Work machine and method for controlling a work machine

Abstract

To reduce operator's operation burden by automatic control of a steering angle.SOLUTION: A work machine comprises a vehicle body, a running wheel, a steering member, an actuator, and a controller. The steering member is operable into a left steering range, a right steering range, and a neutral range. The actuator so makes a steering angle of the running wheel as to be a prescribed neutral angle when the steering member is positioned in the neutral range. The actuator changes the steering angle right and left from the neutral angle according to an operation of the steering member. The controller determines whether the steering angle has returned to the neutral angle when the steering member has been operated into the neutral range from the left steering range or the right steering range. The controller determines a direction of travel of the vehicle body, when the steering angle has returned to the neutral angle, as a target direction. The controller controls the actuator so as to keep the direction of travel of the vehicle body in the target direction.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to a work machine and a method for controlling a work machine. [Background technology]

[0002] A work machine is equipped with a steering member, such as a steering wheel or a steering lever, for steering the running wheels to the left and right. The steering member can be operated to the left and right from a neutral position. When an operator of the work machine operates the steering member, the work machine changes the steering angle of the running wheels from the neutral angle to the left and right. This causes the work machine to turn to the left and right.

[0003] A work machine is prone to deviating from a desired course due to the load of soil and sand or unevenness of the road surface while traveling. Therefore, the operator must operate the steering member while operating the work equipment such as the blade to maintain the course. Such operations are difficult and place a heavy burden on the operator.

[0004] Therefore, Patent Document 1 discloses an automatic steering control that automatically controls the steering angle so that the work machine maintains its traveling direction. In this automatic steering control, the direction of the work machine when the operation of the steering operation member is stopped is determined as the target direction. Then, the steering angle is automatically controlled so that the work machine moves straight toward the target direction. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2021-054269 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when the work machine moves straight in the direction in which it was facing when the operation of the steering operation member was stopped, as in Patent Document 1, the operator may feel uncomfortable with the behavior of the work machine. An object of the present invention is to reduce the operational burden on the operator by automatically controlling the steering angle, and to reduce the sense of discomfort felt by the operator. [Means for solving the problem]

[0007] A work machine according to a first aspect of the present invention includes a vehicle body, running wheels, a steering member, an actuator, an operation sensor, a steering angle sensor, a direction sensor, and a controller. The running wheels are supported by the vehicle body. The steering member can be operated to a left steering range, a right steering range, and a neutral range. The neutral range is located between the left steering range and the right steering range. When the steering member is located in the neutral range, the actuator sets the steering angle of the running wheels to a predetermined neutral angle. The actuator changes the steering angle from the neutral angle to the left or right in response to the operation of the steering member. The operation sensor outputs an operation signal indicative of the operation of the steering member. The steering angle sensor outputs an angle signal indicative of the steering angle. The direction sensor outputs a direction signal that detects the traveling direction of the vehicle body.

[0008] The controller receives the operation signal, the angle signal, and the direction signal. The controller determines whether the steering angle has returned to the neutral angle when the steering member is operated from the left steering range or the right steering range to the neutral range. The controller determines the traveling direction when it is determined that the steering angle has returned to the neutral angle as the target direction. The controller controls the actuator so as to maintain the traveling direction in the target direction.

[0009] A method according to a second aspect of the present invention is a method for controlling a work machine. The work machine includes a vehicle body, running wheels, and an actuator. The running wheels are supported by the vehicle body. The actuator changes the steering angle of the running wheels to the left or right from a predetermined neutral angle. The method according to this aspect includes acquiring an operation signal indicating operation of a steering member that can be operated in a left steering range, a right steering range, and a neutral range between the left steering range and the right steering range, controlling an actuator to set the steering angle to a predetermined neutral angle when the steering member is located in the neutral range, controlling the actuator to change the steering angle from the neutral angle to the left or right in accordance with the operation of the steering member, acquiring an angle signal indicating the steering angle, acquiring a direction signal detecting the traveling direction of the vehicle body, determining whether the steering angle has returned to the neutral angle when the steering member is operated from the left steering range or the right steering range to the neutral range, determining the traveling direction when it is determined that the steering angle has returned to the neutral angle as a target direction, and controlling the actuator to maintain the traveling direction in the target direction. Effect of the Invention

[0010] In the present invention, the actuator is controlled so as to maintain the traveling direction of the vehicle body in a target direction. Also, the traveling direction of the vehicle body when the steering angle returns to the neutral angle, not when the steering member is operated to the neutral range, is determined as the target direction. Therefore, the work machine is controlled so as to travel straight in the traveling direction when the steering angle actually returns to the neutral angle. This reduces the operational burden on the operator and reduces any sense of discomfort felt by the operator. [Brief description of the drawings]

[0011] [Figure 1] 1 is a perspective view of a work machine according to an embodiment. FIG. [Diagram 2] FIG. [Diagram 3] FIG. 1 is a schematic diagram showing a configuration of a work machine. [Figure 4] FIG. 2 is a top view showing the front of the work machine. [Diagram 5]FIG. 4 is a diagram showing an example of steering speed data. [Figure 6] FIG. 4 is a diagram showing an example of travel of a work machine by operation of a first steering member. [Figure 7] 5 is a flowchart showing a process for determining the start of automatic control. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

[0013] The rear frame 12 is connected to the front frame 11. The front frame 11 can articulate left and right with respect to the rear frame 12. In the following description, the front, rear, left and right directions refer to the front, rear, left and right directions of the vehicle body 2 when 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 room 14 are disposed on the rear frame 12. A driver's seat (not shown) is disposed in the cab 13. The power room 14 is disposed 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 work implement 5 is movably connected to the vehicle body 2. The work implement 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 draw bar 17 and a circle 18. The draw bar 17 is disposed below the front frame 11.

[0016] The drawbar 17 is connected to a 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 relative to the front frame 11 so as to be swingable at least in the up-down direction and the left-right direction 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] The circle 18 is connected to the rear of the drawbar 17. The circle 18 is supported rotatably relative 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. As shown in FIG. 2 , the blade 16 is supported by the circle 18 rotatably around a tilt shaft 21. The tilt shaft 21 extends in the left-right direction.

[0018] The work machine 1 is equipped with a plurality of actuators 22-26 for changing the attitude of the work implement 5. The plurality of actuators 22-26 include 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 extend and retract by hydraulic pressure. The plurality of hydraulic cylinders 22-25 change the attitude of the work implement 5 relative to the vehicle body 2 by extending and retracting. In the following description, the extension and retraction of the hydraulic cylinders is referred to as a "stroke operation."

[0019] In detail, the multiple hydraulic cylinders 22-25 include 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 a lifter bracket 29. The left lift cylinder 22 and the right lift cylinder 23 stroke operations cause the drawbar 17 to swing up and down. As a result, 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. The stroke movement of the drawbar shift cylinder 24 causes the drawbar 17 to swing left and right. The blade tilt cylinder 25 is connected to the circle 18 and the blade 16. The stroke movement of the blade tilt cylinder 25 causes the blade 16 to rotate around the tilt shaft 21.

[0021] The multiple actuators 22-26 include a rotation actuator 26. The rotation actuator 26 is connected to the draw bar 17 and the circle 18. The rotation actuator 26 rotates the circle 18 relative to the draw bar 17. This causes the blade 16 to rotate around a rotation axis extending in the vertical direction.

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

[0023] The work machine valve 34 is connected to the first hydraulic pump 32 and the multiple hydraulic cylinders 22-25 via a hydraulic circuit. The work machine valve 34 includes multiple valves connected to the multiple hydraulic cylinders 22-25, respectively. The work machine valve 34 controls the flow rate of the hydraulic oil supplied from the first hydraulic pump 32 to the multiple hydraulic cylinders 22-25. The work machine valve 34 is, for example, an electromagnetic proportional control valve. Alternatively, the work machine 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 machine valve 34 is connected to the first hydraulic pump 32 and the rotary actuator 26 via a hydraulic circuit. The work machine valve 34 controls the flow rate of hydraulic oil supplied from the first hydraulic pump 32 to the rotary actuator 26. 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 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).

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

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

[0028] The controller 37 controls the power transmission device 33 in response to the operation of the shift member 53, thereby switching the working machine 1 between forward and reverse. Alternatively, the shift member 53 may be mechanically connected to the power transmission device 33. The operation of the shift member 53 may be mechanically transmitted to the power transmission device 33, thereby switching the forward and reverse gears of the power transmission device 33.

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

[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 SSDs or HDDs. The storage device 38 stores programs and data for controlling the work machine 1.

[0031] The work machine 1 is equipped 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, for example, by 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 a change in the position of the work machine 1 detected by the direction sensor 52.

[0032] As shown in Fig. 3, the work machine 1 is equipped with 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, 3B by expanding and contracting.

[0033] Fig. 4 is a top view showing the front part of the work machine 1. As shown in Fig. 4, the front wheels 3A, 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 about a first steering shaft 43. The second front wheel 3B is supported by the front frame 11 so as to be rotatable about a 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, 3B and the front frame 11. The steering actuator 41 changes the steering angle θ1 of the front wheels 3A, 3B to the left or right from a predetermined neutral angle. As shown in FIG. 4, the steering angle θ1 is the angle of the orientation of the front wheels 3A, 3B with respect to the fore-and-aft direction of the work machine 1. The fore-and-aft direction of the work machine 1 refers to the fore-and-aft direction of the front frame 11. However, the fore-and-aft direction of the work machine 1 may also refer to the fore-and-aft direction of the rear frame 12.

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

[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 hydraulic oil supplied from the first hydraulic pump 32 to the steering actuator 41. The steering valve 42 is a hydraulic pilot type 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 a 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 work 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 or 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 or right from a neutral position N1. The first steering member 45 is connected to a first operation sensor 51. The first operation sensor 51 outputs a first operation signal indicating an operation of the first steering member 45 by the operator. The controller 37 acquires the operation amount of the first steering member 45 from the first operation signal from the first operation sensor 51.

[0039] The second steering member 46 is a steering wheel. Alternatively, the second steering member 46 may be a member other than a steering wheel. The second steering member 46 is rotatable around a 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 of the second steering member 46 by the operator. For example, the second operation sensor 47 detects an angular displacement of the second steering member 46 around the rotation axis Ax1. The controller 37 obtains the operation amount of the second steering member 46 from the second operation signal from the second operation sensor 47. Note that, when the second steering member 46 is not operated by the operator, it is held in the position where it was last operated.

[0040] The work machine 1 includes a second hydraulic pump 48, a first pilot valve 49, and a second pilot valve 50. The second hydraulic pump 48 is driven by the drive source 31 to discharge hydraulic oil. 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 in response to a first operation signal from the first operation sensor 51, thereby expanding and contracting the steering actuator 41. As a result, the controller 37 controls the steering actuator 41 in response to the operation of the first steering member 45 so as to change the steering angle θ1 of the front wheels 3A, 3B. 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 in response to the operation of the second steering member 46. As a result, the steering actuator 41 changes the steering angle θ1 of the front wheels 3A, 3B so that the steering angle θ1 of the front wheels 3A, 3B becomes an angle corresponding to the amount of operation of the second steering member 46.

[0043] When the amount of operation of the second steering member 46 is held constant, the steering actuator 41 holds the steering angle θ1 of the front wheels 3A, 3B at an angle corresponding to the amount of operation 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 in response 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 determines a target steering speed from the operation amount of the first steering member 45 by referring to the steering speed data. The controller 37 controls the steering actuator 41 so that the steering angle θ1 changes at the target steering speed. The steering speed data specifies the target steering speed for the operation amount of the first steering member 45.

[0045] FIG. 5 is a diagram showing an example of steering speed data. As shown in FIG. 5, the first steering member 45 can be operated to a neutral range, a left steering range, and a right steering range. The neutral range is a position where the operation amount of the first steering member 45 is 0, that is, a range including 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 specifies a target steering speed to the left that increases between 0 and a maximum leftward speed VL in accordance with an increase in the leftward operation amount of the first steering member 45 in the left steering range. Therefore, when the first steering member 45 is located 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 operation amount of the first steering member 45.

[0047] For example, when the first steering member 45 is operated to the left with an operation amount A1, the controller 37 determines a steering speed V1 corresponding to the operation amount A1 as a 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 operation amount A1 to the left, the steering angle θ1 of the front wheels 3A, 3B continues to change to the left at the steering speed V1 until it reaches the maximum steering angle to the left.

[0048] The steering speed data specifies a rightward target steering speed that increases between 0 and a maximum rightward speed VR in accordance with an increase in the amount of rightward operation of the first steering member 45 in the rightward steering range. Therefore, when the first steering member 45 is located within the rightward 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 rightward operation of the first steering member 45.

[0049] For example, when the first steering member 45 is operated with an amount of operation A2 to the right, the controller 37 determines a steering speed V2 corresponding to the amount of operation A2 as a 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 amount of operation A2 to the right, the steering angle θ1 of the front wheels 3A, 3B continues to change to the right at the steering speed V2 until it reaches the maximum steering angle to the right.

[0050] When the first steering member 45 is located within the neutral range, the controller 37 controls the steering actuator 41 to maintain the steering angle θ1 at the neutral angle. For example, when the steering angle θ1 is the neutral angle and the first steering member 45 is located within the neutral range, the steering angle θ1 does not change and is maintained at the neutral angle.

[0051] When the first steering member 45 and the second steering member 46 are operated simultaneously, the controller 37 prioritizes 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 control the steering angle θ1 by the first steering member 45 as described above. Therefore, 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 as to set the steering angle θ1 to a predetermined target angle. The automatic control includes a center return mode and a steering stabilizer mode.

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

[0054] For example, when the steering angle θ1 is 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 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 work machine 1 by operating the first steering member 45. As shown in Fig. 6, when the work machine 1 is at point P1, the first steering member 45 is located in the neutral position N1. The steering angle θ1 is a neutral angle, and the work machine 1 is moving 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 angle θ1 of the front wheels 3A, 3B starts to change from the neutral angle to the left. This causes the work machine 1 to turn to the left.

[0056] If the operator maintains the operation amount A1 of the first steering member 45 between point P2 and point P3, the steering angle θ1 of the front wheels 3A, 3B continues to increase to the maximum steering angle θmax to the left, causing the working machine 1 to continue turning to the left.

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

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

[0059] In detail, 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 reduces the gain as the vehicle speed increases. As a result, the target angle becomes smaller as the vehicle speed increases. The controller 37 controls the steering actuator 41 by feedback control so that the steering angle θ1 is maintained at the target angle.

[0060] The controller 37 may calculate the vehicle speed from a change in the position of the work machine 1 detected by the above-mentioned GNSS receiver. Alternatively, a rotation sensor that detects the output rotation speed of the power transmission device 33 may be provided in 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 whether to start automatic control. As shown in Fig. 7, in step S101, the controller 37 determines whether a steering operation is being performed. When at least one of the first steering member 45 and the second steering member 46 is being operated, the controller 37 determines that a steering operation is being performed.

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

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

[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 the manual mode. That is, the controller 37 does not execute automatic control, and the steering actuator 41 is controlled in response to the operation of the first steering member 45 or the second steering member 46 by the operator, as described above.

[0065] In step S101, when the controller 37 determines that no steering operation has been performed, the process proceeds to step S102. In step S102, the controller 37 determines whether the first steering member 45 of the first steering member 45 and the second steering member 46 was operated last. In step S102, when the controller 37 determines that the first steering member 45 of the first steering member 45 and the second steering member 46 was not operated last, the process proceeds to step S106. In other words, when the second steering member 46 was operated last, 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, the controller 37 determines whether the steering angle θ1 has returned to the neutral angle at least once after the transition from the manual mode to the automatic control. When the controller 37 determines that the steering angle θ1 has never returned to the neutral angle 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, the controller 37 controls the steering actuator 41 so as to return the steering angle θ1 to the neutral angle, as shown in FIG. 6 from point P3 to point P5.

[0068] In step S103, when the controller 37 determines that the steering angle θ1 has returned to the neutral angle even 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 maintain the traveling direction of the vehicle body 2 in the target direction (H1).

[0069] In the work machine 1 according to this embodiment described above, the steering actuator 41 is controlled so as to maintain the traveling direction of the vehicle body 2 in the target direction. Moreover, the traveling direction of the vehicle body 2 when the steering angle θ1 returns to the neutral angle, not when the first steering member 45 is operated into the neutral range, is determined as the target direction.

[0070] For example, as shown at point P3 in Fig. 6, the traveling direction H2 of the vehicle body 2 when the first steering member 45 is operated into the neutral range is different from the traveling direction H1 of the vehicle body 2 when the steering angle θ1 returns to the neutral angle. In the work machine 1 according to this embodiment, the traveling direction H1 of the vehicle body 2 when the steering angle θ1 returns to the neutral angle is determined as the target direction. Therefore, the work machine 1 is controlled so as to travel straight toward the traveling direction H1 when the steering angle θ1 actually returns to the neutral angle. This reduces the operational burden on the operator and reduces the sense of discomfort felt by the operator.

[0071] Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications are possible 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, or a forklift. The number of 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 in 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 a speed control type, and may be a position control type.

[0074] When the vehicle body 2 is moving backward, the controller 37 may reverse the target angle of the steering angle θ1 to the left compared to when the vehicle body 2 is moving forward. For example, when the target direction for moving forward is to the left of the work machine 1, the controller 37 determines the target angle to be an angle to the left of the neutral angle. When the target direction for moving backward is to the left of the work machine 1, the controller 37 determines the target angle to be an angle to the right of the neutral angle. When the target direction for moving forward is to the right of the work machine 1, the controller 37 determines the target angle to be an angle to the right of the neutral angle. When the target direction for moving backward is to the right of the work machine 1, the controller 37 determines the target angle to be an angle to the left of the neutral angle.

[0075] The controller 37 may determine whether the vehicle body 2 is moving forward or backward based on a signal from the shift member 53. Alternatively, the controller 37 may determine whether the vehicle body 2 is moving forward or backward based on a change in the position of the work machine 1 detected by the GNSS receiver. Alternatively, the controller 37 may determine whether the vehicle body 2 is moving forward or backward based on the rotation direction of the output shaft of the power transmission device 33. [Industrial Applicability]

[0076] According to the present invention, the operational burden on the operator can be reduced by automatically controlling the steering angle, and the sense of discomfort felt by the operator can also be reduced. [Explanation of symbols]

[0077] 2: Body 3A,3B: Front wheel 37: Controller 40: Steering angle sensor 41: Steering actuator 45: First steering member 51: First operation sensor 52: Direction sensor

Claims

1. The car body and A running wheel supported on the vehicle body; a steering member operable in a left steering range, a right steering range, and a neutral range between the left steering range and the right steering range; an actuator that, when the steering member is located in the neutral range, sets a steering angle of the running wheels to a predetermined neutral angle, and changes the steering angle to the left or right from the neutral angle in response to an operation of the steering member; an operation sensor that outputs an operation signal indicative of an operation of the steering member; a steering angle sensor that outputs an angle signal indicative of the steering angle; a direction sensor that outputs a direction signal indicating a traveling direction of the vehicle body; a controller that acquires the operation signal, the angle signal, and the direction signal; Equipped with The controller: When the steering member is operated from the left steering range or the right steering range to the neutral range, it is determined whether the steering angle has returned to the neutral angle; determining, as a target direction, the traveling direction when it is determined that the steering angle has returned to the neutral angle; controlling the actuator so as to maintain the traveling direction in the target direction; Working machinery.

2. The controller: determining a target angle of the steering angle based on a difference between the traveling direction and the target direction; controlling the actuator so that the steering angle becomes the target angle; 2. The work machine of claim 1.

3. The controller: Acquire a vehicle speed of the vehicle body; The higher the vehicle speed, the smaller the target angle.

3. A work machine according to claim 2.

4. The controller: determining whether the vehicle body is moving forward or backward; When the vehicle body is moving backward, the target angle is reversed from the target angle when the vehicle body is moving forward. A work machine according to claim 2 or 3.

5. A method for controlling a work machine including a vehicle body, running wheels supported on the vehicle body, and an actuator for changing a steering angle of the running wheels to the left or right from a predetermined neutral angle, comprising: acquiring an operation signal indicating an operation of a steering member operable in a left steering range, a right steering range, and a neutral range between the left steering range and the right steering range; controlling the actuator so that the steering angle is a predetermined neutral angle when the steering member is located in the neutral range; Controlling the actuator so as to change the steering angle from the neutral angle to the left or right in response to an operation of the steering member; obtaining an angle signal indicative of the steering angle; acquiring a direction signal for detecting a traveling direction of the vehicle body; When the steering member is operated from the left steering range or the right steering range to the neutral range, determining whether the steering angle has returned to the neutral angle; determining, as a target direction, the traveling direction when it is determined that the steering angle has returned to the neutral angle; controlling the actuator so as to maintain the traveling direction in the target direction; A method for providing the above.

6. determining a target angle of the steering angle based on a difference between the traveling direction and the target direction; controlling the actuator so that the steering angle becomes the target angle; The method of claim 5 further comprising:

7. Obtaining a vehicle speed of the vehicle body; The higher the vehicle speed, the smaller the target angle. The method of claim 6 further comprising:

8. determining whether the vehicle body is moving forward or backward; When the vehicle body is moving backward, the target angle is reversed from left to right as compared with when the vehicle body is moving forward; The method of claim 6 or 7, further comprising:

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