Work vehicle

Abstract

The present invention improves the traveling performance of a work vehicle comprising a plurality of clutches for switching between forward movement and reverse movement. A work vehicle (1) comprises: a hydraulic forward clutch (75) capable of switching between a connected state, in which power for advancing a travel device (7) that causes a vehicle body (3) to travel is transmitted, and a disconnected state, in which the power is not transmitted; a hydraulic reverse clutch (76) capable of switching between a connected state, in which power for reversing the travel device is transmitted, and a disconnected state, in which the power is not transmitted; and a control device (120). The control device sets the forward clutch to the connected state and the reverse clutch to the disconnected state when a forward instruction is acquired, sets the reverse clutch to the connected state and the forward clutch to the disconnected state when a reverse instruction is acquired, and sets both the forward clutch and the reverse clutch to the connected state when a neutral instruction is acquired.

Description

Work vehicles

[0001] The present invention relates to a work vehicle equipped with a plurality of hydraulic clutches for switching between forward and reverse travel.

[0002] For example, the work vehicle disclosed in Patent Document 1 transmits engine power (output) to a hydromechanical continuously variable transmission, and transmits the power after gear shifting by the hydromechanical continuously variable transmission to a traveling device such as wheels via a hydraulic forward clutch or reverse clutch. A control means included in the ECU controls the clutch pressure, which is the hydraulic pressure acting on the forward clutch and the reverse clutch, in response to switching of the FR lever from the reverse position to the forward position, thereby disengaging the reverse clutch and engaging the forward clutch, thereby transmitting power for forward travel to the traveling device. The control means also controls the clutch pressure in response to switching of the FR lever from the forward position to the reverse position, thereby disengaging the forward clutch and engaging the reverse clutch, thereby transmitting power for reverse travel to the traveling device.

[0003] Japanese Patent Publication No. 2013-2578

[0004] When the traveling device is placed in a neutral state (i.e., stopped state) where it is not moving forward or backward, the clutch oil pressure acting on the forward clutch and reverse clutch is generally reduced to disengage the forward clutch and reverse clutch. However, this causes oil to leak from the forward clutch and reverse clutch, so the next time the traveling device is moved forward or backward, it takes time to fill the corresponding forward clutch or reverse clutch with oil and engage the clutch using oil pressure, delaying the start of the traveling device and reducing the drivability of the work vehicle.

[0005] SUMMARY OF THE INVENTION In view of the above problems, the present invention aims to improve the running performance of a work vehicle equipped with a plurality of clutches for switching between forward and reverse travel.

[0006] The present invention employs the following technical means to achieve the above object.

[0007] A work vehicle according to one aspect of the present invention includes a traveling device that causes a vehicle body to travel, a hydraulic forward clutch that is switchable between an engaged state in which power for moving the traveling device forward and a disengaged state in which power is not transmitted to the traveling device, a hydraulic reverse clutch that is switchable between an engaged state in which power for moving the traveling device backward and a disengaged state in which power is not transmitted to the traveling device, and a control device that receives a forward command to move the traveling device forward, a reverse command to move the traveling device backward, and a neutral command to move the traveling device neither forward nor backward, and controls the forward clutch and the reverse clutch in accordance with the received commands. When the control device receives the forward command, it connects the forward clutch and disengages the reverse clutch, when it receives the reverse command, it connects the reverse clutch and disengages the forward clutch, and when it receives the neutral command, it connects the forward clutch and the reverse clutch,

[0008] In one aspect of the present invention, when the control device receives the neutral command, it increases the forward clutch pressure, which is the hydraulic pressure acting on the forward clutch, to bring the forward clutch into the connected state, and increases the reverse clutch pressure, which is the hydraulic pressure acting on the reverse clutch, to bring the reverse clutch into the connected state; when the control device receives the forward command, it maintains the increased forward clutch pressure, keeping the forward clutch in the connected state, while reducing the reverse clutch pressure, to bring the reverse clutch into the disengaged state; and when the control device receives the reverse command, it maintains the increased reverse clutch pressure, keeping the reverse clutch in the connected state, while reducing the forward clutch pressure, to bring the forward clutch into the disengaged state.

[0009] In one aspect of the present invention, the work vehicle comprises a prime mover mounted on the vehicle body, a transmission that changes the output of the prime mover, a forward transmission mechanism that converts power input from the transmission through the forward clutch into propulsion force for moving the traveling device forward and transmits it to the traveling device, a reverse transmission mechanism that converts power input from the transmission through the reverse clutch into propulsion force for moving the traveling device in reverse and transmits it to the traveling device, and an input device that can input the forward instruction, the reverse instruction, the neutral instruction, and a gear change instruction, and the control device acquires the forward instruction, the reverse instruction, and the neutral instruction respectively via the input device and controls the forward clutch, the reverse clutch, and the transmission in accordance with the acquired instructions, and when the traveling device is in either a forward state or a reverse state, acquires the gear change instruction via the input device, the control device may control the transmission in accordance with the gear change instruction to change the output of the transmission and the vehicle speed, which is the speed of the vehicle body.

[0010] In one aspect of the present invention, when the control device acquires the neutral command, the control device may stop output from the transmission to the forward clutch and the reverse clutch, and place the forward clutch and the reverse clutch in the connected state, respectively.

[0011] In one aspect of the present invention, when the traveling device is in a forward state, the control device may bring the forward clutch into the connected state and the reverse clutch into the disengaged state, and when the shift command is acquired, increase or decrease the output of the transmission in accordance with the shift command, and when the neutral command is acquired, stop the output from the transmission to the forward clutch and the reverse clutch, and then maintain the connected state of the forward clutch and bring the reverse clutch into the connected state.

[0012] In one aspect of the present invention, when the traveling device is in a reverse state, the control device may bring the reverse clutch into the connected state and the forward clutch into the disengaged state, and when the shift command is acquired, increase or decrease the output of the transmission in accordance with the shift command, and when the neutral command is acquired, stop the output from the transmission to the forward clutch and the reverse clutch, and then maintain the connected state of the reverse clutch and bring the forward clutch into the connected state.

[0013] In one aspect of the present invention, when the control device acquires the forward command while the forward clutch and the reverse clutch are each in the connected state in response to the neutral command, the control device may maintain the connected state of the forward clutch and put the reverse clutch in the disengaged state.

[0014] In one aspect of the present invention, the control device may increase the output of the transmission after disengaging the reverse clutch in response to the forward command.

[0015] In one aspect of the present invention, the work vehicle is equipped with a reverse pressure sensor that detects the reverse clutch pressure acting on the reverse clutch, and the control device reduces the reverse clutch pressure in response to the forward command, and increases the output of the transmission in response to the shift command after the detection value of the reverse clutch pressure detected by the reverse pressure sensor falls below a predetermined value corresponding to the disengaged state of the reverse clutch.

[0016] In one aspect of the present invention, when the control device acquires the reverse command while the forward clutch and the reverse clutch are each in the connected state in response to the neutral command, the control device may maintain the connected state of the reverse clutch and put the forward clutch in the disengaged state.

[0017] In one aspect of the present invention, the control device may increase the output of the transmission after disengaging the forward clutch in response to the reverse command.

[0018] In one aspect of the present invention, the work vehicle is equipped with a forward pressure sensor that detects forward clutch pressure, which is the hydraulic pressure acting on the forward clutch, and the control device reduces the forward clutch pressure in response to the reverse command, and after the detection value of the forward clutch pressure detected by the forward pressure sensor falls below a predetermined value corresponding to the disengaged state of the forward clutch, the control device may increase the output of the transmission in response to the shift command.

[0019] In one aspect of the present invention, the transmission includes a continuously variable transmission having a variable displacement traveling hydraulic pump driven by the output of the prime mover and a traveling hydraulic motor driven by the output of the traveling hydraulic pump, and the work vehicle is equipped with a swash plate angle sensor that detects the angle of a swash plate of the traveling hydraulic pump, and the control device may increase or decrease the output of the transmission by changing the angle of the swash plate in response to the shift command, and stop the output from the transmission to the forward clutch and the reverse clutch by setting the angle of the swash plate to a predetermined angle in response to the neutral command.

[0020] In one aspect of the present invention, the work vehicle is equipped with a forward switching valve that can be switched between a supply position that supplies hydraulic oil to the forward clutch and a discharge position that discharges hydraulic oil from the forward clutch, and a reverse switching valve that can be switched between a supply position that supplies hydraulic oil to the reverse clutch and a discharge position that discharges hydraulic oil from the reverse clutch, and the control device may switch the forward switching valve and the reverse switching valve to the supply position, respectively, to increase the forward clutch pressure and the reverse clutch pressure, thereby bringing the forward clutch and the reverse clutch into the connected state, and may switch the forward switching valve and the reverse switching valve to the discharge position, respectively, to decrease the forward clutch pressure and the reverse clutch pressure, thereby bringing the forward clutch and the reverse clutch into the disengaged state.

[0021] In one aspect of the present invention, the work vehicle is equipped with a forward control valve that applies hydraulic pressure to a pressure receiving portion of the forward switching valve, and a reverse control valve that applies hydraulic pressure to a pressure receiving portion of the reverse switching valve, and the control device may input control signals to the forward control valve and the reverse control valve, respectively, and change the hydraulic pressure that is applied from the forward control valve and the reverse control valve to the corresponding pressure receiving portion of the forward switching valve and the pressure receiving portion of the reverse switching valve, thereby switching the positions of the forward switching valve and the reverse switching valve, respectively.

[0022] According to the present invention, it is possible to improve the driving performance of a work vehicle equipped with a plurality of clutches that switch between forward and reverse drive.

[0023] FIG. 1 is a diagram showing an example of a power transmission configuration of a work vehicle. FIG. 2 is a block diagram showing an example of a control configuration of a work vehicle. FIG. 3 is a diagram showing an example of a clutch control configuration of a work vehicle. FIG. 4 is a flowchart showing an example of the operation of a work vehicle. FIG. 5 is a state transition diagram of a work vehicle. FIG. 6 is a time chart showing an example of forward / reverse operation of a work vehicle and changes in clutch pressure and swash plate angle. FIG. 7 is a side view of an example of a work vehicle.

[0024] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0025] 7 is a side view of an example of the work vehicle 1. In this embodiment, a tractor is used as an example of the work vehicle 1, but the work vehicle 1 is not limited to a tractor and may be, for example, an agricultural machine such as a rice transplanter, a civil engineering machine such as an excavator, or a construction machine.

[0026] The work vehicle 1 is equipped with a traveling device 7 for traveling the vehicle body 3, a prime mover 4, a transmission 5, a steering device 29, etc. The traveling device 7 includes front wheels 7F, rear wheels 7R, axles, a differential, etc. The front wheels 7F may be of either a tire type or a crawler type. The rear wheels 7R may also be of either a tire type or a crawler type. The prime mover 4 is mounted on the front of the vehicle body 3. The prime mover 4 is an internal combustion engine such as a gasoline engine or a diesel engine mounted on the vehicle body 3. In this embodiment, the prime mover 4 is a diesel engine.

[0027] A cabin 9 is provided in the center of the vehicle body 3. A driver's seat 10 is provided inside the cabin 9. A lifting device 8 is provided in the rear of the vehicle body 3. A work device 2 can be attached and detached to the lifting device 8. The lifting device 8 can raise and lower the attached work device 2. The work device 2 is a tilling device for tilling, a fertilizer spreading device for spreading fertilizer, a pesticide spreading device for spreading pesticide, a harvesting device for harvesting, a reaping device for reaping grass or the like, a spreading device for spreading grass or the like, a grass collecting device for collecting grass or the like, a shaping device for shaping grass or the like, etc.

[0028] The transmission 5 changes the speed of the output of the prime mover 4 to switch the propulsion force of the traveling device 7. More specifically, the transmission 5 changes the torque and rotational speed of the rotational driving force of the prime mover 4, and the rotational driving force after the speed change is transmitted to the traveling device 7, thereby switching the propulsion force of the traveling device 7 between forward and reverse.

[0029] 1 is a diagram showing an example of a power transmission configuration of a work vehicle 1. The transmission 5 is provided with a continuously variable transmission 50, a planetary gear mechanism 60, and an auxiliary transmission 53. In other words, the transmission 5 includes a hydromechanical continuously variable transmission (HMT) that combines the continuously variable transmission 50 and the planetary gear mechanism 60 as a main transmission that performs main speed changes for the work vehicle 1. The continuously variable transmission 50 is a hydrostatic continuously variable transmission (HST) that continuously changes the speed of the output from the prime mover 4. Hereinafter, the continuously variable transmission 50 will be referred to as the "HST 50."

[0030] The output shaft (crankshaft) 4a of the prime mover 4 is connected to a main shaft (propeller shaft) 54. The rotational force of the output shaft (crankshaft) 4a of the prime mover 4 is transmitted to the main shaft (propeller shaft) 54 via a clutch or the like. A drive gear 59 is provided on the main shaft (propeller shaft) 54. The drive gear 59 rotates in conjunction with the rotation of the main shaft (propeller shaft) 54. A first gear 59a and a second gear 59b are meshed with the drive gear 59. The first gear 59a is provided on an input shaft 56a of the HST 50. The second gear 59b is provided on an output shaft 59c. An input gear 62 of a planetary gear mechanism 60 is provided on the output side end of the output shaft 59c (i.e., the end opposite the end of the output shaft 59c where the second gear 59b is located).

[0031] The HST 50 changes the torque and rotational speed of the power input from the output shaft (crankshaft) 4a of the prime mover 4 via the main shaft (propeller shaft) 54, drive gear 59, and first gear 59a. The HST 50 has a travel hydraulic pump P1 and a travel hydraulic motor M1. The travel hydraulic pump P1 and the travel hydraulic motor M1 are connected by an oil passage (circulation oil passage) 55 (FIG. 2) through which hydraulic oil flows.

[0032] The travel hydraulic pump P1 is a variable displacement pump driven by the output of the prime mover 4, and has an input shaft 56a and a swash plate 56b. The input shaft 56a is connected to a first gear 59a to which the output of the prime mover 4 is transmitted. In other words, the power of the main shaft (propeller shaft) 54 is transmitted to the input shaft 56a of the travel hydraulic pump P1 via the drive gear 59 and the first gear 59a. By transmitting the output of the prime mover 4 to the input shaft 56a in this way, the travel hydraulic pump P1 is driven and hydraulic oil is discharged into the oil passage 55.

[0033] The swash plate 56b is provided on the travel hydraulic pump P1 so as to be able to swing freely. By changing the angle of the swash plate 56b (swash plate angle), the output of the travel hydraulic pump P1 (the discharge amount (flow rate) and pressure of hydraulic oil) is changed. The travel hydraulic motor M1 is driven by the output of the travel hydraulic pump P1. The travel hydraulic motor M1 has an output shaft 58. The rotation speed of the output shaft 58 changes depending on the output of the travel hydraulic pump P1 (the flow rate and pressure of hydraulic oil). In other words, the power after the speed change by the HST 50 is output to the output shaft 58.

[0034] The planetary gear mechanism 60 combines the rotational driving force of the output shaft 58 with the rotational driving force of the output shaft 59c that rotates in accordance with the output of the prime mover 4. That is, the planetary gear mechanism 60 combines the output of the prime mover 4 with the output of the traveling hydraulic motor M1 (HST 50). In other words, the planetary gear mechanism 60 combines the power from the prime mover 4 with the power whose speed has been changed by the HST 50. The output of the planetary gear mechanism 60 (combined driving force) is transmitted to the traveling device 7 via the forward / reverse clutch device 52, the auxiliary transmission device 53, etc.

[0035] The planetary gear mechanism 60 includes an input gear 62, a ring gear (internal gear) 63d, a sun gear 63b, planetary gears 63c, and a carrier 63a. The input gear 62 is provided at the output end of the output shaft 59c to which the output of the prime mover 4 is transmitted. The sun gear 63b is disposed at the center of the circular front surface of the ring gear 63d. The sun gear 63b is connected to the output shaft 58 of the traveling hydraulic motor M1 and is rotatable coaxially with the rotational axis of the ring gear 63d. At least one planetary gear 63c is rotatably disposed between the sun gear 63b and the ring gear 63d. The planetary gear 63c is in mesh with the sun gear 63b and the ring gear 63d.

[0036] The carrier 63a is disposed so as to be rotatable about the same axis as the rotation axis of the ring gear 63d. The carrier 63a supports the planetary gear 63c so as to be movable in the circumferential direction of the ring gear 63d. Because the carrier 63a and the input gear 62 are meshed, the output of the prime mover 4 is transmitted to the carrier 63a. A composite output shaft 64 is provided on the rear surface of the ring gear 63d (the surface opposite to the front surface on which the carrier 63a is located). The composite output shaft 64 is the rotation axis of the ring gear 63d.

[0037] The planetary gear mechanism 60 combines the power transmitted to the sun gear 63b (i.e., the rotational driving force that is the output after speed change by the HST 50) and the power transmitted to the planetary gear 63c via the carrier 63a (i.e., the rotational driving force that is the output of the prime mover 4 that has not been subjected to the speed change action by the HST 50), and outputs the combined driving force to a combined output shaft 64. The HST 50 and planetary gear mechanism 60 described above make it possible to output a combined driving force from a low speed region to a high speed region to the combined output shaft 64.

[0038] A forward / reverse clutch device 52 is provided on the output side of the planetary gear mechanism 60. An input shaft 62f of the forward / reverse clutch device 52 rotates integrally with the composite output shaft 64. The forward / reverse clutch device 52 is a device that integrates a forward clutch 75 and a reverse clutch 76, and switches the travel device 7 (i.e., the vehicle body 3, the work vehicle 1) between forward, reverse, and stopped states. A housing 77 of the forward / reverse clutch device 52 can rotate integrally with the input shaft 62f. The forward clutch 75 and reverse clutch 76 are hydraulic clutches that are switched between an engaged state and a disengaged state by the hydraulic pressure of the hydraulic oil that flows into the housing 77.

[0039] The forward clutch 75 can be switched between an engaged state in which power for moving the traveling device 7 forward is transmitted to the traveling device 7 and a disengaged state in which power is not transmitted. The forward clutch 75 is configured in a first region in the left half of the housing 77 in FIG. 1 . The forward clutch 75 has a housing plate 75a, a cylindrical shaft 75b, a friction plate 75c, and a pressing member 75d. A plurality of housing plates 75a are provided on the inner circumferential surface of the first region of the housing 77. A plurality of friction plates 75c are provided on the outer circumferential surface of the cylindrical shaft 75b. The housing plates 75a and the friction plates 75c are arranged alternately facing each other. The pressing member 75d is configured by a hydraulic cylinder. The tip of the rod of the pressing member 75d is fixed to the friction plate 75c. The pressing member 75d and the friction plate 75c are biased in a direction away from the housing plate 75a by a spring or the like.

[0040] An oil supply / discharge passage 75e is connected to the first region of the housing 77. The oil supply / discharge passage 75e supplies and discharges hydraulic oil to and from the pressing member 75d located inside the first region of the housing 77. After hydraulic oil is supplied through the oil supply / discharge passage 75e and filled inside the pressing member 75d, the forward clutch pressure, which is the oil pressure of the hydraulic oil, increases, causing the pressing member 75d to extend against the elastic force of the spring and press the friction plate 75c. This causes the friction plate 75c to move and come into pressure contact with the housing plate 75a, bringing the forward clutch 75 into an engaged state (connected state).

[0041] Furthermore, when the forward clutch pressure increases and saturates near the first clutch pressure, the friction plate 75c presses against the housing plate 75a with a predetermined first contact pressure, the friction plate 75c and the housing plate 75a become substantially integrated, and the forward clutch 75 enters a fully engaged state (full clutch state). When the forward clutch 75 enters the engaged state, the combined driving force output from the planetary gear mechanism 60 to the combined output shaft 64 is transmitted to the cylindrical shaft 75b via the input shaft 62f and the housing 77, and the combined driving force enables the cylindrical shaft 75b to rotate.

[0042] Furthermore, when the forward clutch pressure rises to a predetermined second clutch pressure that is lower than the first clutch pressure, the friction plate 75c comes into contact with the housing plate 75a at a predetermined second contact pressure that is lower than the first contact pressure, and the friction plate 75c becomes rotatable in unison with the housing 77 and the housing plate 75a. This places the forward clutch 75 in a half-engaged state (half-clutch state). Furthermore, when the forward clutch pressure rises to a predetermined third clutch pressure that is lower than the second clutch pressure, the friction plate 75c begins to come into contact with the housing plate 75a at a predetermined third contact pressure that is lower than the second contact pressure. This places the forward clutch 75 in an initially engaged state (clutch on-going state).

[0043] When hydraulic oil is not supplied to the inside of the pressing member 75d through the oil supply / discharge passage 75e, the pressing member 75d contracts due to the elastic force of the spring and no longer presses the friction plate 75c. As a result, the hydraulic oil inside the pressing member 75d is discharged into the oil supply / discharge passage 75e, i.e., the hydraulic oil is released from the inside of the forward clutch 75, and the forward clutch pressure decreases. Also, the friction plate 75c moves due to the elastic force of the spring and separates from the housing plate 75a, and the forward clutch 75 enters a disengaged state (disconnected state). When the forward clutch 75 enters a disengaged state, the combined driving force output from the planetary gear mechanism 60 to the combined output shaft 64 is no longer transmitted to the housing 77 and the cylindrical shaft 75b via the input shaft 62f, and the cylindrical shaft 76b does not rotate due to the combined driving force.

[0044] The reverse clutch 76 can be switched between an engaged state in which power for moving the traveling device 7 backward is transmitted to the traveling device 7 and a disengaged state in which power is not transmitted to the traveling device 7. The reverse clutch 76 is configured in a second region, which is the right half of the housing 77 in FIG. 1. The reverse clutch 76 has a housing plate 76a, a cylindrical shaft 76b, a friction plate 76c, and a pressing member 76d. The configuration of each part of the reverse clutch 76 is the same as the configuration of each part of the forward clutch 75, so a description thereof will be omitted.

[0045] A supply / discharge oil passage 76e is connected to the second region of the housing 77. The supply / discharge oil passage 76e supplies and discharges hydraulic oil to and from the pressing member 76d located inside the second region of the housing 77. The configuration of the reverse clutch 76 and other components when hydraulic oil is supplied to or discharged from the inside of the pressing member 76d through the supply / discharge oil passage 76e is the same as the configuration of the forward clutch 75 and other components when hydraulic oil is supplied to or discharged through the supply / discharge oil passage 75e, and therefore a description thereof will be omitted. The hydraulic pressure of the hydraulic oil acting on the forward clutch 75 is called the "forward clutch pressure," while the hydraulic pressure of the hydraulic oil acting on the reverse clutch 76 is called the "reverse clutch pressure."

[0046] A forward transmission mechanism 81 is provided on the output side of the forward clutch 75. The forward transmission mechanism 81 converts the power (composite driving force) input from the planetary gear mechanism 60 (transmission device 5) via the forward clutch 75 into a propulsive force that moves the traveling device 7 forward, and transmits the propulsive force to the traveling device 7 via the transmission shaft 66 and the auxiliary transmission device 53. The forward transmission mechanism 81 includes the transmission shaft 66 and a gear 81a provided on the transmission shaft 66. The gear 81a meshes with a gear 78. The gear 78 is provided on the output side end of the cylindrical shaft 75b of the forward clutch 75, and rotates integrally with the cylindrical shaft 75b.

[0047] When the forward clutch 75 is engaged and the composite driving force output from the planetary gear mechanism 60 to the composite output shaft 64 is transmitted to the cylindrical shaft 75b via the input shaft 62f and the housing 77, the cylindrical shaft 75b and the gear 78 rotate, and the gear 81a and the transmission shaft 66 rotate in the forward direction corresponding to the forward movement of the traveling device 7. As a result, the propulsive force (power) for moving the traveling device 7 forward is transmitted to the transmission shaft 66.

[0048] A reverse transmission mechanism 82 is provided on the output side of the reverse clutch 76. The reverse transmission mechanism 82 converts the power (composite driving force) input from the planetary gear mechanism 60 via the reverse clutch 76 into propulsion force for moving the traveling device 7 backward, and transmits the propulsion force to the traveling device 7 via the transmission shaft 66 and the auxiliary transmission device 53. The reverse transmission mechanism 82 includes the transmission shaft 66, a gear 82a provided on the transmission shaft 66, and a reverse gear 82b that meshes with the gear 82a. The reverse gear 82b meshes with a gear 79. The gear 79 is provided on the output side end of the cylindrical shaft 76b of the reverse clutch 76, and rotates integrally with the cylindrical shaft 76b.

[0049] When the reverse clutch 76 is engaged and the combined driving force output from the planetary gear mechanism 60 to the combined output shaft 64 is transmitted to the cylindrical shaft 76b via the input shaft 62f and the housing 77, the cylindrical shaft 76b and the gear 79 rotate, and the rotational force is transmitted to the gear 82a via the reverse gear 82b, causing the gear 82a and the transmission shaft 66 to rotate in the reverse direction corresponding to the reverse movement of the traveling device 7. As a result, the propulsive force (power) for moving the traveling device 7 backward is transmitted to the transmission shaft 66.

[0050] An auxiliary transmission 53 is provided on the output side of the transmission shaft 66. The auxiliary transmission 53 includes a speed change unit 95 and a transmission gear linked thereto. The speed change unit 95 is provided between a first countershaft 91 connected to the transmission shaft 66 and a rear wheel drive shaft 93. The speed change unit 95 is switchable between a high speed range, a normal high speed range, a normal low speed range, and a neutral state by an auxiliary speed change operating member 96 and a mechanical operation transmission mechanism that transmits the operating force of the auxiliary speed change operating member 96. Of these, the vehicle speed of the work vehicle 1 increases in the order of high speed range, normal high speed range, and normal low speed range.

[0051] For example, when the auxiliary transmission operating member 96 is operated to the high-speed position, the transmission unit 95 is switched to the high-speed position by the mechanical operation transmission mechanism, and the power transmitted from the transmission shaft 66 to the first countershaft 91 is shifted to the high-speed range by the transmission unit 95, and the power after the shift is output to the rear-wheel drive shaft 93. When the auxiliary transmission operating member 96 is operated to the high-speed position, the transmission unit 95 is switched to the normal high-speed position by the mechanical operation transmission mechanism, and the power transmitted from the transmission shaft 66 to the first countershaft 91 is shifted to the high-speed range by the transmission unit 95, and the power after the shift is output to the rear-wheel drive shaft 93. When the auxiliary transmission operating member 96 is operated to the low-speed position, the transmission unit 95 is switched to the normal low-speed position by the mechanical operation transmission mechanism, and the power transmitted from the transmission shaft 66 to the first countershaft 91 is shifted to the low-speed range by the transmission unit 95, and the power after the shift is output to the rear-wheel drive shaft 93.

[0052] Neutral positions are provided between the high-speed position and the high-speed position, and between the high-speed position and the low-speed position, as positions at which the auxiliary transmission operating member 96 can be operated. When the auxiliary transmission operating member 96 is operated to the neutral position, the transmission unit 95 is switched to a neutral state by the mechanical operation transmission mechanism, and the power transmitted from the transmission shaft 66 to the first countershaft 91 is not changed in speed by the transmission unit 95, nor is it output to the rear-wheel drive shaft 93.

[0053] The rear wheel drive shaft 93 is included in the traveling device 7. The traveling device 7 is provided on the output side of the auxiliary transmission 53. In addition to the rear wheel drive shaft 93, rear wheels 7R, and front wheels 7F, the traveling device 7 also includes a rear wheel differential 100, rear axles 99, gears 98a, 98b, a drive conversion clutch 102, a front wheel drive shaft 103, a front wheel differential 106, and a front axle 105.

[0054] The power changed in speed by the auxiliary transmission 53 is output to a rear wheel drive shaft 93. The rear wheel drive shaft 93 is connected to a rear wheel differential 100. A rear axle 99 that rotatably supports the rear wheel 7R is also connected to the rear wheel differential 100. Forward thrust is transmitted from the transmission shaft 66 to the rear wheel 7R via the auxiliary transmission 53, the rear wheel drive shaft 93, the rear wheel differential 100, and the rear axle 99. In addition, the forward thrust is transmitted from the rear wheel drive shaft 93 to a front wheel transmission shaft 101 via gears 98a and 98b.

[0055] A drive conversion clutch 102 is provided on the front wheel transmission shaft 101. A front wheel drive shaft 103 is connected to the output side of the drive conversion clutch 102. The front wheel drive shaft 103 is connected to a front wheel differential 106. The front axle 105 is also connected to the front wheel differential 106. The forward thrust transmitted to the front wheel transmission shaft 101 is transmitted to the front wheels 7F via the drive conversion clutch 102, front wheel drive shaft 103, front wheel differential 106, and front axle 105. The forward thrust causes the front wheels 7F and rear wheels 7R to rotate, causing the body 3 (work vehicle 1) to move forward.

[0056] Similar to the forward thrust described above, the reverse thrust is transmitted from the transmission shaft 66 to the rear wheel 7R via the auxiliary transmission 53, the rear drive shaft 93, the rear differential 100, and the rear axle 99. The reverse thrust is also transmitted from the rear drive shaft 93 to the front wheel 7F via gears 98a, 98b, the front drive shaft 101, the drive conversion clutch 102, the front drive shaft 103, the front differential 106, and the front axle 105. The reverse thrust rotates the front wheels 7F and the rear wheels 7R, causing the vehicle body 3 to move backward.

[0057] In addition, by switching between the connected and disconnected states of the drive conversion clutch 102, the vehicle can be switched between a constant speed drive state in which the front wheels 7F and rear wheels 7R rotate at a constant speed, a four-wheel drive state (4WD) in which both the front wheels 7F and rear wheels 7R are driven, and a two-wheel drive state (2WD) in which only the rear wheels 7R are driven.

[0058] A PTO clutch device 110 is provided on the output shaft 56c of the traveling hydraulic pump P1. The PTO clutch device 110 is configured, for example, with a hydraulic clutch. When the hydraulic clutch of the PTO clutch device 110 is engaged, the rotational drive force of the main shaft 54 ​​is transmitted to the PTO propulsion shaft 111. When the hydraulic clutch of the PTO clutch device 110 is disengaged, the rotational drive force of the main shaft 54 ​​is not transmitted to the PTO propulsion shaft 111.

[0059] A PTO transmission 112 is provided midway along the PTO propulsion shaft 111. The PTO transmission 112 changes the speed of the rotational driving force of the PTO propulsion shaft 111, thereby also changing the speed of the rotational driving force of the PTO shaft 16, which is connected to the PTO propulsion shaft 111 via a gear. In other words, the PTO transmission 112 changes the rotational speed and torque of the PTO propulsion shaft 111 and the PTO shaft 16.

[0060] The work vehicle 1 is equipped with a braking device 140. The braking device 140 brakes the traveling device 7. The braking device 140 has a brake operating member 141, a left braking device 142F, and a right braking device 142R. The brake operating member 141 is a member that performs braking operations and is manually operated by the driver of the work vehicle 1. The brake operating member 141 includes a left brake pedal 141F and a right brake pedal 141R. The left brake pedal 141F and the right brake pedal 141R are provided near the driver's seat 10 so as to be able to swing freely, and are operated by the driver of the work vehicle 1 seated in the driver's seat 10. The left braking device 142F and the right braking device 142R are disc-type braking devices that can be switched between a braking state and a braking-released state.

[0061] When the left brake pedal 141F and the right brake pedal 141R are not operated, the left connecting member 143F and the right connecting member 143R are in their normal positions, and the left braking device 142F and the right braking device 142R do not brake the corresponding rear wheel 7R (braking released state). When the driver operates the left brake pedal 141F, the left connecting member 143F moves in the braking direction, and the left braking device 142F brakes the left rear wheel 7R. When the driver operates the right brake pedal 141R, the right connecting member 143R moves in the braking direction, and the right braking device 142R brakes the right rear wheel 7R.

[0062] The left brake pedal 141F and the right brake pedal 141R are connected by a connecting member, so that when the driver operates either the left brake pedal 141F or the right brake pedal 141R, the left and right rear wheels 7R can be braked simultaneously by the left braking device 142F and the right braking device 142R, respectively.

[0063] The brake operating member 141 also includes a parking lever 144. The parking lever 144 is provided, for example, near the left brake pedal 141F and the right brake pedal 141R so that it can swing freely. When the driver operates the parking lever 144, the left brake pedal 141F and the right brake pedal 141R are locked by a link mechanism so that they cannot be operated, and the left braking device 142F and the right braking device 142R are placed in a parking brake state in which they brake the rear wheel 7R.

[0064] 2 is a block diagram showing an example of the control configuration of the work vehicle 1. The work vehicle 1 is equipped with a control device 120, a storage device 121, a communication interface 122, and a steering device 29. The control device 120 (controller) is made up of a CPU, internal memory, electric and electronic circuits, etc. The internal memory of the control device 120 is made up of volatile memory and non-volatile memory. The internal memory of the control device 120 stores software programs and data, etc., used by the CPU to control each part of the work vehicle 1. The control device 120 is a controller that controls each part of the work vehicle 1.

[0065] The storage device 121 is composed of non-volatile memory. Data and the like used by the control device 120 to control each part of the work vehicle 1 is also stored in the storage device 121. The control device 120 stores data and the like used to control each part of the work vehicle 1 in at least one of its internal memory and the storage device 121. The communication interface 122 is composed of an antenna, a communication circuit, and the like that wirelessly communicates with an information processing device and the like outside the work vehicle 1.

[0066] The steering device 29 has a steering wheel 30, a steering shaft 31, and an assist mechanism (power steering mechanism) 32. The steering shaft 31 rotates in accordance with the rotation of the steering wheel 30. The assist mechanism 32 assists in steering by the steering wheel 30. The assist mechanism 32 has a control valve 34 and a steering cylinder 35. The control valve 34 is an electromagnetic valve that can be switched to multiple positions. The hydraulic pump P2 is a pump different from the traveling hydraulic pump P1, and draws hydraulic oil from a tank mounted on the work vehicle 1 and discharges it to a discharge oil passage 131. The control valve 34 is supplied with hydraulic oil from the discharge oil passage 131. The steering cylinder 35 extends and contracts to the left or right of the vehicle body 3 depending on the switching position and opening degree of the control valve 34.

[0067] The control device 120 electrically controls the switching position and opening degree of the control valve 34 to change the hydraulic pressure of the hydraulic oil supplied from the control valve 34 to the steering cylinder 35, thereby extending and retracting the steering cylinder 35 and changing the direction (steering direction) of the front wheels 7F. Furthermore, when the driver of the work vehicle 1 operates the steering wheel 30, the steering shaft 31 rotates in accordance with the operating state, and the position and opening degree of the control valve 34 are switched. In other words, the switching position and opening degree of the control valve 34 can also be changed by manually operating the steering wheel 30, causing the steering cylinder 35 to extend and retract, changing the steering direction of the front wheels 7F.

[0068] As described above, the work vehicle 1 is capable of automatic steering by the control device 120 and manual steering by manually operating the steering wheel 30. The work vehicle 1 is also capable of running and stopping by operating the transmission 5, braking device 140, etc. in response to manual operation of the accelerator operation device 147 and the brake operation member 141. Furthermore, the work vehicle 1 is also capable of running and stopping automatically by controlling the transmission 5, braking device 140, etc. by the control device 120.

[0069] That is, the work vehicle 1 is capable of manual driving in which the driver performs driving and steering operations, automatic driving in which the control device 120 automatically performs driving and steering, and autosteer driving (also called automatic steering or semi-automatic driving) in which the control device 120 automatically performs steering and the driver manually performs driving operations. The work vehicle 1 is also capable of remote driving in which a remote control signal transmitted from a remote control device is received by the communication interface 122, and the control device 120 automatically drives and steers the vehicle body 3 based on the remote control signal.

[0070] The control device 120 is connected to rotation sensors 146a, 146b, 146c, a vehicle speed sensor 146d, a swash plate angle sensor 146e, and pressure sensors 146f, 146g, 146h. The rotation sensor 146a detects the actual rotation speed of the prime mover 4. The rotation sensor 146b detects the actual rotation speed of the output shaft 58 of the traveling hydraulic motor M1. The rotation sensor 146c detects the actual rotation speed of the combined output shaft 64 of the planetary gear mechanism 60. The vehicle speed sensor 146d detects the actual vehicle speed. The swash plate angle sensor 146e detects the actual angle of the swash plate 56b of the traveling hydraulic pump P1. The pressure sensors 146f, 146g, 146h detect the hydraulic pressure of the hydraulic oil flowing through oil passages provided in the work vehicle 1, as will be described later.

[0071] An accelerator operating device 147 and a forward / reverse operating device 148 are also connected to the control device 120. The accelerator operating device 147 and the forward / reverse operating device 148 are installed near the driver's seat 10 and are operated by the driver. The accelerator operating device 147 is a device for inputting the rotation speed of the prime mover 4 and includes an accelerator operating member 147a and an accelerator sensor 147b. The accelerator operating member 147a is, for example, a pedal-type operating member that can be operated continuously from a neutral position. The accelerator operating member 147a may be another type of operating member, such as a lever-type, dial-type, slider-type, or button-type, and may have an operating position that can be changed in multiple stages. The accelerator sensor 147b detects the operating position of the accelerator operating member 147a.

[0072] When the driver operates accelerator operating member 147a while the prime mover 4 is being driven, accelerator sensor 147b outputs a signal corresponding to the operating position of accelerator operating member 147a to control device 120. Based on the output signal from accelerator sensor 147b, control device 120 calculates the target rotation speed of the prime mover 4 corresponding to the operating position of accelerator operating member 147a. That is, control device 120 obtains the target rotation speed of the prime mover 4 from accelerator operating device 147. Then, control device 120 controls the drive of prime mover 4 so that the actual rotation speed of the prime mover 4 detected by rotation sensor 146a matches the target rotation speed.

[0073] The forward / reverse operation device 148 is an input device for inputting a forward command, a reverse command, a neutral command, and a gear change command. The forward command is a command to move the traveling device 7 forward. The reverse command is a command to move the traveling device 7 backward. The neutral command is a command to move the traveling device 7 neither forward nor backward, and is also called a stop command or a neutral traveling command. The gear change command is a command to change gears using the HST 50. The forward / reverse operation device 148 has a forward / reverse operation member 148a and a forward / reverse sensor 148b. The forward / reverse operation member 148a is, for example, a pedal-type operation member that can be operated to a forward position Fp, a neutral position Np, and a reverse position Rp. Note that the forward / reverse operation member 148a may be another type of operation member, such as a lever-type, a dial-type, a slider-type, or a button-type.

[0074] The forward / reverse operation member 148a has a forward position Fp in one direction relative to the neutral position Np, and a reverse position Rp in the opposite direction. Therefore, the forward / reverse operation member 148a passes through the neutral position Np when operated from the forward position Fp to the reverse position Rp, or when operated from the reverse position Rp to the forward position Fp. The forward / reverse sensor 148b detects the operating position of the forward / reverse operation member 148a.

[0075] When the driver operates the forward / reverse operation member 148a to any one of the forward position Fp, reverse position Rp, and neutral position Np while the prime mover 4 is running, the forward / reverse sensor 148b outputs a signal corresponding to the operating position of the forward / reverse operation member 148a to the control device 120. The control device 120 acquires an instruction corresponding to the operating position of the forward / reverse operation member 148a from among a forward instruction, a reverse instruction, a neutral instruction, and a gear change instruction based on the output signal from the forward / reverse sensor 148b. That is, the control device 120 acquires the forward instruction, the reverse instruction, the neutral instruction, and the gear change instruction from the forward / reverse operation device 148, respectively.

[0076] Specifically, when the forward / reverse operation member 148a is operated to the neutral position Np, the control device 120 obtains a neutral command based on the output signal from the forward / reverse sensor 148b. Furthermore, when the forward / reverse operation member 148a is operated to the forward position Fp, the control device 120 obtains a forward command based on the output signal from the forward / reverse sensor 148b. Furthermore, when the forward / reverse operation member 148a is operated to the reverse position Rp, the control device 120 obtains a reverse command based on the output signal from the forward / reverse sensor 148b. Furthermore, when the forward / reverse operation member 148a is operated to both the forward position Fp and the reverse position Rp, the control device 120 obtains a gear shift command (main gear shift command) corresponding to the operating position of the forward / reverse operation member 148a based on the output signal from the forward / reverse sensor 148b. In detail, the control device 120 calculates the target gear ratio between the input and output of the HST 50, the target vehicle speed of the work vehicle 1, and the target angle of the swash plate 56b of the travel hydraulic pump P1 based on the output signal from the forward / reverse sensor 148b, and sets these calculated values ​​as gear change instructions.

[0077] A swash plate control valve 126 is connected to the control device 120. The swash plate control valve 126 is an electromagnetic valve. A discharge oil passage 131 through which hydraulic oil is discharged from the hydraulic pump P2 and a discharge oil passage 132 through which the hydraulic oil is discharged are connected to the swash plate control valve 126. The swash plate control valve 126 and the servo cylinder 125 are connected by an oil passage 127. The servo cylinder 125 expands and contracts in response to the hydraulic oil (pilot oil) supplied from the oil passage 127, thereby oscillating the swash plate 56b of the travel hydraulic pump P1.

[0078] More specifically, the control device 120 energizes a solenoid of the swash plate control valve 126 by passing a current through the solenoid, thereby changing the opening degree of the swash plate control valve 126. For example, as the control device 120 increases the current that energizes the solenoid of the swash plate control valve 126, the opening degree of the swash plate control valve 126 increases. Also, for example, when the control device 120 does not pass a current through the solenoid of the swash plate control valve 126, the solenoid is deenergized, and the swash plate control valve 126 is in a closed state (fully closed state).

[0079] The control device 120 changes the magnitude of the current flowing through the solenoid of the swash plate control valve 126, thereby changing the opening of the swash plate control valve 126, and the servo cylinder 125 operates (expands or contracts) with hydraulic oil supplied from the hydraulic pump P2 via the swash plate control valve 126 and an oil passage 127, thereby changing the angle of the swash plate 56b of the travel hydraulic pump P1. By changing the angle of the swash plate 56b in this way, as described above, the output of the travel hydraulic pump P1 is changed, and the output of the travel hydraulic motor M1, i.e., the outputs of the HST 50 and the transmission 5, are changed.

[0080] When the control device 120 receives a gear shift command while the prime mover 4 is running, it changes the current input to the solenoid of the swash plate control valve 126 to perform feedback control of the angle of the swash plate 56b so that the actual angle of the swash plate 56b detected by the swash plate angle sensor 146e coincides with the target angle included in the gear shift command. That is, the control device 120 controls the HST 50 in accordance with the gear shift command received from the forward / reverse operation device 148, and changes the output of the HST 50 and the vehicle speed, which is the speed of the vehicle body 3.

[0081] The transmission (HMT) 5 is configured so that, for example, when the angle of the swash plate 56b of the traveling hydraulic pump P1 is at its maximum angle, the output (composite driving force) of the planetary gear mechanism 60 is at its maximum, and when the angle of the swash plate 56b is at a predetermined angle, the output of the planetary gear mechanism 60 is zero. Therefore, when the angle of the swash plate 56b is at a predetermined angle, the power transmitted from the HST 50 to the forward / reverse clutch device 52 via the planetary gear mechanism 60 becomes zero, the output of the transmission 5 is stopped (zero state), and the vehicle speed becomes zero, bringing the work vehicle 1 to a halt. In other words, the output of the transmission 5 is stopped when the angle of the swash plate 56b is at a predetermined angle that makes the vehicle speed zero.

[0082] In addition, the control device 120 may control the rotation speed of the traveling hydraulic motor M1 so that the actual vehicle speed matches the target vehicle speed, based on the actual rotation speed of the composite output shaft 64 detected by the rotation sensor 146c, the actual vehicle speed detected by the vehicle speed sensor 146d, the gear shift command from the forward / reverse operation device 148, and the gear shift state of the sub-transmission device 53 (high speed stage, normal high speed stage, normal low speed stage, neutral state).

[0083] A forward control valve 133 and a reverse control valve 134 are connected to the control device 120. The forward control valve 133 and the reverse control valve 134 are each an electromagnetic valve. A discharge oil passage 131 and a discharge oil passage 132 are connected to the forward control valve 133 and the reverse control valve 134, respectively. In addition, an operation oil passage 137 is connected to the forward control valve 133. An operation oil passage 138 is connected to the reverse control valve 134. The forward control valve 133 is a valve for operating the forward clutch 75. The reverse control valve 134 is a valve for operating the reverse clutch 76.

[0084] 3 is a diagram showing an example of a clutch control configuration that controls the forward / reverse clutch device 52 of the work vehicle 1. A discharge oil passage 131 is connected to the input ports of the forward control valve 133 and the reverse control valve 134. A discharge oil passage 132 is connected to the discharge ports of the forward control valve 133 and the reverse control valve 134. One end of an operation oil passage 137 is connected to the output port of the forward control valve 133. The other end of the operation oil passage 137 is connected to the pressure-receiving portion of the forward switchover valve 135. One end of an operation oil passage 138 is connected to the output port of the reverse control valve 134. The other end of the operation oil passage 138 is connected to the pressure-receiving portion of the reverse switchover valve 136. The forward switchover valve 135 is a valve for operating the forward clutch 75. The reverse switchover valve 136 is a valve for operating the reverse clutch 76.

[0085] An oil supply passage 139 is connected to the input ports of the forward selector valve 135 and the reverse selector valve 136, respectively. An oil discharge passage 132 is connected to the discharge ports of the forward selector valve 135 and the reverse selector valve 136, respectively. One end of an oil supply / discharge passage 75e is connected to the output port of the forward selector valve 135. The pressing member 75d of the forward clutch 75 is connected to the other end of the oil supply / discharge passage 75e. A forward pressure sensor 146f is connected to the middle of the oil supply / discharge passage 75e. The forward pressure sensor 146f detects the forward clutch pressure acting on the forward clutch 75.

[0086] One end of a supply / discharge oil passage 76e is connected to the output port of the reverse selector valve 136. The other end of the supply / discharge oil passage 76e is connected to the pressing member 76d of the reverse clutch 76. A reverse pressure sensor 146g is connected to the middle of the supply / discharge oil passage 76e. The reverse pressure sensor 146g detects the reverse clutch pressure acting on the reverse clutch 76.

[0087] The supply oil passage 139 is also connected to the output port of the safety switch valve 152. A safety pressure sensor 146h is also connected to the supply oil passage 139. The safety pressure sensor 146h detects the hydraulic pressure of the working oil acting on the supply oil passage 139. A discharge oil passage 131 is connected to the input port of the safety switch valve 152. A discharge oil passage 132 is connected to the discharge port of the safety switch valve 152. One end of an operation oil passage 153 is connected to the pressure-receiving portion of the safety switch valve 152. The other end of the operation oil passage 153 is connected to the output port of the safety control valve 151. The discharge oil passage 131 is connected to the input port of the safety control valve 151. The discharge oil passage 132 is connected to the discharge port of the safety control valve 151. The safety control valve 151 is a solenoid valve.

[0088] The safety switchover valve 152 is switchable between a supply position 152a where hydraulic oil is supplied to the supply oil passage 139 and a stop position 152b where hydraulic oil is not supplied to the supply oil passage 139. The safety control valve 151 is switchable between an operation position 151a where hydraulic oil is supplied to the operation oil passage 153 and hydraulic pressure is applied to the pressure-receiving portion of the safety switchover valve 152, and a stop position 151b where hydraulic oil is not supplied to the operation oil passage 153 and hydraulic pressure is not applied to the pressure-receiving portion of the safety switchover valve 152. The safety switchover valve 152 and the safety control valve 151 are held at the stop positions 152b and 151b, respectively, by the elastic forces of springs.

[0089] The control device 120 energizes the solenoid of the safety control valve 151 by passing a current through the solenoid, thereby switching the safety control valve 151 to its operating position 151a. As a result, the hydraulic oil discharged from the hydraulic pump P2 to the discharge oil line 131 flows through the safety control valve 151 to the operating oil line 153, and the hydraulic pressure of the hydraulic oil acts on a pressure-receiving portion of the safety switchover valve 152, switching the safety switchover valve 152 to its supply position 152a. Then, the hydraulic oil from the discharge oil line 131 flows through the safety switchover valve 152 to the supply oil line 139.

[0090] When the control device 120 does not apply current to the solenoid of the safety control valve 151, the solenoid is de-energized and the safety control valve 151 is in a stop position 151b. At this time, hydraulic oil in the operation oil passage 153 is discharged to the drain oil passage 132 via the safety control valve 151. Furthermore, because hydraulic pressure of a magnitude sufficient to switch the position of the safety switchover valve 152 does not act on the pressure-receiving portion, the safety switchover valve 152 is also in a stop position 152b. Therefore, hydraulic oil in the supply oil passage 139 is discharged to the drain oil passage 132 via the safety switchover valve 152. The hydraulic oil discharged to the drain oil passage 132 flows to the tank.

[0091] The forward switching valve 135 is switchable between a supply position 135a, which supplies hydraulic oil to the forward clutch 75, and a discharge position 135b, which discharges hydraulic oil from the forward clutch 75. The forward control valve 133 is switchable between an operation position 133a, which supplies hydraulic oil to an operation oil passage 137 and applies hydraulic pressure to a pressure-receiving portion of the forward switching valve 135, and a stop position 133b, which does not supply hydraulic oil to the operation oil passage 137 and does not apply hydraulic pressure to a pressure-receiving portion of the forward switching valve 135. The forward switching valve 135 is held in the discharge position 135b by the elastic force of a spring. The forward control valve 133 is held in the stop position 133b by the elastic force of a spring.

[0092] With the safety control valve 151 switched to the operation position 151a and the safety switchover valve 152 switched to the supply position 152a, the control device 120 energizes the solenoid of the forward control valve 133 by passing a current through the solenoid, thereby switching the forward control valve 133 to the operation position 133a. As a result, hydraulic oil from the discharge oil passage 131 flows through the forward control valve 133 to the operation oil passage 137, and the hydraulic pressure of the hydraulic oil acts on the pressure-receiving portion of the forward switchover valve 135, switching the forward switchover valve 135 to the supply position 135a. Then, the hydraulic oil from the discharge oil passage 131 is supplied to the forward clutch 75 through the forward switchover valve 135 and the supply / discharge oil passage 75e. After hydraulic oil is supplied to the forward clutch 75 and the inside of the pressing member 75d of the forward clutch 75 is filled with hydraulic oil, the forward clutch pressure acting on the forward clutch 75 increases and the forward clutch 75 enters an engaged state.

[0093] The control device 120 changes the magnitude of the current flowing through the solenoid of the forward control valve 133 to change the aperture of the forward control valve 133, which is at the operation position 133a, and changes the magnitude of the hydraulic pressure acting on the pressure-receiving portion of the forward switchover valve 135. This changes the aperture of the forward switchover valve 135, which is at the supply position 135a, and increases or decreases (changes) the forward clutch pressure acting on the forward clutch 75. Also, the engagement state of the forward clutch 75, i.e., the contact pressure between the housing plate 75a and the friction plate 75c, is changed.

[0094] When the control device 120 does not apply current to the solenoid of the forward control valve 133, the solenoid is de-energized, and the forward control valve 133 is in the stop position 133b. At this time, hydraulic oil in the operation oil passage 137 is discharged to the drain oil passage 132 via the forward control valve 133. Also, because hydraulic pressure large enough to switch the position of the forward switchover valve 135 does not act on the pressure-receiving portion, the forward switchover valve 135 is in the drain position 135b. As a result, the forward clutch pressure acting on the forward clutch 75 is reduced, and hydraulic oil is discharged from the forward clutch 75 to the drain oil passage 132 via the supply / drain oil passage 75e and the forward switchover valve 135, so that the forward clutch 75 is in the disengaged state. As described above, the control device 120 changes the forward clutch pressure acting on the forward clutch 75 using the forward control valve 133 and the forward switchover valve 135, switching the forward clutch 75 between the engaged state and the disengaged state.

[0095] The reverse selector valve 136 is switchable between a supply position 136a where hydraulic oil is supplied to the reverse clutch 76 via a supply / discharge oil passage 76e, and a discharge position 136b where hydraulic oil is discharged from the reverse clutch 76. The reverse control valve 134 is switchable between an operation position 134a where hydraulic oil is supplied to an operation oil passage 138 and hydraulic pressure is applied to a pressure-receiving portion of the reverse selector valve 136, and a stop position 134b where hydraulic oil is not supplied to the operation oil passage 138 and hydraulic pressure is not applied to the pressure-receiving portion of the reverse selector valve 136.

[0096] The configurations of the reverse control valve 134, the operating oil passage 138, the reverse switch valve 136, the supply / discharge oil passage 76e, and the reverse clutch 76 are similar to the configurations of the forward control valve 133, the operating oil passage 137, the forward switch valve 135, the supply / discharge oil passage 75e, and the forward clutch 75, respectively, and therefore will not be described again. Furthermore, the configuration by which the control device 120 switches the engagement / disengagement state of the reverse clutch 76 is similar to the configuration by which the control device 120 switches the engagement / disengagement state of the forward clutch 75, and therefore will not be described again. The control device 120 changes the reverse clutch pressure acting on the reverse clutch 76 using the reverse control valve 134 and the reverse switch valve 136, and switches the reverse clutch 76 between the engaged state and the disengaged state.

[0097] During operation of the prime mover 4, the control device 120 normally switches the safety control valve 151 to the operating position 151a and switches the safety switch valve 152 to the supply position 152a. If an abnormality occurs in at least one of the forward switch valve 135 and the reverse switch valve 136, such as a sticking problem that prevents the position from being switched, the detected oil pressure detected by at least one of the forward pressure sensor 146f and the reverse pressure sensor 146g, i.e., the oil pressure acting on at least one of the oil supply / discharge passage 75e and the oil supply / discharge passage 76e, will indicate an abnormal value that is not within a predetermined range.

[0098] When the oil pressure detected by at least one of the forward pressure sensor 146f and the reverse pressure sensor 146g indicates an abnormal value, the control device 120 switches the safety control valve 151 to stop position 151b and also switches the safety switchover valve 152 to stop position 152b, so that hydraulic oil is not supplied to the forward switchover valve 135 and the reverse switchover valve 136. As a result, if an abnormality occurs in at least one of the forward switchover valve 135 and the reverse switchover valve 136, the forward clutch pressure and the reverse clutch pressure do not increase, the forward clutch 75 and the reverse clutch 76 are maintained in a disengaged state, and it is possible to prevent the traveling condition of the traveling device 7 and the work vehicle 1 from becoming abnormal.

[0099] If an abnormality such as poor sticking occurs in the safety switch valve 152, the oil pressure detected by the safety pressure sensor 146h, i.e., the oil pressure acting on the oil supply line 139, will indicate an abnormal value. Even when the oil pressure detected by the safety pressure sensor 146h indicates an abnormal value, the control device 120 switches the safety switch valve 152 to the stop position 152b using the safety control valve 151, and does not supply hydraulic oil to the forward switch valve 135 and the reverse switch valve 136.

[0100] While the prime mover 4 is being driven, the control device 120 acquires a forward command, a reverse command, a neutral command, and a gear change command from the forward / reverse operation device 148, and controls the forward clutch 75 and the reverse clutch 76 using the control valves 133, 134 and the change-over valves 135, 136 in accordance with the acquired commands, while also controlling the transmission 5. For example, when the control device 120 acquires a neutral command from the forward / reverse operation device 148, the control device 120 increases the forward clutch pressure and the reverse clutch pressure using the control valves 133, 134 and the change-over valves 135, 136, bringing the forward clutch 75 and the reverse clutch 76 into an engaged state.

[0101] Furthermore, when the control device 120 receives a forward command from the forward / reverse operation device 148, it increases the forward clutch pressure using the forward control valve 133 and the forward switchover valve 135 to connect the forward clutch 75, and decreases the reverse clutch pressure using the reverse control valve 134 and the reverse switchover valve 136 to connect the reverse clutch 76. Furthermore, when the control device 120 receives a reverse command from the forward / reverse operation device 148, it increases the reverse clutch pressure using the reverse control valve 134 and the reverse switchover valve 136 to connect the reverse clutch 76, and decreases the forward clutch pressure using the forward control valve 133 and the forward switchover valve 135 to connect the forward clutch 75.

[0102] Furthermore, when the travel device 7 is in either a forward or reverse state and receives a gear change command from the forward / reverse operation device 148, the control device 120 controls the HST 50 of the transmission 5 to change the output of the HST 50 and the transmission 5 and also change the vehicle speed. Furthermore, the control device 120 increases or stops the output of the HST 50 in accordance with the forward command, reverse command, or neutral command received from the forward / reverse operation device 148, respectively.

[0103] Figure 4 is a flowchart showing an example of the operation of the work vehicle 1. Each step in Figure 4 is executed by the control device 120 based on software programs and data stored in the internal memory or the storage device 121. Figure 5 is a state transition diagram of the work vehicle 1. Figure 6 is a time chart showing an example of changes in the operating position of the forward / reverse operation member 148a of the work vehicle 1, the forward clutch pressure, the reverse clutch pressure, and the target angle and actual angle of the swash plate 56b of the travel hydraulic pump P1.

[0104] For example, the prime mover 4 starts with the forward / reverse operation member 148a in the neutral position Np and the angle of the swash plate 56b of the travel hydraulic pump P1 of the HST 50 at a predetermined angle that sets the vehicle speed to zero (T0 in FIG. 5). In this case, the control device 120 receives a neutral command from the forward / reverse operation device 148 to stop forward / reverse movement (YES in S1 in FIG. 4). Then, with the outputs of the HST 50 and the transmission (HMT) 5 stopped (zero) (S2), the control device 120 increases the forward clutch pressure and the reverse clutch pressure using the control valves 133, 134 and the selector valves 135, 136 to connect the forward clutch 75 and the reverse clutch 76 (S3). At this time, the control device 120, for example, connects the forward clutch 75 and the reverse clutch 76 fully (fully engaged state). As a result, the traveling device 7 (i.e., the vehicle body 3 and the work vehicle 1) enters a neutral state (stopped state) in which it neither moves forward nor backward (N state in FIG. 5).

[0105] The control device 120 may also determine that the forward clutch 75 is engaged when the forward clutch pressure detected by the forward pressure sensor 146f rises to a predetermined first clutch pressure. The control device 120 may also determine that the forward clutch 75 is disengaged when the forward clutch pressure detected by the forward pressure sensor 146f falls below a predetermined threshold. The predetermined threshold is set to the forward clutch pressure when the friction plate 75c of the forward clutch 75 separates from the housing plate 75a, i.e., the forward clutch pressure corresponding to the disengaged state of the forward clutch 75.

[0106] Similarly, the control device 120 may determine that the reverse clutch 76 is engaged when the detected value of the reverse clutch pressure detected by the reverse pressure sensor 146g rises to the first clutch pressure. Alternatively, the control device 120 may determine that the reverse clutch 76 is disengaged when the detected value of the reverse clutch pressure falls below a predetermined threshold value (the reverse clutch pressure corresponding to the disengaged state of the reverse clutch 76).

[0107] When the forward / reverse operation member 148a is operated to the forward position Fp (T1 in FIG. 5) while the traveling device 7 is in the neutral state (N state in FIG. 5), the control device 120 acquires a forward command from the forward / reverse operation device 148 (S4: YES in FIG. 4). Note that, in order to move the work vehicle 1 forward, the driver operates the auxiliary transmission operation member 96 to one of the high speed, high speed position, or low speed position, and then operates the forward / reverse operation member 148a to the forward position Fp. This switches the speed change section 95 of the auxiliary transmission 53 to one of the high speed stage, normal high speed stage, or normal low speed stage. The same applies when the forward / reverse operation member 148a, described below, is operated to the forward position Fp or the reverse position Rp.

[0108] When the control device 120 acquires a forward command as described above (S4 in FIG. 4: YES), in response to the forward command, it maintains the forward clutch pressure in an increased state using the forward control valve 133 and the forward switchover valve 135, keeping the forward clutch 75 in an engaged state, and reduces the reverse clutch pressure using the reverse control valve 134 and the reverse switchover valve 136, putting the reverse clutch 76 in a disengaged state (S5 in FIG. 4, during the N→F transition in FIG. 5).

[0109] Then, the control device 120 receives a gear shift command from the forward / reverse operation device 148 (S6 in FIG. 4), and if no other command is received (S7: NO), it confirms that the detection value of the reverse clutch pressure detected by the reverse pressure sensor 146g has fallen below the threshold value (S8 in FIG. 4, T2 in FIG. 5, F state), and then controls the HST 50 in accordance with the gear shift command to start outputting from the transmission 5 (S14 in FIG. 4).

[0110] 4, the control device 120 calculates a target angle of the swash plate 56b corresponding to the operating position of the forward / reverse operation member 148a based on the output signal from the forward / reverse sensor 148b. Then, after proceeding through steps S7 and S8, the control device 120 controls the angle of the swash plate 56b using the swash plate control valve 126 and the servo cylinder 125 in step S14 so that the actual angle of the swash plate 56b detected by the swash plate angle sensor 146e coincides with the target angle, thereby increasing the output of the traveling hydraulic motor M1 (i.e., the output of the HST 50). This increases the output of the transmission 5, and power for moving the traveling device 7 forward is transmitted to the traveling device 7, so that the traveling device 7 and the work vehicle 1 also move forward.

[0111] When the operating position of the forward / reverse operation member 148a is changed while the traveling device 7 is in a forward movement state (state F in FIG. 5), the control device 120 acquires a gear shift command from the forward / reverse movement operation device 148 (YES in S15 in FIG. 4). In this case, since the traveling device 7 is not in a neutral state (NO in S16 in FIG. 4), the control device 120 controls at least one of the HST 50 and the auxiliary transmission 53 in accordance with the acquired gear shift command, and changes (increases or decreases) the output of the transmission 5 (S17 in FIG. 4). This changes (increases or decreases) the vehicle speed of the work vehicle 1 while traveling forward.

[0112] Furthermore, when the forward / reverse operating member 148a is operated to the neutral position Np (T3 in FIG. 5) while the traveling device 7 is in the forward (F) state, the control device 120 receives a neutral command from the forward / reverse operating device 148 (YES in S1 in FIG. 4, time point Q1 in FIG. 6). In this case, the control device 120 stops the output of the transmission 5 in response to the neutral command (S2 in FIG. 4, during the F-to-N transition in FIG. 5). Specifically, in step S2 in FIG. 4, the control device 120 controls the angle of the swash plate 56b using the swash plate control valve 126 and the servo cylinder 125 so that the actual angle of the swash plate 56b detected by the swash plate angle sensor 146e coincides with a predetermined angle that reduces the vehicle speed to zero, thereby stopping the output from the HST 50 and the planetary gear mechanism 60 to the forward clutch 75 and the reverse clutch 76.

[0113] 6 illustrates an example in which the driver operates the forward / reverse operation member 148a from the forward position Fp to the neutral position Np, and then operates the forward / reverse operation member 148a to the neutral position Np. When the forward / reverse operation member 148a is operated from the forward position Fp toward the neutral position Np, the target angle of the swash plate 56b calculated by the control device 120 based on the output signal from the forward / reverse sensor 148b gradually decreases, and the actual angle of the swash plate 56b (the value detected by the swash plate angle sensor 146e), which is controlled to match the target angle, also gradually decreases (before time Q1 in FIG. 6 (state F on the left side of Q1)).

[0114] When the forward / reverse operating member 148a is operated to the neutral position Np (time Q1 in FIG. 6), the control device 120 receives a neutral command from the forward / reverse operating device 148, and in response to the neutral command, changes the target angle of the swash plate 56b to a predetermined angle that reduces the vehicle speed to zero, and then changes the angle of the swash plate 56b to match the target angle. As a result, immediately after time Q1, the actual angle of the swash plate 56b reaches the predetermined angle, and the output of the transmission 5 is stopped.

[0115] The control device 120 determines that the output of the HST 50 has stopped when it confirms, for example, that the actual rotation speed of the output shaft 58 of the traveling hydraulic motor M1, detected by the rotation sensor 146b, has become zero. Alternatively or additionally, the control device 120 determines that the output of the transmission 5 has stopped when it confirms at least one of the following: the angle of the swash plate 56b, detected by the swash plate angle sensor 146e, has become a predetermined angle that makes the vehicle speed zero; or the actual rotation speed of the composite output shaft 64 of the planetary gear mechanism 60, detected by the rotation sensor 146c, has become zero.

[0116] After stopping the output of the transmission 5 (S2 in FIG. 4), the control device 120 engages the forward clutch 75 and the reverse clutch 76 using the control valves 133, 134 and the switching valves 135, 136 (S3 in FIG. 4 and T4 in FIG. 5). More specifically, the control device 120 maintains the forward clutch pressure increased using the forward control valve 133 and the forward switching valve 135 to keep the forward clutch 75 engaged, and increases the reverse clutch pressure using the reverse control valve 134 and the reverse switching valve 136 to also engage the reverse clutch 76 (during the F→N transition in FIG. 6).

[0117] At this time, when hydraulic oil begins to be supplied from the reverse selector valve 136 into the pressing member 76d of the reverse clutch 76, the reverse clutch pressure rises to a certain extent, and the reverse clutch pressure remains constant until the hydraulic oil fills the pressing member 76d. After the hydraulic oil fills the pressing member 76d, the reverse clutch pressure rises further. Then, when the reverse clutch pressure is saturated with the first clutch pressure, the reverse clutch 76 is fully engaged (full clutch state), and the traveling device 7 is in a neutral state (N state in FIGS. 6 and 5).

[0118] Thereafter, when the forward / reverse operating member 148a is operated to the forward position Fp (T1 in FIG. 5, time point Q2 in FIG. 6), the control device 120 receives a forward command from the forward / reverse operating device 148 (YES in S4 in FIG. 4). In this case, the control device 120 also responds to the forward command by maintaining the forward clutch pressure increased by the forward control valve 133 and the forward switchover valve 135 to keep the forward clutch 75 engaged, and by reducing the reverse clutch pressure by the reverse control valve 134 and the reverse switchover valve 136 to disengage the reverse clutch 76 (S5 in FIG. 4, during the N→F transition in FIGS. 6 and 5).

[0119] Then, the control device 120 acquires a gear shift command corresponding to the operating position of the forward / reverse operation member 148a from the forward / reverse operation device 148 (S6: YES in FIG. 4), and if no other command is acquired (S7: NO), after confirming that the detected value of the reverse clutch pressure has fallen below the threshold value (S8 in FIG. 4, T2 in FIG. 5, F state in FIGS. 5 and 6), it controls the HST 50 according to the gear shift command and starts outputting from the transmission 5 (S14 in FIG. 4).

[0120] Furthermore, when the travel device 7 is in the neutral state and the forward / reverse operation member 148a is operated to the reverse position Rp (T5 in FIG. 5), the control device 120 acquires a reverse command from the forward / reverse operation device 148 (YES in S9 in FIG. 4). In this case, in response to the acquired reverse command, the control device 120 maintains the increased reverse clutch pressure with the reverse control valve 134 and the reverse switch valve 136, keeping the reverse clutch 76 engaged, and reduces the forward clutch pressure with the forward control valve 133 and the forward switch valve 135, thereby disengaging the forward clutch 75 (S10 in FIG. 4, during the N→R transition in FIG. 5).

[0121] Then, the control device 120 receives a gear shift command from the forward / reverse operation device 148 (S11 in FIG. 4), and if no other command is received (S12: NO), it confirms that the forward clutch pressure detected by the forward pressure sensor 146f has fallen below the threshold value (S13 in FIG. 4, T6 in FIG. 5, R state), and then controls the HST 50 in accordance with the gear shift command to start outputting from the transmission 5 (S14 in FIG. 4).

[0122] When the operating position of the forward / reverse operation member 148a is changed while the traveling device 7 is in reverse (state R in FIG. 5 ), the control device 120 acquires a gear shift command from the forward / reverse operation device 148 (YES in S15 in FIG. 4 ). At this time, the traveling device 7 is not in a neutral state (NO in S16), so the control device 120 changes (increases or decreases) the output of the transmission 5 in accordance with the gear shift command (S17). This changes (increases or decreases) the vehicle speed of the work vehicle 1 while traveling in reverse.

[0123] Furthermore, when the travel device 7 is in reverse and the forward / reverse operation member 148a is operated to the neutral position Np (T7 in FIG. 5), the control device 120 acquires a neutral command from the forward / reverse operation device 148 (S1 in FIG. 4: YES). In this case, the control device 120 controls the HST 50 in response to the neutral command to stop the output from the HST 50 to the forward clutch 75 and the reverse clutch 76 (S2 in FIG. 4, during the R→N transition in FIG. 5).

[0124] Then, the control device 120 connects the forward clutch 75 and the reverse clutch 76 using the control valves 133, 134 and the switching valves 135, 136 (S3 in FIG. 4, T8 in FIG. 5). More specifically, the control device 120 maintains the increased reverse clutch pressure using the reverse control valve 134 and the reverse switching valve 136, keeping the reverse clutch 76 connected, and increases the forward clutch pressure using the forward control valve 133 and the forward switching valve 135, connecting the forward clutch 75 as well. This places the traveling device 7 in a neutral state (N state in FIG. 5).

[0125] If the forward / reverse operation member 148a is operated during a transition of the state of the traveling device 7, an interrupt process is executed. For example, if the forward / reverse operation member 148a is operated to the neutral position Np during a transition of the traveling device 7 from a neutral state to a forward state (during the N-to-F transition in FIG. 5), the control device 120 acquires a neutral command (S7: YES in FIG. 4, S1: YES in FIG. 4). In this case, the control device 120 stops the output of the transmission 5 (S2 in FIG. 4), maintains the forward clutch pressure increased by the forward control valve 133 and the forward switchover valve 135, keeps the forward clutch 75 engaged, and increases the reverse clutch pressure by the reverse control valve 134 and the reverse switchover valve 136 to also engage the reverse clutch 76 (S3 in FIG. 4, during the F-to-N transition from T9 in FIG. 5).

[0126] Furthermore, when the forward / reverse operating member 148a is operated to the neutral position Np during the transition of the traveling device 7 from the neutral state to the reverse state (during the N→R transition in FIG. 5), the control device 120 acquires a neutral command (S12: YES in FIG. 4, S1: YES in FIG. 4). In this case, the control device 120 stops the output of the transmission 5 (S2 in FIG. 4), maintains the reverse clutch pressure increased by the reverse control valve 134 and the reverse switchover valve 136, keeps the reverse clutch 76 engaged, and increases the forward clutch pressure by the forward control valve 133 and the forward switchover valve 135 to also engage the forward clutch 75 (S3 in FIG. 4, during the R→N transition from T11 in FIG. 5).

[0127] Furthermore, when the forward / reverse operating member 148a is operated to the forward position Fp during the transition of the traveling device 7 from a forward state to a neutral state (F→N transition in FIG. 5, S3 in FIG. 4) or during the transition from a reverse state to a neutral state (R→N transition in FIG. 5, S3 in FIG. 4), the control device 120 acquires a forward command (S4: YES in FIG. 4). In these cases, the control device 120 stops the output of the transmission 5 and connects the forward clutch 75 and the reverse clutch 76, then maintains the connection state of the forward clutch 75 and reduces the reverse clutch pressure using the reverse control valve 134 and the reverse switch valve 136 to connect the reverse clutch 76 (S5 in FIG. 4, T10 to T2 in FIG. 5).

[0128] Furthermore, when the forward / reverse operating member 148a is operated to the reverse position Rp during the transition of the traveling device 7 from a forward state to a neutral state (F→N transition in FIG. 5, S3 in FIG. 4) or during the transition from a reverse state to a neutral state (R→N transition in FIG. 5, S3 in FIG. 4), the control device 120 acquires a reverse command (S9: YES in FIG. 4). In these cases, the control device 120 stops the output of the transmission 5 and connects the forward clutch 75 and the reverse clutch 76, then maintains the connection state of the reverse clutch 76 and reduces the forward clutch pressure using the forward control valve 133 and the forward switchover valve 135 to disconnect the forward clutch 75 (S10 in FIG. 4, T12 to T6 in FIG. 5).

[0129] In the embodiment described above, when the control device 120 engages the forward clutch 75 and the reverse clutch 76 in response to a neutral command (S3 in FIG. 4), the control device 120 brings the forward clutch 75 and the reverse clutch 76 into a fully engaged state (full clutch state), but this is not limiting. For example, in S3 in FIG. 4, the control device 120 may bring the forward clutch 75 and the reverse clutch 76 into a half-engaged state (half-clutch state) or a state in which they are just beginning to engage (clutch start state).

[0130] In the above-described embodiment, the forward clutch 75 and the reverse clutch 76 are respectively engaged by increasing the forward clutch pressure and the reverse clutch pressure, and are respectively disengaged by decreasing the forward clutch pressure and the reverse clutch pressure. However, this is not limiting. Alternatively, for example, a configuration may be adopted in which the direction in which the pressing members 75d and 76d press the friction plates 75c and 76c is changed, so that the forward clutch 75 and the reverse clutch 76 are respectively disengaged by increasing the forward clutch pressure and the reverse clutch pressure, and are respectively engaged by decreasing the forward clutch pressure and the reverse clutch pressure. Furthermore, forward clutches and reverse clutches having configurations different from those of the forward clutch 75 and the reverse clutch 76 may also be used.

[0131] In the above-described embodiment, a configuration has been illustrated in which a forward command, a reverse command, a neutral command, and a gear change command are input by the forward / reverse operation device 148, but this is not limiting. Alternatively, for example, a configuration may be adopted in which a forward command, a reverse command, and a neutral command are input by the forward / reverse operation device 148, and a gear change operation device different from the forward / reverse operation device 148 is provided in the work vehicle 1, and the gear change command is input by this gear change operation device. In this case, the gear change operation device is composed of a gear change operation member such as a lever, a sensor that detects the operating position of the gear change operation member, and the control device 120 calculates the target angle of the swash plate 56b of the traveling hydraulic pump P1 based on the output signal of the sensor.

[0132] Furthermore, the work vehicle 1 may be provided with a plurality of planetary gear mechanisms, and the output of at least either the prime mover 4 or the HST 50 may be changed in multiple stages by the plurality of planetary gear mechanisms. Furthermore, the work vehicle 1 may be provided with an auxiliary speed change operating device that electrically operates the auxiliary speed change device 53, and the control device 120 may use an actuator to switch the transmission section 95 of the auxiliary speed change device 53 between a high speed stage, a normal high speed stage, a normal low speed stage, and a neutral state depending on the operating position of the auxiliary speed change operating device, etc. The number of switchable speeds of the transmission section 95 is not limited to three speeds, and may be two speeds, or four or more speeds.

[0133] In the above-described embodiment, the control device 120 stops the output from the transmission 5 to the traveling device 7 by setting the swash plate 56b of the traveling hydraulic pump P1 to a predetermined angle in response to a neutral command, but this is not limiting. Alternatively, the transmission 5 (i.e., the forward transmission mechanism 81, the reverse transmission mechanism 82, and the auxiliary transmission 53) may be configured so that, for example, when both the forward clutch 75 and the reverse clutch 76 are engaged, the power transmitted by the forward transmission mechanism 81 (propulsive force that moves the traveling device 7 forward) and the power transmitted by the reverse transmission mechanism 82 (propulsive force that moves the traveling device 7 backward) cancel each other out, so that the output from the auxiliary transmission 53 to the traveling device 7 becomes substantially zero. Alternatively, for example, the auxiliary transmission 53 may be provided with an electrically controllable actuator, and the control device 120 may stop (reduce to zero) the output from the auxiliary transmission 53 to the traveling device 7 by automatically switching the transmission unit 95 to the neutral position using the actuator.

[0134] In the above-described embodiment, a configuration has been exemplified in which the driver manually controls the forward movement, reverse movement, stopping, and gear shifting of the traveling device 7, but other than this, for example, the control device 120 may automatically control the forward movement, reverse movement, stopping, and gear shifting of the traveling device 7 during automatic driving of the work vehicle 1. In this case, the control device 120 acquires a forward movement instruction, a reverse movement instruction, a neutral instruction, and a gear shift instruction from a software program for automatic driving of the work vehicle 1.

[0135] Furthermore, for example, when the work vehicle 1 is remotely operated, the control device 120 may automatically control the forward movement, reverse movement, stopping, and gear shifting of the traveling device 7. In this case, the control device 120 acquires (receives) the forward movement instruction, reverse movement instruction, neutral instruction, and gear shifting instruction transmitted from the remote operation device via the communication interface 122, and stores them in at least one of the internal memory and the storage device 121. In other words, the communication interface 122 constitutes an input device.

[0136] The work vehicle 1 of the present embodiment described above has the following configuration and provides the following effects.

[0137] (Item 1) The work vehicle 1 comprises a traveling device 7 that causes the vehicle body 3 to travel, a hydraulic forward clutch 75 that can be switched between a connected state in which power for moving the traveling device 7 forward is transmitted to the traveling device 7 and a disconnected state in which power is not transmitted, a hydraulic reverse clutch 76 that can be switched between a connected state in which power for moving the traveling device 7 backward is transmitted to the traveling device 7 and a disconnected state in which power is not transmitted, and a control device 120 that acquires a forward instruction to move the traveling device 7 forward, a reverse instruction to move the traveling device 7 backward, and a neutral instruction to move the traveling device 7 neither forward nor backward, and controls the forward clutch 75 and the reverse clutch 76 in accordance with the acquired instructions, and when the control device 120 acquires a forward instruction, it connects the forward clutch 75 and disconnects the reverse clutch 76, and when it acquires a reverse instruction, it connects the reverse clutch 76 and disconnects the forward clutch 75, and when it acquires a neutral instruction, it connects the forward clutch 75 and the reverse clutch 76.

[0138] According to the configuration of item 1 above, when the traveling device 7 is in a neutral state in which it is neither moving forward nor backward, the forward clutch 75 and the reverse clutch 76 are each in an engaged state. Therefore, when the vehicle next moves forward or backward, the hydraulic oil of the clutch of the forward clutch 75 or the reverse clutch 76 that does not correspond to the direction of travel can be discharged, and only that clutch can be immediately disengaged.

[0139] For example, as shown in FIG. 6 , the forward clutch 75 and reverse clutch 76 require less time to switch from an engaged state to a disengaged state (during the N->F transition in FIG. 6 ) due to the discharge of hydraulic oil and a decrease in clutch pressure than to switch from a disengaged state to an engaged state (during the F->N transition in FIG. 6 ) due to the supply of hydraulic oil and an increase in clutch pressure. Therefore, by keeping the forward clutch 75 and reverse clutch 76 engaged when the traveling device 7 is in a neutral state, the next time the traveling device 7 is moved forward or reverse, the engagement and disengagement states of the forward clutch 75 and reverse clutch 76 can be switched more quickly depending on the traveling direction than if the forward clutch 75 and reverse clutch 76 were left disengaged. As a result, when the work vehicle 1 is switched from a neutral state to a forward state or a reverse state, the responsiveness of the forward clutch 75, reverse clutch 76, and traveling device 7 is improved, allowing the traveling device 7 to start quickly and improving the traveling performance of the work vehicle 1.

[0140] Furthermore, even if the traveling device 7 is switched to the neutral state with the front of the work vehicle 1 facing up or down a slope, for example, the forward clutch 75 and the reverse clutch 76 are both in an engaged state, so the power transmission path is not cut off, and it is possible to prevent the front wheels 7F and rear wheels 7R of the traveling device 7 from rolling due to gravity or the like in a freewheel state. This makes it possible to prevent the work vehicle 1 from rolling down a slope unintentionally by the driver.

[0141] (Item 2) In the work vehicle 1 described in item 1 above, when the control device 120 acquires a neutral command, it increases the forward clutch pressure, which is the hydraulic pressure acting on the forward clutch 75, to connect the forward clutch 75, and increases the reverse clutch pressure, which is the hydraulic pressure acting on the reverse clutch 76, to connect the reverse clutch 76; when the control device 120 acquires a forward command, it maintains the increased forward clutch pressure, keeping the forward clutch 75 connected, but reduces the reverse clutch pressure, to connect the reverse clutch 76; and when the control device 120 acquires a reverse command, it maintains the increased reverse clutch pressure, keeping the reverse clutch 76 connected, but reduces the forward clutch pressure, to connect the forward clutch 75.

[0142] According to the configuration of item 2 above, when moving the work vehicle 1 forward or backward, the forward clutch 75 and the reverse clutch 76 can be easily switched between engaged and disengaged states in a short time, thereby further improving the responsiveness and driving performance of the work vehicle 1.

[0143] (Item 3) In the work vehicle 1 described in item 1 or 2 above, the work vehicle 1 includes a prime mover 4 mounted on the vehicle body 3, a transmission 5 that changes the speed of the output of the prime mover 4, a forward transmission mechanism 81 that converts the power input from the transmission 5 via the forward clutch 75 into a propulsive force for moving the traveling device 7 forward and transmits it to the traveling device 7, a reverse transmission mechanism 82 that converts the power input from the transmission 5 via the reverse clutch 76 into a propulsive force for moving the traveling device 7 backward and transmits it to the traveling device 7, and a power control unit that controls a forward command, a reverse command, a neutral command, and a variable speed command. The control device 120 acquires a forward command, a reverse command, and a neutral command from the input device 148, and controls the forward clutch 75, the reverse clutch 76, and the transmission (HMT) 5 according to the acquired commands. When the traveling device 7 is in either a forward state or a reverse state and acquires a gear change command, the control device 120 controls the transmission 5 according to the gear change command to change the output of the transmission 5 and the vehicle speed, which is the speed of the vehicle body 3.

[0144] According to the configuration of item 3 above, the control device 120 controls the forward clutch 75, the reverse clutch 76, and the transmission 5 in accordance with the forward command, reverse command, neutral command, and gear change command, respectively, acquired by the input device 148, thereby switching the traveling device 7 and the work vehicle 1 between the forward state, the reverse state, and the neutral state, respectively, and changing the vehicle speed. Furthermore, when the traveling device 7 is in the neutral state on a slope, the forward clutch 75 and the reverse clutch 76 are each engaged, and the force that tends to cause the front wheels 7F and the rear wheels 7R to roll due to gravity or the like is absorbed by the traveling device 7, the forward transmission mechanism 81, the reverse transmission mechanism 82, and the transmission 5 (continuously variable transmission (HST) 50, planetary gear mechanism 60), thereby further preventing the freewheel state from occurring.

[0145] (Item 4) In the work vehicle 1 described in Item 3 above, when the control device 120 acquires a neutral command, it stops output from the transmission 5 to the forward clutch 75 and the reverse clutch 76, and connects the forward clutch 75 and the reverse clutch 76, respectively.

[0146] The configuration of item 4 above makes it possible to prevent shocks from occurring when the forward clutch 75 and the reverse clutch 76 are respectively engaged in response to a neutral command. Furthermore, the load on the power transmission components, such as the transmission 5, forward clutch 75, reverse clutch 76, forward transmission mechanism 81, and reverse transmission mechanism 82, is reduced, suppressing wear on each component of the power transmission components and extending their lifespan.

[0147] (Item 5) In the work vehicle 1 described in item 3 or 4 above, when the traveling device 7 is in a forward state, the control device 120 connects the forward clutch 75 and disconnects the reverse clutch 76, and when a gear change command is acquired, increases or decreases the output of the transmission 5 in accordance with the gear change command, and when a neutral command is acquired, stops the output of the transmission 5, then maintains the connected state of the forward clutch 75 and connects the reverse clutch 76.

[0148] According to the configuration of item 5 above, when the work vehicle 1 moves forward, the output of the prime mover 4 is transmitted to the traveling device 7 via the transmission 5, forward clutch 75, and forward transmission mechanism 81, so that the traveling device 7 can be driven forward, and the output of the transmission 5 can be increased or decreased in accordance with a gear change command to change the vehicle speed. Also, in order to transition the work vehicle 1 from a forward state to a neutral state, it is possible to prevent shock from occurring when the reverse clutch 76 is switched to the connected state, reducing the load on the power transmission configuration and suppressing wear on each part, thereby enabling a longer lifespan.

[0149] (Item 6) In the work vehicle 1 described in any one of items 3 to 5 above, when the traveling device 7 is in a reverse state, the control device 120 connects the reverse clutch 76 and disconnects the forward clutch 75, and when a gear change command is acquired, increases or decreases the output of the transmission 5 in accordance with the gear change command, and when a neutral command is acquired, stops the output of the transmission 5, then maintains the connected state of the reverse clutch 76 and connects the forward clutch 75.

[0150] According to the configuration of item 6 above, when the work vehicle 1 moves in reverse, the output of the prime mover 4 is transmitted to the traveling device 7 via the transmission 5, forward clutch 75, and forward transmission mechanism 81, so that the traveling device 7 can be driven forward, and the output of the transmission 5 can be increased or decreased in accordance with a gear change command to change the vehicle speed. Furthermore, in order to transition the work vehicle 1 from a reverse state to a neutral state, it is possible to prevent shock from occurring when the forward clutch 75 is switched to the engaged state, reducing the load on the power transmission configuration and suppressing wear on each part, thereby enabling a longer lifespan.

[0151] (Item 7) In the work vehicle 1 described in any one of items 3 to 6 above, when the control device 120 acquires a forward command while the forward clutch 75 and the reverse clutch 76 are both connected in response to a neutral command, the control device 120 maintains the connected state of the forward clutch 75 and disengages the reverse clutch 76.

[0152] According to the configuration of item 7 above, when moving the work vehicle 1 forward, the forward clutch 75 and the reverse clutch 76 can be switched between engaged and disengaged states in a short time and easily, thereby further improving the responsiveness and driving performance of the work vehicle 1.

[0153] (Item 8) In the work vehicle 1 described in item 7 above, the control device 120 disengages the reverse clutch 76 in response to a forward movement command, and then increases the output of the transmission 5 .

[0154] According to the configuration of item 8 above, when moving the work vehicle 1 forward, the occurrence of gear change shock (impact on the transmission 5) can be prevented, and the work vehicle 1 can be started stably.

[0155] (Item 9) The work vehicle 1 described in item 8 above is provided with a reverse pressure sensor 146g that detects the reverse clutch pressure acting on the reverse clutch 76, and the control device 120 reduces the reverse clutch pressure in response to a forward command, and increases the output of the transmission 5 in response to a gear shift command after the detected value of the reverse clutch pressure detected by the reverse pressure sensor 146g falls below a threshold value corresponding to the disengaged state of the reverse clutch 76. The gear shift command is input to the control device 120 before or after the detected value of the reverse clutch pressure falls below the threshold value.

[0156] According to the configuration of item 9 above, when moving the work vehicle 1 forward, the reverse clutch 76 is reliably disengaged, and then the output of the transmission 5 is transmitted to the traveling device 7 via the forward clutch 75 or the like, allowing the work vehicle 1 to start off stably.

[0157] (Item 10) In the work vehicle 1 described in any one of items 3 to 9 above, when the control device 120 acquires a reverse command while the forward clutch 75 and the reverse clutch 76 are both connected in response to a neutral command, the control device 120 maintains the connected state of the reverse clutch 76 and disengages the forward clutch 75.

[0158] According to the configuration of the above item 10, when the work vehicle 1 is reversed, the forward clutch 75 and the reverse clutch 76 can be switched between their engaged and disengaged states in a short time and easily, thereby further improving the responsiveness and driving performance of the work vehicle 1.

[0159] (Item 11) In the work vehicle 1 described in item 10 above, the control device 120 disengages the forward clutch 75 in response to a reverse command, and then increases the output of the transmission 5.

[0160] According to the configuration of the above item 11, when the work vehicle 1 is moved in reverse, the occurrence of gear shift shock can be prevented, and the work vehicle 1 can be started stably.

[0161] (Item 12) The work vehicle 1 described in item 11 above is provided with a forward pressure sensor 146f that detects forward clutch pressure, which is the hydraulic pressure acting on the forward clutch 75, and the control device 120 reduces the forward clutch pressure in response to a reverse command, and increases the output of the transmission 5 in response to a gear change command after the detected value of the forward clutch pressure detected by the forward pressure sensor 146f falls below a predetermined threshold value that corresponds to the disengaged state of the forward clutch 75. The gear change command is input to the control device 120 before or after the detected value of the forward clutch pressure falls below the threshold value.

[0162] According to the configuration of the above item 12, when the work vehicle 1 is moved in reverse, the forward clutch 75 is reliably disengaged, and then the output of the transmission 5 is transmitted to the traveling device 7 via the reverse clutch 76 or the like, allowing the work vehicle 1 to start off stably.

[0163] (Item 13) In the work vehicle 1 described in any one of items 3 to 12 above, the transmission 5 includes a continuously variable transmission (HST) 50 having a variable displacement traveling hydraulic pump P1 driven by the output of the prime mover 4, and a traveling hydraulic motor M1 driven by the output of the traveling hydraulic pump P1, and the work vehicle 1 is equipped with a swash plate angle sensor 146e that detects the angle of a swash plate 56b of the traveling hydraulic pump P1, and the control device 120 increases or decreases the output of the transmission 5 by changing the angle of the swash plate 56b in response to a shift command, and stops the output from the transmission 5 to the forward clutch 75 and the reverse clutch 76 by setting the angle of the swash plate 56b to a predetermined angle in response to a neutral command.

[0164] According to the configuration of item 13 above, when the work vehicle 1 moves forward or backward, the output of the prime mover 4 is transmitted to the traveling device 7 via the continuously variable transmission 50, the forward clutch 75 or the reverse clutch 76, and the forward transmission mechanism 81 or the reverse transmission mechanism 82, thereby moving the traveling device 7 and the work vehicle 1 forward or backward. The vehicle speed can be changed by changing the angle of the swash plate 56b of the traveling hydraulic pump P1 of the continuously variable transmission 50 in response to a gear change command. Furthermore, when the reverse clutch 76 or the forward clutch 75 is switched to the engaged state to transition the work vehicle 1 from the forward state or the reverse state to the neutral state, the output of the transmission 5 is stopped, thereby preventing shocks from occurring, reducing the load on the power transmission structure, and suppressing wear on each part, thereby extending the life of the parts.

[0165] (Item 14) The work vehicle 1 described in any one of Items 2 to 13 above is equipped with a forward switching valve 135 that can be switched between a supply position 135a that supplies hydraulic oil to the forward clutch 75 and a discharge position 135b that discharges hydraulic oil from the forward clutch 75, and a reverse switching valve 136 that can be switched between a supply position 136a that supplies hydraulic oil to the reverse clutch 76 and a discharge position 136b that discharges hydraulic oil from the reverse clutch 76, and the control device 120 switches the forward switching valve 135 and the reverse switching valve 136 to the supply positions 135a, 136a, respectively, thereby increasing the forward clutch pressure and the reverse clutch pressure, and bringing the forward clutch 75 and the reverse clutch 76 into an engaged state, and switches the forward switching valve 135 and the reverse switching valve 136 to the discharge positions 135b, 136b, respectively, thereby decreasing the forward clutch pressure and the reverse clutch pressure, and bringing the forward clutch 75 and the reverse clutch 76 into a disengaged state.

[0166] According to the configuration of the above item 14, the forward clutch 75 and the reverse clutch 76 can be switched between the engaged state and the disengaged state independently.

[0167] (Item 15) The work vehicle 1 described in Item 14 above is provided with a forward control valve 133 that applies hydraulic pressure to the pressure-receiving portion of the forward switching valve 135, and a reverse control valve 134 that applies hydraulic pressure to the pressure-receiving portion of the reverse switching valve 136, and the control device 120 inputs control signals to the forward control valve 133 and the reverse control valve 134, respectively, and changes the hydraulic pressure that is applied from the forward control valve 133 and the reverse control valve 134 to the corresponding pressure-receiving portion of the forward switching valve 135 and the pressure-receiving portion of the reverse switching valve 136, thereby switching the positions of the forward switching valve 135 and the reverse switching valve 136, respectively.

[0168] According to the configuration of the above item 15, the forward clutch 75 and the reverse clutch 76 can be easily switched between an electrically connected state and a disconnected state independently of each other.

[0169] The above-disclosed embodiments 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.

[0170] REFERENCE SIGNS LIST 1 Work vehicle 3 Vehicle body 4 Prime mover 5 Transmission device 7 Travel device 50 Continuously variable transmission (HST) 56b Swash plate 75 Forward clutch 76 Reverse clutch 81 Forward transmission mechanism 82 Reverse transmission mechanism 120 Control device 133 Forward control valve 134 Reverse control valve 135 Forward switching valve 135a Supply position 135b Discharge position 136 Reverse switching valve 136a Supply position 136b Discharge position 146e Swash plate angle sensor 146f Forward pressure sensor 146g Reverse pressure sensor 148 Forward / reverse operation device (input device) M1 Travel hydraulic motor P1 Travel hydraulic pump

Claims

1. A work vehicle comprising: a traveling device for traveling the vehicle body; a hydraulic forward clutch switchable between a connected state in which power for moving the traveling device forward is transmitted to the traveling device and a disconnected state in which power is not transmitted; a hydraulic reverse clutch switchable between a connected state in which power for moving the traveling device in reverse is transmitted to the traveling device and a disconnected state in which power is not transmitted; and a control device that receives a forward instruction to move the traveling device forward, a reverse instruction to move the traveling device in reverse, and a neutral instruction to move the traveling device neither forward nor reverse, and controls the forward clutch and the reverse clutch in accordance with the received instructions, wherein the control device: when receiving the forward instruction, brings the forward clutch into the connected state and the reverse clutch into the disconnected state; when receiving the reverse instruction, brings the reverse clutch into the connected state and the forward clutch into the disconnected state; and when receiving the neutral instruction, brings the forward clutch and the reverse clutch into the connected state.

2. The work vehicle according to claim 1, wherein the control device, upon receiving the neutral command, increases the forward clutch pressure, which is the hydraulic pressure acting on the forward clutch, to bring the forward clutch into the connected state, and increases the reverse clutch pressure, which is the hydraulic pressure acting on the reverse clutch, to bring the reverse clutch into the connected state; upon receiving the forward command, maintains the increased forward clutch pressure, keeping the forward clutch in the connected state, while reducing the reverse clutch pressure, to bring the reverse clutch into the disengaged state; and upon receiving the reverse command, maintains the increased reverse clutch pressure, keeping the reverse clutch in the connected state, while reducing the forward clutch pressure, to bring the forward clutch into the disengaged state.

3. A work vehicle as claimed in claim 1 or 2, comprising: a prime mover mounted on the vehicle body; a transmission that changes the output of the prime mover; a forward transmission mechanism that converts power input from the transmission via the forward clutch into propulsion force for moving the traveling device forward and transmits it to the traveling device; a reverse transmission mechanism that converts power input from the transmission via the reverse clutch into propulsion force for moving the traveling device in reverse and transmits it to the traveling device; and an input device that can input the forward instruction, the reverse instruction, the neutral instruction, and a shift instruction, wherein the control device acquires the forward instruction, the reverse instruction, and the neutral instruction respectively from the input device and controls the forward clutch, the reverse clutch, and the transmission in accordance with the acquired instructions, and when the traveling device is in either a forward state or a reverse state, controls the transmission in accordance with the shift instruction to change the output of the transmission and the vehicle speed, which is the speed of the vehicle body.

4. A work vehicle as described in claim 3, wherein when the control device receives the neutral command, it brings the forward clutch and the reverse clutch into the connected state while stopping output from the transmission to the forward clutch and the reverse clutch.

5. A work vehicle as claimed in claim 3 or 4, wherein the control device, when the travelling device is in a forward state, brings the forward clutch into the connected state and the reverse clutch into the disengaged state; when receiving the gearshift command, increases or decreases the output of the transmission in accordance with the gearshift command; and when receiving the neutral command, stops the output from the transmission to the forward clutch and the reverse clutch, then maintains the connected state of the forward clutch and brings the reverse clutch into the connected state.

6. A work vehicle as set forth in any one of claims 3 to 5, wherein the control device, when the traveling device is in a reverse state, brings the reverse clutch into the connected state and the forward clutch into the disengaged state, and when the gearshift command is acquired, increases or decreases the output of the transmission in accordance with the gearshift command, and when the neutral command is acquired, stops the output from the transmission to the forward clutch and the reverse clutch, then maintains the connected state of the reverse clutch and brings the forward clutch into the connected state.

7. A work vehicle as described in any one of claims 3 to 6, wherein when the control device receives the forward command while the forward clutch and the reverse clutch are each in the connected state in response to the neutral command, the control device maintains the connected state of the forward clutch and disengages the reverse clutch.

8. A work vehicle according to claim 7, wherein the control device disengages the reverse clutch in response to the forward command, and then increases the output of the transmission.

9. A work vehicle as described in claim 8, further comprising a reverse pressure sensor for detecting reverse clutch pressure acting on the reverse clutch, wherein the control device reduces the reverse clutch pressure in response to the forward command, and increases the output of the transmission in response to the shift command after the detected value of the reverse clutch pressure detected by the reverse pressure sensor falls below a predetermined value corresponding to the disengaged state of the reverse clutch.

10. A work vehicle as described in any one of claims 3 to 9, wherein when the control device receives the reverse command while the forward clutch and the reverse clutch are each in the connected state in response to the neutral command, the control device maintains the connected state of the reverse clutch and disengages the forward clutch.

11. The work vehicle according to claim 10, wherein the control device disengages the forward clutch in response to the reverse command and then increases the output of the transmission.

12. A work vehicle as described in claim 11, further comprising a forward pressure sensor that detects the forward clutch pressure, which is the hydraulic pressure acting on the forward clutch, and wherein the control device reduces the forward clutch pressure in response to the reverse command, and increases the output of the transmission in response to the shift command after the detected value of the forward clutch pressure detected by the forward pressure sensor falls below a predetermined value corresponding to the disengaged state of the forward clutch.

13. A work vehicle according to any one of claims 3 to 12, wherein the transmission includes a continuously variable transmission having a variable displacement traveling hydraulic pump driven by the output of the prime mover and a traveling hydraulic motor driven by the output of the traveling hydraulic pump, the work vehicle is equipped with a swash plate angle sensor that detects the angle of a swash plate of the traveling hydraulic pump, and the control device increases or decreases the output of the transmission by changing the angle of the swash plate in response to the shift command, and stops the output from the transmission to the forward clutch and the reverse clutch by setting the angle of the swash plate to a predetermined angle in response to the neutral command.

14. A work vehicle as claimed in any one of claims 2 to 13, comprising: a forward switching valve switchable between a supply position for supplying hydraulic oil to the forward clutch and a discharge position for discharging hydraulic oil from the forward clutch; and a reverse switching valve switchable between a supply position for supplying hydraulic oil to the reverse clutch and a discharge position for discharging hydraulic oil from the reverse clutch, wherein the control device switches the forward switching valve and the reverse switching valve to their respective supply positions, thereby increasing the forward clutch pressure and the reverse clutch pressure, and bringing the forward clutch and the reverse clutch into their respective connected states, and switches the forward switching valve and the reverse switching valve to their respective discharge positions, thereby decreasing the forward clutch pressure and the reverse clutch pressure, and bringing the forward clutch and the reverse clutch into their respective disconnected states.

15. A work vehicle as described in claim 14, comprising: a forward control valve that applies hydraulic pressure to the pressure-receiving portion of the forward switching valve; and a reverse control valve that applies hydraulic pressure to the pressure-receiving portion of the reverse switching valve, wherein the control device inputs control signals to the forward control valve and the reverse control valve, respectively, and changes the hydraulic pressure applied from the forward control valve and the reverse control valve to the corresponding pressure-receiving portion of the forward switching valve and the pressure-receiving portion of the reverse switching valve, thereby switching the positions of the forward switching valve and the reverse switching valve, respectively.

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