JP2015160526A - Tread changing device of working vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tread changing device of a working vehicle in which a travelling speed of the working vehicle is changed into a low speed for starting a tread width change according to the condition of a road surface, and the work can be started with a desired tread width early when entering the field.SOLUTION: A tread changing device of a working vehicle is made possible to change a tread width of a rear wheel. The tread changing device of the working vehicle is characterized by providing tread changing start speed setting means for setting a travelling speed of the working vehicle being conditions of starting a tread changing operation. Also, the tread changing device of the working vehicle is characterized by configuring such that a street, a farm or a paddy can be selected by the tread changing start speed setting means. The tread changing device of the working vehicle is characterized by starting the change of the tread width at the same time when starting the traveling of the working vehicle when setting a paddy by the tread changing start speed setting means.

Description

  The present invention relates to a tread changing device in a work vehicle such as an agricultural tractor, a riding management machine, or an aerial work vehicle.

  Conventionally, a technique for changing / adjusting a tread of a wheel pivoted on a vehicle is widely known. For example, as disclosed in Japanese Patent No. 982106, a publicly known application filed by the applicant of the present application. There is a technology.

  A tread change device for a work vehicle described in the publication includes a hydraulic cylinder that changes a tread of a front wheel or a rear wheel of a vehicle, and a stroke sensor that detects the tread change. Left and right rear wheel brakes until the on / off switch that changes the tread when it is detected is changed from "On" to "Off" or from "Off" to "On" The vehicle is configured to temporarily check the start of the vehicle.

  As described above, the known technique is a technical means for ensuring the safety of the subsequent traveling accompanying the change of the tread.

Japanese Patent No. 982106

  The wheel tread changing operation is performed when the vehicle speed becomes about 5 km / h of the tread starting speed, for example. If the tread cannot be started on the tread and the tread is changed after entering the field, the tread must be run at the tread start speed before starting the work.

  An object of the present invention is to shorten the distance traveled for changing the tread as much as possible in accordance with the state of the traveling road surface so that the work can be started with a desired tread immediately after entering the field.

The problems of the present invention are solved by the following technical means.
The invention according to claim 1 is a tread change device for a work vehicle in which the tread width of the rear wheel (2) can be changed, and a tread change start speed for setting a travel speed of the work vehicle, which is a condition for starting the tread change operation. A tread changing apparatus for a work vehicle, characterized in that setting means (22) is provided.

  According to a second aspect of the present invention, there is provided a tread change device for a work vehicle according to the first aspect, wherein the tread change start speed setting means (22) can select a road, a field, or a paddy field. .

  According to a third aspect of the present invention, when the setting by the tread change start speed setting means (22) is a field, the change of the tread width is started at a speed slower than that on the road. The tread changing device of the work vehicle.

  According to a fourth aspect of the present invention, when the tread change start speed setting means (22) sets the paddy field, the tread width change is started simultaneously with the start of traveling of the work vehicle. The tread changing device of the work vehicle.

  According to a fifth aspect of the present invention, there is provided a tread changing apparatus for a work vehicle according to the first aspect, further comprising a tire size input means (66) for inputting a tire size of the rear wheel (2).

  According to the first aspect of the present invention, the worker who operates the work vehicle determines the road surface condition, and when the ground is soft, starts the tread change for setting the traveling speed of the work vehicle, which is a condition for starting the tread change operation. By operating the speed setting means (22), the tread width change is started when the traveling speed of the work vehicle is low, and the desired tread width is obtained with a short traveling distance. Thereby, the mileage required for the tread change can be shortened as much as possible, and the work can be started quickly.

  In the invention according to claim 2, in addition to the effect of claim 2, the traveling speed of the work vehicle which is a condition for starting the tread change operation can be set by determining whether the traveling place is on the road, upland, or paddy field. Clear and easy to do.

  In the invention according to claim 3, in addition to the effect of claim 2, when entering the field and changing the tread width, the tread change start condition setting means 22 is used as a field to start the running of the work vehicle. In the early stage, the desired tread width can be changed earlier than when traveling on the road, and the work can be started.

  In the invention according to claim 4, in addition to the effect of claim 2, by setting the tread change start condition setting means 22 as a paddy field, when the tread width is started, a desired tread width is obtained almost simultaneously. Thereby, the work vehicle can start work with a desired tread width from the end of the paddy field without traveling.

  In the invention according to claim 5, in addition to the effect of claim 1, when the tire size of the rear wheel 2 is changed, the traveling speed is accurately calculated with the tire size input by the tire size input means 66. The tread width can be changed at the calculated vehicle travel speed.

Horizontal cross section of rear axle case showing tread adjuster (A) Sectional view of the locking device (b) Perspective view of the locking device Overall side view of tractor Rear view of tractor Schematic of the control operation device of the tread adjusting device Sectional view of part of rear axle case Sectional view of part of rear axle case Sectional view of part of rear axle case Hydraulic circuit diagram of tread adjuster Sectional drawing of a part of a rear axle case of another embodiment Partial bottom view of rear axle case of another embodiment Front view of rear wheel tread location setting dial Front view of the size setting dial that sets the tire size of the rear wheels

Hereinafter, the present invention will be described in detail in an embodiment of a tread adjusting device equipped on an agricultural tractor shown in the drawings.
First, as shown in FIGS. 3 and 4, the tractor 9 has an engine 11 mounted in a front bonnet 10, and a clutch housing and a gear-type transmission that houses a main clutch in the rear of the engine 11. The mission case 12 to be connected is integrally connected. A rear axle case 13 with adjustable tread is provided on both the left and right sides of the transmission case 12, and wheels (rear wheels in the illustrated example) 2 and 2 are attached to the ends of wheel shafts 32 pivoted in the case 13 on the left and right sides. Provided.

  A front axle case is provided below the engine 11 so as to be able to roll around a front and rear axis, and front wheels 14 are provided at both side ends of the front wheel shaft (not shown) in the case.

  The cockpit 15 is provided in a cabin 16 mounted on the vehicle body, and has a configuration in which a meter panel 17, a steering handle 18, and operation levers are concentrated in the front. Further, various setting devices such as a tread adjustment set switch 19 described later, a tread setting dial 20 and a size setting dial 66 for inputting the size of the rear wheel 2 are provided in the vicinity of the levers, and these setting signals are sent to the cockpit. 15 is configured to input to the controller 21 which is a control unit below. The size label 65 displays the tire size set by the size setting dial 66.

  In FIG. 3, a cylinder case 23 having a hydraulic cylinder for raising and lowering the work implement is provided at the rear upper part of the mission case 12. The lift arm 24 is configured to rotate up and down by expanding and contracting the piston of the hydraulic cylinder in the cylinder case 23, and to move up and down the rear rotary tiller 25 connected thereto. One of the lift arms 24 is provided with a potentiometer-type lift arm angle sensor for detecting the height of the work implement, and the detection position of the potentiometer of the work implement lift lever, the rotation setting position of the lift arm 24, and So that the switching control valve for raising or lowering the working machine in the hydraulic circuit is switched by a control signal from the controller for raising / lowering control.

Next, the tread adjusting device will be described.
First, in FIG. 1, drive shafts 28, 28 extended left and right from a rear wheel differential mechanism 27 disposed in the center are respectively connected to left and right transmission cylinders 31 through brake devices 29, 29 and reduction devices 30, 30. The driving power is transmitted to 31. On the other hand, as shown in the drawings, the wheels 2 and 2 are respectively fixed to the wheel shafts 32 and 32 by superimposing the disk 2a on the flanges 32a and tightening them with bolts. , 32 are supported by the wheel support cases 33, 33 via bearings 33a, and the wheel support case 33, the transmission cylinder 31, and the wheel shaft 32 are assembled to the rear axle case 13 in this order.

  As can be seen from FIG. 1, the wheel shafts 32, 32 have a tread that is the distance between the wheels 2, 2 at the front end (outer side) with respect to the transmission cylinders 31, 31 on the vehicle 1 side. The rear wheel differential mechanism 27 is configured so that the traveling power can be transmitted from the rear wheel differential mechanism 27 to the wheels 2 and 2 by being spline-fitted so as to be stretchable.

  The left and right hydraulic cylinders 3 a and 3 b for adjusting the tread are provided between the transmission cylinders 31 and 31 and the wheel support cases 33 and 33 by fixing the cylinder rod 35 to the housing case 37 (transmission cylinder 31 side). The cylinder left chamber 3L and the cylinder right chamber 3R are respectively configured such that the tread can be adjusted by an expansion / contraction operation between the two chambers 3aL, 3aR, 3bL, 3bR.

  More specifically, the hydraulic cylinders 3a and 3b are integrally formed in the upper part of the rear axle case 13, and are housed in housing cases 37 and 37 that are formed in a cylindrical shape along the longitudinal direction of the rear axle case 13, and are respectively cylinder bodies 3aC and 3bC. , Cylinder rods 35, 35, piston members 3aP, 3bP, block members 3aB, 3bB, and the like. Since the left and right hydraulic cylinders 3a and 3b have the same configuration, the left hydraulic cylinder 3a will be mainly described below.

  The cylinder rod 35 of the hydraulic cylinder 3 a is fixed to the housing case 37 at its inner end in a state parallel to the wheel shaft 32. A piston member 3aP is fixed to the outer end portion of the cylinder rod 35, and an oil seal is provided between the cylinder rod 35 and the cylinder body 3aC. The piston member 3aP and the cylinder rod 35 are provided in the cylinder body 3aC, and are further fixed to the cylinder body 3aC to provide a block member 3aB. An oil seal is provided between the block member 3aB and the cylinder rod 35. With such a configuration, the cylinder body 3aC is provided to be slidable in the longitudinal direction with respect to the cylinder rod 35.

  A plug body 3V also serving as a connection fitting is fixed to the outer end of the cylinder body 3aC, and the plug body 3V of the connection fitting is integrally connected to a flange portion 33a formed outside the wheel support case 33. . With this configuration, the sliding of the cylinder body 3aC relative to the cylinder rod 35 is transmitted to the wheel support case 33 via the plug body 3V and the flange portion 33a, and the wheel support case 33 can be slid relative to the rear axle case 13. It has become.

A bellows-like cylinder cover 39 is provided between the end portion of the housing case 37 and the flange portion 33a of the wheel support case 33 so that mud does not enter.
The minimum of the rear wheel 2 tread is determined by the end of the rear axle case 13 coming into contact with the contact surface of the wheel support case 33. However, if a plurality of shims for adjusting the interval can be removed from the contact surface of the wheel support case 33 The minimum value of the rear wheel 2 tread can be changed. Further, if the clamping member interposed between the end portion of the rear axle case 13 and the contact surface of the wheel support case 33 can be adjusted in the axial direction, the minimum value of the rear tread 2 can be changed steplessly.

  Are formed in the cylinder rod 35, and are connected to an oil passage 41 formed in the housing case 37. A part of the oil passages 36, 36,... The other part of the oil passage communicates with the right chamber 3aR formed between the piston member 3aP and the block member 3aB.

The same configuration is adopted for the right rear axle housing.
The oil passage 41 of the housing case 37 communicates with a pair of openings 41a and 41a formed in the housing case 37, and an adapter is fixed to the openings 41a and 41a. A coupler at one end of a pipe from the hydraulic valve is detachably connected to each adapter. When removing the pipe, a blind plug (not shown) is attached.

  In this case, as shown in FIG. 1, the left and right hydraulic valves 4a, 4b are connected to the oil tank T (pump P) and the left and right pipes 5a to the chambers 3aL, 3aR, 3bL, 3bR on the hydraulic cylinders 3a, 3b side, respectively. , 5b. A first pipe 5aL of the left pipe 5a and a first pipe 5bL of the right pipe 5b are connected to the cylinder left chambers 3aL and 3bL of the left and right hydraulic cylinders 3a and 3b, respectively. The cylinder right chambers 3aR and 3bR are connected to the second pipe 5aR of the left pipe 5a and the second pipe 5bR of the right pipe 5b. The first pipe 5aL of the left pipe 5a and the second pipe 5aR of the left pipe 5a are connected to the left hydraulic cylinder 3a by detachable couplers 59a and 59a. The first pipe 5bL of the right pipe 5b and the second pipe 5bR of the right pipe 5b are connected to the right hydraulic cylinder 3b by detachable couplers 59b and 59b.

  In this way, the left hydraulic cylinder 3a is supplied and discharged with oil from the first pipe 5aL of the left pipe 5a and the second pipe 5aR of the left pipe 5a, and the right hydraulic cylinder 3b has a right pipe. Oil supply / discharge oil is performed from the first pipe 5bL of the 5b and the second pipe 5bR of the right pipe 5b, and each of them is configured to expand and contract.

  The left and right hydraulic valves 4a and 4b are provided in a state where they are overlapped on the outer surface of the cylinder case 23, and a pair of pipes extend from the hydraulic valves 4a and 4b. Therefore, when the pipes removed from the adapter parts of the left and right axle cases are attached to the hydraulic cylinders for the work equipment attached to the rear part, the work can be easily performed from the rear side of the machine body.

  When the jack sensor 26S is attached to the bottom of the differential case 26 with the rear wheel differential mechanism 27 and the body is lifted with the jack and the rear wheels 2 and 2 are lifted from the ground, the tread change operation is enabled and assembled. The tread change operation at the time can be confirmed.

  In addition, when an adjustment bolt is attached between the rear axle case 13 and the wheel support case 33 and the hydraulic pressure of the hydraulic cylinders 3a and 3b is released, the adjustment bolt can be manually turned to check the tread change operation. The tread change range can be checked without driving the engine during assembly or maintenance.

  The tread adjusting device configured as described above sets a desired tread width to be adjusted in advance using the tread setting dial 20 shown in FIG. 5, and changes the tread with the tread running place setting dial 22 shown in FIG. Is set to paddy field, field, or road, and the tire size dial 66 shown in FIG. 13 is used to set small (0.9), standard, or large (1.15), and then a tread adjustment set switch. This can be done by turning on 19 and traveling. The tread travel location setting dial 22 is tread change start speed setting means of the present invention. The tread setting dial 20 is provided with a display unit 34 displaying a tread width. The tread travel location setting dial 22 is provided with a display section 68 on a paddy field, a field, or a road.

  The display of the tread travel location setting dial 22 may be replaced with a speed display of 0 km / h, 1 km / h, 5 km / h instead of paddy fields, fields, and roads, or both displays may be written together, and the travel speed is set. When the value is reached, the hydraulic cylinders 3a and 3b are operated to set the set tread.

The tire size set by the tire size dial 66 which is the tire size input means of the present invention is taken into the controller 21 and used for calculation of the traveling speed.
Next, as shown in FIG. 2, the lock device 6 (provided on the left and right wheels 2 side) includes a lock plate 6a and a lock bolt nut 6b, and when tread adjustment is not performed, that is, tread adjustment is unnecessary. In the work machine, the distance between the wheels 2 and 2 is fixed to prevent the tread from being changed.

  10 and 11, the wheel support case 33 and the rear axle case 13 are fixed. After the tread of the rear wheel 2 is changed by the hydraulic cylinders 3a and 3b, the lock plate 6a, the fixing bolt 7 and the adjusting bolt are used. 8 and the adjusting nut 8a. The lock plate 6a is U-shaped in cross section, and the adjusting bolt 8 is inserted into the two long holes 6a1 and the adjusting nut 8a is tightened and fixed. A mud avoidance ring 64 is attached to the end surface of the rear axle case 13 to prevent mud from entering and oil leakage.

  That is, the lock plate 6a is spanned between the wheel support case 33 supporting the wheel 2 and the differential case 26 side, and is fixed by the lock bolt nut 6b. In such a case, the left and right pipes 5a and 5b connected to the left and right hydraulic cylinders 3a and 3b can be removed and switched to the external hydraulic pressure of the other work machines 55 and 57.

  When adjusting the tread of the left and right wheels 2 and 2, loosen the lock bolt nut 6b and then adjust it to any tread. When the adjustment is completed, tighten the lock bolt nut 6b so that the left and right wheels 2 and 2 do not move. To do. As a result, it is possible to prevent the tread from being inadvertently changed due to a load acting on the left and right wheels 2 and 2, causing hydraulic hydraulic fluid to leak.

  Specifically, as shown in FIG. 1, the two couplers 59a and 59a connecting the left pipe 5a and the left hydraulic cylinder 3a are removed from the adapter, and the couplers 59a and 59a are separated from each other. Connect to the hydraulic device 56 of the machine 55. Further, the two couplers 59 b and 59 b connecting the right pipe 5 b and the right hydraulic cylinder 3 b are removed, and the couplers 59 a and 59 a are connected to the hydraulic equipment 58 of another work machine 57.

As a result, the left hydraulic valve 4 a can drive another work machine 55, and the right hydraulic valve 4 b can drive another work machine 57.
Further, the left hydraulic valve 4a can be connected to another working machine 55, and the right hydraulic valve 4b can be connected to the tread adjusting hydraulic cylinder 3b.

  As an example of the other hydraulic devices 56 and 58, another working machine that operates hydraulically by removing the rotary tiller 25 may be mounted, for example, a fertilizer spreader. There is a hydraulic motor that rotates the plate. In addition, the auxiliary lifting cylinder (not shown) of the rotary tiller 25 mounted on the rear portion of the tractor and the lifting hydraulic cylinder 25b of the tool bar 25a for mounting the sub work machine such as a vertical machine may be driven as another hydraulic device. Is possible.

  In the embodiment of the present invention configured as described above, the tread adjustment of the wheel 2 is fixed by the lock device 6 when the other hydraulic devices 56 and 58 are used while the tread adjustment is not performed. Then, the pipes 5a and 5b to the hydraulic cylinders 3a and 3b are also removed and switched to a state where they can be used as external hydraulic pressure. In this way, the hydraulic valves 4a and 4b can be connected to other hydraulic devices 56 and 58 as external hydraulic pressure to feed hydraulic oil, so that the range of use of the work machine can be expanded.

  As already mentioned, the tendency of multiple use of external hydraulic pressure in work vehicles has become extremely strong, and in order to expand the use of work machines that use hydraulic equipment, it is required to add a hydraulic mechanism for external extraction . In response to such a demand, the embodiment increases the utilization of the work vehicle 1 and enables the operation using various hydraulic devices. The hydraulic valves 4a and 4b for adjusting the treads of the wheels 2 and 2 are provided. Is not used for tread adjustment, it can be effectively used as the external take-out hydraulic pressure of the hydraulic equipment (56, 68) of another work machine 55, 57, so that it can be applied to many hydraulic equipment and the working range can be reduced. It is an enlarged one.

  The configuration is advantageous in that it is performed by a very simple means, and the tread adjustment of the wheels 2 and 2 can be easily locked by the lock device 6 so that it can be used as an external hydraulic pressure for driving another work machine. It will be possible.

  The tread change adjustment of the tractor described above is applied to the left and right rear wheels 2 and 2, but it can also be applied to the left and right front wheels 14 and 14, and the tread change adjustment is performed on the left and right front wheels 14 and 14 and the left and right rear wheels 2 and 2. May be possible. In this case, four other hydraulic devices can be used.

Note that protective caps are attached to the tire valves of the front wheel 14 and the rear wheel 2 to prevent damage, rust or sticking.
Hereinafter, the tread adjusting device will be described in detail with the configuration shown in FIGS.

  First, the left and right hydraulic cylinders 3a, 3b for adjusting the tread and the cylinder rod 35 are provided by processing a one-way oil passage 36 in the cylinder rod 35 and fixing it to the housing case 37, and making the cylinder 3 side movable. It is configured to slide left and right. The cylinder rod 35 can be attached at an arbitrary position of 360 degrees when attached, is grooved in the circumferential direction, and has a port hole formed in one direction. The cylinder rod 35 has a configuration in which cut surfaces 40 are formed on both sides of an assembly portion 38 at an end portion attached to the housing case 37 so that the position (direction) of the port hole is understood.

On the other hand, as shown in the drawing, the hydraulic pressures 41 and 41 are formed in the housing case 37 and connected to the port holes (grooves) of the cylinder rod 35.
As described above, in the embodiment, since the cut surfaces 40 are formed on both ends of the cylinder rod 35 and on both sides of the assembly portion 38 to the housing case 37, the direction of the port hole can be easily understood at the time of assembly. The oil passages 41 and 41 can be easily assembled so as to face each other, and the certainty of the hydraulic operation can be maintained.

Next, an embodiment of the automatic check control shown in FIG. 5 will be described.
The tread adjusting device is one that is performed while rotating the wheels 2 and 2 except when the tread traveling place is a paddy field. In other words, the tread adjusting device is an automatic check control device that does not change or adjust while the wheels 2 and 2 are stopped.

That is, the input shaft sensor 43 is a sensor that detects the rotation of the wheels 2 and 2 and is configured to input detection information to the controller (CPU) 21.
In the embodiment shown in FIG. 5, the controller 21 is configured to connect the left and right stroke sensors 44, 44 to the input side in addition to the input shaft sensor 43, and to measure and input the adjustment length. In addition, an electromagnetic valve (hydraulic valves 4a and 4b) is connected to the output side for control.

  As described above, the rotation control of the wheels 2 and 2 is detected by the input shaft sensor 43 so that the tread adjustment can be performed only during the rotation, and the tread adjustment mechanism is protected to ensure safety.

  Further, the automatic check control device may be configured to be able to control to disable the tread adjusting device when the sub-shift lever is in the neutral position when it is detected.

  In short, in the tread adjusting device according to the embodiment, the rotation state of the wheels 2 and 2 is monitored by the automatic check control device, and when not rotating, for example, the adjustment range is set by the tread setting dial 20 and the tread adjustment set is set. Even if the switch 19 is pressed, the adjustment operation is not performed, and there is a feature that the protection and safety of the device can be maintained.

  As another embodiment, the vehicle speed is limited, and the tread width can be adjusted only within a certain vehicle speed range (for example, the vehicle speed is 2 km / h or less). In other words, in the case of the embodiment, the tread adjustment is impossible when the wheels 2 and 2 are stopped, at a very low speed (less than 0.5 km / h), and at a speed higher than 2 km / h. There is a feature that increases.

Moreover, although there is almost no necessity in reality, tread adjustment can be made possible during back travel.
Further, when the position set with the dial 20 is away from the current tread position, the tread adjustment may be made faster.

Next, an embodiment of the transmission mechanism of the wheel 2 equipped with the tread adjusting device will be described with reference to FIG.
First, as shown in the drawings, in the embodiment, a wheel shaft 32 is slidably fitted to a carrier part 45 that has been finally decelerated so that the tread can be adjusted. The end of the carrier part 45 can be adjusted. In this configuration, a right and left backwashing washer 47 for the brake shaft 46 is provided and is applied to the shaft end. Reference numeral 48 denotes an air vent hole.

And the said washer 47 comprises the pin 49 in the peripheral part as shown in the figure, and comprises the rotation stopper.
As described above, in the embodiment, the washer 47 is provided on one side using the cylindrical carrier 45 and received against the end surface of the brake shaft 46 to provide the right and left rattling function, and on the other side, The wheel shaft 32 is spline-fitted freely to allow tread adjustment. The carrier 45 is provided with an air vent hole 48 so that the air inside the carrier 45 can be sucked and discharged so that the wheel shaft 32 can slide smoothly when the wheel shaft 32 is moved and adjusted left and right.

  As described above, the embodiment, after all, has the sufficient function as the tread adjusting device of the work vehicle 1, but eliminates the conventional precision forging method and can be manufactured at a low cost by a simple manufacturing method. Have

Next, an embodiment of the hydraulic circuit of the tread adjusting device will be described.
First, as shown in FIG. 9, the hydraulic circuit 50 of the tread adjusting device has a flow dividing valve 52 that equally divides the oil amount by half to the left and right hydraulic valves 4 a and 4 b on the immediately upper side of the oil passage 51. A hydraulic circuit 53 for horizontal cylinder control is connected to the upper side, and a flow dividing valve 54 is connected to the upper side.

  Therefore, as shown in the circuit diagram of FIG. 9, the hydraulic circuit 53 for controlling the horizontal cylinder performs the control operation of the horizontal cylinder 53a with the hydraulic oil whose flow rate is reduced by the diversion valve 54 connected to the upper side thereof. It is configured to do. The horizontal cylinder 53 a is a hydraulic cylinder that performs horizontal control of the rotary tiller 25. Further, in the hydraulic circuit 50 of the tread adjusting device, hydraulic oil that has passed through the hydraulic circuit 53 for controlling the horizontal cylinder 53a is divided and sent by the diversion valve 52 to the left and right hydraulic valves 4a and 4b by 1/2. In this configuration, the left and right hydraulic cylinders 3a and 3b are supplied.

  In this case, the hydraulic cylinders 3a and 3b for adjusting the tread have a slow expansion / contraction operation because the supply flow rate of the hydraulic oil is small, but this slow expansion / contraction operation is suitable for the tread adjustment.

  As described above, in the hydraulic circuit 50 according to the embodiment, since the flow rate supplied from the upper side is reduced, the expansion and contraction operation of the hydraulic cylinders 3a and 3b for adjusting the tread is performed slowly as described above. The tread adjustment is extremely safe. Further, in the embodiment, the flow rate of the hydraulic oil supplied to the left and right hydraulic valves 4a and 4b of the hydraulic circuit 50 is sent to the left and right evenly divided by ½ by the upper diversion valve 52. The hydraulic cylinders 3a and 3b extend and contract in synchronization with each other accurately, and as shown in FIG. 4, there is almost no difference between the left and right adjustment widths, and there is an excellent feature that the adjustment width can be changed to a preset adjustment width. .

  In the above, the tread change configuration by hydraulic drive has been described, but it is also possible to change the toledo with a plurality of jack bolts.

2 Rear wheel 22 tread change start speed setting means (tread travel location setting dial)
66 Tire size input means (size setting dial)

Claims (5)

  In the tread changing device for a work vehicle in which the tread width of the rear wheel (2) can be changed, tread change start speed setting means (22) for setting the traveling speed of the work vehicle, which is a condition for starting the tread change operation, is provided. A tread change device for a work vehicle characterized by the above.   The tread change device for a work vehicle according to claim 1, wherein the tread change start speed setting means (22) is configured to be able to select a road, a field, or a paddy field.   3. The tread change device for a work vehicle according to claim 2, wherein the tread change start speed setting means (22) starts changing the tread width at a speed slower than that on the road when the setting is a field.   The tread change device for a work vehicle according to claim 2, wherein when the setting is set to be paddy by the tread change start speed setting means (22), the change of the tread width is started simultaneously with the start of traveling of the work vehicle.   The tread changing device for a work vehicle according to claim 1, further comprising tire size input means (66) for inputting a tire size of the rear wheel (2).

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