JP2005263170A - Traveling device for four-wheel drive type tractor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize simplification and miniaturization of a structure of a control part in a front wheel shift mechanism. <P>SOLUTION: The front wheel shift mechanism is constituted such that the standard driving state and the speed increase driving state are brought by operation of a shift clutch constituted to hydraulic operation form. A front wheel control valve V1 for operating the shift clutch is connected to a front wheel steering mechanism and the front wheel control valve V1, an automatic shift selection valve V2 for ON/OFF selecting automatic shift of the front wheel and a check valve V3 connected to a shift operation system of a side-shift mechanism interposed on a front wheel traveling transmission system are arranged in series. When the automatic shift selection valve V2 is switched to an automatic shift ON position and the side shift mechanism is not operated to a high speed position, hydraulic operation of the shift clutch is performed through the front wheel control valve V1, the automatic shift selection valve V2 and the check valve V3. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention switches the steered front wheel between a standard drive state in which the front wheel is driven at a peripheral speed equivalent to the peripheral speed of the rear wheel and a speed-up drive state in which the front wheel is driven at a peripheral speed faster than the peripheral speed of the rear wheel. The present invention relates to a four-wheel drive tractor traveling device that includes a front wheel speed change mechanism that is configured to automatically switch the front wheel speed change mechanism from a standard drive state to an accelerated drive state in conjunction with steering greater than a set angle of the front wheels. .

  The traveling device configured as described above is capable of automatically turning the front wheel and turning smoothly smoothly by turning the front wheel at the time of turning the aircraft at the shore, etc. In recent years, it has been adopted by many tractors as an excellent one.

The front wheel automatic shift is not always required, and depending on the working conditions, it may be better not to perform the front wheel automatic shift, and it may rather not function when traveling at high speeds, such as during traveling Is preferred. In view of this, a selection means for artificially entering the front wheel automatic shift function arbitrarily and a check means for blocking the front wheel automatic shift when the traveling speed becomes high are introduced. As shown in Patent Document 2, a switching lever that arbitrarily switches the front wheel automatic shift function and a sub-shift lever for traveling are mechanically linked, or, as disclosed in Patent Document 2, a front sensor is operated by a steering sensor. The steering angle is detected, the front wheel drive mode is selected with the mode switch, the running speed is detected with the vehicle speed sensor, and the hydraulically operated front wheel transmission mechanism is electrically controlled from these information Have been proposed.
JP-A-10-217788 JP 2001-277880 A

  However, in the former structure that performs mechanical linkage and restraint control, the mechanism is complicated and many parts are required, and the functional characteristics may change due to wear and deformation of the parts. Sufficient maintenance management was necessary to make it happen. In addition, the latter structure that performs electrical control is easier to maintain than the former, but on the other hand, it requires expensive electromagnetic control valves, sensors, and a control device. It was something that could only be installed on high-end models.

  The present invention has been made paying attention to such points, and is capable of suitably exhibiting necessary functions relating to front wheel automatic transmission while being able to be configured at low cost. Is the main purpose.

The first invention includes a standard drive state in which the steered front wheel is driven at a peripheral speed equivalent to the peripheral speed of the rear wheel, and an accelerated drive state in which the front wheel is driven at a peripheral speed faster than the peripheral speed of the rear wheel. A four-wheel drive tractor configured to automatically switch the front wheel speed change mechanism from the standard drive state to the speed increasing drive state in conjunction with the steering more than the set angle of the front wheel. In the traveling device,
The front wheel speed change mechanism is configured such that the standard drive state and the acceleration drive state are brought about by the operation of a hydraulically operated speed change clutch, and the front wheel control valve for operating the speed change clutch is a front wheel steering mechanism. Linked to
The front wheel control valve, an automatic transmission selection valve for selecting whether automatic transmission of the front wheel is turned on and off, and a check valve linked to the transmission operation system of the auxiliary transmission mechanism interposed in the front wheel traveling transmission system are arranged in series.
When the automatic transmission selection valve is switched to the automatic transmission entering position and the auxiliary transmission mechanism is not operated to the high speed position, the hydraulic operation of the transmission clutch is performed through the automatic transmission selection valve, the check valve, and the front wheel control valve. Is configured to be performed.

  According to the above configuration, when the automatic transmission selection valve is switched to the automatic transmission entering position and the sub transmission mechanism is operated to a position other than the high speed position and the aircraft is traveling at a low speed, the steering more than the set angle of the front wheels is performed. The front wheel control valve is switched in conjunction with the automatic transmission selection valve, the check valve, and the front wheel control valve, and the transmission clutch is hydraulically operated through the front wheel speed increase. Also, if the auxiliary transmission mechanism is switched to the high speed position while the automatic transmission selection valve is switched to the automatic transmission entering position, even if the front wheel is steered beyond the set angle and the front wheel control valve is switched, The shift clutch is prevented from being hydraulically operated by the check function on the hydraulic circuit of the check valve, and the front wheel acceleration state is not brought about. In addition, even when the automatic transmission selection valve is switched to the automatic transmission switching position, the automatic transmission selection means that the transmission clutch is hydraulically operated even if the front wheels are steered beyond the set angle and the front wheel control valve is switched. It is blocked by the check function on the hydraulic circuit of the valve, and the front wheel acceleration state is not brought about.

  Therefore, according to the first aspect of the invention, the front wheel automatic shift on / off function and the front wheel speed increase check inhibition function during high speed traveling are exhibited on the hydraulic circuit by the automatic shift selection valve, the check valve, and the front wheel control valve. Therefore, the structure is simpler than that of the conventional mechanical type, and the functional characteristics are hardly changed with the wear and deformation of the parts, so that maintenance management becomes easy. In addition, it can be implemented at a lower cost than the conventional electric control type.

According to a second invention, in the first invention,
The automatic transmission selection valve, the check valve, and the front wheel control valve are each configured as a rotary valve.

  The rotary valve can be manufactured at a lower cost than the type of valve that linearly moves the spool, and the occurrence of backlash and wear is small, and the first invention can be implemented suitably and inexpensively.

According to a third invention, in the first or second invention,
The automatic transmission selection valve, the check valve, and the front wheel control valve are mounted on a single valve casing.

  According to the above configuration, since the oil passage between the valves can be formed in the valve casing, these valve groups can be linked by a hydraulic circuit without the need for external piping. The above-described effects of the present invention are brought about, and the hydraulic control unit is made compact and cost effective.

According to a fourth invention, in the third invention,
Of the automatic transmission selection valve, the check valve, and the front wheel control valve, the spool axial direction of the valve located in the middle of the pressure oil flow direction is different from the spool axial direction of the other valves. And

  According to the above configuration, even if the three valves are arranged close to each other, the spool interval between the other two valves positioned before and after the pressure oil flow direction becomes large. The operation lever can be deployed without interfering, and the three rotary valves can be assembled in a single valve casing in a compact and easy-to-operate state, which promotes the effects of the third invention. .

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows an overall side view of a four-wheel drive agricultural tractor equipped with the transmission structure of the present invention, and FIG. 3 shows a side view of the airframe structure. In this tractor, a clutch housing 2 connected to the rear portion of the engine 1 and a rear transmission case portion including a transmission case 3 and a differential case 5 are connected via a housing frame 4 made of sheet metal to constitute a body body. The left and right rear wheels 6 are pivotally supported on the differential case 5 directly connected to the rear end of the transmission case 3 and the rear PTO shaft 7 protrudes backward, and the left and right front wheels 8 are operated. A front axle case 9 provided so as to be freely oriented is mounted and supported in a freely rolling manner at a lower portion of a front frame 10 connected to the engine 1.

  As shown in FIGS. 4 and 5, a single-plate dry type main clutch 11 is mounted on the upper portion of the clutch housing 2, and a hydraulic continuously variable for traveling is provided at the front end of the transmission case 3 constituting the rear transmission case portion. A transmission case 12 is connected, and the rear end of the housing frame 4 is connected to the hydraulic continuously variable transmission case 12. The hydraulic continuously variable transmission case 12 includes a case main body 12a whose rear side is opened and a thick port block 12b connected to the rear end thereof. The variable capacity type is configured in an axial plunger type above the case. The pump portion P is incorporated, and a constant capacity motor portion M configured in an axial plunger type is incorporated below the case, and the input shaft 13 serving as a pump shaft extends between the case body 12a and the port block 12b. The front projecting end of the input shaft 13 and the clutch output shaft 14 projecting rearward from the clutch housing 2 are concentrically linked via a main transmission shaft 15.

  The hydraulic continuously variable transmission mechanism incorporated in the hydraulic continuously variable transmission case 12 changes the pressure oil discharge amount and the discharge direction by changing the swash plate angle of the pump part P. A well-known structure is employed in which the output shaft 16 is driven in a continuously variable manner in the forward or reverse direction. This hydraulic continuously variable transmission mechanism switches between a continuously variable transmission capable of starting at zero speed and a forward / reverse operation. The main transmission mechanism is a pedal operation type.

  The mission case 3 is opened at the front and rear, and an intermediate partition wall 3a is provided at the front and rear intermediate portion, so that the mission case 3 is divided into the front and rear. A traveling system shaft support part a and a PTO system shaft support part b are formed on the lower and upper parts of the intermediate partition wall 3a, and the transmission of the traveling system supported over the travel system shaft support part a and the front wall 5a of the differential case 5 is performed. The shaft 17 and the output shaft 16 of the motor M are concentrically connected.

  A bevel pinion shaft 18, which is the final transmission shaft, is supported across the intermediate partition wall 3 a and the front wall 5 a of the differential case 5 in a section behind the intermediate partition wall 3 a, and the bevel pinion shaft 18 and the transmission shaft 17 are connected to each other. A sub-transmission mechanism 19 for the traveling system is provided between them. The traveling transmission sub-transmission mechanism 19 shifts the shift gear G1 spline-fitted to the transmission shaft 17 to shift the bevel pinion shaft 18 in three stages, and the left and right sides via the differential mechanism D engaged with the bevel pinion gear Gp. The rear wheel 6 is configured to be driven to change speed.

  More specifically, a large-diameter loosely fitted gear G2 and a small-diameter loosely fitted gear G3 are attached to the front and rear of the transmission shaft 17, and a small-diameter gear G4 that always meshes with the large-diameter loosely fitted gear G2 on the bevel pinion shaft 18. A large-diameter gear G5 that always meshes with the small-diameter loose fitting gear G3 is fixed, and a bevel pinion shaft 18 is fixed with a medium-diameter gear G6 that can be directly engaged with the shift gear G1, and the shift gear G1 is shifted rearward. By engaging the boss portion with the boss portion of the small-diameter loosely fitting gear G3, "low speed" is brought about by the transmission in the gear ratio between the small-diameter loosely-fitting gear G3 and the large-diameter gear G5, and the shift gear G1 is intermediated between the front and rear. By shifting to the position and meshing directly with the medium-diameter gear G6, transmission at the gear ratio between the shift gear G1 and the medium-diameter gear G6 brings about “medium speed”, and further shifts the shift gear G1 forward. Teso By occlusion connecting the boss portion to the boss portion of the large 径遊 fitting gear G2, it is the "fast" is caused by the transmission in the gear ratio between the large 径遊 fitting gear 2 and the small-diameter gear G4.

  As described above, an output gear G7 for power transmission to the front wheels 8 is fixed to the front end portion of the bevel pinion shaft 18 that is continuously variable in the forward and reverse directions hydraulically and is shifted in three stages by the auxiliary transmission mechanism 19. Has been. Further, the intermediate partition wall 3a and the hydraulic continuously variable transmission case 12 are provided with a front wheel drive system shaft support portion c, through which a front wheel drive transmission shaft 20 is penetratingly supported. A shift gear G8 is spline-fitted to the rear end portion of the front wheel drive transmission shaft 20. By shifting the shift gear G8 forward and meshing with the output gear G7 of the bevel pinion shaft 18, the rear wheel drive speed. The four-wheel drive state in which the front-wheel drive power at a speed synchronized with the front-wheel drive is extracted from the front-wheel drive transmission shaft 20, and the shift gear G8 is shifted rearward to release the engagement with the output gear G7. The drive is cut off, and the rear two-wheel drive state by only the rear wheel 6 is brought about.

  On the other hand, as shown in FIG. 2, the clutch housing 2 is provided with a dry clutch chamber d in which the main clutch 11 is accommodated, and a wet (oil bath lubrication) transmission chamber e isolated from the clutch chamber d. The transmission chamber e is equipped with a front-wheel transmission mechanism 21 that receives the front-wheel drive power taken forward from the front-wheel drive transmission shaft 20. The front wheel speed change mechanism 21 includes an input shaft 23 concentrically connected to the front wheel drive transmission shaft 20 via an intermediate shaft 22 and a speed change shaft 24 parallel thereto. The transmission shaft 24 is shifted to two levels by turning the transmission clutch 25 on and off, and this transmission power is transmitted to the front wheel drive shaft 26 arranged at the lower end of the clutch housing 2 and taken out from the front wheel drive shaft 26 forward. Further, it is configured such that the transmission power of two steps of high and low is transmitted to the front axle case 9.

  The input shaft 23 is provided with a large-diameter gear G9 and a small-diameter gear G10, and the transmission shaft 24 is provided with a small-diameter idle gear G11 and a large-diameter idle gear G12 that are always engaged with these gears G9 and G10. ing. As shown in FIG. 6, the transmission clutch 25 provided on the transmission shaft 24 is a multi-plate type between a clutch drum 27 fixed to the transmission shaft 24 and a spline boss portion 28 provided continuously with the small-diameter idle gear G11. The piston member 30 fitted and fitted to the clutch drum 27 is moved forward and backward by the pressure oil supplied and discharged through the in-shaft oil passage and the built-in spring 31. The clutch is engaged or disengaged by pressing or releasing the pressure contact.

  Further, a shift member 32 that is externally fitted to the boss portion of the clutch drum 27 is integrated with the piston member 30 via a connecting pin 33 that penetrates the clutch drum 27, and the piston member 30 is moved forward and backward. Thus, the shift member 32 is integrally shifted.

  In the state where the pressure oil supply is cut off, as shown in FIG. 6, the piston member 30 is displaced backward to the left in the drawing by the spring 31 and the speed change clutch 25 enters the “disengaged” state, and the piston member A shift member 32 integrated with 30 is engaged with the large-diameter idle gear G12 on the side surface, and the power of the input shaft 23 passes through the small-diameter gear G10, the large-diameter idle gear G12, the shift member 32, and the clutch drum 27. After being decelerated and transmitted to the transmission shaft 24, it is taken out from the front end of the transmission shaft 24 and transmitted to the front axle case 9 via the front wheel drive shaft 26. In this case, the front wheels 8 are driven at a peripheral speed equivalent to (or slightly faster than) the rear wheel peripheral speed, so that a standard four-wheel drive mode appears.

  Further, as shown in FIG. 7, the piston member 30 moves to the right in the drawing against the internal spring 31 by the supply of pressure oil and presses the friction transmission portion 29 to bring the transmission clutch 25 into the “on” state. And the shift member 32 integrated with the piston member 30 is released from the large-diameter idle gear G12, and the power of the input shaft 23 is increased by the large-diameter gear G9, the small-diameter idle gear G11, the friction transmission unit 29, and After being transmitted to the transmission shaft 24 through the clutch drum 27, the transmission is transmitted to the front axle case 9 through the front wheel drive shaft 26. In this case, the front wheels 8 are driven at a peripheral speed that is about twice the peripheral speed of the rear wheels, so that a front wheel acceleration drive mode appears.

  As shown in the hydraulic circuit diagram of FIG. 8, the pressure oil supply / discharge oil passage of the transmission clutch 25 is provided with a front wheel control valve V1 that is switched in conjunction with the steering of the front wheels 8, and an automatic transmission of the front wheels 8. An automatic transmission selection valve V2 for selecting on / off and a check valve V3 that is switched in conjunction with the speed change operation of the subtransmission mechanism 19 are arranged in series, and pressure oil from a hydraulic pump OP driven by engine power Is supplied to the front wheel shift hydraulic circuit f after passing through the power steering unit 67 and the oil cooler 68, and the return oil from the front wheel shift hydraulic circuit f is supplied to the charge circuit g of the hydraulic continuously variable transmission case 12. It has become so.

  As shown in FIGS. 6 to 9, the front wheel control valve V <b> 1, the automatic transmission selection valve V <b> 2, and the check valve V <b> 3 are each configured as a rotary valve, and these valves V <b> 1, V <b> 2, V <b> 3 are connected to the rear part of the clutch housing 2. The single valve casing 70 is assembled. While the front wheel control valve V1 and the check valve V3 are arranged in parallel, the automatic transmission selection valve V2 positioned between them has a spool shaft center of the other valves V1 and V2. It is arranged to be orthogonal to.

  An operating lever 74 attached to the spool end of the front wheel control valve V1 is mechanically linked to the steering mechanism 71 of the front wheel 8, and when the front wheel 8 is in a straight traveling state, the oil passage is shut off, and the front wheel 8 is in a straight traveling position. When the steering wheel is steered to the left or right beyond a set angle (for example, 35 °), the front wheel control valve V1 is rotated to open the oil passage. Further, an operation lever 75 attached to the spool end of the automatic transmission selection valve V2 is linked to the switching lever 72. The oil passage is opened at the automatic transmission “ON” position, and the oil passage is opened at the automatic transmission “OFF” position. Blocked. An operation lever 76 attached to the spool end of the check valve V3 is linked to a sub-transmission lever 73 that switches the sub-transmission mechanism 19 that changes the traveling speed in three stages. ”Or“ medium speed ”, the oil passage is opened, and when the auxiliary transmission mechanism 19 is operated“ high speed ”, the oil passage is blocked.

  Accordingly, as shown in FIGS. 7 and 8, the automatic transmission selection valve V2 is selected to the automatic transmission “on” position, the oil passage is opened, and the auxiliary transmission mechanism 19 is operated to “low speed” or “medium speed”. In the state where the check valve V3 opens the oil passage, the front wheel control valve V1 is switched in conjunction with the steering more than the set angle of the front wheel 8, pressure oil is supplied to the transmission clutch 25, and the front wheel 8 Is driven at an increased speed, and a smooth small turn is performed. Even if the automatic transmission selection valve V2 is selected to the automatic transmission “on” position, if the auxiliary transmission mechanism 19 is in “high speed”, the front wheel automatic transmission is performed regardless of the steering angle greater than the set angle of the front wheels 8. Never executed. Further, as shown in FIG. 9, if the automatic transmission selection valve V2 is selected to the automatic transmission “off” position and the oil passage is closed, naturally, the front wheel automatic transmission is also performed by steering the front wheels. Absent.

  Next, the PTO transmission system will be described.

  The rear end of the input shaft 13 penetratingly supported at the upper part of the hydraulic continuously variable transmission case 12 and the PTO transmission shaft 35 supported by the PTO shaft support b of the intermediate partition wall 3a are concentrically arranged. In addition, a multi-plate PTO clutch 36 that is hydraulically operated is interposed between the two.

  As shown in FIG. 11, the PTO clutch 36 includes a clutch drum 37 splined to the rear end of the input shaft 13, a shift member 38 externally fitted to the PTO transmission shaft 35 so as to be shiftable, and the shift member 38. A clutch sleeve 39 that is externally fitted to the member 38 by a spline so as to be relatively shiftable, a multi-plate friction transmission portion 40 that is interposed between the clutch drum 37 and the clutch sleeve 39, and a clutch operating piston member that is internally fitted to the clutch drum 37 41, a spring 42 that urges the piston member 41 in the friction releasing direction, and the like, and is supplied with pressure oil via an in-shaft oil passage to resist the piston member 41 against the spring 42 and to the right in the figure. The clutch is brought into a state in which the friction transmission unit 40 is in pressure contact with each other, the pressure oil supply is released, and the piston member 41 is 42 By displacing to the left in the figure, "clutch disengaging" state pressure has been released the friction transmission portion 40 is adapted to be brought.

  In the “clutch engaged” state, the power transmitted to the clutch sleeve 39 is transmitted to the PTO transmission shaft 35 via the shift member 38 and concentrically connected to the rear end of the PTO transmission shaft 35. It is transmitted to the rear part of the differential case 5 through 43, and is greatly decelerated by gears G13 and G14 mounted on the rear part of the differential case 5 and taken out from the rear PTO shaft 7.

  Further, a PTO braking mechanism 45 that prevents inertial rotation on the lower side of the transmission in conjunction with the “clutch disengagement” operation is disposed at a rear portion of the PTO clutch 36. The PTO braking mechanism 45 includes a friction plate 46 fitted to the clutch sleeve 39 by a spline, a receiving member 47 fixed inside the transmission case 3, and a braking plate engaged and supported in the transmission case 3 so as not to rotate. 48. When the PTO clutch 36 is turned off and the piston member 41 is urged and moved to the left in the drawing by the internal spring 42, the clutch sleeve 39 moves in the same direction as the piston member 41. The friction plate 46 is sandwiched between the receiving member 47 and the brake plate 48 so that the clutch sleeve 39 is braked.

  As shown in FIG. 4, a mid PTO case 51 that projects and supports a mid PTO shaft 50 toward the front is bolted to the lower surface of the transmission case 3 in front of the intermediate partition wall 3a. In the section in front of the intermediate partition wall 3a, the PTO transmission shaft 35 and the mid PTO shaft 50 are gear-linked to the mid PTO transmission mechanism 52, and the power extraction form from the rear PTO shaft 7 and the mid PTO shaft 50 is changed. A PTO mode selection mechanism 53 is provided.

  Here, in the mid PTO transmission mechanism 52, the power take-out gear G15 loosely fitted to the rear portion of the PTO transmission shaft 35 and the gear G16 integrally formed with the mid PTO shaft 50 are connected to the relay gears G17, G18, G19. The relay gear G17 is loosely fitted to the front wheel drive transmission shaft 20, the relay gear G18 is loosely supported on the traveling system transmission shaft 17, and the relay gear G19 is It is loosely supported by a support shaft 54 attached to the lower wall portion of the transmission case 3. The upper back portion of the mounting seat 3b is closed by the bottom wall when the transmission case 3 is molded. However, in the specification in which the mid PTO case 51 is mounted, the upper back portion of the mounting seat 3b is cut for power extraction. It will be chipped.

  The PTO mode selection mechanism 53 shifts the shift member 38 back and forth to transmit power only to the rear PTO shaft 7 and a mode to transmit power to both the rear PTO shaft 7 and the mid PTO shaft 50. A mode for transmitting power only to the mid PTO shaft 50 is selected. As shown in FIG. 12, when the shift member 38 is shifted to the foremost position, the shift member 38 is a spline portion of the PTO transmission shaft 35. The power transmitted to the shift member 38 via the PTO clutch 36 is transmitted only to the rear PTO shaft 7 via the intermediate transmission shaft 43.

  When the shift member 38 is shifted to the front / rear intermediate position, the shift member 38 is splined over the spline portion 35a of the PTO transmission shaft 35 and the boss portion of the power take-out gear G15 as shown in FIG. The power transmitted to the shift member 38 via the PTO clutch 36 is transmitted to the rear PTO shaft 7 via the intermediate transmission shaft 43, and also transmitted to the mid PTO shaft 50 via the mid PTO transmission mechanism 52. The

  As shown in FIG. 13, when the shift member 38 is shifted to the rearmost position, the shift member 38 is splined only to the boss portion of the power take-out gear G15, and the shift member 38 is connected via the PTO clutch 36. The power transmitted to 38 is transmitted only to the mid PTO shaft 50 via the mid PTO transmission mechanism 52.

  Here, when the transmission mode in which only the mid PTO shaft 50 is driven by the PTO mode selection mechanism 53 is selected for the shaft coupling sleeve 55 that is externally splined across the PTO transmission shaft 35 and the intermediate transmission shaft 43. In addition, the rear PTO shaft 7 that has become free functions as a PTO brake B that prevents the rear PTO shaft 7 from rotating together.

  The shaft coupling sleeve 55 is splined so that it can shift back and forth, and its operating system is linked so that the shaft coupling sleeve 55 is shifted in the reverse direction in synchronization with the shift member 38 for selecting the PTO mode. ing. That is, as shown in FIGS. 14 and 15, the operation shaft 56 provided with the eccentric operation pin 56 a engaged with the shift member 38, and the operation shaft 57 provided with the operation arm 57 a engaged with the shaft connection sleeve 55. Is inserted through the side wall of the transmission case 3, an operation pin 56 b provided at the outer end of the operation shaft 56, and a PTO mode selection lever 58 arranged to swing back and forth around the fulcrum p via a rod 59. The linkage lever 57b extended from the outer end of the operation shaft 57 and the operation pin 56b are linked to each other through a long hole, and the shift member 38 and the shaft are pivoted by a forward / backward swing operation of the PTO mode selection lever 58. The connecting sleeve 55 is shifted in the opposite direction.

  Accordingly, the transmission mode in which the shift member 38 is shifted to the foremost position and the front / rear intermediate position and only the rear PTO shaft 7 is driven, or the transmission mode in which both the rear PTO shaft 7 and the mid PTO shaft 50 are driven is selected. In this state, the shaft coupling sleeve 55 is located at the rearmost position or the front / rear intermediate position of the shift range, and the shaft coupling sleeve 55 at this time functions as a mere shaft joint. Then, as shown in FIG. 13, when the shift member 38 is shifted to the rearmost position and the transmission mode in which only the mid PTO shaft 50 is driven is selected, the shaft connection is interlocked with the rear shift of the shift member 38. The sleeve 55 moves forward, and the front end engaging claw 55a of the shaft connecting sleeve 55 is engaged from behind with the rib 60 formed on the rear surface of the intermediate partition wall 3a in the transmission case 3, so that the PTO brake B functions. Thus, the rotation of the PTO transmission shaft 35 and the intermediate transmission shaft 43, which are free to rotate, is prevented.

[Other Embodiments] In the above embodiment, a case where a hydraulic continuously variable transmission mechanism is used as the main transmission mechanism is illustrated. A gear transmission case for switching can be connected to the front end of the transmission case 3 for implementation. In this case, the return oil from the hydraulic circuit of the front wheel transmission mechanism may be returned to the upper part of the gear transmission case and used for lubricating the transmission gear.

Overall side view of tractor Vertical side view of front wheel transmission structure Aircraft structure side view Longitudinal side view showing transmission structure Schematic showing the gear train of the transmission structure Longitudinal side view of front wheel speed change mechanism in standard four-wheel drive mode Longitudinal side view of front wheel speed change mechanism in front wheel acceleration drive mode Sectional view showing the valve structure when pressure oil is supplied to the transmission clutch Sectional drawing which shows the valve structure of the pressure oil cutoff state of a transmission clutch Hydraulic circuit diagram Vertical side view of PTO mode selection mechanism Vertical side view of PTO mode selection mechanism Vertical side view of PTO mode selection mechanism Side view showing operation structure of PTO mode selection mechanism Front view showing the operation structure of the PTO mode selection mechanism

Explanation of symbols

6 Rear wheel 8 Front wheel 19 Subtransmission mechanism 21 Front wheel transmission mechanism 25 Shift clutch 70 Valve casing V1 Front wheel control valve V2 Automatic transmission selection valve V3 Check valve

Claims (4)

Front wheel shift that can be switched between a standard drive state in which the front wheel to be steered is driven at a peripheral speed equivalent to the peripheral speed of the rear wheel and an accelerated drive state in which the front wheel is driven at a higher peripheral speed than the rear wheel. In a four-wheel drive tractor travel device that includes a mechanism and is configured to automatically switch the front wheel speed change mechanism from a standard drive state to an accelerated drive state in conjunction with steering more than a set angle of the front wheels,
The front wheel speed change mechanism is configured such that the standard drive state and the acceleration drive state are brought about by the operation of a hydraulically operated speed change clutch, and the front wheel control valve for operating the speed change clutch is a front wheel steering mechanism. Linked to
The front wheel control valve, an automatic transmission selection valve for selecting whether to automatically change the automatic transmission of the front wheel, and a check valve linked to the transmission operation system of the auxiliary transmission mechanism interposed in the front wheel traveling transmission system are arranged in series.
When the automatic transmission selection valve is switched to the automatic transmission entering position and the auxiliary transmission mechanism is not operated to the high speed position, the hydraulic operation of the transmission clutch is performed through the automatic transmission selection valve, the check valve, and the front wheel control valve. A four-wheel drive tractor travel device characterized in that   The traveling device for a four-wheel drive tractor according to claim 1, wherein the automatic transmission selection valve, the check valve, and the front wheel control valve are each configured as a rotary valve.   The four-wheel drive tractor travel device according to claim 1 or 2, wherein the automatic transmission selection valve, the check valve, and the front wheel control valve are mounted in a single valve casing. Of the automatic transmission selection valve, the check valve, and the front wheel control valve, the spool axial direction of the valve located in the middle of the pressure oil flow direction is different from the spool axial direction of the other valves. The four-wheel drive tractor travel device according to claim 3.

Images