Working machine, and method for controlling working machine

Abstract

To reduce operator's operation burden by automatic control of a steering angle, and suppress the operator's discomfort feeling by automatic control in a work machine.SOLUTION: A work machine comprises a vehicle body, a running wheel, a first steering member, a second steering member, an actuator, and a controller. The actuator changes a steering angle of the running wheel according to operations of the first steering member and the second steering member. The controller executes automatic control to control the actuator so as to set the steering angle to a prescribed target angle when the first steering member is not operated, and it has been determined that the first steering member of the first steering member and the second steering member has been finally operated. The controller does not execute automatic control when it has been determined that the second steering member of the first steering member and the second steering member has been finally operated even if the first steering member is not operated.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention relates to a working machine and a method for controlling the working machine.

Background Art

[0002] Some working machines are provided with a plurality of steering members for steering the traveling wheels left and right. For example, the working machine of Patent Document 1 includes a steering lever and a steering wheel. By an operator of the working machine operating these steering members, the working machine changes the steering angle of the traveling wheels left and right. Thereby, the working machine turns left and right.

[0003] During traveling, the working machine is likely to deviate from the target course due to the load of earth and sand or the unevenness of the road surface. Therefore, the operator needs to simultaneously operate the steering member to maintain the course while operating a working implement such as a blade. Such an operation is highly difficult and imposes a large operation burden on the operator.

[0004] Therefore, Patent Document 1 discloses a steering automatic control that automatically controls the steering angle so that the working machine maintains the traveling direction. In this steering automatic control, the direction of the working machine when the operation of the steering lever is stopped is determined as the traveling direction. Then, the steering angle is automatically controlled so that the working machine travels straight in the traveling direction.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the above-described working machine, when the operator stops operating the steering wheel (handwheel) or the steering lever, automatic control of the steering angle is executed. Therefore, when the operator releases his / her hand from the steering wheel after operating the steering wheel, automatic control may be executed. In that case, for the operator, after operating the steering wheel, the steering angle automatically changes even though the steering wheel is not being operated, resulting in a significant sense of discomfort in the driving feeling. An object of the present invention is to reduce the operation burden on the operator by automatic control of the steering angle in a working machine and to suppress the sense of discomfort to the operator caused by the automatic control.

Means for Solving the Problems

[0007] A working machine according to an aspect of the present invention includes a vehicle body, traveling wheels, a first steering member, a second steering member, an actuator, a first operation sensor, a second operation sensor, and a controller. The traveling wheels are supported by the vehicle body. The first steering member is operable by an operator. The second steering member is operable by an operator. The second steering member is separate from the first steering member. The actuator changes the steering angle of the traveling wheels in response to an operation of the first steering member. The actuator changes the steering angle in response to an operation of the second steering member. The first operation sensor outputs a first operation signal indicating an operation of the first steering member. The second operation sensor outputs a second operation signal indicating an operation of the second steering member. The controller acquires the first operation signal and the second operation signal.

[0008] The controller determines whether the first steering member is being operated. The controller determines which of the first steering member and the second steering member was last operated. When the controller determines that the first steering member is not being operated and that the first steering member was the last one of the first steering member and the second steering member to be operated, the controller executes automatic control to control the actuator so that the steering angle becomes a predetermined target angle. When the controller determines that the second steering member was the last one of the first steering member and the second steering member to be operated even though the first steering member is not being operated, the controller does not execute automatic control.

[0009] A method according to another aspect of the present invention is a method for controlling a work machine. The work machine includes a vehicle body, traveling wheels, and an actuator. The traveling wheels are supported by the vehicle body. The actuator changes the steering angle of the traveling wheels. The method according to this aspect includes obtaining a first operation signal indicating an operation of a first steering member operable to change the steering angle, obtaining a second operation signal indicating an operation of a second steering member operable to change the steering angle and separate from the first steering member, determining whether the first steering member is being operated, determining which of the first steering member and the second steering member was last operated, executing automatic control to control the actuator so that the steering angle becomes a predetermined target angle when the first steering member is not being operated and the first steering member was the last one of the first steering member and the second steering member to be operated, and not executing automatic control when the second steering member was the last one of the first steering member and the second steering member to be operated even though the first steering member is not being operated.

Advantages of the Invention

[0010] According to the present invention, automatic control is executed when the first steering member is not being operated and when the first steering member was last operated. Therefore, the operation burden on the operator is reduced by the automatic control. Also, even when the first steering member is not being operated, if the second steering member was last operated, the automatic control is not executed. Therefore, the operator can drive the work machine without the intervention of the automatic control. Thereby, the discomfort to the operator caused by the automatic control is suppressed.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Mode for Carrying Out the Invention

[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view of a work machine 1 according to an embodiment. FIG. 2 is a side view of the work machine 1. As shown in FIG. 1, the work machine 1 includes a vehicle body 2, front wheels 3A, 3B, rear wheels 4A - 4D, and a work implement 5. The vehicle body 2 includes a front frame 11, a rear frame 12, a cab 13, and a power chamber 14.

[0013] The rear frame 12 is connected to the front frame 11. The front frame 11 is articulable left and right with respect to the rear frame 12. In the following description, the front, rear, left, and right directions each refer to the front, rear, left, and right directions of the vehicle body 2 in a state where the articulation angle is 0, that is, when the front frame 11 and the rear frame 12 are straight.

[0014] The cab 13 and the power unit compartment 14 are arranged on the rear frame 12. A driver's seat (not shown) is arranged in the cab 13. The power unit compartment 14 is arranged behind the cab 13. The front frame 11 extends forward from the rear frame 12. The front wheels 3A, 3B are attached to the front frame 11. The rear wheels 4A - 4D are attached to the rear frame 12.

[0015] The working machine 5 is movably connected to the vehicle body 2. The working machine 5 includes a support member 15 and a blade 16. The support member 15 is movably connected to the vehicle body 2. The support member 15 supports the blade 16. The support member 15 includes a drawbar 17 and a circle 18. The drawbar 17 is arranged below the front frame 11.

[0016] The drawbar 17 is connected to the front portion 19 of the front frame 11. The drawbar 17 extends rearward from the front portion 19 of the front frame 11. The drawbar 17 is supported by the front frame 11 so as to be swingable at least in the vertical and horizontal directions of the vehicle body 2. For example, the front portion 19 includes a ball joint. The drawbar 17 is rotatably connected to the front frame 11 via the ball joint.

[0017] Circle 18 is connected to the rear of the drawbar 17. Circle 18 is rotatably supported with respect to the drawbar 17. Blade 16 is connected to circle 18. Blade 16 is supported by the drawbar 17 via circle 18. As shown in FIG. 2, blade 16 is rotatably supported by circle 18 around the tilt axis 21. The tilt axis 21 extends in the left-right direction.

[0018] The work machine 1 includes a plurality of actuators 22-26 for changing the attitude of the work implement 5. The plurality of actuators 22-26 includes a plurality of hydraulic cylinders 22-25. The plurality of hydraulic cylinders 22-25 are connected to the work implement 5. The plurality of hydraulic cylinders 22-25 expand and contract hydraulically. By expanding and contracting, the plurality of hydraulic cylinders 22-25 change the attitude of the work implement 5 with respect to the vehicle body 2. In the following description, the expansion and contraction of the hydraulic cylinder is referred to as a "stroke operation".

[0019] Specifically, the plurality of hydraulic cylinders 22-25 includes a left lift cylinder 22, a right lift cylinder 23, a drawbar shift cylinder 24, and a blade tilt cylinder 25. The left lift cylinder 22 and the right lift cylinder 23 are arranged apart from each other in the left-right direction. The left lift cylinder 22 and the right lift cylinder 23 are connected to the drawbar 17. The left lift cylinder 22 and the right lift cylinder 23 are connected to the front frame 11 via the lifter bracket 29. By the stroke operation of the left lift cylinder 22 and the right lift cylinder 23, the drawbar 17 swings up and down. Thereby, the blade 16 moves up and down.

[0020] 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 a lifter bracket 29. The drawbar shift cylinder 24 extends obliquely downward from the front frame 11 toward the drawbar 17. Due to the stroke operation of the drawbar shift cylinder 24, the drawbar 17 swings left and right. The blade tilt cylinder 25 is connected to the circle 18 and the blade 16. Due to the stroke operation of the blade tilt cylinder 25, the blade 16 rotates around the tilt axis 21.

[0021] The plurality of actuators 22 - 26 includes a rotary actuator 26. The rotary actuator 26 is connected to the drawbar 17 and the circle 18. The rotary actuator 26 rotates the circle 18 relative to the drawbar 17. Thereby, the blade 16 rotates around a rotation axis extending in the vertical direction.

[0022] FIG. 3 is a schematic diagram showing the configuration of the working machine 1. As shown in FIG. 3, the working machine 1 includes a drive source 31, a first hydraulic pump 32, a power transmission device 33, and a work implement 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 first hydraulic pump 32 discharges hydraulic oil by being driven by the drive source 31.

[0023] The work implement valve 34 is connected to the first hydraulic pump 32 and the plurality of hydraulic cylinders 22 - 25 via a hydraulic circuit. The work implement valve 34 includes a plurality of valves respectively connected to the plurality of hydraulic cylinders 22 - 25. The work implement valve 34 controls the flow rate of the hydraulic oil supplied from the first hydraulic pump 32 to the plurality of hydraulic cylinders 22 - 25. The work implement valve 34 is, for example, an electromagnetic proportional control valve. Alternatively, the work implement valve 34 may be a hydraulic pilot - type proportional control valve.

[0024] In this embodiment, the rotary actuator 26 is a hydraulic motor. The work implement valve 34 is connected to the first hydraulic pump 32 and the rotary actuator 26 via a hydraulic circuit. The work implement valve 34 controls the flow rate of the hydraulic oil supplied from the first hydraulic pump 32 to the rotary actuator 26. Note that the rotary actuator 26 may be an electric motor.

[0025] The power transmission device 33 transmits the driving force from the drive source 31 to the rear wheels 4A - 4D. The power transmission device 33 may include a torque converter and / or a plurality of transmission gears. Alternatively, the power transmission device 33 may be a transmission such as an HST (Hydraulic Static Transmission) or an HMT (Hydraulic Mechanical Transmission).

[0026] The work machine 1 includes a work implement operation member 35, a shift member 53, an accelerator operation member 36, and a controller 37. The work implement operation member 35 is operable by an operator to change the posture of the work implement 5. The work implement operation member 35 includes, for example, a plurality of operation levers. Alternatively, the work implement operation member 35 may be another member such as a switch or a touch panel. The work implement operation member 35 outputs a signal indicating the operation of the work implement operation member 35 by the operator.

[0027] The shift member 53 is operable by an operator to switch between forward and reverse of the work machine 1. The shift member 53 includes, for example, a shift lever. Alternatively, the shift member 53 may be another member such as a switch or a touch panel. The shift member 53 outputs a signal indicating the operation of the shift member 53 by the operator. The accelerator operation member 36 is operable by an operator to run the work machine 1. The accelerator operation member 36 includes, for example, an accelerator pedal. Alternatively, the accelerator operation member 36 may be another member such as a switch or a touch panel. The accelerator operation member 36 outputs a signal indicating the operation of the accelerator operation member 36 by the operator.

[0028] The controller 37 controls the power transmission device 33 according to the operation of the shift member 53 to switch between the forward and reverse movements of the work machine 1. Alternatively, the shift member 53 may be mechanically connected to the power transmission device 33. The operation of the shift member 53 is mechanically transmitted to the power transmission device 33, and the forward and reverse gears of the power transmission device 33 may be switched.

[0029] The controller 37 controls the drive source 31 and the power transmission device 33 according to the operation of the accelerator operation member 36 to drive the work machine 1. Further, the controller 37 controls the first hydraulic pump 32 and the work machine valve 34 according to the operation of the work machine operation member 35 to operate the work machine 5.

[0030] The controller 37 includes a storage device 38 and a processor 39. The processor 39 is, for example, a CPU and executes a program for controlling the work machine 1. The storage device 38 includes memories such as RAM and ROM, and auxiliary storage devices such as SSD or HDD. The storage device 38 stores a program and data for controlling the work machine 1.

[0031] The work machine 1 is provided with a direction sensor 52. The direction sensor 52 detects the traveling direction of the vehicle body 2. The direction sensor 52 outputs a direction signal indicating the traveling direction of the vehicle body 2. The controller 37 acquires the traveling direction of the vehicle body 2 from the direction signal from the direction sensor 52. The traveling direction of the vehicle body 2 is indicated by, for example, the yaw angle of the vehicle body 2. The direction sensor 52 is, for example, an IMU (Inertial Measurement Unit). The controller 37 calculates the traveling direction of the vehicle body 2 based on the acceleration and angular velocity of the vehicle body 2. Alternatively, the direction sensor 52 may be a GNSS (Global Navigation Satellite System) receiver such as a GPS (Global Positioning System). The controller 37 may acquire the traveling direction of the vehicle body 2 from the change in the position of the work machine 1 detected by the direction sensor 52.

[0032] As shown in FIG. 3, the working machine 1 includes a steering angle sensor 40, a steering actuator 41, and a steering valve 42. The steering actuator 41 is a hydraulic cylinder. The steering actuator 41 expands and contracts by hydraulic oil from the first hydraulic pump 32. The steering actuator 41 steers the front wheels 3A and 3B by expanding and contracting.

[0033] FIG. 4 is a top view showing the front part of the working machine 1. As shown in FIG. 4, the front wheels 3A and 3B include a first front wheel 3A and a second front wheel 3B. The first front wheel 3A and the second front wheel 3B are arranged apart in the left-right direction. The first front wheel 3A is supported by the front frame 11 so as to be rotatable around the first steering shaft 43. The second front wheel 3B is supported by the front frame 11 so as to be rotatable around the second steering shaft 44. The first steering shaft 43 and the second steering shaft 44 extend in the vertical direction.

[0034] The steering actuator 41 is connected to the front wheels 3A and 3B and the front frame 11. The steering actuator 41 changes the steering angle θ1 of the front wheels 3A and 3B from a predetermined neutral angle to the left and right. As shown in FIG. 4, the steering angle θ1 is the angle of the direction of the front wheels 3A and 3B with respect to the front-rear direction of the working machine 1. The front-rear direction of the working machine 1 shall mean the front-rear direction of the front frame 11. However, the front-rear direction of the working machine 1 may mean the front-rear direction of the rear frame 12.

[0035] The neutral angle is a steering angle θ1 of 0 degrees. Therefore, the fact that the steering angle θ1 is the neutral angle means that the front wheels 3A and 3B are facing the front of the working machine 1. In FIG. 4, 3A' indicates the first front wheel 3A steered by the steering angle θ1 to the left from the neutral angle. 3B' indicates the second front wheel 3B steered by the steering angle θ1 to the left from the neutral angle.

[0036] The steering valve 42 is connected to the first hydraulic pump 32 and the steering actuator 41 via a hydraulic circuit. The steering valve 42 controls the flow rate of the hydraulic oil supplied from the first hydraulic pump 32 to the steering actuator 41. The steering valve 42 is a hydraulic pilot control valve.

[0037] The steering angle sensor 40 detects the steering angle θ1. The steering angle sensor 40 outputs an angle signal indicating the steering angle θ1. The controller 37 acquires the current steering angle θ1 based on the angle signal from the steering angle sensor 40. The steering angle sensor 40 detects, for example, the stroke amount of the steering actuator 41. The steering angle θ1 is calculated from the stroke amount of the steering actuator 41. Alternatively, the steering angle sensor 40 may directly detect the steering angle θ1.

[0038] The working machine 1 includes a first steering member 45 and a second steering member 46. The first steering member 45 and the second steering member 46 can be operated by an operator to change the steering angle θ1 of the front wheels 3A, 3B to the left and right. The first steering member 45 is a lever such as a joystick. Alternatively, the first steering member 45 may be a member other than a lever. The first steering member 45 can be tilted to the left and right from the neutral position N1. The first steering member 45 is connected to the first operation sensor 51. The first operation sensor 51 outputs a first operation signal indicating the operation of the first steering member 45 by the operator. The controller 37 acquires the operation amount of the first steering member 45 based on the first operation signal from the first operation sensor 51.

[0039] The second steering member 46 is the steering wheel. Alternatively, the second steering member 46 may be a member other than the steering wheel. The second steering member 46 is rotatable about the rotation axis Ax1. A second operation sensor 47 is attached to the second steering member 46. The second operation sensor 47 outputs a second operation signal indicating an operation on the second steering member 46 by the operator. For example, the second operation sensor 47 detects an angular displacement about the rotation axis Ax1 of the second steering member 46. The controller 37 acquires the operation amount of the second steering member 46 based on the second operation signal from the second operation sensor 47. Note that when the second steering member 46 is not being operated by the operator, it is held at the position where it was last operated.

[0040] The working machine 1 includes a second hydraulic pump 48, a first pilot valve 49, and a second pilot valve 50. The second hydraulic pump 48 discharges hydraulic oil when driven by the drive source 31. The first pilot valve 49 is connected to the second hydraulic pump 48 and the steering valve 42 via a hydraulic circuit. The first pilot valve 49 controls the pressure of the hydraulic oil supplied from the second hydraulic pump 48 to the pilot port of the steering valve 42. The first pilot valve 49 is an electromagnetic proportional control valve.

[0041] The first pilot valve 49 is controlled by a signal from the controller 37. The controller 37 controls the first pilot valve 49 according to the first operation signal from the first operation sensor 51 to extend and contract the steering actuator 41. Thereby, the controller 37 controls the steering actuator 41 so as to change the steering angle θ1 of the front wheels 3A, 3B according to the operation of the first steering member 45. The control of the steering angle θ1 by the first steering member 45 will be described in detail later.

[0042] The second pilot valve 50 is connected to the second hydraulic pump 48 and the steering valve 42 via a hydraulic circuit. The second pilot valve 50 is connected to the second steering member 46. The second pilot valve 50 controls the pressure of the hydraulic oil supplied from the second hydraulic pump 48 to the pilot port of the steering valve 42 according to the operation of the second steering member 46. Thereby, the steering actuator 41 changes the steering angle θ1 of the front wheels 3A and 3B so that the steering angle θ1 of the front wheels 3A and 3B becomes an angle corresponding to the operation amount of the second steering member 46.

[0043] When the operation amount of the second steering member 46 is held constant, the steering actuator 41 holds the steering angle θ1 of the front wheels 3A and 3B at an angle corresponding to the operation amount of the second steering member 46. Note that the second pilot valve 50 may be an electromagnetic proportional control valve, similar to the first pilot valve 49. In that case, the controller 37 may control the second pilot valve 50 according to the operation of the second steering member 46.

[0044] Next, the control of the steering angle θ1 by the first steering member 45 will be described. The controller 37 refers to the steering speed data and determines the target steering speed from the operation amount of the first steering member 45. The controller 37 controls the steering actuator 41 so that the steering angle θ1 changes at the target steering speed. The steering speed data defines the target steering speed with respect to the operation amount of the first steering member 45.

[0045] FIG. 5 is a diagram showing an example of the steering speed data. As shown in FIG. 5, the first steering member 45 can be operated in a neutral range, a left steering range, and a right steering range. The neutral range is a range including the position of the operation amount 0 of the first steering member 45, that is, the neutral position N1. The neutral range is located between the left steering range and the right steering range. The left steering range is located to the left of the neutral range. The right steering range is located to the right of the neutral range.

[0046] The steering speed data defines a target steering speed to the left that increases from 0 to the maximum leftward speed VL in the left steering range in response to an increase in the amount of leftward operation of the first steering member 45. Accordingly, when the first steering member 45 is positioned within the left steering range, the controller 37 controls the steering actuator 41 so as to change the steering angle θ1 of the front wheels 3A, 3B to the left at a speed corresponding to the amount of operation of the first steering member 45.

[0047] For example, when the first steering member 45 is operated with an amount of leftward operation A1, the controller 37 determines a steering speed V1 corresponding to the amount of operation A1 as the target steering speed. Then, the controller 37 controls the steering actuator 41 so as to change the steering angle θ1 of the front wheels 3A, 3B to the left at the steering speed V1. Also, while the first steering member 45 is held at the leftward operation amount A1, the steering angle θ1 of the front wheels 3A, 3B continues to change to the left at the steering speed V1 until the maximum leftward steering angle is reached.

[0048] The steering speed data defines a target steering speed to the right that increases from 0 to the maximum rightward speed VR in the right steering range in response to an increase in the amount of rightward operation of the first steering member 45. Accordingly, when the first steering member 45 is positioned within the right steering range, the controller 37 controls the steering actuator 41 so as to change the steering angle θ1 of the front wheels 3A, 3B to the right at a speed corresponding to the amount of operation of the first steering member 45.

[0049] For example, when the first steering member 45 is operated with an amount of rightward operation A2, the controller 37 determines a steering speed V2 corresponding to the amount of operation A2 as the target steering speed. Then, the controller 37 controls the steering actuator 41 so as to change the steering angle θ1 of the front wheels 3A, 3B to the right at the steering speed V2. Also, while the first steering member 45 is held at the rightward operation amount A2, the steering angle θ1 of the front wheels 3A, 3B continues to change to the right at the steering speed V2 until the maximum rightward steering angle is reached.

[0050] When the first steering member 45 is positioned within the neutral range, the controller 37 controls the steering actuator 41 so as to hold the steering angle θ1 at the neutral angle. For example, when the first steering member 45 is positioned within the neutral range while the steering angle θ1 is at the neutral angle, the steering angle θ1 does not change and is held at the neutral angle.

[0051] When the first steering member 45 and the second steering member 46 are operated simultaneously, the controller 37 gives priority to the operation of the second steering member 46. Therefore, when the first steering member 45 and the second steering member 46 are operated simultaneously, the controller 37 does not perform the control of the steering angle θ1 by the first steering member 45 described above. For this reason, the steering angle θ1 changes according to the operation of the second steering member 46.

[0052] Next, the automatic control of the steering angle θ1 will be described. The controller 37 executes automatic control to control the steering actuator 41 so that the steering angle θ1 becomes a predetermined target angle. The automatic control includes a center return mode and a steering stabilizer mode.

[0053] In the center return mode, when the first steering member 45 is returned from the left steering range or the right steering range to the neutral range, the controller 37 controls the steering actuator 41 so as to automatically return the steering angle θ1 to the neutral angle.

[0054] For example, when the steering angle θ1 is at a predetermined angle to the left and the first steering member 45 is returned to the neutral range, the controller 37 controls the steering actuator 41 so that the steering angle θ1 returns from the predetermined angle to the left to the neutral angle. When the steering angle θ1 is at a predetermined angle to the right and the first steering member 45 is returned to the neutral range, the controller 37 controls the steering actuator 41 so that the steering angle θ1 returns from the predetermined angle to the right to the neutral angle.

[0055] FIG. 6 is a diagram showing an example of the traveling of the working machine 1 by the operation of the first steering member 45. As shown in FIG. 6, when the working machine 1 is at point P1, the first steering member 45 is located at the neutral position N1. The steering angle θ1 is the neutral angle, and the working machine 1 is traveling straight ahead. At point P2, when the operator operates the first steering member 45 to an operation amount A1 within the left operation range, the steering angles θ1 of the front wheels 3A and 3B start to change leftward from the neutral angle. Thereby, the working machine 1 turns leftward.

[0056] Between point P2 and point P3, when the operator holds the first steering member 45 at the operation amount A1, the steering angles θ1 of the front wheels 3A and 3B continue to increase to the maximum leftward steering angle θmax. Thereby, the working machine 1 continues to turn leftward.

[0057] Then, at point P3, when the operator returns the first steering member 45 to the neutral range, by the center return mode, the steering angles θ1 of the front wheels 3A and 3B decrease from the maximum steering angle θmax toward the neutral angle. And at point P5, the steering angles θ1 of the front wheels 3A and 3B return to the neutral angle.

[0058] In the steering stabilizer mode, the controller 37 controls the steering angle θ1 so as to hold the traveling direction of the vehicle body 2 in the target direction. As shown in FIG. 6, at point P3, after the operator returns the first steering member 45 to the neutral range, the controller 37 determines whether the steering angle θ1 has returned to the neutral angle. The controller 37 determines at point P5 that the steering angle θ1 has returned to the neutral angle. The controller 37 determines the traveling direction H1 of the vehicle body 2 when it is determined that the steering angle θ1 has returned to the neutral angle as the target direction. Thereafter, the controller 37 controls the steering actuator 41 so as to hold the traveling direction of the vehicle body 2 in the target direction (H1). Thereby, the working machine 1 travels straight ahead toward the target direction (H1).

[0059] Specifically, the controller 37 determines the target angle of the steering angle θ1 based on the difference between the current traveling direction of the vehicle body 2 and the target direction. The controller 37 controls the steering actuator 41 so that the steering angle θ1 becomes the target angle. For example, the controller 37 determines the target angle of the steering angle θ1 by multiplying the difference between the current traveling direction of the vehicle body 2 and the target direction by a predetermined gain. The controller 37 decreases the gain as the vehicle speed increases. Thereby, the higher the vehicle speed, the smaller the target angle. The controller 37 controls the steering actuator 41 by feedback control so that the steering angle θ1 is maintained at the target angle.

[0060] Note that the controller 37 may calculate the vehicle speed from the change in the position of the work machine 1 detected by the above-described GNSS receiver. Alternatively, a rotation sensor for detecting the output rotation speed of the power transmission device 33 may be provided on the work machine 1. The controller 37 may calculate the vehicle speed from the output rotation speed of the power transmission device 33.

[0061] FIG. 7 is a flowchart showing a process for determining the start of automatic control. As shown in FIG. 7, in step S101, the controller 37 determines whether a steering operation is being performed. The controller 37 determines that a steering operation is being performed when at least one of the first steering member 45 and the second steering member 46 is operated.

[0062] The controller 37 determines that the first steering member 45 is being operated when the first steering member 45 is positioned within the left steering range or the right steering range according to the first operation signal. The controller 37 determines that the first steering member 45 is not being operated when the first steering member 45 is positioned within the neutral range according to the first operation signal.

[0063] The controller 37 acquires the operation speed of the second steering member 46 based on the second operation signal. When the operation speed is greater than a threshold value, the controller 37 determines that the second steering member 46 is being operated. When the operation speed is less than or equal to the threshold value, the controller 37 determines that the second steering member 46 is not being operated. For example, the controller 37 calculates the angular velocity of the second steering member 46. When the angular velocity of the second steering member 46 is less than or equal to the threshold value, the controller 37 determines that the second steering member 46 is not being operated.

[0064] In step S101, when the controller 37 determines that a steering operation is being performed, the process proceeds to step S106. In step S106, the steering actuator 41 is controlled in manual mode. That is, the controller 37 does not execute automatic control, and as described above, the steering actuator 41 is controlled according to the operation of the first steering member 45 or the second steering member 46 by the operator.

[0065] In step S101, when the controller 37 determines that no steering operation is being performed, the process proceeds to step S102. In step S102, the controller 37 determines whether the first steering member 45 was the last to be operated out of the first steering member 45 and the second steering member 46. In step S102, when the controller 37 determines that the first steering member 45 was not the last to be operated out of the first steering member 45 and the second steering member 46, the process proceeds to step S106. That is, when the second steering member 46 was the last to be operated, the controller 37 does not execute automatic control, and the steering actuator 41 is controlled in manual mode.

[0066] In step S102, when the controller 37 determines that the first steering member 45 was last operated, the process proceeds to step S103. In step S103, after the transition from the manual mode to the automatic control, the controller 37 determines whether the steering angle θ1 has returned to the neutral angle at least once. When the controller 37 determines that the steering angle θ1 has not returned to the neutral angle even once after the transition from the manual mode to the automatic control, the process proceeds to step S104.

[0067] In step S104, the controller 37 controls the steering actuator 41 in the center return mode. That is, as shown from point P3 to point P5 in FIG. 6, the controller 37 controls the steering actuator 41 so as to return the steering angle θ1 to the neutral angle.

[0068] In step S103, when the controller 37 determines that the steering angle θ1 has returned to the neutral angle at least once after the transition from the manual mode to the automatic control, the process proceeds to step S105. In step S105, the controller 37 controls the steering actuator 41 in the steering stabilizer mode. As shown at point P5 in FIG. 6, in the steering stabilizer mode, the controller 37 controls the steering angle θ1 so as to hold the traveling direction of the vehicle body 2 in the target direction (H1).

[0069] In the working machine 1 according to the present embodiment described above, when the controller 37 determines that the first steering member 45 is not being operated and that the first steering member 45 was last operated among the first steering member 45 and the second steering member 46, the controller 37 executes automatic control. Further, even if the first steering member 45 is not being operated, when the controller 37 determines that the second steering member 46 was last operated among the first steering member 45 and the second steering member 46, the controller 37 does not execute automatic control.

[0070] Therefore, when the operator operates the second steering member 46, the work machine 1 can be driven with a natural driving feeling without the intervention of automatic control. Thereby, the intervention of unintended automatic driving is prevented, and the discomfort felt by the operator is reduced. Further, when the operator operates the first steering member 45, the operator can smoothly start the automatic control without operating a separate switch or the like by stopping the operation of the first steering member 45. Thereby, the operation burden on the operator is further reduced by the automatic driving.

[0071] As described above, one embodiment of the present invention has been described. However, the present invention is not limited to the above embodiment, and various modifications can be made without departing from the gist of the invention.

[0072] The work machine 1 is not limited to a motor grader, and may be other work machines such as a wheel loader, a dump truck, and a forklift. The number of the steering actuators 41 is not limited to one, and may be two or more. The steering actuator 41 is not limited to a hydraulic cylinder, and may be a hydraulic motor or an electric motor.

[0073] The steering speed data is not limited to that of the above embodiment and may be changed. Alternatively, the center return mode may be omitted. In the above embodiment, the controller 37 controls the steering actuator 41 so as to change the steering angle θ1 at a speed corresponding to the operation amount of the first steering member 45. However, the controller 37 may control the steering actuator 41 so that the steering angle θ1 becomes an angle corresponding to the operation amount of the first steering member 45. That is, the control of the steering angle θ1 by the first steering member 45 is not limited to the speed control type, and may be the position control type.

[0074] The processing by the controller 37 in the steering stabilizer mode is not limited to that of the above-described embodiment and may be changed. For example, as shown at point P3 in FIG. 6, the controller 37 may determine the traveling direction H2 of the vehicle body 2 when the operator returns the first steering member 45 to the neutral range as the target direction.

[0075] The automatic control of the steering angle is not limited to the center return mode and the steering stabilizer mode described above and may be changed. For example, the automatic control may include an automatic steering mode in which the work machine 1 travels along a predetermined target path. In the automatic steering mode, the controller 37 may determine the target angle of the steering angle θ1 so that the work machine 1 moves along the target path. The target path may be input to the controller 37 by the operator. The target path may be input to the controller 37 from an external computer. Alternatively, the controller 37 may automatically generate the target path.

Industrial Applicability

[0076] According to the present invention, in a work machine, the operation burden on the operator can be reduced by the automatic control of the steering angle, and the discomfort to the operator due to the automatic control can be suppressed.

Explanation of Signs

[0077] 2: Vehicle body 3A, 3B: Front wheels 37: Controller 41: Steering actuator 45: First steering member 46: Second steering member 47: Second operation sensor 51: First operation sensor

Claims

1. A vehicle body, Traveling wheels supported by the vehicle body, A first steering member operable by an operator, A second steering member operable by an operator and separate from the first steering member, An actuator that changes the steering angle of the traveling wheels in response to an operation of the first steering member and changes the steering angle in response to an operation of the second steering member, A first operation sensor that outputs a first operation signal indicating an operation of the first steering member, A second operation sensor that outputs a second operation signal indicating an operation of the second steering member, A controller that acquires the first operation signal and the second operation signal, Comprising, The controller, Determines whether the first steering member is not being operated, Determines whether the first steering member was the last one to be operated among the first steering member and the second steering member, When it is determined that the first steering member is not being operated and that the first steering member was the last one to be operated among the first steering member and the second steering member, executes automatic control to control the actuator so that the steering angle becomes a predetermined target angle, Does not execute the automatic control when it is determined that the second steering member was the last one to be operated among the first steering member and the second steering member even if the first steering member is not being operated, A working machine.

2. The first steering member is a lever, The working machine according to Claim 1.

3. The second steering member is a steering wheel, The working machine according to Claim 1 or 2.

4. In the automatic control, the controller, Determines a target direction in the traveling direction of the vehicle body, Determines the target angle so as to hold the traveling direction of the vehicle body in the target direction, The working machine according to any one of Claims 1 to 3.

5. The first steering member is operable in a left steering range, a right steering range, and a neutral range between the left steering range and the right steering range, The controller determines that the first steering member is not being operated when the operation position of the first steering member is within the neutral range, The working machine according to any one of Claims 1 to 4.

6. The controller, Determines whether the second steering member is being operated, When it is determined that the second steering member is being operated, the automatic control is not executed. The working machine according to any one of claims 1 to 5.

7. The controller detects the operating speed of the second steering member, and when the operating speed is equal to or lower than a threshold value, determines that the second steering member is not being operated. The working machine according to claim 6.

8. A method for controlling a working machine including a vehicle body, traveling wheels supported by the vehicle body, and an actuator that changes the steering angle of the traveling wheels, the method comprising: acquiring a first operation signal indicating an operation of a first steering member operable to change the steering angle; acquiring a second operation signal indicating an operation of a second steering member operable to change the steering angle and separate from the first steering member; determining whether the first steering member is not being operated; determining which of the first steering member and the second steering member was operated last; when it is determined that the first steering member is not being operated and that the first steering member was operated last among the first steering member and the second steering member, executing automatic control to control the actuator so that the steering angle becomes a predetermined target angle; when it is determined that the second steering member was operated last among the first steering member and the second steering member even if the first steering member is not being operated, not executing the automatic control. A method comprising the above.

9. The first steering member is a lever. The method according to claim 8.

10. The second steering member is a steering wheel. The method according to claim 8 or 9.

11. In the automatic control, determining a target direction of the traveling direction of the vehicle body and determining the target angle so as to hold the traveling direction of the vehicle body in the target direction. The method according to any one of claims 8 to 10, further comprising the above.

12. The first steering member is operable in a left steering range, a right steering range, and a neutral range between the left steering range and the right steering range. When the operating position of the first steering member is within the neutral range, further comprising determining that the first steering member is not being operated. The method according to any one of claims 8 to 11. **Claim 13** Determining whether the second steering member is being operated; When it is determined that the second steering member is being operated, not executing the automatic control; The method according to any one of claims 8 to 12, further comprising the above. **Claim 14** Detecting an operating speed of the second steering member; When the operating speed is equal to or lower than a threshold value, determining that the second steering member is not being operated; The method according to claim 13, further comprising the above.

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