AS1 to be the second reference area REF2, which is the product of the first reference area REF1 and the correction gain K1. That is, the hardware processor 15P calculates the second reference area REF2 based on the following (Equation 1). However, the correction gain K1 may always be set to 1, and the first reference area REF1 may be used instead of the second reference area REF2 in the subsequent processing. REF2=K1×REF1=K1×K0×AS2...(Formula 1)

[0089] The second reference area REF2 (the first reference area REF1 when the correction gain K1 is not taken into account) is the feedforward controller Cf v1 The controller 15 is a feedforward controller Cf v1 In executing the above, the feedforward control amount (FF control amount) u1o of the first pilot control valve 65 and the 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 second reference area REF2 (the first reference area REF1 when the correction gain K1 is not taken into consideration), and the FF control amount u1o is output toward the solenoid 65s of the first pilot control valve 65, and the FF control amount u2o is output toward the solenoid 66s of the second pilot control valve 66. In this way, the hardware processor 15P controls the first spool SPL1 so that the first opening area AS1 approaches the second reference area REF2 (the first reference area REF1 when the correction gain K1 is not taken into consideration), thereby adjusting the implement orientation 41D to the target orientation (for example, P I (t)). <Feedback control>

[0090] Next, feedback control will be described. Referring to Fig. 12, Fig. 14, Fig. 15, and Fig. 16, the hardware processor 15P that executes the feedback converter 152 receives the arm height H A * The hardware processor 15P calculates the arm height H A * The second attitude 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 position detection sensor 56. J * (t) or the position P of the second hydraulic cylinder 48 A * (t) to arm height H A * (t). Then, refer to maps M1 to M3 to find the arm height H A * θ, which is the same timing as (t) I (t)=θ I * (0)+Δθ I (t), θ R (t)=θ R * (0)+Δθ R (t) or P I (t)=P I * (0) + ΔP I (t) is obtained as a target value of the second attitude parameter corresponding to the implement orientation 41D.

[0091] And the feedback controller cb v1The hardware processor 15P executes the above-mentioned process by detecting the detected value (θ I * (t), θ R * (t) or P I * (t)) is obtained by the feedback controller cb v1 The controller 15 executes the detection value (θ I * (t), θ R * (t) or P I * (t)) and the second attitude parameter (θ I (t), θ R (t) or P I When the deviation from the first spool position (t) is greater than or equal to a first threshold, feedback control is performed to reduce the deviation by controlling the first spool position. In other words, the feedback controller cb v1 The controller 15 executes the detection value (θ I * (t), θ R * (t) or P I * (t)) and the second attitude parameter (θ I (t), θ R (t) or P I When the deviation e from the reference area REF2 (t) is equal to or greater than the first threshold, the second opening area AS2 is feedback-controlled to change from the second reference area REF2 (the first reference area REF1 when the correction gain K1 is not taken into account) to the third reference area REF3. Based on this third reference area REF3, the feedback controller cb v1 The control amount (u1 * ,u2 * The detected value (θ I * (t), θ R * (t) or P I * (t)) and the second attitude parameter (θ I(t), θ R (t) or P I The deviation from the detected value (θ I * (t), θ R * (t) or P I * (t)) and the second attitude parameter (θ I (t), θ R (t) or P I The first threshold value is the absolute value of the difference e between the second posture parameter (t) and the second posture parameter (t). The first threshold value may be different depending on the type of the second posture parameter.

[0092] As described above, by performing feedback control in addition to the feedforward control, the controller 15 can detect the detected value (θ I * (t), θ R * (t) or P I * (t)) is converted into the second attitude parameter (θ I (t), θ R (t) or P I The hydraulic circuit 100 can be controlled so as to approach (t).

[0093] When the deviation becomes equal to or greater than the first threshold value, and the result of feedback control of the first opening area AS1 becomes equal to or less than a second threshold value that is smaller than the first threshold value, the hardware processor 15P ends the feedback control. The hardware processor 15P calculates a correction coefficient K2 by dividing the third reference area REF3 by the second reference area REF2 (the first reference area REF1 when the correction gain K1 is not considered). When the correction gain K1 is not considered, the hardware processor 15P determines the product of the first reference area REF1 determined after the feedback control is ended and the correction coefficient K2 to be the first opening area AS1 after the feedback control is ended. When the correction gain K1 is considered, the hardware processor 15P determines the product of the first reference area REF1 determined after the feedback control is ended and the correction gain K1 and the correction coefficient K2 to be the first opening area AS1 after the feedback control is ended. When the feedback control is not performed, the feedback controller cb v1 The output of the first control valve 25 is the control amount (u1 * ,u2 * ) will be 0. <Method of controlling a work vehicle>

[0094] Next, a method for controlling the work vehicle 1 according to this embodiment will be described. Fig. 19 is a flowchart showing the method for controlling the work vehicle 1. In step S1, the arm height H A A first instruction is received via the first input device 16 to perform electric control of the implement attitude to control the implement orientation 41D based on a first correspondence relationship in which a first attitude parameter representing the arm height H A A second instruction for changing the position is received via the second input device (operation lever 55, arm input member 63).

[0095] In step S3, in the control method, the hardware processor 15P calculates the arm height H A The first posture parameter H A * (0) is the arm height H A In step S3, in the control method, the hardware processor 15P calculates a second orientation parameter θ 1 representing an initial implement orientation 41D, which is an implement orientation 41D at the time when the second instruction is accepted after the first instruction is accepted. I * (0), θ R * (0), P I * (0) is calculated from the implement attitude detection sensor 57 configured to detect the implement orientation 41D.

[0096] In step S5, in the control method, the hardware processor 15P calculates a first posture parameter H A * The first reference parameter θ, which is the second attitude parameter associated with (0) I (H A * (0)), θ R (H A * (0)), P I (H A * In step S6, in the control method, the hardware processor 15P acquires the arm height H A In step S7, in the control method, the hardware processor 15P controls the second hydraulic cylinder 48 configured to control the arm height H A The output θ of the arm position detection sensor 56 for detecting J * (t), P A * (t) to arm height H AThe measured value of H A * Find (t).

[0097] In step S8, in the control method, the hardware processor 15P calculates a first attitude parameter H A * A second reference parameter θ, which is the second attitude parameter associated with (t). I (H A * (t)), θ R (H A * (t)), P I (H A * In step S9, in the control method, the hardware processor 15P acquires the arm height H A A second attitude parameter θ representing a target orientation that is a target of the implement orientation 41D when the measured value is I (t), θ R (t) or P I (t) and the second attitude parameter θ representing the starting implement orientation I * (0), θ R * (0), P I * The difference between (0) and the second reference parameter θ I (H A * (t)), θ R (H A * (t)), P I (H A * (t)) and the first reference parameter θ I (H A * (0)), θ R (H A * (0)), P I (H A * (0)) and Δθ I (t), Δθ R (t), ΔP IIn step S9, in the control method, the hardware processor 15P controls the first spool position of the first control valve 25 so that the implement orientation 41D approaches the target orientation. <Effects of the embodiment>

[0098] The hardware processor 15P of the work vehicle 1 in this embodiment can realize horizontal control by the hydraulic circuit 100 when raising the implement 41, and can realize horizontal control by the first pilot control valve 65, the second pilot control valve 66, the third pilot control valve 60, and the fourth pilot control valve 61 when lowering the implement 41. <Modification>

[0099] The above example is a case where the correspondence between the first attitude parameter and the second attitude parameter is directly expressed in the map M1 of Fig. 12. E The correspondence relationship between the first attitude parameter and the second attitude parameter for may be derived from the first correspondence relationship and at least one second correspondence relationship by using linear interpolation or the like as shown in Fig. 17. Fig. 20 shows the relationship for the rotation speed N E The hardware processor 15P calculates the correspondence between the first and second attitude parameters for the detected rotation speed N E Based on the above, a reference correspondence relationship is determined which is referred to from the first correspondence relationship and at least one of the second correspondence relationships. In Fig. 20, the reference correspondence relationship is indicated by a dashed line. This reference correspondence relationship is determined by calculating the detected rotation speed N E and high rotation speed N EH Speed ​​difference between the target rotation speed and N E and the slow rotation speed N EH The hardware processor 15P calculates the first posture parameter H A *The third reference parameter θ', which is the second attitude parameter associated with (0) I (H A * The hardware processor 15P acquires the first attitude parameter H A * The fourth reference parameter θ', which is the second attitude parameter associated with (t) I (H A * The hardware processor 15P acquires a second attitude parameter θ I (t) and the second attitude parameter θ representing the starting implement orientation I * The difference between (0) is the fourth reference parameter θ' I (H A * (t)) and the third reference parameter θ' I (H A * (0)) and Δθ I (t) is equal to (θ I (t)=θ I * (0)+Δθ I (t)) so that the target orientation (θ I The first spool position is controlled to determine the orientation (t) of the rotational axis.

[0100] 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.

[0101] The terms "member," "part," "element," "body," and "structure" may have multiple meanings, such as a single part or multiple parts.

[0102] 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."

[0103] 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."

[0104] 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.

[0105] 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 including the joint and including an arm tip that swingably supports the implement 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 pump configured to supply hydraulic fluid to the first hydraulic cylinder and the second hydraulic cylinder; an engine configured to drive the hydraulic pump; a rotation speed detection sensor for detecting a target rotation speed of the engine; a first control valve having a first spool, and configured to alternatively switch each of two oil chambers of the first hydraulic cylinder between a first supplied oil chamber that supplies the hydraulic oil and a first discharged oil chamber that discharges the hydraulic oil according to a first spool position that is a position of the first spool, and to adjust the amount of the hydraulic oil supplied to the first supplied oil chamber per unit time and the amount of the hydraulic oil discharged from the first discharged oil chamber per unit time according to the first spool position; an arm posture detection sensor for detecting the arm height; an implement attitude detection sensor for detecting an orientation of the implement; a storage device that stores a first correspondence relationship in which a first attitude parameter representing the arm height and a second attitude parameter representing the implement orientation are associated with each other; a processor configured to control the hydraulic pump, the engine, and the first control valve; A first input device configured to receive a first instruction for performing an implement attitude electrical control for controlling the orientation of the implement; a second input device configured to receive a second instruction to change the arm height; The processor, calculating, from an output of the arm posture detection sensor, the first posture parameter that represents an initial arm height, which is the arm height at a time point when the second instruction is accepted after the first instruction is accepted; After the first instruction is accepted, the second attitude parameter representing an initial implement orientation, which is the implement orientation at the time when the second instruction is accepted, is calculated from an output of the implement attitude detection sensor; obtaining a first reference parameter, the first reference parameter being the second posture parameter associated with the first posture parameter representing the starting arm height in the first correspondence relationship; Controlling the second hydraulic cylinder according to the second instruction; determining a measurement value of the arm height from an output of the arm posture detection sensor; obtaining a second reference parameter, the second reference parameter being associated with the first reference parameter representing the measurement value in the first correspondence relationship; determining the target orientation such that a difference between the second attitude parameter representing a target orientation that is a target for the implement orientation when the arm height becomes the measured value and the second attitude parameter representing the starting implement orientation is equal to a difference between the second reference parameter and the first reference parameter; controlling the first spool position so that the implement orientation approaches the target orientation; Work vehicle.

2. In the first correspondence relationship, the first attitude parameter and the second attitude parameter are associated with each other when the engine is rotated at a first rotation speed, the storage device stores at least one second correspondence relationship in which the first attitude parameter and the second attitude parameter are associated with each other when the implement attitude electrical control is performed in a state in which the engine is driven at at least one rotation speed different from the first rotation speed; The processor, determining a reference correspondence relationship to be referenced from the first correspondence relationship and the at least one second correspondence relationship based on the detected rotation speed of the engine; obtaining a third reference parameter, the third reference parameter being the second posture parameter associated with the first posture parameter representing the starting arm height in the reference correspondence relationship; obtaining a fourth reference parameter, the fourth reference parameter being the second posture parameter associated with the first posture parameter representing the measurement value in the reference correspondence relationship; controlling the first spool position to determine the target orientation such that a difference between the second attitude parameter representing the target orientation and the second attitude parameter representing the starting implement orientation is equal to a difference between the fourth reference parameter and the third reference parameter; A work vehicle according to claim 1.

3. a first cylinder hydraulic circuit connecting the first hydraulic cylinder and the hydraulic pump via the first control valve; a second control valve having a second spool, and configured to alternatively switch each of two oil chambers of the second hydraulic cylinder between a second supplied oil chamber that supplies the hydraulic oil and a second discharged oil chamber that discharges the hydraulic oil according to a second spool position that is a position of the second spool, and to adjust the amount of the hydraulic oil supplied to the second supplied oil chamber per unit time and the amount of the hydraulic oil discharged from the second discharged oil chamber per unit time according to the second spool position; a second cylinder hydraulic circuit connecting the second hydraulic cylinder and the hydraulic pump via the second control valve; a pressure control mechanism including a first pressure compensation valve provided in the first cylinder hydraulic circuit between the first control valve and the hydraulic pump, and a second pressure compensation valve provided in the second cylinder hydraulic circuit between the second control valve and the hydraulic pump; Further equipped with the first control valve is configured to change a first opening area, which is an area of ​​a first opening that communicates an oil passage that connects the first supplied oil chamber and the first control valve with an oil passage that connects the hydraulic pump and the first control valve, in accordance with the first spool position; the second control valve is configured to change a second opening area, which is an area of ​​a second opening of the second control valve that communicates an oil passage connecting the second supplied oil chamber and the second control valve with an oil passage connecting the hydraulic pump and the second control valve, in accordance with the second spool position; the pressure control mechanism controls the hydraulic pressure of the hydraulic oil output from the first opening to be lower by a first pressure than the hydraulic pressure of the hydraulic oil input to the first opening, and controls the hydraulic pressure of the hydraulic oil output from the second opening to be lower by the first pressure than the hydraulic pressure of the hydraulic oil input to the second opening, The processor, determining the second spool position according to the second instruction; controlling the second spool so that the position of the second spool is the determined second spool position; determining the second opening area based on the determined second spool position; determining the first opening area to be a first reference area that is a predetermined ratio of the second opening area; The first spool is controlled so that the first opening area approaches the first reference area, thereby causing the implement orientation to approach the target orientation. A work vehicle according to claim 1 or 2.

4. the storage device stores a third correspondence relationship between the rotation speed of the engine and a correction gain, The processor, acquiring a detected rotation speed of the engine detected by the rotation speed detection sensor; determining the correction gain corresponding to the detected rotation speed of the engine based on the third correspondence relationship; The work vehicle according to claim 3 , wherein the first opening area is determined to be a second reference area which is a product of the first reference area and the correction gain.

5. The processor, acquiring a detected value which is the second attitude parameter detected by the implement attitude detection sensor; The work vehicle according to claim 1 , wherein when a deviation of the detected value from the second attitude parameter representing the target orientation is equal to or greater than a first threshold value, the first spool position is feedback controlled so as to reduce the deviation.

6. The processor, acquiring a detected value which is the second attitude parameter detected by the implement attitude detection sensor; when a deviation of the detected value from the second attitude parameter representing the target orientation is equal to or greater than a first threshold, feedback control is performed to change the first opening area from the first reference area to a third reference area so as to reduce the deviation. A work vehicle according to claim 3.

7. The processor, acquiring a detected value which is the second attitude parameter detected by the implement attitude detection sensor; when a deviation of the detected value from the second attitude parameter representing the target orientation is equal to or greater than a first threshold, feedback control is performed to change the first opening area from the second reference area to a third reference area so as to reduce the deviation. A work vehicle according to claim 4.

8. The processor, when the deviation becomes equal to or greater than the first threshold value and, as a result of the feedback control of the first opening area, the deviation becomes equal to or less than a second threshold value that is smaller than the first threshold value, the feedback control is terminated; Calculating a correction coefficient by dividing the third reference area by the first reference area; determining a product of a first reference area determined after the feedback control is terminated and the correction coefficient as the first opening area after the feedback control is terminated; A work vehicle according to claim 6.

9. The processor, when the deviation becomes equal to or greater than the first threshold value and, as a result of the feedback control of the first opening area, the deviation becomes equal to or less than a second threshold value that is smaller than the first threshold value, the feedback control is terminated; Calculating a correction coefficient by dividing the third reference area by the second reference area; determining the first opening area to be a fourth reference area which is a product of the first reference area, the correction gain, and the correction coefficient; A work vehicle according to claim 7.

10. A first oil passage that connects a first chamber of the first hydraulic cylinder into which the hydraulic oil flows when the tip of the implement is tilted downward and the hydraulic pump via the first control valve; A second oil passage connecting a second chamber of the first hydraulic cylinder into which the hydraulic oil flows when the tip of the implement is tilted upward and the first control valve; a third oil passage connecting a third chamber of the second hydraulic cylinder into which the hydraulic oil flows when the arm tip is raised and the hydraulic pump via the second control valve; a fourth oil passage connecting a fourth chamber of the second hydraulic cylinder into which the hydraulic oil flows when the arm tip is lowered and the second control valve; A bypass oil passage configured to connect the fourth oil passage and the first oil passage; A switching mechanism configured to control connection and disconnection between the fourth oil passage and the first oil passage by the bypass oil passage; Further equipped with The switching mechanism includes: a first switching valve that is provided in the fourth oil passage between a first joint that connects the bypass oil passage and the fourth oil passage and the second control valve, has a first pilot port, and is configured to cut off the connection between the second control valve and the fourth chamber via the fourth oil passage when a pilot oil pressure equal to or greater than a first threshold pressure is applied to the first pilot port, and to connect the second control valve and the fourth chamber via the fourth oil passage when a pilot oil pressure smaller than the first threshold pressure is applied to the first pilot port; a solenoid valve switchable between a first position connecting the first pilot port to an oil passage capable of applying a pilot pressure equal to or greater than the first threshold pressure to the first pilot port and a second position connecting the first pilot port to a hydraulic oil tank; Equipped with The first input device is configured to receive a third instruction for performing an implement attitude machine control for controlling an orientation of the implement by changing a connection relationship of a hydraulic circuit; The processor controls the switching mechanism to connect the fourth oil passage and the first oil passage when the third instruction is received and the second instruction to increase the arm height is received. A work vehicle according to claim 1.

11. A first oil passage that connects a first chamber of the first hydraulic cylinder into which the hydraulic oil flows when the tip of the implement is tilted downward and the hydraulic pump via the first control valve; A second oil passage connecting a second chamber of the first hydraulic cylinder into which the hydraulic oil flows when the tip of the implement is tilted upward and the first control valve; a third oil passage connecting a third chamber of the second hydraulic cylinder into which the hydraulic oil flows when the arm tip is raised and the hydraulic pump via the second control valve; a fourth oil passage connecting a fourth chamber of the second hydraulic cylinder into which the hydraulic oil flows when the arm tip is lowered and the second control valve; A bypass oil passage configured to connect the fourth oil passage and the first oil passage; A switching mechanism configured to control connection and disconnection between the fourth oil passage and the first oil passage by the bypass oil passage; Further equipped with The switching mechanism includes: a first switching valve that is provided in the fourth oil passage between a first joint that connects the bypass oil passage and the fourth oil passage and the second control valve, has a first pilot port, and is configured to cut off the connection between the second control valve and the fourth chamber via the fourth oil passage when a pilot oil pressure equal to or greater than a first threshold pressure is applied to the first pilot port, and to connect the second control valve and the fourth chamber via the fourth oil passage when a pilot oil pressure smaller than the first threshold pressure is applied to the first pilot port; a solenoid valve switchable between a first position connecting the first pilot port to an oil passage capable of applying a pilot pressure equal to or greater than the first threshold pressure to the first pilot port and a second position connecting the first pilot port to a hydraulic oil tank; Equipped with The first input device is configured to receive a third instruction for performing an implement attitude machine control for controlling an orientation of the implement by changing a connection relationship of a hydraulic circuit; The processor controls the switching mechanism to connect the fourth oil passage and the first oil passage when the third instruction is received and the second instruction to increase the arm height is received. The work vehicle according to claim 2.

12. Further comprising a third input device configured to receive a third instruction for changing the implement orientation; the first correspondence relationship represents a correspondence relationship between the arm height and the implement orientation that changes when the arm height is set by the second input device to a reference height that is a reference for the arm height, and the implement orientation is set by the third input device to a reference implement orientation that is a reference for the implement orientation, and then the implement attitude machine control is executed; A work vehicle according to claim 10.

13. Further comprising a third input device configured to receive a third instruction for changing the implement orientation; the first correspondence relationship represents a correspondence relationship between the arm height and the implement orientation that changes when, when the rotational speed of the engine is a first rotational speed, the arm height is set by the second input device to a reference height that is a reference for the arm height, and the implement orientation is set by the third input device to a reference implement orientation that is a reference for the implement orientation, and then the implement attitude machine control is executed; the at least one second correspondence relationship represents a correspondence relationship between the arm height and the implement orientation that changes when the rotational speed of the engine is at least one second rotational speed different from the first rotational speed, the arm height is set by the second input device to a reference height that is a reference for the arm height, and the implement orientation is set by the third input device to a reference implement orientation that is a reference for the implement orientation, and then the implement attitude machine control is executed; A work vehicle according to claim 11.

14. the first input device includes a switch electrically connected to the processor for turning on / off the implement attitude electric control; the second input device is an operation lever configured to receive an upward command to increase the arm height and a downward command to decrease the arm height, When the implement attitude electric control is turned on by the switch and the second input device receives the lowering command, the processor switches the solenoid valve to a second position. A work vehicle according to any one of claims 10 to 13.

15. The switch is configured to turn the implement attitude machine control ON / OFF, When the implement attitude machine control is turned on by the switch and the ascent command is received by the second input device, the processor switches the solenoid valve to the first position, When the implement attitude machine control is turned OFF by the switch, the processor switches the solenoid valve to the second position regardless of the operation of the second input device. A work vehicle as claimed in claim 14.

16. the switch is configured to set both the implement attitude electric control and the implement attitude machine control to OFF, and to set both the implement attitude electric control and the implement attitude machine control to ON; A work vehicle as claimed in claim 15.

17. A first oil passage that connects a first chamber of the first hydraulic cylinder into which the hydraulic oil flows when the tip of the implement is tilted downward and the hydraulic pump via the first control valve; A second oil passage connecting a second chamber of the first hydraulic cylinder into which the hydraulic oil flows when the tip of the implement is tilted upward and the first control valve; a third oil passage connecting a third chamber of the second hydraulic cylinder into which the hydraulic oil flows when the arm tip is raised and the hydraulic pump via the second control valve; a fourth oil passage connecting a fourth chamber of the second hydraulic cylinder into which the hydraulic oil flows when the arm tip is lowered and the second control valve; A bypass oil passage configured to connect the fourth oil passage and the first oil passage; an additional bypass oil passage connecting the fourth oil passage between the first switching valve and the second control valve and the second oil passage; a first connection passage connecting the additional bypass oil passage between a second joint connecting the fourth oil passage and the additional bypass oil passage and the third switching valve and the second switching valve; a second connection passage connecting the bypass oil passage between a third joint connecting the bypass oil passage and the first oil passage and the second switching valve; and A switching mechanism configured to control connection and disconnection between the fourth oil passage and the first oil passage by the bypass oil passage; Further equipped with The switching mechanism includes: a first switching valve that is provided in the fourth oil passage between a first joint that connects the bypass oil passage and the fourth oil passage and the second control valve, has a first pilot port, and is configured to cut off the connection between the second control valve and the fourth chamber via the fourth oil passage when a pilot oil pressure equal to or greater than a first threshold pressure is applied to the first pilot port, and to connect the second control valve and the fourth chamber via the fourth oil passage when a pilot oil pressure smaller than the first threshold pressure is applied to the first pilot port; a solenoid valve switchable between a first position connecting the first pilot port to an oil passage capable of applying a pilot pressure equal to or greater than the first threshold pressure to the first pilot port and a second position connecting the first pilot port to a hydraulic oil tank; a second changeover valve that is provided in the bypass oil passage, and that is configured to switch to a first communication position that communicates between the first joint and the third joint when a first oil pressure in the bypass oil passage between the first joint and the second changeover valve is greater than a second oil pressure in the first connection passage, and to switch to a first blocking position that blocks communication between the first joint and the third joint when the second oil pressure is equal to or lower than the first oil pressure; a third changeover valve that is provided in the additional bypass oil passage, and that is configured to switch to a second communication position that connects a fourth joint connecting the second oil passage and the additional bypass oil passage with the second joint when a third oil pressure of the additional bypass oil passage between the second joint and the third changeover valve is lower than a fourth oil pressure of the second connection passage, and to switch to a second blocking position that blocks communication between the second joint and the fourth joint when the fourth oil pressure is equal to or lower than the third oil pressure; Further equipped with The first input device is configured to receive a third instruction for performing an implement attitude machine control for controlling an orientation of the implement by changing a connection relationship of a hydraulic circuit; the processor controls the switching mechanism to connect the fourth oil passage and the first oil passage when the third instruction is received and the second instruction to increase the arm height is received; The second switching valve is controlled to switch between the first communicating position and the first blocking position so that an amount of hydraulic oil output from the second control valve to the second supplied oil chamber per unit time multiplied by the ratio is output from the first control valve to the first supplied oil chamber per unit time. A work vehicle according to claim 3.

18. The arm posture detection sensor is a rotation angle detection sensor configured to detect a rotation angle of a link that swingably supports the arm, The implement attitude detection sensor is a first inertial measurement unit (IMU) attached to the implement; a second inertial measurement unit (IMU) attached to the vehicle body; Equipped with The first posture parameter is a parameter representing the arm height converted from the rotation angle, the second attitude parameter is an angle between the vehicle reference direction and the implement orientation, which is calculated from a first angle between the gravity orientation detected from the output signal of the second inertial measurement unit and a vehicle reference direction for defining the attitude of the vehicle body with respect to the gravity orientation, and a second angle between the gravity orientation detected from the output signal of the first inertial measurement unit, the implement orientation, and the gravity orientation. A work vehicle according to claim 1 or 2.

19. 3. The work vehicle according to claim 2, wherein the processor determines, as the reference correspondence relationship, from among the first correspondence relationship and the at least one second correspondence relationship, a correspondence relationship that corresponds to a rotational speed among the first rotational speed and the at least one rotational speed that is closest to the detected rotational speed of the engine.

20. a first instruction is received for performing implement attitude electrical control for controlling an implement orientation based on a first correspondence relationship in which a first attitude parameter representing an arm height, which is the height of a travel device of a work vehicle relative to a ground contact surface, and a second attitude parameter representing an implement orientation in which a tip of the implement faces from a joint of the implement are associated with each other; Accepting a second instruction to change the arm height; calculating the first posture parameter representing an initial arm height, which is the arm height at a time point when the second instruction is accepted after the first instruction is accepted, from an output of an arm posture detection sensor configured to detect the arm height; After the first instruction is accepted, the second attitude parameter representing an initial implement orientation, which is the implement orientation at the time when the second instruction is accepted, is calculated from an output of an implement attitude detection sensor configured to detect the implement orientation; obtaining a first reference parameter, the first reference parameter being the second posture parameter associated with the first posture parameter representing the starting arm height in the first correspondence relationship; controlling a second hydraulic cylinder configured to control the arm height according to the second instruction; determining a measurement value of the arm height from an output of an arm posture detection sensor for detecting the arm height; obtaining a second reference parameter, the second reference parameter being associated with the first reference parameter representing the measurement value in the first correspondence relationship; determining the target orientation such that a difference between the second attitude parameter representing a target orientation that is a target for the implement orientation when the arm height becomes the measured value and the second attitude parameter representing the starting implement orientation is equal to a difference between the second reference parameter and the first reference parameter; A method for controlling a work vehicle, comprising: controlling a first spool position of a first control valve configured to alternatively switch each of two oil chambers of a first hydraulic cylinder between a first supplied oil chamber that supplies the hydraulic oil and a first discharged oil chamber that discharges the hydraulic oil depending on a first spool position that is a position of the first spool; and adjusting the amount of the hydraulic oil supplied per unit time to the first supplied oil chamber and the amount of the hydraulic oil discharged per unit time from the first discharged oil chamber depending on the first spool position, so that the implement orientation approaches the target orientation.

21. The apparatus includes a storage device configured to store a first correspondence relationship in which a first attitude parameter representing an arm height, which is a height of a traveling device of a work vehicle relative to a ground contact surface, and a second attitude parameter representing an implement direction in which a tip end of the implement faces from a joint of the implement, and a processor; The processor, receiving, from a first input device, a first instruction for performing an electric control of an implement attitude that controls an orientation of the implement based on the first correspondence relationship; receiving a second instruction from a second input device to change the arm height; After the first instruction is accepted, the first attitude parameter representing a starting arm height, which is the arm height at the time when the second instruction is accepted, is calculated from an output of an arm attitude detection sensor configured to detect the arm height; After the first instruction is received, the second attitude parameter representing an initial implement orientation, which is the implement orientation at the time when the second instruction is received, is calculated from an output of an implement attitude detection sensor configured to detect the implement orientation; obtaining a first reference parameter, the first reference parameter being the second posture parameter associated with the first posture parameter representing the starting arm height in the first correspondence relationship; a second hydraulic cylinder configured to control the arm height according to the second instruction; receiving an output of an arm posture detection sensor for detecting the arm height, and determining a measurement value of the arm height; obtaining a second reference parameter, the second reference parameter being associated with the first reference parameter representing the measurement in the first correspondence; determining the target orientation such that a difference between the second attitude parameter representing a target orientation that is a target for the implement orientation when the arm height becomes the measured value and the second attitude parameter representing the starting implement orientation is equal to a difference between the second reference parameter and the first reference parameter; A first control valve has a first spool, and is configured to alternatively switch two oil chambers of the first hydraulic cylinder between a first supplied oil chamber that supplies the hydraulic oil and a first discharged oil chamber that discharges the hydraulic oil according to a first spool position, and to adjust the supply amount of the hydraulic oil per unit time to the first supplied oil chamber and the discharge amount of the hydraulic oil per unit time from the first discharged oil chamber according to the first spool position, and controls the first spool position so that the implement orientation approaches the target orientation. It is configured as follows: Work vehicle controller.

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