Work vehicles

Abstract

To provide a work vehicle in which a load of steering operation can be changed according to a situation during work travel.SOLUTION: A work vehicle includes: a travel vehicle body; a steering wheel that changes a travel direction of the travel vehicle body; a steering wheel for operating the steering wheel; a steering sensor 21 that detects operation of the steering wheel; and a control unit 20 that changes an operation load of the steering wheel. At the time of work in a field, when the control unit 20 determines that turning operation of the steering wheel is performed on the basis of a detection value of the steering sensor 21, the control unit sets the operation load of the steering wheel to be smaller than that when the turning operation is not detected.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to work vehicles such as tractors. [Background technology]

[0002] Conventionally, the steering load on a work vehicle is significantly different when it is traveling on public roads and when it is traveling for work purposes. Therefore, when traveling on public roads, an inexperienced driver may operate the steering wheel in the same way as when traveling for work purposes, causing the vehicle to sway significantly from side to side.

[0003] Therefore, a known work vehicle is equipped with a mode selector switch that switches between work mode and non-work mode, and when the non-work mode is selected, the steering speed of the steered wheels relative to the steering operation speed is set slower than when the work mode is selected (Prior Document 1).

[0004] Such a work vehicle can suppress wobbling when not working. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 10-109660 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in a work vehicle, it may be desirable to vary the steering load even during work, but the above technology does not allow the steering load to be changed depending on the situation during work travel.

[0007] An object of the present invention is to provide a work vehicle that can appropriately change the steering load depending on the situation while traveling for work. [Means for solving the problem]

[0008] The present invention provides A running vehicle body, a steering wheel for changing the direction of travel of the traveling vehicle body; a steering wheel for operating the steering wheels; a steering sensor for detecting an operation of the steering wheel; a control unit for changing the operation load of the steering wheel, a hydraulic power steering mechanism is used to operate the steering wheels with the steering wheel, The hydraulic power steering mechanism includes a hydraulic device that sends hydraulic oil to a steering wheel drive hydraulic cylinder in response to rotation of the steering wheel, When working in the field, When the control unit determines that the steering wheel has been turned based on the detection value of the steering sensor, it adjusts the variable throttle between the hydraulic device and the steering wheel drive hydraulic cylinder to reduce the operating load of the steering wheel compared to when the turning operation is not detected, The steering sensor detects an angular velocity of the steering wheel operation, and the control unit determines that the steering wheel is being turned when the angular velocity exceeds a predetermined value. When the steering wheel operation angle is equal to or greater than a predetermined effective angle, the angle of the steering wheels begins to change, When the control unit determines that the steering wheel has been turned within a range less than the effective angle, the control unit reduces the operating load of the steering wheel compared to when the turning operation is not detected, This work vehicle is characterized in that when the control unit determines that the steering wheel has been turned within a range equal to or greater than the effective angle, it gradually reduces the steering wheel operating load in stages or continuously in accordance with predetermined rules compared to when the turning operation is not detected. First invention related to the present invention teeth, A running vehicle body, a steering wheel for changing the direction of travel of the traveling vehicle body; a steering wheel for operating the steering wheels; a steering sensor for detecting an operation of the steering wheel; a control unit for changing the operation load of the steering wheel, When working in the field, This work vehicle is characterized in that when the control unit determines that the steering wheel has been turned based on the detection value of the steering sensor, it reduces the operating load of the steering wheel compared to when the turning operation is not detected.

[0009] Second invention related to the present invention teeth, The steering sensor detects an angular velocity of the steering wheel operation, and the control unit determines that the steering wheel is being turned when the angular velocity exceeds a predetermined value. First invention related to the present invention It is a work vehicle.

[0010] The third invention related to the present invention teeth, A structure in which the angle of the steering wheel begins to change when the operation angle of the steering wheel is equal to or greater than a predetermined effective angle, and the control unit determines whether or not the turning operation is occurring within a range less than the effective angle, and does not determine whether or not the turning operation is occurring within a range equal to or greater than the effective angle. Second invention related to the present invention It is a work vehicle.

[0011] The fourth invention related to the present invention teeth, When the steering wheel operation angle is equal to or greater than a predetermined effective angle, the angle of the steering wheels begins to change, When the control unit determines that the steering wheel has been turned within a range less than the effective angle, the control unit reduces the operating load of the steering wheel compared to when the turning operation is not detected, When the control unit determines that a turning operation of the steering wheel has been performed within a range equal to or greater than the effective angle, the control unit gradually reduces the operating load of the steering wheel in a stepwise or continuous manner in accordance with a predetermined rule compared to when the turning operation is not detected. Second invention related to the present invention It is a work vehicle.

[0012] Fifth Invention Related to the Present Invention teeth, a hydraulic power steering mechanism is used to operate the steering wheels with the steering wheel, the control unit changes the operation load of the steering wheel by controlling a hydraulic circuit of the hydraulic power steering mechanism. First invention related to the present invention It is a work vehicle.

[0013] The sixth invention related to the present invention teeth, an electric power steering mechanism using an electric motor is used to operate the steering wheels with the steering wheel, the control unit changes the operation load of the steering wheel by controlling the electric power steering mechanism. First invention related to the present invention It is a work vehicle. [Effects of the Invention]

[0014] This invention reduces the burden on the driver by reducing the steering load when turning, which requires a large amount of steering. It also makes it possible to appropriately change the steering load, such as by making the steering load heavier when not turning, such as when traveling straight, compared to when turning, thereby ensuring stability when traveling straight. Furthermore, since it is possible to determine whether a turning operation is being performed almost immediately after the start of the operation, rather than judging by the steering angle, the driver can operate the steering wheel without any discomfort. Furthermore, once the steering wheels have rotated and the vehicle body has begun to turn, any change in steering wheel load while the vehicle body is turning is made gradually, which has the advantage of reducing the sense of discomfort. First invention related to the present invention This allows the steering wheel to be turned with less force by reducing the steering load when turning. By reducing the steering load when turning, which requires a large amount of operation, the burden on the driver can be reduced. When not turning, such as when going straight, the steering load can be made heavier than when turning, ensuring stability when going straight. This allows the steering load to be appropriately changed.

[0015] Second invention related to the present invention Therefore, when detecting the operation angle to determine whether a turn is being made, a certain angle is required to determine whether a turn is being made, but in that case, the load may change during the operation, which can easily cause an uncomfortable feeling in the operation.In contrast, if the determination is made based on the angular velocity, it can be determined whether a turn is being made almost immediately after the operation starts, rather than judging based on the operation angle, so the driver can operate without any discomfort.

[0016] Third invention related to the present invention As a result, based on the premise that the steering wheel will not rotate unless the steering wheel is rotated beyond a predetermined effective angle (play range), the steering wheel operating load is changed before the angle of the steering wheel begins to change, and is not changed after the steering wheel has rotated and the vehicle body has begun to turn, thereby preventing a phenomenon in which the steering wheel load is changed while the vehicle body is turning, causing an uncomfortable feeling.

[0017] The fourth invention related to the present invention This has the advantage that, assuming a mechanism (play range) in which the steering wheel will not rotate unless the steering wheel is rotated beyond a predetermined effective angle, once the steering wheel has rotated and the vehicle body has started to turn, even if the load on the steering wheel is changed while the vehicle body is turning, it is done gradually, so there is little sense of discomfort.

[0018] Fifth Invention Related to the Present Invention This allows the use of a hydraulic power steering mechanism.

[0019] The sixth invention related to the present invention This allows the use of an electric power steering mechanism. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a side view of a tractor according to an embodiment of the present invention; [Figure 2] Plan of the field on which the tractor runs [Figure 3] Diagram of the tractor's main components [Figure 4] Plan view of the steering wheel of the tractor [Figure 5] Control configuration diagram of the tractor [Figure 6] A diagram showing the hydraulic power steering mechanism (neutral state) that is the control target of the control unit of the tractor. [Figure 7] The figure shows the hydraulic power steering mechanism (left turning state) that is the control target of the control unit of the tractor. [Figure 8] The figure shows the hydraulic power steering mechanism (right turning state) that is the control target of the control unit of the tractor. [Figure 9] A diagram showing the electric power steering mechanism that is controlled by the control unit of the tractor. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0022] Fig. 1 shows a tractor as an example of a work vehicle according to an embodiment of the present invention. First, the overall configuration of the tractor 1 will be described with reference to Fig. 1.

[0023] The tractor 1, which is a work vehicle, is an agricultural tractor that performs work in fields or the like, and a driver (also called an operator) rides on it and performs a predetermined task while traveling within the field.

[0024] In the following description, the forward / rearward direction refers to the direction of travel of the tractor 1 when traveling straight, with the forward side of the traveling direction being defined as "front" and the rear side being defined as "rear." The traveling direction of the tractor 1 refers to the direction from the driver's seat 8 (described later) toward the steering wheel (steering device) 9 when traveling straight (see FIG. 1).

[0025] The left-right direction is a direction that is horizontally perpendicular to the front-rear direction. Hereinafter, left and right are defined as facing the "front." That is, when the operator of the tractor 1 (also referred to as the "operator") is seated in the operator's seat 8 and facing forward, the left-hand side is the "left" and the right-hand side is the "right."

[0026] The up-down direction is the vertical direction. The front-rear direction, left-right direction, and up-down direction are perpendicular to each other. Note that each direction is defined for the convenience of explanation, and the present invention is not limited by these directions. In the following, the tractor 1 may be referred to as the "machine body" or "vehicle body."

[0027] As shown in Figure 1, the tractor 1 includes a traveling body 2 and a link mechanism for a work implement at the rear of the traveling body 2. The traveling body 2 includes a body frame 3, front wheels 4, rear wheels 5, a bonnet 6, an engine E, a control section 7, and a transmission case 10. The body frame 3 is the main frame of the traveling body 2.

[0028] The front wheels 4 are a pair of left and right wheels, and are primarily used for steering (steering wheels 4). The rear wheels 5 are a pair of left and right wheels, and are primarily used for driving (driving wheels 5). The tractor 1 may be configured to be switchable between two-wheel drive (2WD) in which the rear wheels 5 are driven, and four-wheel drive (4WD) in which both the front wheels 4 and the rear wheels 5 are driven. In this case, both the front wheels 4 and the rear wheels 5 are driven wheels.

[0029] The hood 6 is provided at the front of the traveling vehicle body 2 so as to be able to be opened and closed freely. The hood 6 can be rotated (opened and closed) in the vertical direction with the rear part as the rotation center. When closed, the hood 6 covers the engine E mounted on the vehicle body frame 3. The engine E is the driving source of the tractor 1 and is a heat engine such as a diesel engine or a gasoline engine. Note that the hood 6 may also rotate with the front part as the rotation center.

[0030] The control unit 7 is provided on top of the traveling vehicle body 2 and includes a control seat 8 and a steering wheel (steering device) 9. The control seat 8 is the driver's seat. The steering wheel 9 is operated by the driver when steering the front wheels 4. The control unit 7 includes a display unit (meter panel) 9a in front of the steering wheel 9 that displays various information.

[0031] The control unit 7 also includes various operation levers such as a forward / reverse lever, an accelerator lever, a main speed change lever, and an auxiliary speed change lever, as well as various operation pedals such as an accelerator pedal, a brake pedal, and a clutch pedal.

[0032] In addition, 10 is a transmission case, 12 is a traction unit, 20 is a control unit, 30 is a GNSS device, S is a navigation satellite, and Vs is a sensor attached to the vehicle frame 3 to detect the speed of the tractor 1.

[0033] Figure 2 shows such a tractor 1 working in field H, with the tractor performing work in a straight line process of traveling back and forth in the center, a turning process of traveling in a circle between the straight line processes, and a circular process on the periphery.

[0034] FIG. 3 is a configuration diagram of the control unit 20. Reference numeral 21 denotes a steering sensor, which in this embodiment is a sensor that detects the angular velocity of the operation angle of the rotation of the steering wheel 9. The detected value of the steering sensor 21 is sent to a determination unit 20a of the control unit 20. On the other hand, the control unit 20 is provided with a numerical value setting unit 20b, which is constantly input to the determination unit 20a. In this embodiment, a predetermined numerical value of the angular velocity is preset in the numerical value setting unit 20b. The value of the predetermined angular velocity is set to a value that, when the predetermined angular velocity is reached, can reliably determine that the steering wheel 9 has been turned by the steering operation of the driver. In addition, it also fulfills the function of distinguishing between a weak turn while traveling straight ahead and a strong turn near a bank.

[0035] As a result, the judgment unit 20a compares the value of the detection signal input from the steering sensor 21 with the numerical value set in the numerical value setting unit 20b, and if the two match, it determines that the steering wheel 9 has been turned.

[0036] In this way, when the determination unit 20a determines that a turning operation has occurred, the determination unit 20a issues an instruction to make the operational load of the steering wheel 9 lighter than when the turning operation has not been detected. In accordance with the instruction, the operational load of the steering wheel 9 is made lighter than the previous state by various methods, which will be described later.

[0037] The detection of the angular velocity of the steering sensor 21 and the determination of the turning operation based thereon may be performed by determining whether or not the turning operation is occurring within a range less than the effective angle, and not determining whether or not the turning operation is occurring within a range equal to or greater than the effective angle. θ in Figure 4 indicates the effective angle.

[0038] In other words, based on the premise that the steering wheels 4,4 will not rotate unless the steering wheel 9 is rotated by a predetermined effective angle θ or more (the so-called play range), the operating load on the steering wheel 9 is changed before the angle of the steering wheels 4,4 begins to change, and not after the steering wheels 4,4 have rotated and the vehicle body 2 has begun to turn, thereby preventing a phenomenon in which the load on the steering wheel 9 is changed while the vehicle body 2 is turning, causing an uncomfortable feeling.

[0039] As a modified example, if the angular velocity does not reach a predetermined value before the effective angle θ, and then reaches the predetermined value, the operation load of the steering wheel 9 may be reduced, but the load may not be reduced suddenly, but may be gradually reduced in stages or continuously according to a predetermined rule in order to reduce the sense of discomfort.

[0040] Next, an embodiment will be described in which a characteristic other than the angular velocity is detected by the steering sensor 21 to determine that the steering wheel 9 has been or will be turned (see FIG. 5). a. An example in which the steering sensor 21 detects the torque applied to the steering wheel 9 and determines that a turning operation has been performed. For example, a strain sensor that detects the twist of the shaft of the steering wheel 9 is used.

[0041] At this time, the steering load may be changed in stages according to the magnitude of the torque. b. This is an example in which the steering sensor 21 detects the turning speed of the steering wheel 9, that is, the circumferential speed, and determines that a turning operation has been performed.

[0042] At this time, if a circumferential speed equal to or greater than a predetermined circumferential speed is detected, it is determined that a turning operation has been performed.

[0043] It is also possible to make such a judgment within the scope of play and not make a judgment beyond that scope.

[0044] The fact that turning judgment is not performed in a range exceeding this range of play can also be applied to other embodiments.

[0045] Alternatively, instead of detecting the angular velocity, angular acceleration may be detected to determine whether the vehicle is turning.

[0046] An embodiment in which turning is detected by a device other than a steering sensor will be described below (see FIG. 5). a. The steering angle sensor 52 detects the steering angle of the steering wheels 4, 4 of the tractor 1, and when a steering angle of a predetermined value or more is detected, it is determined that the tractor is turning.

[0047] In addition, it is also possible to drive the so-called auto-lift of the work machine in conjunction with the detection of the steering angle. b. A load sensor 53 that detects the load on the steering wheel axle detects the load on the axle of the steering wheels 4, 4 of the tractor 1, and if a load exceeding a predetermined value is applied, it is determined that the tractor is turning. For example, a strain sensor may be attached to the traveling axle of the steering wheels 4, 4.

[0048] At this time, an axle load sensor may be used to detect the load shared by the steered wheels 4, 4. When the load shared exceeds a predetermined value, it is determined that the vehicle is turning, and the load on the steering wheel 9 is reduced.

[0049] At this time, it is desirable to change the load on the steering wheel 9 in stages according to the magnitude of the load on the steered wheels 4,4. c. Turning is determined by an IMU 54 such as a gyroscope. The angular velocity around the Z axis is detected, and if it exceeds a predetermined value, it is determined that the aircraft is turning. d. When the output value of the traction sensor (draft sensor) 55 exceeds a certain level, it is determined that the vehicle is going straight, and the load on the steering wheel 9 is increased. e. When the work implement is lowered by the up / down switch 56 of the work implement, it is determined that the work implement is moving straight and the load is increased. f. When the tractor 1 in operation reaches the end of the work position (turning position) of the work route in the field, it determines that it is about to turn and reduces the load on the steering wheel 9.

[0050] To achieve this, a GNSS device 30 is installed in advance, and the shape of the field is roughly grasped by acquiring four points on the field's outline using this. Alternatively, the field to be registered is selected using a map application, and the shape of the target field is roughly grasped from its latitude and longitude information. Meanwhile, the overall width, overall length, work position, work width, etc. of the work vehicle are registered. This work route 59 is generated by setting work information (turning pattern, number of trees to be cultivated around, etc.) based on the registered work vehicle information.

[0051] In a work vehicle that can use the straight-line assist mode function 57 when traveling straight, when the straight-line assist mode is enabled, it is determined that the vehicle will travel straight, and the load on the steering wheel 9 is increased.

[0052] Furthermore, when the straight-line assist function is changed from enabled to disabled, the load on the steering wheel 9 is reduced in anticipation of an upcoming turn.

[0053] In the above embodiment, a mode in which the load on the steering wheel 9 is changed and a mode in which the load is not changed may be prepared so that the operator can select either mode as desired. For this selection, a dial system, a switch system, a memory switch system 58, or the like may be adopted.

[0054] An example of changing the load independently of turning will be described below (see FIG. 5). a. The load can be changed arbitrarily.

[0055] The worker or the like can arbitrarily change the load on the steering wheel 9. It is desirable that the load on the steering wheel 9 can be changed to suit the worker's needs, depending on age, gender, and other factors.

[0056] Specifically, the load on the steering wheel 9 can be set as desired using a steering sensitivity dial installed inside the cabin, including the ROPS. Alternatively, a switch can be used instead of a dial. Alternatively, the load can be easily changed by selecting a pre-registered load on the steering wheel 9 using a memory switch. Furthermore, even after moving to another field, work can be carried out under the same load conditions on the steering wheel 9 as in the previous field. b. The vehicle speed is detected by the vehicle speed sensor Vs, and the load on the steering wheel 9 is changed according to the vehicle speed.

[0057] The load on the steering wheel 9 may be determined in stages in advance according to the vehicle speed range and changed automatically. It may be possible to select whether to enable or disable the mode of changing the load linked to the vehicle speed. A selector switch may be provided for this selection. Alternatively, a selector dial may be used.

[0058] Furthermore, if the vehicle speed is above a certain speed, it may be possible to make it impossible to reduce the load on the steering wheel 9, as this is dangerous. c. The load on the steering wheel 9 is changed depending on the type of gear. For example, the load is changed depending on the positions of the main transmission gear and the auxiliary transmission gear.

[0059] A case where an abnormality occurs in any of the various sensors in the above embodiment will now be described. a. If a detection means such as a sensor becomes abnormal, switching of the load on the steering wheel 9 is prohibited. This ensures safety. b. If a detection means such as a sensor becomes abnormal, a warning will be issued. c. If a detection means such as a sensor becomes abnormal, the details of the abnormality are displayed on the meter panel 9a. d. Alternatively, if a detection means such as a sensor becomes abnormal, the load on the steering wheel 9 is returned to the load at the time of shipment from the factory.

[0060] A method for changing the load on the steering wheel 9 will be described below.

[0061] 1. A case where the load on the steering wheel 9 is changed by the hydraulic power steering mechanism 40 will be described.

[0062] Figure 6, Figures 7 and 8 1 is a structural diagram focusing on the hydraulic circuit of the hydraulic power steering mechanism 40. The hydraulic circuit has the following structure.

[0063] 6 shows the neutral state in which the steering wheel 9 is not rotated. Here, 40c is an actuator that changes the variable throttles 40a and 40b in response to instructions from the control unit 20. These variable throttles 40a and 40b are members that adjust the throttle of the oil passage to the steering wheel drive hydraulic cylinder 40v as described below.

[0064] Also, 40d is a hydraulic device called Orbitroll (registered trademark, the same applies below) that adjusts the amount of hydraulic oil sent to the steering wheel drive hydraulic cylinder 40v according to the amount of rotation of the steering wheel 9. Also, the Orbitroll 40d is connected to an oil path switching circuit 40f for switching the direction of rotation by a shaft 40e or the like, and according to the direction of rotation of the steering wheel 9, the oil path switching circuit 40f is switched to Figure 7 When turning right, Figure 8 It also plays a role in switching between

[0065] In addition, 40g is a return filter, 40h is a relief valve, and 40i is a pump.

[0066] When the control unit 20 issues a command to the actuator 40c to reduce the load on the steering wheel 9, the actuator 40c loosens the throttles of the variable throttles 40a and 40b. Conversely, when the control unit 20 issues a command to the actuator 40c to increase the load on the steering wheel 9, the actuator 40c further tightens the throttles of the variable throttles 40a and 40b.

[0067] In this way, the load on the steering wheel 9 can be changed.

[0068] 2. Next, a case where the load on the steering wheel 9 is changed by the electric power steering mechanism 41 will be described.

[0069] 9 is a diagram showing a schematic configuration of an electric power steering mechanism 41 including a motor control device. In Fig. 9, the electric power steering mechanism 41 includes a motor control device 41a, a motor 41b, a steering wheel 9, a rotation shaft 9b of the steering wheel 9, a reduction gear 41c, etc.

[0070] An instruction signal from the control unit 20 is sent to the motor control device 41a. The motor control device 41a generates a motor drive signal based on the signal and outputs the signal to the motor 41b. The motor 41b, to which the motor drive signal is input, outputs an assist torque for assisting the steering of the steering wheel 9, and the assist torque is transmitted to the rotary shaft 9b via the reduction gear 41c. As a result, the rotation of the rotary shaft 9b is assisted, thereby assisting and lightening the driver's steering effort.

[0071] As described above, the configuration of the present invention may be realized in software or hardware.

[0072] Furthermore, the program of the invention related to the present invention is a program for causing a computer to execute all or part of the steps (or processes, operations and actions, etc.) of the control method of the invention related to the present invention described above, and is a program that operates in cooperation with a computer.

[0073] Furthermore, the recording medium of the invention related to the present invention is a recording medium on which a program is recorded for causing a computer to execute all or some of the operations of all or some of the steps (or processes, actions and functions, etc.) of the control method of the invention related to the present invention described above, and is a computer-readable recording medium in which the read program is used in cooperation with a computer.

[0074] It should be noted that the above-mentioned "some steps (or processes, operations, actions, etc.)" means one or some steps among the plurality of steps.

[0075] Furthermore, the above-mentioned "operations of steps (or processes, operations, actions, etc.)" means the operations of all or part of the above-mentioned steps.

[0076] Furthermore, one form of use of the program of the invention related to the present invention may be a form in which it is transmitted through a transmission medium such as the Internet, light, radio waves, or sound waves, read by a computer, and operates in cooperation with the computer.

[0077] The recording medium also includes a ROM (Read Only Memory).

[0078] Furthermore, a computer is not limited to pure hardware such as a CPU (Central Processing Unit), but may also include firmware, an OS (Operating System), and even peripheral devices. [Industrial Applicability]

[0079] The present invention is a work vehicle that can appropriately change the steering load depending on the situation while traveling for work, and is ideal for tractors. [Explanation of symbols]

[0080] 1. Tractor 2 Running vehicle 3 Body frame 4 Front wheels (steering wheels) 5 Rear wheels (drive wheels) 6. Bonnet 7 Control Unit 8. Cockpit 9. Steering wheel 9a Display section 10 Mission Case 20 Control Unit 20a Judgment section 20b Numerical value setting section 21 Steering sensor 30 GNSS equipment 40 Hydraulic power steering mechanism 40a, 40b variable aperture 40c actuator 40d Orbit Roll 40e shaft 40f oil passage switching circuit 40g return filter 40h relief valve 40i Pump 41 Electric power steering mechanism 41a Motor control device 41b Motor 41c reduction gear θ effective angle E-Engine S navigation satellite Vs Speed ​​detection sensor

Claims

[Claim 1] A running vehicle body, a steering wheel for changing the direction of travel of the traveling vehicle body; a steering wheel for operating the steering wheels; a steering sensor for detecting an operation of the steering wheel; a control unit for changing the operation load of the steering wheel, a hydraulic power steering mechanism is used to operate the steering wheels with the steering wheel, The hydraulic power steering mechanism includes a hydraulic device that sends hydraulic oil to a steering wheel drive hydraulic cylinder in response to rotation of the steering wheel, When working in the field, When the control unit determines that the steering wheel has been turned based on the detection value of the steering sensor, it adjusts the variable throttle between the hydraulic device and the steering wheel drive hydraulic cylinder to reduce the operating load of the steering wheel compared to when the turning operation is not detected, The steering sensor detects an angular velocity of the steering wheel operation, and the control unit determines that the steering wheel is being turned when the angular velocity exceeds a predetermined value. When the steering wheel operation angle is equal to or greater than a predetermined effective angle, the angle of the steering wheels begins to change, When the control unit determines that the steering wheel has been turned within a range less than the effective angle, the control unit reduces the operating load of the steering wheel compared to when the turning operation is not detected, a control unit that, when determining that a turning operation of the steering wheel has been performed within a range equal to or greater than the effective angle, gradually reduces the operating load of the steering wheel in stages or continuously in accordance with a predetermined rule compared to when the turning operation is not detected.

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