JP2023046508A - work vehicle - Google Patents

Abstract

To provide a work vehicle capable of preventing a turning radius from swelling large and of appropriately progressing to the next step.SOLUTION: A riding type rice transplanter P is configured to perform automatic steering control controlling a steering device 9 on the basis of location information on a traveling machine body 1 acquired by a location information acquisition system 41. When the automatic steering control is on and an indicated steering angle for the steering device 9 is over a prescribed turning determined angle from a detection angle of the steering angle sensor 21 or a control part 50, front wheels 10 are steered up to a mechanical limit angle, and a detected angle of the steering angle sensor 21 when the limit angle is reached is set as an indicated steering angle for turning.SELECTED DRAWING: Figure 9

Description

The present invention relates to a work vehicle capable of executing automatic steering control.

2. Description of the Related Art There is known a work vehicle capable of executing automatic steering control for controlling a steering device based on position information of a traveling machine body acquired by a position information acquisition system (see Patent Document 1, for example). This type of work vehicle is equipped with a steering angle sensor that detects the steering angle of the front wheels, and automatic steering control is executed so that the target steering angle (steering angle indicated by the control unit) matches the angle detected by the steering angle sensor. be done.

JP 2020-195285 A

However, in this type of work vehicle, an error such as hysteresis occurs between the angle detected by the steering angle sensor and the actual steering angle of the front wheels due to the characteristics of the steering angle sensor and the mechanical configuration around it. There is a risk that the accuracy of the automatic steering control will decrease. In particular, when the aircraft is turning, the influence of the error becomes large, so there is a possibility that the turning radius will be greatly expanded and it will not be possible to properly enter the next stroke.

The present invention has been created with the aim of solving these problems in view of the actual situation as described above. A position information acquisition system that acquires information, a steering device that steers the front wheels by driving an actuator, a steering angle sensor that detects the steering angle of the front wheels, and the position information of the traveling body acquired by the position information acquisition system. and a control unit configured to be able to execute automatic steering control for controlling the steering device based on When the angle detected by the sensor or the steering angle instructed from the control unit to the steering device exceeds a predetermined turning determination angle, the front wheels are steered to a mechanical limit angle, and the steering at the time when the limit angle is reached. It is characterized by comprising turning instruction steering angle setting means for setting the angle detected by the angle sensor as the turning instruction steering angle.
Further, the invention of claim 2 is the work vehicle according to claim 1, wherein the command steering angle setting means for turning is in an on state of the automatic steering control and the angle detected by the steering angle sensor or the angle detected by the steering angle sensor. When the instructed steering angle exceeds the predetermined turn determination angle, the front wheels are steered to the mechanical limit angle, and then the front wheels are steered in the reverse direction by a predetermined return angle, and the steering angle at that time is determined. The angle detected by the sensor is set as the instructed steering angle for turning.
Further, the invention of claim 3 is the work vehicle according to claim 1, wherein the command steering angle setting means for turning is in the on state of the automatic steering control and the angle detected by the steering angle sensor or the angle detected by the steering angle sensor When the instructed steering angle exceeds the predetermined turn determination angle, the front wheels are steered to a mechanical limit angle, and the angle detected by the steering angle sensor at the time when the limit angle is reached is returned by a predetermined return angle. The subtracted angle is set as the instruction steering angle for turning.
Further, the invention of claim 4 is the work vehicle according to any one of claims 1 to 3, wherein the control unit controls the state in which the automatic steering control is turned off, or the angle detected by the steering angle sensor Alternatively, when the instructed steering angle becomes equal to or less than the predetermined turning determination angle, the instructed steering angle for turning is reset to an initial value.

According to the first aspect of the invention, when the aircraft is turning, the front wheels are steered to the mechanical limit angle, so that the turning radius can be prevented from increasing greatly, and the next stroke can be appropriately entered. In addition, since the angle detected by the steering angle sensor when the limit angle is reached is set as the command steering angle for turning, the front wheels can be mechanically maintained at the limit angle during turning of the aircraft.
According to the invention of claim 2, after the front wheels are steered to the mechanical limit angle, the front wheels are steered in the reverse direction by a predetermined return angle, and the angle detected by the steering angle sensor at that time is used for turning. Since it is set as the instructed steering angle, it is possible to reduce the load on the hydraulic equipment by suppressing the operation of the relief valve that occurs at the limit angle.
Further, according to the third aspect of the present invention, an angle obtained by subtracting a predetermined return angle from the angle detected by the steering angle sensor when the limit angle is reached is set as the instructed steering angle for turning. After reaching the turning point, the front wheels can be steered in the opposite direction by a predetermined return angle based on the decremented turning instruction steering angle.
Further, according to the fourth aspect of the invention, the controller controls the command steering for turning when the automatic steering control is turned off or when the angle detected by the steering angle sensor or the command steering angle becomes equal to or less than a predetermined turning determination angle. Since the angle is reset and returned to the initial value, it is possible to suppress the influence on the automatic steering control when the aircraft is not turning. Sensor error fluctuations can also be handled appropriately.

It is a left view of the riding rice transplanter which concerns on embodiment of this invention. It is a top view of a riding rice transplanter. It is a perspective view of a riding rice transplanter. It is a left side view of a steering device. It is a right side view of a steering device. It is the perspective view which looked the steering apparatus from the right front. FIG. 2 is an explanatory diagram of a steering angle, in which (a) is a plan view of a steering device, and (b) is a diagram showing the relationship between a mechanical steering angle and a steering angle detected by a steering angle sensor; FIG. 10 is a diagram showing an automatic steering unit, (a) is a perspective view of the automatic steering unit, (b) is a front view showing an operation panel of the automatic steering unit, and (c) is a front view showing another example of the operation panel. . It is a block diagram which shows the control structure of a riding rice transplanter. It is explanatory drawing which shows the work driving|running|working path|route of a riding rice transplanter. It is explanatory drawing which shows the turning path|route of a riding rice transplanter. 4 is a flow chart showing a main routine of limit angle forced steering control; 4 is a flowchart showing flag control, which is a subroutine of limit angle forced steering control. 4 is a flowchart showing execution/stop control, which is a subroutine of limit angle forced steering control.

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. In FIGS. 1 to 3, reference numeral 1 denotes a traveling body of a riding rice transplanter P (working vehicle), and to the rear of the traveling body 1, a planting work machine 3 is connected via an elevating link mechanism 2 so as to be able to ascend and descend. It is

The planting machine 3 includes a seedling table 4 on which matted seedlings are placed, and a planting mechanism 5 for scraping the seedlings from the lower end of the seedling table 4 and planting them in a field. The planting machine 3 of the present embodiment has a six-row planting specification capable of planting six seedlings at the same time, and six planting mechanisms 5 are arranged side by side at predetermined intervals in the vehicle width direction. .

The traveling machine body 1 includes an engine mounting section 6 on which an engine (not shown) is mounted, an HST 7 (see FIG. 4) that continuously changes the engine power, and further changes the power input from the HST 7 to change the traveling power and A transmission case 8 (see FIGS. 4 and 5) output as working power, a front wheel 10 driven by the traveling power output by the mission case 8 and steered by a steering device 9 described later, and the transmission case 8 output It has a rear wheel 11 driven by running power and a control section 12 on which a worker rides.

The control unit 12 includes a steering handle 13 for steering the front wheels 10, a main gear shift lever 14 for shifting the HST 7, a work machine lifting lever (not shown) which also serves as a lifting operation tool for the planting work machine 3 and a planting clutch operation tool. ) are arranged.

The steering device 9 is a device that steers the front wheels 10 according to manual operation of the steering handle 13 or operation of an automatic steering unit 15 (see FIG. 8), which will be described later. A pair of left and right front axles 16 that steerably support a pair of front wheels 10, and a torque generator 18 that swings a pitman arm 17 left and right according to manual operation of a steering handle 13 or operation of an automatic steering unit 15, which will be described later. , a pair of left and right steering rods 19 connecting the pitman arms 17 to the left and right front axles 16 .

As shown in FIGS. 4 to 7, the steering device 9 is provided with a steering angle sensor 21 for detecting the steering angle of the front wheels 10 via a sensor interlocking mechanism 20. FIG. The steering angle sensor 21 is, for example, a potentiometer and attached to the sensor bracket 22 .

The sensor interlocking mechanism 20 rotates around a first interlocking arm 24 and a second interlocking arm 25 integrally rotated around a first support shaft 23 and around a second support shaft 26 provided on the sensor bracket 22 . A third interlocking arm 27 , a first interlocking rod 28 connecting the first interlocking arm 24 and the pitman arm 17 , and a second interlocking rod 29 connecting the second interlocking arm 25 and the third interlocking arm 27 are provided.

When the front wheel 10 is steered, the third interlocking arm 27 rotates via the pitman arm 17 , first interlocking rod 28 , first interlocking arm 24 , second interlocking arm 25 and second interlocking rod 29 . The third interlocking arm 27 has a pin 27 a that engages with the sensor arm 21 a of the steering angle sensor 21 , and inputs a rotation angle corresponding to the steering angle of the front wheels 10 to the steering angle sensor 21 .

As shown in FIG. 7A, the steering device 9 can steer the front wheels 10 up to a mechanical limit angle ±α2, and the detection range of the steering angle sensor 21 includes the mechanical limit angle of the front wheels 10 The range -α2 to +α2 is included. However, as shown in FIG. 7B, there is a difference between the angle detected by the steering angle sensor 21 and the actual steering angle of the front wheels 10 due to the characteristics of the steering angle sensor 21 and the surrounding mechanical configuration. However, errors such as hysteresis and offset may occur.

As shown in (a) of FIG. 8 , an automatic steering unit 15 is connected to the steering handle 13 . The automatic steering unit 15 includes a steering motor 30 (see FIG. 9) that rotates the steering handle 13 by motor power in place of the manual operation of the steering handle 13, an operation tool related to automatic steering control and a monitor lamp, which will be described later. and an operation panel 31 to be used. The automatic steering unit 15 also includes a current value sensor 32 (see FIG. 9) that detects the value of current flowing through the steering motor 30. Manual operation of the steering wheel 13 is detected based on the value detected by the current value sensor 32. and has a manual operation priority function for automatically stopping the drive of the steering motor 30 .

As shown in FIG. 8B, the operation panel 31 includes a power switch 33 and an automatic steering control operation for switching from an automatic steering OFF state in which automatic steering is not performed to an automatic steering ON state in which automatic steering is performed. An automatic steering switch 34 capable of switching from a steering ON state to an automatic steering OFF state, a starting point A point registration switch 35 for registering a starting point A, which will be described later, and an end point B point registration switch for registering an end point B, which will be described later. 36, a reset switch 37 arranged near the automatic steering switch 34, and a notification display unit 38 that performs notification by lamp display. In addition, FIG. 8(c) shows the operation panel 31B used when performing automatic steering based on the camera image.

As shown in FIGS. 1 to 3, the control unit 12 is provided with a positioning frame 40 shaped like a letter when viewed from the front. The positioning frame 40 has a pair of left and right vertical frame portions 40a extending upward, and a horizontal frame portion 40b connecting upper ends of the left and right vertical frame portions 40a. Two GNSS antennas 42, 43, etc., which are components of a position information acquisition system 41, which will be described later, are attached to the horizontal frame portion 40b, and a tablet 44 that performs navigation display etc. is attached to one of the left and right vertical frames 40a. installed.

As shown in FIG. 9, the traveling body 1 includes a position information acquisition system 41 and a control unit 50 as control components for performing automatic steering control. As the position information acquisition system 41, for example, an RTK-GNSS positioning system capable of highly accurate positioning with an error of several cm is adopted. The RTK-GNSS positioning system performs GNSS positioning such as GPS using a fixed base station and a moving mobile station, and corrects the positioning data in real time using correction signals sent from the base station to the mobile station. By doing so, highly accurate positioning with an error of several centimeters is realized. In addition, if two GNSS antennas are installed on the mobile station with a predetermined interval, not only the absolute position of the mobile station but also the traveling direction (azimuth) of the mobile station can be detected with high accuracy based on the two positioning results. it becomes possible to

Specifically, as shown in FIG. 9, the position information acquisition system 41 of the present embodiment includes a GNSS unit 45, which is a control unit that performs RTK-GNSS positioning, and a horizontal frame portion 40b of the positioning frame 40. It is equipped with a reference GNSS antenna 42 and an azimuth GNSS antenna 43 mounted at a predetermined interval in the vehicle width direction, and a correction signal receiver 47 for receiving a correction signal from a fixedly installed RTK base station 46 . The GNSS unit 45 transmits positioning data (absolute position data and traveling direction data) by RTK-GNSS positioning to the control unit 50 via wired communication means such as CAN, and wireless communication means such as Bluetooth (registered trademark). to the tablet 44 via.

The control unit 50 is a control unit (including a CPU, a storage unit, a timer, etc.) that executes automatic steering control. As shown in FIG. A current value sensor 32, an automatic steering switch 34, a start point A point registration switch 35, an end point B point registration switch 36, and a reset switch 37 are connected. In addition, a notification buzzer 39 for outputting a notification sound is connected.

In the automatic steering control, based on the position information of the traveling machine body 1 acquired by the position information acquisition system 41, the traveling machine body 1 automatically travels straight along the virtual target traveling line (L1, L2, . . . Ln), and the virtual This is an automatic control function that automatically steers the front wheels 10 so that when the end of the target travel line is reached, the vehicle automatically turns and shifts to the virtual target travel line of the next stroke.

In addition, in the normal rice planting work according to the 6-row planting specification, the first work process (process indicated by circled number 1 in FIG. The second work process for planting on the outer circumference side of the ground (the process indicated by the circled number 2 in FIG. 10) and the third work process for planting on the inner circumference side of the headland (circled in FIG. 10 Step indicated by number 3) is performed. The automatic steering control of the present embodiment includes automatic straight-ahead control and automatic turning control in the first work stroke, but automatic steering control may also be executed in the second and third work strokes.

As shown in FIG. 10, at the start of work, the starting point A point registration switch 35 is operated at the starting point position of the reference traveling line (L0) which is the first planting work process, and the positioning data of the starting point A is registered. At the end point position of the reference travel line (L0), the end point B point registration switch 36 is operated to register the positioning data of the end point B point. As a result, subsequent virtual target travel lines (L1, L2, . . . Ln) are automatically calculated based on the reference travel line (L0).

Further, as shown in FIG. 11, in the automatic steering control, when the traveling machine body 1 (the planting position of the planting machine 3) reaches the end of the virtual target traveling line (the rear end of the traveling machine body 1 is at the T0 position), The planting work machine 3 is automatically raised, and the front wheels 10 are automatically steered to an instructed steering angle for turning to turn the traveling body 1 on the headland. Further, in the automatic steering control, when the rear end of the traveling body 1 reaches the turning end position T1, the front wheels 10 are returned to the straight traveling direction to cause the traveling body 1 to enter the virtual target travel line of the next stroke. Furthermore, in the automatic steering control, when the traveling machine body 1 (the planting position of the planting machine 3) reaches the start end of the virtual target traveling line of the next stroke (the rear end of the traveling machine body 1 is at the T2 position), the planting machine 3 is automatically lowered to start planting travel in the next stroke.

However, as described above, if there is an error such as hysteresis or offset between the angle detected by the steering angle sensor 21 and the actual steering angle of the front wheels 10, the effect of the error increases when the aircraft turns. There is a possibility that the turning radius will be greatly expanded and it will not be possible to properly enter the next stroke.

Therefore, the control unit 50 of the present embodiment includes limit angle forced steering control means (turning instruction steering angle setting means) capable of solving the above problems. When the automatic steering control is on and the angle detected by the steering angle sensor 21 or the steering angle instructed by the control section 50 to the automatic steering unit 15 exceeds a predetermined turning determination angle, the limit angle forced steering control means is configured to rotate the front wheels 10. is steered to a mechanical limit angle, and the angle detected by the steering angle sensor 21 when the limit angle is reached is set as the command steering angle for turning. In addition, when the front wheel 10 reaches the mechanical limit angle, the detected value of the current value sensor 32 exceeds a predetermined threshold, and the duration (hereinafter sometimes referred to as a steering wheel load counter) exceeds a predetermined time. can be determined based on whether or not the

According to such limit angle forced steering control means, when the machine body turns, the front wheels 10 are steered to the mechanical limit angle. . In addition, since the angle detected by the steering angle sensor 21 when the limit angle is reached is set as the command steering angle for turning, the front wheels 10 can be mechanically maintained at the limit angle during turning of the aircraft.

Further, the limit angle forced steering control means of the present embodiment mechanically rotates the front wheels 10 when the automatic steering control is on and the angle detected by the steering angle sensor 21 or the instructed steering angle exceeds a predetermined turning determination angle. At the same time, an angle obtained by subtracting a predetermined return angle from the angle detected by the steering angle sensor 21 when the limit angle is reached is set as the command steering angle for turning. As a result, after the front wheels 10 reach the limit angle, the front wheels 10 can be steered in the reverse direction by a predetermined return angle based on the subtracted turning instruction steering angle. As a result, it is possible to reduce the load on the hydraulic equipment by suppressing the operation of the relief valve that occurs at the mechanical limit angle.

Further, in this embodiment, when the automatic steering control is turned off, or when the angle detected by the steering angle sensor 21 or the instructed steering angle becomes equal to or less than a predetermined turning determination angle, the instructed steering angle for turning is reset to the initial value. back to In this way, it is possible to suppress the influence on the automatic steering control at times other than when the aircraft is turning. can also be handled appropriately.

Next, a processing procedure of limit angle forced steering control for realizing the control function as described above will be described with reference to FIGS. 12 to 14. FIG.

As shown in FIG. 12, the limit angle forced steering control includes flag control (S1) and execution/stop control (S2), which are subroutines. As shown in FIG. 13, in the flag control, the control unit 50 determines whether or not the automatic steering control is ON and the angle detected by the steering angle sensor 21 and the instructed steering angle have exceeded a predetermined threshold value (turning determination angle). is determined (S101), and if the determination result is YES, the limit angle forced steering control flag is set (S102), and if the determination result is NO, the limit angle forced steering control flag is reset (S103). In this embodiment, when the limit angle forced steering control flag is reset, the command steering angle for turning is also reset.

As shown in FIG. 14, in the execution/stop control, the control unit 50 smoothes the steering wheel load counter (S201), determines the state of the limit angle forced steering control flag (S202), and determines the limit angle forced steering control. When it is determined that the flag is in the reset state, after resetting the limit angle arrival flag and the front wheel angle return flag (S203, S204), the process returns to the upper routine.

When the controller 50 determines that the limit angle forced steering control flag is set, the controller 50 compares the steering angle sensor value with the instructed steering angle, and sets the steering wheel load counter value to a predetermined threshold value (limit angle arrival determination value). (S205-S208). Here, if the steering angle sensor value is less than the instructed steering angle and the steering wheel load counter value is less than a predetermined threshold value, the control unit 50 determines that the front wheels 10 have not reached the mechanical limit angle (S205). YES), and if the steering angle sensor value is less than the instructed steering angle and the steering wheel load counter value is equal to or greater than a predetermined threshold value, the front wheels 10 reach the mechanical limit angle even if the steering angle sensor value is less than the instructed steering angle. (YES in S206), and if the steering angle sensor value is equal to or greater than the instructed steering angle and the steering wheel load counter value is less than the predetermined threshold value, the steering angle sensor value is equal to or greater than the instructed steering angle. However, if it is determined that the front wheels 10 have not reached the mechanical limit angle (YES in S207), and if the steering angle sensor value is equal to or greater than the instructed steering angle and the steering wheel load counter value is equal to or greater than a predetermined threshold value determines that the front wheel 10 has reached the mechanical limit angle (YES in S208).

If the determination result in step S205 is YES, the control unit 50 continues the steering of the front wheels 10 in the direction of the limit angle. By gradually adding (S209), the steering of the front wheels 10 in the limit angle direction is continued.

On the other hand, if the determination result in step S206 or step S208 is YES, the controller 50 substitutes the steering angle sensor value for the instructed steering angle (instructed steering angle for turning) (S210, S212). An arrival flag is set (S211, S213). After that, the control unit 50 subtracts a predetermined return angle from the instructed steering angle (S215) in accordance with whether the limit angle arrival flag is set (S214). As a result, after the front wheels 10 reach the limit angle, the front wheels 10 can be steered in the reverse direction by a predetermined return angle based on the subtracted command steering angle. Note that the subtraction process in step S215 is executed only once after the limit angle arrival flag is set, and after the subtraction process is executed, based on the front wheel angle return flag being set (S216), a skip process for skipping step S215 is executed. (S217).

According to the present embodiment configured as described above, the traveling machine body 1 having the front wheels 10 and the rear wheels 11, the position information acquisition system 41 for acquiring the position information of the traveling machine body 1, and the front wheels 10 are steered by driving the actuators. The steering device 9 (automatic steering unit 15), the steering angle sensor 21 for detecting the steering angle of the front wheels 10, and the position information of the traveling machine body 1 acquired by the position information acquisition system 41 are used to control the steering device 9. and a control unit 50 configured to be capable of executing automatic steering control, wherein the control unit 50 controls the detection angle of the steering angle sensor 21 when the automatic steering control is on and the control unit 50 When the commanded steering angle to the steering device 9 exceeds a predetermined turning determination angle, the front wheels 10 are steered to a mechanical limit angle, and the angle detected by the steering angle sensor 21 at the time when the limit angle is reached is used as an instruction for turning. Since a limit angle forced steering control means for setting the steering angle is provided, the front wheels 10 can be steered to the mechanical limit angle when the aircraft is turning. can enter properly. In addition, since the angle detected by the steering angle sensor 21 when the limit angle is reached is set as the command steering angle for turning, the front wheels 10 can be mechanically maintained at the limit angle during turning of the aircraft.

In addition, the limit angle forced steering control means rotates the front wheels 10 up to the mechanical limit angle when the automatic steering control is on and the angle detected by the steering angle sensor 21 or the instructed steering angle exceeds a predetermined turn determination angle. As the vehicle is steered, an angle obtained by subtracting a predetermined return angle from the angle detected by the steering angle sensor 21 at the time when the front wheel 10 reaches the limit angle is set as the instruction steering angle for turning. The front wheels 10 can be steered in the reverse direction by a predetermined return angle based on the subtracted command steering angle for turning, and the relief operation of the hydraulic equipment can be suppressed.

Further, when the automatic steering control is turned off, or when the angle detected by the steering angle sensor 21 or the commanded steering angle becomes equal to or less than a predetermined turn determination angle, the control unit 50 resets the commanded steering angle for turning to the initial value. In addition, by resetting a new instruction steering angle for turning each time the aircraft turns, it is possible to reduce the error fluctuation of the steering angle sensor 21 during work. can respond appropriately.

The present invention is not limited to the above embodiments, and various modifications and changes are possible within the scope of the gist of the present invention described in the claims. For example, when the automatic steering control is ON and the angle detected by the steering angle sensor 21 or the instructed steering angle exceeds a predetermined turn determination angle, the limit angle forced steering control means moves the front wheels 10 up to the mechanical limit angle. After steering, the front wheels 10 may be steered in the reverse direction by a predetermined return angle, and the angle detected by the steering angle sensor 21 at that time may be set as the command steering angle for turning.

1 Traveling body 2 Lifting link mechanism 3 Planting work machine 4 Seedling platform 5 Planting mechanism 6 Engine mounting part 7 HST
8 Transmission case 9 Steering device 10 Front wheel 11 Rear wheel 12 Control unit 13 Steering handle 14 Main transmission lever 15 Automatic steering unit 16 Front axle 17 Pitman arm 18 Torque generator 19 Steering rod 20 Sensor interlocking mechanism 21 Steering angle sensor 21a Sensor arm 22 Sensor Bracket 23 First support shaft 24 First interlocking arm 25 Second interlocking arm 26 Second support shaft 27 Third interlocking arm 27a Pin 28 First interlocking rod 29 Second interlocking rod 30 Steering motors 31, 31B Operation panel 32 Current value sensor 33 power switch 34 automatic steering switch 35 start point A point registration switch 36 end point B point registration switch 37 reset switch 38 notification display section 39 notification buzzer 40 positioning frame 40a vertical frame section 40b horizontal frame section 41 position information acquisition system 42 reference GNSS Antenna 43 Directional GNSS antenna 44 Tablet 45 GNSS unit 46 RTK base station 47 Correction signal receiver 50 Control unit

Claims (4)

A running body having front wheels and rear wheels;
a position information acquisition system for acquiring position information of the traveling machine;
a steering device that steers the front wheels by driving an actuator;
a steering angle sensor that detects the steering angle of the front wheels;
a control unit configured to be capable of executing automatic steering control for controlling the steering device based on the position information of the traveling machine body acquired by the position information acquisition system, wherein
When the automatic steering control is on and the angle detected by the steering angle sensor or the steering angle instructed by the control unit to the steering device exceeds a predetermined turning determination angle, the control unit mechanically rotates the front wheels. a command steering angle setting means for steering the work vehicle up to a limit angle and setting an angle detected by the steering angle sensor at the time when the limit angle is reached as a command steering angle for turning. The instructed steering angle setting means for turning mechanically moves the front wheels when the automatic steering control is on and the angle detected by the steering angle sensor or the instructed steering angle exceeds the predetermined turning determination angle. After the vehicle is steered to the limit angle, the front wheels are steered in the opposite direction by a predetermined return angle, and the angle detected by the steering angle sensor at that time is set as the instruction steering angle for turning. 1. The work vehicle according to 1. The instructed steering angle setting means for turning mechanically moves the front wheels when the automatic steering control is on and the angle detected by the steering angle sensor or the instructed steering angle exceeds the predetermined turning determination angle. The vehicle is steered to a limit angle, and an angle obtained by subtracting a predetermined return angle from the angle detected by the steering angle sensor when the limit angle is reached is set as the command steering angle for turning. Work vehicle described in . The controller resets the command steering angle for turning when the automatic steering control is turned off or when the angle detected by the steering angle sensor or the command steering angle becomes equal to or less than the predetermined turning determination angle. The work vehicle according to any one of claims 1 to 3, wherein the work vehicle is reset to an initial value.

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