JP3236483B2 - Work vehicle traveling speed change structure - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises a hydraulic actuator for shifting the gear transmission by arranging a traveling gear transmission and a traveling clutch hydraulic clutch in series on the lower side of the engine. The present invention relates to a traveling speed change structure of a working vehicle.

[0002]

2. Description of the Related Art An example of a working vehicle having the above-described configuration is disclosed in Japanese Patent Application Laid-Open No. 4-56635. In this configuration, a plurality of hydraulic actuators (11 and 12 in FIG. 1 of the above-mentioned publication) for performing a shift operation by sliding a shift member of a gear transmission, and supplying and discharging hydraulic oil to and from a plurality of hydraulic actuators. A rotary shift control valve (14 in FIG. 1 of the above-mentioned publication) for operating the lever.
A pilot-operated operating valve (35 in FIG. 1 of the above-mentioned publication) that operates to supply and discharge hydraulic oil to and from the hydraulic clutch (3 in FIG. 1 of the above-mentioned publication) to operate the transmission and cutoff of the hydraulic clutch. A pilot pressure system (19, 20, 36 in FIG. 1 of the above publication) for operating an operation valve, and an operating means for changing the pilot pressure of the pilot pressure system in accordance with the operation of the hydraulic actuator (the first publication of the above publication). 26, 27) in the figure.

[0003] When the operator operates the shift control valve with the shift lever and the hydraulic actuator starts shifting operation of the gear transmission by the operating oil from the shift control valve, the pilot pressure of the pilot pressure system is controlled by the operating means. Is changed, and the transmission of the hydraulic clutch is interrupted by the operation valve, and when the shift operation by the hydraulic actuator is completed, the pilot pressure of the pilot pressure system is changed again by the operating means, and the transmission of the hydraulic clutch is performed by the operation valve. Is done. As described above, only by operating the shift control valve with the shift lever, the shift operation of the gear transmission and the transmission interruption and transmission operation of the hydraulic clutch by the hydraulic actuator are automatically performed.

[0004]

With the above configuration,
A shift control valve that performs a shift operation by supplying and discharging hydraulic oil to and from a hydraulic actuator is configured in a rotary manner, and the shift control valve is mechanically operated by a shift lever operated by an operator.

Thus, even when the shift lever (shift control valve) is operated to the same operating position, the operator may operate the shift lever (shift control valve) slowly or quickly, depending on whether the operator operates the shift lever (shift control valve). The timing of the supply / discharge operation of the hydraulic oil is different, and the shift operation by the hydraulic actuator may not be performed smoothly. Conversely, even when the shift lever (shift control valve) is operated in the same manner in both the high-speed range and the low-speed range, the difference in the timing of the supply and discharge operation of the hydraulic oil to and from the hydraulic actuator in the high-speed range and the low-speed range causes The shifting operation by the hydraulic actuator may not be performed smoothly. SUMMARY OF THE INVENTION It is an object of the present invention to provide a traveling gear structure for a working vehicle as described above, in which a shifting operation of a traveling gear transmission by a hydraulic actuator is performed as smoothly as possible.

[0006]

Means for Solving the Problems [I] The characteristic structure according to claim 1 of the present invention is a poor engine.
Gearbox for traveling and hydraulic clutch for traveling gear on the side
Are arranged in series, and the shift member of the gear transmission is
Multiple hydraulic actuators that perform gear shifting operations by guiding
To supply and discharge hydraulic oil to multiple hydraulic actuators.
Operate the solenoid operated valve and the solenoid operated valve
Control means for supplying and discharging hydraulic oil to and from the hydraulic clutch
The hydraulic clutch to transmit and disconnect the transmission.
An pilot operated pilot valve and a pilot valve
The pilot pressure system and the pilot
Operating means for changing the pilot pressure of the
The gearshift operating device that is operated
Detection means for detecting and inputting to the control means.
In addition, connect the solenoid operated valve to the hydraulic oil input port and hydraulic oil output port.
3 port type with a port and a drain port for hydraulic oil.
Supply position of hydraulic oil to hydraulic actuator and hydraulic
Two-position switching of hydraulic oil draining position from actuator
To operate the electromagnetically operated valve based on the operation of the shift operation device.
Hydraulic actuator starts shifting operation, and
The pilot pressure of the pilot pressure system is changed and
The hydraulic valve is operated to cut off the transmission by the operating valve,
When the shifting operation by the pressure actuator is completed,
The pilot pressure of the pilot pressure system is changed by the
So that the hydraulic clutch is transmitted by the operating valve.
It is in the point which constituted.

[0007] As shown in claim According the example 2 to the characteristics of 1, when the operation of the shift operation device 33 is input from the detecting means 34 to the control unit 40, the control unit 40 solenoid operated valve 25 is operated And the hydraulic actuators 11 and 1
2, the shift operation of the shift member is performed, and the gear transmission is shifted. This hydraulic actuator 11,
With the operation of 12, the pilot pressure of the pilot pressure system 20 is changed by the operating means 36 and 37, and the transmission of the hydraulic clutch 3 is interrupted by the operating valve 35, and the shift operation by the hydraulic actuators 11 and 12 is performed. Is completed, the operating means 36 and 37 operate the pilot pressure system 2
The pilot pressure of 0 is changed, and the hydraulic valve 3 is transmitted again by the operation valve 35.

According to the first aspect of the present invention, since the hydraulic actuator is operated by the solenoid operated valve based on the operation of the shift operation tool, when the shift operation tool is operated to the same operation position, the operator can perform the shift operation. Even if the tool is operated slowly or quickly, the timing of operation of the solenoid operated valve is controlled by the control means, so that the timing of supply and discharge of hydraulic oil to the hydraulic actuator can be made the same. . Conversely, in both the high-speed range and the low-speed range, even if the operator operates the shift operation device in the same manner, the timing of the operation of the solenoid operated valve is controlled by the control means, so that the hydraulic actuator in the high-speed range can be operated. The timing of the supply / discharge operation of hydraulic oil and the timing of the supply / discharge operation of hydraulic oil to / from the hydraulic actuator in the low-speed range can be set to be suitable for each of the high-speed range and the low-speed range. In addition, 3-port type (input port, output port and
Lenport), two-position switching type of supply position and oil discharge position
Solenoid operated valves are generally inexpensive and operate reliably.
is there. Therefore, the use of such a solenoid operated valve is
Therefore, the operation of supplying and discharging hydraulic oil to and from the hydraulic actuator is correct.
It can be performed reliably and reliably.

[II] The characteristic configuration according to claim 2 of the present invention is as described in claim 1.
Operating the hydraulic actuator on one side
Shift position, the other operated shift position and both shift positions.
It is configured to be operable at three neutral stop positions between
Hydraulic oil is supplied from the operation valve to the specified position of the hydraulic actuator.
Supply, the hydraulic actuator
Operate to shift position, and operate from hydraulic valve to hydraulic actuator
Hydraulic oil is supplied to another predetermined position of
Make sure that the hydraulic actuator is in the neutral stop position.
The point is that it constitutes a coutuator.

According to the features of claim 2, the case of claim 1
Similarly to the above, it has the “action” described in the preceding section [I].
In addition, it has the following “action”. Claim
2, for example, as shown in FIG.
Hydraulic oil is supplied to predetermined positions of the hydraulic actuators 11 and 12.
When supplied, the hydraulic actuators 11 and 12 move
Position, for example, as shown in FIG.
Supplying hydraulic oil to predetermined positions of the tutors 11 and 12
And the hydraulic actuators 11 and 12 move to the other shift positions.
Operate. Then, for example, as shown in FIG.
When hydraulic oil is supplied to the home position, the hydraulic actuator 1
1, 12 operate in the neutral stop position. For example, by operating the hydraulic actuator to a neutral stop position or the like by shutting off (or draining) hydraulic oil to the hydraulic actuator, if there is leakage of hydraulic oil in the hydraulic circuit system of the hydraulic actuator, Due to this leakage of hydraulic oil, the hydraulic actuator may not operate properly at the neutral stop position or the like. On the other hand, according to the characteristic of the second aspect, the hydraulic actuator is configured to operate the hydraulic actuator by supplying the hydraulic oil at any one of the one shift position and the other shift position and the neutral stop position. Even if there is a leak of hydraulic oil, the hydraulic oil is supplied so as to compensate for the leak, so that the hydraulic actuator operates in one and the other shift positions and the neutral stop position regardless of the leak of the hydraulic oil. I do.

According to a third aspect of the present invention, there is provided a
In the matter according to claim 1, the hydraulic actuator is
One of the shifted positions, one of the shifted positions and
Operable at three neutral stop positions between the two shift positions.
From the solenoid operated valve to the predetermined position of the hydraulic actuator
Hydraulic oil is supplied to the hydraulic actuator,
And the other gear shift position, and the hydraulic
Hydraulic oil is supplied to another predetermined position on the actuator
To keep the hydraulic actuator in the neutral stop position.
As described above, the hydraulic actuator
An auxiliary transmission for traveling is arranged in series with the gear transmission of
And change the position by sliding the shift member of the subtransmission.
Hydraulic cylinder that performs high-speed operation and operates on this hydraulic cylinder
The second place of the three-port type that operates by supplying and discharging oil
A hydraulic cylinder equipped with a solenoid operated valve configured as
Switching the sub-transmission to high / low speed with the two-position switching
The hydraulic cylinder is operated by an electromagnetically operated valve.
A point that is configured to operate by supplying and discharging hydraulic oil
It is in.

[0012]

FIG. 1 shows a transmission system of a four-wheel drive type agricultural tractor, which is an example of a work vehicle, and an engine 1
From the main clutch 2, the main transmission A (corresponding to a gear transmission), a multiple-plate traveling hydraulic clutch 3, a forward / reverse switching device C, a first auxiliary transmission B, and a second auxiliary transmission D
The power transmitted to the rear wheel 4 via the rear wheel differential mechanism 4a and the power branched immediately before the rear wheel differential mechanism 4a is transmitted to the front wheel 5 via the transmission shaft 42 and the front wheel differential mechanism 5a. Power from the engine 1 is transmitted to the PTO shaft 8 via the PTO transmission 6 and the PTO clutch 7.

The main transmission A includes two sets of shift members 9, 1
It is configured as a synchromesh type gear shift type with 0, and can shift to four speeds. The first auxiliary transmission B is also 1
A gear shift type of a synchromesh type equipped with a set of shift members 30 is configured to be able to shift to two speeds, and the forward / reverse switching device C is also a gear shift type of a synchromesh type equipped with a shift member 31. It is configured. The shift members 9 and 10 of the main transmission A are slid by first and second hydraulic cylinders 11 and 12 (corresponding to hydraulic actuators), and the shift member 30 of the first auxiliary transmission B is shifted.
Is slid by the third hydraulic cylinder 13. The shift member 31 of the forward / reverse switching device C is slid by the swing operation type forward / backward lever 16.

Next, the first and second hydraulic cylinders 11, 1
2 will be described. As shown in FIG. 3A, a large-diameter cylinder portion 21 and a small-diameter cylinder portion 22 are formed, and the large-diameter piston 2 is attached to each of the large-diameter and small-diameter cylinder portions 21 and 22.
3 and a small-diameter piston 24 are slidably mounted. A first piston rod 24a is fixed to an end surface of the small-diameter piston 24 opposite to the large-diameter piston 23, and the first piston rod 24a is fixed to the first piston rod 24a.
The piston rod 24a extends to the opposite side of the large-diameter piston 23 and projects from the small-diameter cylinder portion 22. The second end of the small-diameter piston 24 on the side of the large-diameter piston 23 is
The piston rod 24b is fixed, and the second piston rod 24b is slidably penetrated through the opening 23a of the large-diameter piston 23 without projecting from the large-diameter cylinder portion 21.

As shown in FIGS. 3A and 2, in the small-diameter cylinder portion 22, the small-diameter cylinder chamber 22 on the first piston rod 24 a side partitioned by the small-diameter piston 24.
An electromagnetic operation valve 25 for supplying and discharging hydraulic oil is provided for a. In the large-diameter cylinder section 21, an electromagnetically-operated valve 26 for supplying and discharging hydraulic oil is provided in a large-diameter cylinder chamber 21a opposite to the small-diameter piston 24 partitioned by the large-diameter piston 23. The solenoid operated valves 25 and 26 are of a three-port type having an input port for hydraulic oil, an output port for hydraulic oil and a drain port for hydraulic oil, and a supply position for supplying hydraulic oil to the first and second hydraulic cylinders 11 and 12. , And a discharge position for discharging the hydraulic oil. The discharge position is operable and is urged toward the supply position by a spring.

With the above structure, both solenoid operated valves 25,
When the valve 26 is operated to the supply position, the hydraulic oil is supplied to the large-diameter and small-diameter cylinder chambers 21a and 22a of the first and second hydraulic cylinders 11 and 12, as shown in FIG. In this case, the large-diameter piston 23 has a larger pressure-receiving area than the small-diameter piston 24, and the second piston rod 24b has a smaller pressure-receiving area than the small-diameter piston 24. And small diameter piston 2
The large-diameter and small-diameter pistons 23 and 24 try to move to the left in the drawing while the third and the third are pushing each other.
The large-diameter piston 23 hits the step of the large-diameter and small-diameter cylinder portions 21 and 22.
3, 24 are retained. The state shown in FIG. 3A is the neutral stop position of the shift members 9 and 10 shown in FIG.

Next, when the solenoid operated valve 25 is operated to the oil discharge position while the solenoid operated valve 26 is left at the supply position, FIG.
As shown in (b), the hydraulic oil in the small-diameter cylinder chamber 22a is discharged, and the hydraulic oil in the large-diameter cylinder chamber 21a pushes the second piston rod 24b to the left in the drawing. This figure 3
The state shown in (b) is the first speed state or the third speed state of the main transmission A in which the shift members 9 and 10 shown in FIG.

Next, when the solenoid-operated valve 26 is operated to the oil discharge position while the solenoid-operated valve 25 is left at the supply position, FIG.
As shown in (c), the hydraulic oil in the large-diameter cylinder chamber 21a is discharged, and the hydraulic oil in the small-diameter cylinder chamber 22a pushes the large-diameter and small-diameter pistons 23 and 24 integrally rightward on the paper. The state shown in FIG. 3C is the second speed state or the fourth speed state of the main transmission A in which the shift members 9 and 10 shown in FIG.

Next, the third hydraulic cylinder 13 will be described. As shown in FIG. 2, the piston 27 is slidably provided inside, and a piston rod 27a fixed to one end surface of the piston 27 extends and protrudes from the cylinder. A first chamber 13a on the piston rod 27a side partitioned by the piston 27 and a second chamber 13b on the opposite side to the piston rod 27a are formed, and an oil passage 28 branched from an oil passage 17 described below is formed in the first chamber 13a. Connect to
The first chamber 13a is configured to always supply the working oil.

The second chamber 13b is provided with an electromagnetic operation valve 29 for supplying and discharging hydraulic oil. The electromagnetic operation valve 29 has an input port for hydraulic oil, an output port for hydraulic oil, and a drain port for hydraulic oil. The three-port type is configured to be operable at two positions, a supply position for supplying hydraulic oil to the second chamber 13b and a discharge position for discharging hydraulic oil, and is urged toward the supply position by a spring.

When the solenoid operated valve 29 is operated to the supply position by the above structure, hydraulic oil is supplied to the second chamber 13b (the hydraulic oil is also supplied to the first chamber 13a via the oil passage 28). Has been). In this case, the first
Due to the fact that the pressure receiving area on the chamber 13a side is smaller than the pressure receiving area on the second chamber 13b side, the piston 27 moves to the left in the drawing as shown in FIG. The state shown in FIG. 2 is the low-speed position of the first auxiliary transmission B shown in FIG. Next, when the solenoid operated valve 29 is operated to the oil discharging position, the hydraulic oil in the second chamber 13b is discharged, and the hydraulic oil supplied to the first chamber 13a pushes the piston 27 to the right in the drawing. This state is shown in FIG.
At the high speed position of the first auxiliary transmission B shown in FIG.

Next, the first, second, third hydraulic cylinders 11, 1
A hydraulic circuit for the hydraulic clutches 2 and 13 and the hydraulic clutch 3 will be described. As shown in FIG.
18 are branched in parallel, an electromagnetic proportional pressure control valve 14 and a pilot operation type operation valve 35 are connected in series to the oil passage 18, and the hydraulic clutch 3
Is connected. The operation valve 35 is a pilot operation operable to a supply position 35a for supplying hydraulic oil to the hydraulic clutch 3 and transmitting the hydraulic oil, and an oil discharge position 35b for discharging hydraulic oil from the hydraulic clutch 3 and transmitting and shutting the hydraulic oil. This is a type, and is biased toward the oil discharge position 35b by a spring. A pilot oil passage 20 (corresponding to a pilot pressure system) branches from a lower side of the throttle unit 19 in the oil passage 17,
The pilot oil passage 20 is connected to the operation valve 35.

The above-mentioned solenoid operated valves 25, 26 and 29 are connected to the oil passage 17 from the throttle portion 19 to the upper side. Opening / closing valves 36 (corresponding to operating means), 37 (corresponding to operating means), 38, 39 urged to the closing side are connected to the oil path 17 from the throttle portion 19 to the lower side. First
The first piston rod 24a and the piston rod 27a of the hydraulic cylinders 11, 12, and 13 are provided with the gearshift position (1).
(A speed position, a second speed position, a low speed position, etc.), a concave portion is formed, and a neutral portion between the shift positions is formed in a convex shape. An interlocking mechanism 32 that opens and closes the on-off valves 36 to 39 between the shift positions is provided. Shift member 3 in forward / reverse switching device C
The shift shaft for the slide operation is also provided with a concave portion and a convex neutral portion similar to those described above, and is provided with a linkage mechanism 32 for opening the on-off valve 39 between the forward position and the reverse position. .

A shift lever 33 (corresponding to a shift operation tool) having an operation position of a first speed position to an eighth speed position is provided, and the operation position of the shift lever 33 is detected. Potentiometer 34 (corresponding to detecting means)
Is input to the control device 40 (corresponding to control means), and based on the operation of the shift lever 33, the control device 40
Operate the solenoid operated valves 25, 26, 29. A pressure sensor 41 for detecting a pilot pressure of the pilot oil passage 20 is provided below the throttle unit 19 in the oil passage 17, and a signal from the pressure sensor 41 is input to the control device 40.

The state shown in FIG. 2 is a state in which the shift lever 33 is operated to the first speed position, the first hydraulic cylinder 11 is in the first speed position of the main transmission A, the second hydraulic cylinder 12 is in the neutral stop position, The third hydraulic cylinder 13 is in the low speed position of the first auxiliary transmission B and the forward / reverse lever 16 is in the forward first speed state in which the forward / reverse switching device C is in the forward position. As a result, the operation valve 35 is operated to the supply position 35a by the pilot pressure of the pilot oil passage 20, and the transmission operation of the hydraulic clutch 3 is performed.

In the first forward speed state, the shift lever 33
Is operated to the second speed position, for example, the first hydraulic cylinder 11
Is operated from the oil discharge position to the supply position,
The electromagnetic operation valve 26 of the first hydraulic cylinder 11 is operated from the supply position to the discharge position. As a result, the first hydraulic cylinder 11 is moved from the first speed position shown in FIGS.
It operates at the second speed position shown in (c).

During the operation of the first hydraulic cylinder 11,
The on-off valve 36 is opened by the first piston rod 24a and the linkage mechanism 32 (the on-off valve 37 has already been opened because the second hydraulic cylinder 12 is at the neutral stop position). As a result, the pilot pressure in the pilot oil passage 20 decreases, the operating valve 35 is operated from the supply position 35a to the oil discharge position 35b by the urging force of the spring, and the transmission of the hydraulic clutch 3 is interrupted.

Next, when the sliding operation of the shift member 9 by the first hydraulic cylinder 11 is completed and the main transmission A is shifted to the second speed position, the opening and closing valve 36 is opened by the first piston rod 24a and the linkage mechanism 32. As a result of the closing operation, the pilot pressure in the pilot oil passage 20 increases again, and the operation valve 35
Is operated from the oil discharge position 35b to the supply position 35a. As described above, when the pressure sensor 41 detects that the pilot pressure has decreased and increased again in the pilot oil passage 20, the control device 40 operates the electromagnetic proportional pressure control valve 14 to supply the pilot pressure to the hydraulic clutch 3. The hydraulic oil pressure is gradually increased or rapidly increased based on the operating position of the shift lever 33, etc.
The transmission operation of the hydraulic clutch 3 is performed.

[Another Embodiment of the Invention] In the above-described configuration, the speed change lever 33 is used as a speed change operation tool. However, instead of this, a button-type speed change indicating the operation position from the first speed position to the eighth speed position is performed. A switch may be used.

[0030]

According to the first aspect of the present invention, in a traveling speed change structure of a work vehicle configured to perform a speed change operation of a gear transmission by a hydraulic actuator, a difference in operating condition of a speed change operation tool by an operator and a high speed range. And the timing of the operation of supplying and discharging the hydraulic oil to and from the hydraulic actuator can always be made appropriate irrespective of the operation of the shift operating tool in the low-speed range. The operation has been carried out smoothly,
The shifting performance of the work vehicle was improved. Also, cheap
By using a solenoid operated valve that operates reliably at a reasonable price,
The operation of supplying and discharging hydraulic oil to and from hydraulic actuators is accurate and
The reliability of the shift operation of the work vehicle can be improved
It can be further improved.

[0031]

According to the features of claim 2, the case of claim 1
Similarly to the above, the present invention has the above-mentioned “effect of the invention”.
You. According to the feature of the second aspect , the hydraulic actuator operates in one and the other shift positions and the neutral stop position regardless of leakage of hydraulic oil, so that the reliability of the shift operation by the hydraulic actuator increases, and The reliability of the speed change operation can be improved.

[0033]

In the claims, reference numerals are provided for convenience of comparison with the drawings, but the present invention is not limited to the configuration shown in the attached drawings.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a traveling transmission system.

FIG. 2 is a hydraulic circuit diagram for first, second, and third hydraulic cylinders.

FIG. 3 is a diagram showing an operation state of first and second hydraulic cylinders;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine 3 Hydraulic clutch 9,10 Shift member 11,12 Hydraulic actuator 14 Electromagnetic proportional pressure control valve 20 Pilot pressure system 25,26 Electromagnetic operating valve 33 Shift operation tool 34 Detecting means 35 Operating valves 36,37 Operating means 40 Control means A Gear transmission

Continuation of the front page (72) Inventor Akio Hattori 4-15-5 Mokudori, Mihara-cho, Minamikawachi-gun, Osaka Inside Kubota Seiki Co., Ltd. (56) References JP-A-4-56635 (JP, A) JP-A-3 -48063 (JP, A) JP-A-3-51574 (JP, A) JP-A-5-73355 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) F16H 59/00- 61/12 F16H 61/16-61/24 F16H 63/40-63/48 A01D 69/00

Claims (3)

(57) [Claims] 1. A traveling gear transmission (A) and a traveling gear hydraulic clutch (3) are arranged in series on a lower side of an engine (1), and a shift member of the gear transmission (A) is provided. (9), (10)
A plurality of hydraulic actuators (11) and (12) for performing a gear shift operation by sliding operation, and an electromagnetic operation for supplying and discharging hydraulic oil to the plurality of hydraulic actuators (11) and (12) to operate the hydraulic actuators. Valves (25) and (26) and control means (4) for operating the solenoid operated valves (25) and (26).
0), a pilot-operated operating valve (35) for performing a supply / discharge operation of hydraulic oil to / from the hydraulic clutch (3) to transmit and cut off the hydraulic clutch (3); A pilot pressure system (20) for operating the valve (35), and operating means (36) for changing the pilot pressure of the pilot pressure system (20) with the operation of the hydraulic actuators (11) and (12). 37), a shift operation tool (33) that is artificially operated, and a detection unit (34) that detects an operation position of the shift operation tool (33) and inputs the operation position to the control unit (40). And the solenoid operated valves (25) and (26)
And hydraulic oil output port and hydraulic oil drain port.
The hydraulic actuator (11),
(12) Supply position of hydraulic oil to the hydraulic actuator
Of the hydraulic oil discharge position from the eater (11), (12)
The hydraulic actuators (11) and (12) start shifting operations by the solenoid operated valves (25) and (26) based on the operation of the shifting operation tool (33). The pilot pressure system (20) is operated by operating means (36) and (37).
Is operated by changing the pilot pressure of the control valve (35).
When the transmission is interrupted by the hydraulic clutch (3) and the gearshift operation by the hydraulic actuators (11) and (12) is completed, the pilot means of the pilot pressure system (20) is operated by the operating means (36) and (37). A traveling speed change structure of a work vehicle, wherein a pressure is changed and an operation valve (35) is operated to transmit the hydraulic clutch (3). 2. The hydraulic actuator (11), (1)
2) is configured to be operable at three positions: a shift position operated on one side, a shift position operated on the other side, and a neutral stop position between the two shift positions, and the electromagnetically operated valves (25) and (26). The hydraulic oil is supplied to predetermined positions of the hydraulic actuators (11) and (12) from
2) operates to the one and other shift positions, and hydraulic oil is supplied from the solenoid operated valves (25) and (26) to another predetermined position of the hydraulic actuators (11) and (12). , The hydraulic actuator (11), (12)
So that the hydraulic actuator is maintained at the neutral stop position.
2. A tutor (11), (12).
The traveling speed change structure of the working vehicle described in the above . 3. The hydraulic actuator (11), (1)
2) the shift position operated on one side and the shift position operated on the other
Position and a neutral stop position between the two shift positions.
Operable so that the electromagnetic actuated valves (25) and (26)
Hydraulic oil is supplied to predetermined positions of heaters (11) and (12)
As a result, the hydraulic actuators (11), (1)
2) operates in the one and other shift positions, and
Operating valve (25), (26)
Hydraulic oil is supplied to another predetermined position in (11) and (12).
The hydraulic actuators (11), (12)
So that the hydraulic actuator is maintained at the neutral stop position.
In addition to constituting the chutes (11) and (12), the auxiliary transmission device for traveling is provided with respect to the transmission (A) for traveling.
And the shift member (30) of the auxiliary transmission (B) is slid.
A hydraulic cylinder (13) for performing a shift operation by operating
The operation is performed by supplying and discharging hydraulic oil to and from the hydraulic cylinder (13).
3-port type two-position switching type
And a magnetic operating valve (29), auxiliary variables with the 2 position switching of the hydraulic cylinder (13)
The speed device (B) is operable by switching between high and low speeds.
Hydraulic cylinder (13) is operated by the solenoid operated valve (29)
It is configured to operate by supplying and discharging hydraulic oil.
The traveling speed change structure for a working vehicle according to claim 1 .