Work vehicle

Abstract

To provide a work vehicle which can keep a stop position of the work vehicle for a long time in a simple structure.SOLUTION: A work vehicle comprises: a vehicle body 1 with a loading part that can load a cargo; a plurality of traveling wheels 2 which are respectively arranged at a front and rear sides in both right and left sides of the vehicle body 1 to be operable respectively; a steering angle detection part which respectively detects directions of the plurality of the traveling wheels 2; and a controller which can perform drive control respectively driving the plurality of the traveling wheels 2 and direction control respectively changing directions of the plurality of the traveling wheels 2. The controller differentiates, when stopping the drive control, the direction of a first traveling wheel positioned at one side of right and left sides of the vehicle body among the plurality of the traveling wheels 2 from the direction of a second traveling wheel positioned at the other side of the right and left sides of the vehicle body among the plurality of the traveling wheels 2.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a work vehicle having a plurality of independently steerable running wheels. [Background technology]

[0002] For example, the work vehicle disclosed in Patent Document 1 is equipped with multiple running wheels, which are drive-controlled by a control device. The multiple running wheels are also configured so that they can be steered individually by a turning mechanism. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-1443 Summary of the Invention [Problem to be solved by the invention]

[0004] When a work vehicle stops, it is important that the vehicle maintain its stopped position. For this reason, the running wheels are generally equipped with a braking mechanism. However, if the work vehicle remains stopped for an extended period of time, the braking force of the brakes may decrease over time, and the vehicle may not maintain its stopped position for an extended period of time. For this reason, if the work vehicle is stopped on a slope for an extended period of time, for example, there is a possibility that the work vehicle will gradually slide down the slope over time. One way to avoid this inconvenience is to equip the work vehicle with a mechanical parking brake. However, installing such a parking brake increases the number of parts, which increases costs.

[0005] An object of the present invention is to provide a work vehicle that has a simple configuration and is capable of maintaining the stopped position of the work vehicle for a long period of time. [Means for solving the problem]

[0006] The work vehicle of the present invention comprises a vehicle body having a loading section capable of loading cargo, a plurality of traveling wheels located at the front and rear of both the left and right sides of the vehicle body and capable of being steered independently, a plurality of hydraulic motors provided respectively for the plurality of running wheels, the hydraulic motors driving the running wheels by supplying or discharging hydraulic oil and locking the running wheels by cutting off the supply or discharge of the hydraulic oil; and a control valve capable of individually changing the amount of hydraulic oil supplied or discharged to the plurality of hydraulic motors. a steering angle detection unit that detects the direction of each of the plurality of running wheels; a drive control that drives each of the plurality of running wheels; and a control that changes the direction of each of the plurality of running wheels individually. and a control for individually changing the rotation speeds of the plurality of hydraulic motors by changing the supply and discharge amounts of the hydraulic oil. and a control device capable of: When the drive control is stopped, the control valve is closed to cut off the supply and discharge of the hydraulic oil to the plurality of hydraulic motors, thereby locking each of the plurality of traveling wheels; and When the drive control is stopped, the directions of a first running wheel located on one side of the vehicle body among the plurality of running wheels and a second running wheel located on the other side of the vehicle body among the plurality of running wheels are made different from each other.

[0007] According to the present invention, a control device causes the orientations of a first running wheel located on one of the left and right running wheels and a second running wheel located on the other of the left and right running wheels to differ from each other. When the orientations of the left and right running wheels differ from each other, the rolling direction of one of the left and right running wheels differs from the rolling direction of the other of the left and right running wheels. As a result, the left and right running wheels act on each other in directions opposite to their rotational directions, and receive a reaction force from the ground in the direction of skid. In other words, when a running wheel attempts to roll, friction occurs between the running wheel and the ground. This prevents the left and right running wheels from rotating. As a result, the stopped position of the work vehicle can be maintained without the need for a dedicated parking brake, even when the work vehicle is stopped for an extended period of time, for example, on a slope. As a result, a work vehicle that can maintain its stopped position for an extended period of time with a simple configuration is realized.

[0008] In the present invention, when the control device stops the drive control, it is preferable that the direction of each of the first running wheel and the second running wheel is changed so that they are opposite to each other relative to the neutral direction in which the vehicle body moves straight or approximately straight.

[0009] With this configuration, the left and right running wheels act on each other in opposite directions relative to the vehicle's forward direction, causing each wheel to receive a reaction force from the ground in the direction of skidding, preventing it from rotating.

[0010] In the present invention, it is preferable that the control device causes the directions of all of the plurality of running wheels to differ from one another when the drive control is stopped.

[0011] This configuration ensures that the vehicle remains stationary whenever the control device stops drive control. Furthermore, the configuration in which all of the multiple running wheels are oriented in different directions creates strong friction between the running wheels and the ground, ensuring that the vehicle remains stationary.

[0012] In the present invention, it is preferable that an inclination detection unit is provided that detects the inclination state of the vehicle body, and that the control device changes the orientation of the first running wheel located on the lower side of one of the left and right sides among the plurality of running wheels, and the second running wheel located on the lower side of the other of the plurality of running wheels, to be different from each other, based on the inclination state of the vehicle body.

[0013] With this configuration, the first and second running wheels are positioned on the low-ground side, so they can firmly support the weight of the vehicle body, increasing the friction between the running wheels and the ground, and firmly maintaining the vehicle's stopped position.

[0014] In the present invention, an operation detection unit is provided that detects manual operation of the plurality of running wheels, and it is preferable that the control device causes the respective orientations of the first running wheel and the second running wheel to differ from each other when a predetermined time has elapsed since the operation detection unit no longer detects the manual operation. It is preferable that the control device causes the directions of the first running wheel and the second running wheel to differ from each other when a predetermined time has elapsed since the operation detection unit no longer detects the manual operation after the drive control is stopped.

[0015] With this configuration, the stopped position of the work vehicle is reliably maintained each time the operation detection unit no longer detects any manual operation.

[0016] In the present invention, a support mechanism is supported by the vehicle body and supports the plurality of running wheels so that their positions can be changed with respect to the vehicle body. ,before and an inclination detection unit that detects an inclination state of the loading unit, and the control device is configured to be able to control the operation of the support mechanism based on the inclination state of the loading unit so that the loading unit is in a horizontal position. Re It is preferable to have

[0017] According to this configuration, the loading unit can be maintained in a horizontal position based on the operation of the support mechanism. The multiple traveling wheels are driven by hydraulic pressure. Therefore, when the supply and discharge of hydraulic oil to the hydraulic motor is cut off, the traveling wheels stop, and when hydraulic oil inside the hydraulic motor stops flowing, the rotation of the hydraulic motor is locked. In this case, the hydraulic motor functions as a brake for the traveling wheels. However, hydraulic oil may leak from the hydraulic motor, in which case the hydraulic motor will no longer function as a brake. Even in such a case, the stopped position of the work vehicle is firmly maintained by the configuration in which the first traveling wheel and the second traveling wheel are oriented in different directions. Preferably, the control device is configured to be able to calculate the inclination angle of the ground on which the multiple running wheels contact the ground, and is configured not to control the operation of the support mechanism when the ground is inclined within a predetermined set inclination angle range, and to continue to control the operation of the support mechanism when the ground is inclined at an inclination angle equal to or greater than the set inclination angle. It is preferable that a drive source is provided that supplies drive energy to operate the support mechanism, and the control device is configured to allow the drive source to stop driving when the ground is inclined within the set inclination angle range, and to prohibit the drive source from stopping driving when the ground is inclined at an angle equal to or greater than the set inclination angle. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. [Figure 2] FIG. [Figure 3] FIG. [Figure 4] FIG. [Figure 5] FIG. [Figure 6] FIG. [Figure 7] FIG. 10 is a plan view of the work vehicle with the traveling wheels facing in different directions. [Figure 8] FIG. 10 is a flowchart showing control when the vehicle is stopped. DETAILED DESCRIPTION OF THE INVENTION

[0019] An embodiment of the present invention will be described with reference to the drawings. In the following description, the direction of the arrow "FW" shown in the drawings will be referred to as "front," the direction of the arrow "BK" as "rear," the direction of the arrow "RH" as "right," the direction of the arrow "LH" as "left," the direction of the arrow "UP" as "up," and the direction of the arrow "DW" as "down."

[0020] As shown in Figures 1 to 3, the work vehicle is equipped with a vehicle body 1 that is substantially rectangular in plan view, four running wheels 2, four auxiliary wheels 3, a support mechanism A, and four hydraulic motors 4. The vehicle body 1 supports the entire vehicle. The four running wheels 2 support the vehicle body 1. The four auxiliary wheels 3 are provided corresponding to each of the four running wheels 2. The support mechanism A supports the four running wheels 2 so that their position can be changed relative to the vehicle body 1. The hydraulic motors 4 drive the running wheels 2. The hydraulic motors 4 use the supply and discharge of hydraulic oil as driving energy. Each of the four running wheels 2 is independently driven by the four hydraulic motors 4. The running wheel 2 located on either the left or right side corresponds to the "first running wheel" in this invention. The running wheel 2 located on either the left or right side corresponds to the "second running wheel" in this invention.

[0021] The traveling wheels 2 are located at the front and rear of both the left and right sides of the vehicle body 1. In this embodiment, the work vehicle is equipped with four traveling wheels 2, located at the left front, right front, left rear, and right rear. The work vehicle also has four support mechanisms A, located at the left front, right front, left rear, and right rear. The support mechanisms A include an articulating link mechanism 5, four first hydraulic cylinders 6, and four second hydraulic cylinders 7. Each of the four first hydraulic cylinders 6 and the four second hydraulic cylinders 7 is an extension and contraction actuator for changing the position of the traveling wheels 2 relative to the vehicle body 1, and is configured to be able to individually change the attitude of the articulating link mechanism 5.

[0022] A flat loading section 8 capable of loading cargo is provided on the top surface of the vehicle body 1. The loading section 8 is a generally rectangular section in a plan view, extending from the right end to the left end of the vehicle body 1. Cargo can be placed on the loading section 8. Examples of cargo that can be placed on the loading section 8 include agricultural equipment, agricultural supplies such as fertilizer and chemicals, harvested crops and harvest baskets, and pallets on which these are placed.

[0023] A hydraulic supply source 9 is provided under the loading section 8 of the vehicle body 1. (equivalent to the driving source) The hydraulic control system is equipped with a hydraulic cylinder 11, a plurality of hydraulic control valves 12, an ECU 13 (Electronic Control Unit), a battery 11 for power supply, and the like. The hydraulic supply source 9 sends hydraulic oil to the first hydraulic cylinder 6, the second hydraulic cylinder 7, and the hydraulic motor 4. Thus, the hydraulic supply source 9 is configured to be able to supply drive energy for operating the support mechanism A and drive energy for driving the four traveling wheels 2. The plurality of hydraulic control valves 12 adjust the supply state of hydraulic oil from the hydraulic supply source 9. The hydraulic control valves 12 may be proportional valves or PWM controlled solenoid valves. The ECU 13 controls the operation of the hydraulic control valves 12. The hydraulic control valves 12 correspond to the "control valve" of the present invention.

[0024] The hydraulic supply source 9 is supported by an underframe 10. The hydraulic supply source 9 is equipped with an engine 9a, a hydraulic pump 9b, a hydraulic oil tank 9c, a radiator 9d, a fuel tank 9e, etc. The hydraulic pump 9b is driven by the engine 9a. The fuel tank 9e is located at the rear of the vehicle body 1.

[0025] The ECU 13 is equipped with a microcomputer and is capable of executing various controls according to a control program. In this embodiment, a control device C is composed of a plurality of hydraulic control valves 12 and the ECU 13. A generator (not shown) is driven by the power of the engine 9a. The electric power generated by the generator is then charged into the battery 11.

[0026] A driving operation unit 21 is provided behind the loading section 8 of the vehicle body 1. The driving operation unit 21 can be manually operated by an operator from outside the vehicle. The vehicle can be driven by the operator operating the driving operation unit 21. In addition to operating the driving operation unit 21, the vehicle can also be driven by remote control using a wireless remote control device RC. The remote control device RC is, for example, a proportional wireless transmitter, a smartphone, or a tablet computer. The driving operation unit 21 and the remote control device RC are each configured to be able to output driving command signals and turning command signals to the traveling wheels 2, lifting command signals to the articulating link mechanism 5, etc., based on manual operation by the operator.

[0027] [Support mechanism] As described above, the support mechanism A includes the articulating link mechanism 5, a plurality of first hydraulic cylinders 6, and a plurality of second hydraulic cylinders 7. As shown in Fig. 1, the four traveling wheels 2 are supported via the articulating link mechanism 5 so that they can be raised and lowered individually relative to the vehicle body 1. In other words, the support mechanism A is supported by the vehicle body 1 and supports the four traveling wheels 2 so that their positions can be changed relative to the vehicle body 1.

[0028] As shown in Figures 4 and 5, the articulating link mechanism 5 includes a base end portion 14, a first link 15, and a second link 16. The base end portion 14 is supported by the vehicle body 1. An upper end portion of the first link 15 is supported at a lower portion of the base end portion 14 so as to be rotatable about a horizontal axis X1. One end portion of the second link 16 is supported at a lower end portion of the first link 15 so as to be rotatable about a horizontal axis X2. A support bracket 17 is connected to the other end portion of the second link 16. The running wheel 2 is supported by the support bracket 17.

[0029] A boss portion 18 is provided at the swing side end of the second link 16. A support bracket 17 is supported by the boss portion 18 so as to be swingable about a vertical axis Y. A bracket 19 is provided at one end of the second link 16. An arm portion 17a is provided on the support bracket 17. A hydraulically driven swivel cylinder 20 is provided across the bracket 19 and the arm portion 17a.

[0030] The first hydraulic cylinder 6 is configured to be able to change the swing posture of the first link 15 relative to the vehicle body 1. In addition, the second hydraulic cylinder 7 is configured to be able to change the swing posture of the second link 16 relative to the first link 15.

[0031] When the first hydraulic cylinder 6 extends and retracts with the second hydraulic cylinder 7 stopped, the first link 15, the second link 16, and the traveling wheel 2 swing together around the horizontal axis X1 while maintaining a constant relative posture. When the second hydraulic cylinder 7 extends and retracts with the first hydraulic cylinder 6 stopped, the second link 16 and the traveling wheel 2 swing together around the horizontal axis X2 while maintaining a constant posture of the first link 15.

[0032] An auxiliary wheel 3 is rotatably supported at the intermediate bent portion of each of the multiple bent link mechanisms 5. The auxiliary wheel 3 is a wheel with approximately the same outer diameter as the running wheel 2. A first link 15 and a second link 16 are pivotally connected by a support shaft. The support shaft protrudes outward in the lateral width direction of the vehicle body. The auxiliary wheel 3 is rotatably supported at the protruding portion of the support shaft.

[0033] The orientation of the running wheels 2 is changed by the extension and retraction of the swivel cylinder 20. In other words, the running wheels 2 are driven to turn by the extension and retraction of the swivel cylinder 20. The swivel cylinder 20 is arranged on the left-right center side of the vehicle body 1 relative to the running wheels 2 to be turned. When the swivel cylinder 20 extends and retracts, the running wheels 2 rotate around the vertical axis Y relative to the articulating link mechanism 5. This allows the running wheels 2 to be turned.

[0034] The traveling wheel 2 located below the front right portion of the vehicle body 1 turns clockwise when the swivel cylinder 20 extends, and turns counterclockwise when the swivel cylinder 20 retracts. The traveling wheel 2 located below the front left portion of the vehicle body 1 turns counterclockwise when the swivel cylinder 20 extends, and turns clockwise when the swivel cylinder 20 retracts. The traveling wheel 2 located below the rear right portion of the vehicle body 1 turns counterclockwise when the swivel cylinder 20 extends, and turns clockwise when the swivel cylinder 20 retracts. The traveling wheel 2 located below the rear left portion of the vehicle body 1 turns clockwise when the swivel cylinder 20 extends, and turns counterclockwise when the swivel cylinder 20 retracts. When the vehicle body 1 travels straight or approximately straight, the stroke position of each of the four swivel cylinders 20 is located at a neutral stroke position that is preset between the stroke end on the extension side and the stroke end on the retraction side.

[0035] [Regarding control configuration] The control configuration of this embodiment will be described with reference to Fig. 6. The ECU 13 controls the adjustment of the flow rate of hydraulic oil in the hydraulic control valve 12. The hydraulic control valve 12 is configured to be able to adjust the amount of hydraulic oil supplied to and discharged from each of the four hydraulic motors 4, the four first hydraulic cylinders 6, the four second hydraulic cylinders 7, and the four swing cylinders 20. This allows the ECU 13 to control the rotation speed of the hydraulic motors 4, i.e., the rotation speed of the traveling wheels 2.

[0036] This work vehicle is equipped with various sensors. Each of the four first hydraulic cylinders 6 and each of the four second hydraulic cylinders 7 is equipped with a stroke sensor S1. Additionally, each of the four swing cylinders 20 is equipped with a stroke sensor S2 that can detect the stroke position. The vehicle is provided with an inclination sensor S3 capable of detecting the inclination state of the vehicle body 1. Furthermore, a rotation sensor S4 capable of detecting the rotation speed of the traveling wheels 2 is provided near the traveling wheels 2. Additionally, the hydraulic motor 4 is provided with a pressure sensor S5 capable of detecting the pressure of the hydraulic oil. The stroke sensor S2 corresponds to the "steering angle detection unit" of this invention.

[0037] The stroke sensor S1 can detect the stroke position of each of the four first hydraulic cylinders 6 and the four second hydraulic cylinders 7. The stroke position of the first hydraulic cylinders 6 is a detected value corresponding to the swing position of the first link 15. The stroke position of the second hydraulic cylinders 7 is a detected value corresponding to the swing position of the second link 16. In other words, the stroke sensor S1 detects the amount of extension and contraction of each of the first hydraulic cylinders 6 and the second hydraulic cylinders 7.

[0038] The tilt sensor S3 is equipped with an inertial measurement unit (IMU) having a well-known configuration. The IMU has a triaxial acceleration sensor and a gyro sensor, and can detect changes in the attitude of the vehicle body 1, specifically, tilt in the front-rear and left-right directions. The tilt sensor S3 is configured to be able to detect the tilt state of the loading section 8. The tilt sensor S3 corresponds to the "tilt detection section" of the present invention.

[0039] The ECU 13 is connected to an operation detection unit 22. The operation detection unit 22 receives both a signal from the driving operation unit 21 and a wireless signal from a wireless communication remote control device RC. The operation detection unit 22 is configured to detect manual operations on the four traveling wheels 2 and the articulating link mechanism 5.

[0040] The ECU 13 includes a non-volatile memory (not shown) that stores programs corresponding to functional units described below, and a CPU (not shown) that executes the programs. The functions of each functional unit are realized by the CPU executing the programs. The ECU 13 includes, as functional units, an attitude control unit 100, a driving control unit 101, a tilt angle calculation unit 102, etc.

[0041] The inclination angle calculation unit 102 calculates the inclination angle of the ground on which each of the four traveling wheels 2 comes into contact, based on the detection information of the inclination sensor S3, the stroke positions of each of the four first hydraulic cylinders 6, and the stroke positions of the four second hydraulic cylinders 7. In other words, the control device C is configured to be able to calculate the inclination angle of the ground on which the four traveling wheels 2 come into contact. The inclination angle calculation unit 102 corresponds to the "inclination detection unit" of this invention.

[0042] The posture control unit 100 can determine the swing posture of the first link 15 relative to the vehicle body 1, the swing posture of the second link 16 relative to the first link 15, etc. based on the detection value of the stroke sensor S1. As a result, it is possible to calculate the height from the ground contact portion of the running wheel 2 to the vehicle body 1. When the vehicle body is moving, the posture control unit 100 executes horizontal control, which controls the operation of the support mechanism A so that the loading unit 8 of the vehicle body 1 is in a horizontal position, based on the detection information of the inclination sensor S3. In the horizontal control, the posture control unit 100 controls the operation of the four first hydraulic cylinders 6 and the four second hydraulic cylinders 7 so that the tilt angle in the front-to-rear direction and the tilt angle in the left-to-right direction from the horizontal position of the vehicle body 1 become values ​​corresponding to the horizontal position, based on the detection information of the inclination sensor S3 and the detection information of the stroke sensor S1. In this way, the posture control unit 100 of the control device C is configured to be able to control the operation of each of the first hydraulic cylinders 6 and the second hydraulic cylinders 7 of the support mechanism A so that the loading unit 8 is in a horizontal position, based on the tilt state of the vehicle body 1 (loading unit 8) and the extension and contraction amounts of each of the first hydraulic cylinders 6 and the second hydraulic cylinders 7.

[0043] The travel control unit 101 controls the supply and discharge of hydraulic oil to the hydraulic motor 4 based on the rotational speed of the traveling wheels 2 detected by the rotation sensor S4 so that the rotational speed of the traveling wheels 2 becomes a target value. Furthermore, the travel control unit 101 controls the supply (pressure) of hydraulic oil to the hydraulic motor 4 based on the pressure of the hydraulic oil detected by the pressure sensor S5 so that the drive torque of the traveling wheels 2 becomes a target value. The hydraulic control valve 12 is configured to be able to change the amount of hydraulic oil supplied to and discharged from the hydraulic motor 4. The travel control unit 101 performs a switching operation of the hydraulic control valve 12 that supplies and discharges hydraulic oil to the hydraulic motor 4.

[0044] The travel control unit 101 is also configured to be able to change the orientation of the traveling wheels 2 based on the detection value of the stroke sensor S2. Specifically, the travel control unit 101 performs a switching operation of the hydraulic control valve 12 that supplies and discharges hydraulic oil to the swing cylinder 20. The travel control unit 101 is configured to be able to control the changing of the orientation of each of the four traveling wheels 2 individually.

[0045] [Control when the vehicle is stopped] When the vehicle body 1 stops, the travel control unit 101 controls the hydraulic control valve 12 to cut off the supply and discharge of hydraulic oil to the hydraulic motor 4. When the supply and discharge of hydraulic oil to the hydraulic motor 4 is cut off, the hydraulic motor 4 stops. At this time, hydraulic oil stops flowing inside the hydraulic motor 4. As a result, the hydraulic motor 4 becomes unable to rotate, and the rotation of each of the four traveling wheels 2 stops. In other words, when the four traveling wheels 2 are stopped, the travel control unit 101 of the control device C does not supply drive energy to the four hydraulic motors 4, and therefore to the four traveling wheels 2. Because the hydraulic control valve 12 is cut off, hydraulic oil cannot flow in or out of the hydraulic motors 4. As a result, each of the four traveling wheels 2 is locked by the hydraulic oil inside the hydraulic motor 4, and the vehicle body 1 can remain stopped. In this way, the travel control unit 101 of the control device C is configured to stop drive control of the hydraulic motor 4 by closing the hydraulic control valve 12 to cut off the supply and discharge of hydraulic oil to the hydraulic motor 4 when the vehicle is stopped.

[0046] However, hydraulic oil inside the hydraulic motor 4 may leak little by little from the hydraulic control valve 12 over time. In this case, the hydraulic oil inside the hydraulic motor 4 may no longer be able to keep each of the four traveling wheels 2 locked. Particularly on slopes, if hydraulic oil leaks from the hydraulic motor 4, the weight of the work vehicle may cause each of the four traveling wheels 2 to gradually rotate, which could cause the vehicle body 1 to lose its parked position. To avoid such inconveniences, in this embodiment, the travel control unit 101 is configured to orient each of the four traveling wheels 2 in a different direction when the vehicle body 1 is parked.

[0047] 7, when the vehicle body 1 is stopped, the orientation of each of the four running wheels 2 is changed. In other words, when the running control unit 101 in the control device C stops the drive control of the running wheels 2, it causes all of the four running wheels 2 to have different orientations from one another.

[0048] 7, of the left and right running wheels 2 located below the front of the vehicle body 1, the right running wheel 2 turns counterclockwise and the left running wheel 2 turns clockwise. Therefore, for each of the left and right running wheels 2 located below the front of the vehicle body 1, the front part of each of the left and right running wheels 2 is located closer to the center of the vehicle body 1 in the lateral direction than the rear part of each of the left and right running wheels 2.

[0049] Of the left and right running wheels 2 located below the rear of the vehicle body 1, the right running wheel 2 turns clockwise and the left running wheel 2 turns counterclockwise. Therefore, for each of the left and right running wheels 2 located below the rear of the vehicle body 1, the rear part of each of the left and right running wheels 2 is located closer to the center of the vehicle body 1 in the lateral direction than the front part of each of the left and right running wheels 2.

[0050] The orientation of each of the four traveling wheels 2 is changed by the contraction of the swivel cylinder 20 . The cap side end of the swivel cylinder 20 is located closer to the front-rear center of the vehicle body 1 than the rod side end of the swivel cylinder 20. For this reason, when the travel control unit 101 stops drive control of the traveling wheels 2, it controls each of the four swivel cylinders 20 to operate to the retraction side from the neutral stroke position. By this method, the travel control unit 101 of the control device C changes the orientation of each of the four traveling wheels 2 so that the end of the traveling wheels 2 located on the front-rear outer side with respect to the vehicle body 1 is located closer to the left-right center of the vehicle body 1 than the end of the traveling wheels 2 located on the front-rear inner side with respect to the vehicle body 1.

[0051] In this way, when the driving control unit 101 in the control device C stops the drive control of the running wheels 2, it causes the directions of the running wheels 2 located on one of the left and right sides and the running wheels 2 located on the other of the left and right sides to be opposite to each other with respect to the neutral direction in which the vehicle body 1 travels straight or approximately straight. Also, when the driving control unit 101 in the control device C stops the drive control of the running wheels 2, it causes the directions of the running wheels 2 located on one of the front and rear sides and the running wheels 2 located on the other of the front and rear sides of the front and rear running wheels 2 to be different from each other.

[0052] As a result, each of the four running wheels 2 acts on the other in a direction different from the direction of rotation, and receives a reaction force from the ground in the direction of skidding. In other words, when the four running wheels 2 try to roll, friction occurs between each of the running wheels 2 and the ground. This prevents each of the four running wheels 2 from rotating. This allows the work vehicle to maintain its stopped position even when it is stopped for an extended period of time on a slope, for example. Furthermore, when the vehicle body 1 performs a pivot turn, the travel control unit 101 can quickly change the direction of each of the four running wheels 2 to a direction along a tangent on the same arc of a circle whose center is the center of the vehicle body 1.

[0053] Control when the vehicle body 1 stops will be described based on the flowchart of FIG. 8. First, the ECU 13 determines whether the four running wheels 2 have stopped (step #01). If the four running wheels 2 have stopped (step #01: Yes), the ECU 13 determines whether the operation detection unit 22 has detected a manual operation from the driving operation unit 21 or the remote control device RC (step #02). If the operation detection unit 22 has not detected a manual operation (step #02: No), the ECU 13 starts a timer and determines whether a preset time has elapsed since the operation detection unit 22 stopped detecting a manual operation (step #03). The determination of step #03 is repeated until the timer count time has elapsed. Then, when the timer count time has elapsed (step #03: Yes), the traveling control unit 101 causes the four running wheels 2 to face in different directions (step #04). In other words, when a preset time has elapsed since the operation detection unit 22 no longer detects manual operation, the driving control unit 101 of the control device C causes the directions of one of the left and right running wheels 2 and the other of the left and right running wheels 2 to differ from each other.

[0054] When the processing of step #04 is completed, the ECU 13 determines whether the current location of the vehicle body 1 is on a slope based on the detection information of the inclination sensor S3 (step #05). Specifically, the ECU 13 determines whether the inclination angle of the ground calculated by the inclination angle calculation unit 102 is equal to or greater than a preset inclination angle. If the inclination angle of the ground is equal to or greater than the preset inclination angle, the ECU 13 determines that the current location of the vehicle body 1 is on a slope. If the inclination angle of the ground is less than the preset inclination angle, the ECU 13 determines that the current location of the vehicle body 1 is on flat land.

[0055] If the current location of the vehicle body 1 is on a slope (step #05: Yes), the ECU 13 continues control of the attitude control unit 100 (step #06) and prohibits the hydraulic supply source 9 from being stopped (step #07). When the control of the attitude control unit 100 is stopped on a slope, the hydraulic control valves 12 for the first hydraulic cylinder 6 and the second hydraulic cylinder 7 are closed, and the stroke positions of the first hydraulic cylinder 6 and the second hydraulic cylinder 7 are maintained. Therefore, the horizontal position of the loading unit 8 is maintained immediately after the control of the attitude control unit 100 is stopped. However, over time, the hydraulic oil inside the first hydraulic cylinder 6 and the second hydraulic cylinder 7 leaks from the hydraulic control valve 12. When this happens, the weight of the loading unit 8 gradually lowers the articulating link mechanism 5, causing the loading unit 8 to gradually tilt along the slope, and the horizontal position of the loading unit 8 is no longer maintained. To avoid such inconvenience, when the current location of the vehicle body 1 is on a slope, the control of the attitude control unit 100 continues, and the drive of the hydraulic supply source 9 also continues. In other words, the attitude control unit 100 of the control device C is configured to continue to control the operation of each of the first hydraulic cylinder 6 and the second hydraulic cylinder 7 when the four traveling wheels 2 are stopped and the ground is inclined at a set inclination angle or more. This allows the loading unit 8 to be kept horizontal even when the traveling wheels 2 are stopped on a slope.

[0056] If the current location of the vehicle body 1 is not on a slope (step #05: No), the current location of the vehicle body 1 is flat. Therefore, the ECU 13 stops control of the attitude control unit 100 (step #08) and permits the hydraulic supply source 9 to stop driving (step #09). As described above, over time, hydraulic oil leaks from the first hydraulic cylinder 6 and the second hydraulic cylinder 7 through the hydraulic control valve 12. However, because the ground is flat, each of the multiple articulating link mechanisms 5 descends approximately uniformly, maintaining the horizontal state of the loading unit 8. Therefore, if the current location of the vehicle body 1 is on flat ground, the control of the attitude control unit 100 is permitted to stop and the hydraulic supply source 9 is permitted to stop driving. This allows for reduced running costs compared to a configuration in which the attitude control unit 100 of the control device C continues to control the operation of the support mechanism A on flat ground. In other words, the posture control unit 100 of the control device C is configured not to control the operation of each of the first hydraulic cylinder 6 and the second hydraulic cylinder 7 when the four running wheels 2 are stopped and the ground is inclined within the set inclination angle range.

[0057] In this way, when the four traveling wheels 2 are stopped and the ground is inclined within a preset inclination angle range, the control device C is configured not to control the operation of the support mechanism A and is configured to permit the driving of the hydraulic supply source 9 to be stopped. On the other hand, when the four traveling wheels 2 are stopped and the ground is inclined at an inclination angle equal to or greater than the set inclination angle, the control device C is configured to continue to control the operation of the support mechanism A and prohibit the driving of the hydraulic supply source 9 from being stopped.

[0058] [Another embodiment] The present invention is not limited to the configurations exemplified in the above-described embodiments, and other representative embodiments of the present invention will be exemplified below.

[0059] (1) In the above-described embodiment, when the control device C stops the drive control of the running wheels 2, it changes the orientation of all four running wheels 2 individually. The present invention is not limited to this embodiment, and the control device C may be configured to change the orientation of one to three of the four running wheels 2 individually. For example, the control device C may be configured to change the orientation of two running wheels 2 (first running wheel and second running wheel) located on the low ground side of the four running wheels 2, based on the tilt state of the vehicle body 1. For example, the control device C may be configured to change the orientation of one running wheel 2 (first running wheel) located on the low ground side of one of the left and right sides and one running wheel 2 (second running wheel) located on the low ground side of the other of the left and right sides, based on the tilt state of the vehicle body 1.

[0060] (2) The support mechanism A may be a mechanism having one link or three or more links. For example, the support mechanism A may be a mechanism having an electric actuator as a device for changing the posture.

[0061] (3) The traveling wheels 2 may be configured to be driven by an electric motor instead of the hydraulic motor 4, or may be configured to be driven by the engine 9a or the like via a drive mechanism.

[0062] (4) The traveling wheels 2 may be configured to be driven to turn by a hydraulic motor, an electric motor, or the like, instead of the turning cylinder 20.

[0063] (5) In the above-described embodiment, the driving operation unit 21 is provided behind the loading section 8 of the vehicle body 1. For example, the driving operation unit 21 may not be provided. In this case, the operation detection unit 22 may be configured to receive only wireless signals from the remote control device RC using a wireless communication system. Alternatively, the operation detection unit 22 may be configured to receive only signals from the driving operation unit 21.

[0064] (6) The support mechanism A of this embodiment may not be provided. In this case, the loading unit 8 is not maintained in a horizontal position on a slope. However, if the first and second running wheels are configured to face in different directions on a slope, the risk of the work vehicle gradually sliding down the slope due to its own weight can be avoided.

[0065] (7) In the above-described embodiment, the control device C causes the orientations of the first running wheel and the second running wheel to differ from each other when a preset time has elapsed since the operation detection unit 22 stopped detecting a manual operation. This is not limiting, and for example, the control device C may be configured to cause the orientations of the first running wheel and the second running wheel to differ from each other immediately when the operation detection unit 22 stops detecting a manual operation.

[0066] (8) In the above-described embodiment, the support mechanism A is provided with the bending link mechanism 5. However, this is not limited to this embodiment, and for example, the support mechanism A may be configured to be provided with a sliding mechanism that can move up and down instead of the bending link mechanism 5.

[0067] (9) In the above embodiment, the tilt sensor S3 is provided as the tilt detector. However, the present invention is not limited to this embodiment, and the tilt detector may be, for example, a mechanical pendulum sensor or a magnetic sensor.

[0068] (10) In the above-described embodiment, the ECU 13 determines whether the inclination angle of the ground calculated by the inclination angle calculation unit 102 is equal to or greater than a preset inclination angle. If the inclination angle of the ground is equal to or greater than the preset inclination angle, the ECU 13 determines that the current location of the vehicle body 1 is on a slope. This is not limited to the embodiment, and "equal to or greater than the set inclination angle" may refer to an inclination angle that is greater than the set inclination angle but does not include the set inclination angle. If the inclination angle of the ground is equal to the set inclination angle, the ECU 13 may determine that the current location of the vehicle body 1 is on flat land rather than on a slope.

[0069] The configurations disclosed in the above-described embodiments (including other embodiments, the same applies hereinafter) can be applied in combination with configurations disclosed in other embodiments, as long as no contradiction occurs. Furthermore, the embodiments disclosed in this specification are merely examples, and the present invention is not limited to these embodiments, and can be modified as appropriate within the scope of the purpose of the present invention. [Industrial Applicability]

[0070] The present invention is applicable to a work vehicle having a plurality of independently steerable traveling wheels. [Explanation of symbols]

[0071] 1: Vehicle body 2: Running wheels (first running wheel, second running wheel) 4: Hydraulic motor 8: Loading section 12: Hydraulic control valve (control valve) 22: Operation detection unit 102: Tilt angle calculation unit (tilt detection unit) A: Support mechanism C: Control device S2: Stroke sensor (steering angle detection section) S3: Tilt sensor (tilt detection part)

Claims

1. a vehicle body having a loading section capable of loading luggage; a plurality of running wheels located at the front and rear of each of the left and right sides of the vehicle body, each of which can be steered independently; a plurality of hydraulic motors provided respectively for the plurality of running wheels, the hydraulic motors driving the running wheels by supplying or discharging hydraulic oil and locking the running wheels by cutting off the supply or discharge of the hydraulic oil; a control valve capable of individually changing the supply and discharge amounts of the hydraulic oil to and from the plurality of hydraulic motors; a steering angle detection unit that detects the direction of each of the plurality of running wheels; a control device that is capable of controlling the rotation of each of the plurality of hydraulic motors by changing the amount of hydraulic oil supplied and discharged, and a drive control device that is capable of controlling the rotation of each of the plurality of hydraulic motors by changing the amount of hydraulic oil supplied and discharged, When the drive control is stopped, the control device closes the control valve to cut off the supply and discharge of hydraulic oil to the multiple hydraulic motors, thereby locking each of the multiple running wheels, and when the drive control is stopped, the control device changes the orientation of each of the multiple running wheels, a first running wheel located on one side of the vehicle body, and a second running wheel located on the other side of the vehicle body, to be different from each other.

2. The work vehicle according to claim 1, wherein when the control device stops the drive control, the control device changes the orientation of the first running wheel and the second running wheel so that they are opposite to each other with respect to the neutral orientation that causes the vehicle body to travel straight or approximately straight.

3. The work vehicle according to claim 1 , wherein the control device causes all of the plurality of traveling wheels to have different orientations when the drive control is stopped.

4. an inclination detection unit that detects an inclination state of the vehicle body; 2. The work vehicle according to claim 1, wherein the control device changes the orientation of the first running wheel located on the lower ground side on one of the left and right sides of the plurality of running wheels and the second running wheel located on the lower ground side on the other of the plurality of running wheels to be different from each other based on the tilt state of the vehicle body.

5. an operation detection unit that detects a human operation on the plurality of running wheels; The work vehicle described in any one of claims 1 to 4, wherein the control device causes the directions of the first running wheel and the second running wheel to differ from each other when a predetermined time has elapsed since the operation detection unit stopped detecting the manual operation.

6. A work vehicle as described in Claim 5, wherein the control device causes the directions of the first running wheel and the second running wheel to differ from each other when a predetermined time has elapsed since the operation detection unit stopped detecting the manual operation after the drive control was stopped.

7. a support mechanism that is supported by the vehicle body and supports the plurality of running wheels so that their positions can be changed relative to the vehicle body; an inclination detection unit that detects an inclination state of the loading unit, 5. The work vehicle according to claim 1, wherein the control device is configured to be able to control the operation of the support mechanism based on the tilted state of the loading section so that the loading section is in a horizontal position.

8. A work vehicle as described in Claim 7, wherein the control device is configured to be able to calculate the inclination angle of the ground on which the multiple running wheels contact the ground, and is configured not to control the operation of the support mechanism when the ground is inclined within a predetermined set inclination angle range, and to continue to control the operation of the support mechanism when the ground is inclined at an inclination angle greater than the set inclination angle.

9. A drive source is provided to supply drive energy for operating the support mechanism, 9. The work vehicle according to claim 8, wherein the control device is configured to permit the drive source to be stopped when the ground surface is inclined within the set inclination angle range, and to prohibit the drive source from being stopped when the ground surface is inclined at an inclination angle equal to or greater than the set inclination angle.

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