JP2001078506A - Structure for lifting working device of working vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To constitute the subject structure so that automatic upward and downward drives of a working device are suitably carried out corresponding to differences in states of steering of front wheels depending on the difference of skill of driver in the lifting structure of the working device of a working vehicle equipped with an automatic lifting means for automatically driving the working device upward when the front wheels are steered from the position of a straight traveling. SOLUTION: This device for lifting the working device of a working vehicle is equipped with an automatic lifting means for driving the working device upward by a drive mechanism 7 when front wheels 1 are operated to steer in a predetermined angle to right or left from the side of a straight ahead position A. When the steering speed in operating the front wheels to steer in the left or right predetermined angle A1 from the straight ahead position A becomes high, the left or right predetermined angle A1 is changed to the side of the straight ahead position A and the automatic lifting means is brought to act earlier.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a working device lifting and lowering structure for a working vehicle, such as a riding rice transplanter or an agricultural tractor, having a working device mounted on a body so as to be able to move up and down, and having a drive mechanism for driving the working device up and down. About.

[0002]

2. Description of the Related Art In a riding rice transplanter, which is an example of a work vehicle,
When the planting process is completed and the aircraft reaches the ridge, the operator operates the elevating lever to the ascending position to raise the descending seedling planting device (an example of a working device), and raises the control handle. Operate to the right or left to turn the aircraft around the ridge. When the turn on the ridge is completed, the operator returns the steering handle to the straight traveling position, operates the elevating lever to the lowered position, lowers the ascending seedling planting apparatus, and enters the next planting step.

In this case, for example, Japanese Patent Application Laid-Open No. 11-19662
As disclosed in Japanese Unexamined Patent Publication No. 8, when the front wheel is steered to the right or left from the straight traveling position side to start turning around the ridge, the seedling planting apparatus is automatically driven up and the ridge is driven. When the turn at the end is completed and the front wheel is returned to the straight position, the seedling planting device is configured to be automatically driven down, so that the operation at the time of turning at the ridge is easy Some are configured to be.

[0004]

When the driver operates the steering wheel to steer the front wheel at the start and end of the turn on the bank, the state of the steering operation of the front wheel is determined by the operator. May vary by skill level. For example, at the end of a single planting process, a highly skilled pilot operates the control handle quickly after approaching the ridge as much as possible, turning around the ridge with a small turning radius, When the turning is completed, the steering wheel is quickly operated to return the aircraft to the straight-ahead state, and often enters the next planting process quickly.

[0005] On the other hand, an unskilled pilot cannot perform the rapid operation of the steering handle as described above, so that when one planting process is completed, the steering handle is relatively slowly moved slightly before the ridge. Operate and make a turn at the ridge with a relatively large turning radius.When turning at the ridge is completed, operate the control handle relatively slowly to return the aircraft to the straight-ahead state, and a little for the next planting stroke. Often enter late. The present invention is configured such that in a working device elevating structure of a working vehicle, automatic raising and lowering driving of the working device is appropriately performed in response to the difference in the state of the steering operation of the front wheels as described above. It is intended to be.

[0006]

According to a first aspect of the present invention, when the front wheel is steered from a straight traveling position to a right or left set angle, the working mechanism is raised by the drive mechanism. In the case where the automatic ascending means is provided, the steering speed when the front wheel is steered from the straight traveling position side to the right or left set angle side is detected, and when the steering speed becomes high, the right and left steering angles are detected. The set angle is changed to the straight traveling position. Accordingly, when the steering wheel is rapidly operated and the front wheels are rapidly steered right (left) from the straight ahead position side, the right (left) set angle approaches the front wheels, and the front wheels are moved toward the straight ahead position side. When the front wheels quickly reach the right (left) set angle, and the front wheels begin to steer to the right (left) from the straight ahead position side, Then, the start of the operation of the automatic ascent means is hastened.

According to the first aspect of the present invention, for example, when one planting process is completed in a riding type rice transplanter, the operator operates the steering handle quickly after approaching the ridge as much as possible, When turning around the ridge with a small turning radius is started, the automatic raising drive of the seedling planting device by the automatic raising means is started earlier, so that the raising drive of the seedling planting device is delayed and the seedling planting device is moved. It is possible to avoid a state of contacting a ridge or the like.

[II] According to the feature of claim 2, when the front wheel is steered from the right (left) steering limit side to the right (left) set angle (straight forward position side), the driving mechanism is used. Steering when the front wheels are steered from the right (left) steering limit side to the right (left) set angle side (straight forward position side) in the case where the automatic lowering means for driving down the working device is provided. When the speed is detected and the steering speed increases, the right and left set angles are changed to the right and left steering limit sides. Accordingly, when the steering wheel is rapidly operated and the front wheels are rapidly steered from the right (left) steering limit side to the right (left) set angle side (straight forward position side), the right (left) The set angle approaches the front wheel, and the front wheel is quickly steered from the right (left) steering limit side to the right (left) set angle side (straight forward position side). When the front wheel reaches the set angle of (left) quickly and the front wheel starts to be steered from the right (left) steering limit side to the right (left) set angle side (straight forward position side),
The operation of the automatic lowering means is started earlier.

According to the second aspect of the present invention, for example, when the driver turns the steering wheel quickly to return to the straight-ahead state by turning the steering wheel when the turning at the bank is completed in the riding type rice transplanter, for example. Since the automatic lowering drive of the seedling planting apparatus by the automatic lowering means is started earlier, it is possible to start the next planting process earlier.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [1] As shown in FIG. 1, an engine 3 and a driving unit 4 are provided on a body supported by a front wheel 1 and a rear wheel 2 which can be steered right and left. A seedling planting device 6 is connected to a rear portion of the plant through a parallel quadruple link mechanism 5 so as to be able to move up and down, and a single-acting hydraulic cylinder 7 that drives the link mechanism 5 up and down is provided. A riding rice transplanter is configured.

As shown in FIG. 1, the seedling planting device 6 includes a seedling rest 8, which is driven to reciprocate sideways by a predetermined stroke, a planting transmission case 9, and a rotation which is driven to rotate at the rear of the planting transmission case 9. The case 10 includes a pair of planting claws 11 supported by the rotating case 10, a plurality of floats 12, and the like. The seedlings are alternately taken out and planted on the rice field G.

[2] As shown in FIG. 2, the rear portion of the float 12 at the center in the left and right directions is supported swingably around the horizontal axis P1, and the position of the front portion of the float 12 with respect to the seedling planting device 6 is detected. A potentiometer 14 is provided, and the detected value of the potentiometer 14
Is input to the control device 15 as a detected value of the height up to. The hydraulic cylinder 7 is provided with an electromagnetically operated control valve 13 that operates to supply and discharge hydraulic oil to the ascending side and the descending side, and the control device 15 is configured to operate the control valve 13. .

When the seedling planting device 6 moves up and down with respect to the rice field G while the float 12 follows the ground surface G, the detection value of the potentiometer 14 changes. 15, the control valve 13 is automatically operated, the hydraulic cylinder 7 expands and contracts, and the seedling planting device 6 is automatically driven up and down so that the detection value of the potentiometer 14 is maintained at the set value (automatically). Lifting control). As a result, the seedling planting device 6
, The planting depth of the seedling by the planting claws 11 is maintained at the set value. As will be described later, when the seedling planting apparatus 6 is driven to move upward, an upper limit sensor 24 for detecting that the link mechanism 5 has reached a mechanical upper limit position is provided. It is configured to be inputted to.

[3] A hydrostatic continuously variable transmission (not shown) capable of continuously changing the power of the engine 3 to the forward side and the reverse side (not shown), a wet multi-plate type main clutch (not shown), Transmission to a front wheel 1 and a rear wheel 2 via a gear transmission type auxiliary transmission (not shown) that can be shifted to a high speed position H (a position during road running) and a low speed position L (a position during planting work). As shown in FIG. 2, the power from the main clutch is transmitted to the seedling planting apparatus 6 via the planting clutch 16. A motor 17 for operating the planting clutch 16 on the transmission side and the transmission interruption side is provided, and the control device 15 is configured to operate the motor 17.

As shown in FIGS. 2 and 1, a pitman arm 29, which is swingably operated to the right and left by the steering handle 18, and the right and left front wheels 1 are connected by a tie rod 30, and The front wheel 1 is configured to be steerable right and left, and a steering wheel 18 is provided.
A driver's seat 19 is provided in the driver 4. An angle sensor 31 for detecting a swing angle A0 of the pitman arm 29 with respect to the straight traveling position A is provided, and a detection value of the angle sensor 31 is input to the control device 15.

As shown in FIGS. 2 and 1, a main transmission lever 2 for operating a hydrostatic continuously variable transmission in a forward direction and a reverse direction.
1 is provided on the left side of the steering handle 18. A sub-transmission lever 23 for operating the sub-transmission at the high-speed position H and the low-speed position L is provided on the left side of the driver's seat 19, and a low-speed sensor 25 for detecting that the sub-transmission lever 23 has been operated at the low-speed position L. Is provided so that a signal from the low-speed sensor 25 is input to the control device 15. A clutch pedal 26 is provided for operating the main clutch to the transmission interrupting side by stepping on the clutch pedal. A clutch sensor 27 for detecting that the clutch pedal 26 has been stepped on is provided. 15 is input.

As shown in FIGS. 2 and 1, a first elevating lever 28 is provided on the right side of the driver's seat 19, and the first elevating lever 28 is moved up, neutral, down, planting and automatic. It is configured to be operable at any position. Even if the user lifts his / her hand after operating the first elevating lever 28, the first elevating lever 2
8 is configured not to move from that position, and the operation position of the first elevating lever 28 is input to the control device 15.

As shown in FIGS. 2 and 1, the neutral position N,
A second lifting lever 20 operable from a neutral position N to an upward position U upward and from the neutral position N to a downward position D downward.
Is provided on the lower right side of the steering handle 18 and the second
The operation position of the lifting lever 20 is input to the control device 15. The second raising / lowering lever 20 is biased to the neutral position N.
When the hand is released from the lifting lever 20, the second lifting lever 20 automatically returns to the neutral position N.

[4] Next, the case where the first raising / lowering lever 28 is operated to the raising position, the neutral position, the lowering position and the planting position will be described with reference to FIG. 3 and FIG. When the first raising / lowering lever 28 is operated to the raised position (step S1), the planting clutch 16 is operated by the motor 17 to the transmission blocking side (step S2), and the control valve 13 is operated to the raised position (step S3). The seedling planting device 6 is driven upward by the hydraulic cylinder 7. In this case, when the link mechanism 5 reaches the upper limit position and this is detected by the upper limit sensor 24 (step S4), the control valve 13 is operated to the neutral position, the hydraulic cylinder 7 stops (step S6), and the seedling is planted. The device 6 automatically stops at the upper limit position.

When the first raising / lowering lever 28 is operated to the neutral position (step S1), the planting clutch 1 is driven by the motor 17.
6 is operated to the transmission interruption side (step S5), and the control valve 1
3 is operated to the neutral position (Step S6), and the hydraulic cylinder 7 and the seedling plant 6 stop at that position.

When the first raising / lowering lever 28 is operated to the lowering position (step S1), the motor 17 causes the planting clutch 1 to move.
6 is operated to the transmission interruption side (step S7), and the automatic lifting / lowering control described in [2] above is activated (step S7).
8). In this case, if the float 12 is positioned above the rice field G and is hanging down, the detected value of the height from the rice field G to the seedling plant 6 is determined to be too high, and the control valve 13 is turned off. The seedling planting device 6 is moved down by the hydraulic cylinder 7 by being operated to the lowering position, and the seedling planting device 6 is apparently continuously lowered. Thereafter, when the float 12 touches the rice field G, the control valve 13 is automatically operated so that the detection value of the potentiometer 14 is maintained at the set value. Is stopped.

When the first raising / lowering lever 28 is operated to the planting position (step S1), the planting clutch 1 is driven by the motor 17.
6 is operated on the transmission side (step S9), and the preceding item [2]
(Step S10).
As a result, the control valve 13 is automatically operated and the hydraulic cylinder 7 is extended and contracted so that the detected value of the potentiometer 14 is maintained at the set value, and the seedling planting apparatus 6 is maintained at the set height from the rice field G. Therefore, the planting operation is performed in which the planting claws 11 plant the seedlings while the planting depth of the seedlings is maintained at the set value.

As described above, by operating the first raising / lowering lever 28 to the raising position, the neutral position, and the lowering position,
In the range between the upper limit position of the link mechanism 5 and the rice field surface G, the seedling planting device 6 can be driven up and down to an arbitrary height and stopped, and the first raising / lowering lever 28 can be operated to the planting position. Thus, the planting operation is performed while the planting depth of the seedling is maintained at the set value.

[5] Next, a case where the second elevating lever 20 is operated while the first elevating lever 28 is operated at the automatic position will be described with reference to FIGS. In a state in which the first raising / lowering lever 28 is operated to the automatic position (step S1), for example, the seedling planting device 6 is automatically driven up and down so as to be maintained at the set height from the rice field G (operation of the automatic raising / lowering control). In the state of the planting operation in which the planting clutch 16 is operated on the transmission side (steps S32, S33, S
34, S35), when the second elevating lever 20 is operated to the ascending position U (steps S11, S20), the planting clutch 16 is operated by the motor 17 to the transmission interruption side (step S21), and the automatic elevating control is stopped and controlled. The valve 13 is operated to the raised position (step S22), and the hydraulic cylinder 7 drives the seedling plant 6 upward. In this case, even if the second elevating lever 20 is held at the elevating position U, or if the second elevating lever 20 is operated to the elevating position U and then to the neutral position N, the ascending drive of the seedling planting device 6 is performed. Is continued.

When the link mechanism 5 reaches the upper limit position and this is detected by the upper limit sensor 24 (step S2).
3), the control valve 13 is operated to the neutral position, the hydraulic cylinder 7 stops (step S24), and the seedling planting device 6 automatically stops at the upper limit position. Thus, the second lifting lever 20
Is operated to the ascending position U, the planting clutch 16 is operated to the transmission cutoff side by the motor 17, and the seedling planting apparatus 6 can be raised at a stretch to the upper limit position.

Next, when the second raising / lowering lever 20 is operated to the lowering position D with the seedling planting device 6 raised (step S1).
1, S32 (N = 1)), similar to the preceding item [4] and step S8 in FIG. 3, the automatic lifting control is operated in a state where the planting clutch 16 is operated to the transmission cutoff side (step S3).
3, S34). In a state where the automatic elevating control is operated, the seedling planting device 6 is apparently and continuously lowered, and when the float 12 is in contact with the rice field G, the seedling planting device 6 is apparently stopped at the rice field G. Becomes In this case, even if the second elevating lever 20 is held at the lowering position D or the second elevating lever 20 is operated to the lowering position D and then to the neutral position N, the lowering of the seedling planting device 6 is continued. Is done. Thus the second
By operating the raising / lowering lever 20 to the lowering position D, the seedling planting device 6 can be lowered at a stretch until the float 12 touches the rice field surface G.

As described above, when the seedling planting apparatus 6 is lowered (the automatic raising and lowering control is activated), the second raising and lowering lever 20 is operated to the neutral position N and then to the lowering position D again (step S1). S11, S32 (N = 2)), the planting clutch 16 is operated to the transmission side by the motor 17 (step S35), and the preceding item [4] and step S in FIG.
9. The planting operation is started in the same manner as in S10.

In step S22 of FIG. 4, before the seedling planting device 6 reaches the upper limit position while the seedling planting device 6 is being lifted,
When the second raising / lowering lever 20 is operated to the lowering position D (Steps S23, S25), the process proceeds to Steps S33, S34, where the raising drive of the seedling planting device 6 is stopped and the seedling planting device 6 is stopped.
Is driven downward (operation of automatic lifting control). Conversely, in step S34 of FIG. 4, when the second raising / lowering lever 20 is operated to the raising position U before the float 12 reaches the rice field G while the seedling planting device 6 is descending (step S11), steps S20, S21, In S22, the lowering drive of the seedling planting device 6 is stopped, and the seedling planting device 6 is driven up.

[6] Next, a description will be given of a case in which the first elevator lever 28 is operated to the automatic position and a turn is performed near the ridge, with reference to FIGS. As shown in FIG. 2, between the straight traveling position A of the pitman arm 29 and the right and left steering limits B, the right and left first set angles A are set.
1, the right and left second set angles A2 are set, and the angle between the straight traveling position A and the right first set angle A1 (the angle between the straight traveling position A and the left first set angle A1) ) C1 is set to a large value, and the angle between the right steering limit B and the right second set angle A2 (the angle between the left steering limit B and the left second set angle A2) C2 Is set to a small one.

For example, the seedling planting apparatus 6 is automatically moved up and down so as to be maintained at a set height from the rice field G (operation of automatic up / down control), and the planting clutch 16 is operated on the transmission side to perform the planting operation. (Steps S32, S33, S3
4, S35), when one planting process is completed and the aircraft reaches the ridge, the pilot operates the steering handle 18 and the pitman arm 29 moves right (left) from the straight traveling position A side.
It is assumed that the swing operation has begun (step S14).

In this case, the detection value of the angle sensor 31 is differentiated, and the swing speed V of the pitman arm 29 is detected (step S15). First set angle A of
1 is changed to the straight traveling position A (steps S16 and S1).
7) The right and left first set angles A1 are changed to the right and left steering limits B as the swing speed V of the pitman arm 29 decreases (steps S16 and S16).
18), according to the swing speed V of the pitman arm 29,
The right and left first set angles A1 are continuously changed to the straight traveling position A side and the right and left steering limit B sides.

When the swing angle A0 of the pitman arm 29 reaches the right (left) first set angle A1 changed according to the swing speed V of the pitman arm 29 as described above (arrow in FIG. 2). Reference), it is determined that the aircraft has reached the edge of the ridge and has started turning on the edge of the ridge (step S19). Thereby, the process proceeds to steps S20 to S24, and the motor 1
7, the planting clutch 16 is operated to the transmission cutoff side, and the seedling planting device 6 is driven up to the upper limit position.

Generally, in a riding type rice transplanter, the swing angle A0 of the pitman arm 29 is controlled to the right (left) steering limit B from the straight-ahead position A, and a turn is performed near the ridge (arrow in FIG. 2). reference). After the turn on the ridge is completed, the pilot operates the steering handle 18 so that the swing angle A0 of the pitman arm 29 is shifted from the right (left) steering limit B side to the straight traveling position A.
It is assumed that the operation is started on the side (step S26).

In this case, the detection value of the angle sensor 31 is differentiated to detect the swing speed V of the pitman arm 29 (step S27). As the swing speed V of the pitman arm 29 increases, the right and left are increased. Of the second set angle A
2 is changed to the right and left steering limit B (step S2).
8, S29), the lower the swing speed V of the pitman arm 29, the more the right and left second set angles A2 are changed to the straight traveling position A side (steps S28, S3).
0), the right and left second set angles A2 are continuously changed to the right and left steering limit B side and the straight traveling position A side in accordance with the swing speed V of the pitman arm 29.

When the swing angle A0 of the pitman arm 29 reaches the right (left) second set angle A2 changed according to the swing speed V of the pitman arm 29 as described above (arrow in FIG. 2). Reference), it is determined that the turning on the ridge side has been completed (step S31). Thereby, step S3
3, the process moves to S34, and the seedling planting device 6 is driven to descend until the float 12 touches the rice field G (operation of the automatic elevating control). Thereafter, when the second elevating lever 20 is operated to the neutral position N and then to the lowering position D again (step S1).
1, S32 (N = 2)), the planting clutch 16 is operated to the transmission side by the motor 17 (step S35), and the planting operation is started in the same manner as in the previous section [4] and steps S9 and S10 in FIG. Enter the next planting process.

If the clutch pedal 26 is depressed and the main clutch is operated to the transmission interruption side (step S1)
2) Or, when the sub-transmission lever 23 is operated to the high-speed position H (step S13), the pitman arm 29 (the swing angle A0) is operated from the straight traveling position A side to the right (left) first set angle A1. Even if the pitman arm 29 (swing angle A0) is operated from the right (left) steering limit B to the right (left) second set angle A2, the steps S14 to S19 and steps S26 to S31 are performed. Do not migrate.

[Another Embodiment of the Invention] First Lifting Lever 2
When the device 8 is operated to the automatic position, a setting switch (not shown) which can be set to shift to steps S14 to S19 and steps S26 to S31 shown in FIG. In this case, if the setting switch has been operated to the ON position, the transition from step S11 to step S12 is permitted. If the setting switch has been operated to the OFF position, the operation returns unconditionally from step S11 (steps S14 to S19). And step S26-
(Not shifting to S31)
It is provided between step S11 and step S12 in FIG.

In steps S16, S17 and S18 of FIG. 4, when the swing speed V of the pitman arm 29 becomes higher than the set swing speed, the right and left first and second swing speeds are set in accordance with the swing speed V of the pitman arm 29. The first set angle A1 is configured so that the first set angle A1 is continuously changed to the straight traveling position A side and the swing speed V of the pitman arm 29 is lower than the set swing speed. May be configured not to be changed from the initially set state.

In steps S28, S29 and S30 of FIG. 4, when the swing speed V of the pitman arm 29 is higher than the set swing speed, the right and left first and second swing speeds V are set in accordance with the swing speed V of the pitman arm 29. 2 so that the setting angle A2 is continuously changed to the right and left steering limits B.
If the swing speed V of the pitman arm 29 is lower than the set swing speed, the right and left second set angles A2 may be configured not to be changed from the initial set state.

The present invention can be applied not only to a riding type rice transplanter but also to a riding type direct sowing machine having a direct sowing device (working device) at the rear part of the machine body, and a rotary plowing device (working device) at the rear portion of the machine body. And a combine tractor provided with a reaper (working device) at the front of the body so as to be able to move up and down. In the case of agricultural tractors and combines, Figure 4
When the working device is driven up in step S22, step S21 may be deleted so that the working clutch of the working device is left on the transmission side (the working clutch of the working device is not operated to the transmission cutoff side). May be configured). With this configuration, step S in FIG.
32 and S35 become unnecessary.

[0041]

According to the first aspect of the present invention, when the front wheel is steered from the straight position to the right or left set angle, the work mechanism is provided with automatic ascending means for ascending and driving the working device by the drive mechanism. In the vehicle working device elevating structure, when the front wheels start to be steered to the right (left) rapidly from the straight traveling position, the automatic ascending means automatically starts the ascending drive of the working device early. This prevents problems caused by a delay in the automatic raising operation of the working device (for example, in the case of a riding type rice transplanter, the seedling planting device comes into contact with the ridge at the start of turning at the ridge). As a result, workability at the time of turning the work vehicle could be improved.

According to the feature of the second aspect, the front wheel is right (left)
When the steering operation is performed to the right (left) set angle (the straight traveling position side) from the steering limit side of the working vehicle, the working device lifting / lowering structure of the working vehicle provided with automatic lowering means for driving the working device downward by the drive mechanism, When the front wheel starts to be steered from the right (left) steering limit side to the right (left) set angle side (straight-moving position side) rapidly, the automatic lowering means of the automatic lowering means causes the automatic lowering drive of the working device to be performed earlier. By being configured to be started, a problem caused by a delay in the automatic lowering drive of the working device (for example, in a riding type rice transplanter, a delay in entering the next planting process at the end of a turn on a ridge, etc.) ) Can be avoided,
Workability during turning of the work vehicle could be improved.

[Brief description of the drawings]

FIG. 1 is an overall side view of a riding rice transplanter.

FIG. 2 is a diagram showing a relationship between control systems.

FIG. 3 is a diagram showing a flow of a first half of control;

FIG. 4 is a diagram showing a flow of the latter half of control;

[Explanation of symbols]

 Reference Signs List 1 front wheel 6 work device 7 drive mechanism A straight traveling position A1, A2 right and left set angle B right and left steering limit V steering speed

Claims (2)

[Claims] 1. A work device is provided on a body so as to be able to move up and down, and a drive mechanism for driving the work device up and down is provided. Right and left set angles are set from a straight-ahead position. When the steering operation is performed to the left set angle, the driving mechanism is provided with an automatic ascending means for ascendingly driving the working device, and the front wheels are steered from the straight traveling position side to the right or left set angle side. Speed detection means for detecting the steering speed when the front wheel is steered from the straight running position side to the right or left set angle side when the steering speed becomes high, the right and left A work device lifting / lowering structure of a work vehicle, comprising a change means for changing a set angle to a straight traveling position side. 2. A work device is provided on the body so as to be able to move up and down freely, and a drive mechanism for driving the work device up and down is provided, and right and left set angles are set from right or left steering limits,
When the front wheel is steered from the right or left steering limit side to the right or left set angle, the drive mechanism is provided with automatic lowering means for driving the working device downward, and the right or left steering is performed. A speed detecting means for detecting a steering speed when the front wheel is steered from the limit side to the right or left set angle side; and the right or left set angle from the right or left steering limit side. When the steering speed at the time when the front wheels are steered is increased, the working device lifting / lowering of the working vehicle is provided with changing means for changing the right and left set angles to the right and left steering limit sides. Construction.