WORK MACHINE AND METHOD FOR CONTROLLING WORK MACHINE

Abstract

A work machine includes a vehicle body, a work implement movably supported relative to the vehicle body, an actuator connected to the work implement, and a controller. The actuator is configured to cause the work implement to move. The controller is configured to perform an automatic control to control the actuator so that a height of the work implement in a gravity direction is maintained even when a posture of the vehicle body changes, determine whether the work machine is in a non-working state in which the work machine does not perform work with the work implement, and stop the automatic control when the work machine is in the non-working state.

Claims

1. A work machine comprising: a vehicle body: a work implement movably supported relative to the vehicle body: an actuator connected to the work implement, the actuator being configured to cause the work implement to move; and a controller configured to perform an automatic control to control the actuator so that a height of the work implement in a gravity direction is maintained even when a posture of the vehicle body changes, determine whether the work machine is in a non-working state in which the work machine does not perform work with the work implement, and stop the automatic control when the work machine is in the non-working state.

2. The work machine according to claim 1, further comprising: an operating device manually operable by an operator to cause the work implement to move, the controller being configured to control the actuator according to a manual operation of the operating device upon stopping the automatic control.

3. The work machine according to claim 1, wherein the vehicle body is configured to switch a travel mode between forward, reverse, and neutral, and the controller is configured to determine whether the work machine is in the non-working state according to the travel mode of the vehicle body.

4. The work machine according to claim 3, wherein the controller is configured to stop the automatic control when the travel mode is switched from forward to neutral or from neutral to reverse.

5. The work machine according to claim 1, wherein the controller is configured to determine whether the work machine is in the non-working state according to a position of the work implement.

6. The work machine according to claim 5, wherein the actuator includes a lift cylinder, the lift cylinder being configured to cause the work implement to move up and down, and the controller is configured to stop the automatic control when a length of the lift cylinder is less than or equal to a predetermined length threshold.

7. The work machine according to claim 1, wherein the controller is configured to acquire a vehicle speed of the work machine, and stop the automatic control when the vehicle speed is greater than or equal to a predetermined speed threshold.

8. The work machine according to claim 1, wherein the controller is configured to determine whether a predetermined reactivation condition is satisfied after the automatic control is stopped, and reactivate the automatic control when the predetermined reactivation condition is satisfied.

9. A method for controlling a work machine that includes a vehicle body, a work implement movably supported relative to the vehicle body, and an actuator connected to the work implement and configured to cause the work implement to move, the method comprising: performing an automatic control to control the actuator so that a height of the work implement in a gravity direction is maintained even when a posture of the vehicle body changes: determining whether the work machine is in a non-working state in which the work machine does not perform work with the work implement; and stopping the automatic control when the work machine is in the non-working state.

10. The method according to claim 9, further comprising: acquiring an operation signal indicative of a manual operation from an operating device, the operating device being operable by an operator to cause the work implement to move: and controlling the actuator according to the manual operation of the operating device upon stopping the automatic control.

11. The method according to claim 9, wherein the vehicle body is configured to switch a travel mode between forward, reverse, and neutral, and the method further comprises determining whether the work machine is in the non-working state according to the travel mode.

12. The method according to claim 11, wherein the controller is configured to stop the automatic control when the travel mode is switched from forward to neutral or from neutral to reverse.

13. The method according to claim 9, further comprising: determining whether the work machine is in the non-working state according to a position of the work implement.

14. The method according to claim 13, wherein the actuator includes a lift cylinder, the lift cylinder being configured to cause the work implement to move up and down, and the method further comprises stopping the automatic control when a length of the lift cylinder is less than or equal to a predetermined length threshold.

15. The method according to claim 9, further comprising: acquiring a vehicle speed of the work machine; and stopping the automatic control when the vehicle speed is greater than or equal to a predetermined speed threshold.

16. The method according to claim 9, further comprising: determining whether a predetermined reactivation condition is satisfied after the automatic control is stopped; and reactivating the automatic control when the predetermined reactivation condition is satisfied.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0009] FIG. 1 is a side view of a work machine according to an embodiment.

[0010] FIG. 2 is a perspective view of a front part of the work machine.

[0011] FIG. 3 is a schematic diagram illustrating a drive system and a control system of the work machine.

[0012] FIG. 4 is a schematic rear view of the work machine illustrating a posture of a work implement.

[0013] FIG. 5 is a schematic plan view of the work machine illustrating a posture of the work implement.

[0014] FIG. 6 is a schematic enlarged side view of the work machine illustrating a posture of the work implement.

[0015] FIG. 7 is a schematic plan view of the work machine illustrating a posture of the work implement.

[0016] FIG. 8 is a schematic plan view of the work machine illustrating a posture of the work implement.

[0017] FIG. 9 is a schematic side view illustrating a vehicle body coordinate system of the work machine.

[0018] FIG. 10 is a schematic rear view illustrating the vehicle body coordinate system of the work machine.

[0019] FIG. 11 is a flowchart illustrating processes of an automatic control of the work implement.

[0020] FIG. 12 is a schematic side view illustrating the vehicle body coordinate system of the work machine.

[0021] FIG. 13 is flowchart illustrating processes for limiting the automatic control.

[0022] FIG. 14A is a front view schematically illustrating a configuration of the work machine.

[0023] FIG. 14B is a front view schematically illustrating the configuration of the work machine.

DETAILED DESCRIPTION OF EMBODIMENTS

[0024] An embodiment of the present disclosure will be described below with reference to the drawings. FIG. 1 is a side view of a work machine 1 according to the embodiment. FIG. 2 is a perspective view of a front part of the work machine 1. The work machine 1 according to the present embodiment is a motor grader. As illustrated in FIG. 1, the work machine 1 includes a vehicle body 2 and a work implement 3. The work implement 3 is supported so as to be movable with respect to the vehicle body 2. The vehicle body 2 includes a vehicle body frame 4, a tandem drive 5, front wheels 6, and rear wheels 7A and 7B.

[0025] The vehicle body frame 4 supports the front wheels 6 and the work implement 3. The vehicle body frame 4 includes a front frame 11 and a rear frame 12. The rear frame 12 is connected to the front frame 11. The front frame 11 is configured to articulate to the left and right with respect to the rear frame 12. In the following description, the front, rear, left, and right directions means the front, rear, left, and right directions of the vehicle body 2 while the articulation angle is zero, that is, while the front frame 11 and the rear frame 12 are straight.

[0026] A cab 13 and a power compartment 14 are disposed on the rear frame 12. An unillustrated operator's seat is disposed in the cab 13. A drive system which will be described below is disposed in the power compartment 14. The front frame 11 extends forward from the rear frame 12. The front wheels 6 are attached to the front frame 11.

[0027] The tandem drive 5 is connected to the rear frame 12. The tandem drive 5 supports the rear wheels 7A and 7B and drives the rear wheels 7A and 7B. The tandem drive 5 includes a rear axis 10 that extends in the left-right direction. The tandem drive 5 supports the rear frame 12 of the vehicle body frame 4 so that the rear frame 12 is swingable about the rear axis 10. When the front wheels 6 move up and down due to undulations of a road surface that is not graded by the work implement 3, the vehicle body frame 4 swings about the rear axis 10 (see FIG. 9).

[0028] The rear wheels 7A and 7B include a pair of first rear wheels 7A and a pair of second rear wheels 7B. In FIG. 1, only the first rear wheel 7A at the left side and the second rear wheel 7B at the left side are illustrated. The second rear wheels 7B are disposed behind the first rear wheels 7A. The rear axis 10 is disposed between the first rear wheels 7A and the second rear wheels 7B. The rear axis 10 serves as the center of swing of the vehicle body frame 4 with respect to the tandem drive 5.

[0029] The work implement 3 is movably connected to the vehicle body 2. The work implement 3 includes a supporting member 15 and a blade 16. The supporting member 15 is movably connected to the vehicle body 2. The supporting member 15 supports the blade 16. The supporting member 15 includes a drawbar 17 and a circle 18. The drawbar 17 and the circle 18 are disposed below the front frame 11.

[0030] As illustrated in FIG. 2, the drawbar 17 is connected to a shaft support part 19 of the front frame 11. The shaft support part 19 is disposed at a front part of the front frame 11. The drawbar 17 extends rearward from the front part of the front frame 11. The drawbar 17 is supported so as to be swingable at least in the up-down direction and the left-right direction of the vehicle body 2 with respect to the front frame 11. For example, the shaft support part 19 includes a ball joint. The drawbar 17 is rotatably connected to the front frame 11 via the ball joint.

[0031] The circle 18 is connected to a rear part of the drawbar 17. The circle 18 is supported so as to be rotatable with respect to the drawbar 17. The blade 16 is connected to the circle 18. The blade 16 is supported by the drawbar 17 via the circle 18. The blade 16 is supported by the circle 18 so as to be rotatable about a tilt shaft 21. The tilt shaft 21 extends in the left-right direction. The blade 16 is supported by the circle 18 so as to be slidable in the left-right direction.

[0032] The work machine 1 includes a plurality of actuators 22 to 27 for changing the posture of the work implement 3. The plurality of actuators 22 to 27 include a plurality of hydraulic cylinders 22 to 26. The plurality of hydraulic cylinders 22 to 26 are connected to the work implement 3. The plurality of hydraulic cylinders 22 to 26 extend and contract due to hydraulic pressure. The plurality of hydraulic cylinders 22 to 26 extend and contract, thereby changing the posture of the work implement 3 with respect to the vehicle body 2. In the following explanation, the extension and contraction of the hydraulic cylinder is referred to as a stroke motion.

[0033] Specifically, the plurality of hydraulic cylinders 22 to 26 include a left lift cylinder 22, a right lift cylinder 23, a drawbar shift cylinder 24, a blade tilt cylinder 25, and a blade shift cylinder 26. The left lift cylinder 22 and the right lift cylinder 23 are disposed apart from each other in the left-right direction. The left lift cylinder 22 is connected to a left part of the drawbar 17. The right lift cylinder 23 is connected to a right part of the drawbar 17. The left lift cylinder 22 and the right lift cylinder 23 are connected so as to be swingable to the left and right with respect to the draw bar 17.

[0034] The left lift cylinder 22 and the right lift cylinder 23 are connected so as to be swingable to the left and right with respect to the front frame 11. Specifically, the left lift cylinder 22 and the right lift cylinder 23 are connected to the front frame 11 via a lifter bracket 29. The lifter bracket 29 is connected to the front frame 11. The lifter bracket 29 supports the left lift cylinder 22 and the right lift cylinder 23 so that the left lift cylinder 22 and the right lift cylinder 23 are swingable to the left and right. Due to the stroke motions of the left lift cylinder 22 and the right lift cylinder 23, the drawbar 17 swings up and down about the shaft support part 19. As a result, the blade 16 moves up and down.

[0035] The drawbar shift cylinder 24 is connected to the drawbar 17 and the front frame 11. The drawbar shift cylinder 24 is connected to the front frame 11 via the lifter bracket 29. The drawbar shift cylinder 24 is connected so as to be swingable with respect to the front frame 11. The drawbar shift cylinder 24 is connected so as to be swingable with respect to the drawbar 17. The drawbar shift cylinder 24 extends diagonally downward from the front frame 11 toward the drawbar 17. The drawbar shift cylinder 24 extends to the left and right from one side to the opposite side of the front frame 11. Due to the stroke motion of the drawbar shift cylinder 24, the drawbar 17 swings to the left and right about the shaft support part 19.

[0036] As illustrated in FIG. 1, the blade tilt cylinder 25 is connected to the circle 18 and the blade 16. The blade 16 rotates about the tilt shaft 21 due to the stroke motion of the blade tilt cylinder 25. As illustrated in FIG. 2, the blade shift cylinder 26 is connected to the circle 18 and the blade 16. The blade 16 slides to the left and right with respect to the circle 18 due to the stroke motion of the blade shift cylinder 26.

[0037] The plurality of actuators 22 to 27 include a rotary actuator 27. The rotary actuator 27 is connected to the drawbar 17 and the circle 18. The rotary actuator 27 causes the circle 18 to rotate with respect to the drawbar 17. As a result, the blade 16 rotates about a rotation axis that extends in the up-down direction.

[0038] FIG. 3 is a schematic diagram illustrating a drive system 8 and a control system 9 of the work machine 1. As illustrated in FIG. 3, the work machine 1 includes a drive source 31, a hydraulic pump 32, a power transmission device 33, and a control valve 34. The drive source 31 is, for example, an internal combustion engine. Alternatively, the drive source 31 may be an electric motor or a hybrid of an internal combustion engine and an electric motor. The hydraulic pump 32 is driven by the drive source 31 to discharge hydraulic fluid.

[0039] The control valve 34 is connected to the hydraulic pump 32 and the plurality of hydraulic cylinders 22 to 26 through a hydraulic circuit. The control valve 34 includes a plurality of valves respectively connected to the plurality of hydraulic cylinders 22 to 26. The control valve 34 controls the flow rate of hydraulic fluid supplied from the hydraulic pump 32 to the plurality of hydraulic cylinders 22 to 26.

[0040] In the present embodiment, the rotary actuator 27 is a hydraulic motor. The control valve 34 is connected to the hydraulic pump 32 and the rotary actuator 27 through a hydraulic circuit. The control valve 34 controls the flow rate of hydraulic fluid supplied from the hydraulic pump 32 to the rotary actuator 27. The rotary actuator 27 may be an electric motor.

[0041] The power transmission device 33 transmits the driving force from the drive source 31 to the rear wheels 7A and 7B. The power transmission device 33 may include a torque converter and/or a plurality of speed change gears. Alternatively, the power transmission device 33 may be a transmission such as a hydraulic static transmission (HST) or a hydraulic mechanical transmission (HMT). The work machine 1 includes a shift operating member 47. The shift operating member 47 is operable at a neutral position N, a forward position F, and a reverse position R. The power transmission device 33 switches a travel mode between forward, reverse, and neutral according to the operating position of the shift operating member 47.

[0042] As illustrated in FIG. 3, the work machine 1 includes an operating device 35 and a controller 36. The operating device 35 is operable by an operator for changing the posture of the work implement 3. The posture of the work implement 3 indicates a position and an orientation of the blade 16 with respect to the vehicle body 2. FIG. 4 is a schematic rear view of the work machine 1 illustrating the posture of the work implement machine 3. As illustrated in FIG. 4, the height of a left end portion 161 and the height of a right end portion 162 of the blade 16 are changed according to an operation of the operating device 35.

[0043] A yaw angle 1, a pitch angle 2, and a roll angle 3 of the drawbar 17 are changed according to an operation of the operating device 35. FIG. 5 is a schematic plan view of the work machine 1 illustrating the posture of the work implement 3. As illustrated in FIG. 5, the yaw angle 1 of the drawbar 17 is a tilt angle of the drawbar 17 in the left-right direction with respect to the front-rear direction of the vehicle body 2. The yaw angle 1 of the drawbar 17 may be a tilt angle of the drawbar 17 in the left-right direction with respect to the front-rear direction of the front frame 11. The position of the blade 16 in the left-right direction changes according to the yaw angle 1 of the drawbar 17.

[0044] FIG. 6 is a schematic side view of the work machine 1 illustrating the posture of the work implement 3. As illustrated in FIG. 6, the pitch angle 2 of the drawbar 17 is a tilt angle of the drawbar 17 in the up-down direction with respect to the front-rear direction of the vehicle body 2. As illustrated in FIG. 4, the roll angle 3 of the drawbar 17 is a tilt angle of the drawbar 17 about a roll axis Al that extends in the front-rear direction of the vehicle body 2.

[0045] According to an operation of the operating device 35, a rotation angle 4 of the circle 18, a tilt angle 5 of the blade 16, and a shift amount W1 of the blade 16 are changed. FIG. 7 is a schematic plan view of the work machine 1 illustrating the posture of the work implement 3. As illustrated in FIG. 7, the rotation angle 4 of the circle 18 is the rotation angle 4 of the circle 18 with respect to the front-rear direction of the vehicle body 2. As illustrated in FIG. 6, the tilt angle 5 of blade 16 is a tilt angle of the blade 16 about the tilt shaft 21 that extends in the left-right direction. FIG. 8 is a schematic plan view of the work machine 1 illustrating the posture of the work implement 3. As illustrated in FIG. 8, the shift amount W1 of the blade 16 is an amount by which the blade 16 slides in the left-right direction with respect to the circle 18.

[0046] The operating device 35 includes a plurality of operating members 41 to 46. The plurality of operating members 41 to 46 are provided respectively corresponding to the left lift cylinder 22, the right lift cylinder 23, the drawbar shift cylinder 24, the blade tilt cylinder 25, the blade shift cylinder 26, and the rotary actuator 27.

[0047] The plurality of operating members 41 to 46 include a left lift lever 41, a right lift lever 42, a drawbar shift lever 43, a rotation lever 44, a blade tilt lever 45, and a blade shift lever 46. The left lift cylinder 22 extends and contracts according to an operation of the left lift lever 41. The right lift cylinder 23 extends and contracts according to an operation of the right lift lever 42.

[0048] The drawbar shift cylinder 24 extends and contracts according to an operation of the drawbar shift lever 43. The rotary actuator 27 rotates according to an operation of the rotation lever 44. The blade tilt cylinder 25 extends and contracts according to an operation of the blade tilt lever 45. The blade shift cylinder 26 extends and contracts according to an operation of the blade shift lever 46. Each of the plurality of operating members 41 to 46 outputs a signal indicative of the operation by the operator for each of the operating members 41 to 46.

[0049] The controller 36 controls the drive source 31 and the power transmission device 33, thereby causing the work machine 1 to travel. Further, the controller 36 controls the hydraulic pump 32 and the control valve 34, thereby causing the work implement 3 to move. The controller 36 includes a processor 37 and a storage device 38. The processor 37 is, for example, a CPU and executes a program for controlling the work machine 1. The storage device 38 includes a memory such as a RAM or a ROM, and an auxiliary storage devices such as an SSD or an HDD. The storage device 38 stores programs and data for controlling the work machine 1.

[0050] As illustrated in FIG. 3, the work machine 1 includes a work implement sensor 48 for detecting the posture of the work implement 3 described above. The work implement sensor 48 includes a plurality of sensors S1 to S8. The plurality of sensors S1 to S8 are, for example, magnetic sensors. The plurality of sensors S1 to S8 may be sensors of another type such as an optical sensor. The plurality of sensors S1 to S5 detect stroke lengths of the plurality of hydraulic cylinders 22 to 26 described above. The plurality of sensors S1 to S5 include a left lift sensor S1, a right lift sensor S2, a drawbar shift sensor S3, a blade tilt sensor S4, and a blade shift sensor S5.

[0051] The left lift sensor S1 detects a stroke length of the left lift cylinder 22. The right lift sensor S2 detects a stroke length of the right lift cylinder 23. The drawbar shift sensor S3 detects a stroke length of the drawbar shift cylinder 24. The blade tilt sensor S4 detects a stroke length of the blade tilt cylinder 25. The blade shift sensor S5 detects a stroke length of the blade shift cylinder 26.

[0052] The plurality of sensors S1 to S8 include a rotation sensor S6. The rotation sensor S6 detects the rotation angle 4 of the circle 18. The plurality of sensors S1 to S8 output signals indicative of the stroke lengths and the rotation angle 4 detected by the respective sensors. The plurality of sensors S1 to S8 include a left cylinder angle sensor S7 and a right cylinder angle sensor S8. The left cylinder angle sensor S7 detects a swing angle of the left lift cylinder 22 in the left-right direction with respect to the lifter bracket 29. The right cylinder angle sensor S8 detects a swing angle of the right lift cylinder 23 in the left-right direction with respect to the lifter bracket 29. By means of these sensors S1 to S8, a posture of the drawbar 17 with respect to the vehicle body 2 is detected and a posture of the blade 16 with respect to the draw bar 17 is detected. That is, the posture of the blade 16 with respect to the vehicle body 2 is detected by these sensors S1 to S8.

[0053] The work machine 1 includes a vehicle body sensor 49 and a vehicle speed sensor 50. The vehicle speed sensor 50 detects the vehicle speed of the work machine 1. The vehicle body sensor 49 is, for example, an inertial measurement unit (IMU). The vehicle body sensor 49 detects vehicle body posture data indicative of a posture of the vehicle body 2. The vehicle body posture data includes a pitch angle and a roll angle of the vehicle body 2. Note that the vehicle body sensor 49 is not limited to the IMU. The vehicle body sensor 49 may be any means that measures the pitch angle and the roll angle of the vehicle body 2, and may be an inclinometer, for example.

[0054] The vehicle body sensor 49 is attached to the vehicle body frame 4. Therefore, as illustrated in FIG. 9, a pitch angle 06 of the vehicle body 2 is a tilt angle of the vehicle body frame 4 in the up-down direction with respect to a horizontal direction. As illustrated in FIG. 10, a roll angle 07 of the vehicle body 2 is a tilt angle of the vehicle body frame 4 in the left-right direction with respect to the horizontal direction. Note that the vehicle body sensor 49 may be attached to another place on the vehicle body 2 where the position relative to the vehicle body frame 4 does not change, instead of the vehicle body frame 4. For example, the vehicle body sensor 49 may be disposed on any of other places excluding the tandem drive 5 or the drawbar 17 where the position relative to the vehicle body frame 4 changes.

[0055] The controller 36 acquires work implement posture data indicative of the posture of the work implement 3 with respect to the vehicle body 2 based on a signal from the work implement sensor 48. The work implement posture data includes the height of the left end portion 161 and the height of the right end portion 162 of the blade 16, the yaw angle 1, the pitch angle 2, the roll angle 3 of the drawbar 17, the rotation angle 4 of the circle 18, the tilt angle 5 of the blade 16, and the shift amount W1 of the blade 16 described above. The controller 36 acquires the vehicle body posture data based on a signal from the vehicle body sensor 49. The controller 36 controls the plurality of actuators 22 to 27 according to the operations of the plurality of operating members 41 to 46, thereby changing the posture of the work implement 3.

[0056] Further, the controller 36 performs an automatic control of the work implement 3 based on the aforementioned vehicle body posture data and work implement posture data. The controller 36 controls the left lift cylinder 22 and the right lift cylinder 23 so that the work implement 3 is maintained at a target height under the automatic control of the work implement 3. Processes of the automatic control of the work implement 3 will be described as below. FIG. 11 is a flowchart illustrating the processes of the automatic control of the work implement 3.

[0057] As illustrated in FIG. 11, in step S101, the controller 36 determines whether the operating device 35 is being operated. The controller 36 may determine that the operating device 35 is no longer operated when an operation input on the operating device 35 is not performed for a certain period of time. When at least one of the aforementioned operating members 41 to 46 is being operated, the controller 36 does not perform the automatic control of the work implement 3. Therefore, the controller 36 controls the plurality of actuators 22 to 27 according to the operations of the plurality of operating members 41 to 46, thereby changing the posture of the work implement 3. When the operating members 41 to 46 are not being operated, the process proceeds to step S102.

[0058] In step S102, the controller 36 acquires a current posture of the vehicle body 2. Here, the controller 36 acquires the current posture of the vehicle body 2 from the vehicle body posture data. In step S103, the controller 36 acquires a current posture of the work implement 3. Here, the controller 36 acquires the current posture of the work implement 3 from the work implement posture data.

[0059] In step S104, the controller 36 calculates a current height of the work implement 3. The controller 36 calculates the height of the work implement 3 based on the vehicle body posture data and the work implement posture data. For example, the height of the work implement 3 is the height of the left end portion 161 and the height of the right end portion 162 of the blade 16. Here, the height of the work implement 3 means the height in the gravity direction from an origin O1 taking the origin O1 of the vehicle body 2 illustrated in FIG. 12 as a reference point. For example, the height of the work implement 3 means the height of the work implement 3 in the gravity direction from a horizontal surface including the origin O1 of the vehicle body 2.

[0060] As illustrated in FIG. 12, in a case where the work machine 1 performs work while traveling forward, the origin O1 of the vehicle body 2 is positioned on the tandem drive 5. For example, the origin O1 of the vehicle body 2 is positioned at the center of the rear axis 10 in the left-right direction. In FIG. 12, a Z1 axis indicates the gravity direction. An X1 axis indicates the front-rear direction of the vehicle body 2 that is perpendicular to the gravity direction. In FIG. 4, a Y1 axis indicates the left-right direction of the vehicle body 2 that is perpendicular to the gravity direction. The posture of the vehicle body 2 changes about the origin O1 of the vehicle body 2. For example, as illustrated in FIG. 9, the pitch angle 6 of the vehicle body 2 changes about the origin O1. As illustrated in FIG. 10, the roll angle 07 of the vehicle body 2 changes about the origin O1.

[0061] In step S105, the controller 36 determines a target posture of the work implement 3. The controller 36 calculates the target posture of the work implement 3 so that the height of the work implement 3 is the target height. Note that the controller 36 stores, as the target height, the height of the work implement 3 when it is determined that the operating device 35 is no longer operated. For example, the controller 36 calculates a target pitch angle and a target roll angle of the drawbar 17 so that the height of the work implement 3 is the target height.

[0062] In step S106, the controller 36 controls at least one of the actuators 22 to 27 so that the height of the work implement 3 is the target height. For example, the controller 36 controls the lift cylinders 22 and 23 and the drawbar shift cylinder 24 so that the pitch angle 2 of the drawbar 17 is the target pitch angle and the roll angle 3 of the drawbar 17 is the target roll angle.

[0063] In this case, the controller 36 controls the lift cylinders 22 and 23 and the drawbar shift cylinder 24 so that a position of the blade 16 in the left-right position does not change. That is, in the work machine 1, due to the extension and contraction of the lift cylinders 22 and 23, not only the height direction of the blade 16 but also the position of the blade in the left-right changes. Therefore, the controller 36 controls the drawbar shift cylinder 24 so as to offset a change in position of the blade 16 in the left-right position due to the extension and contraction of the lift cylinders 22 and 23. As a result, the height of the work implement 3 is maintained at the target height and the position of the work implement 3 in the left-right direction is maintained.

[0064] By repeating the aforementioned processes of steps S102 to S106, the controller 36 controls the actuators 22 to 27 so that the work implement 3 is maintained at the target height. When the operating device 35 is operated during the automatic control, the controller 36 ends the automatic control (step S101).

[0065] With the work machine 1 according to the present embodiment described above, the work implement 3 is maintained at the target height of the work implement 3 by the automatic control. The target height is the height in the gravity direction from the origin O1 of the vehicle body 2, and the work implement 3 is maintained at the target height of the work implement 3 even when the posture of the vehicle body 2 changes. Therefore, the work implement 3 is accurately maintained at the target height even when the work machine 1 travels on a ground with undulations.

[0066] For example, in FIG. 9, the blade 16 depicted with a dashed line indicates the position of the blade 16 when the automatic control is not performed. As illustrated in FIG. 9, in a case where the automatic control is not performed, the blade 16 is raised above the position of the blade 16 illustrated in FIG. 12 when the front wheels 6 travel over a bump. However, in the work machine 1 according to the present embodiment, the blade 16 is maintained at the target height of the work implement 3 in the gravity direction by the automatic control as illustrated in FIG. 9. Therefore, even if the front wheels 6 travel over a bump, the controller 36 controls the actuators 22 to 27, thereby causing the blade 16 to be accurately maintained at the target height.

[0067] Next, processes for limiting the automatic control will be described. FIG. 13 is a flowchart illustrating the processes for limiting the automatic control. When the automatic control is enabled, the controller 36 performs the processes illustrated in FIG. 13 to determine whether to limit the automatic control. As illustrated in FIG. 13, in step S201, the controller 36 determines whether the work machine 1 is in a non-working state. The non-working state indicates a state in which the work machine 1 does not perform work with the work implement 3.

[0068] The controller 36 determines whether the work machine 1 is in the non-working state according to the travel mode of the vehicle body 2. Specifically, the controller 36 determines that the work machine 1 is in the non-working state when the travel mode is switched from forward to neutral or from neutral to reverse. The switching of the travel mode from forward to neutral or from neutral to reverse means that the work machine 1 stops or travels in reverse. In such a case, since the work machine 1 does not perform work with the work implement 3, the controller 36 determines that the work machine 1 is in the non-working state.

[0069] For example, the controller 36 determines that the work machine 1 is in the non-working state when the shift operating member 47 is switched from the forward position F to the neutral position N. The controller 36 determines that the work machine 1 is in the non-working state when the shift operating member 47 is switched from the neutral position N to the reverse position R.

[0070] Further, the controller 36 determines whether the work machine 1 is in the non-working state according to a position of the work implement 3. Specifically, the controller 36 determines that the work machine 1 is in the non-working state when a stroke length of the left lift cylinder 22 is less than or equal to a length threshold and a stroke length of the right lift cylinder 23 is less than or equal to the length threshold.

[0071] For example, FIGS. 14A and 14B are front views schematically illustrating a configuration of the work machine 1. In FIG. 14A, a stroke length L1 of the left lift cylinder 22 is greater than a first length threshold and a stroke length L2 of the right lift cylinder 23 is greater than the first length threshold. In FIG. 14B, the stroke length L1 of the left lift cylinder 22 is less than or equal to the first length threshold and the stroke length L2 of the right lift cylinder 23 is less than or equal to the first length threshold.

[0072] As illustrated in FIG. 14A, when the stroke length L1 of the left lift cylinder 22 is greater than the first length threshold and the stroke length L2 of the right lift cylinder 23 is greater than the first length threshold, the blade 16 is at a first height position. The first height position is the position of the blade 16 when the work machine 1 performs work with the work implement 3.

[0073] As illustrated in FIG. 14B, when the stroke length L1 of the left lift cylinder 22 is less than or equal to the first length threshold and the stroke length L2 of the right lift cylinder 23 is less than or equal to the first length threshold, the blade 16 is at a second height position. The second height position is the position of the blade 16 when the work machine 1 travels without performing work with the work implement 3. The second height position is higher than the first height position.

[0074] As described above, when the blade 16 is at the second height position, the work machine 1 travels without performing work with the work implement 3. Therefore, the controller 36 determines that the work machine 1 is in the non-working state when the stroke length L1 of the left lift cylinder 22 is less than or equal to the first length threshold and the stroke length L2 of the right lift cylinder 23 is less than or equal to the first length threshold. Conversely, the controller 36 determines that the work machine 1 is not in the non-working state when the stroke length L1 of the left lift cylinder 22 is greater than the first length threshold and the stroke length L2 of the right lift cylinder 23 is greater than the first length threshold.

[0075] Further, the controller 36 determines that the work machine 1 is in the non-working state when the vehicle speed is greater than or equal to a predetermined first speed threshold. For example, the first speed threshold is set to a value to the degree that the work machine 1 can be considered to travel at a high speed. When the work machine 1 travels at a high speed, work with the work implement 3 is not performed. Therefore, the controller 36 determines that the work machine 1 is in the non-working state when the vehicle speed is greater than or equal to the predetermined first speed threshold.

[0076] When it is determined in step S201 that the work machine 1 is in the non-working state, the process proceeds to step S202. In step S202, the controller 36 stops the automatic control. When the controller 36 stops the automatic control, the controller 36 controls the actuators 22 to 27 according to a manual operation of the operating device 35.

[0077] When the controller 36 determines in step S201 that the work machine 1 is not in the non-working state, the automatic control is maintained. That is, when the controller 36 determines that the work machine 1 is in a working state in which the work machine 1 performs work with the work implement 3, the automatic control is maintained.

[0078] After the automatic control is stopped in step S202, the process proceeds to step S203. In step S203, the controller 36 determines whether a predetermined reactivation condition is satisfied. The reactivation condition includes the fact that the travel mode has been switched from neutral to forward or from reverse to neutral. For example, the controller 36 determines that the reactivation condition is satisfied when the shift operating member 47 is switched from the neutral position N to the forward position F. The controller 36 determines that the reactivation condition is satisfied when the shift operating member 47 is switched from the reverse position R to the neutral position N.

[0079] The reactivation condition includes the fact that the stroke length L1 of the left lift cylinder 22 is greater than a second length threshold and the stroke length L2 of the right lift cylinder 23 is greater than the second length threshold. The second length threshold may be the same as or different from the first length threshold. The controller 36 determines that the reactivation condition is satisfied when the stroke length L1 of the left lift cylinder 22 is greater than the second length threshold and the stroke length L2 of the right lift cylinder 23 is greater than the second length threshold.

[0080] The reactivation condition includes the fact that the vehicle speed is less than a predetermined second speed threshold. The second speed threshold may be the same as or different from the first speed threshold. The controller 36 determines that the reactivation condition is satisfied when the vehicle speed is less than the predetermined second speed threshold.

[0081] When it is determined in step S203 that the reactivation condition is satisfied, the process proceeds to step S204. When it is determined in step S203 that the reactivation condition is not satisfied, the stop of the automatic control is maintained.

[0082] In step S204, the controller 36 reactivates the automatic control. Upon reactivating the automatic control, the controller restarts the processes of the automatic control illustrated in FIG. 11.

[0083] In the work machine 1 according to the present embodiment described above, the automatic control is stopped when the work machine 1 is in the non-working state in which the work machine 1 does not perform work with the work implement 3. As a result, it is possible to reduce an unintended movement of the work implement 3 while the work machine 1 is not performing work. For example, the automatic control is stopped while the work machine 1 is performing a shuttle operation. As a result, it is possible to reduce the unintended movement of the work implement 3 during the shuttle operation. The automatic control is also stopped when the work machine 1 travels for a return trip. As a result, it is possible to reduce the unintended movement of the work implement 3 while the work machine 1 travels for a return trip.

[0084] Although one embodiment of the present disclosure has been described above, the present disclosure is not limited to the above embodiment and various modifications can be made without departing from the gist of the invention.

[0085] The work machine 1 is not limited to a motor grader and may be another work machine 1 such as a bulldozer. In another work machine 1 such as a bulldozer, a position of the origin O1 can be set according to a structural characteristic of the work machine 1. The configuration of the work implement 3 is not limited to that of the above embodiment and may be changed. For example, the work implement 3 may include the blade 16 and a lift arm. The lift arm may support the blade 16 and be connected to the vehicle body. The parameters indicative of the posture of the work implement 3 are not limited to those of the above embodiment and may be changed.

[0086] The plurality of operating members 41 to 46 are not limited to those of the above embodiment and may be changed. For example, the operating member is not limited to a lever and may be another member such as a joystick, a switch, or a touch screen. The plurality of operating members 41 to 46 may directly operate the respective actuators 22 to 27.

[0087] The sensors for detecting the posture of the work implement 3 are not limited to those of the above embodiment and may be changed. The sensors S1 to S5 may directly detect angles, instead of the stroke lengths. The work implement sensor 48 may include an inertial measurement unit (IMU). The IMU may be mounted on the drawbar 17. The posture of the drawbar 17 may be detected by the IMU. Either of the left cylinder angle sensor S7 or the right cylinder angle sensor S8 may be omitted.

[0088] The operating device 35 may include an operating member for the automatic control. The controller 36 may start the automatic control according to an operation of the operating member for the automatic control. The controller 36 may end the automatic control according to an operation of the operating member for the automatic control. According to an operation of the operating member for the automatic control, the controller 36 may store, as the target height, the height of the work implement 3 when the automatic control is started.

[0089] In the aforementioned automatic control, in a case where the posture (angle) or the change in posture (angular velocity) of the vehicle body 2 exceeds a predetermined value, a detection error of the sensors S1 to S8 may be large. Further, in a case where a sudden acceleration or a sudden deceleration that exceeds a predetermined amount occurs, a reaction speed of the sensors S1 to S8 may not be able to keep up. In this case, the controller 36 may temporarily release the automatic control. The controller 36 may temporarily release the automatic control when a difference between the target posture and the current posture of the work implement 3 exceeds a predetermined threshold.

[0090] In the aforementioned embodiment, the automatic control when the work machine 1 performs work while traveling forward has been described, but the present invention may be applied when the work machine 1 performs work while traveling in reverse. In this case, the origin O of the vehicle body 2 may be a center position between the left and right front wheels 6.

[0091] In the aforementioned embodiment, the controller 36 acquires the posture of the work implement 3 when the operating device 35 is not operated for a certain period of time and acquires the height of the work implement 3 at that time as the current height of the work implement 3. However, the method for acquiring the current height of the work implement 3 is not limited to this and may be changed. For example, the controller 36 may acquire the posture of the work implement 3 when the operating device such as a push button is operated and acquire the height of the work implement 3 at that time as the current height of the work implement 3. A switch for increasing or decreasing the acquired height of the work implement 3 by a predetermined amount may be provided. The controller 36 may change the target posture of the work implement 3 according to an operation of the switch. As a result, the target posture of the work implement 3 can be finely adjusted.

[0092] The processes for limiting the automatic control is not limited to those described above and may be changed. For example, the conditions indicative of the non-working state are not limited to those described above and may be changed. The reactivation conditions are not limited to those described above and may be changed.

[0093] According to the present disclosure, the work implement is accurately maintained at the target height even when the work machine travels on a ground with undulations. In addition, it is possible to reduce the unintended movement of the work implement while the work machine is not performing work.