Work vehicle

Abstract

Provided is a work vehicle for which it is possible to increase the steering angle thereof.　A work vehicle (1) comprises: a vehicle body (2); wheels including left wheels (left front wheel 3LF, left rear wheel 3LB) disposed on the left side of the vehicle body and right wheels (right front wheel 3RF, right rear wheel 3RB) disposed on the right side of the vehicle body; a steering mechanism (60) for changing the direction of the wheels; and a distance change mechanism (80) for increasing the distance between the left wheels and the right wheels during steering by the steering mechanism.

Description

Work vehicles

[0001] The present invention relates to a work vehicle for performing work such as agricultural work.

[0002] A known work vehicle (tractor) is disclosed in Patent Document 1. The work vehicle disclosed in Patent Document 1 includes a steering device that steers the left and right front wheels, left and right braking devices that brake the left and right rear wheels, and a control device that can operate the left and right braking devices separately using actuators.

[0003] Japanese Patent Publication No. 2020-043837

[0004] In the above-described work vehicle, when the steering angle of the front wheels exceeds a predetermined angle, the control device activates the brake device of the rear wheel, which is on the inside of the turn, using an actuator to make the vehicle turn in a tight radius. However, because the front wheels are located close to the vehicle body, it is difficult to increase the steering angle of the front wheels.

[0005] The present invention has been made in consideration of the above problems, and has an object to provide a work vehicle that can increase the steering angle.

[0006] A work vehicle according to one embodiment of the present invention comprises a vehicle body, wheels including a left wheel disposed on the left side of the vehicle body and a right wheel disposed on the right side of the vehicle body, a steering mechanism that changes the direction of the wheels, and a distance change mechanism that increases the distance between the left wheel and the right wheel when steering by the steering mechanism.

[0007] The left wheels may include a left front wheel and a left rear wheel, the right wheels may include a right front wheel and a right rear wheel, the steering mechanism may change the direction of the left front wheel and the right front wheel when steering, and the distance change mechanism may increase the distance between the left front wheel and the right front wheel when steering by the steering mechanism.

[0008] The left wheels may include a left front wheel and a left rear wheel, the right wheels may include a right front wheel and a right rear wheel, the steering mechanism may change the direction of the left rear wheel and the right rear wheel when steering, and the distance change mechanism may increase the distance between the left rear wheel and the right rear wheel when steering by the steering mechanism.

[0009] The steering mechanism may change the direction of the left front wheel and the right front wheel, and the direction of the left rear wheel and the right rear wheel, when steering, and the distance change mechanism may increase the distance between the left front wheel and the right front wheel, and the distance between the left rear wheel and the right rear wheel, when steering by the steering mechanism.

[0010] The steering mechanism may change the orientation of the left wheel and the right wheel so that the forward portion of the wheels in the direction of travel moves away from the vehicle body when the vehicle body is traveling, and the distance change mechanism may increase the distance by utilizing a reaction force from the ground generated by the change in orientation of the left wheel and the right wheel by the steering mechanism.

[0011] The distance change mechanism may have an actuator that moves the left wheel and the right wheel in the vehicle body width direction, and may increase the distance by utilizing the reaction force and the force of the actuator.

[0012] The work vehicle is equipped with a power unit that generates power to rotate the wheels, and the wheels include steered wheels whose direction is changed by the steering mechanism when the vehicle body turns, and non-steered wheels whose direction is not changed, and when the vehicle body turns, the direction of the steered wheels is changed by the steering mechanism, and the power unit may rotate the non-steered wheels on the turning side and the non-steered wheels on the non-turning side of the left wheel and right wheel, which are the non-steered wheels, in opposite directions to each other.

[0013] When the vehicle body of the work vehicle is turning, the power unit may rotate the non-steered wheels on the turning side and the non-steered wheels and the steered wheels on the non-turning side in opposite directions.

[0014] When the work vehicle turns, the steering mechanism may steer the left and right wheels, which are the steered wheels, in opposite directions to each other, and the power unit may rotate the non-steered wheels on the turning side and the non-steered wheels on the non-turning side in opposite directions to each other.

[0015] When the vehicle body is turning, the work vehicle may be configured such that the steering mechanism steers the left and right wheels, which are the steerable wheels, in opposite directions so that the sides of the wheels face the center of turning of the vehicle body.

[0016] When the vehicle body of the work vehicle is turning, the power unit may rotate the left wheel and the right wheel in opposite directions.

[0017] According to the work vehicle of the present invention, the steering angle can be increased when steering to change the direction of the wheels.

[0018] 1 is a perspective view showing an embodiment of a work vehicle; FIG. 2 is a left side view showing an embodiment of a work vehicle; FIG. 3 is a right side view showing an embodiment of a work vehicle; FIG. 4 is a front view showing an embodiment of a work vehicle; FIG. 5 is a rear view showing an embodiment of a work vehicle; FIG. 6 is a plan view showing an embodiment of a work vehicle; FIG. 7 is a block diagram showing an example of the overall configuration of a work vehicle; FIG. 8 is a perspective view of a frame structure; FIG. 9 is an exploded perspective view of side frames (left frame, right frame); FIG. 10 is a perspective view showing an upper frame (lateral frame) and a side frame separately; FIG. 11 is a view of a first drive unit (including a steering mechanism) as seen from the right rear; FIG. 12 is a plan view showing a steering mechanism (left steering mechanism) and wheels (left front wheel); FIG. 13 is a plan view showing a state in which the rod of a cylinder of the steering mechanism (left steering mechanism) is extended; FIG. 14 is a plan view showing a state in which the rod of a cylinder of the steering mechanism (left steering mechanism) is retracted; FIG. 15 is a schematic plan view showing a work vehicle with the rods of the left and right cylinders retracted; FIG. 16 is a plan view showing a work vehicle with the rods of the left and right cylinders extended. 22. A schematic plan view showing a work vehicle equipped with a distance change mechanism including a first change mechanism, a second change mechanism, a third change mechanism, and a fourth change mechanism. FIG. 23 is a diagram showing a first example of a wheel range increasing operation when steering. FIG. 24 is a diagram showing a second example of a wheel range increasing operation when steering. FIG. 25 is a diagram showing a third example of a wheel range increasing operation when steering (for a work vehicle equipped with the distance change mechanism shown in FIG. 17). FIG. 26 is a diagram showing a third example of a wheel range increasing operation when steering (for a work vehicle equipped with the distance change mechanism shown in FIG. 15). A schematic plan view showing a work vehicle equipped with a distance change mechanism having a configuration for executing a first modified example of a wheel range increasing operation when steering. A schematic cross-sectional view showing an example of the configuration of an extension / contraction mechanism. A diagram showing a wheel range increasing operation when steering in a work vehicle having the configuration shown in FIG. 22. A schematic plan view showing a work vehicle equipped with a distance change mechanism having another configuration for executing the first modified example. A diagram showing a wheel range increasing operation when steering in a work vehicle having the configuration shown in FIG. 25. A schematic plan view showing a work vehicle equipped with a distance change mechanism having a configuration for executing a second modified example of a wheel range increasing operation when steering. FIG. 10 is a schematic plan view showing a work vehicle equipped with a distance change mechanism having another configuration for implementing the second modified example.30 is a diagram showing the wheel tracking increasing operation when steering in a work vehicle having the configuration shown in FIG. 29. FIG. 31 is a diagram explaining a first specific example of the wheel tracking increasing operation when steering. FIG. 32 is a diagram explaining a first specific example of the wheel tracking increasing operation when steering. FIG. 33 is a diagram explaining a first specific example of the wheel tracking increasing operation when steering. FIG. 34 is a diagram explaining a second specific example of the wheel tracking increasing operation when steering. FIG. 35 is a diagram explaining a second specific example of the wheel tracking increasing operation when steering. FIG. 36 is a diagram explaining a second specific example of the wheel tracking increasing operation when steering. FIG. 37 is a diagram explaining a second specific example of the wheel tracking increasing operation when steering. FIG. 38 is a diagram explaining another method of shortening the distance between the left wheel and the right wheel in the second specific example. FIG. 39 is a schematic plan view showing the state in which the width of a second ridge is detected when the work vehicle is traveling along a first ridge. FIG. 39 is a diagram showing a modified example of the first example of the wheel tracking increasing operation when steering. FIG. 39 is a diagram showing a modified example of the second example of the wheel tracking increasing operation when steering. FIG. 39 is a diagram explaining a modified example of the third example of the wheel tracking increasing operation when steering. FIG. 39 is a schematic plan view showing the turning operation of a conventional work vehicle. 10A and 10B are schematic plan views illustrating a first example of a turning operation and a second example of a turning operation, respectively;

[0019] A preferred embodiment of a work vehicle 1 according to the present invention will now be described. Figures 1 to 7 are diagrams showing one embodiment of the work vehicle 1. Figure 1 is a perspective view of the work vehicle 1. Figure 2 is a left side view of the work vehicle 1. Figure 3 is a right side view of the work vehicle 1. Figure 4 is a front view of the work vehicle 1. Figure 5 is a rear view of the work vehicle 1. Figure 6 is a plan view of the work vehicle 1. Figure 7 is a block diagram showing the overall configuration of the work vehicle 1.

[0020] In the following description, the direction indicated by arrow X1 in the drawings is referred to as the forward direction, the direction indicated by arrow X2 as the backward direction, the direction indicated by arrow Y1 as the left direction, the direction indicated by arrow Y2 as the right direction, the direction indicated by arrow Z1 as the upward direction, and the direction indicated by arrow Z2 as the downward direction. In addition, the direction indicated by arrow X3 is referred to as the forward / backward direction, the direction indicated by arrow Y3 as the left / right direction, and the direction indicated by arrow Z3 as the up / down direction.

[0021] Examples of work performed by the work vehicle 1 include, but are not limited to, agricultural work, industrial (civil engineering, construction, etc.) work, and transportation work. In a preferred embodiment of the present invention, the work performed by the work vehicle 1 is agricultural work (farm work). Below, an example will be described in which the work performed by the work vehicle 1 is farm work. In this case, the work vehicle 1 is an agricultural work vehicle.

[0022] As shown in Figures 1 to 6, the work vehicle 1 includes a vehicle body 2 and a traveling device 3 that supports the vehicle body 2 so that it can travel. In this embodiment, the vehicle body 2 is formed in a substantially rectangular parallelepiped shape with an internal space. However, the shape of the vehicle body 2 is not limited to a substantially rectangular parallelepiped shape. The internal space of the vehicle body 2 houses various devices and equipment.

[0023] As shown in Figures 2 and 3, a power unit 4 for driving the traveling device 3 is mounted (housed) in the internal space of the vehicle body 2. The power unit 4 generates power to drive the traveling device 3, and the power is supplied to the traveling device 3. More specifically, the power unit 4 generates power to rotate the wheels of the traveling device 3, and the wheels of the traveling device 3 are rotated by the power. As shown in Figure 7, the power unit 4 includes a motor 5 and a battery 7. In this embodiment, the vehicle body 2 is mounted (housed) with the battery 7 as the power unit 4.

[0024] The motor 5 is a traveling system motor that generates power to drive the traveling device 3. The motor 5 is an electric motor that is driven by electricity. An inverter 23 (see FIG. 7) is connected to the motor 5. The inverter 23 controls the rotation of the motor 5 based on a control signal from a control device 15, which will be described later. The battery 7 stores the power supplied to the motor 5. However, the power device 4 may include an engine instead of the motor 5. The power device 4 may also include a fuel cell.

[0025] As shown in FIG. 7 , the work vehicle 1 is equipped with a motor 5, which is a traveling motor, and a motor 6, which is a working motor. The working motor generates power to drive devices and mechanisms other than the traveling device 3. The motor 6 is an electric motor that is driven by power supplied from a battery 7. The rotation of the motor 6 can be controlled by an inverter 23. Hereinafter, the motor 5 may be referred to as the "traveling motor 5," and the motor 6 may be referred to as the "working motor 6."

[0026] The motors (traveling motor 5, working motor 6) can be mounted on the vehicle body 2. The traveling motor 5 and working motor 6 can be driven independently of each other. The working motor 6 is a motor for driving a hydraulic pump that operates a hydraulic cylinder, which will be described later. The working motor 6 also drives the external output shaft 8.

[0027] The work system motor 6 may be a hydraulic motor. The hydraulic motor is driven by hydraulic oil supplied from a hydraulic pump. In this case, for example, the hydraulic pump is driven by the travel system motor 5, the hydraulic oil supplied from the hydraulic pump drives the hydraulic motor (work system motor 6), and the external output shaft 8 is driven by the hydraulic motor. Furthermore, the work vehicle 1 may be equipped with a work system motor 6 that is a hydraulic motor, in addition to the work system motor 6 that is an electric motor.

[0028] As described above, the battery 7, which is part of the power unit 4, is housed in the vehicle body 2 (see FIGS. 2 and 3). Although not shown, the vehicle body 2 also houses a cooling system (radiator, fan, water pump, compressor, etc.) that cools the power unit 4 (motor 5, motor 6, battery 7, etc.), and a hydraulic system (control valves, etc.) that actuates hydraulic cylinders (cylinder 62, left cylinder 81L, right cylinder 81R) and other components described below based on control signals from the control device 15.

[0029] As shown in Figure 2, the external output shaft 8 protrudes rearward from the rear of the vehicle body 2. The external output shaft 8 is an output shaft for extracting the power of the work motor 6 to the outside of the vehicle body 2. The external output shaft 8 is, for example, a PTO shaft. The power extracted from the external output shaft 8 is input to a work implement 200 for performing work. This drives the work implement 200 to perform work.

[0030] Examples of the working device 200 include, but are not limited to, devices that perform agricultural work (farm work), devices that perform civil engineering work, devices that perform construction work, devices that perform transportation work, etc. In the embodiment described below, the working device 200 is a device that performs farm work.

[0031] Examples of the working device 200 for performing agricultural work include a spraying device for spreading fertilizer, chemicals, and other spray materials, a sowing device for sowing seeds, a tilling device for tilling the soil, a tilling device (plow) for tilling the soil, a weeding device for weeding, and a soil-piling device for piling up soil. However, the type of working device 200 is not particularly limited as long as it is a device for performing agricultural work. Furthermore, if the working device 200 is an electrically powered working device, it may be driven by power extracted from the battery 7 via a power line to the outside of the vehicle body 2, instead of being driven by power extracted from the external output shaft 8.

[0032] The vehicle body 2 is capable of traveling by being driven by the traveling devices 3. As shown in Figures 4, 5, etc., the traveling devices 3 include a left traveling device 3L provided on the left side of the vehicle body 2 and a right traveling device 3R provided on the right side of the vehicle body 2. The vehicle body 2 is located between the left traveling device 3L and the right traveling device 3R. As shown in Figure 2, the left traveling device 3L includes a left front wheel 3LF and a left rear wheel 3LB. As shown in Figure 3, the right traveling device 3R includes a right front wheel 3RF and a right rear wheel 3RB.

[0033] In the following description, the left front wheel 3LF and the left rear wheel 3LB are collectively referred to as the "left wheels." The right front wheel 3RF and the right rear wheel 3RB are collectively referred to as the "right wheels." The left wheel refers to the left front wheel 3LF and / or the left rear wheel 3LB (either one or both of the left front wheel 3LF and the left rear wheel 3LB). The right wheel refers to the right front wheel 3RF and / or the right rear wheel 3RB (either one or both of the right front wheel 3RF and the right rear wheel 3RB). In addition, the left front wheel 3LF, right front wheel 3RF, left rear wheel 3LB, and right rear wheel 3RB may be collectively referred to as the "wheels 30."

[0034] The wheels 30 (left front wheel 3LF, right front wheel 3RF, left rear wheel 3LB, and right rear wheel 3RB) are arranged on the sides of the vehicle body 2. The left front wheel 3LF and the left rear wheel 3LB are arranged on the left side of the vehicle body 2. The right front wheel 3RF and the right rear wheel 3RB are arranged on the right side of the vehicle body 2.

[0035] In the case of the work vehicle 1 of this embodiment, the size (diameter and width) of the rear wheels (left rear wheel 3LB, right rear wheel 3RB) is larger than the size (diameter and width) of the front wheels (left front wheel 3LF, right front wheel 3RF). However, the size of the front wheels (left front wheel 3LF, right front wheel 3RF) and the size of the rear wheels (left rear wheel 3LB, right rear wheel 3RB) may be the same, or the size of the front wheels may be larger than the size of the rear wheels.

[0036] In this embodiment, the traveling device 3 is a wheel-type traveling device in which the front wheels (left front wheel 3LF, right front wheel 3RF) and rear wheels (left rear wheel 3LB, right rear wheel 3RB) are all tires. However, the traveling device 3 may be a crawler-type traveling device in which the left traveling device 3L and the right traveling device 3R are crawlers. Furthermore, the traveling device 3 may be a traveling device in which one of the front wheels or the rear wheels is a wheel and the other is a crawler.

[0037] 1 to 3, the work vehicle 1 is equipped with a fender 55L that covers the upper and front of the left rear wheel 3LB, and a fender 55R that covers the upper and front of the right rear wheel 3RB. The fender 55L is attached to a first connector 19L3 (see FIG. 8) of the frame structure 18, which will be described later. The fender 55R is attached to a first connector 21R3 (see FIG. 8) of the frame structure 18, which will be described later. Although not shown, the work vehicle 1 may also be equipped with fenders that cover the front wheels (left front wheel 3LF, right front wheel 3RF).

[0038] As shown in Figure 7, the work vehicle 1 is equipped with a transmission 9. The transmission 9 is capable of switching the propulsion force of the traveling device 3 by changing gears. The transmission 9 is also capable of switching between forward and reverse travel of the traveling device 3. The transmission 9 may be equipped with a speed change clutch that can switch between a four-wheel drive state (4WD) in which all four wheels (left front wheel 3LF, right front wheel 3RF, left rear wheel 3LB, right rear wheel 3RB) are driven, and a two-wheel drive state (2WD) in which only the rear wheels (left rear wheel 3LB, right rear wheel 3RB) or only the front wheels (left front wheel 3LF, right front wheel 3RF) are driven.

[0039] As shown in Figures 2, 3, 5, and 6, the work vehicle 1 is equipped with a mounting unit 10 to which a work device 200 for performing the above-mentioned work is attached. The work device 200 is detachably attached to the mounting unit 10. The mounting unit 10 is provided at the rear of the vehicle body 2. Figure 5 is a view of the mounting unit 10 as seen from the rear. However, the mounting unit 10 may also be provided at the front or side (left or right) of the vehicle body 2.

[0040] The mounting part 10 is composed of a three-point link mechanism. Specifically, as shown in FIG. 5, the mounting part 10 has a lift arm 10a, a lower link 10b, a top link 10c, a lift rod 10d, and a lift cylinder 10e. The front end of the lift arm 10a is supported on the upper rear part of the vehicle body 2 so that it can swing upward or downward. The lift arm 10a swings (lifts and lowers) by driving the lift cylinder 10e. The lift cylinder 10e is composed of a hydraulic cylinder. The lift cylinder 10e is connected to a hydraulic pump (not shown) via a control valve (not shown).

[0041] The hydraulic pump is driven by the work system motor 6. The control valve is an electromagnetic valve or the like whose flow path is controlled to open or close by the control device 15. The flow of hydraulic oil discharged from the hydraulic pump is controlled by the control valve, thereby allowing the lift cylinder 10e to extend or retract.

[0042] The front end of the lower link 10b is supported on the rear lower part of the vehicle body 2 so as to be able to swing upward or downward. The front end of the top link 10c is supported on the rear part of the vehicle body 2 above the lower link 10b so as to be able to swing upward or downward. A lift rod 10d connects the lift arm 10a to the lower link 10b. A working device 200 is connected to the rear part of the lower link 10b and the rear part of the top link 10c. When the lift cylinder 10e is driven (extends and retracts), the lift arm 10a rises and falls, and the lower link 10b, which is connected to the lift arm 10a via the lift rod 10d, rises and falls. As a result, the working device 200 swings upward or downward (lifts and falls) around the front part of the lower link 10b as a fulcrum.

[0043] The work device 200 attached to the attachment unit 10 is towed and moved by the work vehicle 1 as the work vehicle 1 travels. Note that instead of the work device 200, a cart or the like for transporting agricultural produce or the like may be attached to the attachment unit 10. The attachment unit 10 may also be provided in a part other than the rear of the vehicle body 2 (for example, the front or side). The work device 200 may be placed on top of the work vehicle 1 instead of being attached to the attachment unit 10. In this case, the work device 200 moves while being placed on top of the work vehicle 1 as the work vehicle 1 travels.

[0044] 7, the work vehicle 1 is equipped with a positioning device 11. The positioning device 11 can detect the position of the vehicle body 2 (positioning information including latitude and longitude) using a satellite positioning system (positioning satellite) such as D-GPS, GPS, GLONASS, Beidou, Galileo, or Michibiki. That is, the positioning device 11 receives satellite signals (position of the positioning satellite, transmission time, correction information, etc.) transmitted from the positioning satellites, and detects the position of the vehicle body 2 (for example, latitude and longitude) based on the satellite signals.

[0045] The positioning device 11 has a receiving device 12 and an inertial measurement unit (IMU) 13. The receiving device 12 has an antenna and the like and is a device that receives satellite signals transmitted from positioning satellites, and is attached to the vehicle body 2. The inertial measurement unit 13 has an acceleration sensor that detects acceleration, a gyro sensor that detects angular velocity, and the like. The inertial measurement unit 13 is attached to the vehicle body 2. The inertial measurement unit 13 can detect the roll angle, pitch angle, yaw angle, etc. of the vehicle body 2. Note that the yaw angle may be detected by installing multiple positioning devices 11.

[0046] As shown in FIG. 7 , the work vehicle 1 is equipped with a communication device 14. The communication device 14 includes a communication circuit for communicating via an on-board network and a wireless communication circuit for wireless communication. The wireless communication circuit can directly or indirectly communicate wirelessly with an external device using communication standards such as IEEE 802.11 series Wi-Fi (Wireless Fidelity, registered trademark), BLE (Bluetooth (registered trademark) Low Energy), LPWA (Low Power Wide Area), and LPWAN (Low-Power Wide-Area Network). As another example, the communication device 14 may be provided with a communication circuit capable of wirelessly communicating with an external device via, for example, a mobile phone communication network or a data communication network. Examples of external devices include a personal computer, a smartphone, a tablet computer, a PDA, or a server. Examples of external devices include an operation device 101, which will be described later.

[0047] As shown in Fig. 7, the work vehicle 1 is equipped with a control device 15. The control device 15 is a device that performs various controls of the work vehicle 1. The control device 15 is equipped with a calculation unit (CPU, etc.) and a storage unit (RAM, ROM, etc.). The storage unit may include an external memory provided outside the control device 15. The control device 15 is connected to the various devices and mechanisms shown in Fig. 7 via an in-vehicle LAN (on-board network) such as a CAN (Controller Area Network) or a communication line.

[0048] The control device 15 controls the operation of various devices and mechanisms communicably connected to the control device 15 by having the calculation unit execute various control programs stored in the memory unit. The functions of each control unit of the control device 15 (autonomous driving control unit 15A, distance change control unit 15B, turning operation control unit 15C) described below are realized by having the calculation unit execute predetermined control programs stored in the memory unit.

[0049] As shown in Fig. 7, the control device 15 includes an automatic driving control unit 15A. The automatic driving control unit 15A controls the automatic driving of the work vehicle 1. The automatic driving control unit 15A is capable of executing line-type automatic driving control and autonomous-type automatic driving control. In line-type automatic driving control, the automatic driving control unit 15A controls the operation of the steering mechanism 60, transmission 9, motor 5, etc., which will be described later, so that the work vehicle 1 (vehicle body 2) moves along a predetermined planned driving line.

[0050] In autonomous automatic driving control, the automatic driving control unit 15A sets the direction of travel (steering direction) and vehicle speed (velocity) of the vehicle body 2 based on the results of sensing (detecting objects) around the work vehicle 1 (vehicle body 2) using a positioning device 11, etc., and controls the operation of the steering mechanism 60, transmission 9, motor 5, etc. so that the set steering and vehicle speed are achieved.

[0051] Note that the line-type automatic driving control and the autonomous-type automatic driving control may be switchable using a switch or the like. Also, the automatic driving control unit 15A may be configured to be able to execute either the line-type automatic driving control or the autonomous-type automatic driving control. Note that the configuration of the automatic driving control unit 15A is not limited to the configuration described above.

[0052] The work vehicle 1 can perform automatic driving (unmanned driving) without an operator on board because the control device 15 includes the automatic driving control unit 15A. Therefore, the work vehicle 1 in the illustrated embodiment does not have a driver's seat where an operator sits. However, the work vehicle 1 may also be a vehicle that performs automatic driving with an operator on board. Alternatively, the work vehicle 1 may be a vehicle that is driven and driven by an operator on board. When the work vehicle 1 is a vehicle in which an operator rides, a driver's seat is provided in the vehicle body 2.

[0053] As shown in FIG. 7 , the work vehicle 1 is equipped with a lighting device 16. The lighting device 16 is provided on the vehicle body 2. The lighting device 16 includes at least a headlight that illuminates the area ahead of the vehicle body 2. In addition to the headlight, the lighting device 16 may also include a plurality of work lights that illuminate the area around the vehicle body 2. The work lights can, for example, illuminate the sides (left and right) of the vehicle body 2 or the area behind the vehicle body 2. The lighting device 16 may also include status indicator lights, left and right lights, brake lights, etc.

[0054] As shown in Fig. 7, the work vehicle 1 is equipped with an alarm device 17. The alarm device 17 uses sound, light, etc. to alert people around the vehicle body 2 of danger (such as the approach of the vehicle body 2). The alarm device 17 is composed of a speaker, a warning light, etc.

[0055] As shown in Figure 1 and other figures, the work vehicle 1 is equipped with a frame structure 18 that is arranged around the vehicle body 2 and attached to the vehicle body 2. As shown in Figure 8 and other figures, the frame structure 18 includes a left frame 18L, a right frame 18R, and a lateral frame 18M. As shown in Figures 1 and 4 and other figures, the left frame 18L is provided on the left side of the vehicle body 2. The left frame 18L extends in the up-down direction along the vehicle body 2. The left frame 18L also extends in the front-rear direction along the vehicle body 2. The right frame 18R is provided on the right side of the vehicle body 2. The right frame 18R extends in the up-down direction along the vehicle body 2. The right frame 18R also extends in the front-rear direction along the vehicle body 2.

[0056] The left frame 18L connects the left front wheel 3LF and the left rear wheel 3LB. The right frame 18R connects the right front wheel 3RF and the right rear wheel 3RB. The left frame 18L and the right frame 18R are frames disposed on the sides of the vehicle body 2. For this reason, the left frame 18L and the right frame 18R may be collectively referred to as the "side frame 18LR."

[0057] The horizontal frame 18M connects the left frame 18L and the right frame 18R. More specifically, the horizontal frame 18M connects the upper part of the left frame 18L and the upper part of the right frame 18R. The horizontal frame 18M is a frame (upper frame) that is disposed above the vehicle body.

[0058] 4, the vehicle body 2 is disposed between the left frame 18L and the right frame 18R in a front view. In other words, the vehicle body 2 is disposed in a position sandwiched between the left frame 18L and the right frame 18R. The vehicle body 2 is also disposed below the lateral frame 18M. Therefore, the vehicle body 2 is disposed in a position surrounded by the left frame 18L, the right frame 18R, and the lateral frame 18M in a front view.

[0059] As shown in FIG. 9 and other figures, the left frame 18L is composed of a first left frame 19L and a second left frame 20L. The first left frame 19L includes a first front support pillar 19L1, a first rear support pillar 19L2, and a first connector 19L3. The first front support pillar 19L1 and the first rear support pillar 19L2 are spaced apart in the front-to-rear direction and extend parallel to each other in the up-down direction. As shown in FIGS. 1 and 4, the first front support pillar 19L1 is located on the left side of the front of the vehicle body 2. As shown in FIG. 5, the first rear support pillar 19L2 is located on the left side of the rear of the vehicle body 2. The first front support pillar 19L1 and the first rear support pillar 19L2 are formed in a cylindrical (rectangular) shape.

[0060] As shown in FIG. 9 , the first connector 19L3 connects the first front support 19L1 and the first rear support 19L2. The first connector 19L3 is composed of frame members 19AL, 19BL, 19CL, 19DL, and 19EL. The frame member 19AL extends in the front-to-rear direction and connects the upper portion of the first front support 19L1 to the upper portion of the first rear support 19L2. The frame member 19BL extends in the front-to-rear direction to the left of the frame member 19AL. The frame member 19CL connects the front portion of the frame member 19AL to the front portion of the frame member 19BL. The frame member 19DL connects the rear portion of the frame member 19AL to the rear portion of the frame member 19BL. The frame member 19EL connects a midpoint in the front-rear direction of the frame member 19AL and a midpoint in the front-rear direction of the frame member 19BL.

[0061] As shown in FIG. 9 , the second left frame 20L is composed of a second front support 20L1, a second rear support 20L2, and a second connector 20L3. The second front support 20L1 and the second rear support 20L2 are spaced apart in the front-to-rear direction and extend parallel to each other in the up-down direction. The second connector 20L3 connects the second front support 20L1 and the second rear support 20L2. The second connector 20L3 is composed of frame members 20FL, 20GL, 20HL, and 20IL. The frame member 20FL extends in the front-to-rear direction and connects the upper portion of the second front support 20L1 to the upper portion of the second rear support 20L2. The frame member 20GL extends rightward from the front portion of the right surface of the frame member 20FL. The frame member 20HL extends rightward from the rear portion of the right surface of the frame member 20FL. The frame member 20IL extends rightward from the middle portion of the right surface of the frame member 20FL in the front-to-rear direction.

[0062] As shown by the downward arrow in Figure 9, the second front support 20L1 is inserted from above into the cylindrical first front support 19L1. The second rear support 20L2 is inserted from above into the cylindrical first rear support 19L2. This combines the first left frame 19L and the second left frame 20L (see Figure 10). The second front support 20L1 can move up and down along the first front support 19L1. The second rear support 20L2 can move up and down along the first rear support 19L2. This allows the second left frame 20L to move up and down relative to the first left frame 19L.

[0063] As shown in FIG. 9 , the right frame 18R is composed of a first right frame 21R and a second right frame 22R. The first right frame 21R includes a first front support pillar 21R1, a first rear support pillar 21R2, and a first connector 21R3. The first front support pillar 21R1 and the first rear support pillar 21R2 are spaced apart in the front-to-rear direction and extend parallel to each other in the up-down direction. As shown in FIGS. 1 and 4 , the first front support pillar 21R1 is located on the right side of the front portion of the vehicle body 2. As shown in FIG. 5 , the first rear support pillar 21R2 is located on the right side of the rear portion of the vehicle body 2. The first front support pillar 21R1 and the first rear support pillar 21R2 are formed in a cylindrical (rectangular) shape.

[0064] The first connector 21R3 connects the first front support 21R1 and the first rear support 21R2. The first connector 21R3 is composed of frame members 21AR, 21BR, 21CR, 21DR, and 21ER. The frame member 21AR extends in the front-to-rear direction and connects the upper part of the first front support 21R1 to the upper part of the first rear support 21R2. The frame member 21BR extends in the front-to-rear direction to the right of the frame member 21AR. The frame member 21CR connects the front part of the frame member 21AR to the front part of the frame member 21BR. The frame member 21DR connects the rear part of the frame member 21AR to the rear part of the frame member 21BR. The frame member 21ER connects the midpoint of the frame member 21AR to the midpoint of the frame member 21BR in the front-to-rear direction.

[0065] The second right frame 22R is composed of a second front support 22R1, a second rear support 22R2, and a second connector 22R3. The second front support 22R1 and the second rear support 22R2 are spaced apart in the front-to-rear direction and extend parallel to each other in the up-down direction. The second connector 22R3 connects the second front support 22R1 and the second rear support 22R2. The second connector 22R3 is composed of frame members 22FR, 22GR, 22HR, and 22IR. The frame member 22FR extends in the front-to-rear direction and connects the upper part of the second front support 22R1 to the upper part of the second rear support 22R2. The frame member 22GR extends leftward from the front portion of the left surface of the frame member 22FR. The frame member 22HR extends leftward from the rear portion of the left surface of the frame member 22FR. The frame member 22IR extends leftward from a midpoint in the front-to-rear direction of the left surface of the frame member 22FR.

[0066] As shown by the downward arrow in Figure 9, the second front support 22R1 is inserted from above into the cylindrical first front support 21R1. The second rear support 22R2 is inserted from above into the cylindrical first rear support 21R2. This combines the first right frame 21R and the second right frame 22R (see Figure 10). The second front support 22R1 can move up and down along the first front support 21R1. The second rear support 22R2 can move up and down along the first rear support 21R2. This allows the second right frame 22R to move up and down relative to the first right frame 21R.

[0067] As shown in Figure 10, the horizontal frame 18M is composed of frame members 18MA, 18MB, 18MC, 18MD, and 18ME. The frame member 18MA is located on the left side of the horizontal frame 18M and extends in the front-to-rear direction. The frame member 18MB is located on the right side of the horizontal frame 18M and extends in the front-to-rear direction. The frame members 18MA and 18MB are arranged parallel to each other with a gap in the left-to-right direction.

[0068] Frame members 18MC, 18MD, and 18ME extend parallel to one another in the left-right direction. Frame member 18MC connects the front of frame member 18MA to the front of frame member 18MB. Frame member 18MD connects the rear of frame member 18MA to the rear of frame member 18MB. Frame member 18ME connects the midpoint of frame member 18MA in the front-to-rear direction to the midpoint of frame member 18MB in the front-to-rear direction.

[0069] The frame members 18MC, 18MD, and 18ME are each formed in a cylindrical (rectangular) shape. As shown by the arrows in Figure 10, the frame member 20GL is inserted into the frame member 18MC from the left, and the frame member 22GR is inserted from the right. The frame member 20HL is inserted into the frame member 18MD from the left, and the frame member 22HR is inserted from the right. The frame member 20IL is inserted into the frame member 18ME from the left, and the frame member 22IR is inserted from the right. This combines the horizontal frame 18M, the second left frame 20L, and the second right frame 22R.

[0070] The frame member 20GL inserted into the frame member 18MC from the left can move left and right along the frame member 18MC. The frame member 20HL inserted into the frame member 18MD from the left can move left and right along the frame member 18MD. The frame member 20IL inserted into the frame member 18ME from the left can move left and right along the frame member 18ME. This allows the left frame 18L to move left and right relative to the horizontal frame 18M, to the left of the horizontal frame 18M.

[0071] The frame member 22GR inserted into the frame member 18MC from the right can move left and right along the frame member 18MC. The frame member 22HR inserted into the frame member 18MD from the right can move left and right along the frame member 18MD. The frame member 22IR inserted into the frame member 18ME from the right can move left and right along the frame member 18ME. This allows the right frame 18R to move left and right relative to the horizontal frame 18M, to the right of the horizontal frame 18M.

[0072] As described above, the left frame 18L and the right frame 18R can move left and right relative to the lateral frame 18M. Because the vehicle body 2 is fixed to the lateral frame 18M, the left frame 18L and the right frame 18R can move left and right relative to the vehicle body 2. Specifically, the left frame 18L can move in a direction away from the vehicle body 2 (leftward) and a direction toward the vehicle body 2 (rightward). The right frame 18R can move in a direction away from the vehicle body 2 (rightward) and a direction toward the vehicle body 2 (leftward).

[0073] Because the left traveling unit 3L is attached to the left frame 18L (first left frame 19L), the left traveling unit 3L can move left and right as the left frame 18L moves left and right. Because the right traveling unit 3R is attached to the right frame 18R (first right frame 21R), the right traveling unit 3R can move left and right as the right frame 18R moves left and right.

[0074] 7, the work vehicle 1 is equipped with a drive unit 40 for driving the wheels (left front wheel 3LF, right front wheel 3RF, left rear wheel 3LB, and right rear wheel 3RB). The drive unit 40 has a drive device 45 that generates power, a transmission mechanism 50 that transmits the power generated by the drive device 45 to the wheels 30, and a steering mechanism 60 that changes the direction of the wheels (left front wheel 3LF, right front wheel 3RF).

[0075] In the present embodiment, the steering mechanism 60 is a mechanism that changes the direction of the front wheels (left front wheel 3LF, right front wheel 3RF), but it may also be a mechanism that changes the direction of the rear wheels (left rear wheel 3LB, right rear wheel 3RB). The steering mechanism 60 may also be a mechanism that changes the direction of both the front wheels and the rear wheels. The steering mechanism 60 may also be a mechanism that independently changes the direction of the left front wheel 3LF, right front wheel 3RF, left rear wheel 3LB, and right rear wheel 3RB. The steering mechanism 60 that changes the direction of the front wheels and the steering mechanism 60 that changes the direction of the rear wheels may have the same configuration.

[0076] 2 and 3, the drive unit 40 includes a first drive unit 41 for driving the left front wheel 3LF, a second drive unit 42 for driving the right front wheel 3RF, a third drive unit 43 for driving the left rear wheel 3LB, and a fourth drive unit 44 for driving the right rear wheel 3RB. The first drive unit 41, the second drive unit 42, the third drive unit 43, and the fourth drive unit 44 each have a drive device 45 and a transmission mechanism 50, which will be described later. The first drive unit 41 and the second drive unit 42 each have a steering mechanism 60, which will be described later. Each drive unit is attached to the frame structure 18.

[0077] In this embodiment, the drive device 45 is a motor. More specifically, the drive device 45 is the traveling motor 5 described above. In other words, the motor that constitutes the drive device 45 is the same as the motor included in the power unit 4 described above. As will be described below, the motors 5 that constitute the drive device 45 of the drive unit 40 include a motor 5LF, a motor 5RF, a motor 5LB, and a motor 5RB.

[0078] 2, the first drive unit 41 includes a motor 5LF and a transmission mechanism 50LF that transmits the power of the motor 5LF to the left front wheel 3LF. The transmission mechanism 50LF is composed of a gear mechanism including a plurality of gears. When the first drive unit 41 drives the motor 5LF, the power of the motor 5LF is transmitted to the left front wheel 3LF via the transmission mechanism 50LF.

[0079] 3, the second drive unit 42 includes a motor 5RF and a transmission mechanism 50RF that transmits the power of the motor 5RF to the right front wheel 3RF. The transmission mechanism 50RF is composed of a gear mechanism including multiple gears. When the second drive unit 42 drives the motor 5RF, the power of the motor 5RF is transmitted to the right front wheel 3RF via the transmission mechanism 50RF.

[0080] 2, the third drive unit 43 includes a motor 5LB and a transmission mechanism 50LB that transmits the power of the motor 5LB to the left rear wheel 3LB. The transmission mechanism 50LB is composed of a gear mechanism including multiple gears. When the third drive unit 43 drives the motor 5LB, the power of the motor 5LB is transmitted to the left rear wheel 3LB via the transmission mechanism 50LB.

[0081] 3, the fourth drive unit 44 has a motor 5RB and a transmission mechanism 50RB that transmits the power of the motor 5RB to the right rear wheel 3RB. The transmission mechanism 50RB is composed of a gear mechanism including a plurality of gears. When the fourth drive unit 44 drives the motor 5RB, the power of the motor 5RB is transmitted to the right rear wheel 3RB via the transmission mechanism 50RB.

[0082] As shown in Fig. 7, the drive unit 40 has a steering mechanism 60 that changes the direction of the wheels 30. In the present embodiment, the steering mechanism 60 is a mechanism that changes the direction of the front wheels (left front wheel 3LF and right front wheel 3RF) among the wheels 30. As shown in Figs. 2 and 3, the steering mechanism 60 includes a left steering mechanism 60L that changes the direction of the left front wheel 3LF and a right steering mechanism 60R that changes the direction of the right front wheel 3RF.

[0083] As shown in Fig. 2, the first drive unit 41 is equipped with a left steering mechanism 60L. As shown in Fig. 3, the second drive unit 42 is equipped with a right steering mechanism 60R. The configurations of the left steering mechanism 60L and the right steering mechanism 60R are the same except that they are symmetrical across the center in the width direction (left-right direction) of the vehicle body 2. Therefore, hereinafter, as the configuration of the steering mechanism 60, the configuration of the left steering mechanism 60L will be described, and a description of the configuration of the right steering mechanism 60R will be omitted.

[0084] As shown in FIGS. 2 and 11 , the steering mechanism 60 (left steering mechanism 60L) has a rotating body 61 that rotates about an axis AX1 in the vertical direction when steering the wheel (left front wheel 3LF). The axis AX1 of the rotating body 61 is located above the wheel (left front wheel 3LF). The axis AX1 of the rotating body 61 is located in a position that overlaps with the wheel (left front wheel 3LF) in a plan view (see FIG. 12 ). The rotating body 61 has a first portion 611, a second portion 612, a third portion 613, and a fourth portion 614. The first portion 611, the second portion 612, the third portion 613, and the fourth portion 614 are integrated to form a single rotating body 61.

[0085] The first portion 611 is formed in a cylindrical shape with its central axis facing up and down. The central axis of the first portion 611 (the central axis of the cylinder) coincides with the axis AX1 described above. Therefore, the central axis of the first portion 611 is located above the left front wheel 3LF. When the left front wheel 3LF is steered, the rotating body 61 rotates around the axis of the central axis of the first portion 611 (i.e., around the axis AX1). A protrusion 611a is provided on the outer peripheral surface of the first portion 611, protruding in the radial direction of the first portion 611 (the horizontal direction away from the central axis of the first portion 611).

[0086] The second portion 612 is formed in a tubular (cylindrical) shape with its central axis facing the vertical direction. The second portion 612 is disposed inward (to the right of) the wheel (left front wheel 3LF).

[0087] The third portion 613 connects the lower end of the first portion 611 and the upper end of the second portion 612. The third portion 613 is located above the left front wheel 3LF. The third portion 613 is formed in a generally elliptical shape in a plan view.

[0088] The fourth part 614 is connected to the lower end of the second part 612. The fourth part 614 has a cylindrical part 614a connected to the lower end of the second part 612 and a conical part 614b provided at the lower end of the cylindrical part 614a. The fourth part 614 is disposed inward (to the right) of the left front wheel 3LF.

[0089] The conical portion 614b of the fourth portion 614 is connected to the left front wheel 3LF. As a result, when the rotating body 61 rotates about the axis AX1 and the fourth portion 614 rotates about the axis AX1, the left front wheel 3LF also rotates about the axis AX1. In other words, as the rotating body 61 rotates about the axis AX1, the left front wheel 3LF also rotates about the axis AX1. Note that the fourth portion 614 does not rotate together with the rotation of the left front wheel 3LF when the work vehicle 1 is traveling.

[0090] 11 and 12, the steering mechanism 60 has a cylinder 62 with a rod 62a that extends and retracts in a direction perpendicular to the axis AX1 (the front-rear direction). The cylinder 62 is a hydraulic cylinder. The rotating body 61 has a first connection part 61a to which the rod 62a is connected and a second connection part 61b to which the wheel (left front wheel 3LF) is connected.

[0091] The first connecting portion 61a is composed of the protrusion 611a described above. A shaft 61c passes through the protrusion 611a constituting the first connecting portion 61a in the vertical direction. A tip member 62b attached to the tip of a rod 62a is fitted into the upper part of the shaft 61c. The tip member 62b can rotate around the central axis of the shaft 61c.

[0092] The second connection part 61b is composed of the above-mentioned fourth part 614. The second connection part 61b is connected to the inside (right side) of the wheel (left front wheel 3LF) at the bottom of the rotating body 61. The second connection part 61b is connected via a bearing or the like so as not to rotate together with the wheel (left front wheel 3LF) when traveling.

[0093] The cylinder 62 rotates the rotor 61 around the axis AX1 by extending and retracting the rod 62a, thereby rotating the left front wheel 3LF around the axis AX1. First, we will describe what happens when the rod 62a extends. As shown in FIG. 13 , when the rod 62a extends (see arrow R1), the first part 611 rotates around the axis AX1 together with the protrusion 611a (see arrow R2). When the first part 611 rotates around the axis AX1, the second part 612, the third part 613, and the fourth part 614, which are integrated with the first part 611, also rotate around the axis AX1. When the fourth part 614 rotates around the axis AX1, the left front wheel 3LF, which is connected to the fourth part 614, also rotates around the axis AX1 (see arrow R3). As a result, the left front wheel 3LF changes orientation so that its front portion faces outward (leftward).

[0094] Next, we will explain what happens when the rod 62a is retracted. As shown in FIG. 14 , when the rod 62a is retracted (see arrow R4), the first part 611 rotates around the axis AX1 together with the protrusion 611a (see arrow R5). The rotation direction at this time is opposite to that when the rod 62a is extended. When the first part 611 rotates around the axis AX1, the second part, the third part 613, and the fourth part 614, which are integrated with the first part 611, also rotate around the axis AX1. When the fourth part 614 rotates around the axis AX1, the left front wheel 3LF, which is connected to the fourth part 614, also rotates around the axis AX1 (see arrow R6). As a result, the left front wheel 3LF changes orientation so that its front portion faces inward (to the right).

[0095] As described above, the left steering mechanism 60L can rotate the left front wheel 3LF about the axis AX1 by driving the cylinder 62 to extend and retract the rod 62a. Similarly, the right steering mechanism 60R can rotate the right front wheel 3RF about the axis AX1 by driving the cylinder 62 to extend and retract the rod 62a. In this way, the traveling direction of the work vehicle 1 can be changed by driving the steering mechanism 60 to change the orientation of the left front wheel 3LF and the right front wheel 3RF.

[0096] As is clear from the above explanation, the axis AX1, which is the rotation axis of the wheels (left front wheel 3LF, right front wheel 3RF), becomes the steering axis when the wheels (left front wheel 3LF, right front wheel 3RF) are steered. Here, as described above, the axis AX1, which is the steering axis, is located above the wheels (front wheels). In the case where the steering mechanism 60 is a mechanism that steers the rear wheels (left rear wheel 3LB, right rear wheel 3RB), the steering axis of the rear wheels is located above the rear wheels. This prevents the wheels (front wheels, rear wheels) from intruding into the vehicle body 2 when steering, compared to when the steering axis is located inward of the wheels.

[0097] The configuration of the steering mechanism 60 is not limited to the above-described configuration. For example, a general tractor steering mechanism using a knuckle arm or the like can also be used. As another embodiment of the drive unit 45, the motor of the drive unit 45 may be an in-wheel motor. In this case, all of the left front wheel 3LF, right front wheel 3RF, left rear wheel 3LB, and right rear wheel 3RB may be driven by the in-wheel motor, or only some of the wheels (for example, the left front wheel 3LF and the right front wheel 3RF, or the left rear wheel 3LB and the right rear wheel 3RB) may be driven by the in-wheel motor.

[0098] As shown in FIG. 7 , the work vehicle 1 is equipped with a first detection device 70. The first detection device 70 detects the conditions around the vehicle body 2. The first detection device 70 detects road information, which is information about roads on which the traveling devices 3 can travel, as the conditions around the vehicle body 2. More specifically, the first detection device 70 detects road information, which is values ​​related to the roads on which the traveling devices 3 can travel. The first detection device 70 detects, for example, the width of the traveling path as the road information. The width of the traveling path detected by the first detection device 70 is the width of an object that the work vehicle 1 attempts to straddle between the left traveling device 3L and the right traveling device 3R. The first detection device 70 detects, for example, the width of a ridge on the ground or the width of an obstacle on the ground that obstructs traveling, as the width of the traveling path. Examples of obstacles that obstruct traveling include grooves or holes formed in the ground, crops planted on the ground, and obstacles on the ground (e.g., stones or artificial installations).

[0099] 7, the first detection device 70 includes a camera (image capture device) 71, a sensor 72, and a calculation unit 73. In the present embodiment, the first detection device 70 includes both the camera 71 and the sensor 72, but may include only one of them.

[0100] The camera 71 is composed of a CCD camera equipped with a CCD (Charge Coupled Devices) image sensor, a CMOS camera equipped with a CMOS (Complementary Metal Oxide Semiconductor) image sensor, or the like. The camera 71 is mounted on the vehicle body 2 and captures images of the surroundings of the vehicle body 2. The camera 71 may be capable of capturing images in at least one direction among the front, rear, left, and right of the vehicle body 2, including at least the traveling direction of the vehicle body 2. Preferably, the camera 71 is positioned so as to capture images in the front, rear, and sides (left and right) of the vehicle body 2. The camera 71 may also be positioned so as to capture images in directions other than the front, rear, and sides (left and right) of the vehicle body 2 (for example, the right front, left front, front-downward, rear-downward, etc.).

[0101] The camera 71 captures images of the surroundings of the vehicle body 2 and generates an image signal. The calculation unit 73 is composed of a computer or the like including a signal processing circuit that processes the generated image signal. The signal processing circuit detects the state of the object (presence or absence of the object, the position of the object, the type of the object, the size of the object, etc.) based on the image signal output from the camera 71. The object includes the aforementioned ridges, obstacles, etc.

[0102] The sensor 72 is an optical sensor, and is configured, for example, by a LiDAR (Light Detection And Ranging) sensor. The sensor 72 may also be an acoustic sensor. The sensor 72 preferably includes both an optical sensor and an acoustic sensor, but may also include either one of them. The acoustic sensor is configured, for example, by an airborne ultrasonic sensor such as a sonar.

[0103] The sensor 72 described above is mounted on the vehicle body 2 and detects objects around the vehicle body 2. The sensor 72 only needs to be able to detect objects in at least one direction, including the traveling direction of the vehicle body 2, among the front, rear, left, and right of the vehicle body 2. Preferably, the sensor 72 is arranged to detect objects in the front, rear, and sides (left and right) of the vehicle body 2. The sensor 72 may also be arranged to detect objects in directions other than the front, rear, and sides (left and right) of the vehicle body 2 (for example, in the front right, front left, front-downward, rear-downward, etc.).

[0104] 7, the work vehicle 1 is equipped with a second detection device 75. The second detection device 75 detects the distance between the left and right wheels. As the second detection device 75, for example, the optical sensor or sonic sensor described above can be used.

[0105] The distance between the left and right wheels detected by the second detection device 75 is the distance between the inner surfaces of the left and right wheels. Specifically, it is the smaller of the distance between the inner surfaces of the left front wheel 3LF and the right front wheel 3RF and the distance between the inner surfaces of the left rear wheel 3LB and the right rear wheel 3RB.

[0106] 6, if the distance DB between the inner surfaces of the left rear wheel 3LB and the right rear wheel 3RB is smaller than the distance DF between the inner surfaces of the left front wheel 3LF and the right front wheel 3RF (DB<DF), the second detection device 75 detects the distance DB between the inner surfaces of the left rear wheel 3LB and the right rear wheel 3RB as the distance between the left wheel and the right wheel.If the distance DF between the inner surfaces of the left front wheel 3LF and the right front wheel 3RF and the distance DB between the inner surfaces of the left rear wheel 3LB and the right rear wheel 3RB are the same (DB=DF), the second detection device 75 detects either the distance DF or the distance DB as the distance between the left wheel and the right wheel. If the distance DF between the inner surface of the left front wheel 3LF and the inner surface of the right front wheel 3RF is smaller than the distance DB between the inner surface of the left rear wheel 3LB and the inner surface of the right rear wheel 3RB (DB > DF), the second detection device 75 detects the distance DF between the inner surface of the left front wheel 3LF and the inner surface of the right front wheel 3RF as the distance between the left wheel and the right wheel.

[0107] As shown in Fig. 7, the work vehicle 1 is equipped with a distance change mechanism 80. The distance change mechanism 80 changes the distance between the left and right wheels. As shown in Figs. 6 and 15, the distance change mechanism 80 includes a left change mechanism 80L that changes the left-right position of the left wheel, and a right change mechanism 80R that changes the left-right position of the right wheel. Note that Fig. 15 is a simplified view of Fig. 6.

[0108] As shown in Figures 6 and 15, the left changing mechanism 80L has a left cylinder 81L that moves the left wheel left or right. The left cylinder 81L moves the left front wheel 3LF and the left rear wheel 3LB left or right. The left front wheel 3LF and the left rear wheel 3LB are connected by a left connector 82L. As a result, the left cylinder 81L can move the left connector 82L left or right, thereby moving the left front wheel 3LF and the left rear wheel 3LB together left or right.

[0109] As shown in Figures 6 and 15, the right change mechanism 80R has a right cylinder 81R that moves the right wheel left or right. The right cylinder 81R moves the right front wheel 3RF and the right rear wheel 3RB left or right. The right front wheel 3RF and the right rear wheel 3RB are connected by a right connector 82R. As a result, the right cylinder 81R can move the right connector 82R left or right, thereby moving the right front wheel 3RF and the right rear wheel 3RB together left or right.

[0110] In this embodiment, the left coupling part 82L is the left frame 18L of the frame structure 18. The right coupling part 82R is the right frame 18R of the frame structure 18. The left front wheel 3LF is rotatably attached to the first left frame 19L (see FIG. 9 ) of the left frame 18L via the above-mentioned first drive unit 41 and the like. The left rear wheel 3LB is rotatably attached to the first left frame 19L of the left frame 18L via the above-mentioned third drive unit 43 and the like during traveling.

[0111] The right front wheel 3RF is rotatably attached to the first right frame 21R of the right frame 18R (see FIG. 9) via the above-mentioned second drive unit 42, etc. The right rear wheel 3RB is rotatably attached to the first right frame 21R of the right frame 18R via the above-mentioned fourth drive unit 44, etc. during traveling.

[0112] This allows the left front wheel 3LF and the left rear wheel 3LB (i.e., the left traveling device 3L) to move left and right together with the left frame 18L. Also, the right front wheel 3RF and the right rear wheel 3RB (i.e., the right traveling device 3R) to move left and right together with the right frame 18R.

[0113] The right cylinder 81R and the left cylinder 81L are hydraulic cylinders that are operated (extended and retracted) by hydraulic oil supplied from a hydraulic pump driven by the working motor 6 described above.

[0114] As shown in Figures 6 and 15, the left cylinder 81L has a cylinder tube 81La attached to the vehicle body 2 and a rod 81Lb that protrudes from the cylinder tube 81La and extends to the left. A left coupling 82L is connected to the tip of the rod 81Lb of the left cylinder 81L. When the rod 81Lb of the left cylinder 81L extends to the left, the left coupling 82L moves to the left, and the left front wheel 3LF and the left rear wheel 3LB move together to the left. When the rod 81Lb of the left cylinder 81L contracts to the right, the left coupling 82L moves to the right, and the left front wheel 3LF and the left rear wheel 3LB move together to the right.

[0115] As shown in Figures 6 and 15, the right cylinder 81R has a cylinder tube 81Ra attached to the vehicle body 2 and a rod 81Rb that protrudes from the cylinder tube 81Ra and extends to the right. A right coupling 82R is connected to the tip of the rod 81Rb of the right cylinder 81R. When the rod 81Rb of the right cylinder 81R extends to the right, the right coupling 82R moves to the right, and the right front wheel 3RF and the right rear wheel 3RB move together to the right. When the rod 81Rb of the right cylinder 81R contracts to the left, the right coupling 82R moves to the left, and the right front wheel 3RF and the right rear wheel 3RB move together to the left.

[0116] As described above, the left front wheel 3LF and the left rear wheel 3LB (left wheels) can be changed in lateral position by operating (extending and retracting) the left cylinder 81L. Also, the right front wheel 3RF and the right rear wheel 3RB (right wheels) can be changed in lateral position by operating (extending and retracting) the right cylinder 81R. Therefore, the distance between the left wheel and the right wheel can be changed by operating one or both of the left cylinder 81L and the right cylinder 81R.

[0117] When changing the distance between the left and right wheels, it is preferable to move (extend or shorten) the rods of the left cylinder 81L and the right cylinder 81R the same distance in opposite directions. However, when changing the distance between the left and right wheels, it is also possible to move the rods of the left cylinder 81L and the right cylinder 81R by different distances in opposite directions, or to move the rods of the left cylinder 81L and the right cylinder 81R by different distances in the same direction.

[0118] In the following description, the rod 81Lb of the left cylinder 81L and the rod 81Rb of the right cylinder 81R may be collectively referred to as the "rod 81b." The rod 81b refers to the rod 81Lb of the left cylinder 81L and / or the rod 81Rb of the right cylinder 81R.

[0119] 6 and 15 show a state in which the rods of the left cylinder 81L and the right cylinder 81R are retracted. In this state, the distance DB (see FIG. 6) between the left and right wheels is short. By extending the rods of the left cylinder 81L and the right cylinder 81R from this state (see arrows YL and YR in FIG. 16), the left wheels (left front wheel 3LF, left rear wheel 3LB) and the right wheels (right front wheel 3RF, right rear wheel 3RB) move in opposite directions (see arrows in FIG. 15). This allows the distance DB (see FIG. 6) between the left and right wheels to be lengthened, as shown in FIG. 16.

[0120] FIG. 17 shows a modified example of the distance change mechanism 80. As shown in FIG. 17 , the distance change mechanism 80 may include a first change mechanism 801 that changes the left-right position of the left front wheel 3LF, a second change mechanism 802 that changes the left-right position of the left rear wheel 3LB, a third change mechanism 803 that changes the right-left position of the right front wheel 3RF, and a fourth change mechanism 804 that changes the right-left position of the right rear wheel 3RB. In this case, the left change mechanism 80L includes the first change mechanism 801 and the second change mechanism 802. The right change mechanism 80R includes the third change mechanism 803 and the fourth change mechanism 804.

[0121] In this case, the left cylinder 81L includes a left front cylinder 81LF that moves the left front wheel 3LF left or right and a left rear cylinder 81LB that moves the left rear wheel 3LB left or right. The right cylinder 81R includes a right front cylinder 81RF that moves the right front wheel 3RF left or right and a right rear cylinder 81RB that moves the right rear wheel 3RB left or right.

[0122] In this case, there is no left connecting portion 82L connecting the left front wheel 3LF and the left rear wheel 3LB, and the left front wheel 3LF and the left rear wheel 3LB are not connected. The left frame 18L is divided into two, front and rear, with the left front wheel 3LF attached to the front left frame 18LF and the left rear wheel 3LB attached to the rear left frame 18LB. This allows the left front wheel 3LF and the left rear wheel 3LB to move left and right independently of each other.

[0123] Furthermore, there is no right coupling portion 82R connecting the right front wheel 3RF and the right rear wheel 3RB, and the right front wheel 3RF and the right rear wheel 3RB are not connected. The right frame 18R is divided into two, front and rear, with the right front wheel 3RF attached to the front right frame 18RF and the right rear wheel 3RB attached to the rear right frame 18RB. This allows the right front wheel 3RF and the right rear wheel 3RB to move left and right independently of each other.

[0124] The first changing mechanism 801, the second changing mechanism 802, the third changing mechanism 803, and the fourth changing mechanism 804 can be driven independently. Specifically, the left front cylinder 81LF, the left rear cylinder 81LB, the right front cylinder 81RF, and the right rear cylinder 81RB can be operated independently. This allows the left and right positions of the left front wheel 3LF, the left and right rear wheel 3LB, the right front wheel 3RF, and the right rear wheel 3RB to be changed independently.

[0125] The arrows in Figure 17 indicate the state in which the left and right positions of the left front wheel 3LF, the left and right positions of the left rear wheel 3LB, the right front wheel 3RF, and the right rear wheel 3RB are each changed independently by extending the rods of the left front cylinder 81LF, the left rear cylinder 81LB, the right front cylinder 81RF, and the right rear cylinder 81RB.

[0126] The distance change mechanism 80 changes the distance between the left and right wheels by operating both or one of the left change mechanism 80L and right change mechanism 80R of the distance change mechanism 80. When the left change mechanism 80L is operated, the rod of the left cylinder 81L extends or retracts, changing the left-right position of the left wheel. When the right change mechanism 80R is operated, the rod of the right cylinder 81R extends or retracts, changing the left-right position of the right wheel. By changing the left-right position of both or one of the left and right wheels, the distance between the left and right wheels is changed. Preferably, the distance change mechanism 80 changes the left-right position of both the left and right wheels by the same distance in opposite directions.

[0127] The second detection device 75 can detect the distance between the left and right wheels by detecting the amount of extension and contraction of each of the left change mechanism 80L and the right change mechanism 80R. Specifically, the second detection device 75 can detect the distance between the left and right wheels by detecting the amount of extension and contraction of the rod of the left cylinder 81L of the left change mechanism 80L and the amount of extension and contraction of the rod of the right cylinder 81R of the right change mechanism 80R.

[0128] In this case, information such as the relationship between the amount of extension and contraction of the rod of the left cylinder 81L and the position of the left wheel, the relationship between the amount of extension and contraction of the rod of the right cylinder 81R and the position of the right wheel, and the relationship between "the positions of the left and right wheels" and "the distance between the left and right wheels" is stored in advance in the memory unit of the control device 15. The second detection device 75 detects the amount of extension and contraction of the rods of the left cylinder 81L and the right cylinder 81R, and detects the distance between the left and right wheels based on the detection results and the information stored in the memory unit.

[0129] The distance change mechanism 80 increases the distance between the left wheel (left front wheel 3LF and / or left rear wheel 3LB) and the right wheel (right front wheel 3RF and / or right rear wheel 3RB) when steering by the steering mechanism 60. Here, "increasing the distance between the left wheel and the right wheel when steering" means "increasing the distance between the left wheel and the right wheel when steering" and does not mean "increasing the distance between the left wheel and the right wheel at the same time as steering."

[0130] When the control device 15 controls the steering mechanism 60 to perform steering, it also controls the distance change mechanism 80 to increase the distance between the left and right wheels. At this time, the operation of the distance change mechanism 80 to increase the distance between the left and right wheels is performed before the steering operation by the steering mechanism 60.

[0131] In other words, the distance change mechanism 80 increases the distance between the left wheels (left front wheel 3LF and / or left rear wheel 3LB) and the right wheels (right front wheel 3RF and / or right rear wheel 3RB) before steering by the steering mechanism 60 (for example, immediately before steering). In the following description, this operation of the distance change mechanism 80 will be referred to as the "wheel distance increasing operation during steering." The wheel distance increasing operation during steering is performed while the work vehicle 1 is traveling, but can also be performed before traveling.

[0132] The steering wheel distance increasing operation will be described below with a number of examples. In the following description, "during steering" can be read as "before steering" or "immediately before steering."

[0133] As an example (first example) of the wheel distance increasing operation during steering, the distance change mechanism 80 increases the distance between the left front wheel 3LF and the right front wheel 3RF when the left front wheel 3LF and the right front wheel 3RF are steered by the steering mechanism 60. In other words, the distance change mechanism 80 increases the distance between the left front wheel 3LF and the right front wheel 3RF when the steering mechanism 60 changes the direction of the left front wheel 3LF and the right front wheel 3RF.

[0134] As another example (second example) of the wheel distance increasing operation during steering, the distance change mechanism 80 increases the distance between the left rear wheel 3LB and the right rear wheel 3RB when the left rear wheel 3LB and the right rear wheel 3RB are steered by the steering mechanism 60. In other words, the distance change mechanism 80 increases the distance between the left rear wheel 3LB and the right rear wheel 3RB when the steering mechanism 60 changes the direction of the left rear wheel 3LB and the right rear wheel 3RB.

[0135] As another example (third example) of the wheel distance increasing operation during steering, the distance change mechanism 80 increases the distance between the left front wheel 3LF and the right front wheel 3RF and the distance between the left rear wheel 3LB and the right rear wheel 3RB when the left front wheel 3LF, the right front wheel 3RF, the left rear wheel 3LB, and the right rear wheel 3RB are steered by the steering mechanism 60. In other words, the distance change mechanism 80 increases the distance between the left front wheel 3LF and the right front wheel 3RF and the distance between the left rear wheel 3LB and the right rear wheel 3RB when the steering mechanism 60 changes the orientation of the left front wheel 3LF and the right front wheel 3RF and the orientation of the left rear wheel 3LB and the right rear wheel 3RB.

[0136] FIG. 18 is a diagram showing a first example of the wheel range increasing operation during steering. The wheel range increasing operation during steering of the first example can be performed by a work vehicle 1 equipped with the distance change mechanism 80 shown in FIG. 17. The distance change mechanism 80 shown in FIG. 17 includes a first change mechanism 801 that changes the left-right position of the front left wheel 3LF, a second change mechanism 802 that changes the left-right position of the rear left wheel 3LB, a third change mechanism 803 that changes the left-right position of the front right wheel 3RF, and a fourth change mechanism 804 that changes the left-right position of the rear right wheel 3RB. However, the distance change mechanism 80 for performing the wheel range increasing operation during steering of the first example only needs to include at least the first change mechanism 801 and the third change mechanism 803, and does not necessarily have to include the second change mechanism 802 and the fourth change mechanism 804.

[0137] 18(a), when the work vehicle 1 is traveling straight, the distance between the left front wheel 3LF and the right front wheel 3RF is a first distance A1, which is a reference distance. When the distance between the left front wheel 3LF and the right front wheel 3RF is the first distance A1, the rods of the left front cylinder 81LF and the right front cylinder 81RF are not extended (retracted).

[0138] 18(b), the work vehicle 1 increases the distance between the left front wheel 3LF and the right front wheel 3RF to a second distance A2 that is greater than the first distance A1 when the left front wheel 3LF and the right front wheel 3RF are steered by the steering mechanism 60 (see the left front wheel 3LF and the right front wheel 3RF shown by the imaginary lines). This increase in distance is achieved by extending the rod of the left front cylinder 81LF and the rod of the right front cylinder 81RF.

[0139] As a result, when the left front wheel 3LF and the right front wheel 3RF are steered, the distance between the left front wheel 3LF and the vehicle body 2 and the distance between the right front wheel 3RF and the vehicle body 2 are increased. This increases the angle at which the left front wheel 3LF and the right front wheel 3RF can be steered without interfering with the vehicle body 2 (the angle at which they can rotate about the steering axis AX1). This allows the steering angle of the left front wheel 3LF and the right front wheel 3RF to be increased (see the imaginary line in (b) of FIG. 18).

[0140] The second distance A2 is preferably a distance that allows the steering angle of the left front wheel 3LF and the right front wheel 3RF to be 90°. In other words, when the distance between the left front wheel 3LF and the right front wheel 3RF is the second distance A2, the maximum steering angle of the left front wheel 3LF and the right front wheel 3RF is preferably 90°. However, when the distance between the left front wheel 3LF and the right front wheel 3RF is the second distance A2, the maximum steering angle of the left front wheel 3LF and the right front wheel 3RF may be an angle smaller than 90°.

[0141] As described above, by executing the steering wheel distance increasing operation of the first example, the steering angle of the left front wheel 3LF and the right front wheel 3RF can be increased, thereby reducing the turning radius when the front wheels of the work vehicle 1 are steered to turn the vehicle body 2.

[0142] Figure 19 is a diagram showing a second example of the steering wheel range increasing operation. The steering wheel range increasing operation of the second example can be performed by a work vehicle 1 equipped with the distance change mechanism 80 shown in Figure 17. However, the distance change mechanism 80 for performing the steering wheel range increasing operation of the second example only needs to include at least the second change mechanism 802 and the fourth change mechanism 804, and does not necessarily have to include the first change mechanism 801 and the third change mechanism 803.

[0143] 19(a), when the work vehicle 1 is traveling straight, the distance between the left rear wheel 3LB and the right rear wheel 3RB is a first distance B1, which is a reference distance. When the distance between the left rear wheel 3LB and the right rear wheel 3RB is the first distance B1, the rods of the left rear cylinder 81LB and the right rear cylinder 81RB are not extended (retracted).

[0144] 19(b), the work vehicle 1 increases the distance between the left rear wheel 3LB and the right rear wheel 3RB to a second distance B2 that is greater than the first distance B1 when the left rear wheel 3LB and the right rear wheel 3RB are steered by the steering mechanism 60. This increase in distance is achieved by extending the rod of the left rear cylinder 81LB and the rod of the right rear cylinder 81RB.

[0145] As a result, when the left rear wheel 3LB and the right rear wheel 3RB are steered, the distance between the left rear wheel 3LB and the vehicle body 2 and the distance between the right rear wheel 3RB and the vehicle body 2 increase. This increases the angle at which the left rear wheel 3LB and the right rear wheel 3RB can be steered without interfering with the vehicle body 2 (the angle at which they can rotate about the steering axis AX2). This allows the steering angle of the left rear wheel 3LB and the right rear wheel 3RB to be large (see the imaginary line in (b) of FIG. 19 ).

[0146] The second distance B2 is preferably a distance that allows the steering angle of the left rear wheel 3LB and the right rear wheel 3RB to be 90°. In other words, when the distance between the left rear wheel 3LB and the right rear wheel 3RB is the second distance B2, the maximum steering angle of the left rear wheel 3LB and the right rear wheel 3RB is preferably 90°. However, when the distance between the left rear wheel 3LB and the right rear wheel 3RB is the second distance B2, the maximum steering angle of the left rear wheel 3LB and the right rear wheel 3RB may be an angle smaller than 90°.

[0147] As described above, by executing the steering wheel distance increasing operation of the second example, the steering angle of the left rear wheel 3LB and the right rear wheel 3RB can be increased, thereby reducing the turning radius when the rear wheels of the work vehicle 1 are steered to turn the vehicle body 2.

[0148] 20 and 21 are diagrams showing a third example of the wheel range increasing operation when steering. The third example of the wheel range increasing operation when steering can be performed by a work vehicle 1 equipped with the distance change mechanism 80 shown in FIG. 15 or 17. FIG. 20 shows a work vehicle 1 equipped with the distance change mechanism 80 shown in FIG. 17. FIG. 21 shows a work vehicle 1 equipped with the distance change mechanism 80 shown in FIG. 15.

[0149] First, a third example of the wheel distance increasing operation during steering of the work vehicle 1 equipped with the distance changing mechanism 80 shown in FIG. 17 will be described with reference to FIG.

[0150] As shown in (a) of Figure 20, when the work vehicle 1 is traveling straight, the distance between the left front wheel 3LF and the right front wheel 3RF is a first distance C1F, which is a reference distance, and the distance between the left rear wheel 3LB and the right rear wheel 3RB is a first distance C1B, which is also a reference distance. When the distance between the left front wheel 3LF and the right front wheel 3RF is the first distance C1F, the rods of the left front cylinder 81LF and the right front cylinder 81RF are in a non-extended state (shortened state). When the distance between the left rear wheel 3LB and the right rear wheel 3RB is the first distance C1B, the rods of the left rear cylinder 81LB and the right rear cylinder 81RB are in a non-extended state (shortened state).

[0151] 20(b), when the steering mechanism 60 steers the left front wheel 3LF and the right front wheel 3RF, and the left rear wheel 3LB and the right rear wheel 3RB, the work vehicle 1 increases the distance between the left front wheel 3LF and the right front wheel 3RF to a second distance C2F that is larger than the first distance C1F, and increases the distance between the left rear wheel 3LB and the right rear wheel 3RB to a second distance C2B that is larger than the first distance C1B. This increase in distance is achieved by extending the rods of the left front cylinder 81LF, the right front cylinder 81RF, the left rear cylinder 81LB, and the right rear cylinder 81RB.

[0152] As a result, when steering the left front wheel 3LF and the right front wheel 3RF, and the left rear wheel 3LB and the right rear wheel 3RB, the distance between the left front wheel 3LF and the vehicle body 2, the distance between the right front wheel 3RF and the vehicle body 2, the distance between the left rear wheel 3LB and the vehicle body 2, and the distance between the right rear wheel 3RB and the vehicle body 2 increases. This increases the angle at which the left front wheel 3LF, the right front wheel 3RF, the left rear wheel 3LB, and the right rear wheel 3RB can be steered without interfering with the vehicle body 2. This allows for a larger steering angle for the left front wheel 3LF, the right front wheel 3RF, the left rear wheel 3LB, and the right rear wheel 3RB (see the imaginary line in (b) of FIG. 20).

[0153] The second distance C2F is preferably set to a distance that allows the steering angle of the left front wheel 3LF and the right front wheel 3RF to be 90°, but may be an angle smaller than 90°. The second distance C2B is preferably set to a distance that allows the steering angle of the left rear wheel 3LB and the right rear wheel 3RB to be 90°, but may be an angle smaller than 90°.

[0154] As described above, by executing the steering wheel distance increasing operation during steering of the third example, the steering angles of the left front wheel 3LF, the right front wheel 3RF, the left rear wheel 3LB, and the right rear wheel 3RB can be increased, thereby reducing the turning radius when the front and rear wheels of the work vehicle 1 are steered to turn the vehicle body 2.

[0155] Next, a third example of the wheel range increasing operation during steering of the work vehicle 1 equipped with the distance change mechanism 80 shown in Fig. 15 will be described with reference to Fig. 21. This description will focus only on the points that differ from the description with reference to Fig. 20 (the third example of the wheel range increasing operation during steering of the work vehicle 1 equipped with the distance change mechanism 80 shown in Fig. 17).

[0156] As shown in (a) of Figure 21, when the distance between the left front wheel 3LF and the right front wheel 3RF is the first distance C1F and the distance between the left rear wheel 3LB and the right rear wheel 3RB is the first distance C1B, the rod of the left cylinder 81L and the rod of the right cylinder 81R are in a non-extended state (shortened state).

[0157] 21(b), when the steering mechanism 60 steers the left front wheel 3LF and the right front wheel 3RF, and the left rear wheel 3LB and the right rear wheel 3RB, the work vehicle 1 increases the distance between the left front wheel 3LF and the right front wheel 3RF to a second distance C2F that is larger than the first distance C1F, and increases the distance between the left rear wheel 3LB and the right rear wheel 3RB to a second distance C2B that is larger than the first distance C1B. These distances are increased by extending the rod 81Lb of the left cylinder 81L and the rod 81Rb of the right cylinder 81R.

[0158] As a result, when steering the left front wheel 3LF and the right front wheel 3RF, and the left rear wheel 3LB and the right rear wheel 3RB, the distance between the left front wheel 3LF and the vehicle body 2, the distance between the right front wheel 3RF and the vehicle body 2, the distance between the left rear wheel 3LB and the vehicle body 2, and the distance between the right rear wheel 3RB and the vehicle body 2 increases. This increases the angle at which the left front wheel 3LF, the right front wheel 3RF, the left rear wheel 3LB, and the right rear wheel 3RB can be steered without interfering with the vehicle body 2. This allows for a larger steering angle for the left front wheel 3LF, the right front wheel 3RF, the left rear wheel 3LB, and the right rear wheel 3RB (see the imaginary line in (b) of FIG. 21 ).

[0159] As described above, in the work vehicle 1, by having the distance change mechanism 80 perform any of the first to third examples of wheel distance increasing operations during steering, the distance between the wheels and the vehicle body 2 can be increased, thereby enabling a larger steering angle of the wheels. This makes it possible to reduce the turning radius of the vehicle body 2, and enables the vehicle body 2 to turn even in a narrow space.

[0160] Furthermore, since it is possible to increase the steering angle of the wheels, the distance between the vehicle body 2 and the wheels (steered wheels) before the steering wheel distance increasing operation can be set small. In other words, even if the space required for steering is not secured between the vehicle body 2 and the wheels (steered wheels) from the beginning, the space required for steering can be secured by the distance change mechanism 80 performing the steering wheel distance increasing operation. In other words, since the work vehicle 1 becomes steerable when the distance change mechanism 80 performs the steering wheel distance increasing operation, the space required for steering does not need to be secured between the vehicle body 2 and the wheels (steered wheels) before the steering wheel distance increasing operation is performed. This makes it possible to increase the width of the vehicle body 2 close to the wheels (steered wheels) (reduce the distance between the vehicle body 2 and the wheels). As a result, the width of the vehicle body 2 can be increased without increasing the width of the work vehicle 1, making it possible to secure a large interior space for accommodating equipment in the vehicle body 2.

[0161] As described above, the steering wheel range increasing operation of the distance change mechanism 80 can be performed by driving the actuators (left cylinder 81L and right cylinder 81R) of the distance change mechanism 80 during steering by the steering mechanism 60. However, the steering wheel range increasing operation can also be performed by a method that does not use the actuators (left cylinder 81L and right cylinder 81R) of the distance change mechanism 80. Hereinafter, the steering wheel range increasing operation using this method will be referred to as the "first modified example."

[0162] In the first modified example, the steering mechanism 60 changes the orientation of the left and right wheels while the vehicle body 2 is traveling so that the forward portions of the wheels in the traveling direction move away from the vehicle body 2. The distance change mechanism 80 increases the distance between the left and right wheels by utilizing a reaction force from the ground generated by the change in orientation of the left and right wheels by the steering mechanism 60. This will be explained in more detail below.

[0163] Figure 22 is a schematic plan view showing a work vehicle 1 equipped with a distance change mechanism 80 having a configuration for implementing a first modified example (hereinafter referred to as "first configuration A"). The distance change mechanism 80 having first configuration A is equipped with a telescopic mechanism 83. The telescopic mechanism 83 includes a left telescopic mechanism 83L and a right telescopic mechanism 83R. The work vehicle 1 shown in Figure 22 is equipped with a left telescopic mechanism 83L instead of the left cylinder 81L of the work vehicle 1 shown in Figure 15, and a right telescopic mechanism 83R instead of the right cylinder 81R.

[0164] Fig. 23 is a diagram showing an example of the configuration of the extension / retraction mechanism 83. However, the configuration of the extension / retraction mechanism 83 is not limited to the configuration shown in Fig. 23. The extension / retraction mechanism 83 includes a cylindrical body 83a and a rod 83b. The rod 83b is housed inside the cylindrical body 83a, and the tip thereof protrudes from the cylindrical body 83a. The rod 83b is movable relative to the cylindrical body 83a (along the cylindrical body 83a). By moving the rod 83b relative to the cylindrical body 83a, the length of the protruding portion from the cylindrical body 83a changes.

[0165] The central axis of the cylindrical body 83a and the rod 83b faces the left-right direction (vehicle body width direction). Therefore, the rod 83b is movable left-right relative to the cylindrical body 83a. The cylindrical body 83a is fixed to the vehicle body 2. The tip of the rod 83b is fixed to the left traveling unit 3L or the right traveling unit 3R. The tip of the rod 83b of the left telescopic mechanism 83L is fixed to the left traveling unit 3L. The tip of the rod 83b of the right telescopic mechanism 83R is fixed to the right traveling unit 3R. More specifically, the tip of the rod 83b of the left telescopic mechanism 83L is fixed to the left frame 18L that supports the left traveling unit 3L. The tip of the rod 83b of the right telescopic mechanism 83R is fixed to the right frame 18R that supports the right traveling unit 3R.

[0166] As a result, the rod 83b of the left telescopic mechanism 83L extends (the amount of protrusion from the cylindrical body 83a increases) when the left traveling device 3L moves leftward, and contracts (the amount of protrusion from the cylindrical body 83a decreases) when the left traveling device 3L moves rightward. The rod 83b of the right telescopic mechanism 83R extends when the right traveling device 3R moves rightward, and contracts when the right traveling device 3R moves leftward.

[0167] Figure 24 is a diagram showing the wheelbase increasing operation during steering in a work vehicle 1 equipped with the configuration shown in Figure 22 (first configuration A). As shown in Figure 24(a), when the work vehicle 1 is traveling (when the vehicle body 2 is traveling straight) before steering, the rod of the left telescopic mechanism 83L and the rod of the right telescopic mechanism 83R are in a non-extended state (retracted state).

[0168] As shown in (b) of Figure 24, when the vehicle body 2 is traveling, the steering mechanism 60 changes the direction of the left wheels (left front wheel 3LF, left rear wheel 3LB) and right wheels (right front wheel 3RF, right rear wheel 3RB) so that the forward parts of the wheels (left front wheel 3LF, right front wheel 3RF, left rear wheel 3LB, right rear wheel 3RB) in the direction of travel move away from the vehicle body 2.

[0169] That is, when the vehicle body 2 is moving forward (as shown in FIG. 24 ), the directions of the left wheels (left front wheel 3LF, left rear wheel 3LB) and the right wheels (right front wheel 3RF, right rear wheel 3RB) are changed so that the front portions of the wheels (left front wheel 3LF, right front wheel 3RF, left rear wheel 3LB, right rear wheel 3RB) move away from the vehicle body 2. When the vehicle body 2 is moving backward (not shown), the directions of the left wheels (left front wheel 3LF, left rear wheel 3LB) and the right wheels (right front wheel 3RF, right rear wheel 3RB) are changed so that the rear portions of the wheels (left front wheel 3LF, right front wheel 3RF, left rear wheel 3LB, right rear wheel 3RB) move away from the vehicle body 2.

[0170] When the orientations of the left and right wheels are changed in this way, the orientations of the left and right wheels no longer match the traveling direction of the vehicle body 2, and the left and right wheels receive a reaction force from the ground. A portion of this reaction force (a component of this reaction force) acts leftward on the left wheel and rightward on the right wheel. Therefore, when the left and right wheels receive a reaction force from the ground, the rod 83b of the left telescopic mechanism 83L and the rod 83b of the right telescopic mechanism 83R extend. This increases the distance between the left frame 18L and the right frame 18R, and increases the distance between the left and right wheels (see (c) in Figure 24).

[0171] After the distance between the left and right wheels has increased, the steering mechanism 60 returns the orientation of the left wheels (left front wheel 3LF, left rear wheel 3LB) and the right wheels (right front wheel 3RF, right rear wheel 3RB) to their original orientation (the orientation before the distance between the left and right wheels increased) while the distance remains increased (see (d) in Figure 24).

[0172] When the distance between the left and right wheels is reduced, the steering mechanism 60 changes the orientation of the left wheels (left front wheel 3LF, left rear wheel 3LB) and the right wheels (right front wheel 3RF, right rear wheel 3RB) so that the front portions of the wheels (left front wheel 3LF, right front wheel 3RF, left rear wheel 3LB, right rear wheel 3RB) in the traveling direction move closer to the vehicle body 2 (see (e) in FIG. 24). When the orientation of the left and right wheels is changed in this way, the left and right wheels receive a reaction force from the ground directed inward (towards the vehicle body 2). This shortens the rod 83b of the left telescopic mechanism 83L and the rod 83b of the right telescopic mechanism 83R, reducing the distance between the left and right wheels.

[0173] Figure 25 is a schematic plan view showing a work vehicle 1 equipped with a distance change mechanism 80 having another configuration (hereinafter referred to as "first configuration B") for implementing the first modified example. The distance change mechanism 80 having first configuration B includes a left front telescopic mechanism 83LF, a left rear telescopic mechanism 83LB, a right front telescopic mechanism 83RF, and a right rear telescopic mechanism 83RB as the telescopic mechanism 83. The work vehicle 1 shown in Figure 25 is equipped with a left front telescopic mechanism 83LF instead of the left front cylinder 81LF of the work vehicle 1 shown in Figure 17, a left rear telescopic mechanism 83LB instead of the left rear cylinder 81LB, a right front telescopic mechanism 83RF instead of the right front cylinder 81RF, and a right rear telescopic mechanism 83RB instead of the right rear cylinder 81RB.

[0174] Figure 26 is a diagram showing the wheelbase increasing operation during steering in a work vehicle 1 equipped with the configuration shown in Figure 25 (first configuration B). As shown in (a) in Figure 26, when the work vehicle 1 is traveling with the vehicle body 2 before steering (when the vehicle body 2 is traveling straight), the rods of the left front telescopic mechanism 83LF, left rear telescopic mechanism 83LB, right front telescopic mechanism 83RF, and right rear telescopic mechanism 83RB are not extended (retracted).

[0175] As shown in (b) of Figure 26, when the vehicle body 2 is traveling, the steering mechanism 60 changes the direction of the left wheels (left front wheel 3LF, left rear wheel 3LB) and right wheels (right front wheel 3RF, right rear wheel 3RB) so that the forward parts of the wheels (left front wheel 3LF, right front wheel 3RF, left rear wheel 3LB, right rear wheel 3RB) in the direction of travel move away from the vehicle body 2.

[0176] When the orientation of the left and right wheels is changed in this way, the left and right wheels receive a reaction force from the ground, causing the rod 83b of the left front telescopic mechanism 83LF, the rod 83b of the left rear telescopic mechanism 83LB, the rod 83b of the right front telescopic mechanism 83RF, and the rod 83b of the right rear telescopic mechanism 83RB to extend. This increases the distance between the left frame 18LF and the right frame 18RF, and the distance between the left frame 18LB and the right frame 18RB, and therefore the distance between the left and right wheels (see (c) in Figure 26).

[0177] After the distance between the left and right wheels has increased, the steering mechanism 60 returns the orientation of the left wheels (left front wheel 3LF, left rear wheel 3LB) and the right wheels (right front wheel 3RF, right rear wheel 3RB) to their original orientation (the orientation before the distance between the left and right wheels increased) while the distance remains increased (see (d) in Figure 26).

[0178] When reducing the distance between the left and right wheels, the steering mechanism 60 changes the orientation of the left wheels (left front wheel 3LF, left rear wheel 3LB) and right wheels (right front wheel 3RF, right rear wheel 3RB) so that the front portions of the wheels (left front wheel 3LF, right front wheel 3RF, left rear wheel 3LB, right rear wheel 3RB) in the traveling direction move closer to the vehicle body 2 (see (e) in Figure 26). When the orientation of the left and right wheels is changed in this way, the left and right wheels receive a reaction force from the ground that moves inward (towards the vehicle body 2). This shortens the rods 83b of the left front telescopic mechanism 83LF, left rear telescopic mechanism 83LB, right front telescopic mechanism 83RF, and right rear telescopic mechanism 83RB, reducing the distance between the left and right wheels.

[0179] 24 and 26, the distance change mechanism 80 having the first configuration A or the first configuration B increases the distance between the left and right wheels without using the actuators (left front cylinder 81LF, left rear cylinder 81LB, right front cylinder 81RF, right rear cylinder 81RB) by utilizing the reaction force from the ground generated by a change in the direction of the left and right wheels by the steering mechanism 60. Therefore, it is possible to omit the actuator for increasing the distance between the left and right wheels.

[0180] In the case of the distance change mechanism 80 having the first configuration B, the distance between the left wheel and the right wheel can be increased or decreased for only one of the front wheels or the rear wheels.

[0181] When the distance between the left and right wheels is increased for only the front wheels, the steering mechanism 60 changes the orientation of the left front wheel 3LF and the right front wheel 3RF while the vehicle body 2 is traveling so that the forward portions of the left front wheel 3LF and the right front wheel 3RF in the traveling direction move away from the vehicle body 2. When the distance between the left and right wheels is reduced for only the front wheels, the steering mechanism 60 changes the orientation of the left front wheel 3LF and the right front wheel 3RF while the vehicle body 2 is traveling so that the forward portions of the left front wheel 3LF and the right front wheel 3RF in the traveling direction move closer to the vehicle body 2.

[0182] When the distance between the left and right wheels is increased for only the rear wheels, the steering mechanism 60 changes the orientation of the left rear wheel 3LB and the right rear wheel 3RB while the vehicle body 2 is traveling so that the forward portions of the left rear wheel 3LB and the right rear wheel 3RB in the traveling direction move away from the vehicle body 2. When the distance between the left and right wheels is reduced for only the rear wheels, the steering mechanism 60 changes the orientation of the left rear wheel 3LB and the right rear wheel 3RB while the vehicle body 2 is traveling so that the forward portions of the left rear wheel 3LB and the right rear wheel 3RB in the traveling direction move closer to the vehicle body 2.

[0183] The wheelbase increasing operation during steering can also be performed by a method that uses the actuators (left cylinder 81L and right cylinder 81R) of the distance change mechanism 80 in combination with the extension / retraction mechanism 83. Hereinafter, the wheelbase increasing operation during steering that uses this method will be referred to as the "second modified example." In the second modified example, as in the first modified example, the steering mechanism 60 changes the orientation of the left and right wheels while the vehicle body 2 is traveling so that the forward portions of the wheels in the traveling direction move away from the vehicle body 2.

[0184] In the second modified example, the distance change mechanism 80 increases the distance between the left and right wheels by utilizing a reaction force from the ground generated by a change in the direction of the left and right wheels by the steering mechanism 60, and the left cylinder 81L and the right cylinder 81R (actuators that move the left and right wheels in the vehicle body width direction). This will be explained in more detail below.

[0185] Figure 27 is a schematic plan view showing a work vehicle 1 equipped with a distance change mechanism 80 having a configuration for implementing a second modified example (hereinafter referred to as "second configuration A"). The distance change mechanism 80 having second configuration A is equipped with a telescopic mechanism 83 in addition to a left cylinder 81L and a right cylinder 81R. The telescopic mechanism 83 includes a left telescopic mechanism 83L and a right telescopic mechanism 83R. The work vehicle 1 shown in Figure 27 is equipped with a left telescopic mechanism 83L in addition to the left cylinder 81L of the work vehicle 1 shown in Figure 15, and a right telescopic mechanism 83R in addition to the right cylinder 81R.

[0186] Figure 28 is a diagram showing the wheelbase increasing operation during steering in a work vehicle 1 equipped with the configuration shown in Figure 27 (second configuration A). As shown in Figure 28(a), when the work vehicle 1 is traveling (when the vehicle body 2 is traveling straight) before steering, the rods of the left telescopic mechanism 83L and the right telescopic mechanism 83R are not extended (retracted). In addition, the rods of the left cylinder 81L and the right cylinder 81R are also not extended (retracted).

[0187] As shown in (b) of Figure 28, when the vehicle body 2 is traveling, the steering mechanism 60 changes the direction of the left wheels (left front wheel 3LF, left rear wheel 3LB) and right wheels (right front wheel 3RF, right rear wheel 3RB) so that the forward parts of the wheels (left front wheel 3LF, right front wheel 3RF, left rear wheel 3LB, right rear wheel 3RB) in the direction of travel move away from the vehicle body 2.

[0188] When the orientation of the left and right wheels is changed in this way, the left and right wheels receive a reaction force from the ground, which causes a force to act in the extension direction on the rods of the left telescopic mechanism 83L and the right telescopic mechanism 83R. At this time (when the orientation of the left and right wheels is changed), the left cylinder 81L and the right cylinder 81R are driven to extend the rods 81b of the left cylinder 81L and the right cylinder 81R. This extends the rods 81b of the left cylinder 81L and the right cylinder 81R, and also extends the rods 83b of the left telescopic mechanism 83L and the right telescopic mechanism 83R. As a result, the distance between the left frame 18L and the right frame 18R increases, and the distance between the left and right wheels increases (see (c) in Figure 28).

[0189] After the distance between the left and right wheels has increased, the steering mechanism 60 returns the orientation of the left wheels (left front wheel 3LF, left rear wheel 3LB) and the right wheels (right front wheel 3RF, right rear wheel 3RB) to their original orientation (the orientation before the distance between the left and right wheels increased) while the distance remains increased (see (d) in Figure 28).

[0190] When the distance between the left and right wheels is reduced, the orientation of the left wheels (left front wheel 3LF, left rear wheel 3LB) and right wheels (right front wheel 3RF, right rear wheel 3RB) is changed so that the front portions of the wheels (left front wheel 3LF, right front wheel 3RF, left rear wheel 3LB, right rear wheel 3RB) in the direction of travel move closer to the vehicle body 2, and the left cylinder 81L and right cylinder 81R are driven to reduce the rods 81b of the left cylinder 81L and right cylinder 81R. As a result, the left and right wheels receive a reaction force from the ground directed inward (towards the vehicle body 2), and also receive a force directed inward (towards the vehicle body 2) from the left cylinder 81L and right cylinder 81R. As a result, the rods 83b of the left telescopic mechanism 83L and right telescopic mechanism 83R are reduced, reducing the distance between the left and right wheels (see (e) in FIG. 28 ).

[0191] As described above, the distance change mechanism 80 having the second configuration A increases the distance between the left and right wheels by using both the reaction force from the ground generated by the steering mechanism 60 changing the direction of the left and right wheels and the actuators (left cylinder 81L and right cylinder 81R) that move the left and right wheels in the vehicle body width direction. Therefore, the distance between the left and right wheels can be increased with less force than when using only the actuators (left cylinder 81L and right cylinder 81R). Furthermore, by using the actuators (left cylinder 81L and right cylinder 81R), the distance between the left and right wheels can be increased more reliably than when using only the reaction force from the ground.

[0192] Figure 29 is a schematic plan view showing a work vehicle 1 equipped with a distance change mechanism 80 having another configuration (hereinafter referred to as "second configuration B") for implementing the second modified example. The distance change mechanism 80 having second configuration B includes a left front telescopic mechanism 83LF, a left rear telescopic mechanism 83LB, a right front telescopic mechanism 83RF, and a right rear telescopic mechanism 83RB as the telescopic mechanism 83. The work vehicle 1 shown in Figure 29 is equipped with a left front telescopic mechanism 83LF in addition to the left front cylinder 81LF of the work vehicle 1 shown in Figure 17, a left rear telescopic mechanism 83LB in addition to the left rear cylinder 81LB, a right front telescopic mechanism 83RF in addition to the right front cylinder 81RF, and a right rear telescopic mechanism 83RB in addition to the right rear cylinder 81RB.

[0193] Figure 30 is a diagram showing the wheelbase expanding operation during steering in a work vehicle 1 equipped with the configuration shown in Figure 29 (second configuration B). As shown in (a) in Figure 30, when the vehicle body 2 of the work vehicle 1 is traveling before steering (when the vehicle body 2 is traveling straight), the rods of the left front telescopic mechanism 83LF, the left rear telescopic mechanism 83LB, the right front telescopic mechanism 83RF, and the right rear telescopic mechanism 83RB are not extended (retracted). In addition, the rods of the left front cylinder 81LF, the left rear cylinder 81LB, the right front cylinder 81RF, and the right rear cylinder 81RB are also not extended (retracted).

[0194] As shown in (b) of Figure 30, when the vehicle body 2 is traveling, the steering mechanism 60 changes the direction of the left wheels (left front wheel 3LF, left rear wheel 3LB) and right wheels (right front wheel 3RF, right rear wheel 3RB) so that the forward parts of the wheels (left front wheel 3LF, right front wheel 3RF, left rear wheel 3LB, right rear wheel 3RB) in the direction of travel move away from the vehicle body 2.

[0195] When the orientation of the left and right wheels is changed in this way, the left and right wheels receive a reaction force from the ground, which causes an extension force to act on the rods of the left front telescopic mechanism 83LF, left rear telescopic mechanism 83LB, right front telescopic mechanism 83RF, and right rear telescopic mechanism 83RB. At this time (when the orientation of the left and right wheels is changed), the left front cylinder 81LF, left rear cylinder 81LB, right front cylinder 81RF, and right rear cylinder 81RB are driven to extend the rods 81b of each cylinder. As a result, the rods 81b of the left front cylinder 81LF, left rear cylinder 81LB, right front cylinder 81RF, and right rear cylinder 81RB extend, and the rods 83b of the left front telescopic mechanism 83LF, left rear telescopic mechanism 83LB, right front telescopic mechanism 83RF, and right rear telescopic mechanism 83RB also extend. As a result, the distance between the left frame 18LF and the right frame 18RF and the distance between the left frame 18LB and the right frame 18RB increase, and the distance between the left wheel and the right wheel increases (see (c) in Figure 30).

[0196] After the distance between the left and right wheels has increased, the steering mechanism 60 returns the orientation of the left wheels (left front wheel 3LF, left rear wheel 3LB) and the right wheels (right front wheel 3RF, right rear wheel 3RB) to their original orientation (the orientation before the distance between the left and right wheels increased) while the distance remains increased (see (d) in Figure 30).

[0197] When the distance between the left and right wheels is reduced, the orientation of the left wheels (left front wheel 3LF, left rear wheel 3LB) and right wheels (right front wheel 3RF, right rear wheel 3RB) is changed so that the front portions of the wheels (left front wheel 3LF, right front wheel 3RF, left rear wheel 3LB, right rear wheel 3RB) in the direction of travel move closer to the vehicle body 2, and the left front cylinder 81LF, left rear cylinder 81LB, right front cylinder 81RF, and right rear cylinder 81RB are driven to shorten the rods 81b of each cylinder. As a result, the left and right wheels receive a reaction force from the ground directed inward (towards the vehicle body 2), and also receive forces directed inward (towards the vehicle body 2) from the left front cylinder 81LF, left rear cylinder 81LB, right front cylinder 81RF, and right rear cylinder 81RB. As a result, the rods 83b of the left front telescopic mechanism 83LF, left rear telescopic mechanism 83LB, right front telescopic mechanism 83RF, and right rear telescopic mechanism 83RB shorten, reducing the distance between the left and right wheels (see (e) in Figure 30).

[0198] As described above, the distance change mechanism 80 having the second configuration B increases the distance between the left and right wheels by using both the reaction force from the ground generated by the steering mechanism 60 changing the direction of the left and right wheels and the actuators (left front cylinder 81LF, left rear cylinder 81LB, right front cylinder 81RF, and right rear cylinder 81RB) that move the left and right wheels in the vehicle width direction. Therefore, the distance between the left and right wheels can be increased with less force than when using only the actuators (left front cylinder 81LF, left rear cylinder 81LB, right front cylinder 81RF, and right rear cylinder 81RB). Furthermore, by using the actuators (left front cylinder 81LF, left rear cylinder 81LB, right front cylinder 81RF, and right rear cylinder 81RB), the distance between the left and right wheels can be increased more reliably than when using only the reaction force from the ground.

[0199] In the case of the distance change mechanism 80 having the second configuration B, the distance between the left wheel and the right wheel can be increased or decreased for only one of the front wheels or the rear wheels.

[0200] When the distance between the left and right wheels is increased for the front wheels only, the orientation of the left front wheel 3LF and the right front wheel 3RF is changed and the left front cylinder 81LF and the right front cylinder 81RF are driven to extend the rod 81b of each cylinder so that the forward portions of the left front wheel 3LF and the right front wheel 3RF in the direction of travel move away from the vehicle body 2 while the vehicle body 2 is traveling. When the distance between the left and right wheels is decreased for the front wheels only, the orientation of the left front wheel 3LF and the right front wheel 3RF is changed and the left front cylinder 81LF and the right front cylinder 81RF are driven to shorten the rod 81b of each cylinder while the vehicle body 2 is traveling.

[0201] When the distance between the left and right wheels only is increased, the orientation of the left rear wheels 3LB and the right rear wheels 3RB is changed while the vehicle body 2 is traveling, and the left rear cylinder 81LB and the right rear cylinder 81RB are driven to extend the rod 81b of each cylinder so that the forward portions of the left rear wheels 3LB and the right rear wheels 3RB in the direction of travel move away from the vehicle body 2. When the distance between the left and right wheels only is decreased while the vehicle body 2 is traveling, the orientation of the left rear wheels 3LB and the right rear wheels 3RB is changed while the vehicle body 2 is traveling, and the left rear cylinder 81LB and the right rear cylinder 81RB are driven to shorten the rod 81b of each cylinder.

[0202] The above-mentioned steering wheel range increasing operation and the steering wheel range increasing operation described later are performed under the control of the distance change control unit 15B (see FIG. 7) of the control device 15. More specifically, the steering wheel range increasing operation can be performed by the distance change control unit 15B of the control device 15 controlling the operation of the distance change mechanism 80 or the operation of the steering mechanism 60 and the distance change mechanism 80.

[0203] More specifically, when the wheel range increasing operation during steering does not utilize reaction force from the ground (see FIGS. 18 to 21), the wheel range increasing operation during steering can be performed by the distance change control unit 15B controlling the operation of the distance change mechanism 80. When the wheel range increasing operation during steering utilizes reaction force from the ground (see FIGS. 24, 26, 28, and 30), the wheel range increasing operation during steering can be performed by the distance change control unit 15B controlling the operation of the steering mechanism 60 and the distance change mechanism 80.

[0204] When the distance change control unit 15B controls the operation of the steering mechanism 60, it controls the operation of the cylinder 62 (the extension and contraction of the rod 62a) of the steering mechanism 60. When the distance change control unit 15B controls the operation of the distance change mechanism 80, it controls the operation of the left cylinder 81L and the right cylinder 81R of the distance change mechanism 80 (the extension and contraction of the rod 81b).

[0205] A specific example (application example) of the wheel tracking expansion operation during steering will be described below. The specific example described below is an example of the wheel tracking expansion operation during steering when the work vehicle 1 performs work while traveling along (straddling) the ridges of a field. In the description of the specific example below, the "distance between the left wheel and the right wheel" means the smaller of the distance between the inner surface of the left front wheel 3LF and the inner surface of the right front wheel 3RF, and the distance between the inner surface of the left rear wheel 3LB and the inner surface of the right rear wheel 3RB.

[0206] 31 to 34 are diagrams showing a first specific example. The first specific example is a specific example of the wheel range increasing operation during steering of the third example described above (see FIGS. 20 and 21). More specifically, it is a specific example of the third example of the wheel range increasing operation during steering of a work vehicle 1 equipped with the distance change mechanism 80 shown in FIG. 15. However, the first specific example is also applicable to the wheel range increasing operation during steering of a work vehicle 1 equipped with the distance change mechanism 80 shown in FIG. 17.

[0207] 31 shows the state in which the work vehicle 1 is traveling along (straddling) the first ridge UN1. In this state, the distance D1 between the left and right wheels is set to a distance (D1≧W1) that matches the width W1 of the first ridge UN1.

[0208] As shown in Figure 32, after the work vehicle 1 passes the first ridge UN1, the distance change mechanism 80 extends the rods 81b of the left cylinder 81L and right cylinder 81R, thereby increasing the distance D1 between the left and right wheels. The steering mechanism 60 then steers the left wheels (left front wheel 3LF, left rear wheel 3LB) and right wheels (right front wheel 3RF, right rear wheel 3RB) to turn toward the second ridge UN2 adjacent to the first ridge UN1 (see arrow S1 in Figure 33). In this way, the change (increase) of the distance D1 between the left and right wheels is performed after passing the first ridge UN1 and before turning toward the second ridge UN2.

[0209] After steering the left and right wheels to turn while the distance D1 between the left and right wheels is enlarged, the rods 81b of the left cylinder 81L and the right cylinder 81R are shortened (see FIG. 34). As a result, the distance D1 between the left and right wheels of the work vehicle 1 returns to its original distance (the distance when traveling along the first ridge UN1), and the work vehicle 1 travels toward the second ridge UN2. Note that if the width W2 of the second ridge UN2 is different from the width W1 of the first ridge UN1, when shortening the rods 81b of the left cylinder 81L and the right cylinder 81R, the distance D1 between the left and right wheels is set to a distance that matches the width W2 of the second ridge UN2 (D1≧W2).

[0210] 35 to 38 are diagrams showing a second specific example. The second specific example is a specific example of the wheel base expansion operation during steering according to the second modified example described above. The following describes the case where distance change mechanism 80 has second configuration A (see FIG. 27), but distance change mechanism 80 may also have second configuration B (see FIG. 29).

[0211] 35 shows the state in which the work vehicle 1 is traveling along (straddling) the first ridge UN1. In this state, the distance D1 between the left and right wheels is set to a distance (D1≧W1) that matches the width W1 of the first ridge UN1.

[0212] As shown in FIG. 36 , after the work vehicle 1 passes the first furrow UN1, the steering mechanism 60 changes the orientation of the left wheels (left front wheel 3LF, left rear wheel 3LB) and right wheels (right front wheel 3RF, right rear wheel 3RB) while the vehicle body 2 is traveling so that the front portions of the wheels (left front wheel 3LF, right front wheel 3RF, left rear wheel 3LB, right rear wheel 3RB) in the traveling direction move away from the vehicle body 2. As a result, the left and right wheels receive a reaction force from the ground, and the rods 83b of the left telescopic mechanism 83L and right telescopic mechanism 83R are extended. Furthermore, after the orientation of the left and right wheels is changed, the rods 81b of the left cylinder 81L and right cylinder 81R are extended. As a result, the distance between the left and right wheels increases due to the reaction force from the ground and the driving force of the left cylinder 81L and right cylinder 81R (the force that extends the rods 81b).

[0213] Thereafter, the left wheels (left front wheel 3LF, left rear wheel 3LB) and right wheels (right front wheel 3RF, right rear wheel 3RB) are steered to turn toward the second ridge UN2 adjacent to the first ridge UN1 (see arrow S2 in Figure 37). In this way, the change (increase) in the distance between the left and right wheels is performed after passing the first ridge UN1 and before turning toward the second ridge UN2.

[0214] After steering the left and right wheels to turn while the distance between them is increased, the rods 81b of the left cylinder 81L and the right cylinder 81R are retracted, which also retracts the rods 83b of the left telescopic mechanism 83L and the right telescopic mechanism 83R (see FIG. 38).

[0215] As a method for shortening the rods 83b of the left telescopic mechanism 83L and the right telescopic mechanism 83R, the distance between the left and right wheels may be shortened by utilizing the reaction force from the ground generated by a change in the direction of the left and right wheels by the steering mechanism 60. Below, a method for utilizing the reaction force from the ground will be described in a second specific example.

[0216] When utilizing the reaction force from the ground, while the work vehicle 1 is traveling, the orientation of the left wheels (left front wheel 3LF, left rear wheel 3LB) and right wheels (right front wheel 3RF, right rear wheel 3RB) is changed and the rods 81b of the left cylinder 81L and right cylinder 81R are shortened so that the front portions of the wheels (left front wheel 3LF, right front wheel 3RF, left rear wheel 3LB, right rear wheel 3RB) in the traveling direction move closer to the vehicle body 2. This makes it possible to shorten the rods 83b of the left telescopic mechanism 83L and right telescopic mechanism 83R by utilizing the reaction force from the ground acting on the wheels, thereby shortening the distance between the left and right wheels (see FIG. 39 ). After the distance between the left and right wheels is shortened, the orientation of the left wheels (left front wheel 3LF, left rear wheel 3LB) and right wheels (right front wheel 3RF, right rear wheel 3RB) is returned to their original orientation.

[0217] As a result, the distance between the left and right wheels of the work vehicle 1 returns to the original distance (the distance when traveling along the first ridge UN1), and the work vehicle 1 travels toward the second ridge UN2. If the width W2 of the second ridge UN2 is different from the width W1 of the first ridge UN1, when the rods 81b of the left cylinder 81L and right cylinder 81R are shortened, the distance D1 between the left and right wheels is set to a distance (D1≧W2) that matches the width W2 of the second ridge UN2.

[0218] In the first and second specific examples described above, if the width W1 of the first ridge UN1 and the width W2 of the second ridge UN2 are different and the distance D1 between the left wheel and the right wheel is set to a distance that matches the width W2 of the second ridge UN2, the width W2 of the second ridge UN2 can be detected when the work vehicle 1 is traveling along the first ridge UN1.

[0219] In this case, as shown in Figure 40, the first detection device 70 detects the width W2 of the second ridge UN2 adjacent to the first ridge UN1 while the vehicle body 2 is traveling along the first ridge UN1. Detection of the width W2 of the second ridge UN2 is possible by installing the first detection device 70 at a higher position than the second ridge UN2. If the first detection device 70 is a camera, the camera 71 captures an image of the second ridge UN2 on the side of the vehicle body 2 and generates an image signal. The calculation unit 73 detects the width W2 of the second ridge UN2 based on the generated image signal.

[0220] Meanwhile, the second detector 75 detects the distance D1 between the left and right wheels. The width W2 and the distance D1 are detected before the vehicle body 2 reaches the second ridge UN2. The detection of the width W2 and the distance D1 may be performed either first or simultaneously.

[0221] The distance change control unit 15B compares the ridge width W2 detected by the first detection device 70 with the distance D1 detected by the second detection device 75. Based on the comparison result, the distance change control unit 15B drives the left cylinder 81L and the right cylinder 81R to set the distance D1 between the left wheel and the right wheel to a distance that matches the width W2 of the second ridge UN2.

[0222] As shown in the first and second specific examples above, by increasing the distance between the left and right wheels, the steering angle (the range of steerable angles) of the left and right wheels can be increased. This allows the work vehicle 1 to turn with a small turning radius. This allows the work vehicle 1 to easily and quickly move toward the second ridge UN2 even when the distance between the first ridge UN1 and the second ridge UN2 is narrow.

[0223] Furthermore, while the work vehicle 1 is traveling along a ridge, the distance between the left and right wheels is limited by the presence of an adjacent ridge, but this limitation is lifted after the work vehicle 1 has passed the ridge. Therefore, by increasing the distance between the left and right wheels after passing the first ridge UN1 (see Figures 32 and 36), the work vehicle 1 can make a small-radius turn toward the second ridge UN2 (see Figures 33 and 37).

[0224] The distance change control unit 15B can also detect the width of a ridge ahead in the traveling direction of the vehicle body 2 using the first detection device 70. In this case, the distance change control unit 15B compares the width of the ridge ahead in the traveling direction of the vehicle body 2 detected by the first detection device 70 with the distance D1 between the left wheel and the right wheel, and sets the distance D1 to a distance that matches the width of the ridge ahead in the traveling direction.

[0225] In the above description of the wheelbase widening operation during steering, a work vehicle 1 in which the left wheel is attached to the left frame 18L and the right wheel is attached to the right frame 18R is used as an example. However, the work vehicle 1 that performs the above-described wheelbase widening operation during steering (including the first and second modified examples) may also be a work vehicle in which the left and right wheels are attached to the vehicle body 2 without the frame structure 18. Hereinafter, this work vehicle will be referred to as the modified work vehicle 1.

[0226] In order to perform the wheelbase expansion operation during steering in the work vehicle 1 of the modified example, the axle of the wheel steered by the steering mechanism 60 is made extendable. The extendable axle can be configured, for example, from a cylindrical body and a rod that is movable relative to (along) the cylindrical body. In this case, the cylindrical body is attached to the vehicle body 2, and the wheel is attached to the rod. Furthermore, the wheel is attached to the tip end of the rod, and the base end of the rod is housed in the cylindrical body. The extension and contraction operation of the axle can be performed, for example, by a cylinder device such as a hydraulic cylinder or an electric cylinder. Furthermore, the extendable axle itself may be configured from an extendable rod of a cylinder device such as a hydraulic cylinder or an electric cylinder.

[0227] In the case of the modified work vehicle 1, the left wheel is attached to an axle extending leftward from the vehicle body 2, and the right wheel is attached to an axle extending rightward from the vehicle body 2. Specifically, the left front wheel 3LF is attached to the left front axle extending leftward from the front left part of the vehicle body 2. The right front wheel 3RF is attached to the right front axle extending rightward from the front right part of the vehicle body 2. The left rear wheel 3LB is attached to the left rear axle extending leftward from the rear left part of the vehicle body 2. The right rear wheel 3RB is attached to the right rear axle extending rightward from the rear right part of the vehicle body 2.

[0228] A specific example of the modified work vehicle 1 is one in which the axles of the tractor are configured to be extendable and retractable. In this case, the modified work vehicle 1 may be one in which the left and right front axles of the tractor are configured to be extendable and retractable, or the left and right rear axles are configured to be extendable and retractable, or the left and right front axles, the left and right rear axles are configured to be extendable and retractable.

[0229] 41 is a diagram showing a modified example of the first example of the wheel range expanding operation during steering. This modified example uses a modified work vehicle 1 in the first example of the wheel range expanding operation during steering described above. In this case, of the axles protruding from the vehicle body 2, the axles (left front axle 3LFa, right front axle 3RFa) of the front wheels (left front wheel 3LF, right front wheel 3RF) that are steered are made extendable and retractable.

[0230] 41(a), when the work vehicle 1 is traveling straight, the distance between the left front wheel 3LF and the right front wheel 3RF is a first distance A1, which is a reference distance. When the distance between the left front wheel 3LF and the right front wheel 3RF is the first distance A1, the left front axle 3LFa and the right front axle 3RFa are not extended (retracted).

[0231] 41(b), the work vehicle 1 increases the distance between the left front wheel 3LF and the right front wheel 3RF to a second distance A2 that is greater than the first distance A1 when the left front wheel 3LF and the right front wheel 3RF are steered by the steering mechanism 60 (see the left front wheel 3LF and right front wheel 3RF shown by imaginary lines). This increase in distance is achieved by extending the left front axle 3LFa and the right front axle 3RFa.

[0232] As a result, when the left front wheel 3LF and the right front wheel 3RF are steered, the distance between the left front wheel 3LF and the vehicle body 2 and the distance between the right front wheel 3RF and the vehicle body 2 are increased. This increases the angle at which the left front wheel 3LF and the right front wheel 3RF can be steered without interfering with the vehicle body 2. This allows the left front wheel 3LF and the right front wheel 3RF to be steered at a larger angle.

[0233] 42 is a diagram showing a modification of the second example of the wheelbase increasing operation during steering. This modification uses the modified work vehicle in the second example of the wheelbase increasing operation during steering. In this case, of the axles protruding from the vehicle body 2, the axles (left rear axle 3LBa, right rear axle 3RBa) of the rear wheels (left rear wheel 3LB, right rear wheel 3RB) that are steered are configured to be extendable and retractable.

[0234] 42(a), when the work vehicle 1 is traveling straight, the distance between the left rear wheel 3LB and the right rear wheel 3RB is a first distance B1, which is a reference distance. When the distance between the left rear wheel 3LB and the right rear wheel 3RB is the first distance B1, the left rear axle 3LBa and the right rear axle 3RBa are not extended (retracted).

[0235] 42(b), when the left rear wheel 3LB and the right rear wheel 3RB are steered by the steering mechanism 60 (see the left rear wheel 3LB and the right rear wheel 3RB shown by imaginary lines), the work vehicle 1 increases the distance between the left rear wheel 3LB and the right rear wheel 3RB to a second distance B2 that is greater than the first distance B1. This increase in distance is achieved by extending the left rear axle 3LBa and the right rear axle 3RBa.

[0236] As a result, when steering the left rear wheel 3LB and the right rear wheel 3RB, the distance between the left rear wheel 3LB and the vehicle body 2 and the distance between the right rear wheel 3RB and the vehicle body 2 increase. This increases the angle at which the left rear wheel 3LB and the right rear wheel 3RB can be steered without interfering with the vehicle body 2. This allows the left rear wheel 3LB and the right rear wheel 3RB to be steered at a larger angle.

[0237] 43 is a diagram showing a modified example of the third example of the wheelbase widening operation during steering. This modified example uses the modified work vehicle in the third example of the wheelbase widening operation during steering. In this case, of the axles protruding from the vehicle body 2, the axles (left front axle 3LFa, right front axle 3RFa) of the front wheels (left front wheel 3LF, right front wheel 3RF) that are steered and the axles (left rear axle 3LBa, right rear axle 3RBa) of the rear wheels (left rear wheel 3LB, right rear wheel 3RB) are configured to be extendable and retractable.

[0238] As shown in (a) of Figure 43, when the work vehicle 1 is traveling straight, the distance between the left front wheel 3LF and the right front wheel 3RF is a first distance C1F, which is a reference distance, and the distance between the left rear wheel 3LB and the right rear wheel 3RB is a first distance C1B, which is also a reference distance. When the distance between the left front wheel 3LF and the right front wheel 3RF is the first distance C1F, the left front axle 3LFa and the right front axle 3RFa are in a non-extended state (shortened state). When the distance between the left rear wheel 3LB and the right rear wheel 3RB is the first distance C1B, the left rear axle 3LBa and the right rear axle 3RBa are in a non-extended state (shortened state).

[0239] 43(b), when the work vehicle 1 steers the left front wheel 3LF and the right front wheel 3RF, and the left rear wheel 3LB and the right rear wheel 3RB by the steering mechanism 60, the work vehicle 1 increases the distance between the left front wheel 3LF and the right front wheel 3RF to a second distance C2F that is larger than the first distance C1F, and increases the distance between the left rear wheel 3LB and the right rear wheel 3RB to a second distance C2B that is larger than the first distance C1B. This increase in distance is achieved by extending the left front axle 3LFa, the right front axle 3RFa, the left rear axle 3LBa, and the right rear axle 3RBa.

[0240] As a result, when steering the left front wheel 3LF and the right front wheel 3RF and the left rear wheel 3LB and the right rear wheel 3RB (see the left front wheel 3LF, right front wheel 3RF, left rear wheel 3LB, and right rear wheel 3RB shown by imaginary lines), the distance between the left front wheel 3LF and the vehicle body 2, the distance between the right front wheel 3RF and the vehicle body 2, the distance between the left rear wheel 3LB and the vehicle body 2, and the distance between the right rear wheel 3RB and the vehicle body 2 increases. Therefore, the angle at which the left front wheel 3LF, right front wheel 3RF, left rear wheel 3LB, and right rear wheel 3RB can be steered without interfering with the vehicle body 2 increases. This allows for a large steering angle for the left front wheel 3LF, right front wheel 3RF, left rear wheel 3LB, and right rear wheel 3RB.

[0241] The wheelbase increasing operation during steering of the work vehicle 1 of the modified example can also be performed by a method (see FIGS. 24 and 26) of increasing the distance between the left and right wheels by utilizing a reaction force from the ground generated by a change in the direction of the left and right wheels by the steering mechanism 60 described above. The wheelbase increasing operation during steering of the work vehicle 1 of the modified example can also be performed by a method (see FIGS. 28 and 30) of increasing the distance between the left and right wheels by using in combination a reaction force from the ground generated by a change in the direction of the left and right wheels by the steering mechanism 60 described above and an actuator that moves the left and right wheels in the vehicle body width direction.

[0242] 44 to 46, a description will be given of the turning operation for turning the vehicle body 2 of the work vehicle 1. In Figures 44 to 46, solid lines indicate the position of the work vehicle 1 before turning, and imaginary lines indicate the position of the work vehicle 1 during or after turning.

[0243] The work vehicle that performs the turning operation described below is preferably a work vehicle that is equipped with the configuration for performing the wheelbase expansion operation when steering described above, but it may also be a work vehicle that does not have the configuration for performing the wheelbase expansion operation when steering.

[0244] First, we will explain the turning operation of the conventional work vehicle 1. Figure 44 is a schematic plan view illustrating the turning operation of the conventional work vehicle 1.

[0245] The wheels of the work vehicle 1 include steered wheels whose direction is changed by the steering mechanism 60 when the vehicle body 2 turns, and non-steered wheels whose direction is not changed. In the example shown in Figure 44, the steered wheels are the front wheels (left front wheel 3LF, right front wheel 3RF), and the non-steered wheels are the rear wheels (left rear wheel 3LB, right rear wheel 3RB).

[0246] In a conventional turning operation, the direction of the steered wheels (left front wheel 3LF, right front wheel 3RF) is changed to the turning side (right side in the case of FIG. 44), and the non-steered wheel (right rear wheel 3RB) on the turning side (right side) is locked (made non-rotatable) by braking, and the other wheels (left front wheel 3LF, right front wheel 3RF, left rear wheel 3LB) are rotated. As a result, the vehicle body 2 turns around the locked non-steered wheel (right rear wheel 3RB).

[0247] In a conventional turning operation, the center of the locked non-steered wheel (right rear wheel 3RB) becomes the turning center CT1. In other words, the locked non-steered wheel does not move but rotates around an axis in the vertical direction in place. This causes a problem that the ground that the locked non-steered wheel comes into contact with is significantly scraped, causing the ground to become rough. Another problem is that the turning radius becomes relatively large, as shown by arrow R1.

[0248] Next, examples (first example and second example) of turning operations of the work vehicle 1 for solving the above-mentioned problems will be described. Fig. 45 is a schematic plan view illustrating the first example of turning operations. Fig. 46 is a schematic plan view illustrating the second example of turning operations. In these first and second example turning operations, when the vehicle body 2 turns, the steering mechanism 60 changes the direction of the steered wheels, and the power unit 4 rotates the non-steered wheels on the turning side and the non-steered wheels on the non-turning side of the left and right wheels, in opposite directions to each other.

[0249] First, a first example of a turning operation will be described with reference to Figure 45. The wheels of the work vehicle 1 include steered wheels whose direction is changed by the steering mechanism 60 when the vehicle body 2 turns, and non-steered wheels whose direction is not changed. In the example shown in Figure 45, the steered wheels are the front wheels (left front wheel 3LF, right front wheel 3RF), and the non-steered wheels are the rear wheels (left rear wheel 3LB, right rear wheel 3RB).

[0250] In the case of the turning operation of the first example, the steering mechanism 60 changes the direction of the steered wheels (left front wheel 3LF, right front wheel 3RF) to the turning side (right side in the case of Figure 45), and the power unit 4 (motor 5) rotates the non-steered wheels (left rear wheel 3RB) on the turning side (right side in the case of Figure 45) of the left rear wheel 3LB and right rear wheel 3RB, which are the non-steered wheels, in opposite directions to each other.

[0251] More specifically, when the vehicle body 2 turns, the power unit 4 (motor 5) rotates the non-steered wheel (right rear wheel 3RB) on the turning side and the non-steered wheel (left rear wheel 3LB) and steered wheels (left front wheel 3LF, right front wheel 3RF) on the non-turning side in opposite directions. In other words, the rotation direction of the non-steered wheel (right rear wheel 3RB) on the turning side is opposite to the rotation direction of the remaining three wheels. In the example shown in FIG. 45 , the non-steered wheel (right rear wheel 3RB) on the turning side rotates backward (the direction when moving backward), and the remaining three wheels rotate forward (the direction when moving forward).

[0252] As a result, the vehicle body 2 turns with a turning center CT2 at a position between the non-steered wheel on the turning side (right rear wheel 3RB) and the non-steered wheel on the non-turning side (left rear wheel 3LB), and close to the non-steered wheel on the turning side (right rear wheel 3RB).

[0253] In the case of the turning operation of the first example, the non-steered wheel on the turning side (right rear wheel 3RB) and the turning center CT2 are positioned offset (positions that do not overlap in a plan view), so the ground that the non-steered wheel comes into contact with during turning is not significantly scraped away, preventing roughening of the ground. Also, because the turning center CT2 is positioned between the non-steered wheel on the turning side and the non-steered wheel on the non-turning side, the turning radius can be reduced.

[0254] The turning operation of the first example described above can be used, for example, when working on multiple ridges formed in a farm field, by traveling along a first ridge and then moving toward a second ridge adjacent to the first ridge after passing the first ridge. In this case, the turning operation of the first example can reduce the turning radius, so that even if the distance between the first and second ridges is short, the turning operation of the first example can easily and quickly move toward the second ridge after passing the first ridge.

[0255] In the turning operation of the first example described above, the steered wheels may be rear wheels (left rear wheel 3LB, right rear wheel 3RB) and the non-steered wheels may be front wheels (left front wheel 3LF, right front wheel 3RF). In this case, the steering mechanism 60 changes the direction of the steered wheels (left rear wheel 3LB, right rear wheel 3RB) toward the turning side, and rotates the non-steered wheel (e.g., right front wheel 3RF) on the turning side and the non-steered wheel (e.g., left front wheel 3LF) on the non-turning side of the non-steered wheels (left front wheel 3LF and right front wheel 3RB) in opposite directions. In this case, the rotation direction of the non-steered wheel (e.g., right front wheel 3RF) on the turning side is opposite to the rotation direction of the steered wheels (left rear wheel 3LB, right rear wheel 3RB).

[0256] Specifically, when the vehicle body 2 turns, the power unit 4 (motor 5) rotates the non-steered wheel on the turning side (e.g., right front wheel 3RF) and the non-steered wheels on the non-turning side (left front wheel 3LF) and the steered wheels (left rear wheel 3LB, right rear wheel 3RB) in opposite directions to each other. In other words, the rotation direction of the non-steered wheel on the turning side (e.g., right front wheel 3RF) is set to be opposite to the rotation direction of the remaining three wheels.

[0257] As a result, the vehicle body 2 turns with a turning center at a position between the non-steered wheel on the turning side (e.g., the right front wheel 3RF) and the non-steered wheel on the non-turning side (e.g., the left front wheel 3LF), and close to the non-steered wheel on the turning side (e.g., the right front wheel 3RF).

[0258] Next, a second example of a turning operation will be described with reference to Figure 46. The wheels of the work vehicle 1 include steered wheels whose direction is changed by the steering mechanism 60 when the vehicle body 2 turns, and non-steered wheels whose direction is not changed. In the example shown in Figure 46, the steered wheels are the front wheels (left front wheel 3LF, right front wheel 3RF), and the non-steered wheels are the rear wheels (left rear wheel 3LB, right rear wheel 3RB).

[0259] In the case of the turning operation of the first example, the steering mechanism 60 changes the direction of the steered wheels (left front wheel 3LF, right front wheel 3RF) to the turning side (right side in the case of Figure 45), and the power unit 4 (motor 5) rotates the non-steered wheels (left rear wheel 3RB) on the turning side and the non-steered wheel (left rear wheel 3LB) on the non-turning side (left side in the case of Figure 45) of the non-steered wheels, that is, the left rear wheel 3LB and the right rear wheel 3RB, in opposite directions to each other.

[0260] In the case of the turning operation of the second example, when the vehicle body 2 turns, the steering mechanism 60 steers the steered wheels, that is, the left front wheel 3LF and the right front wheel 3RF, in opposite directions, and the power unit 4 (motor 5) rotates the non-steered wheel (right rear wheel 3RB) on the turning side (right side in the case of FIG. 46) and the non-steered wheel (left rear wheel 3LB) on the non-turning side (left side in the case of FIG. 46) in opposite directions. The power unit 4 (motor 5) also rotates the left wheels (left front wheel 3LF, left rear wheel 3LB) and the right wheels (right front wheel 3RF, right rear wheel 3RB) in opposite directions.

[0261] As a result, the non-steered wheel (right rear wheel 3RB) and steered wheel (right front wheel 3RF) on the turning side and the non-steered wheel (left rear wheel 3LB) and steered wheel (left front wheel 3LF) on the non-turning side rotate in opposite directions. In the example shown in Figure 46, the non-steered wheel (right rear wheel 3RB) and steered wheel (right front wheel 3RF) on the turning side rotate backward (the direction in which the vehicle moves backward), and the non-steered wheel (left rear wheel 3LB) and steered wheel (left front wheel 3LF) on the non-turning side rotate forward (the direction in which the vehicle moves forward).

[0262] During the turning operation described above, the left front wheel 3LF and the right front wheel 3RF, which are the steered wheels, are steered in opposite directions by the steering mechanism 60 so that the sides of the wheels face the turning center CT3 of the vehicle body 2. Specifically, the steered wheel (right front wheel 3RF) on the turning side (right side in the case of FIG. 46) is steered to the opposite side (left side) from the turning side, and the steered wheel (left front wheel 3LF) on the non-turning side (left side in the case of FIG. 46) is steered to the turning side (right side). In the example shown in FIG. 46, to turn to the right, the left front wheel 3LF is steered to the right, and the right front wheel 3RF is steered to the left.

[0263] As a result, the vehicle body 2 turns with a turning center CT3 located midway between the non-steered wheel on the turning side (right rear wheel 3RB) and the non-steered wheel on the non-turning side (left rear wheel 3LB). The turning center CT3 is located at the center of the vehicle body 2 in the width direction.

[0264] In the case of the turning operation of the second example, the non-steered wheel (right rear wheel 3RB) on the turning side and the turning center CT3 are offset (positions that do not overlap in a plan view), so the ground that the non-steered wheel comes into contact with during turning is not significantly scraped away, preventing roughening of the ground. Also, the vehicle can turn on the spot with the center in the width direction of the vehicle body 2 as the turning center CT3. Therefore, the turning radius can be smaller than that of the turning operation of the first example.

[0265] The turning operation of the second example described above can be used, for example, when working on a plurality of ridges formed in a farm field, by traveling along a first ridge to perform work, passing the first ridge, and then returning to the first ridge to perform work again. In this case, the turning operation of the second example allows the vehicle body 2 to turn and reverse on the spot, making it easy to move toward the first ridge again after passing the first ridge.

[0266] In the turning operation of the second example described above, the steered wheels may be rear wheels (left rear wheel 3LB, right rear wheel 3RB) and the non-steered wheels may be front wheels (left front wheel 3LF, right front wheel 3RF). In this case, when turning the vehicle body 2, the steering mechanism 60 steers the steered left rear wheel 3LB and right rear wheel 3RB in opposite directions, and the power unit 4 (motor 5) rotates the non-steered wheel (right front wheel 3RF) on the turning side (e.g., the right side) and the non-steered wheel (left front wheel 3LF) on the non-turning side (e.g., the left side) in opposite directions. The power unit 4 (motor 5) also rotates the left wheels (left front wheel 3LF, left rear wheel 3LB) and the right wheels (right front wheel 3RF, right rear wheel 3RB) in opposite directions. As a result, the non-steered wheels (right front wheel 3RF) and steered wheels (right rear wheel 3RB) on the turning side and the non-steered wheels (left front wheel 3LF) and steered wheels (left rear wheel 3LB) on the non-turning side rotate in opposite directions to each other.

[0267] During the turning operation described above, the steering mechanism 60 steers the left rear wheel 3LB and the right rear wheel 3RB, which are the steered wheels, in opposite directions so that the side surfaces of the wheels face the turning center of the vehicle body 2. More specifically, the steered wheel (right rear wheel 3RB) on the turning side (right side) is steered to the opposite side (left side) from the turning side, and the steered wheel (left rear wheel 3LB) on the non-turning side (left side) is steered to the turning side (right side). As a result, the vehicle body 2 turns around a turning center centered at a position midway between the non-steered wheel (right front wheel 3RF) on the turning side and the non-steered wheel (left front wheel 3LF) on the non-turning side.

[0268] The turning operations of the first and second examples may be performed by widening the distance between the left and right steered wheels by the above-described wheel spacing widening operation during steering, or may be performed without widening the distance between the left and right steered wheels (without widening the distance between the left and right steered wheels). When the turning operations of the first and second examples are performed by widening the distance between the left and right steered wheels by the wheel spacing widening operation during steering, the steering angle of the steered wheels can be increased, making it possible to reliably reduce the turning radius.

[0269] The turning operations of the first and second examples can be performed by the control device 15 controlling the operation of the steering mechanism 60 and the traveling motor 5. The control device 15 has a turning operation control unit 15C (see FIG. 7 ) for performing the turning operations of the first and second examples by controlling the operation of the steering mechanism 60 and the traveling motor 5. When the worker performs a predetermined operation (for example, an operation using the operating device 101), control by the turning operation control unit 15C is executed, and the turning operations of the first and second examples are performed.

[0270] Furthermore, when the work vehicle 1 moves (travels) based on a predetermined travel route under control by the automatic driving control unit 15A, the turning location and required turning radius are determined in advance. Therefore, the control device 15 (automatic driving control unit 15A) can perform the above-mentioned turning operation by controlling the operation of the steering mechanism 60 and the traveling motor 5 based on information about the turning location and turning radius included in the information about the travel route that has been set in advance and stored in the storage unit. The control device 15 (automatic driving control unit 15A) automatic driving control unit 15A can also perform the above-mentioned wheel range expansion operation during steering by controlling the operation of the steering mechanism 60 and the distance change mechanism 80 based on information about the turning location and turning radius included in the information about the travel route that has been set in advance and stored in the storage unit.

[0271] A preferred embodiment of the present invention provides a work vehicle 1 as described in the following items.

[0272] (Item 1) A work vehicle 1 comprising a body 2, wheels 30 including a left wheel located on the left side of the body 2 and a right wheel located on the right side of the body 2, a steering mechanism 60 that changes the direction of the wheels 30, and a distance change mechanism 80 that increases the distance between the left wheel and the right wheel when steering by the steering mechanism 60.

[0273] According to the work vehicle 1 according to this item 1, the steering angle can be increased by increasing the distance between the left and right wheels during steering, thereby reducing the turning radius of the vehicle body 2.

[0274] (Item 2) The left wheels include a left front wheel 3LF and a left rear wheel 3LB, the right wheels include a right front wheel 3RF and a right rear wheel 3RB, the steering mechanism 60 changes the orientation of the left front wheel 3LF and the right front wheel 3RF when steering, and the distance change mechanism 80 increases the distance between the left front wheel 3LF and the right front wheel 3RF when steering by the steering mechanism 60, in the work vehicle 1 described in item 1.

[0275] According to the work vehicle 1 according to this item 2, the steering angle of the left front wheel 3LF and the right front wheel 3RF can be increased, and therefore the turning radius of the vehicle body 2 can be reduced when turning by steering the left front wheel 3LF and the right front wheel 3RF.

[0276] (Item 3) The left wheels include a left front wheel 3LF and a left rear wheel 3LB, the right wheels include a right front wheel 3RF and a right rear wheel 3RB, the steering mechanism 60 changes the orientation of the left rear wheel 3LB and the right rear wheel 3RB when steering, and the distance change mechanism 80 increases the distance between the left rear wheel 3LB and the right rear wheel 3RB when steering by the steering mechanism 60. This is the work vehicle 1 described in Item 1.

[0277] According to the work vehicle 1 according to this item 3, the steering angle of the left rear wheel 3LB and the right rear wheel 3RB can be increased, and therefore the turning radius of the vehicle body 2 can be reduced when turning by steering the left rear wheel 3LB and the right rear wheel 3RB.

[0278] (Item 4) A work vehicle 1 described in any one of items 1 to 3, wherein the steering mechanism 60 changes the orientation of the left front wheel 3LF and the right front wheel 3RF, and the orientation of the left rear wheel 3LB and the right rear wheel 3RB, when steering, and the distance change mechanism 80 increases the distance between the left front wheel 3LF and the right front wheel 3RF, and the distance between the left rear wheel 3LB and the right rear wheel 3RB, when steering by the steering mechanism 60.

[0279] According to the work vehicle 1 according to this item 4, the steering angles of the left front wheel 3LF, the right front wheel 3RF, the left rear wheel 3LB, and the right rear wheel 3RB can be increased, and therefore the turning radius of the vehicle body 2 can be reduced when turning by steering the left front wheel 3LF, the right front wheel 3RF, the left rear wheel 3LB, and the right rear wheel 3RB.

[0280] (Item 5) A work vehicle 1 described in any one of items 1 to 4, wherein the steering mechanism 60 changes the orientation of the left wheel and the right wheel so that the forward portion of the wheels in the direction of travel moves away from the vehicle body 2 when the vehicle body 2 is traveling, and the distance change mechanism 80 increases the distance by utilizing a reaction force from the ground generated by the change in orientation of the left wheel and the right wheel by the steering mechanism 60.

[0281] According to the work vehicle 1 relating to this item 5, the distance between the left wheel and the right wheel can be increased by utilizing the reaction force from the ground, so that the actuator for increasing the distance between the left wheel and the right wheel can be omitted or made smaller.

[0282] (Item 6) The distance change mechanism 80 has actuators (left cylinder 81L, right cylinder 81R) that move the left wheel and the right wheel in the vehicle width direction, and the work vehicle 1 described in Item 5 increases the distance by utilizing the reaction force and the force of the actuators.

[0283] According to the work vehicle 1 according to this item 6, the distance between the left and right wheels can be increased by using both the reaction force from the ground and the actuator. Therefore, the distance between the left and right wheels can be increased with less force than when using only the actuator. Furthermore, the distance between the left and right wheels can be increased more reliably than when using only the reaction force from the ground.

[0284] (Item 7) A work vehicle 1 described in any one of items 1 to 6, which is equipped with a power unit 4 that generates power to rotate the wheels, and the wheels include steered wheels whose direction is changed by the steering mechanism 60 when the vehicle body 2 turns, and non-steered wheels whose direction is not changed, and when the vehicle body 2 turns, the direction of the steered wheels is changed by the steering mechanism 60, and the power unit 4 rotates the non-steered wheels on the turning side and the non-steered wheels on the non-turning side of the left wheel and the right wheel, which are the non-steered wheels, in opposite directions to each other.

[0285] According to the work vehicle 1 according to this item 7, the non-steered wheel on the turning side and the turning center are positioned offset (positions that do not overlap in a plan view), so that the ground that the non-steered wheel comes into contact with is not significantly scraped away during turning, and roughening of the ground can be prevented. Also, because the turning center is positioned between the non-steered wheel on the turning side and the non-steered wheel on the non-turning side, the turning radius can be made small.

[0286] (Item 8) A work vehicle 1 according to Item 7, wherein when the vehicle body 2 turns, the power unit 4 rotates the non-steered wheels on the turning side and the non-steered wheels and the steered wheels on the non-turning side in opposite directions to each other.

[0287] According to the work vehicle 1 relating to this item 8, the turning radius can be more reliably reduced by rotating the non-steered wheel on the turning side and the non-steered wheel and steered wheel on the non-turning side in opposite directions.

[0288] (Item 9) A work vehicle 1 as described in Item 7, in which, when the vehicle body 2 turns, the steering mechanism 60 steers the left wheel and the right wheel, which are the steered wheels, in opposite directions to each other, and the power unit 4 rotates the non-steered wheels on the turning side and the non-steered wheels on the non-turning side in opposite directions to each other.

[0289] According to the work vehicle 1 according to this item 9, the non-steered wheel on the turning side and the turning center CT3 are positioned offset (positions that do not overlap in a plan view), so the ground that the non-steered wheel comes into contact with during turning is not significantly scraped away, and roughening of the ground can be prevented. Also, because it is possible to turn on the spot with the center in the width direction of the vehicle body 2 as the turning center CT3, the turning radius can be made smaller.

[0290] (Item 10) A work vehicle 1 according to Item 9, wherein when the vehicle body 2 turns, the steering mechanism 60 steers the left and right wheels, which are the steering wheels, in opposite directions so that the sides of the wheels face the center of turning of the vehicle body 2.

[0291] According to the work vehicle 1 relating to this item 10, when the vehicle body 2 turns, the turning radius can be more reliably reduced by steering the left and right steered wheels in opposite directions so that the side surfaces of the wheels face the center of turning of the vehicle body 2.

[0292] (Item 11) The work vehicle 1 according to item 9 or 10, wherein the power unit 4 rotates the left wheel and the right wheel in opposite directions when the vehicle body 2 turns.

[0293] According to the work vehicle 1 according to this item 11, when the vehicle body 2 turns, the power unit 4 rotates the left and right wheels in opposite directions, thereby making it possible to more reliably reduce the turning radius.

[0294] Although the embodiments of the present invention have been described above, the embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims.

[0295] REFERENCE SIGNS LIST 1 Work vehicle 2 Vehicle body 3LF Left front wheel 3LB Left rear wheel 3RF Right front wheel 3RB Right rear wheel 4 Power unit 30 Wheels 60 Steering mechanism 80 Distance change mechanism 81L Left cylinder (actuator) 81R Right cylinder (actuator)

Claims

1. A work vehicle comprising a vehicle body, wheels including a left wheel disposed on the left side of the vehicle body and a right wheel disposed on the right side of the vehicle body, a steering mechanism for changing the direction of the wheels, and a distance changing mechanism for expanding the distance between the left wheel and the right wheel during steering by the steering mechanism.

2. The work vehicle according to claim 1, wherein the left wheel includes a left front wheel and a left rear wheel, the right wheel includes a right front wheel and a right rear wheel, the steering mechanism changes the directions of the left front wheel and the right front wheel during steering, and the distance changing mechanism expands the distance between the left front wheel and the right front wheel during steering by the steering mechanism.

3. The work vehicle according to claim 1, wherein the left wheel includes a left front wheel and a left rear wheel, the right wheel includes a right front wheel and a right rear wheel, the steering mechanism changes the directions of the left rear wheel and the right rear wheel during steering, and the distance changing mechanism expands the distance between the left rear wheel and the right rear wheel during steering by the steering mechanism.

4. The work vehicle according to claim 2 or 3, wherein the steering mechanism changes the directions of the left front wheel and the right front wheel and the directions of the left rear wheel and the right rear wheel during steering, and the distance changing mechanism expands the distance between the left front wheel and the right front wheel and the distance between the left rear wheel and the right rear wheel during steering by the steering mechanism.

5. The work vehicle according to claim 1, wherein the steering mechanism changes the directions of the left wheel and the right wheel such that a portion in front of the traveling direction of the wheels moves away from the vehicle body during traveling of the vehicle body, and the distance changing mechanism expands the distance by utilizing the reaction force from the ground generated by the change in the directions of the left wheel and the right wheel by the steering mechanism.

6. The work vehicle according to claim 5, wherein the distance changing mechanism has an actuator for moving the left wheel and the right wheel in the vehicle body width direction, and expands the distance by utilizing the reaction force and the force of the actuator.

7. The work vehicle according to claim 1, comprising a power device that generates power for rotating the wheels, wherein the wheels include a steering wheel whose direction is changed by the steering mechanism and a non-steering wheel whose direction is not changed when the vehicle body turns, and when the vehicle body turns, the steering mechanism changes the direction of the steering wheel, and the power device rotates the non-steering wheel on the turning side and the non-steering wheel on the non-turning side among the left wheel and the right wheel, which are non-steering wheels, in opposite directions to each other.

8. The work vehicle according to claim 7, wherein when the vehicle body turns, the power device rotates the non-steering wheel on the turning side, the non-steering wheel on the non-turning side, and the steering wheel in opposite directions to each other.

9. The work vehicle according to claim 7, wherein when the vehicle body turns, the steering mechanism steers the left wheel and the right wheel, which are the steering wheels, in opposite directions to each other, and the power device rotates the non-steering wheel on the turning side and the non-steering wheel on the non-turning side in opposite directions to each other.

10. The work vehicle according to claim 9, wherein when the vehicle body turns, the steering mechanism steers the left wheel and the right wheel, which are the steering wheels, in opposite directions to each other so that the side surfaces of the wheels face the turning center of the vehicle body.

11. The work vehicle according to claim 9 or 10, wherein when the vehicle body turns, the power device rotates the left wheel and the right wheel in opposite directions.

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