Hydraulic clutch, power transmission device for travel, and work vehicle

Abstract

To configure a hydraulic clutch, when an intermediate position for a piston of the hydraulic clutch is set between a pressing position and a separated position, to keep the piston stably at the intermediate position.SOLUTION: A hydraulic clutch is provided with friction plates 57 capable of transmitting motive power. A piston 58 is provided that is movable between a pressing position, at which the piston presses the friction plates 57 to obtain a transmission state for transmitting motive power, and a separated position, at which the piston is apart from the friction plates 57 to obtain a cutoff state for cutting off motive power, and the piston is operated to the pressing position with hydraulic fluid supplied for operation toward the pressing position. A holder 59 is provided that can hold the piston 58 at an intermediate position A3 between the pressing position and the separated position with the piston coming into contact with the holder, and that can release the piston 58 from the intermediate position.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a hydraulic clutch equipped with a friction plate and a piston, a transmission device for traveling equipped with a hydraulic clutch, and a work vehicle. [Background technology]

[0002] In a hydraulic clutch, when hydraulic oil is supplied to the piston and the piston is operated to a pressing position where it presses the friction plate, it is in a transmission state where power is transmitted, and when the hydraulic oil is discharged and the piston is operated to a releasing position where it separates from the friction plate, it is in a cut-off state where power is cut off.

[0003] When a hydraulic clutch is disengaged, friction torque occurs between adjacent friction plates, which can cause power loss. Therefore, in order to suppress friction torque (power loss), it is preferable that the piston separation position is sufficiently far away from the friction plates.

[0004] On the other hand, when the hydraulic clutch is operated to the transmission state, if the piston's separated position is away from the friction plate, it takes time to operate the piston from the separated position to the pressed position, which may cause a response delay in the operation of the hydraulic clutch to the transmission state. Therefore, in order to suppress the response delay in the operation of the hydraulic clutch to the transmission state, it is preferable that the piston's separated position is close to the friction plate.

[0005] In order to address the above-mentioned opposing states, in Patent Document 1, in a hydraulic clutch, the piston separation position is set at a position sufficiently distant from the friction plate, and an intermediate position is set between the piston pressing position and the separation position.

[0006] In Patent Document 1, when the hydraulic clutch is maintained in a disengaged state, the piston is operated and maintained at a position sufficiently separated from the friction plate, thereby suppressing friction torque (power loss). When the hydraulic clutch is operated to the transmission state, the piston is operated in advance from the separated position to the intermediate position. Next, when an operation command to switch to the transmission state is given, the piston is moved from the intermediate position to the pressed position. This improves the responsiveness of the operation to switch the hydraulic clutch to the transmission state. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent Publication No. 2021-85430 Summary of the Invention [Problem to be solved by the invention]

[0008] The hydraulic clutch of Patent Document 1 is equipped with a spring that biases the piston to the separated position, and when hydraulic oil is supplied to operate the piston toward the pressed position, the hydraulic oil operates the piston to the pressed position against the spring. In this way, in Patent Document 1, the pressure of the hydraulic oil and the biasing force of the spring are balanced, and the piston is operated and maintained in the intermediate position.

[0009] However, it is expected that it will be difficult to accurately maintain the hydraulic oil pressure at a value that balances the biasing force of the spring due to temperature changes in the hydraulic oil, vibrations in the hydraulic clutch, etc. As a result, it is thought that subtle changes in the hydraulic oil pressure will cause the intermediate position to move from the appropriate position toward the pressed position or toward the separated position.

[0010] As described above, if an unstable intermediate position occurs, it is considered difficult to improve the responsiveness of the hydraulic clutch to the transmission state while suppressing friction torque (power loss), so there is room for improvement.

[0011] The present invention aims to provide a configuration in which, in a hydraulic clutch, a traveling transmission device equipped with a hydraulic clutch, and a work vehicle, when an intermediate position between a pressed position and a released position is set for the piston of the hydraulic clutch, the piston is stably held in the intermediate position. [Means for solving the problem]

[0012] The hydraulic clutch of the present invention is provided with a friction plate capable of transmitting power, a piston that can be moved to a pressing position where the friction plate is pressed to obtain a transmission state in which power is transmitted, and to a separated position where the piston moves away from the friction plate to obtain a cut-off state in which power is cut off, and that is operated to the pressing position by supplying hydraulic oil that operates the piston toward the pressing position, and a holding member that can hold and release the piston at an intermediate position between the pressing position and the separated position by contact with the piston.

[0013] According to the present invention, in a hydraulic clutch, when the piston is operated to a pressing position where it presses the friction plate, a power transmission state is obtained, and the piston is operated to the pressing position by supplying hydraulic oil that operates the piston toward the pressing position. When the piston is operated to a separating position where it separates from the friction plate, a power interruption state is obtained.

[0014] According to the present invention, compared to the configuration of Patent Document 1 in which the piston is held in an intermediate position by a balance between the pressure of the hydraulic oil and the spring force, the piston is pressed against a retaining member and is held sufficiently stably in an intermediate position between the pressed position and the separated position without being affected by pressure vibrations of the hydraulic oil, etc. As a result, the piston is stably held in the intermediate position by the holding member, thereby making it possible to improve the responsiveness of the hydraulic clutch when it is operated to be in the transmission state while suppressing friction torque (power loss).

[0015] In the present invention, it is preferable that the intermediate position is set closer to the friction plate than a central position between the pressing position and the separating position.

[0016] According to the present invention, the intermediate position is set at a position close to the pressed position, and the time it takes for the piston to be operated from the intermediate position to the pressed position is further shortened, which is advantageous in terms of improving the responsiveness of the operation to change the hydraulic clutch to the transmission state.

[0017] In the present invention, it is preferable that the intermediate position is set farther from the friction plate than a central position between the pressing position and the separated position.

[0018] According to the present invention, the intermediate position is set far from the pressing position, and the piston at the intermediate position does not get too close to the friction plate, which is advantageous in that it improves the responsiveness of the hydraulic clutch to the transmission state while suppressing friction torque (power loss).

[0019] In the present invention, it is preferable that the retaining member is movable to a retaining position where the piston can be retained at the intermediate position, and to an allowable position that is located on the side of the friction plate with respect to the retaining position and allows movement of the piston to the pressing position, and that the retaining member is provided with a first biasing member that biases the retaining member toward the retaining position, and a second biasing member that biases the piston toward the pressing position and has a biasing force smaller than that of the first biasing member, and that the piston, which attempts to move toward the pressing position by the second biasing member, hits the retaining member operated to the retaining position by the first biasing member, thereby retaining the piston at the intermediate position.

[0020] According to the present invention, in a state where hydraulic oil for operating the piston toward the pressing position is not supplied, the piston is moved to the pressing position by the second biasing member, whereas the holding member is positioned at the holding position by the first biasing member, and the piston is held at the intermediate position by contacting the holding member. In this case, since the biasing force of the second biasing member is set to be smaller than the biasing force of the first biasing member, the retaining member is not moved from the retaining position toward the allowable position by the piston and the second biasing member, and is stably positioned in the retaining position.

[0021] This has the advantage that the holding member is stably positioned in the holding position, thereby improving the responsiveness of the hydraulic clutch to the transmission state while suppressing friction torque (power loss).

[0022] In the present invention, it is preferable that hydraulic oil is supplied to operate the piston toward the pressing position, so that the piston is operated to the pressing position against the first biasing member, and the retaining member is operated to the permissible position by the piston.

[0023] According to the present invention, the piston is operated to the pressed position by hydraulic oil which operates the piston toward the pressed position, and the piston operates the retaining member to the permissible position, and the first biasing member provides resistance to the operation of the piston to the pressed position. In this case, the pressure of the hydraulic oil is set to a sufficiently high level required to operate the piston to the pressed position, and the biasing force of the first biasing member is reduced by the biasing force of the second biasing member, so that the piston is operated from the intermediate position to the pressed position without delay. This allows the piston to be operated from the intermediate position to the pressed position without delay, which is advantageous in terms of improving the responsiveness of the operation to switch the hydraulic clutch to a transmission state.

[0024] In the present invention, it is preferable that the piston is operated to the separated position against the second biasing member by supplying hydraulic oil that operates the piston toward the separated position.

[0025] According to the present invention, the piston is operated to the separated position by the hydraulic oil operating the piston toward the separated position, and the hydraulic clutch is disengaged. In this case, the second biasing member provides resistance to the operation of the piston to the separated position, but because the pressure of the hydraulic oil is set to a sufficiently high pressure and the biasing force of the second biasing member is relatively small, the piston is operated to the separated position without delay. As a result, the piston is operated to the separated position without delay, thereby improving the responsiveness of the operation to disengage the hydraulic clutch.

[0026] In the present invention, it is preferable that an oil chamber is provided between the piston and the retaining member, and by supplying hydraulic oil to the oil chamber, the piston is operated to the separated position against the second biasing member, and the retaining member is operated to the permissible position against the first biasing member.

[0027] According to the present invention, hydraulic oil is supplied to an oil chamber formed between the piston and the retaining member, so that the hydraulic oil acts on both the piston and the retaining member, and the piston is smoothly operated to the separated position by the hydraulic oil.

[0028] The present invention is a transmission device for traveling comprising a transmission system with a plurality of gears having different transmission ratios, and a transmission clutch provided in each of the transmission systems, the transmission clutch having a friction plate capable of transmitting power, and a piston that can be moved to a pressing position where the friction plate is pressed to obtain a transmission state in which power is transmitted, and a separated position where the piston is separated from the friction plate to obtain a disconnected state in which power is disconnected, the piston being operated to the pressing position by supplying hydraulic oil that operates the piston toward the pressing position, and in which the transmission clutch is operated into a transmission state, and in which power is transmitted through the transmission system, at least one of the transmission clutches is the hydraulic clutch described in any one of claims 1 to 6.

[0029] 2. Description of the Related Art Some traveling transmission devices are provided with a transmission system having a plurality of speed stages with different transmission ratios, and each transmission system is provided with a transmission clutch having a friction plate and a piston. In this traveling transmission device, when the transmission clutch of one of the multiple transmission systems is operated to a transmission state, power is transmitted through this transmission system. When the transmission clutch of another transmission system is operated to a transmission state, power is transmitted through this transmission system. Speed ​​changes are performed by changing the transmission clutch operated to the transmission state.

[0030] According to the present invention, in the aforementioned traveling transmission device, at least one of the transmission clutches is a hydraulic clutch having a retaining member in addition to the friction plate and the piston. When shifting from a state in which power is transmitted through one transmission system to a state in which power is transmitted through a transmission system having a hydraulic clutch, the piston of the hydraulic clutch can be held in an intermediate position in advance by a holding member. When a gear change is performed, in a transmission system to which power is being transmitted, a transmission clutch is operated to a disengaged state. In a transmission system having a hydraulic clutch, a piston of the hydraulic clutch is operated from an intermediate position to a pressing position, and the hydraulic clutch is operated to a transmitting state.

[0031] This makes it possible to obtain a driving transmission device in which shifting from a state in which power is transmitted via one transmission system to a state in which power is transmitted via a transmission system having a hydraulic clutch can be performed responsively while suppressing friction torque (power loss).

[0032] In the present invention, in the transmission system of a gear stage in the low speed range among all gear stages, and in the transmission system of a gear stage in the high speed range among all gear stages, it is preferable that the transmission clutch of the transmission system of the gear stage in the low speed range is the hydraulic clutch.

[0033] In a driving transmission device, when power is transmitted through a high-speed transmission system, the driving speed is high and the driving inertia is large, so even if it takes time for the piston of the transmission clutch to be operated from the separated position to the pressed position during a gear change, the change in driving speed during this time is small, and it is thought that the shock when the transmission clutch is operated to the transmitting state is relatively small.

[0034] In contrast, when power is transmitted through a low-speed transmission system, the driving speed is low and the driving inertia is small, so if it takes time for the piston of the transmission clutch to be operated from the released position to the pressed position during a gear change, the change in driving speed during this time is large, and the shock when the transmission clutch is operated into the transmission state is thought to be relatively large.

[0035] According to the present invention, the transmission clutch of the transmission system for the gear stage in the low speed range is a hydraulic clutch having a retaining member in addition to a friction plate and a piston. This is advantageous in that in a transmission system for low-speed range gears where driving inertia is small and changes in driving speed are large when shifting gears, by making the transmission clutch a hydraulic clutch having a retaining member in addition to a friction plate and piston, it is possible to obtain a driving transmission device in which friction torque (power loss) is suppressed and gear changes are performed responsively.

[0036] In the present invention, it is preferable that, in the distance between the pressed position and the separated position, the distance of the transmission clutch of the transmission system in the high speed region gear shift stage is set to be smaller than the distance of the hydraulic clutch of the transmission system in the low speed region gear shift stage.

[0037] According to the present invention, the distance between the pressed position and released position of the piston is set to a small distance for the transmission clutch of the transmission system for the high speed range gear ratio, thereby suppressing the response delay in operating the transmission clutch to the transmission state even if the transmission clutch is not provided with a retaining member.

[0038] In a transmission system for a high-speed range gear shift, high-speed, low-torque power is often transmitted, and the number of friction plates in the transmission clutch is often set to a small number. Therefore, even if the distance between the pressing position and releasing position of the piston of the transmission clutch is set to a small value in a transmission system for a high-speed range gear shift, the problem of increased friction torque (power loss) is unlikely to occur.

[0039] This is advantageous in that, in a transmission system for high-speed range gear ratios where high-speed, low-torque power is often transmitted, by setting the distance between the pressing position and releasing position of the piston of the transmission clutch to a small value, friction torque (power loss) can be suppressed while obtaining a transmission device for driving in which gear changes are performed responsively.

[0040] In the present invention, it is preferable that an operating unit is provided which holds the piston of the hydraulic clutch in the intermediate position by the retaining member when the transmission clutch of the transmission system having an adjacent transmission ratio to the transmission system having the hydraulic clutch is operated into a transmission state.

[0041] For example, assume that the transmission clutch of the second gear stage transmission is a hydraulic clutch having a retaining member in addition to friction plates and a piston. According to the present invention, in the above-mentioned assumption, for example, when the transmission clutch of the first-speed transmission system is operated to a transmission state so that power is transmitted through the first-speed transmission system, the piston of the hydraulic clutch of the second-speed transmission system adjacent to the first-speed transmission system is held in an intermediate position.

[0042] Thereafter, when the gear shift is from a state in which power is transmitted through the first-speed transmission system to a state in which power is transmitted through the second-speed transmission system, the transmission clutch of the first-speed transmission system is operated to a disengaged state. In the hydraulic clutch of the second-speed transmission system, the piston is operated from the intermediate position to the pressed position, and the hydraulic clutch is put into a transmitting state.

[0043] According to the present invention, in a transmission system in which the difference in driving speed is small, the gear change is performed by a hydraulic clutch that has a retaining member in addition to friction plates and pistons and has good responsiveness, thereby further reducing shock during gear changes. This is advantageous in that it is possible to obtain a transmission device for traveling in which the friction torque (power loss) is suppressed while the gear shift is performed responsively, and it is advantageous in that it is possible to obtain a transmission device for traveling in which the shock during gear shifting is small.

[0044] In the present invention, it is preferable that when the transmission clutch of the transmission system of the lowest gear among all gears is operated to a transmission state, the operating unit holds the piston of the hydraulic clutch of the transmission system of a gear that is one step faster than the transmission system of the lowest gear, at the intermediate position by the holding member, and when the transmission clutch of the transmission system of a gear that is faster than the transmission system of the lowest gear, is operated to a transmission state, the operating unit holds the piston of the hydraulic clutch of the transmission system of the gear that is one step lower than the transmission system in which the transmission clutch is operated to the transmission state, at the intermediate position by the holding member.

[0045] For example, assuming that the lowest gear transmission system among all gears is a 1st gear transmission system, and that the gear higher than the lowest gear transmission system is a 3rd gear transmission system, it is assumed that the transmission clutch of the 2nd gear transmission system, which is one step lower than the 3rd gear transmission system, is a hydraulic clutch having a retaining member in addition to friction plates and a piston.

[0046] According to the present invention, in the above-mentioned assumption, for example, when the transmission clutch of the third-speed transmission system is operated to a transmission state so that power is transmitted through the third-speed transmission system, the piston of the hydraulic clutch of the second-speed transmission system is held in an intermediate position.

[0047] Thereafter, when the gear shift is changed from a state in which power is transmitted through the third-speed transmission system to a state in which power is transmitted through the second-speed transmission system, the transmission clutch of the third-speed transmission system is operated to a disengaged state. In the hydraulic clutch of the second-speed transmission system, the piston is operated from the intermediate position to the pressed position, and the hydraulic clutch is put into a transmitting state.

[0048] According to the present invention, when shifting to a state in which power is transmitted through the transmission system of a gear shift stage one step lower, the shifting is performed by a hydraulic clutch having a retaining member in addition to friction plates and pistons, thereby reducing shock during the shift.

[0049] For example, assume that the transmission system of the lowest gear among all gears is the 1st gear transmission system, and that the transmission clutch of the 2nd gear transmission system, which is one step faster, is a hydraulic clutch having a retaining member in addition to friction plates and a piston.

[0050] According to the present invention, in the above-mentioned assumption, for example, when the transmission clutch of the first-speed transmission system is operated to a transmission state so that power is transmitted through the first-speed transmission system, the piston of the hydraulic clutch of the second-speed transmission system is held in an intermediate position.

[0051] Thereafter, when the gear shift is from a state in which power is transmitted through the first-speed transmission system to a state in which power is transmitted through the second-speed transmission system, the transmission clutch of the first-speed transmission system is operated to a disengaged state. In the hydraulic clutch of the second-speed transmission system, the piston is operated from the intermediate position to the pressed position, and the hydraulic clutch is put into a transmitting state.

[0052] According to the present invention, when shifting from a state in which power is transmitted through the transmission system of the lowest gear to a state in which power is transmitted through the transmission system of the next higher gear, shock during the gear change is reduced by configuring the gear change to be performed by a hydraulic clutch having a retaining member in addition to friction plates and pistons.

[0053] This is advantageous in that it is possible to obtain a transmission device for traveling in which the friction torque (power loss) is suppressed while the gear shift is performed responsively, and it is advantageous in that it is possible to obtain a transmission device for traveling in which the shock during gear shifting is small.

[0054] In the present invention, in the transmission system of the low speed range gear stage among all gear stages, and the transmission system of the high speed range gear stage among all gear stages, the transmission clutch of the transmission system of the low speed range gear stage is the hydraulic clutch, and in the transmission system of a high speed range high speed stage which is on the higher speed side relative to the transmission system of the lowest speed gear stage among the transmission systems of the high speed range gear stages, it is preferable that the operating unit does not hold the piston of the hydraulic clutch of the transmission system of the low speed range gear stage in the intermediate position even when the transmission clutch of the transmission system of the high speed range high speed stage is operated to a transmitting state.

[0055] In a driving transmission device, when power is transmitted through a high-speed transmission system, the driving speed is high and the driving inertia is large, so even if it takes time for the piston of the transmission clutch to be operated from the released position to the pressed position during a gear change, the change in driving speed during this time is small, and it is thought that the shock when the transmission clutch is operated to the transmitting state is relatively small.

[0056] In contrast, when power is transmitted through a low-speed transmission system, the driving speed is low and the driving inertia is small, so if it takes time for the piston of the transmission clutch to be operated from the released position to the pressed position during a gear change, the change in driving speed during this time is large, and the shock when the transmission clutch is operated into the transmission state is thought to be relatively large.

[0057] According to the present invention, the transmission clutch of the transmission system for the gear stage in the low speed range is a hydraulic clutch having a retaining member in addition to a friction plate and a piston. This is advantageous in that in a transmission system for low-speed range gears where driving inertia is small and changes in driving speed are large when shifting gears, by making the transmission clutch a hydraulic clutch having a retaining member in addition to a friction plate and piston, it is possible to obtain a driving transmission device in which friction torque (power loss) is suppressed and gear changes are performed responsively.

[0058] For example, it is assumed that the transmission systems of the gear stages in the low speed range are the 1st gear stage transmission system and the 2nd gear stage transmission system, and that the 1st gear stage transmission system and the 2nd gear stage transmission system are provided with hydraulic clutches having a retaining member in addition to friction plates and pistons, and that the transmission systems of the gear stages in the high speed range are the 3rd gear stage transmission system and the 4th gear stage transmission system. In this case, of the 3rd gear (high speed range) transmission system and the 4th gear (high speed range) transmission system, the high speed range high speed transmission system, which is on the higher speed side compared to the 3rd gear (lowest speed in the high speed range), is assumed to be the 4th gear transmission system.

[0059] According to the present invention, under the above assumption, for example, even if the transmission clutch of the 4th gear (high speed range, high speed range) transmission system is operated to a transmission state, the pistons are not held in an intermediate position in the hydraulic clutches of the 1st gear (low speed range) transmission system and the 2nd gear (low speed range) transmission system. In other words, when shifting from a state in which power is transmitted through a 4th gear (high speed range) transmission system, the gear is shifted to a state in which power is transmitted through a 3rd gear (high speed range) transmission system, which is one step lower, or a state in which power is transmitted through a 5th gear (high speed range) transmission system, which is one step higher, so there is no need to hold the pistons in an intermediate position in the hydraulic clutches of the 1st gear (low speed range) transmission system and the 2nd gear (low speed range) transmission system.

[0060] This avoids the problem of increased friction torque (power loss) caused by the piston being held in an intermediate position in the hydraulic clutch of the transmission system for low-speed gear ratios, and is advantageous in terms of obtaining a driving transmission device in which gear changes are responsive while friction torque (power loss) is suppressed.

[0061] In the present invention, it is preferable that the hydraulic clutch of the transmission system in the low speed range gear stage is the hydraulic clutch described in claim 6, and the operating unit is a branched oil passage that branches off from a supply oil passage that supplies hydraulic oil that operates the piston of the transmission clutch of the transmission system in the high speed range high speed stage toward the pressing position, is connected to the oil chamber, and supplies a portion of the hydraulic oil in the supply oil passage to the oil chamber.

[0062] According to the present invention, in the above-mentioned assumption, for example, when hydraulic oil is supplied to the transmission clutch of the fourth-speed (high-speed region, high-speed) transmission system and this transmission clutch is operated to a transmission state, a part of the hydraulic oil is supplied to the oil chambers of the hydraulic clutches of the first-speed (low-speed region) transmission system and the second-speed (low-speed region) transmission system via a branch oil passage. In this hydraulic clutch, the piston is operated to the separated position, the holding member is operated to the allowable position, and the piston is not held at the intermediate position.

[0063] As a result, by providing a branch oil passage to the oil passage for supplying hydraulic oil to the transmission clutch of the transmission system for the high-speed stage in the high-speed region, a configuration can be obtained in which the piston of the hydraulic clutch of the transmission system for the high-speed stage in the low-speed region is not held in an intermediate position, thereby simplifying the structure.

[0064] The work vehicle of the present invention is equipped with a power source, a traveling device, and a transmission system that transmits the power of the power source to the traveling device, and the hydraulic clutch described in any one of claims 1 to 7 is provided in the transmission system.

[0065] According to the present invention, when a work vehicle is operated from a state in which power to the traveling gear is cut off to a state in which power is transmitted to the traveling gear, the piston of the hydraulic clutch can be held in an intermediate position by a holding member in advance. When the operation to transmit power to the traveling gear is performed, the piston of the hydraulic clutch is operated from the intermediate position to the pressed position, and the hydraulic clutch is operated to the transmission state.

[0066] As a result, the operation from a state in which power to the traveling gear is cut off to a state in which power is transmitted to the traveling gear can be performed responsively while suppressing friction torque (power loss), resulting in a work vehicle with excellent transmission performance.

[0067] The work vehicle of the present invention comprises a power source, a traveling device, and the transmission device for traveling as recited in claim 8, which transmits the power of the power source to the traveling device.

[0068] 2. Description of the Related Art A driving transmission device provided on a work vehicle includes a transmission system with a plurality of gears with different transmission ratios, each of which is provided with a transmission clutch having a friction plate and a piston. In this traveling transmission device, when the transmission clutch of one of the multiple transmission systems is operated to a transmission state, power is transmitted through this transmission system. When the transmission clutch of another transmission system is operated to a transmission state, power is transmitted through this transmission system. Speed ​​changes are performed by changing the transmission clutch operated to the transmission state.

[0069] According to the present invention, in the aforementioned traveling transmission device, at least one of the transmission clutches is a hydraulic clutch having a retaining member in addition to the friction plate and the piston. When shifting from a state in which power is transmitted through one transmission system to a state in which power is transmitted through a transmission system having a hydraulic clutch, the piston of the hydraulic clutch can be held in an intermediate position in advance by a holding member. When a gear change is performed, in a transmission system to which power is being transmitted, a transmission clutch is operated to a disengaged state. In a transmission system having a hydraulic clutch, a piston of the hydraulic clutch is operated from an intermediate position to a pressing position, and the hydraulic clutch is operated to a transmitting state.

[0070] This makes it possible to obtain a work vehicle that can responsively change gears from one state in which power is transmitted via a transmission system to one in which power is transmitted via a transmission system having a hydraulic clutch while minimizing friction torque (power loss). [Brief description of the drawings]

[0071] [Figure 1] FIG. [Diagram 2] FIG. 2 is a schematic view showing the inside of a transmission case. [Diagram 3] FIG. [Figure 4] FIG. 4 is a cross-sectional view showing a state in which a piston is operated to an intermediate position in the first clutch. [Diagram 5] 4 is a cross-sectional view showing a state in which a piston is operated to a pressing position in the first clutch. FIG. [Figure 6] FIG. 4 is a cross-sectional view showing a state in which the piston is operated to a separated position in the first clutch. [Figure 7] 4 is a diagram showing the relationship between the rotation speed of the output shaft and the speed change position of the continuously variable transmission. FIG. [Figure 8] FIG. 4 is a diagram showing the relationship between the operation position (first to fourth range) of the speed change pedal and the positions of the pistons (holding members) of the first to fourth clutches. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0072] A tractor, which is an example of a work vehicle equipped with the hydraulic clutch and a traveling transmission device of the present invention, is shown in Figures 1 to 8. In Figure 1, F indicates the front direction, B indicates the rear direction, U indicates the upward direction, and D indicates the downward direction.

[0073] (Overall configuration of the tractor) 1, right and left front wheels 6 (corresponding to the running gear) and right and left rear wheels 7 (corresponding to the running gear) are provided on an airframe 5, and the airframe 5 is supported by the front wheels 6 and the rear wheels 7. The airframe 5 has an engine 1 (corresponding to the power source), a flywheel housing 2 connected to the rear of the engine 1, a transmission case 3 connected to the rear of the flywheel housing 2, a front frame 4 connected to the front of the engine 1, etc.

[0074] Front wheels 6 are mounted on the front frame 4, rear wheels 7 are mounted on the rear of the transmission case 3, and engine 1 is covered by a bonnet 8. A driver's section 9 is mounted on the aircraft body 5 and is covered by a cabin 12. A driver's seat 10 and a steering wheel 11 for steering the front wheels 6 are provided in the driver's section 9.

[0075] A link mechanism 13 capable of connecting various working devices (not shown) is provided at the rear of the machine body 5, and a PTO shaft 14 for transmitting power to the working devices is provided at the rear of the transmission case 3.

[0076] (Overview of the inside of the transmission case) As shown in FIG. 2, the transmission case 3 is provided with a first planetary gear 40, a second planetary gear 50, a continuously variable transmission 18, a transmission 19 (corresponding to a transmission for driving), a forward / reverse switching device 20, a rear wheel differential device 21, a front wheel transmission 22, a PTO clutch 23, and a PTO transmission 24.

[0077] The power of the output shaft 15 of the engine 1 is transmitted to the input shaft 17 of the transmission case 3 via the damper disc 16, and is then transmitted from the input shaft 17 to a transmission shaft 25 and a transmission shaft 26. The power of the transmission shaft 26 is transmitted to a PTO clutch 23, has its speed changed by a PTO transmission device 24, and is then transmitted to the PTO shaft 14.

[0078] The power of the output shaft 15 of the engine 1 is transmitted via the damper disc 16 to the first planetary device 40, the second planetary device 50, the continuously variable transmission 18 and the transmission device 19, where the speed is changed, and then transmitted to the output shaft 27.

[0079] The power of the output shaft 27 is transmitted from a transmission shaft 28 to the forward / reverse switching device 20. The power of the forward / reverse switching device 20 is transmitted from a cylindrical transmission shaft 29 rotatably attached to the transmission shaft 26 to a transmission shaft 30, then to the rear wheel differential device 21, and then to the right and left rear wheels 7.

[0080] The power of the transmission shaft 30 is transmitted to the transmission shaft 31, and then to the front wheel transmission 22 via the transmission shaft 32. The power of the front wheel transmission 22 is transmitted from the front wheel output shaft 33 to the front wheel differential device 35 via the transmission shaft 34, and then to the right and left front wheels 6.

[0081] (Configuration of the first planetary device, the second planetary device, and the continuously variable transmission) 2, the first planetary device 40 has a sun gear 41, a ring gear 42, and a plurality of planetary gears 43. The second planetary device 50 has a sun gear 51, a ring gear 52, and a plurality of planetary gears 53 and .

[0082] There is provided a carrier 55 shared by the first planetary device 40 and the second planetary device 50. In the first planetary device 40, the planet gear 43 meshes with the sun gear 41 and the ring gear 42, and is rotatably attached to the carrier 55.

[0083] In the second planetary device 50, the planetary gears 53, 54 are connected to each other so as to be rotatable together, and are rotatably attached to a carrier 55. The planetary gear 54 meshes with the planetary gear 43, and the planetary gear 53 meshes with the sun gear 51 and the ring gear 52.

[0084] The power of the input shaft 17 is transmitted to a ring gear 42 of the first planetary device 40 via a transmission shaft 36. The power of the input shaft 17 is transmitted from a transmission gear 37, which connects the transmission shaft 25 and the transmission shaft 26, to the continuously variable transmission 18 via a transmission shaft 38. The continuously variable transmission 18 is configured as a hydrostatic type, and outputs forward rotation power and reverse rotation power. The forward rotation power and reverse rotation power of the continuously variable transmission 18 are transmitted from an output shaft 39 to a sun gear 41 of the first planetary device 40.

[0085] The power transmitted from the engine 1 to the sun gear 41 of the first planetary gear 40 via the continuously variable transmission 18 and the power transmitted from the engine 1 to the ring gear 42 of the first planetary gear 40 without passing through the continuously variable transmission 18 are combined by the first planetary gear 40 and the second planetary gear 50.

[0086] The power combined by the first planetary gear 40 and the second planetary gear 50 is transmitted from the ring gear 52 of the second planetary gear 50 to the cylindrical output shaft 44, from the carrier 55 to the cylindrical output shaft 45, and from the sun gear 51 of the second planetary gear 50 to the cylindrical output shaft 46.

[0087] (Configuration of the transmission device) As shown in FIGS. 2 and 3, the transmission device 19 includes a first clutch CL1, a second clutch CL2, a third clutch CL3, a fourth clutch CL4, input gears 61, 62, 63, 64, an output shaft 27, and the like.

[0088] The output gear 44a of the output shaft 44 meshes with the input gear 61 of the first clutch CL1. The output gear 46a of the output shaft 46 meshes with the input gear 62 of the second clutch CL2, and the output gear 46b of the output shaft 46 meshes with the input gear 64 of the fourth clutch CL4. The output gear 45a of the output shaft 45 meshes with the input gear 63 of the third clutch CL3.

[0089] When the first clutch CL1 is operated into a transmission state, the power combined by the first planetary device 40 and the second planetary device 50 is transmitted from the ring gear 52 of the second planetary device 50 to the output shaft 27 via the output gear 44a and input gear 61 of the output shaft 44, and the first clutch CL1.

[0090] When the second clutch CL2 is operated to a transmission state, the power combined by the first planetary device 40 and the second planetary device 50 is transmitted from the sun gear 51 of the second planetary device 50 to the output shaft 27 via the output gear 46a and input gear 62 of the output shaft 46, and the second clutch CL2.

[0091] When the third clutch CL3 is operated into a transmission state, the power combined by the first planetary device 40 and the second planetary device 50 is transmitted from the carrier 55 to the output shaft 27 via the output gear 45a and input gear 63 of the output shaft 45, and the third clutch CL3.

[0092] When the fourth clutch CL4 is operated into a transmission state, the power combined by the first planetary device 40 and the second planetary device 50 is transmitted from the sun gear 51 of the second planetary device 50 to the output shaft 27 via the output gear 46b and input gear 64 of the output shaft 46, and the fourth clutch CL4.

[0093] (Correspondence to claims regarding transmission devices) As shown in Figures 2 and 3, in the transmission device 19, the input gear 61 is a transmission system of the first gear (the lowest gear among all gears), and the first clutch CL1 is a transmission clutch and a hydraulic clutch provided in the transmission system of the first gear.

[0094] The input gear 62 is a second-speed transmission system that is one step faster than the first-speed transmission system, and the second clutch CL2 is a transmission clutch and a hydraulic clutch provided in the second-speed transmission system. The input gear 63 is a third-speed transmission system that is one step faster than the second-speed transmission system, and the third clutch CL3 is a transmission clutch provided in the third-speed transmission system. The input gear 64 is a fourth-speed transmission system that is one step faster than the third-speed transmission system, and the fourth clutch CL4 is a transmission clutch provided in the fourth-speed transmission system.

[0095] With the above configuration, a transmission system (input gears 61-64) with a plurality of gear stages having different transmission ratios and transmission clutches (first clutch CL1-fourth clutch CL4) provided in each of the transmission systems (input gears 61-64) are provided, and a driving transmission device 19 is provided in which power is transmitted via the transmission system (input gears 61-64) in which the transmission clutches (first clutch CL1-fourth clutch CL4) are operated to a transmitting state.

[0096] At least one of the transmission clutches (first clutch CL1 to fourth clutch CL4) is the hydraulic clutch (first clutch CL1 and second clutch CL2) according to any one of claims 1 to 6.

[0097] In the transmission system (input gears 61, 62) for the low-speed range gears (1st and 2nd gears) among all gears (1st to 4th gears), and in the transmission system (input gears 63, 64) for the high-speed range gears (3rd and 4th gears) among all gears (1st to 4th gears), the transmission clutches (first clutch CL1 and second clutch CL2) of the transmission system (input gears 61, 62) for the low-speed range gears (1st and 2nd gears) are hydraulic clutches (first clutch CL1 and second clutch CL2).

[0098] (Configuration of forward / reverse switching device) As shown in FIG. 2, the forward / reverse switching device 20 includes a forward clutch CLF, a reverse clutch CLR, transmission shafts 28 and 29, an intermediate gear 47, etc., and the power of the output shaft 27 is transmitted to the transmission shaft .

[0099] In the forward / reverse switching device 20, when the forward clutch CLF is operated to the transmission state, the power of the transmission shaft 28 is transmitted in the forward state via the forward clutch CLF to the transmission shaft 29, and then transmitted from the transmission shaft 29 to the rear wheel differential device 21 via the transmission shaft 30.

[0100] In the forward / reverse switching device 20, when the reverse clutch CLR is operated to the transmission state, the power of the transmission shaft 28 is transmitted to the transmission shaft 29 in the reverse state via the reverse clutch CLR and the relay gear 47, and then transmitted from the transmission shaft 29 to the rear wheel differential device 21 via the transmission shaft 30.

[0101] (Configuration of front wheel transmission) As shown in FIG. 2, the front wheel transmission 22 includes a standard clutch CLT, a speed increasing clutch CLH, a transmission shaft 32, a front wheel output shaft 33, and the like.

[0102] When the front wheels 6 are operated within a set angle range to the right or left from the straight ahead position, the standard clutch CLT is operated into a transmission state in the front wheel transmission 22. In this state, the power of the transmission shaft 30 is transmitted to the front wheel output shaft 33 via the transmission shafts 31, 32 and the standard clutch CLT, and is then transmitted to the front wheels 6 via the transmission shaft 34 and the front wheel differential device 35, so that the front wheels 6 and rear wheels 7 are driven at the same speed.

[0103] When the front wheels 6 are steered to the right (left) beyond the set right (left) angle, the speed-increasing clutch CLH is operated to a transmission state in the front wheel transmission 22. In this state, the power of the transmission shaft 30 is transmitted to the front wheel output shaft 33 via the transmission shafts 31, 32 and the speed-increasing clutch CLH, and is then transmitted to the front wheels 6 via the transmission shaft 34 and the front wheel differential device 35, so that the front wheels 6 are driven at a higher speed than the rear wheels 7.

[0104] (Configuration of the third clutch and the fourth clutch) As shown in FIG. 3, in the transmission device 19, the third clutch CL3 and the fourth clutch CL4 are configured as a hydraulic multi-plate type, and include a casing 56, friction plates 57, a piston 58, a spring receiving member 60, a spring 49, and the like.

[0105] The casing 56 is connected to the output shaft 27 so as to be rotatable integrally therewith. Cylindrical support portions 63a, 64a are provided on the input gears 63, 64 and extend into the inside of the casing 56. Inside the casing 56, friction plates 57 which rotate integrally with the casing 56 and friction plates 57 which rotate integrally with the input gears 63, 64 (support portions 63a, 64a) are alternately arranged.

[0106] The piston 58 is configured in a ring shape and disposed inside the casing 56 . The piston 58 is movable between a pressing position A 1 where the piston 58 presses the friction plate 57 and a spaced position A 2 where the piston 58 is spaced from the friction plate 57 .

[0107] The spring receiving member 60 is formed in a disk shape, and is fixed inside the casing 56. The spring 49 is provided across the piston 58 and the spring receiving member 60, and the spring 49 urges the piston 58 toward the separated position A2.

[0108] (Configuration of the first clutch and the second clutch) 3, in the transmission 19, the first clutch CL1 and the second clutch CL2 are configured as a hydraulic multi-plate type, and include a casing 56, friction plates 57, a piston 58, a retaining member 59, a spring receiving member 60, a spring 65 (corresponding to a first biasing member), and a spring 66 (corresponding to a second biasing member), etc. The first clutch CL1 shares the casing 56 with the third clutch CL3, and the second clutch CL2 shares the casing 56 with the fourth clutch CL4.

[0109] Cylindrical support portions 61a, 62a are provided on the input gears 61, 62 and extend into the casing 56. Inside the casing 56, friction plates 57 that rotate integrally with the casing 56 and friction plates 57 that rotate integrally with the input gears 61, 62 (support portions 61a, 62a) are alternately arranged.

[0110] The piston 58 is configured in a ring shape and disposed inside the casing 56. The piston 58 is movable between a pressing position A1 (see FIG. 5) where it presses the friction plate 57 and a spaced position A2 (see FIG. 6) away from the friction plate 57.

[0111] 5 and 6, an oil chamber 67 is formed between the casing 56 and the back surface of the piston 58. A spring 66 is provided in the oil chamber 67, and the spring 66 biases the piston 58 toward the pressing position A1.

[0112] As shown in Figures 3 to 6, in the first clutch CL1 and the second clutch CL2, the retaining member 59 is configured in a ring shape and arranged inside the casing 56, and is movable to a retaining position B1 (see Figure 4) and an allowable position B2 (see Figures 5 and 6) located on the side of the friction plate 57 with respect to the retaining position B1.

[0113] The spring receiving member 60 is formed in a disk shape and is fixed inside the casing 56. A spring 65 is provided across the holding member 59 and the spring receiving member 60, and the holding member 59 is biased to the holding position B1 by the spring 65. The biasing force of the spring 66 is set to a value smaller than the biasing force of the spring 65. An oil chamber 68 is formed between the piston 58 and the holding member 59, and hydraulic oil is supplied to and discharged from the oil chambers 67, 68 as described below.

[0114] (Relationship between friction plates and pistons in the first to fourth clutches) As shown in FIG. 3, in the first clutch CL1 of the first gear transmission system to the fourth clutch CL4 of the fourth gear transmission system, the number of friction plates 57 of the first clutch CL1 is set to be greater than the number of friction plates 57 of the second clutch CL2.

[0115] The number of friction plates 57 of the third clutch CL3 is set to be smaller than the number of friction plates 57 of the second clutch CL2. The number of friction plates 57 of the fourth clutch CL4 is set to be smaller than the number of friction plates 57 of the third clutch CL3.

[0116] As shown in Figures 5 and 6, in the distance between the pressed position A1 and the released position A2 of the piston 58, the distance W1 of the piston 58 of the first clutch CL1 and the distance W1 of the piston 58 of the second clutch CL2 are set to the same value.

[0117] 3, in the interval between the pressing position A1 and the releasing position A2 of the pistons 58, the interval W3 of the pistons 58 of the third clutch CL3 is set to a value smaller than the interval W1 (see FIGS. 5 and 6) of the pistons 58 of the first clutch CL1 (second clutch CL2). The interval W4 of the pistons 58 of the fourth clutch CL4 is set to a value smaller than the interval W3 of the pistons 58 of the third clutch CL3.

[0118] (Correspondence to claims regarding pistons of the first to fourth clutches) With the above configuration, in the distance between the pressed position A1 and the released position A2, the distance W3, W4 between the transmission clutches (third clutch CL3 and fourth clutch CL4) of the transmission system (input gears 63, 64) of the high-speed range gears (3rd and 4th gears) is set to be smaller than the distance W1 between the hydraulic clutches (first clutch CL1 and second clutch CL2) of the transmission system (input gears 61, 62) of the low-speed range gears (1st and 2nd gears).

[0119] (Configuration of hydraulic oil supply system for the first to fourth clutches) 3 to 6, oil supply passages 71, 72, 73, and 74 are provided inside output shaft 27. Hydraulic oil from a pump (not shown) is supplied to oil supply passages 71 to 74 via control valves (not shown), and the hydraulic oil is discharged from oil supply passages 71 to 74 via the control valves.

[0120] The oil supply passage 71 is connected to the oil chamber 67 of the first clutch CL1, and the oil supply passage 72 is connected to the oil chamber 67 of the second clutch CL2. The oil supply passage 73 is connected to the oil chamber between the casing 56 and the back surface of the piston 58 of the third clutch CL3.

[0121] The supply oil passage 74 is connected to an oil chamber between the casing 56 of the fourth clutch CL4 and the back portion of the piston 58, and a branched oil passage 69 (corresponding to the operating section) branching off from the supply oil passage 74 is connected to the oil chambers 68 of the first clutch CL1 and the second clutch CL2.

[0122] (Operation of the 3rd and 4th clutches) 3, when hydraulic oil is supplied to the oil chamber of the third clutch CL3 through the oil supply passage 73, the piston 58 is operated to the pressing position A1, and the third clutch CL3 is operated to the transmission state. When hydraulic oil in the oil chamber of the third clutch CL3 is discharged through the oil supply passage 73, the piston 58 is operated to the disengaged position A2, and the third clutch CL3 is operated to the disengaged state.

[0123] When hydraulic oil is supplied to the oil chamber of the fourth clutch CL4 through the oil supply passage 74, the piston 58 is operated to the pressing position A1, and the fourth clutch CL4 is operated to the transmission state. When hydraulic oil in the oil chamber of the fourth clutch CL4 is discharged through the oil supply passage 74, the piston 58 is operated to the disengaged position A2, and the fourth clutch CL4 is operated to the disengaged state.

[0124] As shown in Figure 6, hydraulic oil is supplied to the oil chamber of the fourth clutch CL4 through the supply oil passage 74, and when the fourth clutch CL4 is operated into a transmission state, hydraulic oil branched off from the supply oil passage 74 is supplied to the oil chambers 68 of the first clutch CL1 and the second clutch CL2 through the branch oil passage 69.

[0125] As shown in Figures 4 and 5, the hydraulic oil in the oil chamber of the fourth clutch CL4 is discharged through the supply oil passage 74, and when the fourth clutch CL4 is operated to the disengaged state, the hydraulic oil in the oil chamber 68 of the first clutch CL1 and the second clutch CL2 is discharged through the branch oil passage 69 and the supply oil passage 74.

[0126] (Operation of the first clutch) - 1 As shown in Figure 5, when hydraulic oil is supplied to the oil chamber 67 of the first clutch CL1 through the supply oil passage 71, the second, third, and fourth clutches CL2, CL3, and CL4 are operated in a disconnected state, so that the hydraulic oil in the oil chamber 68 of the first clutch CL1 is discharged through the branch oil passage 69 and the supply oil passage 74.

[0127] When hydraulic oil is supplied to oil chamber 67 and hydraulic oil is discharged from oil chamber 68, the pressure of the hydraulic oil supplied to oil chamber 67 is sufficiently stronger than the biasing force of spring 65, so piston 58 is operated to pressing position A1 and presses friction plate 57 while pressing retaining member 59 to allowable position B2 against spring 65. This places first clutch CL1 in a transmission state.

[0128] (Operation of the first clutch) - 2 As shown in Figure 4, when the hydraulic oil in the oil chamber 67 of the first clutch CL1 is discharged through the supply oil passage 71, when the fourth clutch CL4 is operated to the disengaged state, the hydraulic oil in the oil chamber 68 of the first clutch CL1 is discharged through the branch oil passage 69 and the supply oil passage 74.

[0129] When the hydraulic oil is discharged from the oil chambers 67, 68, the retaining member 59 is moved to the retaining position B1 by the spring 65, and is stopped at the retaining position B1. The piston 58 is moved toward the pressing position A1 by the spring 66, but is stopped by the retaining member 59 at the retaining position B1.

[0130] As described above, since the biasing force of spring 66 is smaller than the biasing force of spring 65, piston 58 (spring 66) cannot press holding member 59 against spring 65, and is held in the position shown in Fig. 4. The position shown in Fig. 4 is intermediate position A3 between pressing position A1 and separating position A2.

[0131] When the piston 58 is positioned at the intermediate position A3, the intermediate position A3 (holding position B1) is set so that the distance W11 between the casing 56 and the back of the piston 58 and the distance W12 between the friction plate 57 and the piston 58 are greater than the distance W12.

[0132] As a result, the piston 58 in the intermediate position A3 is located closer to the friction plates 57 than the center position between the pressing position A1 and the separating position A2. In this case, the piston 58 is not pressing the friction plates 57, and the first clutch CL1 is in a disengaged state. The intermediate position A3 (holding position B1) of the second clutch CL2 is configured in the same manner as the first clutch CL1.

[0133] (Operation of the first clutch) - 3 As shown in Figure 6, when the hydraulic oil in the oil chamber 67 of the first clutch CL1 is discharged through the supply oil passage 71, when the fourth clutch CL4 is operated into the transmission state, hydraulic oil branched off from the supply oil passage 74 is supplied to the oil chamber 68 of the first clutch CL1 through the branch oil passage 69.

[0134] When the hydraulic oil is discharged from the oil chamber 67 and supplied to the oil chamber 68, the pressure of the hydraulic oil supplied to the oil chamber 68 is sufficiently stronger than the biasing forces of the springs 65, 66, so that the piston 58 is operated to the separated position A2 against the spring 66, and the holding member 59 is operated to the allowable position B2 against the spring 65. This causes the first clutch CL1 to enter a disengaged state.

[0135] (Operation of the second clutch) The second clutch CL2 is operated in the same manner as the first clutch CL1 described above, as will be described below.

[0136] When hydraulic oil is supplied to the oil chamber 67 of the second clutch CL2 via the supply oil passage 72, the first, third and fourth clutches CL1, CL3 and CL4 are operated to a disconnected state, so that the hydraulic oil in the oil chamber 68 of the second clutch CL2 is discharged via the branch oil passage 69 and the supply oil passage 74. As a result, the piston 58 of the second clutch CL2 is operated to the pressing position A1, and the second clutch CL2 is in a transmission state (see FIG. 5).

[0137] In the case where the hydraulic oil in the oil chamber 67 of the second clutch CL2 is discharged via the supply oil passage 72, when the fourth clutch CL4 is operated to the disengaged state, the hydraulic oil in the oil chamber 68 of the second clutch CL2 is discharged via the branch oil passage 69 and the supply oil passage 74. As a result, the piston 58 of the second clutch CL2 is operated to the intermediate position A3, and the second clutch CL2 is disengaged (see FIG. 4).

[0138] When the hydraulic oil in the oil chamber 67 of the second clutch CL2 is discharged via the supply oil passage 72, when the fourth clutch CL4 is operated into the transmission state, the hydraulic oil branched off from the supply oil passage 74 is supplied to the oil chamber 68 of the second clutch CL2 via the branch oil passage 69. As a result, the piston 58 of the second clutch CL2 is operated into the disengaged position A2, and the second clutch CL2 is put into the disengaged state (see FIG. 6).

[0139] (Correspondence to claims regarding the first to fourth clutches) With the above-described configuration, the transmission clutch (third clutch CL3 and fourth clutch CL4) has friction plates 57 capable of transmitting power, and a piston 58 that can move to a pressing position A1 where the friction plates 57 are pressed to obtain a transmission state in which the power is transmitted, and to a separated position A2 where the piston moves away from the friction plates 57 to obtain a cut-off state in which the power is cut off, and is operated to the pressing position A1 by supplying hydraulic oil that operates the piston toward the pressing position A1.

[0140] The hydraulic clutch (first clutch CL1 and second clutch CL2) is provided, which includes a friction plate 57 capable of transmitting power, a piston 58 which can move to a pressing position A1 where the friction plate 57 is pressed to obtain a transmission state in which power is transmitted, and a separation position A2 where the piston 58 moves away from the friction plate 57 to obtain a cut-off state in which the power is cut off, and which is operated to the pressing position A1 by supplying hydraulic oil that operates the piston 58 toward the pressing position A1, and a holding member 59 which can hold and release the piston 58 at an intermediate position A3 between the pressing position A1 and the separation position A2 by the piston 58 hitting it. The intermediate position A3 is set closer to the friction plate 57 than the central position between the pressing position A1 and the separating position A2.

[0141] The retaining member 59 is movable to a retaining position B1 where it can retain the piston 58 at the intermediate position A3, and to an allowing position B2 which is located on the side of the friction plate 57 relative to the retaining position B1 and allows the piston 58 to move to the pressing position A1.

[0142] A first biasing member (spring 65) is provided to bias the holding member 59 toward the holding position B1. A second biasing member (spring 66) is provided to bias the piston 58 toward the pressing position A1 and has a biasing force smaller than that of the first biasing member (spring 65).

[0143] The piston 58, which is attempting to move toward the pressing position A1 by the second biasing member (spring 66), hits the holding member 59, which has been operated to the holding position B1 by the first biasing member (spring 65), thereby holding the piston 58 in the intermediate position A3.

[0144] By supplying hydraulic oil that operates the piston 58 toward the pressing position A1, the piston 58 is operated to the pressing position A1 against the first biasing member (spring 65), and the piston 58 operates the retaining member 59 to the allowable position B2.

[0145] By supplying hydraulic oil that operates the piston 58 toward the separated position A2, the piston 58 is operated to the separated position A2 against the second biasing member (spring 66). An oil chamber 68 is formed between the piston 58 and the holding member 59. When hydraulic oil is supplied to the oil chamber 68, the piston 58 is operated to the separated position A2 against the second biasing member (spring 66), and the holding member 59 is operated to the allowable position B2 against the first biasing member (spring 65).

[0146] (Overview of speed change using continuously variable transmissions and transmission devices) As shown in FIG. 1, a speed change pedal 48 is provided on the driving section 9. The speed change pedal 48 can be depressed from a stop position to a maximum speed position, and is biased to the stop position. A first-speed range, a second-speed range, a third-speed range, and a fourth-speed range are set in the operation range between the stop position and the maximum speed position of the speed change pedal 48. The stop position of the speed change pedal 48 is the lowest speed position of the first speed range, and the maximum speed position of the speed change pedal 48 is the maximum speed position of the fourth speed range.

[0147] Figure 7 shows the relationship between the continuously variable transmission 18 and the first clutch CL1 to the fourth clutch CL4 in the 1st to 4th gear ranges, and also shows the rotational speed V of the output shaft 27 (see Figures 2 and 3), the neutral position N of the continuously variable transmission 18, the maximum forward speed position FMAX, and the maximum reverse speed position RMAX.

[0148] Figure 8 shows the relationship between the operating position of the shift pedal 48 (1st range to 4th range) and the positions of the piston 58 and retaining member 59 of the first clutch CL1, the piston 58 and retaining member 59 of the second clutch CL2, the position of the piston 58 of the third clutch CL3, and the position of the piston 58 of the fourth clutch CL4.

[0149] As described later, when the speed change pedal 48 is operated to the first gear range, the first clutch CL1 is operated to a transmission state, and the continuously variable transmission 18 is operated within the range of the maximum forward speed position FMAX and the maximum reverse speed position RMAX, corresponding to the operating position of the speed change pedal 48. When the speed change pedal 48 is operated to the second speed range, the second clutch CL2 is operated to a transmission state, and the continuously variable transmission 18 is operated within the range of the maximum forward speed position FMAX and the maximum reverse speed position RMAX, corresponding to the operating position of the speed change pedal 48.

[0150] As described later, when the speed change pedal 48 is operated to the third gear range, the third clutch CL3 is operated to a transmission state, and the continuously variable transmission 18 is operated within the range of the maximum forward speed position FMAX and the maximum reverse speed position RMAX, corresponding to the operating position of the speed change pedal 48. When the speed change pedal 48 is operated to the fourth speed range, the fourth clutch CL4 is operated to a transmission state, and the continuously variable transmission 18 is operated within the range of the maximum forward speed position FMAX and the maximum reverse speed position RMAX, corresponding to the operating position of the speed change pedal 48.

[0151] (Speed ​​changing state of the continuously variable transmission and the transmission device when the speed change pedal is in the stopped position) When the speed change pedal 48 is operated to the stop position, as shown in FIG. 3, the hydraulic oil is discharged from the supply oil passages 71-74 and the branch oil passage 69, and the continuously variable transmission 18 is operated to the maximum reverse speed position RMAX.

[0152] As shown in Fig. 8, in the first clutch CL1 and the second clutch CL2, the holding member 59 is operated to the holding position B1, and the piston 58 is operated to the intermediate position A3 (see Fig. 4). In the third clutch CL3 and the fourth clutch CL4, the piston 58 is operated to the disengaged position A2. As a result, the first clutch CL1 to the fourth clutch CL4 are operated to the disengaged state.

[0153] (Gear change state by the continuously variable transmission and transmission device in the 1st gear range of the gear change pedal) When the speed change pedal 48 is operated to the first gear range, the hydraulic oil is supplied to the supply oil passage 71, and the hydraulic oil is discharged from the supply oil passages 72, 73, 74 and the branch oil passage 69, as shown in FIG.

[0154] As shown in Fig. 8, in the first clutch CL1, the piston 58 is operated to the pressing position A1, and the holding member 59 is operated to the allowing position B2 (see Fig. 5). In the second clutch CL2, the holding member 59 is operated to the holding position B1, and the piston 58 is operated to the intermediate position A3 (see Fig. 4). In the third clutch CL3 and the fourth clutch CL4, the piston 58 is operated to the disengaged position A2. As a result, the first clutch CL1 is operated to the transmission state, and the second, third and fourth clutches CL2, CL3 and CL4 are operated to the disengaged state.

[0155] As shown in FIG. 2, when the first clutch CL1 is operated into a transmission state, the power combined by the first planetary device 40 and the second planetary device 50 is transmitted from the ring gear 52 of the second planetary device 50 to the output shaft 27 via the first clutch CL1.

[0156] In the above-mentioned state, as shown in the 1st gear range in FIG. 7, the continuously variable transmission 18 is operated by the speed change pedal 48 to the maximum reverse speed position RMAX at the lowest speed position of the 1st gear range (the stop position of the speed change pedal 48), and the continuously variable transmission 18 is operated to the maximum forward speed position FMAX at the highest speed position of the 1st gear range, so that the continuously variable transmission 18 is operated between the maximum reverse speed position RMAX and the maximum forward speed position FMAX, and the rotational speed V of the output shaft 27 is changed steplessly between zero speed and speed V1.

[0157] (Gear change status by the continuously variable transmission and transmission device in the 2nd gear range of the gear change pedal) When the speed change pedal 48 is operated to the second range, the hydraulic oil is supplied to the supply oil passage 72, and the hydraulic oil is discharged from the supply oil passages 71, 73, 74 and the branch oil passage 69, as shown in FIG.

[0158] As shown in Fig. 8, in the first clutch CL1, the holding member 59 is operated to the holding position B1, and the piston 58 is operated to the intermediate position A3 (see Fig. 4). In the second clutch CL2, the piston 58 is operated to the pressing position A1, and the holding member 59 is operated to the allowing position B2 (see Fig. 5). In the third clutch CL3 and the fourth clutch CL4, the piston 58 is operated to the disengaged position A2. As a result, the second clutch CL2 is operated to the transmission state, and the first, third and fourth clutches CL1, CL3 and CL4 are operated to the disengaged state.

[0159] As shown in Figure 2, when the second clutch CL2 is operated to a transmission state, the power combined by the first planetary device 40 and the second planetary device 50 is transmitted from the sun gear 51 of the second planetary device 50 to the output shaft 27 via the second clutch CL2.

[0160] In the above-mentioned state, as shown in the second speed range in FIG. 7, the continuously variable transmission 18 is operated by the speed change pedal 48 to the maximum forward speed position FMAX at the lowest speed position of the second speed range, and to the maximum reverse speed position RMAX at the highest speed position of the second speed range, so that the continuously variable transmission 18 is operated between the maximum forward speed position FMAX and the maximum reverse speed position RMAX, and the rotational speed V of the output shaft 27 is changed steplessly between the speed V1 and the speed V2.

[0161] (Gear change status by the continuously variable transmission and transmission device in the 3rd gear range of the gear change pedal) When the speed change pedal 48 is operated to the third range, the hydraulic oil is supplied to the supply oil passage 73, and the hydraulic oil is discharged from the supply oil passages 71, 72, 74 and the branch oil passage 69, as shown in FIG.

[0162] As shown in Fig. 8, in the first clutch CL1 and the second clutch CL2, the holding member 59 is operated to the holding position B1, and the piston 58 is operated to the intermediate position A3 (see Fig. 4). In the third clutch CL3, the piston 58 is operated to the pressing position A1. In the fourth clutch CL4, the piston 58 is operated to the disengaged position A2. As a result, the third clutch CL3 is operated to the transmission state, and the first, second and fourth clutches CL1, CL2 and CL4 are operated to the disengaged state.

[0163] As shown in FIG. 2, when the third clutch CL3 is operated into a transmission state, the power combined by the first planetary device 40 and the second planetary device 50 is transmitted from the carrier 55 to the output shaft 27 via the third clutch CL3.

[0164] In the above-mentioned state, as shown in the third speed range in FIG. 7, the continuously variable transmission 18 is operated by the speed change pedal 48 to the maximum reverse speed position RMAX at the lowest speed position of the third speed range, and to the maximum forward speed position FMAX at the highest speed position of the third speed range, so that the continuously variable transmission 18 is operated between the maximum reverse speed position RMAX and the maximum forward speed position FMAX, and the rotational speed V of the output shaft 27 is changed steplessly between the speed V2 and the speed V3.

[0165] (Gear change status by the continuously variable transmission and transmission device in the 4-speed range of the gear change pedal) When the speed change pedal 48 is operated to the fourth range, the hydraulic oil is supplied to the supply oil passage 74 and the branch oil passage 69, and the hydraulic oil is discharged from the supply oil passages 71, 72, and 73, as shown in FIG.

[0166] As shown in Fig. 8, in the first clutch CL1 and the second clutch CL2, the piston 58 is operated to the disengaged position A2, and the holding member 59 is operated to the permitted position B2 (see Fig. 6). In the third clutch CL3, the piston 58 is operated to the disengaged position A2. In the fourth clutch CL4, the piston 58 is operated to the pressed position A1. As a result, the fourth clutch CL4 is operated to the transmission state, and the first, second and third clutches CL1, CL2 and CL3 are operated to the disengaged state.

[0167] As shown in Figure 2, when the fourth clutch CL4 is operated to a transmission state, the power combined by the first planetary device 40 and the second planetary device 50 is transmitted from the sun gear 51 of the second planetary device 50 to the output shaft 27 via the fourth clutch CL4.

[0168] In the above-mentioned state, as shown in the 4th speed range in FIG. 7, the continuously variable transmission 18 is operated to the maximum forward speed position FMAX by the speed change pedal 48 at the lowest speed position of the 4th speed range, and is operated to the maximum reverse speed position RMAX at the highest speed position of the 4th speed range (the highest speed position of the speed change pedal 48), so that the continuously variable transmission 18 is operated between the maximum forward speed position FMAX and the maximum reverse speed position RMAX, and the rotational speed V of the output shaft 27 is changed steplessly between speed V3 and speed V4.

[0169] (Correspondence to claims regarding branch oil passages) With the above configuration, when the transmission clutch (third clutch CL3) of the transmission system (input gear 63) having an adjacent transmission ratio to the transmission system (input gears 61, 62) having the hydraulic clutches (first clutch CL1 and second clutch CL2) is operated into a transmission state, an operating unit (branch oil passage 69) is provided which holds the piston 58 of the hydraulic clutch (first clutch CL1 and second clutch CL2) at the intermediate position A3 by the holding member 59.

[0170] When the transmission clutch (first clutch CL1) of the transmission system (input gear 61) of the lowest gear (1st gear) of all the gears is operated to a transmitting state, the operating unit (branch oil passage 69) holds the piston 58 of the hydraulic clutch (second clutch CL2) of the transmission system (input gear 62) of the gear (2nd gear) that is one step faster than the transmission system (input gear 61) of the lowest gear (1st gear) in an intermediate position A3 by the holding member 59.

[0171] When the transmission clutch (third clutch CL3) of the transmission system (input gear 63) of the gear stage (3rd gear) higher than the lowest gear stage (1st gear) of the transmission system (input gear 61) is operated to the transmission state, the operating unit (branch oil passage 69) holds the piston 58 of the hydraulic clutch (second clutch CL2) of the transmission system (input gear 62) of the gear stage (2nd gear) one step lower than the transmission system (input gear 63) in which the transmission clutch (third clutch CL3) is operated to the transmission state, in the intermediate position A3 by the holding member 59.

[0172] Among the transmission systems (input gears 63, 64) for the high-speed range gears (3rd gear and 4th gear), there is a transmission system (input gear 63) for the lowest gear (3rd gear), and a transmission system (input gear 64) for the high-speed range high-speed gear (4th gear), which is on the higher speed side.

[0173] Even if the transmission clutch (fourth clutch CL4) of the transmission system (input gear 64) of the high speed range high speed stage (4th gear) is operated to the transmitting state, the operating section (branch oil passage 69) does not hold the piston 58 of the hydraulic clutch (first clutch CL1 and second clutch CL2) of the transmission system (input gears 61, 62) of the low speed range gear stages (1st gear stage and 2nd gear stage) in the intermediate position A3.

[0174] The operating section (branch oil passage 69) is a branch oil passage 69 that branches off from a supply oil passage 74 that supplies hydraulic oil to operate the piston 58 of the transmission clutch (fourth clutch CL4) of the transmission system (input gear 64) of the high-speed range high-speed gear (4th gear) toward the pressing position A1, is connected to the oil chamber 68, and supplies a portion of the hydraulic oil from the supply oil passage 74 to the oil chamber 68.

[0175] (Response to claims regarding work vehicles) With the above configuration, the work vehicle (tractor) is equipped with a power source (engine 1), traveling gear (front wheels 6 and rear wheels 7), and a transmission system (input gears 61, 62) that transmits the power of the power source (engine 1) to the traveling gear (front wheels 6 and rear wheels 7), and the hydraulic clutch (first clutch CL1 and second clutch CL2) described in any one of claims 1 to 7 is provided in the transmission system (input gears 61, 62).

[0176] This is a work vehicle (tractor) equipped with a power source (engine 1), running gear (front wheels 6 and rear wheels 7), and a traveling transmission device 19 as described in claim 8 that transmits the power of the power source (engine 1) to the running gear (front wheels 6 and rear wheels 7).

[0177] (First Alternative Embodiment of the Invention) The branch oil passage 69 shown in Figures 3 to 6 may be eliminated, and an oil passage (not shown) and a control valve (not shown) for supplying and discharging hydraulic oil to the oil chamber 68 of the first clutch CL1, and an oil passage (not shown) and a control valve (not shown) for supplying and discharging hydraulic oil to the oil chamber 68 of the second clutch CL2 may be provided.

[0178] In the above-described configuration, the state shown in Figure 8 can be obtained by operating four control valves that supply and discharge hydraulic oil to and from the supply oil passages 71-74 and two control valves that supply and discharge hydraulic oil to and from the oil chambers 68 of the first clutch CL1 and the second clutch CL2. In this case, the oil passages and the control valves that supply and discharge the hydraulic oil to and from the oil chambers 68 of the first clutch CL1 and the second clutch CL2 serve as the operating portion.

[0179] (Second Alternative Embodiment of the Invention) Of the first clutch CL1 to the fourth clutch CL4 shown in Figures 2 and 3, only one may be configured to have a retaining member 59 so that the intermediate position A3 can be set, and the other three may be configured not to have the retaining member 59 so that the intermediate position A3 cannot be set.

[0180] Of the first clutch CL1 to the fourth clutch CL4 shown in Figures 2 and 3, only three of them may have a retaining member 59 and be configured so that the intermediate position A3 can be set, and the remaining one may be configured so that it does not have a retaining member 59 and the intermediate position A3 cannot be set. All of the first clutch CL1 to the fourth clutch CL4 shown in FIG. 2 and FIG. 3 may be configured to have a retaining member 59 and to be able to set the intermediate position A3.

[0181] (Third Alternative Embodiment of the Invention) When configured as described above in the (second variant embodiment of the invention), the configuration described above in the (first variant embodiment of the invention) may be adopted.

[0182] (Fourth Alternative Embodiment of the Invention) In the transmission device 19, in addition to the four transmission systems, one or more additional transmission systems may be added, and the additional transmission systems may be provided with transmission clutches (hydraulic clutches).

[0183] 2 and 3, when five transmission systems are provided, the first and second speed stages may be transmission systems for low speed range gears, and the third, fourth and fifth speed stages may be transmission systems for high speed range gears. In this case, when the transmission clutch for the fourth or fifth speed stage is operated to a transmission state, the pistons 58 of the first and second clutches CL1 and CL2 of the first and second speed stages may be configured to be operated to an intermediate position A3.

[0184] 2 and 3, when five transmission systems are provided, the first, second and third gears may be transmission systems for low-speed range gears, and the fourth and fifth gears may be transmission systems for high-speed range gears. In this case, when the transmission clutch for the fifth gear is operated to a transmitting state, the pistons 58 of the first, second and third clutches CL1, CL2 and CL3 of the first, second and third gear transmission systems may be configured to be operated to an intermediate position A3.

[0185] (Fifth Alternative Embodiment of the Invention) In the first clutch CL1 and the second clutch CL2, the intermediate position A3 may be set to a central position between the pressing position A1 and the separation position A2, or may be set farther from the friction plate 57 than the central position between the pressing position A1 and the separation position A2.

[0186] (Correspondence to claims in the fifth embodiment of the invention) With the above-mentioned configuration, the intermediate position A3 is set farther from the friction plate 57 than the central position between the pressing position A1 and the separating position A2.

[0187] (Sixth Alternative Embodiment of the Invention) The intermediate position A3 of the first clutch CL1 may be set farther from the friction plate 57 than the central position between the pressing position A1 and the separation position A2, and the intermediate position A3 of the second clutch CL2 may be set closer to the friction plate 57 than the central position between the pressing position A1 and the separation position A2.

[0188] The intermediate position A3 of the first clutch CL1 may be set closer to the friction plate 57 than the central position between the pressing position A1 and the separation position A2, and the intermediate position A3 of the second clutch CL2 may be set farther from the friction plate 57 than the central position between the pressing position A1 and the separation position A2.

[0189] The intermediate position A3 of the first clutch CL1 and the intermediate position A3 of the second clutch CL2 are set closer to the friction plate 57 than the central position between the pressing position A1 and the separating position A2, and may be set at different positions from each other in this state.

[0190] The intermediate position A3 of the first clutch CL1 and the intermediate position A3 of the second clutch CL2 are set farther from the friction plate 57 than the central position between the pressing position A1 and the separating position A2, and may be set at different positions from each other in this state.

[0191] (Seventh Alternative Embodiment of the Invention) The first planetary gear 40 and the second planetary gear 50 shown in FIG. 2 may be eliminated, and a plurality of transmission devices 19 may be connected in series, so that the power transmission system for the traveling system is constructed inside the transmission case 3.

[0192] In a configuration in which a plurality of transmission devices 19 are connected in series, the numbers of transmission systems of the transmission devices 19 may be set to be different from each other. In this case, the transmission device 19 having the greater number of transmission systems may be set as the main transmission device 19, and the transmission device 19 having the smaller number of transmission systems may be set as the sub transmission device 19.

[0193] (Eighth Alternative Embodiment of the Invention) A motor (not shown) may be provided as a power source instead of the engine 1, and a hybrid type power source may be provided by combining the engine 1 and a motor (not shown).

[0194] (Ninth Alternative Embodiment of the Invention) A crawler traveling device may be provided as the rear traveling device instead of the rear wheels 7. According to this configuration, right and left front wheels 6 are provided as the front traveling devices, and right and left crawler traveling devices are provided as the rear traveling devices. The front wheels 6 and rear wheels 7 may be eliminated, and right and left crawler running devices may be provided as the running devices. [Industrial Applicability]

[0195] The present invention can be applied not only to tractors, but also to agricultural work vehicles such as combine harvesters and riding rice transplanters, and to the hydraulic clutches and transmission devices for traveling that are equipped on these agricultural work vehicles.The present invention can also be applied to construction work vehicles such as backhoes and wheel loaders, and to the hydraulic clutches and transmission devices for traveling that are equipped on these construction work vehicles. [Explanation of symbols]

[0196] 1 Engine (power source) 6 Front wheels (running gear) 7 Rear wheels (running gear) 19 Transmission 57 Friction plate 58 Piston 59 Retaining member 61 Input gear (transmission system) 62 Input gear (transmission system) 63 Input gear (transmission system) 64 Input gear (transmission system) 65 Spring (first biasing member) 66 Spring (second biasing member) 68 Oil room 69 Branch oil passage (operating part) 74 Oil supply line A1 Pressing position A2 Separate position A3 intermediate position B1 holding position B2 Permitted position CL1 First clutch (transmission clutch) (hydraulic clutch) CL2 Second clutch (transmission clutch) (hydraulic clutch) CL3 3rd clutch (transmission clutch) CL1 4th clutch (transmission clutch) W1 Spacing W3 Spacing W4 Spacing

Claims

1. A friction plate capable of transmitting power; a piston that is movable between a pressing position where the friction plate is pressed to obtain a power transmission state and a separated position where the friction plate is separated to obtain a power interruption state, and that is operated to the pressing position by supplying hydraulic oil that operates the piston toward the pressing position; a hydraulic clutch provided with a holding member that can hold and release the piston at an intermediate position between the pressed position and the separated position by contact with the piston;

2. 2. The hydraulic clutch according to claim 1, wherein the intermediate position is set closer to the friction plates than a center position between the pressed position and the separated position.

3. 2. The hydraulic clutch according to claim 1, wherein the intermediate position is set farther from the friction plates than a center position between the pressed position and the separated position.

4. the retaining member is movable to a retaining position capable of retaining the piston at the intermediate position, and a permitting position located on a side of the friction plate with respect to the retaining position and permitting movement of the piston to the pressing position, A first biasing member that biases the holding member toward the holding position; a second biasing member that biases the piston toward the pressing position and has a biasing force smaller than that of the first biasing member, 2. The hydraulic clutch according to claim 1, wherein the piston is held in the intermediate position by the piston attempting to move toward the pressing position by the second biasing member hitting the holding member operated to the holding position by the first biasing member.

5. 5. The hydraulic clutch according to claim 4, wherein the piston is operated to the pressing position against the first biasing member by supplying hydraulic oil that operates the piston toward the pressing position, and the retaining member is operated to the permissible position by the piston.

6. 5. The hydraulic clutch according to claim 4, wherein the piston is operated to the separated position against the second biasing member by supplying hydraulic oil that operates the piston toward the separated position.

7. an oil chamber is provided between the piston and the holding member; 7. The hydraulic clutch according to claim 6, wherein the piston is operated to the separated position against the second biasing member, and the retaining member is operated to the permitted position against the first biasing member, by supplying hydraulic oil to the oil chamber.

8. A transmission system having a plurality of gear stages with different transmission ratios; a transmission clutch provided in each of the transmission systems; The transmission clutch includes a friction plate capable of transmitting power, and a piston that is movable between a pressing position where the friction plate is pressed to obtain a transmission state in which power is transmitted, and a separation position where the piston is separated from the friction plate to obtain a disconnection state in which power is disconnected, and is operated to the pressing position by supplying hydraulic oil that operates the piston toward the pressing position, A driving transmission device in which power is transmitted through the transmission system in which the transmission clutch is operated to a transmission state, A transmission device for traveling, wherein at least one of the transmission clutches is the hydraulic clutch according to any one of claims 1 to 7.

9. 9. The driving transmission device according to claim 8, wherein in the transmission system of a gear in a low speed range among all gears and the transmission system of a gear in a high speed range among all gears, the transmission clutch of the transmission system of the gear in the low speed range is the hydraulic clutch.

10. 10. The driving transmission device according to claim 9, wherein the distance between the pressed position and the separated position of the transmission clutch of the transmission system for the gear shift stage in the high speed region is set to be smaller than the distance between the hydraulic clutch of the transmission system for the gear shift stage in the low speed region.

11. 9. A transmission device for traveling as described in claim 8, further comprising an operating unit that holds the piston of the hydraulic clutch in the intermediate position by the retaining member when the transmission clutch of the transmission system having an adjacent transmission ratio to the transmission system having the hydraulic clutch is operated into a transmission state.

12. The operation unit includes: When the transmission clutch of the transmission system of the lowest gear among all the gears is operated to a transmission state, the piston of the hydraulic clutch of the transmission system of the gear that is one step higher than the transmission system of the lowest gear is held at the intermediate position by the holding member, 12. A driving transmission device as described in claim 11, wherein when the transmission clutch of the transmission system of a gear stage higher than the lowest gear stage is operated into a transmission state, the piston of the hydraulic clutch of the transmission system of the gear stage one stage lower than the transmission system in which the transmission clutch is operated into the transmission state is held in the intermediate position by the holding member.

13. In the transmission system of a gear stage in a low speed range among all the gear stages and the transmission system of a gear stage in a high speed range among all the gear stages, the transmission clutch of the transmission system of the gear stage in the low speed range is the hydraulic clutch, In the transmission system of a high speed region high speed stage, which is a high speed side with respect to the transmission system of a lowest speed gear stage among the transmission systems of the high speed region gear stages, The operation unit includes:

13. A driving transmission device according to claim 12, wherein even if the transmission clutch of the transmission system of the high speed range high speed stage is operated to a transmission state, the piston of the hydraulic clutch of the transmission system of the low speed range gear stage is not held in the intermediate position.

14. The hydraulic clutch of the transmission system for the gear stage in the low speed range is the hydraulic clutch according to claim 7, The operation unit includes:

14. A traveling transmission device as described in claim 13, wherein the branch oil passage is branched off from a supply oil passage that supplies hydraulic oil for operating the piston of the transmission clutch of the transmission system in the high-speed region high-speed stage toward the pressing position, is connected to the oil chamber, and supplies a portion of the hydraulic oil from the supply oil passage to the oil chamber.

15. A power source; The running gear, a transmission system that transmits the power of the power source to the traveling device, A work vehicle, comprising: a hydraulic clutch according to any one of claims 1 to 7; and a transmission system provided with the hydraulic clutch.

16. A power source; The running gear, A work vehicle comprising: the transmission device for traveling according to claim 8, which transmits the power of the power source to the traveling device.

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