Work vehicle

Abstract

To improve drivability of a work vehicle provided with a plurality of clutches which switches between forward and backward travel.SOLUTION: A work vehicle comprises: a hydraulic forward travel clutch capable of switching between a connected state to transmit power to move forward a travel device enabling a vehicle body to travel and a disconnected state not to transmit the power; a hydraulic backward travel clutch capable of switching between the connected state to transmit the power to move backward the travel device and the disconnected state not to transmit the power; and a control device. The control device puts: the forward clutch into the connected state and the backward clutch into the disconnected state when acquiring an instruction for forward travel; the backward clutch into the connected state and the forward clutch into the disconnected state when acquiring an instruction for backward travel; and both the forward and backward clutches into the connected state when acquiring an instruction for neutrality.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[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 the speed change by the hydromechanical continuously variable transmission to a traveling device such as wheels via a hydraulic forward clutch or reverse clutch. Then, a control means provided 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, to disengage the reverse clutch and connect the forward clutch, thereby transmitting the power for moving forward to the traveling device. Also, the control means controls the clutch pressure in response to switching of the FR lever from the forward position to the reverse position, to disengage the forward clutch and connect the reverse clutch, thereby transmitting the power for moving backward to the traveling device. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2013-2578 A Summary of the Invention [Problem to be solved by the invention]

[0004] When the traveling device is put into a neutral state (i.e., stopped state) where it is not moving forward or backward, it is common to reduce the clutch oil pressure acting on the forward clutch and the reverse clutch to disengage the forward clutch and the reverse clutch. However, this causes oil to drain from the forward clutch and the reverse clutch, so that the next time the traveling device is moved forward or backward, it takes time to fill the corresponding clutch of the forward clutch and the reverse clutch with oil and to connect the clutch by oil pressure, which delays the start of the traveling device and reduces the drivability of the work vehicle.

[0005] SUMMARY OF THE PRESENT DISCLOSURE In view of the above problems, an object of the present invention is to improve the running performance of a work vehicle equipped with a plurality of clutches for switching between forward and reverse drive. [Means for solving the problem]

[0006] The present invention employs the following technical means to achieve the above object. The work vehicle of the present invention comprises a traveling device for traveling a vehicle body, a hydraulic forward clutch switchable between a connected state in which power for moving the traveling device forward and a disconnected state in which power is not transmitted to the traveling device, a hydraulic reverse clutch switchable between a connected state in which power for moving the traveling device backward and a disconnected state in which power is not transmitted to the traveling device, and a control device that acquires 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 acquired commands. When the forward command is acquired, the control device sets the forward clutch to the connected state and the reverse clutch to the disconnected state, when the reverse command is acquired, the control device sets the reverse clutch to the connected state and the forward clutch to the disconnected state, and when the neutral command is acquired, the control device sets the forward clutch and the reverse clutch to the connected state.

[0007] If the above configuration is the first aspect, in a second aspect of the present invention, by quoting the first aspect, the control device, upon obtaining the neutral command, may increase a forward clutch pressure, which is a hydraulic pressure acting on the forward clutch, to bring the forward clutch into the connected state, and increase a reverse clutch pressure, which is a hydraulic pressure acting on the reverse clutch, to bring the reverse clutch into the connected state; upon obtaining the forward command, may maintain the increased state of the forward clutch pressure, while keeping the forward clutch in the connected state, reduce the reverse clutch pressure, to bring the reverse clutch into the disengaged state; and upon obtaining the reverse command, may maintain the increased state of the reverse clutch pressure, while keeping the reverse clutch in the connected state, reduce the forward clutch pressure, to bring the forward clutch into the disengaged state.

[0008] In a third aspect of the present invention, by citing at least one of the first aspect and the second aspect, the work vehicle includes a prime mover mounted on the vehicle body, a transmission that changes the speed of an output of the prime mover, a forward transmission mechanism that converts the power input from the transmission through the forward clutch into a propulsive force for moving the traveling device forward and transmits it to the traveling device, a reverse transmission mechanism that converts the power input from the transmission through the reverse clutch into a propulsive force for moving the traveling device backward and transmits it to the traveling device, and and an input device capable of inputting a forward instruction, a reverse instruction, and a gear shift instruction, wherein the control device acquires the forward instruction, the reverse instruction, and the neutral instruction via the input device, respectively, and controls the forward clutch, the reverse clutch, and the transmission in accordance with the acquired instructions, and when the control device acquires the gear shift instruction via the input device when the traveling device is in either a forward state or a reverse state, the control device controls the transmission in accordance with the gear shift instruction to change the output of the transmission and the vehicle speed, which is the speed of the vehicle body.

[0009] In a fourth aspect of the present invention, referring to the third aspect, when the control device obtains the neutral command, the control device may bring 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.

[0010] In a fifth aspect of the present invention, by citing the third or fourth aspect, 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 upon obtaining the gear shift command, increase or decrease the output of the transmission in accordance with the gear shift command, and upon obtaining the neutral command, stop 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.

[0011] In a sixth aspect of the present invention, by citing at least any of the third to fifth aspects, 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 upon obtaining the gear shift command, increase or decrease the output of the transmission in accordance with the gear shift command, and upon obtaining the neutral command, stop 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.

[0012] In a seventh aspect of the present invention, by citing at least any of the third to sixth aspects, when the control device has the forward clutch and the reverse clutch each in the connected state in response to the neutral instruction, upon obtaining the forward instruction, the control device may maintain the connected state of the forward clutch and set the reverse clutch to the disengaged state.

[0013] In an eighth aspect of the present invention, referring to the seventh aspect, the control device may increase the output of the transmission after putting the reverse clutch into the disengaged state in response to the forward command.

[0014] In a ninth aspect of the present invention, referring to the eighth aspect, the work vehicle further comprises a reverse clutch. a reverse clutch pressure sensor for detecting a 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 a 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.

[0015] In a tenth aspect of the present invention, by citing at least any one of the third to ninth aspects, when the control device has the forward clutch and the reverse clutch each in the connected state in response to the neutral instruction, upon obtaining the reverse instruction, the control device may maintain the connected state of the reverse clutch and set the forward clutch in the disengaged state.

[0016] In an eleventh aspect of the present invention, referring to the tenth aspect, the control device may increase the output of the transmission after putting the forward clutch into the disengaged state in response to the reverse command.

[0017] In a twelfth aspect of the present invention, while citing the eleventh aspect, the work vehicle is provided with a forward pressure sensor which detects a forward clutch pressure which is an oil pressure acting on the forward clutch, and the control device reduces the forward clutch pressure in response to the reverse command, and after a detection value of the forward clutch pressure detected by the forward pressure sensor falls below a predetermined value which corresponds to the disengaged state of the forward clutch, the control device may increase the output of the transmission in response to the shift command.

[0018] In a thirteenth aspect of the present invention, by citing at least any one of the third to twelfth aspects, 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 provided 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 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.

[0019] In a 14th aspect of the present invention, while citing at least any of the second to thirteenth aspects, the work vehicle is provided with a forward switching valve that is 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 that is 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, 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 switch the forward switching valve and the reverse switching valve to the discharge position, respectively, to reduce the forward clutch pressure and the reverse clutch pressure, thereby bringing the forward clutch and the reverse clutch into the disengaged state.

[0020] In a 15th aspect of the present invention, by citing at least any of the third to fourteenth aspects, the work vehicle may include 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 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. Effect of the Invention

[0021] According to the present invention, it is possible to improve the driving performance of a work vehicle equipped with a plurality of clutches for switching between forward and reverse drive. [Brief description of the drawings]

[0022] [Figure 1] FIG. 2 is a diagram illustrating an example of a power transmission configuration of a work vehicle. [Diagram 2] 2 is a block diagram showing an example of a control configuration for a work vehicle. FIG. [Diagram 3] FIG. 2 is a diagram illustrating an example of a clutch control configuration of a work vehicle. [Figure 4] 4 is a flowchart showing an example of the operation of the work vehicle. [Diagram 5] FIG. 4 is a state transition diagram of a work vehicle. [Figure 6] 4 is a time chart showing an example of a forward / reverse operation of a work vehicle and changes in clutch pressure and swash plate angle. [Figure 7] 1 is a side view of an example of a work vehicle. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. 7 is a side view of an example of the work vehicle 1. In this embodiment, a tractor is illustrated as 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.

[0024] 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, an axle, a differential gear, 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.

[0025] 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 at the rear of the vehicle body 3. A working device 2 can be attached and detached to the lifting device 8. The lifting device 8 can raise and lower the attached working device 2. The working 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.

[0026] The transmission 5 changes the output of the prime mover 4 to switch the propulsion force of the traveling device 7. In detail, 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.

[0027] 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. That is, 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 change of the work vehicle 1. The continuously variable transmission 50 is a hydrostatic continuously variable transmission (HST) that changes the speed of the output from the prime mover 4 steplessly. Hereinafter, the continuously variable transmission 50 will be referred to as "HST 50."

[0028] 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 meshed with the input shaft 5 of the HST 50. 6a. The second gear 59b is provided on the 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 of the output shaft 59c opposite to the end where the second gear 59b is provided).

[0029] The HST 50 changes the torque and rotation speed of the power input from the output shaft (crankshaft) 4a of the prime mover 4 via a main shaft (propulsion shaft) 54, a drive gear 59, and a 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.

[0030] The traveling 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 (propulsion shaft) 54 is transmitted to the input shaft 56a of the traveling 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 manner, the traveling hydraulic pump P1 is driven and hydraulic oil is discharged to the oil passage 55.

[0031] 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 (discharge amount (flow rate) of hydraulic oil, pressure) 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 according to the output of the travel hydraulic pump P1 (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.

[0032] The planetary gear mechanism 60 combines the rotational driving force of the output shaft 58 and the rotational driving force of the output shaft 59c that rotates according to the output of the prime mover 4. That is, the planetary gear mechanism 60 combines the output of the prime mover 4 and 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 and the power whose speed is 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 sub-transmission device 53, etc.

[0033] The planetary gear mechanism 60 includes an input gear 62, a ring gear (internal gear) 63d, a sun gear 63b, a planetary gear 63c, and a carrier 63a. The input gear 62 is provided at the output side 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 can rotate on the same axis as the rotation 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 engaged with the sun gear 63b and the ring gear 63d.

[0034] 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. Since the carrier 63a and the input gear 62 are engaged with each other, 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.

[0035] The planetary gear mechanism 60 is a combination of the power transmitted to the sun gear 63b (i.e., the rotational driving force which is the output after the 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 which 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 resulting combined driving force to a combined output shaft 64. The above-described HST 50 and planetary gear mechanism 60 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.

[0036] 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 forward, reverse, and stopped states of the traveling device 7 (i.e., the vehicle body 3, the work vehicle 1). A housing 77 of the forward / reverse clutch device 52 is rotatable integrally with the input shaft 62f. The forward clutch 75 and the 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.

[0037] The forward clutch 75 can be switched between a connected state in which the power for moving the traveling device 7 forward is transmitted to the traveling device 7 and a disconnected state in which the 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 the housing plates 75a are provided on the inner circumferential surface of the first region of the housing 77. A plurality of the 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 so as to face each other alternately. The pressing member 75d is configured of 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.

[0038] A supply / drain oil passage 75e is connected to the first region of the housing 77. The supply / drain oil passage 75e supplies and discharges hydraulic oil to and from the pressing member 75d inside the first region of the housing 77. After hydraulic oil is supplied through the supply / drain oil passage 75e and filled inside the pressing member 75d, the forward clutch pressure, which is the hydraulic pressure of the hydraulic oil, rises, and the pressing member 75d expands against the elastic force of the spring and presses the friction plate 75c. As a result, the friction plate 75c moves and comes into pressure contact with the housing plate 75a, and the forward clutch 75 enters an engaged state (connected state).

[0039] Furthermore, when the forward clutch pressure rises and saturates near the first clutch pressure, the friction plate 75c is pressed against the housing plate 75a with a predetermined first contact pressure, the friction plate 75c and the housing plate 75a are substantially integrated, and the forward clutch 75 is in a fully engaged state (full clutch state). When the forward clutch 75 is in an engaged state, a 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.

[0040] Furthermore, when the forward clutch pressure rises to a predetermined second clutch pressure lower than the first clutch pressure, the friction plate 75c comes into contact with the housing plate 75a at a predetermined second contact pressure lower than the first contact pressure, and the friction plate 75c becomes rotatable in synchronization with the housing 77 and the housing plate 75a. This causes the forward clutch 75 to enter a half-engaged state (half-clutch state). Furthermore, when the forward clutch pressure rises to a predetermined third clutch pressure 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 lower than the second contact pressure. This causes the forward clutch 75 to enter a state in which it begins to engage (clutch start state).

[0041] When the 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 to the supply / discharge oil passage 75e, i.e., the hydraulic oil escapes from inside the forward clutch 75, and the forward clutch pressure drops. 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 composite driving force output from the planetary gear mechanism 60 to the composite 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 is no longer rotated by the composite driving force.

[0042] 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. 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 configurations of the respective parts of the reverse clutch 76 are similar to those of the forward clutch 75, and therefore description thereof will be omitted.

[0043] A supply / drain oil passage 76e is connected to the second region of the housing 77. The supply / drain oil passage 76e supplies and discharges hydraulic oil to and from the pressing member 76d inside the second region of the housing 77. The configuration of the reverse clutch 76 and the like when hydraulic oil is supplied to or discharged from the inside of the pressing member 76d through the supply / drain oil passage 76e is the same as the configuration of the forward clutch 75 and the like when hydraulic oil is supplied to or discharged through the supply / drain 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", whereas the hydraulic pressure of the hydraulic oil acting on the reverse clutch 76 is called the "reverse clutch pressure".

[0044] 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 for moving the traveling device 7 forward, and transmits the propulsive force to the traveling device 7 via the transmission shaft 66 and the sub-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 the 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.

[0045] When the forward clutch 75 is in an engaged state 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 propulsion force (power) for moving the traveling device 7 forward is transmitted to the transmission shaft 66.

[0046] 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 a propulsive force for moving the traveling device 7 backward, and transmits the propulsive 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 meshing with the gear 82a. The reverse gear 82b meshes with the 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.

[0047] When the reverse clutch 76 is in an engaged state and the composite driving force output from the planetary gear mechanism 60 to the composite 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.

[0048] The 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 stage, a normal high speed stage, a normal low speed stage, 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 the high speed stage, the normal high speed stage, and the normal low speed stage.

[0049] 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 stage 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 stage 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 stage 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 stage by the transmission unit 95, and the power after the shift is output to the rear-wheel drive shaft 93.

[0050] A neutral position is 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.

[0051] 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 subtransmission device 53. In addition to the rear wheel drive shaft 93, rear wheels 7R, and front wheels 7F, the traveling device 7 includes a rear wheel differential 100, a rear axle 99, gears 98a, 98b, a drive conversion clutch 102, a front wheel drive shaft 103, a front wheel differential 106, a front axle 105, etc.

[0052] The power changed in speed by the sub-transmission device 53 is output to a rear wheel drive shaft 93. The rear wheel drive shaft 93 is connected to a rear wheel differential device 100. A rear axle 99 that rotatably supports the rear wheel 7R is also connected to the rear wheel differential device 100. Forward thrust is transmitted from the transmission shaft 66 through the sub-transmission device 53, the rear wheel drive shaft 93, the rear wheel differential device 100, and the rear axle 99 to the rear wheel 7R. In addition, the forward thrust is transmitted from the rear wheel drive shaft 93 to a front wheel transmission shaft 101 through gears 98a and 98b.

[0053] 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, the front wheel drive shaft 103, the front wheel differential 106, and the front axle 105. The forward thrust causes the front wheels 7F and rear wheels 7R to rotate, causing the vehicle body 3 (work vehicle 1) to move forward.

[0054] The reverse 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. The reverse thrust is also transmitted from the rear wheel drive shaft 93 to the gears 98a, 98b, the front wheel transmission shaft 101, the drive The power is transmitted to the front wheels 7F via the power conversion clutch 102, the front wheel drive shaft 103, the front wheel differential 106, and the front axle 105. The front wheels 7F and the rear wheels 7R rotate due to the reverse propulsive force, causing the vehicle body 3 to move backward.

[0055] 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.

[0056] The output shaft 56c of the traveling hydraulic pump P1 is provided with a PTO clutch device 110. The PTO clutch device 110 is composed of, for example, a hydraulic clutch. When the hydraulic clutch of the PTO clutch device 110 is in an engaged state, the rotational driving 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 in a disengaged state, the rotational driving force of the main shaft 54 ​​is not transmitted to the PTO propulsion shaft 111.

[0057] A PTO transmission 112 is provided at the middle of 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 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.

[0058] 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 operates the brakes, 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 in the vicinity of 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 release state.

[0059] 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 release 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.

[0060] 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.

[0061] 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 as to be able to 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 as not to be operable, and a parking brake state is established in which the left braking device 142F and the right braking device 142R brake the rear wheel 7R.

[0062] 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 composed of a CPU, internal memory, electric and electronic circuits, etc. The internal memory of the control device 120 is composed of volatile memory and non-volatile memory. The internal memory of the control device 120 stores software programs and data for 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.

[0063] The storage device 121 is composed of a non-volatile memory. Data and the like used by the control device 120 to control each part of the work vehicle 1 are 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 and a communication circuit that wirelessly communicates with an information processing device and the like outside the work vehicle 1.

[0064] The steering device 29 has a handle (steering wheel) 30, a steering shaft (rotating shaft) 31, and an assist mechanism (power steering mechanism) 32. The steering shaft 31 rotates in conjunction with the rotation of the handle 30. The assist mechanism 32 assists steering by the handle 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 a plurality of 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.

[0065] The control device 120 electrically controls the switching position and opening 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, and expands and contracts the steering cylinder 35 to change the direction (steering direction) of the front wheels 7F. Also, 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 of the control valve 34 are switched. That is, the switching position and opening of the control valve 34 are also changed by manually operating the steering wheel 30, and the steering cylinder 35 expands and contracts to change the steering direction of the front wheels 7F.

[0066] 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 actuating the transmission 5 and the brake 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 capable of automatically running and stopping by controlling the transmission 5 and the brake device 140, etc. by the control device 120.

[0067] 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 performs driving and steering automatically, and autosteer driving (also called automatic steering or semi-automatic driving) in which the control device 120 performs steering automatically and the driver performs driving operations manually. 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 performs driving and steering of the vehicle body 3 based on the remote control signal.

[0068] 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 composite 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 an oil passage provided in the work vehicle 1, as described below.

[0069] Further, an accelerator operation device 147 and a forward / reverse operation device 148 are connected to the control device 120. The accelerator operation device 147 and the forward / reverse operation device 148 are installed near the driver's seat 10 and are operated by the driver. The accelerator operation device 147 is a device for inputting the rotation speed of the prime mover 4, and has an accelerator operation member 147a and an accelerator sensor 147b. The accelerator operation member 147a is, for example, a pedal-type operation member, and can be operated steplessly from a neutral position. The accelerator operation member 147a may be another type of operation member, such as a lever type, a dial type, a slider type, or a button type, and may be capable of changing the operation position in a plurality of steps. The accelerator sensor 147b detects the operation position of the accelerator operation member 147a.

[0070] 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. Control device 120 calculates a target rotation speed of prime mover 4 corresponding to the operating position of accelerator operating member 147a based on the output signal from accelerator sensor 147b. That is, control device 120 obtains the target rotation speed of prime mover 4 from accelerator operating device 147. Then, control device 120 controls the driving of prime mover 4 so that the actual rotation speed of prime mover 4 detected by rotation sensor 146a matches the target rotation speed.

[0071] The forward / reverse operation device 148 is an input device for inputting a forward command, a reverse command, a neutral command, and a gear shift 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 not move the traveling device 7 forward or backward, and is also called a stop command or a neutral running command. The gear shift command is a command to change the gear by 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, and can be operated to a forward position Fp, a neutral position Np, and a reverse position Rp. 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.

[0072] 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 it is operated from the forward position Fp to the reverse position Rp, or when it is operated from the reverse position Rp to the forward position Fp. The forward / reverse sensor 148b detects the operation position of the forward / reverse operation member 148a.

[0073] 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 being driven, the forward / reverse sensor 148b outputs a signal corresponding to the operation position of the forward / reverse operation member 148a to the control device 120. The control device 120 acquires an instruction corresponding to the operation position of the forward / reverse operation member 148a from among a forward instruction, a reverse instruction, a neutral instruction, and a gear shift instruction based on the output signal from the forward / reverse sensor 148b. That is, the control device 120 acquires a forward instruction, a reverse instruction, a neutral instruction, and a gear shift instruction from the forward / reverse operation device 148, respectively.

[0074] 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 an output signal from the forward / reverse sensor 148b. 8b. Also, when the forward / reverse operation member 148a is operated to the reverse position Rp, the control device 120 acquires 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 the forward position Fp and the reverse position Rp, the control device 120 acquires a gear shift command (main gear shift command) according to the operation 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 of 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 traveling hydraulic pump P1 based on the output signal from the forward / reverse sensor 148b, and determines these calculated values ​​as the gear shift command.

[0075] 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 the hydraulic oil is discharged from the hydraulic pump P2 and a discharge oil passage 132 through which the hydraulic oil is discharged are respectively 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 traveling hydraulic pump P1.

[0076] In detail, the control device 120 changes the opening degree of the swash plate control valve 126 by passing a current through a solenoid of the swash plate control valve 126 to excite the solenoid. For example, as the control device 120 increases the current for exciting 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 demagnetized and the swash plate control valve 126 is in a closed state (fully closed state).

[0077] 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 and 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 traveling hydraulic pump P1. By changing the angle of the swash plate 56b in this way, as described above, the output of the traveling hydraulic pump P1 is changed, and the output of the traveling hydraulic motor M1, i.e., the output of the HST 50 and the transmission 5, is changed.

[0078] When the control device 120 receives a gear shift command while the prime mover 4 is in operation, it changes the current input to the solenoid of the swash plate control valve 126 to execute 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. In other words, the control device 120 controls the HST 50 in accordance with the gear shift command received from the forward / reverse operation device 148 to change the output of the HST 50 and the vehicle speed, which is the speed of the vehicle body 3.

[0079] The transmission (HMT) 5 is configured such that, for example, when the angle of the swash plate 56b of the traveling hydraulic pump P1 is at the maximum angle, the output (composite driving force) of the planetary gear mechanism 60 becomes maximum, and when the angle of the swash plate 56b is at a predetermined angle, the output of the planetary gear mechanism 60 becomes zero. For this reason, 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 further the vehicle speed becomes zero, and the work vehicle 1 comes to a stopped state. In other words, when the angle of the swash plate 56b is at a predetermined angle that makes the vehicle speed zero, the output of the transmission 5 is stopped.

[0080] 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, a 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).

[0081] 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.

[0082] 3 is a diagram showing an example of a clutch control configuration for controlling 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. A pressure receiving portion of the forward switch valve 135 is connected to the other end of the operation oil passage 137. One end of an operation oil passage 138 is connected to the output port of the reverse control valve 134. A pressure receiving portion of the reverse switch valve 136 is connected to the other end of the operation oil passage 138. The forward switch valve 135 is a valve for operating the forward clutch 75. The reverse switch valve 136 is a valve for operating the reverse clutch 76.

[0083] A supply oil passage 139 is connected to the input ports of the forward switch valve 135 and the reverse switch valve 136. A discharge oil passage 132 is connected to the discharge ports of the forward switch valve 135 and the reverse switch valve 136. One end of a supply / discharge oil passage 75e is connected to the output port of the forward switch valve 135. The pressing member 75d of the forward clutch 75 is connected to the other end of the supply / discharge oil passage 75e. A forward pressure sensor 146f is connected to the middle of the supply / discharge oil passage 75e. The forward pressure sensor 146f detects the forward clutch pressure acting on the forward clutch 75.

[0084] One end of a supply / drain oil passage 76e is connected to the output port of the reverse selector valve 136. The other end of the supply / drain oil passage 76e is connected to a pressing member 76d of the reverse clutch 76. A reverse pressure sensor 146g is connected to a middle portion of the supply / drain oil passage 76e. The reverse pressure sensor 146g detects the reverse clutch pressure acting on the reverse clutch 76.

[0085] The supply oil passage 139 is also connected to an output port of a safety switching 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 hydraulic oil acting on the supply oil passage 139. A discharge oil passage 131 is connected to an input port of the safety switching valve 152. A discharge oil passage 132 is connected to an exhaust port of the safety switching valve 152. One end of an operation oil passage 153 is connected to a pressure receiving portion of the safety switching valve 152. The other end of the operation oil passage 153 is connected to an output port of the safety control valve 151. A discharge oil passage 131 is connected to an input port of the safety control valve 151. A discharge oil passage 132 is connected to an exhaust port of the safety control valve 151. The safety control valve 151 is a solenoid valve.

[0086] The safety switch 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 switch 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 switch valve 152. The safety switch valve 152 and the safety control valve 151 are held in the stop positions 152b and 151b, respectively, by the elastic forces of springs.

[0087] The control device 120 switches the safety control valve 151 to an operation position 151a by applying a current to a solenoid of the safety control valve 151 to excite the solenoid. As a result, the hydraulic oil discharged from the hydraulic pump P2 to the discharge oil passage 131 flows through the safety control valve 151 to the operation oil passage 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 the supply position 152a. Then, the hydraulic oil from the discharge oil passage 131 flows through the safety switchover valve 152 to the supply oil passage 139.

[0088] When the control device 120 does not pass current through the solenoid of the safety control valve 151, the solenoid is de-energized and the safety control valve 151 is in the stop position 151b. At this time, the hydraulic oil in the operation oil passage 153 is discharged to the drain oil passage 132 via the safety control valve 151. Also, since the hydraulic pressure large enough 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 the stop position 152b. Therefore, the 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 into the tank.

[0089] The forward switching valve 135 is switchable between a supply position 135a where hydraulic oil is supplied to the forward clutch 75, and a discharge position 135b where hydraulic oil is discharged from the forward clutch 75. The forward control valve 133 is switchable between an operation position 133a where hydraulic oil is supplied to an operation oil passage 137 and hydraulic pressure is applied to a pressure receiving portion of the forward switching valve 135, and a stop position 133b where hydraulic oil is not supplied to the operation oil passage 137 and hydraulic pressure is not applied 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.

[0090] 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, the 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.

[0091] The control device 120 changes the magnitude of the current flowing through the solenoid of the forward control valve 133 to change the opening of the forward control valve 133 at the operation position 133a and change the magnitude of the hydraulic pressure acting on the pressure-receiving portion of the forward switchover valve 135. This changes the opening of the forward switchover valve 135 at the supply position 135a, and increases or decreases (changes) the forward clutch pressure acting on the forward clutch 75. Also, the connection state of the forward clutch 75, i.e., the contact pressure between the housing plate 75a and the friction plate 75c, is changed.

[0092] When the control device 120 does not apply a current to the solenoid of the forward control valve 133, the solenoid is demagnetized and the forward control valve 133 is in the stop position 133b. At this time, the hydraulic oil in the operation oil passage 137 is discharged to the discharge oil passage 132 via the forward control valve 133. Also, since the hydraulic pressure large enough to switch the position of the forward switching valve 135 does not act on the pressure receiving portion, the forward switching valve 135 is in the discharge position 135b. Therefore, the forward clutch pressure acting on the forward clutch 75 is in a reduced state, and the hydraulic oil is discharged from the forward clutch 75 to the discharge oil passage 132 via the supply and discharge oil passage 75e and the forward switching valve 135, and the forward clutch 75 is in a disengaged state. As described above, the control device 120 changes the forward clutch pressure acting on the forward clutch 75 by the forward control valve 133 and the forward switching valve 135, and switches the forward clutch 75 between the engaged state and the disengaged state.

[0093] The reverse switch valve 136 is switchable between a supply position 136a where hydraulic oil is supplied to the reverse clutch 76 and a discharge position 136b where hydraulic oil is discharged from the reverse clutch 76 via a supply / discharge oil passage 76e. 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 switch 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 switch valve 136.

[0094] The configurations of the reverse control valve 134, the operation oil passage 138, the reverse switch valve 136, the supply and discharge oil passage 76e, and the reverse clutch 76 are similar to the configurations of the forward control valve 133, the operation oil passage 137, the forward switch valve 135, the supply and discharge oil passage 75e, and the forward clutch 75, respectively, and therefore a description thereof will be omitted. In addition, the configuration in which the control device 120 switches the engagement and disengagement state of the reverse clutch 76 is similar to the configuration in which the control device 120 switches the engagement and disengagement state of the forward clutch 75, and therefore a description thereof will be omitted. The control device 120 changes the reverse clutch pressure acting on the reverse clutch 76 by the reverse control valve 134 and the reverse switch valve 136, and switches the reverse clutch 76 between the engagement and disengagement states.

[0095] During the operation of the prime mover 4, the control device 120 normally switches the safety control valve 151 to the operation position 151a and switches the safety switching valve 152 to the supply position 152a. If an abnormality occurs in at least one of the forward switching valve 135 and the reverse switching valve 136, such as a sticking failure 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 supply / discharge oil passage 75e and the supply / discharge oil passage 76e, indicates an abnormal value that is not within a predetermined range.

[0096] 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 switch valve 152 to stop position 152b, so as not to supply hydraulic oil to the forward switch valve 135 and the reverse switch valve 136. As a result, when an abnormality occurs in at least one of the forward switch valve 135 and the reverse switch valve 136, the forward clutch pressure and the reverse clutch pressure do not increase, the forward clutch 75 and the reverse clutch 76 are held in a disengaged state, and it is possible to prevent the traveling condition of the traveling gear 7 and the work vehicle 1 from becoming abnormal.

[0097] If an abnormality such as a sticking failure occurs in the safety switch valve 152, the detected oil pressure detected by the safety pressure sensor 146h, i.e., the oil pressure acting on the supply oil passage 139, indicates an abnormal value. Even when the detected 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 by the safety control valve 151, and does not supply hydraulic oil to the forward switch valve 135 and the reverse switch valve 136.

[0098] During the driving of the prime mover 4, 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 by the control valves 133, 134 and the change-over valves 135, 136 in accordance with the acquired commands, while controlling the transmission 5. For example, when the control device 120 acquires a neutral command from the forward / reverse operation device 148, it increases the forward clutch pressure and the reverse clutch pressure by 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.

[0099] In addition, when the control device 120 receives a forward command from the forward / reverse operation device 148, the control device 120 increases the forward clutch pressure by the forward control valve 133 and the forward switching valve 135 to operate the forward clutch 75. and reduces the reverse clutch pressure by the reverse control valve 134 and the reverse switch valve 136 to disengage the reverse clutch 76. When the control device 120 receives a reverse command from the forward / reverse operation device 148, it increases the reverse clutch pressure by the reverse control valve 134 and the reverse switch valve 136 to connect the reverse clutch 76, and reduces the forward clutch pressure by the forward control valve 133 and the forward switch valve 135 to disengage the forward clutch 75.

[0100] Furthermore, when the travel device 7 is in either a forward or reverse state, the control device 120, upon receiving a gear shift command from the forward / reverse operation device 148, controls the HST 50 of the transmission 5 to change the output of the HST 50 and the transmission 5, and also changes 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.

[0101] Fig. 4 is a flow chart showing an example of the operation of the work vehicle 1. Each step in Fig. 4 is executed by the control device 120 based on software programs and data stored in the internal memory or the storage device 121. Fig. 5 is a state transition diagram of the work vehicle 1. Fig. 6 is a time chart showing an example of changes in the operation 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.

[0102] For example, the prime mover 4 starts in a state where the forward / reverse operation member 148a is in the neutral position Np and the angle of the swash plate 56b of the traveling hydraulic pump P1 of the HST 50 is a predetermined angle that makes the vehicle speed zero (T0 in FIG. 5). In this case, the control device 120 acquires a neutral command not to move forward or backward from the forward / reverse operation device 148 (S1 in FIG. 4: YES). Then, the control device 120 increases the forward clutch pressure and the reverse clutch pressure by the control valves 133, 134 and the changeover valves 135, 136 while stopping (zero state) the output of the HST 50 and the transmission (HMT) 5 (S2), and brings the forward clutch 75 and the reverse clutch 76 into an engaged state (S3). At this time, the control device 120 brings, for example, the forward clutch 75 and the reverse clutch 76 into a fully engaged state (fully clutch state). As a result, the traveling device 7 (that is, the vehicle body 3 and the work vehicle 1) is in a neutral state (stopped state) in which it neither moves forward nor backward (N state in FIG. 5).

[0103] The control device 120 may also determine that the forward clutch 75 is in an engaged state when the detection value of 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 in a disengaged state when the detection value of the forward clutch pressure detected by the forward pressure sensor 146f falls below a predetermined threshold value. The predetermined threshold value is set to the forward clutch pressure when the friction plate 75c of the forward clutch 75 separates from the housing plate 75a, that is, the forward clutch pressure corresponding to the disengaged state of the forward clutch 75.

[0104] Similarly, the control device 120 may determine that the reverse clutch 76 is in the engaged state when the detection value of the reverse clutch pressure detected by the reverse pressure sensor 146g rises to the first clutch pressure. The control device 120 may also determine that the reverse clutch 76 is in the disengaged state when the detection 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).

[0105] When the traveling device 7 is in a neutral state (N state in FIG. 5), if the forward / reverse operation member 148a is operated to the forward position Fp (T1 in FIG. 5), the control device 120 acquires a forward command from the forward / reverse operation device 148 (S4 in FIG. 4: YES). 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. As a result, the auxiliary transmission The same applies when a forward / reverse operation member 148a, which will be described later, is operated to the forward position Fp or the reverse position Rp.

[0106] 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, keeps 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, thereby disengaging the reverse clutch 76 (S5 in FIG. 4, during the N→F transition in FIG. 5).

[0107] 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 the transmission 5 (S14 in FIG. 4).

[0108] 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 steps S7 and S8, the control device 120 controls the angle of the swash plate 56b by 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, and increases the output of the traveling hydraulic motor M1 (i.e., the output of the HST 50). As a result, the output of the transmission 5 increases and power for moving the traveling device 7 forward is transmitted to the traveling device 7, so that the traveling device 7 moves forward and the work vehicle 1 also moves forward.

[0109] When the traveling device 7 is in a forward movement state (state F in FIG. 5), if the operation position of the forward / reverse operation member 148a is changed, the control device 120 acquires a gear shift command from the forward / reverse 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 sub-transmission device 53 in accordance with the acquired gear shift command, and changes (increases or decreases) the output of the transmission device 5 (S17 in FIG. 4). As a result, the vehicle speed of the work vehicle 1 moving forward is changed (increased or decelerated).

[0110] Also, when the travel device 7 is in a forward state (F state), if the forward / reverse operation member 148a is operated to the neutral position Np (T3 in FIG. 5), the control device 120 acquires a neutral command from the forward / reverse operation device 148 (S1 in FIG. 4: YES, time point Q1 in FIG. 6). In this case, the control device 120 stops the output of the transmission 5 in response to the acquired neutral command (S2 in FIG. 4, during F→N transition in FIG. 5). More specifically, in step S2 in FIG. 4, the control device 120 stops the output from the HST 50 and the planetary gear mechanism 60 to the forward clutch 75 and the reverse clutch 76 by controlling the angle of the swash plate 56b by 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 makes the vehicle speed zero.

[0111] 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 detection value of the swash plate angle sensor 146e), which is controlled to match the target angle, also gradually decreases (before time Q1 in FIG. 6 (F state on the left side of Q1)).

[0112] Then, when the forward / reverse operation member 148a is operated to the neutral position Np (time point Q1 in FIG. 6), the control device 120 obtains a neutral command from the forward / reverse operation device 148, and in response to the neutral command, changes the target angle of the swash plate 56b to a predetermined angle that makes the vehicle speed zero, and changes the angle of the swash plate 56b to match the target angle. As a result, immediately after time point Q1, the actual angle of the swash plate 56b becomes the predetermined angle, and the output of the transmission 5 stops.

[0113] 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 in addition, 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; and 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.

[0114] After stopping the output of the transmission 5 (S2 in FIG. 4), 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, T4 in FIG. 5). In detail, the control device 120 maintains the increased state of the forward clutch pressure using the forward control valve 133 and the forward switching valve 135 to keep the forward clutch 75 connected, and increases the reverse clutch pressure using the reverse control valve 134 and the reverse switching valve 136 to also connect the reverse clutch 76 (during the F→N transition in FIG. 6).

[0115] At this time, when hydraulic oil starts to be supplied from the reverse switch 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, and then the reverse clutch pressure rises further after the hydraulic oil fills the pressing member 76d. 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).

[0116] Thereafter, when the forward / reverse operation member 148a is operated to the forward position Fp (T1 in FIG. 5, time point Q2 in FIG. 6), the control device 120 acquires a forward command from the forward / reverse operation device 148 (S4 in FIG. 4: YES). In this case as well, in response to the forward command, the control device 120 maintains the forward clutch pressure in an increased state using the forward control valve 133 and the forward switchover valve 135, keeps 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 to disengage the reverse clutch 76 (S5 in FIG. 4, during the N→F transition in FIG. 6 and FIG. 5).

[0117] 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), then it confirms that the detected value of the reverse clutch pressure has dropped below the threshold value (S8 in FIG. 4, T2 in FIG. 5, F state in FIGS. 5 and 6), and then controls the HST 50 according to the gear shift command and starts outputting the transmission 5 (S14 in FIG. 4).

[0118] Furthermore, when the traveling device 7 is in the neutral state, if 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 (S9 in FIG. 4: YES). In this case, in response to the acquired reverse command, the control device 120 maintains the increased state of the reverse clutch pressure with the reverse control valve 134 and the reverse switch valve 136, keeps the reverse clutch 76 engaged, and reduces the forward clutch pressure with the forward control valve 133 and the forward switch valve 135 to disengage the forward clutch 75 (S10 in FIG. 4, during the N→R transition in FIG. 5).

[0119] 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 detection value of 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 the transmission 5 (S14 in FIG. 4).

[0120] When the traveling device 7 is in a reverse state (R state in FIG. 5), if the operating position of the forward / reverse operation member 148a is changed, the control device 120 acquires a gear shift command from the forward / reverse operation device 148 (S15 in FIG. 4: YES). At this time, the traveling device 7 is not in a neutral state (S16: NO), 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 during reverse travel.

[0121] Furthermore, when the traveling device 7 is in a reverse state, if 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).

[0122] 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). In detail, the control device 120 maintains the increased state of the reverse clutch pressure using the reverse control valve 134 and the reverse switching valve 136 to keep the reverse clutch 76 connected, and increases the forward clutch pressure using the forward control valve 133 and the forward switching valve 135 to also connect the forward clutch 75. This places the traveling device 7 in a neutral state (N state in FIG. 5).

[0123] When the forward / reverse operation member 148a is operated during the transition of the state of the traveling device 7, an interrupt process is executed. For example, when the forward / reverse operation member 148a is operated to the neutral position Np during the transition of the traveling device 7 from the neutral state to the forward state (during N→F transition in FIG. 5), the control device 120 acquires a neutral command (S7: YES in FIG. 4, S1: YES). In this case, the control device 120 maintains the forward clutch pressure increase state by the forward control valve 133 and the forward switching valve 135 while stopping the output of the transmission 5 (S2 in FIG. 4), keeps the forward clutch 75 in the connected state, and increases the reverse clutch pressure by the reverse control valve 134 and the reverse switching valve 136 to also connect the reverse clutch 76 (S3 in FIG. 4, during F→N transition from T9 in FIG. 5).

[0124] Also, when the forward / reverse operation member 148a is operated to the neutral position Np during the transition from the neutral state of the traveling device 7 to the reverse state (during N→R transition in FIG. 5), the control device 120 acquires a neutral command (S12: YES, S1: YES in FIG. 4). In this case, the control device 120 maintains the increased state of the reverse clutch pressure by the reverse control valve 134 and the reverse switch valve 136 while stopping the output of the transmission 5 (S2 in FIG. 4), keeps the reverse clutch 76 in the connected state, and increases the forward clutch pressure by the forward control valve 133 and the forward switch valve 135 to also bring the forward clutch 75 into the connected state (S3 in FIG. 4, during the R→N transition from T11 in FIG. 5).

[0125] Furthermore, when the forward / reverse operation member 148a is operated to the forward position Fp during the transition of the traveling device 7 from the forward state to the neutral state (during the F→N transition in FIG. 5, S3 in FIG. 4) or during the transition from the reverse state to the neutral state (during the R→N transition in FIG. 5, S3 in FIG. 4), the control device 120 acquires a forward command (S4 in FIG. 4: YES). 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, and then maintains the connection state of the forward clutch 75 and reduces the reverse clutch pressure by the reverse control valve 134 and the reverse changeover valve 136 to disconnect the reverse clutch 76 (S5 in FIG. 4, T10 to T2 in FIG. 5).

[0126] Furthermore, when the forward / reverse operation member 148a is operated to the reverse position Rp during the transition of the traveling device 7 from the forward state to the neutral state (during the F→N transition in FIG. 5, S3 in FIG. 4) or during the transition from the reverse state to the neutral state (during the R→N transition in FIG. 5, S3 in FIG. 4), the control device 120 acquires a reverse command (S9 in FIG. 4: YES). 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, and then maintains the connection state of the reverse clutch 76, and reduces the forward clutch pressure by the forward control valve 133 and the forward changeover valve 135 to disengage the forward clutch 75 (S10 in FIG. 4, T12 to T6 in FIG. 5).

[0127] In the above embodiment, when the control device 120 connects the forward clutch 75 and the reverse clutch 76 in response to a neutral command (S3 in FIG. 4), the control device 120 connects the forward clutch 75 and the reverse clutch 76 in a fully connected state (full clutch state), but the present invention is not limited to this. For example, the control device 120 may connect the forward clutch 75 and the reverse clutch 76 in a half connected state (half clutch state) or a state in which they are just starting to connect (clutch start state) in S3 in FIG. 4.

[0128] In the above embodiment, the forward clutch 75 and the reverse clutch 76 are respectively connected by increasing the forward clutch pressure and the reverse clutch pressure, and the forward clutch 75 and the reverse clutch 76 are respectively disconnected by decreasing the forward clutch pressure and the reverse clutch pressure, but the present invention is not limited to this. In addition, for example, the direction in which the friction plates 75c and 76c are pressed by the pressing members 75d and 76d may be changed, and the forward clutch 75 and the reverse clutch 76 may be respectively disconnected by increasing the forward clutch pressure and the reverse clutch pressure, and the forward clutch 75 and the reverse clutch 76 may be respectively connected by decreasing the forward clutch pressure and the reverse clutch pressure. In addition, forward clutches and reverse clutches having different configurations from the forward clutch 75 and the reverse clutch 76 may be used.

[0129] In the above-described embodiment, a configuration has been exemplified in which a forward command, a reverse command, a neutral command, and a gear shift command are input by the forward / reverse operation device 148, but the present invention is not limited to this. Alternatively, for example, a forward command, a reverse command, and a neutral command may be input by the forward / reverse operation device 148, and a gear shift operation device different from the forward / reverse operation device 148 may be provided in the work vehicle 1, and the gear shift command may be input by the gear shift operation device. In this case, the gear shift operation device may be composed of a gear shift operation member such as a lever, a sensor that detects the operation position of the gear shift operation member, and the control device 120 may calculate the target angle of the swash plate 56b of the traveling hydraulic pump P1, etc., based on an output signal from the sensor.

[0130] Furthermore, a plurality of planetary gear mechanisms may be provided in the work vehicle 1, and the output of at least either the prime mover 4 or the HST 50 may be changed into a plurality of stages by the plurality of planetary gear mechanisms. Furthermore, an auxiliary speed change operation device that electrically operates the auxiliary speed change device 53 may be provided in the work vehicle 1, and the control device 120 may switch the transmission section 95 of the auxiliary speed change device 53 to a high speed stage, a normal high speed stage, a normal low speed stage, or a neutral state by an actuator according to the operation position of the auxiliary speed change operation device, etc. The switchable speed stages of the transmission section 95 are not limited to three speed stages, and may be two speed stages, or four or more speed stages.

[0131] In the above 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 the configuration is not limited to this. In addition, the transmission 5 (i.e., the forward transmission mechanism 81, the reverse transmission mechanism 82, and the sub-transmission 53) may be configured so that, for example, when both the forward clutch 75 and the reverse clutch 76 are connected, the power transmitted by the forward transmission mechanism 81 (propulsive force for moving the traveling device 7 forward) and the power transmitted by the reverse transmission mechanism 82 (propulsive force for moving the traveling device 7 backward) are offset, so that the output from the sub-transmission 53 to the traveling device 7 becomes substantially zero. In addition, for example, the sub-transmission 53 may be provided with an electrically controllable actuator, and the control device 120 may automatically switch the speed change section 95 to the neutral position using the actuator, thereby stopping (reducing to zero) the output from the sub-transmission 53 to the traveling device 7.

[0132] In the above-described embodiment, a configuration has been exemplified in which the driver manually operates 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 obtains a forward movement instruction, a reverse movement instruction, a neutral instruction, and a gear shift instruction from a software program for automatically driving the work vehicle 1.

[0133] 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 by 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.

[0134] As described above, in the work vehicle 1 of this embodiment, when a forward command is received, the control device 120 connects the forward clutch 75 and disconnects the reverse clutch 76, when a reverse command is received, the control device 120 connects the reverse clutch 76 and disconnects the forward clutch 75, and when a neutral command is received, the forward clutch 75 and the reverse clutch 76 are each connected. As a result, when the traveling device 7 is in a neutral state where it is not moving forward or backward, the forward clutch 75 and the reverse clutch 76 are each connected, so that the next time it moves forward or backward, the hydraulic oil of the clutch that does not correspond to the traveling direction among the forward clutch 75 and the reverse clutch 76 can be discharged, and only that clutch can be immediately disconnected.

[0135] For example, as shown in FIG. 6, the forward clutch 75 and the reverse clutch 76 require less time to switch from a disconnected state to a disconnected state (during the N→F transition in FIG. 6) by discharging hydraulic oil and lowering clutch pressure than to switch from a disconnected state to a connected state (during the F→N transition in FIG. 6) by supplying hydraulic oil and increasing clutch pressure. Therefore, by keeping the forward clutch 75 and the reverse clutch 76 in a connected state when the traveling device 7 is in a neutral state, the next time the traveling device 7 is moved forward or backward, the connected and disconnected states of the forward clutch 75 and the reverse clutch 76 can be switched quickly depending on the traveling direction, compared to when the forward clutch 75 and the reverse clutch 76 are kept in a disconnected state. 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, the reverse clutch 76, and the traveling device 7 can be improved, and the traveling device 7 can be started quickly, thereby improving the traveling performance of the work vehicle 1.

[0136] Furthermore, even if the traveling gear 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 gear 7 from going into a freewheel state in which they roll due to gravity or the like. This makes it possible to prevent the work vehicle 1 from rolling down a slope unintentionally by the driver.

[0137] In addition, when the control device 120 receives a neutral command, it increases the forward clutch pressure, which is the hydraulic pressure acting on the forward clutch 75, to bring the forward clutch 75 into an engaged state, and increases the reverse clutch pressure, which is the hydraulic pressure acting on the reverse clutch 76, to bring the reverse clutch 76 into an engaged state. When the control device 120 receives a forward command, it maintains the increased state of the forward clutch pressure, With the latch 75 in the connected state, the reverse clutch pressure is reduced to disengage the reverse clutch 76, and when a reverse command is obtained, the reverse clutch pressure is maintained in an increased state, the reverse clutch 76 is kept in the connected state, and the forward clutch pressure is reduced to disengage the forward clutch 75. This makes it possible to quickly and easily switch between the connected and disconnected states of the forward clutch 75 and reverse clutch 76 when moving the work vehicle 1 forward or reverse, making it possible to further improve the responsiveness and driving performance of the work vehicle 1.

[0138] Furthermore, the control device 120 acquires a forward command, a reverse command, and a neutral command via the input device (forward / reverse operation device) 148, and controls the forward clutch 75, the reverse clutch 76, and the transmission (HMT) 5 in accordance with the acquired commands, and when a gear shift command is acquired while the traveling device 7 is in either a forward state or a reverse state, the control device 120 controls the transmission 5 in accordance with the gear shift command to change the output of the transmission 5 and the vehicle speed, which is the speed of the vehicle body 3. As a result, the control device 120 can switch the traveling device 7 and the work vehicle 1 between the forward state, reverse state, and neutral state, respectively, and change the vehicle speed, in accordance with the forward command, reverse command, neutral command, and gear shift command acquired via the input device 148, by controlling the forward clutch 75, the reverse clutch 76, and the transmission 5. In addition, when the traveling gear 7 is in a neutral position on a slope, the forward clutch 75 and the reverse clutch 76 are each in a connected state, so that the force that causes the front wheels 7F and rear wheels 7R to roll due to gravity or the like is absorbed by the traveling gear 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 occurrence of a freewheel state.

[0139] Furthermore, when the control device 120 acquires a neutral command, it connects the forward clutch 75 and the reverse clutch 76 while stopping the output from the transmission 5 to the forward clutch 75 and the reverse clutch 76. This makes it possible to prevent shocks from occurring when the forward clutch 75 and the reverse clutch 76 are connected in response to the neutral command. It also reduces the load on the power transmission configuration, such as the transmission 5, the forward clutch 75, the reverse clutch 76, the forward transmission mechanism 81, and the reverse transmission mechanism 82, suppressing wear on each part of the power transmission configuration and lengthening its lifespan.

[0140] Furthermore, 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 shift command is acquired, increases or decreases the output of the transmission 5 in response to the shift command, and when a neutral command is acquired, stops the output of the transmission 5, maintains the forward clutch 75 in a connected state, and connects the reverse clutch 76. As a result, when the work vehicle 1 moves forward, the output of the prime mover 4 is transmitted to the traveling device 7 by the transmission 5, the forward clutch 75, and the 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 response to the shift command to change the vehicle speed. Furthermore, when the work vehicle 1 transitions from a forward state to a neutral state, it is possible to prevent the occurrence of an impact when the reverse clutch 76 is switched to a connected state, reduce the load on the power transmission configuration, suppress wear on each part, and extend the life of the parts.

[0141] Furthermore, 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 shift command is acquired, increases or decreases the output of the transmission 5 in response to the shift command, and when a neutral command is acquired, stops the output of the transmission 5, maintains the reverse clutch 76 in a connected state, and connects the forward clutch 75. As a result, when the work vehicle 1 moves backward, the output of the prime mover 4 is transmitted to the traveling device 7 by the transmission 5, the forward clutch 75, and the 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 response to the shift command to change the vehicle speed. Furthermore, when the work vehicle 1 transitions from a reverse state to a neutral state, it is possible to prevent the occurrence of an impact when the forward clutch 75 is switched to a connected state, reduce the load on the power transmission configuration, suppress wear on each part, and extend the life of the parts.

[0142] Furthermore, 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. This makes it possible to quickly and easily switch between the connected and disengaged states of the forward clutch 75 and the reverse clutch 76 when moving the work vehicle 1 forward, thereby making it possible to further improve the responsiveness and driving performance of the work vehicle 1.

[0143] Furthermore, 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. This prevents the occurrence of gear shift shock (shock at the transmission 5) when moving the work vehicle 1 forward, allowing the work vehicle 1 to start stably.

[0144] Furthermore, 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 the gear shift command after the detection 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 detection value of the reverse clutch pressure falls below the threshold value. As a result, when moving the work vehicle 1 forward, the reverse clutch 76 is reliably put into a disengaged state, 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 stably.

[0145] Furthermore, 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, it maintains the connected state of the reverse clutch 76 and disengages the forward clutch 75. This makes it possible to quickly and easily switch between the connected and disengaged states of the forward clutch 75 and the reverse clutch 76 when reversing the work vehicle 1, thereby making it possible to further improve the responsiveness and driving performance of the work vehicle 1.

[0146] Furthermore, the control device 120 disengages the forward clutch 75 in response to a reverse command, and then increases the output of the transmission 5. This prevents the occurrence of gear shift shock when the work vehicle 1 is reversed, allowing the work vehicle 1 to start stably.

[0147] Furthermore, 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 the gear shift command after the detection value of the forward clutch pressure detected by the forward pressure sensor 146f falls below a predetermined threshold value corresponding to the disengaged state of the forward clutch 75. The gear shift command is input to the control device 120 before or after the detection value of the forward clutch pressure falls below the threshold value. As a result, when the work vehicle 1 is reversed, the forward clutch 75 is reliably disengaged, and then the output of the gear shift 5 is transmitted to the traveling device 7 via the reverse clutch 76 or the like, allowing the work vehicle 1 to start stably.

[0148] The control device 120 detects the angle of the swash plate 56b of the variable displacement traveling hydraulic pump P1 of the continuously variable transmission 50 included in the transmission 5 by the swash plate angle sensor 146e, and 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. As a result, when the work vehicle 1 moves forward or backward, the output of the prime mover 4 is transmitted to the traveling device 7 by the continuously variable transmission 50, the forward clutch 75 or the reverse clutch 76, the forward transmission mechanism 81 or the reverse transmission mechanism 82, and the traveling device 7 and the work vehicle 1 can move forward or backward. Then, 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 shift command. In addition, when the reverse clutch 76 or the forward clutch 75 is switched to the connected state in order to transition the work vehicle 1 from the forward or reverse state to the neutral state, the output of the transmission 5 is stopped, which prevents the occurrence of shocks, reduces the load on the power transmission structure, and suppresses wear on each part. It is possible to achieve a longer life.

[0149] Moreover, the control device 120 switches the forward switch valve 135 and the reverse switch valve 136 to supply positions 135a and 136a, respectively, to increase the forward clutch pressure and the reverse clutch pressure, respectively, to connect the forward clutch 75 and the reverse clutch 76, respectively, and switches the forward switch valve 135 and the reverse switch valve 136 to discharge positions 135b and 136b, respectively, to decrease the forward clutch pressure and the reverse clutch pressure, respectively, to disconnect the forward clutch 75 and the reverse clutch 76, respectively. This allows the forward clutch 75 and the reverse clutch 76 to be independently switched between connected and disconnected states.

[0150] Furthermore, 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 applied from the forward control valve 133 and the reverse control valve 134 to the pressure receiving portion of the corresponding forward switchover valve 135 and the pressure receiving portion of the reverse switchover valve 136, respectively, thereby switching the positions of the forward switchover valve 135 and the reverse switchover valve 136, respectively. This makes it possible to easily switch the forward clutch 75 and the reverse clutch 76 independently between an electrically connected state and a disconnected state, respectively.

[0151] The above-disclosed embodiments should be considered as illustrative and not restrictive in all respects. The scope of the present invention is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0152] 1 Work vehicle 3. Body 4. Prime Mover 5. Gearbox 7 Running gear 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 Ejection position 136 Reverse switching valve 136a Supply position 136b Ejection 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 running device that runs the vehicle body; a hydraulic forward clutch that can be switched 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 to the traveling device; a hydraulic reverse clutch that can be switched 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 to the traveling device; a control device that acquires 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 acquired commands; The control device includes: When the forward command is obtained, the forward clutch is brought into the connected state and the reverse clutch is brought into the disengaged state; When the reverse command is obtained, the reverse clutch is brought into the connected state and the forward clutch is brought into the disengaged state; When the neutral command is acquired, the work vehicle brings the forward clutch and the reverse clutch into the connected state.

2. The control device includes: When the neutral command is acquired, a forward clutch pressure, which is a hydraulic pressure acting on the forward clutch, is increased to bring the forward clutch into the connected state, and a reverse clutch pressure, which is a hydraulic pressure acting on the reverse clutch, is increased to bring the reverse clutch into the connected state; When the forward command is acquired, the forward clutch pressure is maintained in an increased state, and the forward clutch is kept in the connected state, while the reverse clutch pressure is reduced, and the reverse clutch is put in the disengaged state; 2. The work vehicle according to claim 1, wherein, when the reverse command is acquired, the reverse clutch pressure is maintained in an increased state, the reverse clutch is kept in the connected state, and the forward clutch pressure is reduced to put the forward clutch in the disengaged state.

3. A prime mover mounted on the vehicle body; A transmission that changes the speed of the output of the prime mover; a forward transmission mechanism that converts the power input from the transmission via the forward clutch into a propulsive force for moving the traveling device forward and transmits the propulsive force to the traveling device; a reverse transmission mechanism that converts the power input from the transmission via the reverse clutch into a propulsive force for moving the traveling device in reverse and transmits the propulsive force to the traveling device; an input device capable of inputting the forward command, the reverse command, the neutral command, and a gear shift command, The control device includes: acquiring the forward command, the reverse command, and the neutral command through the input device, and controlling the forward clutch, the reverse clutch, and the transmission in accordance with the acquired commands; 2. The work vehicle according to claim 1, wherein when the travelling device is in either a forward or reverse state and the gear shift command is acquired by the input device, the gear shift device is controlled in accordance with the gear shift command to change the output of the gear shift device and the vehicle speed, which is the speed of the vehicle body.

4. 4. The work vehicle according to claim 3, wherein when the control device acquires the neutral command, the control device 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. The control device includes: When the traveling device is in a forward traveling state, the forward traveling clutch is brought into the connected state and the reverse traveling clutch is brought into the disengaged state; When the gear shift command is acquired, the output of the transmission is increased or decreased in response to the gear shift command; 4. The work vehicle according to claim 3, wherein when the neutral command is acquired, output from the transmission to the forward clutch and the reverse clutch is stopped, and then the connected state of the forward clutch is maintained and the reverse clutch is brought into the connected state.

6. The control device includes: When the traveling device is in a reverse state, the reverse clutch is brought into the connected state and the forward clutch is brought into the disengaged state; When the gear shift command is acquired, the output of the transmission is increased or decreased in response to the gear shift command; 4. The work vehicle according to claim 3, wherein when the neutral command is acquired, output from the transmission to the forward clutch and the reverse clutch is stopped, the reverse clutch is maintained in the connected state, and the forward clutch is brought into the connected state.

7. 4. The work vehicle according to claim 3, wherein 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 maintains the connected state of the forward clutch and disengages the reverse clutch.

8. The work vehicle according to claim 7, wherein the control device increases an output of the transmission after putting the reverse clutch into the disengaged state in response to the forward movement command.

9. a reverse clutch pressure sensor for detecting a reverse clutch pressure acting on the reverse clutch; 9. The work vehicle according to claim 8, 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 a 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.

10. 4. The work vehicle according to claim 3, wherein 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 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 increases an output of the transmission after putting the forward clutch into the disengaged state in response to the reverse command.

12. A forward pressure sensor is provided to detect a forward clutch pressure, which is a hydraulic pressure acting on the forward clutch.

12. The work vehicle according to claim 11, 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 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.

13. 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 provided with a swash plate angle sensor that detects the angle of a swash plate of the traveling hydraulic pump, The control device includes: By changing the angle of the swash plate in response to the shift command, the output of the transmission is increased or decreased; 4. The work vehicle according to claim 3, wherein the angle of the swash plate is set to a predetermined angle in response to the neutral command, thereby stopping outputs from the transmission to the forward clutch and the reverse clutch.

14. a forward switching valve that is 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; a reverse clutch switch valve that is 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, The control device includes: by switching the forward switching valve and the reverse switching valve to the supply position, respectively, the forward clutch pressure and the reverse clutch pressure are increased, respectively, and the forward clutch and the reverse clutch are brought into the connected state, 3. The work vehicle according to claim 2, wherein the forward clutch pressure and the reverse clutch pressure are respectively reduced by switching the forward switch valve and the reverse switch valve to the discharge position, thereby bringing the forward clutch and the reverse clutch into the disengaged state.

15. a forward control valve that applies hydraulic pressure to a pressure receiving portion of the forward switching valve; a reverse control valve that applies hydraulic pressure to a pressure receiving portion of the reverse switching valve, 15. The work vehicle according to claim 14, wherein the control device inputs control signals to the forward control valve and the reverse control valve, respectively, to change hydraulic pressure applied from the forward control valve and the reverse control valve to the pressure receiving portion of the corresponding forward switchover valve and the pressure receiving portion of the corresponding reverse switchover valve, thereby switching positions of the forward switchover valve and the reverse switchover valve, respectively.

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