JPH07144657A - Traveling operation structure of work vehicle - Google Patents

Abstract

PURPOSE:To prevent the phenomena of a changeover valve sticking in a slow turning position or a sharp turning position, in case that a work vehicle is left as it is for a long period. CONSTITUTION:This structure is equipped with a retaining means 51, which can retain a changeover valve 18 for changeover, in the position corresponding to the middle position between the position of slowly turning a changeover valve and the position of sharply turning it, and the changeover lever 18 is retained in the middle position in case of placing a work vehicle for a long period.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a traveling operation structure for a work vehicle provided with a pair of left and right traveling devices such as multi-wheel type or crawler type having four wheels on each side.

[0002]

2. Description of the Related Art An example of a work vehicle as described above is a combine equipped with a pair of left and right crawler type traveling devices.
In such a combine, for example, Japanese Patent Laid-Open No. 4-11
As disclosed in Japanese Patent No. 8384, a hydraulic slow turning mechanism (1 in FIG. 1 and FIG. 2 of the above publications, which gives a speed difference to a pair of left and right traveling devices to turn a vehicle body to the right or left.
2), a hydraulic rapid turning mechanism that applies a speed difference larger than that of the slow turning mechanism to the left and right traveling devices to rapidly turn the machine body to the right or left (28 in FIG. 1 and FIG. 2 of the publication). Three
Some have 0).

Then, a gentle turning position (35c in FIG. 1 of the above publication) for supplying and discharging the operating oil to the gentle turning mechanism and a sudden turning position for supplying and discharging the working oil to the rapid turning mechanism (see the above publication). A switching valve (35a, 35b in FIG. 1) capable of switching operation (35 in FIG. 1 of the publication) and a switching lever mechanically linked to the switching valve (see FIG. 1 of the publication). 18)
(Corresponding to a switching operation tool). Thus, by performing the switching operation of the switching valve in advance by the switching lever, it is possible to select the gentle turning with the comparatively large turning radius by the gentle turning mechanism and the sharp turning with the turning radius smaller than the gentle turning. it can.

[0004]

In a work vehicle such as the above-mentioned combine, when one work period ends, it may be left in a warehouse or the like for several days until the next work period begins. is there. Therefore, as described above, in the case of the work vehicle configured to select the gentle turning and the sharp turning in advance by the switching operation tool and the switching valve, the switching operation tool and the switching valve are operated to the gentle turning position or the sharp turning position. If left in this state for several days, fine dust or the like may attach to the spool of the switching valve and be caught in the spool, so that the switching valve may be stuck in the gentle turning position or the rapid turning position. If the switching valve sticks in this way, the switching operation of the switching valve cannot be performed, and the subsequent repair and adjustment of the switching valve becomes troublesome. As described above, the present invention provides a simple structure of a traveling operation structure of a work vehicle equipped with a switching valve for selecting a turning state, which can prevent sticking phenomenon of the switching valve when left for a long time. The purpose is to do.

[0005]

The feature of the present invention resides in the following construction in the traveling operation structure of the work vehicle as described above. That is, a hydraulic slow swing mechanism that gives a speed difference to a pair of left and right traveling devices provided on the aircraft to turn the aircraft to the right or left, and a speed difference larger than that of the gentle swing mechanism to the left and right traveling devices. It is equipped with a hydraulic swivel mechanism that swivels the aircraft to the right or left, and is located at a slow swivel position where the slow swivel mechanism feeds and discharges hydraulic fluid, and a quick swivel position where the hydraulic swivel mechanism feeds and drains hydraulic oil. A switching valve that can be switched and a switching operation tool that is mechanically linked to the switching valve to artificially switch the switching valve are provided, and the intermediate position between the gentle turning position and the sudden turning position of the switching valve is provided. Is provided with a holding position for holding the switching operation tool at a position corresponding to the above, and a holding means capable of switching operation at a holding release position allowing the switching operation of the switching operation tool.

[0006]

With the structure of the present invention, the holding means is switched to the holding position when it is left for a long period of time,
Hold the switching control in the intermediate position. When the switching operation tool is held at the intermediate position in this way, the switching valve is also held at the intermediate position between the gentle turning position and the sudden turning position.
In this case, assuming that the switching valve has a structure as shown in FIG. 8, for example, at the intermediate position of the switching valve 35, the oil passage 48 on the slow turning mechanism side, the oil passage 45 on the rapid turning mechanism side, and the pump side. The small diameter portion 35g of the spool 35e is located at the boundary portion 35h with the oil passage 34, and the oil passage 34 and the oil passages 48 and 45 are in communication with each other. In this way, spool 3
If there is a sufficient gap between the small-diameter portion 35g of 5e and the boundary portion 35h to allow hydraulic oil to pass, the small-diameter portion 35
Grain and other debris accumulate between g and the boundary 35h,
It will not be caught in the spool 35e. or,
Even if fine dust or the like stays in the boundary portion 35h, the fine dust or the like will be washed away when the hydraulic oil is next supplied from the oil passage 34 on the pump side.

When the holding means as described above is provided, it may be possible to provide it on the switching valve. However, if the holding means is provided on the switching valve which is arranged at a deep position inside the work vehicle, the holding means is provided. The switching operation itself is difficult and troublesome. On the other hand, according to the present invention, since the holding means is provided for the switching operation tool that the operator actually operates with the hands or feet, the switching operation of the holding means can be easily performed.

[0008]

As described above, in the work vehicle provided with the switching valve for selecting the turning state, the switching operation tool and the switching valve can be held at the intermediate position, so that the working vehicle can be left for a long time. It was possible to prevent the stuck phenomenon of the switching valve in the case of being set, and to reduce the repair adjustment of the switching valve due to the stuck of the switching valve. Further, by providing the switching operation tool with the holding means, the switching operation tool can be easily held at the intermediate position and the operability is improved.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. (1) FIG. 2 shows a structure inside a transmission case 8 of a traveling system of a combine, which is an example of a work vehicle, in which power from an engine (not shown) is provided with a belt transmission mechanism (not shown) having a tension clutch. ) Is transmitted to the input pulley 2 of the hydrostatic continuously variable transmission 1, and the power from the output shaft 3 of the hydrostatic continuously variable transmission 1 is transmitted via the first transmission shaft 4 to the front portion of the machine body. It is transmitted to a reaper (not shown).

Power from the first transmission shaft 4 is transmitted to the second transmission shaft 11 via the first gear 9 and the second gear 10.
A shift gear 14 is slidably fitted to the second transmission shaft 11 by a spline structure, while a high speed gear 16, a medium speed gear 17, and a low speed gear 6 are fixed to a third transmission shaft 15 corresponding thereto. . With the above structure, the shift gear 14 is slid to engage the high-speed gear 7, the medium-speed gear 17, or the low-speed gear 6 that meshes with the high-speed gear 16, and the forward rotation power for straight traveling can be shifted to three stages of high, medium, and low. Because
This normal rotation power is applied to the first transmission gear 1 that meshes with the medium speed gear 17.
9 is transmitted. As described above, the shift gear 14, the high speed gear 7 and the like constitute the gear shift type transmission 13.

A right side gear 21R and a left side gear 21L are relatively rotatably fitted on a support shaft 20 for supporting the first transmission gear 19, and an input gear 23 of a left and right axle shaft 22 is a left and right side gear 21R, 21L is always occluded. As a result, the right or left side gear 21R, 2
1L is slid on the first transmission gear 19 so as to be engaged and separated from each other, and power transmission and transmission interruption operations are performed on the pair of left and right traveling devices 24 of the crawler type. Side clutches 25R and 25L are formed between the side gears 21R and 21L.

(2) Next, description will be given of a structure in which one traveling device 24 is reversed to make a super turning turn (corresponding to a sharp turn). As shown in FIG. 2, the third gear 37 that meshes with the high speed gear 16 of the third transmission shaft 15 is fitted onto the fourth transmission shaft 27 so as to be relatively rotatable, and the third gear 37 and the fourth transmission shaft 27 are connected to each other. A reverse clutch 30 (corresponding to a sharp turning mechanism) is provided between them. The second transmission gears 26R are provided at the left and right ends of the support shaft 20,
26L is bearing-supported, and each of the fourth transmission gears 29 fixed to both ends of the fourth transmission shaft 27 meshes with the second transmission gears 26R and 26L.

As a result, the right side gear 21R or the left side gear 21L is connected to the right or left second transmission gear 26.
When the reverse clutch 30 is engaged and operated with the R and 26L engaged, the power from the high-speed gear 16 is transmitted in reverse to the traveling device 24 while being decelerated by 1/3. In this case, since the other side gears 21R and 21L are engaged with the first transmission gear 19 and are normally driven,
Due to the large speed difference between the left and right traveling devices 24, the airframe makes a super turning turn.

(3) Next, a description will be given of a structure in which one of the traveling devices 24 is normally driven at a lower speed than the other to make a gentle turn. As shown in FIG. 2, a small-diameter output gear 38 is fixed to the boss portion of the first transmission gear 19, and a large-diameter third transmission gear 40 is externally fitted to the fourth transmission shaft 27 so as to be relatively rotatable. The 3 transmission gear 40 meshes with the output gear 38. Then, the slow swing clutch 12 (corresponding to a slow swing mechanism) is provided between the third transmission gear 40 and the fourth transmission shaft 27.

As a result, the right or left side gear 21
When the slow turning clutch 12 is engaged and operated while the R and 21L are engaged with the right or left second transmission gears 26R and 26L, the straight forward drive power transmitted to the first transmission gear 19 is output gear 38. , Through the third transmission gear 40, the slow swing clutch 12, the fourth transmission shaft 27, the fourth transmission gear 29, and the right or left second transmission gear 26R, 26L as a normal rotation power reduced to 1/3. It is transmitted to one of the traveling devices 24. In this case, since the other side gears 21R and 21L are engaged with the first transmission gear 19 and are normally driven at a predetermined speed, the machine body makes a gentle turn due to a small speed difference between the left and right traveling devices 24. .

(4) -1 Next, a hydraulic oil supply structure for the hydraulic cylinders 31R, 31L for sliding the left and right side gears 21R, 21L, and the slow turning and reverse rotation clutches 12, 30 will be described. As shown in FIG. 1, hydraulic oil from the pump 32 is supplied to the hydraulic cylinders 31R and 31L for the left and right side gears 21R and 21L via the first switching valve 33, and the oil passage 34 from the side surface of the hydraulic cylinders 31R and 31L is supplied. Is connected to the second directional control valve 35 (corresponding to the directional control valve of the present invention) for the slow swing and reverse rotation clutches 12 and 30. Further oil passage 34
A variable relief valve 36 for the slow swing and reverse rotation clutches 12 and 30 is connected to.

A switching lever 18 (corresponding to a switching operation tool) is provided in the control section of the machine body, and the switching lever 18 and the second switching valve 35 are mechanically interlocked with each other.
The second switching valve 35 is controlled by the slow turning position 35a for supplying hydraulic oil to the slow turning clutch 12, and the reverse rotation clutch 30.
Switching operation is performed to the super-spinning turning position 35b (corresponding to the sudden turning position) for supplying hydraulic oil to The operation lever 39 provided in the control section of the machine body, the first switching valve 33 and the variable relief valve 36 are mechanically linked via the linkage mechanism 41 and the wire 42.

(4) -2 With the above structure, first, the second switching valve 35 is operated to the gentle turning position 35a by the switching lever 18. When the operation lever 39 is operated to the neutral position N in this state, the first switching valve 33 is also operated to the neutral position and the left and right hydraulic cylinders 31 are operated.
R and 31L contract, and left and right side gears 21R and 21L
L meshes with the first transmission gear 19. As a result, the normal rotation power transmitted to the first transmission gear 19 is transmitted to the left and right traveling devices 24, the left and right traveling devices 24 are driven at the same speed, and the machine body travels straight.

Next, when the operating lever 39 is operated from the neutral position N to the first turning position R1 on the right side or the first turning position L1 on the left side, only the first switching valve 33 is operated and the hydraulic cylinder 3 is operated.
By 1R or 31L, right or left operation unit 46R, 46
Via L, the right or left side gear 21R, 21L that has been meshed with the first transmission gear 19 is separated from the first transmission gear 19 and meshes with the right or left second transmission gear 26R, 26L.

In this case, since the variable relief valve 36 is not yet operated and is in the fully open state, and the slow swing clutch 12 is in the disengaged state, the transmission to the right or left traveling device 24 is cut off (side). The transmission of the clutch 25R or 25L is cut off), and the aircraft gently turns to the right or left. Sequence valve 47 provided in the oil passage 34
Is for ensuring the pressure necessary for the right or left side gears 21R, 21L to completely mesh with the right or left second transmission gears 26R, 26L in the hydraulic cylinders 31R, 31L.

Next, the operating lever 39 is moved from the right or left first turning position R1, L1 to the right or left second turning position R2, L.
When you move to 2, the right or left side gear 21R, 2
1L is engaged with the right or left second transmission gears 26R, 26L, and the second switching valve 35 is operated to the gentle turning position 35a, and the variable relief valve 36 is gradually operated from the fully opened state to the closed side. Go away. As a result, the loose swing clutch 1
2 starts to operate, the right or left traveling device 24 is gradually driven to rotate at a low speed in the forward direction, and the body slowly turns to the right or left. Then, at the right or left second turning position R2, L2 of the operating lever 39, the slow turning speed becomes maximum.

(4) -3 Next, the second switching valve 35 is operated by the switching lever 18 to the superposition turning position 35b. In this state, the operation lever 39
When the control lever 39 is operated to the neutral position N, it goes straight as described above. When the operation lever 39 is operated from the neutral position N to the first turning position R1 or L1 on the right or left, the right or The transmission cut-off state of the left side clutch 25R, 25L appears.

Next, the operation lever 39 is moved from the right or left first turning position R1, L1 to the right or left second turning position R2, L.
When you move to 2, the right or left side gear 21R, 2
In the state where 1L is engaged with the right or left second transmission gears 26R, 26L, and the second switching valve 35 is operated to the super trust turning position 35b, the variable relief valve 36 is opened from the fully opened state as described above. It is gradually operated toward the closed side. This allows
The right or left traveling device 2 after the reverse clutch 30 starts to operate.
4 is gradually driven in the reverse direction, and the aircraft makes a super turning turn to the right or left. The reverse rotation speed becomes maximum at the right or left second turning position R2, L2 of the operating lever 39.

(5) Next, the linkage structure of the switching lever 18 and the second switching valve 35 will be described. As shown in FIGS. 6 and 7, the second switching valve 35 and the variable relief valve 36 are arranged vertically, and the second switching valve 35 is constituted by a spool 35e that is slid, and the spool 35e is a spring 35c. Is urged to the right in the plane of FIG. The operation shaft 5 is rotatably supported, and one operation arm 5a fixed to the operation shaft 5 faces the spool 35e of the second switching valve 35 and is fixed to the other end of the operation shaft 5. The arm 5b and the switching lever 18 shown in FIGS. 1 and 3 are connected by a wire 43. As shown in FIG. 3, the switching lever 18 is swingably supported around the horizontal axis P1 of the control section of the airframe, and the toggle spring 44 that holds the switching lever 18 at the gentle turning position or the super-spinning turning position is provided. It is equipped.

The state shown in FIGS. 3 and 6 is the switching lever 18.
Is in a state of operating to a super-coordinated turning position, and in FIG. 6, the spool 35e of the second switching valve 35 has a super-coordinated turning position 35b on the right side of the drawing due to the urging force of the spring 35c (see FIG. 1).
It is located at. In this state, the working oil from the oil passage 34 shown in FIG. 6 and FIG.
Reverse spool clutch 3 from the spool 35e through the oil passage 45
Supplied to zero.

When the switching lever 18 is operated to the gentle turning position, the wire 43 is pulled to the switching lever 18 side, and the operating arm 5a is swung to the left side of the paper surface of FIG. Spool 3 of switching valve 35
5e is pushed to the gentle turning position 35a (see FIG. 1) on the left side of the paper against the biasing force of the spring 35c. In this state, the hydraulic oil from the oil passage 34 shown in FIGS. 1 and 6 is
The slow swing clutch 12 is supplied from the spool 35e of the second switching valve 35 via the oil passage 48.

As shown in FIGS. 3, 4 and 5, the switching lever 18
A bracket 50 is fixed to a lateral side portion of the lever guide 49 of the U-shaped holding member 51 (corresponding to a holding means).
Is swingably supported around the horizontal axis P2 of the bracket 50. The holding member 51 is held at two positions, a holding release position shown by a solid line in FIG. 5 and a holding position shown by a chain double-dashed line, by an internal detent mechanism (not shown). When the holding member 51 is operated to the holding release position as shown by the solid line in FIGS. 3 and 5, the switching lever 18 can be freely operated to the gentle turning position and the super-sight turning position. Then, as shown in FIG. 4, the switching lever 18 is operated to an intermediate position between the gently swiveling position and the super-spinning swivel position, and the holding member 51 is moved.
When the switch is operated to switch to the holding position, the switching lever 18 can be held at the intermediate position by the holding member 51.

As described above, in the second switching valve 35 with the switching lever 18 held in the intermediate position, the large diameter portion 35f and the small diameter portion 35g of the spool 35e of the second switching valve 35 are shown in FIG. Is the oil passage 4
The oil passage 34 on the case side is reached when it reaches the position facing 8 and 45.
The small diameter portion 35g of the spool 35e is located at a pair of boundary portions 35h between the oil passages 48 and 45 and the oil passage 34 and the oil passage 4
8 and 45 are in communication with each other. Thus, the small diameter portion 35g of the spool 35e and the boundary portion 35h
If a sufficient space is provided between the small diameter portion 35g and the boundary portion 35h, a small dust or the like may be retained between the small diameter portion 35g and the boundary portion 35h and be caught in the spool 35e. Absent. Further, even if fine dust or the like stays in the boundary portion 35h, the fine dust or the like will flow when the hydraulic oil is supplied from the pump 32 to the oil passage 34 next time.

As shown in FIGS. 6 and 7, the second switching valve 3
5, a variable relief valve 36 is arranged above the variable relief valve 36. The variable relief valve 36 is configured to urge the poppet 36a toward the closing side by a spring 36b and a receiving member 36c of the spring 36b. A cylindrical shaft 28 is fitted onto the operation shaft 5 so as to be relatively rotatable, and one operation arm 28a fixed to the cylindrical shaft 28 faces a receiving member 36c of the variable relief valve 36. The operation arm 28b fixed to the end and the operation lever 39 shown in FIG. As a result, when the operation lever 39 is operated from the right or left first turning position R1, L1 to the right or left second turning position R2, L2 as described in (4) -2, 3 above. , The wire 42 is pulled to the operation lever 39 side, and the operation arm 28a is moved to the position shown in FIG.
Of the variable relief valve 36 is operated to the closed side from the fully opened state by swinging to the left side of the paper and pushing the receiving member 36c to the left side of the paper.

(6) As shown in FIG. 1, a brake pedal 52 is provided in the control section of the fuselage, and the release wire 5
The inner part of 3 is the brake pedal 52 and one operation part 46.
The outer portion of the release wire 53 is connected to the other operation portion 46R. 1 and 2
As shown in, the brake 54 is provided for the fourth transmission shaft 27, and the brake 54 and the brake pedal 52 are connected by the wire 55. As shown in FIGS. 1 and 7, the operation arm 28c fixed to the cylindrical shaft 28 on the variable relief valve 36 side and the brake pedal 52 are connected by a wire 56.

When the brake pedal 52 is depressed by the above structure, the release wire 53 causes the pair of operating portions 46R and 46L to swing to the left and right in the plane of FIG.
The left and right side gears 21R, 21L are engaged with the left and right second transmission gears 26R, 26L, the brake 54 is turned on and operated, and the left and right traveling devices 24 are braked. At the same time, the operation arm 28 is pulled by pulling the wire 56.
6a is oscillated rightward on the paper surface of FIG. 6, and the variable relief valve 36 is returned to the fully open state shown in FIG.

[First Embodiment] The holding member 51 shown in FIGS. 3, 4 and 5 is omitted, and the lever guide 4 is provided as shown in FIG.
9 is provided with a recess 49a (corresponding to a holding means), the switching lever 18 is configured to be laterally bendable, and the switching lever 18 is provided with the recess 49a so as to be located at an intermediate position between the gently swiveling position and the supersatellite turning position. It may be configured to be held at.

[Second Embodiment] A structure as shown in FIG. 10 may be added to the structure in the vicinity of FIG. That is, the brake pedal 52 and the second switching valve 3 having the configuration shown in FIG.
The operation arm 5b on the fifth side is connected by a wire 57 as shown in FIG. In the case of the configuration of FIG. 10, the spool 35e of the second switching valve 35 is connected to the operation arms 28a and 28b.
As a result, when pushed in against the spring 35c, the second switching valve 3
5 is operated to the super-trust turning position 35b, and the spool 35e
When the operating arms 28a and 28b are separated from the spool 35e, the spool 35e is moved in the opposite direction by the urging force of the spring 35c, and the second switching valve 35 is operated to the gentle turning position 35a. The positional relationship between the gentle turning position 35a and the super-sight turning position 35b in the configuration is opposite.

As a result, when the brake pedal 52 is depressed while the second switching valve 35 is operated to the gentle turning position 35a or the super-sight turning position 35b, the wire 57 is pulled to operate the operation arm 5b and the second arm. The switching valve 35 is operated to an intermediate position between the gentle turning position 35a and the super-sight turning position 35b.

[Third Embodiment] FIG. 1 in the configuration of FIG.
As shown in FIG. 1, the wire 57 (see FIG. 10) connected to the brake pedal 52 may be eliminated and the pin 28d may be fixed to the operation arm 28b. As a result, the operation arm 5
When the brake pedal 52 is stepped on while the b and the second switching valve 35 are being operated to the super-confidential turning position 35b, the wire 56 (see FIG. 1) connected to the brake pedal 52 is pulled and the cylinder The shaft 28 and the operation arms 28b and 28c rotate in the clockwise direction on the paper surface of FIG. 11, and the variable relief valve 36 is operated to the fully open state. By this operation, the pin 28d of the operation arm 28b contacts the operation arm 5b on the second switching valve 35 side, and the operation arm 5b
And, the second switching valve 35 is operated to the intermediate position.

[Fourth Embodiment] In the above-mentioned [Embodiment] [First to Third Embodiments], a side brake (instead of a super-spinning state in which one traveling device 24 is driven in reverse) is used. By setting the traveling device 24 on one side by means of a brake (not shown), the solid turning is set as the sudden turning state, and the switching lever 1
It may be configured such that the switching operation of 8 allows selection between a solid turning state by the side brake and a slow turning state by the slow turning clutch 12.

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

[Brief description of drawings]

FIG. 1 is a hydraulic circuit diagram of left and right side gear hydraulic cylinders, a first switching valve, a second switching valve, a variable relief valve, and the like.

FIG. 2 is a schematic diagram showing a transmission structure in a mission case.

FIG. 3 is a side view of the vicinity of the switching lever and the holding member in a state in which the switching lever is operated to a super-position turning position.

FIG. 4 is a plan view showing a state in which the switching lever is operated to an intermediate position between a gentle turning position and a super-spinning turning position, and the holding member holds the switching lever at this intermediate position.

FIG. 5 is a rear view near the switching lever and the holding member.

FIG. 6 is a vertical sectional side view in the vicinity of a second switching valve and a variable relief valve.

FIG. 7 is a rear view showing the operation system of the second switching valve and the variable relief valve.

FIG. 8 is a vertical cross-sectional side view near the spool of the second switching valve in a state in which the switching lever is being operated to an intermediate position between the gentle turning position and the super-position turning position.

FIG. 9 is a plan view of the vicinity of a switching lever and a lever guide in the first alternative embodiment.

FIG. 10 is a side view of an operation system of a second switching valve and a variable relief valve in a second alternative embodiment.

FIG. 11 is a side view of the operation system of the second switching valve and the variable relief valve in the third alternative embodiment.

[Explanation of symbols]

 12 Slow turning mechanism 18 Switching operation tool 24 Traveling device 30 Rapid turning mechanism 35 Switching valve 35a Slow turning position of switching valve 35b Rapid turning position of switching valve 49a, 51 Holding means

Claims (1)

[Claims] 1. A hydraulic gentle turning mechanism (12) for turning a vehicle to the right or left by giving a speed difference to a pair of left and right traveling devices (24) provided on the vehicle, and the gentle turning mechanism (1).
2) The left and right traveling devices (24) have a greater speed difference than
A hydraulic swivel mechanism (30) for swirling the machine body to the right or left suddenly, and a slow swivel position (35a) for supplying and discharging hydraulic oil to and from the slow swivel mechanism (12); A switching valve (35) which can be switched to a sudden turning position (35b) for supplying and discharging hydraulic oil to and from a turning mechanism (30), and the switching valve (35) mechanically linked to the switching valve (35). And a switching operation tool (18) for artificially switching the switching valve, and switching to a position corresponding to an intermediate position between the gentle turning position (35a) and the sudden turning position (35b) of the switching valve (35). A traveling operation of a work vehicle provided with holding means (49a), (51) that can be switched to a holding position for holding the operation tool (18) and a holding release position for allowing the switching operation of the switching operation tool (18). Construction.