JP3479452B2 - Work equipment steering system - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steering device for a working machine such as a combine, and more particularly, to a drive wheel and a clutch engagement position which is interlocked with the left and right axles. Providing left and right passive wheel bodies that can be shifted and moved to the clutch disengaged position where the interlock is released, and a piston that shifts the passive wheel body from the clutch engaged position to the clutch disengaged position with the supply of pressure oil to the oil chamber, The present invention relates to a device provided with valve means for discharging the oil from the oil chamber to maintain the passive wheel at the clutch disengaged position when the passive wheel is shifted to the clutch disengaged position.

[0002]

2. Description of the Related Art Conventionally, as seen in Japanese Patent Laid-Open No. 9-323560, a piston is provided so as to be fitted to a shaft that rotatably supports a passive wheel body, and the valve body of valve means is composed of the piston. However, the passive wheel is closed by the piston until it shifts to the clutch disengaged position, while when the passive wheel shifts to the clutch disengaged position, the blockage by the piston is released and the oil chamber communicates with the oil discharge passage. The oil drainage port that switches to is formed on the shaft to keep the passive wheel at the clutch disengaged position.

[0003]

However, according to the above-mentioned conventional technique, since the valve element is composed of the piston, the piston is required to have a piston function and a valve element function.
As a result, the shape and structure of the piston is restricted, and the degree of freedom in designing the piston and valve body is reduced.As a result, the piston function is reduced and the shift mobility of the passive wheel is reduced.
Alternatively, there is a risk that the valve body function may be deteriorated and the pressure oil may leak.

An object of the present invention is to increase the degree of freedom in designing a piston / valve body.

[0005]

The features, functions and effects of the first invention according to claim 1 are as follows.

[Characteristics] Left and right passive wheels that are shift-movable between a drive wheel and a clutch engaged position that is interlocked with the drive wheel and a clutch disengaged position that is disengaged in a state of interlocking with each of the left and right axles. And a piston that shifts the passive wheel body from the clutch engaged position to the clutch disengagement position when pressure oil is supplied to the oil chamber, and when the passive wheel body shifts to the clutch disengaged position, oil is drained from the oil chamber. A steering device for a working machine provided with valve means for maintaining the passive wheel at the clutch disengagement position, wherein each of the valve means is a valve whose valve element is displaced in accordance with shift movement of the passive wheel. In this configuration, the valve element is provided separately from the piston.

[Operation] According to the first aspect of the present invention, since the valve body of the valve means that is displaced along with the shift movement of the passive wheel body is provided separately from the piston, it is not necessary for the piston to have a valve body function. Further, it is not necessary for the valve body to have a piston function, and the piston and the valve body can be configured in a shape and structure in which those functions are given the highest importance.

[Effect] Therefore, according to the first aspect of the present invention, the degree of freedom in designing the piston and the valve body can be increased, and the piston and the valve body can both be made highly functional.

The features, operations, and features of the second invention according to claim 2
The effects are as follows.

[Characteristics] In the above characteristics of the first invention,
In the valve means, a support shaft rotatably supporting a passive wheel is provided with a discharge port connected to a pressure oil supply path to an oil chamber and an oil discharge port connected to an oil discharge path. It is fitted to the support shaft while moving integrally with the body, disconnecting the communication between the discharge port and the oil drain port until the passive wheel shifts to the clutch disengagement position, while the passive wheel moves to the clutch disengagement position. The point is that a cylindrical valve body is provided which connects the drain port and the drain port when the shift position is established.

[Operation] In the second aspect of the present invention, the tubular valve body is fitted with the valve body of the valve means so as to move integrally with the passive wheel body on the shaft that rotatably supports the passive wheel body. By integrally moving this valve body with the passive wheel, the communication between the discharge port and the oil drain port is cut off until the passive wheel shifts to the clutch disengagement position, and the passive wheel moves to the clutch disengagement position. In this case, the oil is drained by connecting the drain port and the oil drain port to each other.Since the tubular valve element is supported on the same shaft as the passive wheel, it is only necessary to fit the valve element to the shaft. The valve body can be assembled to the passive wheel body in a positioned state.

[Effect] Therefore, according to the second aspect of the present invention, the valve body can be assembled with good workability while the position of the passive wheel body is adjusted.

Features, operations, and features of the third invention according to claim 3
The effects are as follows.

[Characteristics] In the characteristics of the first invention and the second invention, the piston and the oil chamber are annular and positioned around the axis.

[Operation] In the third aspect of the present invention, since the piston and the oil chamber are annular around the axis, the piston is made to act uniformly on the entire area of the passive wheel body in the circumferential direction, and the passive wheel body is thus made. Can be shifted.

[Effect] Therefore, according to the third aspect of the present invention, the passive wheel can be smoothly shifted without causing an inclination of the passive wheel with respect to the axis.

Features, operations, and features of the fourth invention according to claim 4
The effects are as follows.

[Characteristics] In the characteristics of the first invention, the second invention, and the second invention, a detent for preventing rotation of the piston around the shaft center is formed in the transmission case that supports the axle. It is in.

[Operation] According to the fourth aspect of the invention, since the detent for preventing rotation of the piston around the shaft center is directly formed on the mission case, the member for coupling the piston to the mission case is detented. Is unnecessary.

[Effect] Therefore, according to the fourth aspect of the present invention, the rotation of the piston can be stopped with a simple structure.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION [First Embodiment] As shown in FIG. 1, a combine, which is an example of a working machine, is provided in front of a self-propelled machine body frame 2 having a pair of left and right crawler type traveling devices 1L and 1R. A mowing device 3 for mowing the planted grain culm is connected to the section so as to be able to move up and down, and the mowing device 3 is attached to the self-propelled machine body frame 2.
A threshing device 4 for threshing the grain culms supplied from and a boarding operation unit 5 are mounted.

As shown in FIG. 2, the transmission system from the engine mounted on the self-propelled machine body frame 2 to the traveling devices 1L and 1R includes a high-low two-stage auxiliary transmission device 7 and a forward drive 3
A main transmission 8 having a first gear and a reverse gear and a steering device 9 are provided in the order listed, and the auxiliary transmission 7, the main transmission 8 and the steering device 9 are the traveling devices 1L and 1R. It is installed in a mission case M that supports the respective axles 15L and 15R.

The auxiliary transmission 7 has a first transmission gear 10 for low speed transmission and a second transmission gear for high speed transmission on an input shaft 7A equipped with an input pulley 7a for transmitting engine power through a belt. 11 are rotatably attached to the input shaft 7A, a low speed state in which the first transmission gear 10 is interlocked with the input shaft 7A, a high speed state in which the second transmission gear 11 is interlocked with the input shaft 7A, and 1 transmission gear 10 and 2nd transmission gear 1
1 is provided with a speed change clutch 12 using a pawl clutch that can be operated to switch to a neutral state in which both are not interlocked with the input shaft 7A, and the output shaft 7B is provided with a first passive gear 13 that is constantly meshed with the first transmission gear 10 and a first passive gear 13. The second transmission gear 11 and the second passive gear 14 which is always meshed with the second transmission gear 11 are mounted so as to rotate integrally with the output shaft 7B. That is, the auxiliary transmission device 7 performs low-speed transmission by interlocking the first transmission gear 10 with the input shaft 7A, and the second transmission gear 1
High speed transmission is performed by interlocking 1 with the input shaft 7A.

The main transmission 8 has a transmission case M.
A center gear 17, which is an example of a drive wheel, is mounted on a support shaft 16 rotatably supported by the center gear 17 in a state of being positioned in the axial direction.
A forward first clutch 18 utilizing a hydraulic clutch for connecting and disconnecting the transmission to the low speed forward transmission system is interposed between the output shaft 7B and the output shaft 7B.
From the output shaft 7B to the center gear 17, the transmission is interrupted by the forward second clutch 19 using the hydraulic clutch for connecting and disconnecting the transmission to the center gear 17 from the output shaft 7B to the center gear 17. And a reverse clutch 21 using a hydraulic clutch for connecting / disconnecting the transmission from the output shaft 7B to the reverse transmission system from the output gear 7B to the center gear 17. There is. That is, the forward first speed state is revealed by operating only the first forward clutch 18, the second forward speed state is revealed by operating only the second forward clutch 19, and only the third forward clutch 20 is engaged. By operating, the third forward speed state is revealed, by operating only the reverse clutch 21 to show the reverse state, and when all the clutches 18, 19, 20, 21 are disengaged, the neutral state in which no power is transmitted is displayed. It is supposed to be released.

Therefore, in the mission case M, a combination of the shift of the auxiliary transmission 7 and the shift of the main transmission 8 enables 6-speed forward and 2-speed reverse.

As shown in detail in FIG. 3, the steering device 9 includes the left and right axles 15L, 15 from the center gear 17.
Passive gears 22L and 2 attached to the respective Rs in an integrally rotating state
The left and right steering clutches 23L and 23R for interrupting the transmission are interposed in the transmission system to the 2R, and left and right multi-plate brakes BL and BR are provided.

The steering clutches 23L and 23R are shifted to a clutch engaged position which is meshed and interlocked with the center gear 17 and a clutch disengaged position which is disengaged while being meshed and interlocked with the left and right passive gears 22L and 22R, respectively. Movable left and right shift gears 24L, 24R
An example of a passive wheel is rotatably mounted on the support shaft 16, springs 25L and 25R for separately urging the shift gears 24L and 24R to move to the clutch engagement position are provided, and the oil chamber 26
The shift gears 24L, 24L,
Pistons 28L and 28R for pushing and shifting 24R from the clutch engaged position to the clutch disengaged position through thrust bearings 27L and 27R are provided against the biasing force of the springs 25L and 25R.
Oil chamber 26 when R shifts to the clutch disengagement position
Valve means is provided to maintain the shift gears 24L and 24R in the clutch disengagement position by draining oil from L and 26R.

The oil chambers 26L and 26R are formed between the mission case M and the pistons 28L and 28R, and the oil chambers 26L and 26R and the piston 28 are formed.
L and 28R are annular members positioned around the axis of the support shaft 16, and are connected to a hydraulic pump P for generating pressure oil driven by the engine 6 from pressure oil supply paths 29L and 29R to oil chambers 26L thereof. , 26R are formed in the mission case M.

The pistons 28L and 28R are prevented from rotating, and the rotation stopping means are pistons 28L and 28R.
Piston 2 by engaging pins 60L and 60R connected to R
Anti-rotation hole 6 to prevent rotation of 8L and 28R around the axis
This is a means for forming 1L and 61R on the mission case M.

As shown in FIG. 4, the valve means is a cylindrical valve body whose flange portion is sandwiched by springs 25L and 25R and pistons 28L and 28R and which moves integrally with the pistons 28L and 28R in the axial direction. 30L and 30R are fitted to the support shaft 16, and the support shaft 16 is provided with discharge ports pL and pR and a discharge oil passage 35 that branch-connect to the pressure oil supply passages 29L and 29R, respectively.
And oil drain ports 31L and 31R connected to the shafts are formed at intervals in the axial direction, and the valve bodies 30L and 30R are drained until the shift gears 24L and 24R shift from the clutch engaged position to the clutch disengaged position. Oil port 31L,
31R is closed and drain ports pL and pR and drain port 3
When the valve seats VL and VR, which cut off the communication with the 1L and 31R, and the shift gears 24L and 24R are located at the clutch disengaged position, the oil drain ports 31L and 31R are opened to release the drain port p.
L, pR and the oil drain ports 31L, 31R are formed with grooves 32L, 32R that communicate with each other. Part of the oil passages LL and LR for branching and connecting the discharge ports pL and pR to the pressure oil supply passages 29L and 29R and a part of the oil discharge passage 35 are formed in the support shaft 16.

By operating the steering operation lever 33 (an example of the steering operation tool) which is rocked to the left and right to the straight-ahead position N, pressure oil is supplied to both the pressure oil supply paths 29L and 29R. Instead, the steering clutches 23L and 23R are switched to the straight running state by engaging the clutches, and the steering operation lever 33 is operated to the left setting position L1, so that only the pressure oil supply passage 29L on the left side is pressurized. Is supplied to switch the steering wheel to the left by turning only the left steering clutch 23L, and the steering operation lever 33 is operated to the right setting position R1. There is provided a steering valve 34 that switches to a right turning state by operating only the right steering clutch 23R by supplying pressure oil to the right steering clutch 23R.

In the drainage passage 35, a steering operation exceeding the setting of the steering operation lever 33, that is, a left setting position L1 and a right setting position R1 to a second left setting position L2 and a second right setting is performed. A pressure regulating valve 36 that reversibly increases the pressure in the oil chambers 26L and 26R by applying resistance to the discharged oil in accordance with the steering operation to the position R2 is interposed,
The pistons 28L, 28R, that is, the shift gears 24L,
24R shifts beyond the clutch disengagement position when the pressure in these oil chambers 26L, 26R rises above a set level.

The brakes BL and BR are shown in FIG.
As also shown in FIG. 5, a plurality of gears that are pressed by the shift gears 24L and 24R that shifts beyond the clutch disengaged position to exert a braking force on the shift gears 24L and 24R and that rotate integrally with the shift gears 24L and 24R. This is a multi-plate brake including friction plates 37L and 37R and a plurality of friction plates 38L and 38R supported by the transmission case M in a non-rotating state.

Therefore, in this steering device 9, by operating the <1> steering operation lever 33 to the straight-ahead position N, both shift gears 24L and 24R are positioned at the clutch engagement positions, and both traveling devices 1L and 1R are operated. Is driven by the center gear 17 to perform straight running, and <2> the steering operation lever 33 is operated to the left setting position L1 to hold the right shift gear 24R in the clutch engaged position and the left shift gear 24L. To the clutch disengagement position to free the left traveling device 1L and to drive the right traveling device 1R with the center gear 17 to perform one-sided drive left turn,
<3> By operating the steering operation lever 33 to the right setting position R1, the right shift gear 24R is positioned at the clutch disengaged position while the left shift gear 24L is held at the clutch engaged position, and the right traveling device 1R is operated. And the left traveling device 1L is driven by the center gear 17 to perform one-sided drive right turn, and <4> steering operation lever 33
Is operated to the second left set position L2 to bring the left shift gear 24L to the braking position while holding the right shift gear 24R in the clutch engaged position to brake the left travel device 1L and operate the right operation. The turning device 1R is driven by the center gear 17 to make a left turn, and <5>
By operating the steering operation lever 33 to the second right setting position R2, the right shift gear 24R is brought to the braking position while the left shift gear 24L is held at the clutch engaged position, and the right traveling device 1R is braked. In addition, the steering device 1L on the left side is driven by the center gear 17 to perform a right turn.

As the detent means, as shown in FIG. 5, a brake pressing member 65 which is detented with respect to the pistons 28L and 28R and moves integrally with the pistons 28L and 28R is formed in the mission case M. It may be a means provided in a state of being engaged with the friction plate detent groove 66 and being detented.

[Second Embodiment] The steering device 9 is constructed as follows. As shown in FIG. 6, the transmission shaft 41 on the transmission upper side
A center gear 17 that interlocks with the output shaft of the transmission, etc.
And a pair of left and right side gears 17L and 17R are rotatably mounted on the support shaft 16, and the side gears 17L and 17R are attached.
Is provided with deceleration means for synchronously driving the gears in the same direction as the center gear 17, reverse rotation means for synchronously driving the side gears 17L, 17R in the opposite direction, and braking means for applying equal braking force to the side gears 17L, 17R. , 15R passive gears 22L, 22R are rotatably mounted on the support shaft 16 so that a pair of left and right shift gears 24L, 24R that are shift-movable in a state of being interlocked with each other are provided between the center gear 17 and the shift gears 24L, 24R. 24L, 24
When R is located at one end of the movement range, the center gear 17 is switched to a clutch engagement state in which the shift gears 24L and 24R are interlocked, and when the shift gears 24L and 24R are located at the middle and the other end of the movement range, the center gear 17
A pair of left and right center clutches C that switch to a clutch disengaged state that disconnects the shift gears 24L and 24R from each other.
L and CR are provided, and the shift gears 24L and 24R are interlocked with the side gears 17L and 17R and the shift gears 24L and 24R between the corresponding ones when the shift gears 24L and 24R are located at the other end of the movement range. When the shift gears 24L and 24R are switched to the clutch engaged state and the shift gears 24L and 24R are located at the middle and one end of the moving range, the pair of left and right side clutches SL and SR are switched to the clutch disengaged state, which disconnects the shift gears 24L and 24R from the side gears 17L and 17R. Set up. The speed reducing means is provided with a steering shaft 43 that interlocks with the side gears 17L and 17R via gears 42L and 42R, respectively, and a deceleration interlocking passive gear that interlocks with a transmission gear 44 for deceleration transmission that rotates integrally with the center gear 17. A wet type in which the gear 45 is rotatably attached to the steering shaft 43 and is switched to a clutch engaged state in which the passive gear 45 is interlocked with the steering shaft 43 by pressure oil supply and is disengaged from the clutch by draining oil. A deceleration clutch 46 using a multi-plate hydraulic clutch is provided. That is, the deceleration clutch 4
By turning 6 on and off, the rotation of the transmission shaft 41 is decelerated and transmitted to the side gears 17L, 17R. In the reversing means, a passive gear 47 for reverse rotation transmission interlocking with the transmission shaft 41 is rotatably mounted on the steering shaft 43, and the passive gear 47 is supplied to the steering shaft 43 by supplying pressure oil.
A reverse clutch 48 using a wet multi-plate hydraulic clutch is provided, which switches to a clutch engaged state in which it is interlocked with and is switched to a clutch disengaged state in which the interlock is disengaged by draining oil. That is, the reverse rotation clutch 48 is turned on and operated to reverse the rotation of the transmission shaft 41 and transmit the rotation to the side gears 17L and 17R. The braking means resists the bias due to the pressure oil supply and operates the steering shaft 43.
Is provided with a wet multi-plate hydraulic brake 49 that applies a braking force to the steering wheel and releases the braking on the steering shaft 43 in association with the drained oil.

The deceleration clutch 46 and the reverse rotation clutch 4
8. The hydraulic brake 49 operates with pressure oil having a pressure higher than the set pressure. That is, when the steering operation lever 33 is operated to the second left setting position L2 and the second right setting position R2, it operates with pressure oil corresponding to the pressure oil generated in the oil chambers 26L and 26R.

Then, the shift gears 24L and 24R are shift-moved by the structure described in the first embodiment. That is, one end position of the movement range corresponds to the clutch engagement position, the intermediate position corresponds to the clutch disengagement position, and the other end position corresponds to the brake position.

Further, as shown in FIG. 7, a turning mode selecting tool 50 and a mode selecting valve 51 are provided, and when the turning mode selecting tool 50 is located at the first position P1, the deceleration clutch 4 is provided.
6 is connected to the oil discharge passage 35, and the mode selection valve 51 is changed to a state in which the reverse rotation clutch 48 is connected to the oil discharge passage 35 when the turning mode selection tool 50 is located at the second position P2. And a turning mode control device 50C for switching the mode selection valve 51 to a state in which the hydraulic brake 49 communicates with the oil discharge passage 35 when the turning mode selection tool 50 is located at the third position P3. With the selection tool 50 operated to the first position P1, the steering operation lever 33 is moved to the second left setting position L2 and the second position.
By operating to the right setting position R2, the deceleration clutch 4
6 engages the clutch to operate the side gears 17L, 17R
Is operated to decelerate and the turning mode selector 50 is operated to the second position P2, and the steering operation lever 33 is moved to the second left setting position L.
2 and the second right setting position R2, the reverse rotation clutch 48 is engaged and actuated to operate the side gear 17
L and 17R are driven in reverse, and the turning mode selector 50 is set to the third position.
By operating the steering operation lever 33 to the second left setting position L2 and the second right setting position R2 while operating to the position P3, the hydraulic brake 49 is braked to operate the side gear 1.
It is configured to brake 7L and 17R.

Therefore, according to this steering device 9, <1>
With the turning mode selector 50 operated to the first position P1, the steering operation lever 33 is moved to the left setting position L1 or the right setting position R.
When operated to 1, the left or right shift gear 24L or 24
By the shift movement of R to the intermediate position, the left or right traveling device 1L or 1L or 1L is maintained while the drive by the center gear 17 for the right or left traveling device 1R or 1L is maintained.
When the drive for R is cut off, left or one side drive turning is performed by driving only the right or left traveling device 1R or 1L, and further, the steering operation lever 33 is moved to the second left setting position L2. Alternatively, when the second right setting position R2 is operated, the left or right shift gear 24L or 24R shifts to the other end position, and the drive by the center gear 17 for the right or left traveling device 1R or 1L is maintained. The left or right traveling device 1L or 1R is decelerated by the left or right side gear 17L or 17R, and a slow turn is performed by reducing the traveling speed of the left or right traveling device 1L or 1R. When the steering operation lever 33 is operated to the left setting position L1 or the right setting position R1 while the turning mode selection tool 50 is operated to the second position P2, the left or right shift gear 24L or 24R By shifting to the intermediate position, the drive for the left or right traveling device 1L or 1R is cut off while the drive by the center gear 17 for the right or left traveling device 1R or 1L is maintained, and the right or left traveling device 1R or 1L is stopped. Left one side drive turning or right one side drive turning is performed by driving only the traveling device 1R or 1L, and further, the steering operation lever 3
When 3 is operated to the second left setting position L2 or the second right setting position R2, the left or right shift gear 24L or 24R shifts to the other end position, and thereby the center gear for the right or left traveling device 1R or 1L. While the drive by 17 is maintained, the left or right traveling device 1L or 1R is reversely driven by the left or right side gear 17L or 17R to reverse the left or right traveling device 1L or 1R. When the turning operation is performed and the steering operation lever 33 is operated to the left setting position L1 or the right setting position R1 while the <3> turning mode selection tool 50 is operated to the third position P3, the left or right shift gear 24L or 24R. Shifts to an intermediate position, the left or right traveling device 1L is maintained with the drive by the center gear 17 for the right or left traveling device 1R or 1L being maintained. Is not driven for 1R, the left one side drive turning or the right one side drive turning is performed by driving only the right or left traveling device 1R or 1L, and further, the steering operation lever 33 is set to the second left setting position. L2 or second right setting position R
When operated to 2, the left or right shift gear 24L or 24
When R shifts to the other end position, the left or right traveling device 1L or 1L or 1L is maintained while the drive by the center gear 17 for the right or left traveling device 1R or 1L is maintained.
Left or right side gear 17L or 1 with R braked
The vehicle is braked by being linked to the 7R, and the left or right traveling device 1L or 1R is braked to perform a turning turn. Of course, in any mode, by operating the steering operation lever 33 to the straight-ahead position N, both shift gears 24L and 24R are both positioned at one end position, and both traveling devices 1L and 1R are driven at a constant speed. Driving is performed.

[Other Embodiments] The structures and shapes of the pistons 28L and 28R can be appropriately changed.

The valve bodies 30L and 30R are connected to the passive wheel bodies 24L and 2
The structure for moving integrally with the 4R can be appropriately changed.

The present invention can be applied to various working machines other than combine harvesters.

[Brief description of drawings]

FIG. 1 Side view of combine

[Fig. 2] Travel transmission system diagram

FIG. 3 is a vertical sectional front view of the steering device.

FIG. 4 is a vertical cross-sectional front view of a main portion of a steering device in a clutch disengaged state.

FIG. 5 is a vertical cross-sectional front view of a main portion of a steering device showing a modified example of the rotation stopping means.

FIG. 6 is a schematic vertical sectional front view of a steering apparatus showing another embodiment.

[Figure 7] Steering operation system diagram

[Explanation of symbols]

15L, 15R axle 16 spindles 17 Drive wheel 24L, 24R passive wheel 26L, 26R oil chamber 28L, 28R piston 29L, 29R Pressure oil supply path 30L, 30R valve body 31L, 31R Oil drain port 35 oil drain 61L, 61R Non-rotating pL, pR discharge port M mission case

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) B62D 11/00

Claims (4)

(57) [Claims] 1. A driving wheel body, and left and right passive wheel bodies that are shiftably movable between a clutch engagement position that is interlocked with the drive wheel body and a clutch disengagement position that is disengaged in a state of interlocking with each of the left and right axles. A piston is provided to shift the passive wheel body from the clutch engaged position to the clutch disengagement position when pressure oil is supplied to the oil chamber. A steering device for a working machine provided with valve means for maintaining a passive wheel at a clutch disengagement position, each of the valve means comprising:
A steering device for a working machine, comprising a valve in which a valve body is displaced along with a shift movement of a passive wheel body, the valve body being provided separately from a piston. 2. The valve means comprises a support shaft for rotatably supporting a passive wheel, and a discharge port connected to a pressure oil supply passage to an oil chamber and an oil discharge port connected to an oil discharge passage. Is formed and fitted to the support shaft while moving integrally with the passive wheel, and disconnects the communication between the discharge port and the oil drain port until the passive wheel shifts to the clutch disengagement position. 2. The steering apparatus for a working machine according to claim 1, further comprising a tubular valve element that connects the discharge port and the oil discharge port when the shift position is shifted to the clutch disengagement position. 3. The steering apparatus for a working machine according to claim 1, wherein the piston and the oil chamber are annular ones and are located around the axis. 4. The steering apparatus for a working machine according to claim 1, wherein the transmission case for supporting the axle is formed with a detent for preventing rotation of the piston around the shaft center.