Work vehicles

Abstract

To provide a work vehicle which can suppress a deviation from a design path of a travel position of the work vehicle when an excessive unbalanced load is applied from a work machine to the work vehicle and stably maintain a control system of automatic steering.SOLUTION: A work vehicle comprises: a pair of left lower link (7L) and right lower link (7R) that attach a work machine in a rear part of the work vehicle; a left sensor (64L) which measures a load applied from the work machine to the left lower link (7L); and a right sensor (64R) which measures the load applied from the work machine to the right lower rink (7R). A controller (50) operates turning of a front wheel (2) via steering devices (73L, 73R) of the work vehicle when the unbalanced load of the left load measured by the left sensor (64L) and the right load measured by the right sensor (64R) is equal to or greater than a preset set unbalanced load.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to a work vehicle that automatically travels along a set route set in a farm field. [Background technology]

[0002] There is known a technology for automatically steering a work vehicle towing a work implement that is offset in the left-right direction perpendicular to the direction of travel, while automatically traveling along a preset route (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-106975 Summary of the Invention [Problem to be solved by the invention]

[0004] However, with the technology of Patent Document 1, if an excessively large unbalanced load is applied from a work machine that is offset from the work vehicle, there is a risk that the work vehicle's traveling position may deviate significantly from the designed path, or that the control system that automatically steers the work vehicle may become unstable.

[0005] Therefore, the present invention aims to provide a work vehicle that can suppress deviation of the work vehicle's traveling position from the designed path when excessive unbalanced load is applied to the work vehicle from a work machine, thereby maintaining a stable automatic steering control system. [Means for solving the problem]

[0006] The present invention, which has solved the above problems, is as follows. That is, the invention of claim 1 relates to a work vehicle equipped with a controller (50) that automatically drives the work vehicle along a set route (61) set in a farm field, and an antenna (23B) that receives information on the travel position of the work vehicle from a positioning satellite, A pair of left and right lower links (7L and 7R) for mounting a work implement are provided at the rear of the work vehicle, a left sensor (64L) for measuring the load applied from the work implement is provided on the left lower link (7L), and a right sensor (64R) for measuring the load applied from the work implement is provided on the right lower link (7R), and the controller (50) controls the steering of the front wheels (2) via the steering devices (73L, 73R) of the work vehicle when the offset between the load measured by the left sensor (64L) and the load measured by the right sensor (64R) is equal to or greater than a preset offset load. If the load measured by the left sensor (64L) is greater than the load measured by the right sensor (64R), the front wheels (2) are turned clockwise, and if the load measured by the right sensor (64R) is greater than the load measured by the left sensor (64L), the front wheels (2) are turned counterclockwise. After turning the front wheels (2), if the deviation between the travel position of the work vehicle and the set route (61) is equal to or greater than a preset deviation, the controller (50) activates the braking device of the work vehicle. The left rear wheel (3L) and the right rear wheel (3R) are braked via the left sensor (46L, 46R), and when the load measured by the left sensor (64L) is greater than the load measured by the right sensor (64R) and the running position of the work vehicle deviates to the left side of the set route (61), the right rear wheel (3R) is braked, and when the load measured by the right sensor (64R) is greater than the load measured by the left sensor (64L) and the running position of the work vehicle deviates to the right side of the set route (61), the left rear wheel (3L) is braked. This is a work vehicle characterized by the above.

[0007]

[0008]

[0009]

[0010] Claim 2 The invention described in the claims is characterized in that, after the front wheels (2) are turned or the left rear wheels (3L) and the right rear wheels (3R) are braked, the controller (50) increases the braking of the left rear wheels (3L) and the right rear wheels (3R) via the oil pressure booster device (42) of the work vehicle when the front of the work vehicle rises higher than the rear and the pitching angle is equal to or greater than a preset pitching angle. 1 This is a work vehicle as described.

[0011] Claim 3 The invention described in the claims is characterized in that, after the front wheels (2) are turned or the left rear wheel (3L) and the right rear wheel (3R) are braked, the controller (50) raises the work equipment via the lifting device (9) of the work vehicle when the front part of the work vehicle is raised higher than the rear part and the pitching angle is equal to or greater than a preset pitching angle. 1 This is a work vehicle as described.

[0012] Claim 4 The invention described is a work vehicle according to claim 1, wherein the center of the work implement is offset in either the left or right direction of the work vehicle in a plan view. [Effects of the Invention]

[0013] According to the invention of claim 1, a pair of left and right lower links (7L and 7R) for mounting a work implement to the rear of a work vehicle are provided, a left sensor (64L) for measuring the load applied from the work implement is provided on the left lower link (7L), and a right sensor (64R) for measuring the load applied from the work implement is provided on the right lower link (7R), and a controller (50) controls the steering of the front wheels (2) via the steering devices (73L, 73R) of the work vehicle when the imbalance between the load measured by the left sensor (64L) and the load measured by the right sensor (64R) is equal to or greater than a preset imbalance load. If the load measured by the left sensor (64L) is greater than the load measured by the right sensor (64R), the front wheels (2) are turned clockwise, and if the load measured by the right sensor (64R) is greater than the load measured by the left sensor (64L), the front wheels (2) are turned counterclockwise. After turning the front wheels (2), the controller (50) activates the brakes (4) of the work vehicle when the deviation between the travel position of the work vehicle and the set route (61) is equal to or greater than a preset deviation. The left rear wheel (3L) and the right rear wheel (3R) are braked via the left sensor (64L, 46R). When the load measured by the left sensor (64L) is greater than the load measured by the right sensor (64R) and the running position of the work vehicle deviates to the left side of the set route (61), the right rear wheel (3R) is braked, and when the load measured by the right sensor (64R) is greater than the load measured by the left sensor (64L) and the running position of the work vehicle deviates to the right side of the set route (61), the left rear wheel (3L) is braked. Therefore, it is possible to prevent the travel position of the work vehicle from deviating from the set route 61. In addition, since steering is performed before the grip force of the front wheels 2 becomes weak, it is possible to prevent the automatic operation control system from becoming unstable.

[0014]

[0015]

[0016]

[0017] Claim 2 According to the invention described, claims 1 In addition to the effects of the invention described above, after the front wheels (2) are turned or the left rear wheel (3L) and the right rear wheel (3R) are braked, if the front of the work vehicle is raised higher than the rear and the pitching angle is equal to or greater than a preset pitching angle, the controller (50) increases the braking of the left rear wheel (3L) and the right rear wheel (3R) via the oil boost device (42) of the work vehicle, thereby keeping the front and rear of the work vehicle level.

[0018] Claim 3 According to the invention described, claims 1In addition to the effects of the invention described above, after the front wheels (2) are turned or the left rear wheel (3L) and right rear wheel (3R) are braked, if the front of the work vehicle is raised higher than the rear and the pitching angle is equal to or greater than a preset pitching angle, the controller (50) raises the work equipment via the lifting device (9) of the work vehicle, thereby preventing the load imbalance applied to the left lower link (7L) and right lower link (7R) from becoming excessively large and further suppressing deviation of the travel position of the work vehicle from the set route (61).

[0019] Claim 4 According to the described invention, in addition to the effect of the invention described in claim 1, when viewed in a plane, the center of the work implement is shifted in either the left or right direction of the work vehicle, so there is a risk that the loads applied to the left lower link (7L) and the right lower link (7R) will be significantly different. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 2 is a left side view of the work vehicle towing the work implement. [Figure 2] FIG. 2 is a plan view of the work vehicle towing the work implement. [Figure 3] FIG. 2 is a connection diagram of the positioning unit. [Figure 4] This is a diagram of the engine output rotation and hydraulic oil transmission. [Figure 5] FIG. 2 is a connection diagram of a controller. [Figure 6] FIG. 2 is an explanatory diagram of a reference route and a set route. [Figure 7] FIG. 4 is an explanatory diagram of a method for steering the front wheels. [Figure 8] FIG. 2 is an explanatory diagram of an automatic driving method for a work vehicle. [Figure 9] FIG. 1 is a plan view of a work vehicle with the front wheels turned clockwise. DETAILED DESCRIPTION OF THE INVENTION

[0021] As shown in FIG. 1, a work vehicle such as a tractor has a pair of left and right front wheels 2 provided at the front lower part of a body frame 1, and a pair of left and right rear wheels 3 provided at the rear lower part of the body frame 1.

[0022] A bonnet 4 on which an engine E is mounted is provided at the front upper part of the machine frame 1, and a control section 5 on which an operator sits is provided behind the bonnet 4. A PTO shaft 6 extending in the front-to-rear direction for transmitting the output rotation of the engine E to a work implement 10 towed by the work vehicle, and a pair of left and right lower links 7 to which the front parts of the work implement 10 are attached are provided below and behind the control section 5. The lower links 7 are provided with a lifting cylinder (referred to as a "lifting device" in the claims) 9 that lifts and lowers the rear parts of the lower links 7 in the vertical direction via a connecting arm 8.

[0023] The control section 5 has a steering wheel 12 provided in front of a cockpit 11, and the steering wheel 12 is supported by a steering column 13 via a steering shaft. A clutch pedal 14 is provided on the left side below the steering column 13, and an accelerator pedal 15 is provided on the right side. The cockpit 11 and other components are covered by a cabin 16.

[0024] The working machine 10 may be a tiller (plow) for tilling the field, a harvester for harvesting grains in the field, a reaper for cutting grass in the field, or the like, and FIGS. 1 and 2 show a tiller as the working machine.

[0025] As shown in FIG. 2, a gyro sensor 63 is provided in the middle of the machine frame 1 in the longitudinal direction. The gyro sensor 63 measures the pitch angle, which is the tilt angle of the machine frame 1 in the longitudinal direction, the roll angle, which is the tilt angle of the machine frame 1 in the lateral direction, and the yaw angle, which is perpendicular to the pitch angle and roll angle of the machine frame 1. This makes it easy to measure the pitch angle, etc., of the machine frame 1. Preferably, a load sensor such as a strain gauge is provided on the left drive shaft supporting the left front wheel 2L to measure the load applied from the field to the left drive shaft, and a load sensor such as a strain gauge is provided on the right drive shaft supporting the right front wheel 2R to measure the load applied from the field to the right drive shaft. This makes it possible to quickly detect a state in which an excessive load is applied from the work implement 10 to the work vehicle, causing the left front wheel 2L or right front wheel 2R to move away from the field, i.e., the front of the work vehicle to move away from the field.

[0026] The left lower link 7L is provided with a left load sensor (referred to as a "left sensor" in claims) 64L such as a strain gauge that measures the load applied by the work implement 10 to the left lower link 7L, and the right lower link 7R is provided with a right load sensor (referred to as a "right sensor" in claims) 64R such as a strain gauge that measures the load applied by the work implement 10 to the right lower link 7R. This makes it possible to calculate the total load, which is the sum of the loads applied to the left lower link 7L and the right lower link 7R, and the unbalanced load, which is the difference between the load applied to the left lower link 7L and the load applied to the right lower link 7R. In this specification, the left load sensor 64L and the right load sensor 64R are collectively referred to as load sensors 64.

[0027] As shown in Figure 3, positioning unit 20, which uses the RTK-GPS positioning method, is made up of positioning satellite 21, base station 22 installed at a known position, and mobile station 23 installed on the work vehicle. This makes it possible to accurately obtain the position of mobile station 23, i.e., the position of the work vehicle, from the position information transmitted from positioning satellite 21 to mobile station 23 and the correction position information transmitted from base station 22 to mobile station 23.

[0028] The base station 22 is composed of a fixed communication device 22A, a fixed GPS antenna 22B that receives position information from the positioning satellite 21, and a fixed data transmission antenna 22C that transmits corrective position information to the mobile station 23.

[0029] The mobile station 23 is composed of a mobile communication device 23A, a mobile GPS antenna (referred to as "antenna" in the claims) 23B that receives position information from the positioning satellite 21, and a mobile data transmission antenna 23C that receives corrective position information from the base station 22. The mobile GPS antenna 23B and the mobile data transmission antenna 23C are provided on the upper wall of the cabin 16 of the control unit 5.

[0030] As shown in Fig. 4, the output rotation of the engine E is transmitted to a hydraulic continuously variable transmission 31 via a forward / reverse clutch 30, and the hydraulic continuously variable transmission 31 increases or decreases the rotation speed and switches the direction of the output rotation. The output rotation of the hydraulic continuously variable transmission 31 is transmitted to a gear box 32, and is increased or decreased by the gear box 32. The output rotation of the gear box 32 is transmitted to an output shaft 33, and the output rotation of the output shaft 334 is transmitted to a pair of left and right rear wheels 3 via a rear wheel differential gear 34.

[0031] The output rotation of the output shaft 33 is transmitted to the rear output shaft 36B via a pair of gears 35, and the output rotation of the rear output shaft 36B is transmitted to the front output shaft 36A via a 4WD clutch 37. The output rotation of the front output shaft 36A is transmitted to a pair of left and right front wheels 2 via a front wheel differential gear 38. Reference numeral 39A denotes an angle sensor that measures the steering angle, and reference numeral 39B denotes a vehicle speed sensor that measures the output rotation speed of the output shaft 33.

[0032] A left steering arm 70L extending substantially in the longitudinal direction is provided inside the left front wheel 2L, and the front portion of the left steering arm 70L is connected to the left portion of a tie rod 71 extending in the left-right direction. Also, a right steering arm 70R extending substantially in the longitudinal direction is provided inside the right front wheel 2R, and the front portion of the right steering arm 70R is connected to the right portion of the tie rod 71 extending in the left-right direction.

[0033] A left steering cylinder (referred to as a "steering device" in the claims) 73L having a rod that expands and contracts in response to the rotation of the steering wheel 12 is connected to the left steering arm 70L. Also, a right steering cylinder (referred to as a "steering device" in the claims) 73R having a rod that expands and contracts in response to the rotation of the steering wheel 12 is connected to the right steering arm 70R. In this specification, the left steering cylinder 73L and the right steering cylinder 73R are collectively referred to as steering cylinders 73.

[0034] Hydraulic oil stored in an oil tank 40 is supplied via a pump 41 to a pressure proportional valve (referred to as an "oil pressure boosting device" in claims) 42, where it is boosted to a predetermined pressure. The boosted hydraulic oil is supplied via a first solenoid valve 43 on the upstream side and a second solenoid valve 44 on the downstream side to a left brake cylinder (referred to as a "brake device" in claims) 46L that drives a left brake 45L that brakes the left rear wheel 3L, and a right brake cylinder (referred to as a "brake device" in claims) 46R that drives a right brake 45R that brakes the right rear wheel 3R. In this embodiment, a five-port, three-position directional solenoid valve is used as the first solenoid valve 43, and a four-port, two-position directional solenoid valve is used as the second solenoid valve 44. In this specification, the left brake 45L and the right brake 45R are collectively referred to as brakes 45, and the left brake cylinder 46L and the right brake cylinder 46R are collectively referred to as brake cylinders 46.

[0035] The left brake cylinder 46L is provided with a left brake pedal 47L that an operator operates the left brake cylinder 46L, and the right brake cylinder 46R is provided with a right brake pedal 47R that an operator operates the right brake cylinder 46R. As a result, during normal work, the operator can brake the left rear wheel 3L and the right rear wheel 3R by stepping on the left brake pedal 47L or the right brake cylinder 46R. In this specification, the left brake pedal 47L and the right brake pedal 47R are collectively referred to as the brake pedal 47.

[0036] When braking the left rear wheel 3L and the right rear wheel 3R, a controller 50 (described later) energizes the left solenoid of the first solenoid valve 43 to excite the left solenoid of the first solenoid valve 43, and energizes the solenoid of the second solenoid valve 44 to excite the solenoid of the second solenoid valve 44. As a result, the hydraulic oil pressurized by the pressure proportional valve 42 flows through the first solenoid valve 43 and the second solenoid valve 44 and is supplied to the left brake cylinder 46L and the right brake cylinder 46R, and the left brake 45L and the right brake 45R are driven to brake the left rear wheel 3L and the right rear wheel 3R.

[0037] When braking the left rear wheel 3L and releasing the braking of the right rear wheel 3R, the controller 50 energizes the left solenoid of the first solenoid valve 43 to excite it, and does not energize the solenoid of the second solenoid valve 44 to not excite it. As a result, the hydraulic oil pressurized by the pressure proportional valve 42 flows through the first solenoid valve 43 and the second solenoid valve 44 to be supplied to the left brake cylinder 46L, which drives the left brake 45L to brake the left rear wheel 3L. In addition, the hydraulic oil in the right brake cylinder 46R flows through the second solenoid valve 44 and the first solenoid valve 43 to be drained into the oil tank 40, which stops the drive of the right brake 45R and releases the braking of the right rear wheel 3R.

[0038] When braking the right rear wheel 3R and releasing the brake on the left rear wheel 3L, the controller 50 energizes the right solenoid of the first solenoid valve 43 to excite it, and does not energize the solenoid of the second solenoid valve 44 to not excite it. As a result, the hydraulic oil pressurized by the pressure proportional valve 42 flows through the first solenoid valve 43 and the second solenoid valve 44 to be supplied to the right brake cylinder 46R, driving the right brake 45R to brake the right rear wheel 3R. In addition, the hydraulic oil in the left brake cylinder 46L flows through the second solenoid valve 44 and the first solenoid valve 43 to be drained into the oil tank 40, driving the left brake 45L is stopped, and the braking of the left rear wheel 3L can be released.

[0039] When releasing the brakes on the left rear wheel 3L and the right rear wheel 3R, the controller 50 does not energize the left solenoid and right solenoid of the first solenoid valve 43, thereby not energizing the left solenoid and right solenoid of the first solenoid valve 43, and does not energize the solenoid of the second solenoid valve 44, thereby not energizing the solenoid of the second solenoid valve 44. As a result, the hydraulic oil pressurized by the pressure proportional valve 42 cannot flow through the first solenoid valve 43. Furthermore, the hydraulic oil in the left brake cylinder 46L and the right brake cylinder 46R passes through the second solenoid valve 44 and the first solenoid valve 43 and is drained into the oil tank 40, and the drive of the left brake 45L and the right brake 45R stops, releasing the brakes on the left rear wheel 3L and the right rear wheel 3R. Reference numeral 48A denotes a relief valve that discharges hydraulic oil above a predetermined level supplied to the pressure proportional valve 42 to the oil tank 40, and reference numeral 48B denotes a filter that removes impurities from the hydraulic oil.

[0040] As shown in FIG. 5, the controller 50 is made up of a processing unit 51 consisting of a CPU or the like, a storage unit 52 consisting of a ROM, RAM, hard disk drive, flash memory or the like, and a communication unit 53 for data communication with the outside.

[0041] The processing unit 51 sets a set path 61 based on the reference path 60, steers the left front wheel 2L and the right front wheel 2R based on the deviation between the set path and the path on which the work vehicle is automatically traveling, brakes the left rear wheel 3L and the right rear wheel 3R based on the yaw angle and unbalanced load, and drives the extension and retraction of the lifting cylinder 9 based on the pitching angle and total load.

[0042] The storage unit 52 stores information such as a reference path 60, a set path 61, a set deviation, a set knitting load, and a set pitching angle.

[0043] The communication unit 53 communicates information such as the reference route 60 to the base station 22 via the mobile communication device 23A.

[0044] The input side of the controller 50 is connected via a predetermined input interface circuit to a mobile GPS antenna 23B that receives position information from positioning satellites 21, a mobile data transmission antenna 23C that receives corrective position information from base station 22, a reference route switch 60S that sets a reference route 60, a set route switch 61S that sets a set route 61 for causing the work vehicle to travel automatically based on the reference route 60, a changeover switch 62S that switches the work vehicle to automatic travel, a gyro sensor 63 provided on the body frame 1, a left load sensor 64L provided on the left lower link 7L, and a right load sensor 64R provided on the right lower link 7R.

[0045] On the output side of the controller 50, there are provided an automatic steering switch 65S that automatically steers the front wheels 2 of the work vehicle, a first left first left excitation switch 66S that excites the left solenoid of the first solenoid valve 43, a first right first right excitation switch 67S that excites the right solenoid of the first solenoid valve 43, a second excitation switch 68S that excites the solenoid of the second solenoid valve 44, and an extension switch 69S that drives the lifting cylinder 9 that raises and lowers the work implement 10.

[0046] As shown in Figure 6, the set route 61 is set parallel to the reference route 60, separated by the working width input from the touch panel monitor of the operation unit 5. The reference route 60 along which the worker operates the steering wheel 12 to drive the work vehicle is shown by a solid line, and the set route 61 along which the processing unit 51 of the controller 50 automatically drives the work vehicle is shown by a dashed line.

[0047] 7, when the worker is driving the work vehicle, the rotation angle of the steering wheel 12 is input to the controller 50, and the controller 50 excites the solenoid of the solenoid valve 72 based on the rotation angle of the steering wheel 12 to extend and retract the rods of the left steering cylinder 73L and the right steering cylinder 73R, thereby moving the tie rod 71 in the left and right directions via the left steering arm 70L and the right steering arm 70R to steer the left front wheel 2L and the right front wheel 2R. Note that a 5-port 3-position directional solenoid valve similar to the first solenoid valve 43 is used as the solenoid valve 72.

[0048] When the work vehicle is driven automatically by the controller 50, information on the work vehicle's travel position from the positioning satellite 21 and the base station 22 is input to the controller 50, and the controller 50 excites the solenoid of the electromagnetic valve 72 based on the deviation between the set route 61 and the work vehicle's travel position, thereby extending and retracting the rods of the left steering cylinder 73L and the right steering cylinder 73R, and moving the tie rod 71 left and right via the left steering arm 70L and right steering arm 70R to steer the left front wheel 2L and the right front wheel 2R.

[0049] This makes it easy to switch between driving the work vehicle by the worker and automatic driving of the work vehicle by the controller 50, and also makes it possible to suppress an increase in the number of parts.

[0050] <Automatic driving method for work vehicles> As shown in Fig. 8, in step S1 while the work vehicle is being automatically driven by the processing unit 51 of the controller 50, the processing unit 51 determines whether the unbalanced load, which is the load difference between the load applied to the left lower link 7L and the load applied to the right lower link 7R, is equal to or greater than a preset unbalanced load. If the unbalanced load is equal to or greater than the set unbalanced load, the process proceeds to step S2, and if the unbalanced load is less than the set unbalanced load, step S1 is repeated. The load applied to the left lower link 7L is measured by the left load sensor 64L, and the load applied to the right lower link 7R is measured by the right load sensor 64R.

[0051] If, in step S2, the processing unit 51 determines that the load applied to the left lower link 7L is greater than the load applied to the right lower link 7R, it energizes the left solenoid of the solenoid valve 72 to excite the left solenoid, extending the rod of the left steering cylinder 73L and shortening the rod of the right steering cylinder 73R, and then proceeds to step S3. As a result, as shown in Fig. 9, the left front wheel 2L and the right front wheel 2R are turned clockwise relative to the direction of travel, preventing the automatic driving position of the work vehicle from deviating to the left from the set route 61.

[0052] On the other hand, if the processing unit 51 determines that the load applied to the right lower link 7R is greater than the load applied to the left lower link 7L, it energizes the right solenoid of the solenoid valve 72 to excite the right solenoid, extending the rod of the right steering cylinder 73R and shortening the rod of the left steering cylinder 73L, and proceeds to step S3. This makes it possible to prevent the left front wheel 2L and the right front wheel 2R from turning counterclockwise relative to the direction of travel, thereby preventing the automatic driving position of the work vehicle from deviating to the right from the set route 61.

[0053] In step S3, the processing unit 51 determines whether the deviation between the automatic travel position of the work vehicle and the planned route 61 is equal to or greater than a preset deviation. If the deviation is equal to or greater than the preset deviation, the process proceeds to step S4, and if the deviation is less than the preset deviation, the process returns to step S1.

[0054] In step S4, if the processing unit 51 determines that the automatic travel position of the work vehicle is located to the left of the set route 61, that is, if it determines that the load applied to the left lower link 7L is greater than the load applied to the right lower link 7R, it energizes the right solenoid of the first solenoid valve 43 to excite it, and does not energize the solenoid of the second solenoid valve 44 to excite it, and proceeds to step S5. As a result, the hydraulic oil pressurized by the pressure proportional valve 42 is supplied to the right brake cylinder 46R, which drives the right brake 45R to brake the right rear wheel 3R, making it possible to prevent the automatic travel position of the work vehicle from deviating to the left of the set route 61.

[0055] On the other hand, if the processing unit 51 determines that the automatic travel position of the work vehicle is located to the right of the set route 61, that is, if it determines that the load applied to the right lower link 7R is greater than the load applied to the left lower link 7L, it energizes the left solenoid of the first solenoid valve 43 to excite it, and does not energize the solenoid of the second solenoid valve 44 to excite it, and proceeds to step S5. As a result, the hydraulic oil pressurized by the pressure proportional valve 42 is supplied to the left brake cylinder 46L, which drives the left brake 45L to brake the left rear wheel 3L, thereby preventing the automatic travel position of the work vehicle from deviating to the right of the set route 61.

[0056] In step S5, the processing unit 51 determines whether the front of the work vehicle is higher than the rear in the vertical direction and the pitching angle in the longitudinal direction is equal to or greater than a preset pitching angle. If the pitching angle is equal to or greater than the preset pitching angle, the process proceeds to step S6, and if the pitching angle is less than the set pitching angle, the process returns to step S1.

[0057] In step S6, the processing unit 51 drives the pressure proportional valve 42 to increase the pressure of the hydraulic oil, and then proceeds to step S7. This increases the braking force on the left rear wheel 3L and the right rear wheel 3R, thereby suppressing an increase in the pitching angle of the work vehicle.

[0058] In step S7, the processing unit 51 determines whether the front of the work vehicle is higher than the rear in the vertical direction and the pitching angle in the longitudinal direction is equal to or greater than a preset pitching angle. If the pitching angle is equal to or greater than the preset pitching angle, the process proceeds to step S8, and if the pitching angle is less than the set pitching angle, the process returns to step S1.

[0059] In step S8, the processing unit 51 drives the lifting cylinder 9 to move the work implement 10 upward via the connecting arm 8, and then returns to step S1. As a result, the lower part of the work implement 10 that has descended into the field moves onto the field surface, reducing the load applied from the field to the work implement 10, and reducing the load applied from the work implement 10 to the left lower link 7L and the right lower link 7R, thereby suppressing an increase in the pitching angle of the work vehicle. [Explanation of symbols]

[0060] 2 front wheels 7L Left lower link 7R Right Lower Link 9 Lifting cylinder (lifting device) 23B Mobile GPS Antenna (Antenna) 42 Pressure proportional valve (oil booster) 46L Left brake cylinder (braking device) 46R Left brake cylinder (braking device) 50 Controllers 61 Setting Route 64L Load sensor (left sensor) 64R Load sensor (right sensor) 73L Left steering cylinder (steering device) 73R Right steering cylinder (steering device)

Claims

1. A work vehicle equipped with a controller (50) that automatically drives the work vehicle along a set route (61) set in a farm field, and an antenna (23B) that receives information on the travel position of the work vehicle from a positioning satellite, A pair of left and right lower links (7L and 7R) for mounting a work implement to the rear of the work vehicle are provided, a left sensor (64L) for measuring a load applied from a work machine to the left lower link (7L); a right sensor (64R) for measuring a load applied to the right lower link (7R) from a work machine; When the biased load between the load measured by the left sensor (64L) and the load measured by the right sensor (64R) is equal to or greater than a preset biased load, the controller (50) operates the steering of the front wheels (2) via the steering devices (73L, 73R) of the work vehicle, If the load measured by the left sensor (64L) is greater than the load measured by the right sensor (64R), the front wheel (2) is turned clockwise; If the load measured by the right sensor (64R) is greater than the load measured by the left sensor (64L), the front wheel (2) is turned counterclockwise, After the front wheels (2) are turned, if the deviation between the travel position of the work vehicle and the set route (61) is equal to or greater than a preset deviation, the controller (50) operates the brakes of the left rear wheel (3L) and the right rear wheel (3R) via the braking devices (46L, 46R) of the work vehicle, When the load measured by the left sensor (64L) is greater than the load measured by the right sensor (64R) and the traveling position of the work vehicle deviates to the left side of the set route (61), the right rear wheel (3R) is braked; A work vehicle characterized in that, when the load measured by the right sensor (64R) is greater than the load measured by the left sensor (64L) and the running position of the work vehicle deviates to the right side of the set route (61), the left rear wheel (3L) is braked.

2. 2. The work vehicle according to claim 1, wherein, after the front wheels (2) are turned or the left rear wheels (3L) and right rear wheels (3R) are braked, the controller (50) increases the braking of the left rear wheels (3L) and right rear wheels (3R) via an oil pressure booster device (42) of the work vehicle when the front of the work vehicle rises higher than the rear and the pitching angle is equal to or greater than a preset pitching angle.

3. 2. A work vehicle according to claim 1, wherein, after the front wheels (2) are turned or the left rear wheel (3L) and the right rear wheel (3R) are braked, the controller (50) raises the work implement via the lifting device (9) of the work vehicle if the front of the work vehicle is raised higher than the rear and the pitching angle is equal to or greater than a preset pitching angle.

4. 2. The work vehicle according to claim 1, wherein the center of the work implement is offset in either the left or right direction of the work vehicle in a plan view.

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