JPH06323428A - Running shifting structure for working vehicle - Google Patents

Abstract

PURPOSE:To restrain a shock at operating a shifting clutch to the transmission side after shifting operation is finished at shifting operation with a large running load in the running shifting structure for a working vehicle which is so constituted that a gear shifter for running is automatically operated by an actuator and a shift clutch. CONSTITUTION:A transmission clutch E is provided which takes out power of an engine 1 from the upper side of a gear shifter A and a shifting clutch 19 and can transmits it to the lower side of the gear shifter A and the shifting clutch 19. With start of shifting operation by actuators T1 and T2, the shifting clutch 19 is operated to the transmission shut-off side and the transmission clutch E is operated to the transmission side so as to restrain deterioration in running speed of a body. In this case, operating pressure of the transmission clutch E is automatically changed so that the speed becomes the middle between before and after the shifting. With end of shifting operation, the shifting clutch 19 is operated to the transmission side and the transmission clutch E is operated to the transmission shut-off side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a traveling speed change structure for a work vehicle equipped with a gear speed change device, which automatically operates a speed change clutch for traveling speed change to a transmission disengagement side based on an operation command for speed change. The present invention relates to a gear shift device provided with a structure for performing a gear shift operation and automatically again operating a gear shift clutch to a transmission side.

[0002]

2. Description of the Related Art An example of a traveling speed change structure for a work vehicle as described above is disclosed in Japanese Patent Laid-Open No. 3-209056. With this structure, the engine (1 in FIG. 4 of the publication)
On the lower side of the actuator, the actuator (1 in FIG.
1, a gear shift device (A in FIG. 4 of the publication) which is operated by a gear shift, and a shift clutch for traveling gear shifting (3 in FIG. 4 of the publication) are arranged in series. . As a result, the shift clutch is automatically operated to the transmission interruption side based on the operation command for shifting, and the gear shift device is shifted by the actuator. Then, when the shift operation by the actuator is completed, the shift clutch is automatically operated to the transmission side.

[0003]

Work vehicles equipped with the above-described traveling speed change structure are generally used for traveling on soft ground having a large traveling resistance or for towing a truck carrying a load. As described above, when the shift clutch is operated to the transmission cut-off side during gear shifting, the power of the engine is not transmitted to the traveling system at this time, and the traveling speed of the aircraft may suddenly decrease due to the traveling load.

As a result, if the speed change clutch is operated to the transmission side and the power of the engine is supplied to the running system in the state where the traveling speed of the machine body is greatly reduced at the end of the gear shift operation by the actuator, the machine body is lowered. There will be room for improvement in terms of riding comfort, as it will result in a shock due to sudden acceleration to the previous speed. The present invention is
It is an object of the present invention to provide a traveling gear shift structure for a work vehicle configured to shift gears for traveling by means of an actuator and a shift clutch so that the gear shift operation can be performed with less shock.

[0005]

The feature of the present invention resides in that the traveling speed change structure for a work vehicle as described above is configured as follows. In other words, on the lower side of the engine, a gear transmission for traveling and a shift clutch for traveling shifting are arranged in series, and an actuator for performing a shift operation by sliding a shift gear of the gear transmission based on an operation command is provided. , The power of the engine is taken from the upper side of the gear transmission and the speed change clutch, and this power is transmitted to the lower side of the speed change gear and the speed change clutch. It is equipped with an operating pressure changing means for changing the operating pressure of the clutch to change the power transmitted by this transmission clutch to high and low, and a rotation speed sensor for detecting the rotation speed of the traveling system, and the gear shift operation by the actuator is started. Then, the gear shift operation by the first control means for operating the gear shift clutch to the transmission interruption side in conjunction with this and the actuator is started. , The transmission clutch while adjusting the operating pressure of the transmission clutch by operating the operating pressure changing means so that the detection value of the rotation speed sensor is between the rotation speed before the shift and the rotation speed after the shift. The second control means for operating the transmission to the transmission side, and the gear shift clutch is operated to the transmission side in conjunction with the completion of the shift operation by the actuator,
Further, it is provided with a third control means for operating the transmission clutch to the transmission cutoff side.

[0006]

When configured as in the present invention, for example, FIGS.
As shown in FIG.
When the shift gear S1 of the gear transmission A is started to be slid by 1 and T2 and the gear shift operation is started, the gear shift clutch 19 is operated to the transmission cutoff side, and at the same time, the transmission clutch E is operated to the transmission side. In this way, when the transmission clutch 19 is operated to the transmission interruption side, the transmission clutch 19
Is on the lower side of the gear transmission A, the gear transmission A and the running system are disconnected, and when the speed change clutch 19 is on the upper side of the gear transmission A, the gear transmission A and the engine are And 1 are cut off. As a result, the actuator T
The sliding operation of the shift gear S1 of the gear transmission A by 1 and T2 is smoothly performed, and the gear shifting operation is performed.

In this case, if the speed change clutch 19 shown in FIG. 1 is operated to the transmission cutoff side, the power of the engine 1 will not flow from the speed change clutch 19 to the lower drive system.
At the same time, the transmission clutch E is operated to the transmission side, so that the power of the engine 1 extracted from the upper side of the gear transmission A and the transmission clutch 19 is transmitted to the traveling system via the transmission clutch E. Become.

Thus, when the speed change clutch 19 is operated to the transmission disengagement side during the speed change operation by the actuators T1 and T2, even if the traveling speed of the airframe is reduced due to a traveling load or a towing load, the transmission clutch E is operated. Due to the power, the aircraft will run without slowing down too much. Therefore, after the gear shift operation by the actuators T1 and T2,
When the speed change clutch 19 is operated to the power transmission side (the power transmission clutch E is operated to the power transmission disengagement side accordingly), the speed change clutch 19 is operated to the power transmission side in a state where the traveling speed of the machine body is not significantly reduced. It is possible to prevent a situation in which the shift clutch 19 is operated to the transmission side to cause a shock after the traveling speed of the vehicle has dropped extremely.

In this case, since the rotation speed sensor for detecting the rotation speed of the traveling system is provided, if the rotation speed of the traveling system (corresponding to the traveling speed of the machine body) before the start of the gear shifting operation by the actuator is detected, From this rotation speed, the rotation speed of the traveling system after the gear shift operation can be predicted. As a result, when the actuator starts the gear shifting operation, the rotational speed of the traveling system during the gear shifting operation is irrespective of the load applied to the aircraft and the traveling state.
The operating pressure of the transmission clutch (the power transmitted from the transmission clutch to the traveling system) so that the value is between the rotational speed of the traveling system before the start of the shifting operation and the predicted rotational speed of the traveling system after the shifting operation. Is changed and adjusted.

[0010]

As described above, when the gear shift clutch is operated to the transmission cutoff side during the gear shift operation of the gear transmission by the actuator, the power is transmitted to the traveling system by another transmission system and transmission clutch that bypass the gear transmission. Since the decrease in the traveling speed of the aircraft is suppressed, the entire gear shifting operation can be performed smoothly with less shock, and the riding comfort of the work vehicle can be improved. Further, since the rotation speed of the traveling system (corresponding to the traveling speed of the machine body) during the gear change operation is maintained at a value before and after the gear change operation, shock caused when the gear change clutch is operated to the transmission side after the gear change operation is prevented. It is possible to suppress the load irrespective of the load applied to the vehicle and the traveling state, and it is possible to further improve the riding comfort of the work vehicle.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. (1) FIG. 1 shows the inside of a mission case 8 of a four-wheel drive type agricultural tractor which is an example of a work vehicle.
From the P via the transmission shaft 2 and the clutch mechanism 3.
The PTO system is configured by being transmitted to the TO shaft 4. The power from the engine 1 is the forward clutch 5 or the reverse clutch 6, the cylindrical shaft 11, the main transmission A (corresponding to a gear transmission), the transmission clutch 19, the first auxiliary transmission B, the second auxiliary transmission C, and the rear wheels. The traveling system is configured by being transmitted to the rear wheel 7 via the differential device 7a. Then, the power branched from immediately before the rear wheel differential device 7a is configured to be transmitted to the front wheels 10 via the transmission shaft 9, the hydraulic clutch type front wheel transmission device D, the front wheel transmission shaft 12, and the front wheel differential device 10a. .

The forward clutch 5 and the reverse clutch 6 are multi-plate friction type hydraulically operated systems in which a friction plate (not shown) and a piston (not shown) are combined, and are supplied to the transmission side by supplying hydraulic oil. Operated. Then, when the forward clutch 5 is operated to the transmission side, the power of the engine 1 directly flows from the forward clutch 5 to the cylindrical shaft 11 to move the vehicle body forward. When the reverse clutch 6 is operated to the transmission side, the power of the engine 1 is transmitted to the cylindrical shaft 11 in the reverse rotation state via the reverse clutch 6 and the transmission shaft 31, and the machine body moves backward.

The main transmission A is constructed in a synchromesh type in which two sets of shift gears S1 are slidably operated, and is capable of shifting in four stages. Power from the cylindrical shaft 11 on the engine 1 side is transmitted to the transmission shaft 35, This transmission shaft 35 is transmitted to the cylindrical transmission shaft 50, is operated in four stages, and is transmitted to the shift clutch 19. The first auxiliary transmission B is also of a synchromesh type for sliding the shift gear S2. Then, both shift gears S1 of the main transmission A
The hydraulic cylinders T1 and T2 (corresponding to actuators) for sliding the gears, and the hydraulic cylinder T3 for sliding the shift gear S2 of the first auxiliary transmission B are provided.

When a shift operation is performed by the hydraulic cylinders T1, T2, T3, the shift clutch 19 is operated to the transmission cutoff side in conjunction with the start of the shift operation, so that the hydraulic cylinders T1, T2
A hydraulic control system is provided for operating the transmission side of the speed change clutch 19 in conjunction with the completion of the speed change operation by T2 and T3, so that the speed change operation can be performed by hydraulic pressure.
The second auxiliary transmission C is a manually operated type in which the shift gear is directly slid by a shift lever (not shown).

(2) As shown in FIG. 1, the hydraulic cylinder T
When the shift clutch 19 is operated to the transmission interruption side during the shift operation of the main transmission device A by T1 and T2, the shift clutch 19
The transmission shaft 34 of the first auxiliary transmission B on the lower side and the transmission shaft 3 of the forward and reverse clutches 5 and 6 of the main transmission A.
A transmission clutch E that can be connected to the vehicle 5 is provided.

Next, the transmission clutch E will be described. As shown in FIG. 2, the transmission shaft 35 on the forward and reverse clutches 5, 6 side of the main transmission A and the transmission shaft 34 on the first auxiliary transmission B side are arranged concentrically. The support member 28 is fixed to the transmission shaft 34 on the first auxiliary transmission B side,
A clutch case 29 is fixed to a transmission shaft 35 on the forward and reverse clutches 5 and 6, and a plurality of friction plates 30 are provided between the clutch case 29 and the support member 28. A piston 32 is installed in the clutch case 29 so as to be slidable in the left-right direction of the drawing, and a spring 36 for urging the piston 32 in a direction away from the friction plate 30 is provided.

With the above structure, when the hydraulic oil is drained from between the piston 32 and the clutch case 29 through the oil passage 35a of the transmission shaft 35 on the forward and reverse clutches 5 and 6, the spring 36 is attached. Due to the force, the piston 32 moves to the left side of the drawing as shown in FIG. 2 and separates from the friction plate 30. As a result, the transmission clutch E enters the transmission cutoff state and the transmission shaft 35 on the main transmission A side and the transmission shaft 3 on the first auxiliary transmission B side.
4 is disconnected, and this transmission cutoff state is the normal traveling state of the airframe.

On the contrary, if hydraulic oil is supplied between the piston 32 and the clutch case 29 via the oil passage 35a of the transmission shaft 35 on the forward and reverse clutches 5 and 6, the spring 3
The piston 32 moves to the right in the drawing from the state of FIG. 2 against the biasing force of 6, and presses the friction plate 30. This allows
The transmission clutch E is in the transmission state, and the transmission shaft 35 on the main transmission A side and the transmission shaft 34 on the first auxiliary transmission B side are connected to each other, and the power of the engine 1 shown in FIG. It is transmitted to the front wheels 10 and the rear wheels 7 via the transmission shafts 35 and 34. This transmission state corresponds to the hydraulic cylinder T1 of FIG.
This is a state in which the main transmission A is being shifted by T2.

(3) Next, the hydraulic cylinders T1, T2, T
3, the hydraulic control system of the speed change clutch 19 and the transmission clutch E will be described. As shown in FIG. 3, the hydraulic pump 13
Is supplied to the three sets of hydraulic cylinders T1, T2, T3 via the rotary valve 15, and the pilot working oil is supplied / discharged during the operation of these three sets of hydraulic cylinders T1, T2, T3. A pilot oil passage 16 is provided. The hydraulic oil from the hydraulic pump 13 is supplied to the rotary valve 15 via the oil passage 17, and the hydraulic oil is supplied to the oil passage 1
It is supplied to the forward and reverse clutches 5 and 6 via the valve 8 and the forward / reverse switching valve 27.

Hydraulic oil is supplied from the oil passage 20 branched from the oil passage 18 to the speed change clutch 19 via the pilot operated switching valve 26, and the pilot oil passage 16 is connected to the switching valve 26. Control valves 21 and 22 for controlling the supply and discharge of pilot hydraulic oil in the pilot oil passage 16 are provided, and the pilot oil passages 23 and 24 from the hydraulic cylinders T1 and T2 for the main transmission device A, and the first sub gear shift. The pilot oil passage 25 from the hydraulic cylinder T3 for the device B is connected to the control valves 21 and 22 as shown in FIG.

As shown in FIG. 3, the hydraulic oil in the oil passage 38 branched from the oil passage 18 is supplied to the transmission clutch E via a pressure control valve 39 (corresponding to operating pressure changing means) of an electromagnetic proportional type. A pilot operated switching valve 40 is provided between the pressure control valve 39 and the transmission clutch E, and a pilot oil passage 41 branched from between the switching valve 26 and the speed change clutch 19 is used as the switching valve 40. Connected to.

As shown in FIG. 3, a pressure sensor 44 for detecting the pilot pressure in the pilot oil passage 16 and a position sensor 4 for detecting the operating position of the shift lever 14 described later.
It is equipped with 5. As shown in FIG. 1, the second auxiliary transmission C
Pinion shaft 4 for transmitting power from the rear wheel diff device 7a
A rotation speed sensor 43 for detecting the rotation speed of 2 is provided. Then, the rotary valve 15 is mechanically set to the neutral position and 1
The shift lever 14 that can be operated in the 8th to 8th speed positions is provided,
A forward / reverse lever 33 that can operate the forward / reverse switching valve 27 at three positions of a forward drive position F, a neutral position N, and a reverse drive position R is provided.

(4) Next, the operation of each part during a gear shift operation will be described. FIG. 3 shows a state in which the forward / reverse lever 33 is operated to the forward position F and the speed change lever 14 is operated to the first speed position. The hydraulic cylinder T1 of the main transmission A moves to the first speed position and the hydraulic cylinder T2. Is in the neutral position,
The hydraulic cylinder T3 of the first auxiliary transmission B is located on the low speed side. As a result, the control valve 21 is switched by the pilot hydraulic oil from the hydraulic cylinder T1, and the pilot hydraulic oil from the hydraulic cylinder T3 enters the pilot oil passage 16 via the pilot oil passage 25 and the control valves 22 and 21. After being supplied, the switching valve 26 is switched to the communication position shown in FIG.

Therefore, the hydraulic oil from the oil passage 18 is supplied to the forward clutch 5 via the forward / reverse switching valve 27 and is operated to the transmission side (the reverse clutch 6 is shut off by the forward / reverse switching valve 27). Operate on the side). The hydraulic oil from the oil passage 20 is supplied to the speed change clutch 19 via the switching valve 26, and the speed change clutch 19 is operated on the transmission side. The switching valve 40 is switched to the oil discharge position shown in FIG. 3 and the transmission clutch E is operated to the transmission interruption side, so that the machine body is traveling in the first forward speed state.

With the above structure, the forward movement 1 as shown in FIG.
It is assumed that, in the high speed state, the shift lever 14 is started to be operated from the first speed position to the second speed position. In this case, when the hydraulic cylinder T1 starts to move from the first speed position to the second speed position by the hydraulic oil from the rotary valve 15, the pilot pressure in the pilot oil passage 23 decreases and the control is performed as shown in FIGS. Valve 21
Is operated to switch the pilot oil passage 16 to the oil discharge state. As a result, the switching valve 26 is switched and hydraulic oil is drained from the speed change clutch 19, and the speed change clutch 19 is operated to the transmission cutoff side (the above is equivalent to the first control means).
As a result, when the pilot oil passage 41 is discharged, the switching valve 40 is operated to the communicating position, and the pressure sensor 44 detects that the pilot pressure in the pilot oil passage 16 has decreased. The valve 39 is operated, the hydraulic oil is supplied from the oil passage 38 to the transmission clutch E, and the transmission clutch E is operated to the transmission side (time point A in FIG. 4).
1).

Thus, the shift clutch 19 shown in FIG.
Is operated to the transmission cutoff side, the first auxiliary transmission B and the second auxiliary transmission C on the lower side from the speed change clutch 19
The power of the engine 1 stops flowing. However, at the same time, the transmission clutch E is operated to the transmission side, so that the power of the engine 1 is the forward clutch 5 (or the reverse clutch 6), the cylindrical shaft 11, the transmission shaft 35 of the main transmission A, the transmission clutch E.
Also, the power is transmitted from the first auxiliary transmission B and the second auxiliary transmission C to the front wheels 10 and the rear wheels 7 via the transmission shaft 34, and the vehicle body moves forward even if there is a traveling load or a traction load.

In this case, as shown in FIGS. 1 and 3, since the rotation speed sensor 43 for detecting the rotation speed of the pinion shaft 42 is provided, the pinion in the forward first speed state before the start of the gear shifting operation by the hydraulic cylinder T1. If the rotation speed of the shaft 42 is detected, the rotation speed of the pinion shaft 42 after shifting to the forward second speed position can be predicted from this rotation speed. Therefore, when the hydraulic cylinder T1 starts to move from the first speed position to the second speed position, the rotational speed of the pinion shaft 42 (detection value of the rotational speed sensor 43) during the gear shifting operation is the forward speed 1 before the gear shifting operation is started.
Operation of the transmission clutch E by the control device 37 and the pressure control valve 39 so that the rotation speed of the pinion shaft 42 in the high speed state and the predicted rotation speed of the pinion shaft 42 in the second forward speed position become an intermediate value. The pressure is changed and adjusted, and the power transmitted from the transmission clutch E to the front wheels 10 and the rear wheels 7 is adjusted to high and low (the above is equivalent to the second control means).

As described above, while the transmission clutch E is operated to the transmission side and the power of the engine 1 is transmitted to the front wheels 10 and the rear wheels 7 to advance the machine body, a time point A shown in FIG.
From 1 to time point A2, the shift operation to the second speed position by the hydraulic cylinder T1 is performed. When this shift operation is completed, as shown in FIG. 3, pilot hydraulic oil is supplied again from the hydraulic cylinder T1 to the pilot oil passage 23, the control valve 21 is switched to the position shown in FIG. 3, and the pilot oil passage 16 Pilot oil is supplied again to the switching valve 2
6 is switched to the communication position shown in FIG. As a result, hydraulic oil is supplied to the shift clutch 19 as shown from time A2 to time A3 in FIG.
Is operated by the transmission side. As described above, when the hydraulic oil is supplied to the speed change clutch 19, the pilot hydraulic oil from between the switching valve 26 and the speed change clutch 19 causes the changeover valve 4 to operate.
0 is switched to the oil discharge position shown in FIG. 3, and this transmission clutch E is operated to the transmission interruption side (the above corresponds to the third control means).

The above states are between the forward first speed state and the forward second speed state, and between the forward fifth speed state and the forward sixth speed state, but between the forward third speed state and the forward fourth speed state. , Between the seventh forward speed state and the eighth forward speed state, the hydraulic cylinder T2 of FIG.
And the control valve 22 is switched to perform the automatic operation as described above, and the hydraulic cylinders T1, T2, T3 are operated between the fourth forward speed state and the fifth forward speed state. The automatic operation as described above is performed. Even in the reverse state in which the forward / reverse lever 33 is operated to the reverse position R and the hydraulic oil is supplied to the reverse clutch 6, the automatic operation as described above is performed between the reverse first speed state and the reverse speed eighth state. It is done.

[Other Embodiments] In the hydraulic control system shown in FIG. 3, the switching valve 40 and the pilot oil passage 41 are eliminated and the hydraulic pressure control system shown in FIG.
It may be configured as shown in. In the configuration shown in FIGS. 3 and 5, as shown in FIG. 4, the pinion shaft 4 during the gear shifting operation is performed.
Instead of adjusting the operating pressure of the transmission clutch E so that the rotation speed of 2 becomes an intermediate value of the rotation speed before and after the gear shifting operation, the rotation speed of the pinion shaft 42 during the gear shifting operation is set to the rotation speed before and after the gear shifting operation. It may be configured so that the setting can be artificially changed so as to obtain a desired rotation speed within the range. In this case, the rotation speed of the pinion shaft 42 during the gear shifting operation is maintained at the rotation speed before the gear shifting operation, and the pinion shaft 42 during the gear shifting operation is maintained.
It may be possible to artificially set the number of revolutions so that it becomes the number of revolutions predicted after the gear shift operation.

In the hydraulic control system of FIGS. 3 and 5, the oil passage 2
0 may be provided with an electromagnetic proportional type pressure control valve (not shown), a variable reducing valve (not shown), or the like to control the pressure of the hydraulic oil to the speed change clutch 19. In this case, when the speed change clutch 19 is operated to the transmission side after the end of the speed change operation as shown from time point A2 to time point A3 in FIG. 4, the pressure increasing characteristic of the hydraulic oil pressure to the speed change clutch 19 is changed to drive the vehicle. The shift clutch 19 is smoothly operated to the transmission side according to the load or the traction load. A variable reducing valve (not shown) may be used in place of the electromagnetic proportional type pressure control valve 39 in FIGS. 3 and 5. Further, in the configuration shown in FIG. 1, the transmission clutch 19 disposed between the main transmission A and the first auxiliary transmission B is a cylindrical shaft between the forward and reverse clutches 5 and 6 and the main transmission A. You may prepare for the 11th part.

It should be noted that reference numerals are given in the claims for convenience of comparison with the drawings, but the present invention is not limited to the configurations of the accompanying drawings by the entry.

[Brief description of drawings]

FIG. 1 is a diagram showing an outline of a traveling transmission system in a mission case.

FIG. 2 is a vertical sectional side view of the transmission clutch.

FIG. 3 is a hydraulic circuit diagram of a hydraulic cylinder for speed change operation, a speed change clutch, a transmission clutch, forward and reverse clutches, etc.

FIG. 4 is a diagram showing states of a hydraulic cylinder, a speed change clutch, a transmission clutch, and a rotation speed sensor during a speed change operation from a forward first speed position to a forward second speed position.

FIG. 5 is a hydraulic cylinder for gear shift operation in another embodiment,
Hydraulic circuit diagram for speed change clutch, transmission clutch, forward and reverse clutch, etc.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 engine 19 speed change clutch 39 operating pressure changing means 43 rotation speed sensor A gear speed changer S1 gear shifter gear T1, T2 actuator E transmission clutch

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshifumi Horiuchi 64 Ishizukita-machi, Sakai City, Osaka Prefecture Kubota Sakai Factory

Claims (1)

[Claims] 1. A gear transmission (A) for traveling and a shift clutch (19) for traveling shifting are provided on the lower side of the engine (1).
Are arranged in series, and equipped with actuators (T1) and (T2) that perform a shift operation by sliding the shift gear (S1) of the gear transmission (A) based on an operation command. ) And the speed change clutch (19) from the upper side, and the power of the engine (1) is taken out, and this power is transferred to the gear transmission (A) and the speed change clutch (1).
9) Hydraulically operated frictional transmission clutch (E) capable of transmission and transmission interruption operation to the lower side, and power for transmitting the transmission clutch (E) by changing the operating pressure of the transmission clutch (E) Is provided with an operating pressure changing means (39) capable of changing the height to a low level, and a rotation speed sensor (43) for detecting the rotation speed of the traveling system, and a shift operation by the actuators (T1), (T2) is started. And the gear change clutch (1
When the gear shift operation by the first control means for operating 9) to the transmission cutoff side and the actuators (T1) and (T2) is started, the detected value of the rotation speed sensor (43) becomes the rotation speed before the shift. The transmission clutch (E) is moved to the transmission side while adjusting the operation pressure of the transmission clutch (E) by operating the operation pressure changing means (39) so that the rotation speed is between the rotation speed after the shift. Operating the second control means and the actuators (T1), (T2) in conjunction with the completion of the speed change operation, the speed change clutch (19) is operated to the transmission side, and the transmission clutch (E) is transmitted. A traveling speed change structure for a work vehicle, comprising: a third control means that is operated on a shutoff side.