JPH0245275A - Steering control structure for work vehicle - Google Patents

Abstract

PURPOSE:To improve the controllability and running performance of a work vehicle by allowing the sequential operation of a selector valve for ON-OFF control of a pair of right and left side clutches and a control valve changing the operation pressure of a side brake with the serial operation of a control lever. CONSTITUTION:In a work vehicle equipped with a crawler running device, there are provided side clutches 25R, 25L blocking the power transmission to a pair of right and left running devices, a side brake 28 braking the respective running devices, and a reverse transmission device 30 driving one of the running device in the reverse direction with respect to the other. A selector valve 33 for ON-OFF control of the side clutch and a control lever 39 are connected and interlocked through a resilient body such as herical coil spring or the like. A control valve 36 change-controlling the operation pressure of the side brake 28 and the lever 39 are connected and interlocked. It is thus possible to sequentially control the valves 33, 36 through the serial operation of the lever 39.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention provides a pair of hydraulically operated side clutches that turn on and off power to a pair of left and right traveling devices, and a system that applies braking to one of the traveling devices. The present invention relates to a steering operation structure for a work vehicle equipped with a hydraulically operated handbrake.

[Conventional technology]

The combine harvester, which is one of the above-mentioned work vehicles, is equipped with a pair of side gears that transmit power to a pair of left and right crawler traveling devices, as disclosed in Japanese Patent Laid-Open No. 63-13866, for example. By sliding the side gear with a hydraulic cylinder and separating it from the transmission side gear, transmission to one crawler traveling device is cut off and a gentle turn is performed (side clutch disengaged state), and then the side gear is further slid with the hydraulic cylinder. Some crawler vehicles are configured to perform a pivot turn by applying a brake to one of the crawler traveling devices by pressing a multi-disc handbrake using a side gear.

[Problem to be solved by the invention]

In the disclosed structure, the piston in the hydraulic cylinder is protruded by approximately one hand stroke to disengage the side clutch, and the piston is protruded by approximately a full stroke to operate the handbrake. One operation is to maintain the piston in a state in which it is protruded by approximately one hand stroke (side clutch disengaged state), and to change the braking force of the handbrake in the handbrake state where the piston is in a state in which the piston is protruded by approximately a full stroke. It is relatively difficult to perform hydraulic control using a set of hydraulic cylinders and a control valve for the cylinders.

Therefore, in recent years, the direct relationship between the hydraulic cylinder for operating the side clutch and the handbrake has been separated.
It has been proposed to include a switching valve for manual operation of the side clutch and a control valve for changing the operating pressure of the side brake. However, when two sets of valves are provided in this way, a structure is required that allows one operating lever to successfully operate the two sets of valves. The object of the present invention is to operate two sets of valves with the / bar and to be configured so that the side clutch disengaged state and the side brake operated state can be accurately displayed.

[Means to solve the problem]

A feature of the present invention is that in the above-mentioned steering operation structure for a work vehicle, the switching valve for manual operation of the side clutch and the operation lever are interlocked and connected via an elastic body, and the operating pressure of the side brake is controlled. The control valve to be changed and the operation lever are interlocked and connected via mechanical flexibility that absorbs an operation stroke less than the setting, and the control valve is switched after the switching valve is operated by a series of operations of the operation lever. The valve is configured to be operated, and its functions and effects are as follows.

[For production]

With the above-described structure, when the operating lever is moved from the neutral position, the switching valve for side clutch open operation is operated via the elastic body, and the side clutch is disengaged.

However, the control valve for the handbrake is not operated due to mechanical flexibility, and the handbrake remains in the off state. In this way, by operating the operating lever within the range until mechanical flexibility is lost, the side clutch can be turned on and off while the handbrake remains off.

Then, when the operating lever is moved further from the state where mechanical flexibility has disappeared, the control valve is operated and the handbrake is turned on, even if the switching valve for the side clutch reaches the stroke end. Since the above movement of the operating lever is absorbed by the elastic body, there is no problem in operating the operating lever.

〔Effect of the invention〕

As described above, when equipped with a switching valve for hand-off operation of the side clutch and a control valve for changing the handbrake operating pressure, these two sets of valves can be successfully operated with one operating lever to disengage the side clutch. It became possible to accurately display the condition and the handbrake condition, thereby improving the operability and running performance of the work vehicle.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

Figure 13 shows the structure inside the traveling transmission case (8) of a combine harvester, which is one of the working vehicles.
The power from the hydrostatic continuously variable transmission (not shown) is transmitted through a belt transmission mechanism (not shown) equipped with a tension clutch.
At the same time, the power from the output shaft (3) of the hydrostatic continuously variable transmission (1) is transmitted from the first transmission shaft (4) to the one-way clutch (5). ) and the output turnip-'J-(7), the reaping part shown in FIG. 14 (
6).

The 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), and the second transmission shaft (11) A first high speed gear (12) and a first low speed gear (13) are fitted on the outside so as to be relatively rotatable, and a shift gear (14) is fitted on the outside so as to be freely slidable with a spline structure.

On the other hand, the second high speed gear (16) and the second low speed gear (17) fixed to the third transmission shaft (15) mesh with the first high speed gear (12) and the first low speed gear (13). A medium speed gear (18) is fixed to the third transmission shaft (15).

With the above structure, by sliding the shift gear (14) and engaging it with the first high speed gear (I2), medium speed gear (18), and first low speed gear (13>), the power can be shifted into three stages: high, medium and low. This power is transmitted through a medium speed gear (18
) is transmitted to the third gear (19) that meshes with the third gear (19).

A right side gear (21R) and a left side gear (21) are fitted onto the support shaft (20) that supports the third gear (19) so as to be relatively rotatable, and left and right axles (22L) are fitted onto the support shaft (20) that supports the third gear (19).
, (22R)'s input gears (23R), (23L) are always engaged with the left and right side gears (21L), (21R). This allows the right or left side gear (
21R), (21+,) are slid against the third gear (19) to engage and separate them, and power transmission is turned on and off to the block (24a) of the crawler traveling device (24) shown in Fig. 14. The third gear (19)
Side clutches (25R) and (25L) are constructed between the left and right side gears (21I, (21R)) and the left and right side gears (21R).

Next, to explain in detail the structure for applying braking to one axle (22R) or (22L), as shown in the same figure, the right fourth gear (26R) and the left fourth gear (26R) are connected to the support shaft (20).
6L) is relatively rotatably supported by a bearing, and
A pair of fifth gears (29) fixed to the fourth transmission shaft (27)
) is the right 4th gear (26R) and the left 4th gear (26L)
It's interlocking. A multi-plate hydraulically operated handbrake (28) is provided at one end of the fourth transmission shaft (27), and is connected to the right side gear (21R) or the left side gear (21R).
LL) is separated from the third gear (19) and the right fourth gear (2
Braking can be applied to one axle (22R) or (22L) by engaging the left fourth gear (26L) or the left fourth gear (26L) and turning on the handbrake (28).

Next, to explain in detail the structure for reversing one axle (22R) or (22L), as shown in the same figure, the sixth gear ( 62) is fitted onto the fourth transmission shaft (27) so as to be relatively rotatable, and the sixth gear (62) and the fourth transmission shaft (27)
A hydraulic clutch (30) is provided between the two. As a result, the right side gear (21R) or the left side gear (21R)
LL) is engaged with the fourth right gear (26R) or the fourth left gear (26L) as described above, and when the hydraulic clutch (30) is engaged, the power from the second high speed gear (16) is reversed. state, and the axle (22
R) or (22L).

Next, the hydraulic cylinders (31R) and (31R) slide the left and right side gears (21L) and (21R).
L), hand brake (28) and hydraulic clutch (30
), as shown in Fig. 1, the hydraulic oil from the pump (32) is supplied to the first switching valve (3
3) through the left and right side gears (21, (21R)
Hydraulic cylinder for (31R), (31L)
Hydraulic cylinder (31R), (3
The oil passage (34) from the side of the handbrake (2L)
8) and the second switching valve (3) for the hydraulic clutch (30).
5), and the oil passage (34) is further connected to a control valve (
Variable IJ IJ-F valve as 36) is connected. Further, the IJ IJ-F valve (61) maintains the pressure of the entire hydraulic circuit at a safe allowable pressure.

Next, the first switching valve (33), the second switching valve (35), the variable I
The operation structure of the J IJ-F valve (36) will be described in detail. As shown in Fig. 2, it is a frame that is swingably supported around the left and right axis (p+) of the aircraft control section (not shown). An operating lever (39) is swingably supported around the front-back axis (P2) of 38), so that the operating lever (39) can be swinged back and forth, left and right.

A first arm (40) is fixed to this operating lever (39), and this first arm (40) and a first switching valve (39) are fixed to each other.
3) are linked. This structure is located at the front and rear axis (P3) of the mission case (8) as shown in Figure 2.3.4.
There are operation panels (43) on the front and back of the spindle (4 pieces) that can be rotated around it.
and the arm (41a) are fixed, one arm (41a) is connected to the spool (not shown) of the first control valve (33), and the other operation plate (43) is connected to the actuator (42). has been done.

The operation panel (43) is provided with an elongated portion (43a),
The pin (45a) of the bushing full wire (45) connected to the first arm (40) of the operating lever lever (39) is engaged with this long (43a), and furthermore, this pin (45a) is
A helical spring serving as an elastic body (44) is attached so as to sandwich both the pin (43b) of the operating plate (43).

With the above structure, the front and rear axis (P
2) By swinging the surroundings, the bushing full wire (45
) is pushed or pulled, the operation plate (43) and arm (41a) are swung through the helical spring (44), and the first switching valve (33) is switched. Even after the spool of the first switching valve (33) reaches the stroke end, the operation lever (39) can be further oscillated by the flexibility of the helical spring (44) and the elongated length (43a). . As a result, hydraulic oil is supplied to one of the hydraulic cylinders (31R) or (31L), the piston (31RP) or (311P) protrudes downward, the side gear arm (46R) or (46L) is oscillated, and the right side gear is (21R) or left side gear (
21L) is separated from the third gear (19), and the right fourth gear (21L) is separated from the third gear (19).
6R) or left 4th gear (26L). This is the disengaged state of the left and right side clutches (25L) and (25R).

Also, as shown in Fig. 1, a hydraulic cylinder (31R).

The sequence valve (47) provided in the oil path (34) from (31L) controls the left and right side gears (2LL), (2
The pressure required for the gears (1R) to fully engage the left and right 4th gears (26L) and (26R) is the hydraulic cylinder (31R).
, (31L). This is the fifth
As shown in the figure, the piston (31RP) or (311P
) begins to protrude downward, the cylinder (31R5), (
This is because the oil passage (34) connected to
), (26R) to prevent the pistons (31RP) and (31LP) from stopping at positions where they do not completely engage.

The actuator (42) is used to automatically switch the first switching valve (33) when the aircraft automatically travels along the planted culm, and is operated by the operation lever (39) as described above. It is in a state where it can move freely during manual operation.

Also, as shown in FIG. 5, a hydraulic cylinder (3), R).

(31 cylinder (31R3), (31LS)
The inner diameter of the oil passage (34) portion (31a) is cut so as to be slightly larger;
34) When the hydraulic oil is drained from the cylinder (31R3),
Make sure that the hydraulic oil drains as evenly as possible from the radial direction of the piston (31RP) and (31LP).
This is to prevent twisting caused by uneven contact.

Next, the linkage structure between the operation lever (39), the second switching valve 35) and the variable IJ valve (36) will be explained in detail. The second arm (49) equipped with the pin (49a) is fixed, and the first swing arm (50) and the second swing arm (51) rotate around the front-rear axis (P2), and the operating lever (3)
9) is supported so that it can swing freely. The fixed arm (38) extends downward from the frame body (38).
The pin (38b) of 3B&) is connected to the first and second swing arms (5
0), (51), and the spring (52) is inserted between the first and second swing arms (50), (51).
The inner wire (53a) of the release wire (53) is attached to the first swing arm (50), and the outer wire (53111) is attached to the second swing arm (51).

On the other hand, as shown in Fig. 6.7.8, the second switching valve (
A second switching valve (35) and a variable relief valve (36) are installed in parallel.
), the first support shaft (54) is rotatable around the axis (P4) perpendicular to the spools (35a) and (36a).
A second operating arm (55) is fixed to the outer side of the operating arm (48) and the support shaft (54). An inner wire (53a) of the release wire (53) is connected to the second operating arm (55) via a spring (56). The state shown in Fig. 8 and Fig. 2 is a state in which the operating lever (39) is operated to the neutral position (N), and the pin (55a) of the second operating arm (55) and the spring (56) are in contact with each other. between, and inner wire (53a)
In this state, flexibility (AI), (A2) is generated between the bottle (53c) and the spring (56). Further, the second imitation arm (55) and the first operating arm (48) are biased clockwise in FIG. 8 and counterclockwise in FIG. 6 by a helical spring (63).

As shown in Fig. 2, move the operating lever (39) to
2) When the right side clutch is turned down, for example, to the disengaged side, the second swing arm (51) contacts the pin (38b) and is stopped, and the pin (49) of the second arm (49)
a) causes the first swing arm (50) to swing and pull the inner wire (53a); conversely, by operating the operating lever (39) to disengage the left side clutch, the first swing arm (50) swings and pulls the inner wire (53a). With the movable arm (50) being stopped by the bottle (38b), the second swing arm (51) is operated to swing, and even in this state, the inner wire (53a) is pulled against the outer wire (53b). will be manipulated. However, even if the operating lever (39) is swung in the range between the right side clutch disengagement position and the left side clutch disengagement position, the flexibility (AI) and (A2) shown in FIG.
(see Fig. 9), and within this range, the first switching valve (33) is connected via the first arm (40).
is operated and the left and right side clutches (25L), (25R
) only the on/off operation is performed.

Then, move the operating lever (39) to the left and right side clutches (2
5L), (25R) and move to the right or left braking position, the pulling action of the inner wire (53a) changes the state from the state shown in Fig. 6 to the state shown in Fig. 10, as shown in Fig. 1. The operating arm (48) is oscillated and the spool (36a) of the variable relief valve (36) is pushed to the throttle opening closing side by the first contact portion (48a) of the first operating arm (48). Go (see Figure 12). In this operating range, the first imitation arm (48) does not come into contact with the spool (35a) of the second switching valve (35), and the second switching valve (35)
) is an internal detent mechanism (57) and spring (
58) is held on the hydraulic oil supply side of the handbrake (28) (the rightward protruding side of the spool (35a) in Fig. 6.10). Therefore, as shown in FIGS. 2 and 12, by tilting and operating the operating lever (39) from the left and right side clutch disengaged positions, the braking force of the handbrake (28) can be gradually increased. It is.

When the operating lever (39) is moved from the right or left braking position to the right or left reverse position, the inner wire (
53a) is further pulled, and the first operating arm (48) changes from the state shown in FIG. 10 to the state shown in FIG.
While the spool (36a) of the variable IJ valve (36) is further pushed in by the first contact part (48a) of the first operating arm (48), the second contact part (413b) of the first operating arm (48)
The spool (35a) of the second switching valve (35) is pushed in, and the second switching valve (35) is operated to the hydraulic oil supply side to the reverse hydraulic clutch (30), and one crawler traveling device (24) is operated. ) is driven in reverse while being decelerated to 1/2 (see Figures 2 and 12).

As shown in FIGS. 1 and 2, the operating lever (39
) and the frame (38) swingably around the left and right axis (Pl), and a third switching valve (37) for the hydraulic cylinder (60) for lifting and lowering the reaping part (6). ) are mechanically interlocked and connected, and by swinging the operating lever (39) around the left and right axis (P, ), the reaping part (
6) can be raised and lowered.

In addition, this machine is equipped with a check mechanism that prevents one of the crawler traveling devices (24) from being reversed to make a super turn while traveling at high speed.The detailed structure of this mechanism is shown in Figure 8. As shown in the figure, a fan-shaped restraining member (65) is supported, which can swing freely around the horizontal axis (P,) and is biased counterclockwise in the drawing by a helical spring (64).

On the other hand, the first shift lever (66) for changing the swash plate angle in the hydrostatic continuously variable transmission (1) and the check member (
65) are connected to each other via the inner wire (67a) of the release wire (67). A second speed change lever (68) for sliding the shift gear (14) in FIG. 13 is connected to the outer wire (67b) of the release wire (67).

With the above structure, when the first shift lever (66) is operated to the high speed position (H') side, the inner wire (67a) is pulled and the check member (65) is rotated clockwise in the drawing. 1 speed lever (66) high speed position H
’) side exceeds the setting, the second operation arm (
A check member (6) is placed within the trajectory of the bottle (55b) inside the bottle (55).
5) enters. As a result, the first and second operating arms (48) and (55) can be operated to the braking position (the state shown in Fig. 10), but further operation to the reverse position (the state shown in Fig. 11) is prohibited. Check member (65) for bottle (55b)
This becomes impossible due to contact with the

The state shown in FIG. 8 is a state in which the first shift lever (66) and the second shift lever (68) are operated to low speed positions (B) and (L). When the 2-speed shift lever (68) is operated to the medium speed position (M) and the high speed position (H), the outer wire (67b) is operated and the inner wire (67a) is pulled, causing a check. The member (65) is in the medium speed position (λ1) and the high speed position (H
) in the clockwise direction on the page. In other words, the more the second shift lever (68) corresponding to the auxiliary shift is operated to the high speed side, the more the first shift lever (66) corresponding to the main shift changes from the low speed position (Lo) to the high speed position (H゛). When operating the vehicle, a situation quickly arises in which one of the crawler traveling devices (24) cannot be reversed to perform a super-turn.

[First Alternative Embodiment] Although the first switching valve (33) and the operating lever (39) are connected to each other, the following structure may be adopted. In other words, as shown in FIGS. 15 and 16, the first arm (70) and the second arm (71) are fixed to both ends of a support shaft (69) that is rotatable around the front-rear axis (P3). , second arm (71
) is connected to a spool (not shown) of the first switching valve (33), and the first arm (70) is connected to the actuator (42). Then, the balance arm (7) is connected to the support shaft (69).
2) is fitted on the outside so as to be relatively rotatable, and this balance arm (72
) and the bushing full wire (45) in FIG.
A helical spring serving as an elastic body (73) is attached so as to sandwich a) and (72a).

Also, as shown in the same figures, the second bin (72b) provided on the balance arm (72) and the convex portion (8a) on the front surface of the mission case (8) are both inserted between the two (72b) and (8a). A helical spring (74) for neutral biasing is attached to the balance arm (72).

When the structure is as shown in FIGS. 15 and 16, the operation lever (39), the second switching valve (35) and the variable I
The linking structure with the JIJ valve (36) is as shown in FIGS. 17 and 18. In other words, the axis (P,)
A first arm (7
6) and the second arm (77), the second arm (77) is provided with an elongated length for mechanical flexibility (77a), and the release wire (53) in FIG. 2 is attached to this elongated length (77a). The inner wire (53a) is engaged. A third arm (78) is fitted onto the support shaft (75) so as to be relatively rotatable, and the bottle (76a) of the first arm (76) and the third arm (78)
A helical spring (79) is attached so as to sandwich both (76a) and (78a) of the bottle (78a).

With the structure shown in Figures 2.15.16.17.18 above, if the operating lever (39) is oscillated between the right side clutch disengaged position and the left side clutch disengaged position, The inner wire (53a) is only pulled within the length range (77a) in FIG. 17, and the first switching valve (33) is operated via the first arm (40) within this range. , only the on/off operations of the left and right side clutches (25L) and (25R) are performed.

When the operating lever (39) is operated beyond the right or left side clutch disengaged position to the right or left braking position, the accommodating effect of the elongated hole (77a) disappears, and the state shown in FIG. 17 changes to the state shown in FIG. 19. As shown in FIG. 3, due to the pulling action of the inner wire (53a), the third arm (78) swings together with the first arm (76), and the spool (36a) of the variable relief valve (36) moves into the third position. The arm (78) pushes the aperture opening toward the closed side.

In this operating range, the spool (35) of the second switching valve (35)
a), the second switching valve (35) is connected to the handbrake (28) hydraulic oil supply side (17th In the figure, the spool (35a) is held on the right protruding side). Therefore, the braking force of the handbrake (28) can be gradually increased by tilting and operating the operating lever (39) from the left and right side clutch disengaged positions.

Then, when the operation lever (39) is pushed down further from the right or left braking position, the inner wire (53a) is pulled further, and the third arm ( While the spool (36a) of the variable relief valve (36) remains pushed in by the first arm (76), the second switching valve (35) is opened by the first arm (76).
spool (35a) is pushed in, and the second switching valve (35a) is pushed in.
5) is operated to supply hydraulic oil to the reverse hydraulic clutch (30), and one crawler traveling device (24> is connected to 17
It is driven in reverse while being decelerated to 2.

[Second Alternative Embodiment] The connection structure between the first switching valve (33) and the operating lever (39) may be constructed as shown in FIGS. 21 and 22.

That is, the first arm (81) and the second arm (82) are fixed to both ends of the support shaft (80) which is rotatable around the axis (P4), and the second arm (82) is connected to the first switching valve. (33
) is connected to the spool (not shown) of the first arm (81
) is connected to the actuator (42).

A long wire (81a) is provided at the lower part of the first arm (81), and a bushing full wire (45) is attached to this long wire (81a).
) and engage the pin (49a) of the first arm (8
A helical pie as an elastic body (83) is attached so as to sandwich both the pin (81a) of 1) and the pin (45a) of the bushing full wire (45). There is.

Incidentally, although reference numerals are written in the claims section for convenient comparison with the drawings, the present invention is not limited to the structure shown in the accompanying drawings.

[Brief explanation of the drawing]

The drawings show an embodiment of the steering operation structure for a working vehicle according to the present invention, and FIG. 1 shows the first, second and third switching valves in a combine harvester,
A hydraulic circuit diagram showing the connection state of the hydraulic cylinder and the variable relief valve, FIG. 2 is a perspective view showing the structure near the operating lever,
Fig. 3 is a front view of the operating system and hydraulic cylinder of the first switching valve, Fig. 4 is a vertical side view showing the operating system of the first switching valve, and Fig. 5 is a front view of the operating system of the first switching valve.
The figure is a vertical front view of the hydraulic cylinder, Figure 6 is the second switching valve,
Figure 2 shows the variable IJ IJ-F valve and its operating system, and is a longitudinal sectional front view corresponding to the state in which the operating lever is operated to the neutral position. Figure 7 shows the second switching valve and the variable IJ IJ-F valve FIG. 8 is a longitudinal sectional side view showing the operation system, and FIG. 8 is a front view (FIG. 6
Figure 9 is a front view of the operating system of the second switching valve and variable relief valve corresponding to when the operating lever in Figure 2 is operated to the right or left side clutch disengaged position;
Figure 0 is a longitudinal sectional front view of the second switching valve, variable IJ IJ-F valve, and its operating system corresponding to when the operating lever in Figure 2 is operated to the right or left braking position, and Figure 11 is a longitudinal sectional front view of the operating system in Figure 2. A vertical cross-sectional front view of the second switching valve, variable IJ valve and its operating system corresponding to when the operating lever is operated to the right or left reverse position, and Figure 12 shows the operating pressure of the handbrake and hydraulic clutch and the operating lever. Fig. 13 is a longitudinal sectional front view of the transmission case of the combine harvester, Fig. 14 is a side view of the front half of the combine harvester, and Fig. 15 is a diagram showing the relationship between the operating angle around the longitudinal axis of 1 is a front view showing the operating system of the first switching valve, FIG. 16 is a longitudinal side view showing the operating system of the first switching valve in the first alternative embodiment, and FIG. 17 is a front view showing the operating system of the first switching valve in the first alternative embodiment. 18 is a longitudinal sectional front view showing the operating system of the relief valve, FIG. 18 is a longitudinal sectional side view showing the operating system of the second switching valve and variable relief valve in the first alternative embodiment, and FIG. The second control lever shown in Figure 2 corresponds to the case where the operating lever is operated to the right or left braking position.
FIG. 20 is a longitudinal sectional front view of the operation system of the switching valve and the variable IJ IJ-F valve.
FIG. 21 is a front view showing the operating system of the first switching valve in the second alternative embodiment, and FIG. 22 is a front view showing the operating system of the first switching valve in the second alternative embodiment. FIG. 1 is a longitudinal sectional side view showing the operating system of the 1-way switching valve.

Claims (1)

[Claims] A pair of hydraulically operated side clutches (25R) that turn on and off the power to the left and right traveling devices (24), (24).
), (25L) and a hydraulically operated handbrake (28) that applies braking to one of the traveling devices (24), (24).
), the switching valve (33) for on/off operation of the side clutch (25R), (25L) and the operating lever (39) are connected to an elastic body (44), (
a control valve (3) which is interlocked and connected via (73) and (83) and which changes the operating pressure of the handbrake (28);
6) and the operating lever (39) are mechanically flexible (A_1) and (A_2) to absorb the operating stroke less than the setting.
), (77a) are interlocked and connected to operate the operating lever (3).
9) A steering operation structure for a work vehicle configured such that the switching valve (33) is switched and then the control valve (36) is operated.