JPH05262151A - Four-wheel driving working vehicle - Google Patents

Abstract

PURPOSE:To carry out the small turn without roughening a road surface in the turn in the intermediate speed traveling state by installing a restraining means for operating the first and second operating means so that only a front wheel speed change device is selected to a boosting speed state, in the turn in the intermediate speed traveling state. CONSTITUTION:When a speed change device for traveling is operated to a high speed range H, the operations of the first and the second operating means 16 are suspended by the third restraining means 19 and 24 in interlocking with the above mentioned operation, When the speed change device is operated to an intermediate speed range M, the selection operation to the boosting state of a front wheel speed change device 6 by the first operating means 16 in interlocking with the above-mentioned operation is permitted by the second restraining means 19 and 24, and the operation to the brake side of the side brakes 11R and 11L on the turning center side by the second operating means is permitted by the second restraining means 9 and 24 in the brake power state lower than the brake power by the first restraining means 9 and 24. Accordingly, the small turn without roughening the road surface can be carried out.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a four-wheel drive type work vehicle represented by an agricultural tractor, a riding type rice transplanter and the like.

[0002]

2. Description of the Related Art In an agricultural tractor, which is an example of a four-wheel drive type work vehicle, a standard in which front wheels and rear wheels are driven at substantially the same speed, as disclosed in, for example, Japanese Patent Laid-Open No. 243429/1993. State, and the front wheel transmission (6 in FIG. 1 of the above-mentioned publication), which can be switched to a speed increasing state in which the front wheels are driven at a higher speed than the rear wheels, and each of the left and right rear wheels can be independently brake-operated. Some have a pair of left and right side brakes (13R, 13L in FIG. 1 of the above publication). In this case, when the front wheels are steered from the straight ahead position to the right or left over the set angle, the front wheel transmission is automatically switched from the standard state to the speed-up state, and the side brakes on the turning center side are automatically changed. It is configured to be operated on the braking side. As a result, the pulling action of the front wheels, which has been accelerated by the front wheel transmission, in the turning direction and the braking action on the rear wheels on the turning center side enable a very small small turn turning centering on the rear wheels on the turning center side. Become.

[0003]

In the case of the structure described above, the front wheel transmission is switched to the speed-increasing state and the side brake on the turning center side is operated to the braking side when turning at a high speed. If so, a very small small turn is made in the high speed running state, and thus such a very small small turn must be made in the low speed running state. Therefore, in the configuration of the above publication, a manually operated switching valve that prevents the front wheel transmission from being switched from the standard state to the speed-increasing state during turning and prevents the side brake on the turning center side from being operated toward the braking side. (25 in FIG. 1 of the above publication). In this case, in the high speed running state, it is necessary to operate the switching valve in advance so that the front wheel transmission is not switched to the speed increasing state and the side brake is not operated to the braking side. If the operator forgets to operate the switching valve when the vehicle is running and makes a turn in that state, it will suddenly start a small turn, which is an improvement in terms of operability and safety. There is room.

Further, in the configuration of the above publication, both the front wheel transmission and the side brake are automatically operated during turning by operating the switching valve (acceleration side and braking side), and front wheel shifting during turning. It is possible to switch between two states in which both the device and the side brake are not operated.
As a result, whether the operator should operate both the front wheel transmission and the side brakes automatically during the medium speed traveling state between the high speed traveling state and the low speed traveling state, You may be confused about whether to operate both side brakes so that they are not operated. Therefore, if both the front wheel transmission and the side brakes are automatically operated in the middle-speed traveling state, a small turn may be suddenly made when turning. On the contrary, if both the front wheel transmission and the side brake are not operated in the middle speed running state, there may be a case where a small turn cannot be performed. The present invention relates to a four-wheel drive work vehicle configured to automatically operate a front wheel transmission and side brakes when turning, and switches to a state in which both the front wheel transmission and side brakes are not operated during high-speed traveling. It is an object of the present invention to be configured so that an operation can be performed without forgetting, and a small turning turn suitable for a medium speed running state can be performed.

[0005]

A feature of the present invention is that the four-wheel drive type working vehicle as described above is configured as follows. That is, the front wheel transmission that can be switched between a standard state in which the front wheels and the rear wheels are driven at substantially the same speed and a speed increase state in which the front wheels are driven at a higher speed than the rear wheels, and the pair of left and right rear wheels A pair of left and right side brakes that can brake the selected one, steering angle detection means that detects the left and right steering angles of the front wheels from the straight ahead position, and the front wheels steer from the straight ahead position to the left or right beyond the set angle. When operated, the first operation means for switching the front-wheel transmission from the standard state to the speed-increasing state in conjunction with this steering operation, and the front wheels are steered from the straight-ahead position to the left or right over a set angle. And second operating means for operating the turning center side of the side brake to the braking side in conjunction with this steering operation, and when the traveling transmission is operated in the high speed range, this operation is performed. Stops the operation of the first and second operating means in conjunction When the first restraint means and the transmission are operated in the medium speed range, the second restraint means that allows the operation of the first operating means and stops the operation of the second operating means in conjunction with this operation, When the device is operated in the low speed range, it is provided with a third restraint means for allowing the operation of the first and second operation means in conjunction with this operation.

[0006]

With the above-mentioned structure, when the operator shifts the traveling transmission to a high speed range (corresponding to a high speed traveling state), the front wheel transmission is switched from the standard state to the speed increasing state during turning. The side brake on the turning center side is not operated to the braking side. As a result, it is possible to safely make a turn in a high-speed traveling state. Conversely, if the operator shifts the traveling transmission to a low speed range (corresponding to a low speed traveling state), the front wheel transmission is switched from the standard state to the speed increasing state during turning, and the side brake on the center side of the turning is operated. Is also operated on the braking side. As a result, the pulling action of the front wheels in the turning direction, which has been accelerated by the front wheel transmission, and the braking action on the rear wheels on the turning center side, make a very small small turn around the turning wheels on the turning center side slower. It can be done safely while driving. As described above, the front wheel transmission and the side brakes are both automatically operated (in a high-speed traveling state) and both are operated (in a low-speed traveling state) automatically in conjunction with the gear shifting operation performed by the operator. ) Is performed, the switching operation to a state in which neither the front wheel transmission nor the side brake is operated is never forgotten during high-speed traveling.

When the worker shifts the transmission for traveling to the medium speed range (corresponding to the medium speed traveling state), the front wheel transmission is switched from the standard state to the speed increasing state during turning. The side brake on the turning center side is not operated by the braking side. Comparing the turning using only the front wheel transmission and the turning using only the side brakes,
When turning using only the front wheel transmission, all four front and rear wheels are driven, so the increased front wheel pulling action in the turning direction enables smooth small turns without ruining the ground. Become. On the other hand, when turning using only the side brakes, the rear wheels on the turning center side are in a substantially stopped state by the side brakes, so a small turn can be made around the rear wheels on the turning center side. It is possible to turn smaller than when using only the front wheel transmission. However, there are many cases where the rear wheel on the turning center side under braking is dragged to damage the ground.
Therefore, when comparing turning using only the front wheel transmission and turning using only the side brakes, when turning in the medium speed range of the transmission for traveling, turning is performed only by the speed increasing action of the front wheel transmission. Is preferable in terms of safety because it does not make a sharp turn around abruptly, and also in terms of turning performance because it does not roughen the ground.
In this case, automatically in conjunction with the shift operation performed by the operator,
Since the switching operation is performed so that the front wheel transmission is operated and the side brake is not operated, the switching operation to the above-mentioned state will not be forgotten in the middle speed running state.

[0008]

As described above, at the time of turning in the high speed running state, the front wheel transmission is not switched to the speed increasing state, and the side brake on the turning center side is always switched to the state not being operated to the braking side. It was possible to improve the safety when turning in a high-speed traveling state. Further, the above-mentioned switching operation can be automatically performed at the same time when shifting to the high-speed running state, and the operability can be improved. Further, when the vehicle is turning in the medium speed running state, only the front wheel transmission is switched to the speed increasing state so that the turning can be performed at a high speed and at a low speed because the turning is not so rapid and the ground is not roughened. It was possible to improve the safety and turning performance when turning in an intermediate state of the running state. Further, since appropriate turning is automatically set for each of the high speed traveling state, the medium speed traveling state and the low speed traveling state, it is possible to improve the turning performance of the work vehicle as a whole.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. 1 and 11 show an agricultural tractor which is an example of a four-wheel drive type work vehicle. An engine 3 is provided at the front part of a vehicle body supported by a pair of left and right front wheels 1 and a pair of left and right rear wheels 2, and a mission is provided at the rear part. An agricultural tractor is provided with the case 4. The power from the engine 3 is the mission case 4
Main transmission (multi-stage gear shift type) (not shown),
Also, the power is transmitted from the rear wheel differential mechanism 5 to the left and right rear wheels 2 via an auxiliary transmission (a high, middle, low, and low gear shift type, which corresponds to a traveling transmission) (not shown). Then, the power branched from immediately before the rear wheel differential mechanism 5 is transmitted to the left and right front wheels 1 via the front wheel transmission 6, the front wheel output shaft 7, and the front wheel differential mechanism 8.

The front wheel transmission 6 shown in FIG. 1 has a normal state in which the front wheel 1 is driven at substantially the same speed as the rear wheel 2, and a state in which the front wheel 1 is driven at a higher speed than the rear wheel 2. It is possible to perform switching operation between two states, that is, a transmission speed increasing state. As shown in FIG. 1, the shift member 9 for two-state switching operation is a spring 10
Is urged toward the side of engagement with the standard gear 20, and the shift member 9 is normally engaged with the standard gear 20 to be in the standard state. Then, when hydraulic oil is supplied into an oil chamber (not shown) formed between the shift member 9 and the standard gear 20, the shift member 9 slides to the left side of the drawing and the friction clutch 21 is pressed and operated. A speed-up state can be obtained.

As shown in FIG. 2, with respect to the left and right rear wheels 2,
Side brakes 11 that can independently brake each rear wheel 2
R and 11L are provided. As shown in FIGS. 1 and 10, the side brake pedal 12 is provided on the right side of the floor surface of the control section.
A pair of left and right R and 12L are arranged. The left and right side brake pedals 12R and 12L and the side brake 11 are arranged.
R and 11L are interlockingly connected via the cylinders 13R and 13L and the linkage rod 14.

With the above structure, the left and right side brake pedals 12R and 11L can be independently operated by depressing the left and right side brake pedals 12R and 12L. Then, as shown in FIG. 10, the cylinders 13R and 13L are urged toward the extension side by the spring 13a, and by supplying hydraulic oil to contract the cylinders 13R and 13L, the left and right side brakes 11R and
It is possible to operate 11L to the braking side.

Next, the operation of steering the front wheel 1 and the linkage between the left and right side brakes 11R and 11L and the front wheel transmission 6 will be described. As shown in FIGS. 1 and 2, the pump 15
From the oil is supplied to the left and right side brakes 11R and 11L and the front wheel transmission 6 via the oil passage 28 in the block-shaped valve unit 22 and the control valve 16 (corresponding to the first and second operating means). Has been done. The control valve 16 includes an oil chamber between the shift member 9 and the standard gear 20 in the front wheel transmission 6, and the left and right side brake pedals 12R and 1R.
The straight traveling position 16N in which the 2L cylinders 13R, 13L are in an oil draining state, hydraulic oil from the pump 15 is supplied to the oil chamber of the front wheel transmission 6 and the right cylinder 13R, and the left cylinder 13L is in an oil draining state. Turning position 16R, and
The hydraulic oil is supplied to the oil chamber of the front wheel transmission 6 and the left cylinder 13
It is a three-position switching type of a left turning position 16L that supplies oil to L and puts the right cylinder 13R in an oil draining state.

As shown in FIGS. 1 and 2, a fan-shaped cam plate 18 (corresponding to steering angle detecting means) is fixed to a pitman arm 17 for steering operation of the front wheels 1, and a control valve 16 is provided.
Of the spool 16a comes into contact with the cam plate 18,
A spring 16b for urging a toward the contact side is provided. The state shown in FIG. 1 and FIG. 2 is a state in which the front wheel 1 is operated to the straight traveling position, and the control valve 16 is operated to the straight traveling position 16N. In this state, the hydraulic oil from the oil passage 28 is discharged via the drain oil passages 33 and 34 and the drain portion 35. As a result, the left and right side brakes 11
R and 11L are in the non-braking state, the shift member 9 of the front wheel transmission 6 is engaged with the standard gear 20, and the front wheel 1 is in the standard state in which the rear wheel 2 is driven at substantially the same speed.

When the front wheel 1 is steered to the right from the state shown in FIGS. 1 and 2 over a set angle, the spool 16a of the control valve 16 is pushed by the cam plate 18 to the right in the drawing to the right turning position. 16R (see FIG. 1). As a result, the hydraulic oil from the oil passage 28 is supplied from the right brake port 36R to the right cylinder 13R and also supplied from the front wheel transmission port 37 to the front wheel transmission 6. Therefore, the friction clutch 21 of the front wheel transmission 6 is engaged and operated, so that the front wheel 1 is driven at a higher speed than the rear wheel 2, and the right cylinder 13R contracts to operate the right side brake 11R. It is operated on the braking side.

On the contrary, from the state shown in FIG. 1 and FIG.
When the steering wheel is turned to the left over a set angle, the spool 16a of the control valve 16 moves to the left side of the drawing, and the left turning position 16L is reached.
(See FIG. 1). As a result, the hydraulic oil from the oil passage 28 is supplied from the left brake port 36L to the left cylinder 13L and also supplied from the front wheel transmission port 37 to the front wheel transmission 6. Therefore, the friction clutch 21 of the front wheel transmission 6 is engaged and operated so that the front wheel 1 is driven at a higher speed than the rear wheel 2, and the left cylinder 13 is driven.
L contracts and the left side brake 11L is operated to the braking side.

In this agricultural tractor, the automatic operation of the side brakes 11R and 11L to the braking side as described above and the speed increase of the front wheel transmission 6 are performed in accordance with the shift position of the auxiliary transmission in the transmission case 4. It is configured to switch between a state in which an operation is performed on the state side and a state in which the operation is not performed. Next, this switching structure will be described. Figure 1,
As shown in FIGS. 2 and 3, the hydraulic oil from the pump 15 is supplied to the oil passage 23 of the valve unit 22 and the rotary switching valve 24.
(Corresponding to 1st, 2nd, 3rd restraint means), oil passages 25, 26, 2
It is supplied to the control valve 16 via 7, 28.

As shown in FIGS. 2 and 3, a pressure regulating valve 19 (corresponding to the first, second and third restraint means) is connected to the oil passage 26. The pressure regulating valve 19 includes a valve body 19a and a valve body 19a.
And a support member 19c for supporting the rear end of the spring 19b. As a result, when the pressure in the oil passage 26 exceeds the pressure set by the spring 19b, the valve element 19a opens to the right on the paper surface and the working oil is discharged through the drain oil passage 38.
The operating hydraulic pressure supplied to 6 is determined by the urging force of the spring 19b of the pressure regulating valve 19, that is, the position of the support member 19c of the spring 19b.

The spool 29 of the switching valve 24 is shown in FIGS.
As shown in FIG. 1, a first land portion 29A having a pair of notches 29a and 29b and a drain hole 29c, and a second land portion 29B having a first arc surface 29d and a second arc surface 29e are provided. The rear end of the support member 19c of the pressure regulating valve 19 is abutted against the first arc surface 29d, and the position of the support member 19c is determined. Then, at the three positions shown in FIGS.
Three recesses 29f for holding the position of the spool 29 by receiving the detent balls 43 therein are provided at the rear end of the spool 29. As shown in FIGS. 3 and 4, the operation plate 30 is fixed to the tip of the spool 29 of the switching valve 24 outside the valve unit 22, and the shift lever 31 and the operation plate 30 for the auxiliary transmission are connected by a wire. They are connected by 32. Further, a spring (not shown) for urging the spool 29 counterclockwise in the drawing is provided, and the urging force of this spring is set to be stronger than the urging force of the spring 19b and the holding action of the detent ball 43. Has been done.

The state shown in FIG. 4 and FIG.
1 is in the state of operating the low speed position L (corresponding to the low speed range of the transmission for traveling). In this state, the pump 15
From the oil passage 23, the first cutout portion 29a in the spool 29 of the switching valve 24, and the oil passages 25, 26, 27, 2
It is supplied to the control valve 16 via 8. Then, the support member 19c of the pressure regulating valve 19 is connected to the first arc surface 2 of the spool 29.
9d is pressed to the left side of the drawing, and the spring 19b of the pressure regulating valve 19 is compressed and the action of the pressure regulating valve 19 causes the working hydraulic pressure supplied to the control valve 16 to reach a second set pressure P2 described later. Has been maintained.

As shown in FIG. 8, the front wheel transmission 6 is switched from the standard state to the speed increasing state at a relatively low first set pressure P1, but at the first set pressure P1, the side brake 1 is operated.
1R and 11L are not operated to the braking side. Then, at the second set pressure P2 higher than the first set pressure P1, the side brakes 11R and 11L are in the weak braking state, and the front wheel transmission 6 is also switched from the standard state to the speed increasing state. The weak braking state of the side brakes 11R and 11L means that when the rear wheel 2 on the braking side is in a state of being dragged as the vehicle body advances, this dragging action causes
In this state, the rear wheel 2 on the braking side is rotated by overcoming R and 11L.

As shown in FIGS. 4 and 2, the shift lever 31
When the front wheel 1 is steered rightward or leftward over the set angle as described above in the state where the engine is operated to the low speed position L, the spool 16a of the control valve 16 is slid by the cam plate 18 and the oil passage The hydraulic fluid from 28 is supplied to the right or left cylinder 1 from the right or brake ports 36R, 36L.
It is supplied to the 3R and 13L, and the front wheel shift port 37
Is supplied to the front wheel transmission 6.

In this case, the working hydraulic pressure supplied as described above is maintained at the second set pressure P2 by the action of the pressure regulating valve 19. Therefore, as shown by the solid line A2 in FIGS. 9 and 8, the friction clutch 21 of the front wheel transmission 6 is engaged and operated,
The front wheels 1 are driven at a higher speed than the rear wheels 2, and the right or left cylinders 13R, 13L contract to operate the right or left side brakes 11R, 11L in a weak braking state. This makes it possible to make a very small small turn by the pulling action in the turning direction by the increased front wheel 1 and the braking action on the rear wheel 2 on the turning center side. In this case, when the rear wheel 2 on the braking side is dragged along with the turning of the airframe, the rear wheel 2 on the braking side is rotated, so that the rear wheel 2 on the braking side may roughen the ground. Few.

Next, as shown in FIG. 5, the shift lever 31
5 to the middle speed position M (corresponding to the middle speed range of the transmission for traveling), the spool 29 of the switching valve 24 is rotated by a predetermined angle in the clockwise direction of the drawing from the state shown in FIG.
Located at the angle shown in. In this case, the first spool 29
On the arc surface 29d, the portion of the pressure regulating valve 19 that comes into contact with the support member 19c is slightly retracted to the right of the drawing. Then, along with this, the support member 19c also slides to the right in the drawing and the spring 1
The biasing force of 9b is slightly weakened, and the hydraulic pressure supplied to the control valve 16 is maintained at the first set pressure P1 which is lower than the second set pressure P2.

Therefore, in this state, the front wheel 1 is steered to the right or left over a set angle, and the working oil from the oil passage 28 is supplied to the right or left cylinders 13R, 13L and the front wheel transmission 6. In the case of
As shown in FIG. 1, the friction clutch 21 of the front wheel transmission 6 is engaged and operated, and the speed increasing state in which the front wheel 1 is driven at a higher speed than the rear wheel 2 is revealed. On the other hand, the right or left cylinder 13R, 13L does not contract, and the right or left side brake 11R, 11L is not operated to the braking side. As a result, a smooth small turn can be made only by the pulling action of the accelerated front wheels 1 in the turning direction. in this case,
Since the left and right rear wheels 2 are also driven, the rear wheels 2 on the turning center side
The rear wheel 2 on the turning center side without being dragged.
It doesn't hurt the ground.

Next, as shown in FIG. 6, when the speed change lever 31 is operated to the high speed position H (corresponding to the high speed range of the transmission for traveling), the spool 29 of the switching valve 24 changes from the state shown in FIG. Direction is further rotated by a predetermined angle,
It is located at the angle shown in FIG. In this case, the drain hole 29c of the first land portion 29A of the spool 29 communicates with the drain oil passage 39 (which communicates with the drain portion 35 of FIG. 2). As a result, the hydraulic oil from the pump 15 is discharged through the oil passage 23, the drain hole 29c of the first land portion 29A, and the drain oil passage 39.

Therefore, in this state, even if the front wheel 1 is steered rightward or leftward over the set angle, as shown by the chain double-dashed line A4 in FIG. 9 and FIG.
No hydraulic oil is supplied to the R, 13L and the front wheel transmission 6. As a result, the front wheel transmission 6 maintains the standard state during turning, the right or left side brakes 11R and 11L are not operated to the braking side, and the four wheels, the front wheel 1 and the rear wheel 2, are at substantially the same speed. Turning is performed in a driven state.

In the above structure, the front wheel transmission 6 and the side brakes 11R, 11 are arranged in accordance with the shift position of the auxiliary transmission.
Although the three states of L are selected, this agricultural tractor is constructed so that the above-mentioned three states can be selected also by the switching lever 40. Next, this structure will be described. Figure 4
As shown in FIG. 11, the switching lever 40 is arranged on the right side of the steering handle 41 (see FIG. 11) and can be operated at the first position B1, the second position B2, and the third position B3, and can be held at each position. is there. The operating rod 42 is connected to the operating plate 30 fixed to the spool 29 of the switching valve 24, and the upper end of the operating rod 42 is abutted against the lower surface of the switching lever 40.

The state shown in FIG. 4 is a state in which the switching lever 40 is operated and held at the first position B1, and the front wheel transmission 6 is increased during turning according to the operation position of the transmission lever 31 for the auxiliary transmission. In a state in which the side brakes 11R, 11L on the turning center side are operated in a weak braking state (see solid line A2 in FIGS. 9 and 8), the front wheel transmission 6 is switched to a speed increasing state during turning. Side brake 11R,
11L is not operated to the braking side (see the alternate long and short dash line A1 in FIGS. 9 and 8), and the front wheel transmission 6 is not switched to the speed increasing state at the time of turning, and the side brakes 11R and 11L.
Three states are also selected, in which L is not operated to the braking side (see the chain double-dashed line A4 in FIGS. 9 and 8).

Next, in the state shown in FIG. 4, when the switching lever 40 is operated and held at the second position B2, the operation plate 30 is rotated clockwise by a predetermined angle, and the switching valve 24 is operated.
The spool 29 is rotated to the angle shown in FIG. As a result, even when the speed change lever 40 is operated to the low speed position L, the front wheel transmission 6 is switched to the speed increasing state at the time of turning as in the case of the medium speed position M.
R and 11L are in a state where they are not operated to the braking side. When the gear shift lever 31 is operated to the high speed position H in this state, the front wheel transmission 6 is not switched to the speed increasing state during turning, and the side brakes 11R and 11L are not operated to the braking side.

Next, when the switching lever 40 is operated and held at the third position B3, the operation plate 30 is further rotated clockwise in the drawing, and the spool 29 of the switching valve 24 is rotated to the angle shown in FIG. It As a result, even when the speed change lever 40 is operated to the low speed position L and the medium speed position M, the front wheel transmission 6 is not switched to the speed increasing state at the time of turning and the side brakes 11R, 11L is also in a state where it is not operated to the braking side.

With the above structure, when the vehicle is turning (the shift lever 31
Is in the low speed position L, the switching lever 40 is in the first position B1),
Although the side brakes 11R and 11L on the turning center side are configured to be operated in a weak braking state, this agricultural tractor has side brakes 11R and 1L on the turning center side when turning.
The 1L is configured so that it can be switched to a state in which it is operated forcibly. Next, this structure will be described. As shown in FIG. 4, in the second land portion 29B of the spool 29 of the switching valve 24, a second circular arc surface 29e is provided on the side opposite to the first circular arc surface 29d. As a result, when the forced operation state of the side brakes 11R and 11L is to be revealed at the time of turning, the spool 29 is pulled out of the valve unit 22 and inverted 180 degrees, and the valve unit 22 is again turned.
Then, as shown in FIG. 7, the second circular arc surface 29e of the spool 29 is applied to the support member 19c of the pressure regulating valve 19.

In this case, at the angle of the spool 29 shown in FIG. 7, the second arc surface 29e is located on the left side of the drawing with respect to the first arc surface 29d shown in FIG. 19c is pushed further to the left in the drawing than the state shown in FIG. As a result, the spring 19b of the pressure regulating valve 19 is further compressed from the state shown in FIG.
The hydraulic pressure supplied to the control valve 16 by the action of
The third set pressure P3, which is higher than the set pressure P2, is maintained.
In addition, at the three positions of FIGS.
Three other recesses (not shown) for holding the position of the spool 29 by entering the detent ball 43 in 2 are provided on the surface 180 degrees opposite to the recess 29f shown in FIG. ..

In the state shown in FIG. 7 (the shift lever 31 is in the low speed position L and the switching lever 40 is in the first position B1), when the front wheel 1 is steered to the right or left over a set angle or more, FIGS. As indicated by a solid line A3 in FIG. 8, the friction clutch 21 of the front wheel transmission 6 is engaged and operated, and the front wheel 1 is driven at a higher speed than the rear wheel 2, and the right or left cylinder 13R, 13L contracts, and the right or left side brake 11R, 11L is operated to the forced operation state. As a result, a very small small turn can be performed by the increased pulling action in the turning direction by the front wheel 1 and the strong braking action on the rear wheel 2 on the turning center side.

In this case, the side brake 1 on the turning center side
Since 1R and 11L are operated in the forced motion state, even if the rear wheel 2 on the braking side is dragged as the vehicle turns, the rear wheel 2 on the braking side is not rotated. It is possible to make a smaller turn than the turn in the state shown by the solid line A2 in FIG.

Even in the state shown in FIG. 7, if the speed change lever 31 is operated to the medium speed position M, the front wheel transmission 6 is switched to the speed increasing state at the time of turning, and the side brakes 11R, 1R1.
1L is in a state where it is not operated to the braking side (see the alternate long and short dash line A1 in FIG. 9 and FIG. 8), and if the transmission lever 31 is operated to the high speed position H, the front wheel transmission 6 is not switched to the speed increasing state during turning and the side The brakes 11R and 11L are also not operated to the braking side (see the chain double-dashed line A4 in FIGS. 9 and 8).

If the switching lever 40 is operated and held at the first position B1, the front wheel transmission 6 is switched to the speed increasing state at the time of turning according to the operation position of the transmission lever 31 for the auxiliary transmission, as described above. Operated side brake 1 on the turning center side
A state in which 1R and 11L are operated in a forced motion state (see solid line A3 in FIGS. 9 and 8), a front wheel transmission 6 is switched to a speed-up state during turning, and side brakes 11R and 11L are not operated in a braking side. (One-dot chain line A1 in FIGS. 9 and 8)
3), and the state in which the front wheel transmission 6 is not switched to the speed increasing state during turning and the side brakes 11R and 11L are not operated to the braking side (see the chain double-dashed line A4 in FIGS. 9 and 8). To be done.

Next, when the switching lever 40 is operated and held in the second position B2 in the state shown in FIG.
Even when the vehicle is operated to the low speed position L, as in the case of the medium speed position M, the front wheel transmission 6 is switched to the speed increasing state during turning, and the side brakes 11R and 11L are not operated to the braking side. When the gear shift lever 31 is operated to the high speed position H in this state, the front wheel transmission 6 is not switched to the speed increasing state during turning, and the side brakes 11R and 11L are not operated to the braking side. And the switching lever 4
When 0 is operated and held at the third position B3, the high speed position H is obtained even if the speed change lever 40 is operated at the low speed position L and the medium speed position M.
In the same manner as in the above case, the front wheel transmission 6 is not switched to the speed increasing state during turning, and the side brakes 11R and 11L are not operated to the braking side.

[Other Embodiment] In the above embodiment, the control valve 1 is used.
6, the switching valve 24 and the pressure regulating valve 19 are all mechanically operated, but the control valve 16 and the switching valve 24 are electromagnetically operated, and the pressure regulating valve 19 is an electromagnetic proportional pressure reducing valve type. You may. In the above-described embodiment, the operation of the front wheel transmission 6 and the operation of the side brakes 11R and 11L are performed by one control valve 16, and the pressure adjustment of the pressure regulating valve 19 switches the front wheel transmission 6 to the speed increasing state. The state where the side brakes 11R and 11L on the turning center side are operated to the braking side, the state where the front wheel transmission 6 is switched to the speed increasing state and the side brakes 11R and 11L are not operated to the braking side, and the front wheels during turning. The transmission 6 is not switched to the speed increasing state and the side brakes 11R and 11L are not operated to the braking side. this,
Control valve for front wheel transmission 6 and side brakes 11R, 1
A control valve for 1L may be separately provided, and the operation of the two control valves may be mechanically restrained by a stopper or the like according to the shift state of the traveling transmission. Further, in the above-described embodiment, the above-mentioned three states are selected according to the shift position of the auxiliary transmission for traveling that is capable of shifting to high, medium, and low three speeds. The sixth speed and the fifth speed are set as the high speed range, the fourth speed and the third speed are set as the middle speed range, and the second speed and the first speed are set as the low speed range.
The state may be selected.

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

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a linked state of left and right side brakes, a front wheel transmission, a control valve, a switching valve and a pressure regulating valve.

FIG. 2 is a vertical cross-sectional side view of a valve unit incorporating a control valve, a switching valve, and a pressure regulating valve.

3 is a cross-sectional view taken along the line CC of FIG.
View from the bottom to the top of the paper

FIG. 4 is a diagram showing a state of a switching valve, a pressure regulating valve and the like in a state where a shift lever is operated to a low speed position.

FIG. 5 is a diagram showing a state of a switching valve, a pressure regulating valve and the like in a state where a shift lever is operated to a medium speed position.

FIG. 6 is a diagram showing a state of a switching valve, a pressure regulating valve and the like in a state where a shift lever is operated to a high speed position.

FIG. 7 is a view showing the switching valve angle set to 180 in the state shown in FIG.
Figure showing the state of the switching valve and pressure regulating valve etc.

FIG. 8 is a diagram illustrating a first operation in which the front wheel transmission is switched to a speed-up state.
The set pressure, the front wheel transmission is switched to the speed increasing state and the side brake is operated to the weak braking state. The second set pressure, the front wheel transmission is switched to the speed increasing state, and the side brake is operated to the forced operation state. The figure which shows the relationship between the pressure of three sets of 3rd setting pressure, and the operation position of a gearshift lever.

FIG. 9 is a table showing the relationship between the two positions, that is, the state where the front wheel transmission is switched to the speed increasing state and the state where the side brake is operated to the braking side, and the operation position of the shift lever.

FIG. 10 is a vertical sectional side view of a connection state of a side brake pedal and a side brake and a cylinder for connection.

FIG. 11 is an overall side view of an agricultural tractor.

[Explanation of symbols]

1 Front Wheel 2 Rear Wheel 6 Front Wheel Transmission 11R, 11L Side Brake 16 First Operating Means, Second Operating Means 18 Steering Angle Detecting Means 19, 24 First Checking Means, Second Checking Means, Third Checking Means H For Running High speed range of the transmission M Medium speed range of the transmission L Low speed range of the transmission

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[Procedure amendment]

[Submission date] April 12, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Full text

[Correction method] Change

[Correction content]

[Document name] Statement

[Title of Invention] Four-wheel drive work vehicle

[Claims]

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a four-wheel drive type work vehicle represented by an agricultural tractor, a riding type rice transplanter and the like.

[0002]

2. Description of the Related Art In an agricultural tractor, which is an example of a four-wheel drive type work vehicle, a standard in which front wheels and rear wheels are driven at substantially the same speed, as disclosed in, for example, Japanese Patent Laid-Open No. 243429/1993. State, and the front wheel transmission (6 in FIG. 1 of the above-mentioned publication), which can be switched to a speed increasing state in which the front wheels are driven at a higher speed than the rear wheels, and each of the left and right rear wheels can be independently brake-operated. Some have a pair of left and right side brakes (13R, 13L in FIG. 1 of the above publication). In this case, when the front wheels are steered from the straight ahead position to the right or left over the set angle, the front wheel transmission is automatically switched from the standard state to the speed-up state, and the side brakes on the turning center side are automatically changed. It is configured to be operated on the braking side. As a result, the pulling action of the front wheels, which has been accelerated by the front wheel transmission, in the turning direction and the braking action on the rear wheels on the turning center side enable a very small small turn turning centering on the rear wheels on the turning center side. Become.

[0003]

In the case of the structure described above, the front wheel transmission is switched to the speed-increasing state and the side brake on the turning center side is operated to the braking side when turning at a high speed. If so, a very small small turn is made in the high speed running state, and thus such a very small small turn must be made in the low speed running state. Therefore, in the configuration of the above publication, a manually operated switching valve that prevents the front wheel transmission from being switched from the standard state to the speed-increasing state during turning and prevents the side brake on the turning center side from being operated toward the braking side. (25 in FIG. 1 of the above publication). In this case, the front wheel transmission is not switched operation speed increasing state by operating the pre-switching valve in the high-speed running state, the parking brake it is also necessary to switch the operation to a state that is not operated to the braking side, but faster Running
The operator may forget to operate the switching valve when in line.
There is room for improvement in terms of operability.

Further, in the configuration of the above publication, both the front wheel transmission and the side brake are automatically operated during turning by operating the switching valve (acceleration side and braking side), and front wheel shifting during turning. It is possible to switch between two states in which both the device and the side brake are not operated.
As a result, whether the operator should operate both the front wheel transmission and the side brakes automatically during the medium speed traveling state between the high speed traveling state and the low speed traveling state, You may be confused about whether to operate both side brakes so that they are not operated. Therefore, if both the front wheel transmission and the side brakes are automatically operated in the middle-speed traveling state, a small turn may be suddenly made when turning. On the contrary, if both the front wheel transmission and the side brake are not operated in the middle speed running state, there may be a case where a small turn cannot be performed. The present invention relates to a four-wheel drive work vehicle configured to automatically operate a front wheel transmission and side brakes when turning, and switches to a state in which both the front wheel transmission and side brakes are not operated during high-speed traveling. It is an object of the present invention to be configured so that an operation can be performed without forgetting, and a small turning turn suitable for a medium speed running state can be performed.

[0005]

A feature of the present invention is that the four-wheel drive type working vehicle as described above is configured as follows. That is, the front wheel transmission that can be switched between a standard state in which the front wheels and the rear wheels are driven at substantially the same speed and a speed increase state in which the front wheels are driven at a higher speed than the rear wheels, and the pair of left and right rear wheels A pair of left and right side brakes that can brake the selected one, steering angle detection means that detects the left and right steering angles of the front wheels from the straight ahead position, and the front wheels steer from the straight ahead position to the left or right beyond the set angle. When operated, the first operation means for switching the front-wheel transmission from the standard state to the speed-increasing state in conjunction with this steering operation, and the front wheels are steered from the straight-ahead position to the left or right over a set angle. And a second operating means for operating the turning center side of the side brakes to the braking side in conjunction with this steering operation, and the transmission has a low speed.
When operated to the area, the first and second operations are linked with this operation.
The operation of switching the front wheel transmission to the speed increasing state by the operating means,
And the operation of the side brake on the turning center side to the braking side is permitted.
When the first restraint means and the transmission are operated in the medium speed range,
In conjunction with this operation, the front wheel transmission by the first operating means
The switching operation to the speed-up state is permitted, and the second operation means
Operation of the side brake on the turning center side to the braking side.
1 Braking force of the side brake on the turning center side by the restraint means
Second restraint means that allows a lower braking force than that for running
When the transmission of is operated in the high speed range,
Speed increasing state of the front wheel transmission by the first and second operating means
Changeover operation and side brake control on the turning center side
And a third restraint means for restraining restraint on the operation side.
It

[0006]

With the above-mentioned structure, when the operator shifts the traveling transmission to a high speed range (corresponding to a high speed traveling state), the front wheel transmission is switched from the standard state to the speed increasing state during turning. The side brake on the turning center side is not operated to the braking side . Conversely, if the operator shifts the traveling transmission to a low speed range (corresponding to a low speed traveling state), the front wheel transmission is switched from the standard state to the speed increasing state during turning, and the side brake on the center side of the turning is operated. Is also operated on the braking side. This makes it possible to perform a very small small-turn turn centered on the rear wheel on the turning center side by the pulling action of the front wheel in the turning direction, which has been accelerated by the front wheel transmission, and the braking action on the rear wheel on the turning center side . is there.
As described above, the front wheel transmission and the side brakes are both automatically operated (in a high-speed traveling state) and both are operated (in a low-speed traveling state) automatically in conjunction with the gear shifting operation performed by the operator. ) Is performed, the switching operation to a state in which neither the front wheel transmission nor the side brake is operated is never forgotten during high-speed traveling.

When the worker shifts the transmission for traveling to the medium speed range (corresponding to the medium speed traveling state), the front wheel transmission is switched from the standard state to the speed increasing state during turning. The side brake on the turning center side is not operated by the braking side. Comparing the turning using only the front wheel transmission and the turning using only the side brakes,
When turning using only the front wheel transmission, all four front and rear wheels are driven, so the increased front wheel pulling action in the turning direction enables smooth small turns without ruining the ground. Become. On the other hand, when turning using only the side brakes, the rear wheels on the turning center side are in a substantially stopped state by the side brakes, so a small turn can be made around the rear wheels on the turning center side. It is possible to turn smaller than when using only the front wheel transmission. However, there are many cases where the rear wheel on the turning center side under braking is dragged to damage the ground.
Therefore, when comparing turning using only the front wheel transmission and turning using only the side brakes, when turning in the medium speed range of the transmission for traveling, turning is performed only by the speed increasing action of the front wheel transmission. Will not damage the ground as well
This is a favorable state in terms of turning performance. In this case, since the front wheel transmission is operated and the side brake is not operated automatically in conjunction with the gear shift operation performed by the operator, the operation of switching to the above state is forgotten when the vehicle is running at medium speed. It will not be done.

[0008]

As described above, at the time of turning in a high speed running state, the front wheel transmission is not automatically switched to the speed increasing state, and the side brake on the center side of the turning is always automatically switched to the state not being operated to the braking side. Can be configured to be operated
Can improve the operability of the four-wheel drive work vehicle.
It was Further, when the vehicle is turning in the medium speed running state, only the front wheel transmission is switched to the speed increasing state so that the turning can be performed at a high speed and at a low speed because the turning is not so rapid and the ground is not roughened. In the middle of running state
It was possible to improve the turning performance when turning in the state.
Further, since appropriate turning is automatically set for each of the high speed traveling state, the medium speed traveling state and the low speed traveling state, it is possible to improve the turning performance of the work vehicle as a whole.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. 1 and 11 show an agricultural tractor which is an example of a four-wheel drive type work vehicle. An engine 3 is provided at the front part of a vehicle body supported by a pair of left and right front wheels 1 and a pair of left and right rear wheels 2, and a mission is provided at the rear part. An agricultural tractor is provided with the case 4. The power from the engine 3 is the mission case 4
Main transmission (multi-stage gear shift type) (not shown),
Also, the power is transmitted from the rear wheel differential mechanism 5 to the left and right rear wheels 2 via an auxiliary transmission (a high, middle, low, and low gear shift type, which corresponds to a traveling transmission) (not shown). Then, the power branched from immediately before the rear wheel differential mechanism 5 is transmitted to the left and right front wheels 1 via the front wheel transmission 6, the front wheel output shaft 7, and the front wheel differential mechanism 8.

The front wheel transmission 6 shown in FIG. 1 has a normal state in which the front wheel 1 is driven at substantially the same speed as the rear wheel 2, and a state in which the front wheel 1 is driven at a higher speed than the rear wheel 2. It is possible to perform switching operation between two states, that is, a transmission speed increasing state. As shown in FIG. 1, the shift member 9 for two-state switching operation is a spring 10
Is urged toward the side of engagement with the standard gear 20, and the shift member 9 is normally engaged with the standard gear 20 to be in the standard state. Then, when hydraulic oil is supplied into an oil chamber (not shown) formed between the shift member 9 and the standard gear 20, the shift member 9 slides to the left side of the drawing and the friction clutch 21 is pressed and operated. A speed-up state can be obtained.

As shown in FIG. 2, with respect to the left and right rear wheels 2,
Side brakes 11 that can independently brake each rear wheel 2
R and 11L are provided. As shown in FIGS. 1 and 10, the side brake pedal 12 is provided on the right side of the floor surface of the control section.
A pair of left and right R and 12L are arranged. The left and right side brake pedals 12R and 12L and the side brake 11 are arranged.
R and 11L are interlockingly connected via the cylinders 13R and 13L and the linkage rod 14.

With the above structure, the left and right side brake pedals 12R and 11L can be independently operated by depressing the left and right side brake pedals 12R and 12L. Then, as shown in FIG. 10, the cylinders 13R and 13L are urged toward the extension side by the spring 13a, and by supplying hydraulic oil to contract the cylinders 13R and 13L, the left and right side brakes 11R and
It is possible to operate 11L to the braking side.

Next, the operation of steering the front wheel 1 and the linkage between the left and right side brakes 11R and 11L and the front wheel transmission 6 will be described. As shown in FIGS. 1 and 2, the pump 15
From the oil is supplied to the left and right side brakes 11R and 11L and the front wheel transmission 6 via the oil passage 28 in the block-shaped valve unit 22 and the control valve 16 (corresponding to the first and second operating means). Has been done. The control valve 16 includes an oil chamber between the shift member 9 and the standard gear 20 in the front wheel transmission 6, and the left and right side brake pedals 12R and 1R.
The straight traveling position 16N in which the 2L cylinders 13R, 13L are in an oil draining state, hydraulic oil from the pump 15 is supplied to the oil chamber of the front wheel transmission 6 and the right cylinder 13R, and the left cylinder 13L is in an oil draining state. Turning position 16R, and
The hydraulic oil is supplied to the oil chamber of the front wheel transmission 6 and the left cylinder 13
It is a three-position switching type of a left turning position 16L that supplies oil to L and puts the right cylinder 13R in an oil draining state.

As shown in FIGS. 1 and 2, a fan-shaped cam plate 18 (corresponding to steering angle detecting means) is fixed to a pitman arm 17 for steering operation of the front wheels 1, and a control valve 16 is provided.
Of the spool 16a comes into contact with the cam plate 18,
A spring 16b for urging a toward the contact side is provided. The state shown in FIG. 1 and FIG. 2 is a state in which the front wheel 1 is operated to the straight traveling position, and the control valve 16 is operated to the straight traveling position 16N. In this state, the hydraulic oil from the oil passage 28 is discharged via the drain oil passages 33 and 34 and the drain portion 35. As a result, the left and right side brakes 11
R and 11L are in the non-braking state, the shift member 9 of the front wheel transmission 6 is engaged with the standard gear 20, and the front wheel 1 is in the standard state in which the rear wheel 2 is driven at substantially the same speed.

When the front wheel 1 is steered to the right from the state shown in FIGS. 1 and 2 over a set angle, the spool 16a of the control valve 16 is pushed by the cam plate 18 to the right in the drawing to the right turning position. 16R (see FIG. 1). As a result, the hydraulic oil from the oil passage 28 is supplied from the right brake port 36R to the right cylinder 13R and also supplied from the front wheel transmission port 37 to the front wheel transmission 6. Therefore, the friction clutch 21 of the front wheel transmission 6 is engaged and operated, so that the front wheel 1 is driven at a higher speed than the rear wheel 2, and the right cylinder 13R contracts to operate the right side brake 11R. It is operated on the braking side.

On the contrary, from the state shown in FIG. 1 and FIG.
When the steering wheel is turned to the left over a set angle, the spool 16a of the control valve 16 moves to the left side of the drawing, and the left turning position 16L is reached.
(See FIG. 1). As a result, the hydraulic oil from the oil passage 28 is supplied from the left brake port 36L to the left cylinder 13L and also supplied from the front wheel transmission port 37 to the front wheel transmission 6. Therefore, the friction clutch 21 of the front wheel transmission 6 is engaged and operated so that the front wheel 1 is driven at a higher speed than the rear wheel 2, and the left cylinder 13 is driven.
L contracts and the left side brake 11L is operated to the braking side.

In this agricultural tractor, the automatic operation of the side brakes 11R and 11L to the braking side as described above and the speed increase of the front wheel transmission 6 are performed in accordance with the shift position of the auxiliary transmission in the transmission case 4. It is configured to switch between a state in which an operation is performed on the state side and a state in which the operation is not performed. Next, this switching structure will be described. Figure 1,
As shown in FIGS. 2 and 3, the hydraulic oil from the pump 15 is supplied to the oil passage 23 of the valve unit 22 and the rotary switching valve 24.
(Corresponding to 1st, 2nd, 3rd restraint means), oil passages 25, 26, 2
It is supplied to the control valve 16 via 7, 28.

As shown in FIGS. 2 and 3, a pressure regulating valve 19 (corresponding to the first, second and third restraint means) is connected to the oil passage 26. The pressure regulating valve 19 includes a valve body 19a and a valve body 19a.
And a support member 19c for supporting the rear end of the spring 19b. As a result, when the pressure in the oil passage 26 exceeds the pressure set by the spring 19b, the valve element 19a opens to the right on the paper surface and the working oil is discharged through the drain oil passage 38.
The operating hydraulic pressure supplied to 6 is determined by the urging force of the spring 19b of the pressure regulating valve 19, that is, the position of the support member 19c of the spring 19b.

The spool 29 of the switching valve 24 is shown in FIGS.
As shown in FIG. 1, a first land portion 29A having a pair of notches 29a and 29b and a drain hole 29c, and a second land portion 29B having a first arc surface 29d and a second arc surface 29e are provided. The rear end of the support member 19c of the pressure regulating valve 19 is abutted against the first arc surface 29d, and the position of the support member 19c is determined. Then, at the three positions shown in FIGS.
Three recesses 29f for holding the position of the spool 29 by receiving the detent balls 43 therein are provided at the rear end of the spool 29. As shown in FIGS. 3 and 4, the operation plate 30 is fixed to the tip of the spool 29 of the switching valve 24 outside the valve unit 22, and the shift lever 31 and the operation plate 30 for the auxiliary transmission are connected by a wire. They are connected by 32. Further, a spring (not shown) for urging the spool 29 counterclockwise in the drawing is provided, and the urging force of this spring is set to be stronger than the urging force of the spring 19b and the holding action of the detent ball 43. Has been done.

The state shown in FIG. 4 and FIG.
1 is in the state of operating the low speed position L (corresponding to the low speed range of the transmission for traveling). In this state, the pump 15
From the oil passage 23, the first cutout portion 29a in the spool 29 of the switching valve 24, and the oil passages 25, 26, 27, 2
It is supplied to the control valve 16 via 8. Then, the support member 19c of the pressure regulating valve 19 is connected to the first arc surface 2 of the spool 29.
9d is pressed to the left side of the drawing, and the spring 19b of the pressure regulating valve 19 is compressed and the action of the pressure regulating valve 19 causes the working hydraulic pressure supplied to the control valve 16 to reach a second set pressure P2 described later. Has been maintained.

As shown in FIG. 8, the front wheel transmission 6 is switched from the standard state to the speed increasing state at a relatively low first set pressure P1, and the side brake 1 is operated at this first set pressure P1.
1R and 11L are operated in a fine braking state with very low braking force.
Be done. Then, the second set pressure P2 higher than the first set pressure P1
The side brakes 11R and 11L are
The front wheel transmission 6 is also switched from the standard state to the speed increasing state by operating in a weak braking state having a braking force higher than that in the dynamic state .
The weak braking state of the side brakes 11R and 11L is
When the rear wheel 2 on the braking side is dragged as the aircraft progresses, this dragging action overcomes the side brakes 11R, 11L and the rear wheel 2 on the braking side is rotated. ..

As shown in FIGS. 4 and 2, the shift lever 31
When the front wheel 1 is steered rightward or leftward over the set angle as described above in the state where the engine is operated to the low speed position L, the spool 16a of the control valve 16 is slid by the cam plate 18 and the oil passage The hydraulic fluid from 28 is supplied to the right or left cylinder 1 from the right or brake ports 36R, 36L.
It is supplied to the 3R and 13L, and the front wheel shift port 37
Is supplied to the front wheel transmission 6.

In this case, the working hydraulic pressure supplied as described above is maintained at the second set pressure P2 by the action of the pressure regulating valve 19. Therefore, as shown by the solid line A2 in FIGS. 9 and 8, the friction clutch 21 of the front wheel transmission 6 is engaged and operated,
The front wheels 1 are driven at a higher speed than the rear wheels 2, and the right or left cylinders 13R, 13L contract to operate the right or left side brakes 11R, 11L in a weak braking state. As a result, a very small small turn can be performed by the increased pulling action in the turning direction by the front wheel 1 and the weak braking action on the rear wheel 2 on the turning center side. In this case, when the rear wheel 2 on the braking side is dragged along with the turning of the airframe, the rear wheel 2 on the braking side is rotated, so that the rear wheel 2 on the braking side may roughen the ground. Few.

Next, as shown in FIG. 5, the shift lever 31
5 to the middle speed position M (corresponding to the middle speed range of the transmission for traveling), the spool 29 of the switching valve 24 is rotated by a predetermined angle in the clockwise direction of the drawing from the state shown in FIG.
Located at the angle shown in. In this case, the first spool 29
On the arc surface 29d, the portion of the pressure regulating valve 19 that comes into contact with the support member 19c is slightly retracted to the right of the drawing. Then, along with this, the support member 19c also slides to the right in the drawing and the spring 1
The biasing force of 9b is slightly weakened, and the hydraulic pressure supplied to the control valve 16 is maintained at the first set pressure P1 which is lower than the second set pressure P2.

Therefore, in this state, the front wheel 1 is steered to the right or left over a set angle, and the working oil from the oil passage 28 is supplied to the right or left cylinders 13R, 13L and the front wheel transmission 6. In the case of
As shown in FIG. 1, the friction clutch 21 of the front wheel transmission 6 is engaged and operated to bring up the speed increasing state in which the front wheel 1 is driven at a higher speed than the rear wheel 2 , and the right or left cylinder 13R, 1
By 3L, the right or left side brake 11R, 11L
It is operated in a slight braking state. By this, before being accelerated
Pulling action in the turning direction by wheel 1 and turning center side
A slight turning action on the rear wheel 2 enables a smooth small turn.
You can do it. In this case, the rear wheel 2 on the turning center side is slightly braked.
However, since the left and right rear wheels 2 are sufficiently driven,
The rear wheel 2 on the turning center side is not dragged,
Things that would damage the ground with the rear wheel 2 on the turning center side
There is no.

Next, as shown in FIG. 6, when the speed change lever 31 is operated to the high speed position H (corresponding to the high speed range of the transmission for traveling), the spool 29 of the switching valve 24 changes from the state shown in FIG. Direction is further rotated by a predetermined angle,
It is located at the angle shown in FIG. In this case, the drain hole 29c of the first land portion 29A of the spool 29 communicates with the drain oil passage 39 (which communicates with the drain portion 35 of FIG. 2). As a result, the hydraulic oil from the pump 15 is discharged through the oil passage 23, the drain hole 29c of the first land portion 29A, and the drain oil passage 39.

Therefore, in this state, even if the front wheel 1 is steered rightward or leftward over the set angle, as shown by the chain double-dashed line A4 in FIG. 9 and FIG.
No hydraulic oil is supplied to the R, 13L and the front wheel transmission 6. As a result, the front wheel transmission 6 maintains the standard state during turning, the right or left side brakes 11R and 11L are not operated to the braking side, and the four wheels, the front wheel 1 and the rear wheel 2, are at substantially the same speed. Turning is performed in a driven state.

In the above structure, the front wheel transmission 6 and the side brakes 11R, 11 are arranged in accordance with the shift position of the auxiliary transmission.
Although the three states of L are selected, this agricultural tractor is constructed so that the above-mentioned three states can be selected also by the switching lever 40. Next, this structure will be described. Figure 4
As shown in FIG. 11, the switching lever 40 is arranged on the right side of the steering handle 41 (see FIG. 11) and can be operated at the first position B1, the second position B2, and the third position B3, and can be held at each position. is there. The operating rod 42 is connected to the operating plate 30 fixed to the spool 29 of the switching valve 24, and the upper end of the operating rod 42 is abutted against the lower surface of the switching lever 40.

The state shown in FIG. 4 is a state in which the switching lever 40 is operated and held at the first position B1, and the front wheel transmission 6 is increased during turning according to the operation position of the transmission lever 31 for the auxiliary transmission. In a state in which the side brakes 11R, 11L on the turning center side are operated in a weak braking state (see solid line A2 in FIGS. 9 and 8), the front wheel transmission 6 is switched to a speed increasing state during turning. Side brake 11R,
The state in which 11L is operated in the slight braking state (see the alternate long and short dash line A1 in FIGS. 9 and 8) and the front wheel transmission 6 during turning.
Is not switched to the speed-up state and the side brakes 11R, 1
Three states of 1L are also selected which are not operated to the braking side (see the chain double-dashed line A4 in FIGS. 9 and 8).

Next, in the state shown in FIG. 4, when the switching lever 40 is operated and held at the second position B2, the operation plate 30 is rotated clockwise by a predetermined angle, and the switching valve 24 is operated.
The spool 29 is rotated to the angle shown in FIG. As a result, even when the speed change lever 40 is operated to the low speed position L, the front wheel transmission 6 is switched to the speed increasing state at the time of turning, similarly to the case of the medium speed position M, and the side brakes 11R,
11L will be in the state of being operated to the fine braking state. And
If the speed change lever 31 is operated to the high speed position H in this state,
When turning, the front wheel transmission 6 is not switched to the speed increasing state, and the side brakes 11R and 11L are not operated to the braking side.

Next, when the switching lever 40 is operated and held at the third position B3, the operation plate 30 is further rotated clockwise in the drawing, and the spool 29 of the switching valve 24 is rotated to the angle shown in FIG. It As a result, even when the speed change lever 40 is operated to the low speed position L and the medium speed position M, the front wheel transmission 6 is not switched to the speed increasing state at the time of turning and the side brakes 11R, 11L is also in a state where it is not operated to the braking side.

With the above structure, when the vehicle is turning (the shift lever 31
Is in the low speed position L, the switching lever 40 is in the first position B1),
Although the side brakes 11R and 11L on the turning center side are configured to be operated in a weak braking state, this agricultural tractor has side brakes 11R and 1L on the turning center side when turning.
The 1L is configured so that it can be switched to a state in which it is operated forcibly. Next, this structure will be described. As shown in FIG. 4, in the second land portion 29B of the spool 29 of the switching valve 24, a second circular arc surface 29e is provided on the side opposite to the first circular arc surface 29d. As a result, when the forced operation state of the side brakes 11R and 11L is to be revealed at the time of turning, the spool 29 is pulled out of the valve unit 22 and inverted 180 degrees, and the valve unit 22 is again turned.
Then, as shown in FIG. 7, the second circular arc surface 29e of the spool 29 is applied to the support member 19c of the pressure regulating valve 19.

In this case, at the angle of the spool 29 shown in FIG. 7, the second arc surface 29e is located on the left side of the drawing with respect to the first arc surface 29d shown in FIG. 19c is pushed further to the left in the drawing than the state shown in FIG. As a result, the spring 19b of the pressure regulating valve 19 is further compressed from the state shown in FIG.
The hydraulic pressure supplied to the control valve 16 by the action of
The third set pressure P3, which is higher than the set pressure P2, is maintained.
In addition, at the three positions of FIGS.
Three other recesses (not shown) for holding the position of the spool 29 by entering the detent ball 43 in 2 are provided on the surface 180 degrees opposite to the recess 29f shown in FIG. ..

In the state shown in FIG. 7 (the shift lever 31 is in the low speed position L and the switching lever 40 is in the first position B1), when the front wheel 1 is steered to the right or left over a set angle or more, FIGS. As indicated by a solid line A3 in FIG. 8, the friction clutch 21 of the front wheel transmission 6 is engaged and operated, and the front wheel 1 is driven at a higher speed than the rear wheel 2, and the right or left cylinder 13R, 13L contracts, and the right or left side brake 11R, 11L is operated to the forced operation state. As a result, a very small small turn can be performed by the increased pulling action in the turning direction by the front wheel 1 and the strong braking action on the rear wheel 2 on the turning center side.

In this case, the side brake 1 on the turning center side
Since 1R and 11L are operated in the forced motion state, even if the rear wheel 2 on the braking side is dragged as the vehicle turns, the rear wheel 2 on the braking side is not rotated. It is possible to make a smaller turn than the turn in the state shown by the solid line A2 in FIG.

Even in the state shown in FIG. 7, if the speed change lever 31 is operated to the medium speed position M, the front wheel transmission 6 is switched to the speed increasing state at the time of turning, and the side brakes 11R, 1R1.
1L is in the state of being operated to the fine braking state (see the alternate long and short dash line A1 in FIGS. 9 and 8), and the transmission lever 31 is moved to the high speed position H.
If it is operated to, the front wheel transmission 6 is not switched to the speed increasing state during turning, and the side brakes 11R and 11L are not operated to the braking side (see the chain double-dashed line A4 in FIGS. 9 and 8).
Becomes

If the switching lever 40 is operated and held at the first position B1, the front wheel transmission 6 is switched to the speed increasing state at the time of turning according to the operation position of the transmission lever 31 for the auxiliary transmission, as described above. Operated side brake 1 on the turning center side
In the state where 1R and 11L are forcibly operated (see solid line A3 in FIGS. 9 and 8), the front wheel transmission 6 is switched to the speed increasing state during turning, and the side brakes 11R and 11L are slightly moved.
The state of being operated to the braking state (dotted line A in FIGS. 9 and 8)
1) and the state in which the front wheel transmission 6 is not switched to the speed increasing state during turning and the side brakes 11R and 11L are not operated to the braking side (see the chain double-dashed line A4 in FIGS. 9 and 8). To be selected.

Next, when the switching lever 40 is operated and held in the second position B2 in the state shown in FIG.
Even when the vehicle is operated to the low speed position L, as in the case of the medium speed position M, the front wheel transmission 6 is switched to the speed increasing state at the time of turning.
The side brakes 11R and 11L are operated to the fine braking state.
Will be in a state where When the gear shift lever 31 is operated to the high speed position H in this state, the front wheel transmission 6 is not switched to the speed increasing state during turning, and the side brakes 11R and 11L are not operated to the braking side. When the switching lever 40 is operated and held at the third position B3, the speed change lever 40
Even if the vehicle is operated to the low speed position L and the medium speed position M, as in the case of the high speed position H, the front wheel transmission 6 is not switched to the speed increasing state during turning, and the side brakes 11R and 11L are not operated to the braking side. It becomes a state.

[Other Embodiment] In the above embodiment, the control valve 1 is used.
6, the switching valve 24 and the pressure regulating valve 19 are all mechanically operated, but the control valve 16 and the switching valve 24 are electromagnetically operated, and the pressure regulating valve 19 is an electromagnetic proportional pressure reducing valve type. You may. In the above-described embodiment, the operation of the front wheel transmission 6 and the operation of the side brakes 11R and 11L are performed by one control valve 16, and the pressure adjustment of the pressure regulating valve 19 switches the front wheel transmission 6 to the speed increasing state. The side brakes 11R and 11L on the turning center side are operated to a strong or weak braking state, and the front wheel transmission 6 is switched to a speed increasing state to operate the side brakes 11R and 11L to a slight braking state.
Three states are selected: a state in which the front wheel transmission 6 is operated and a state in which the side brakes 11R and 11L are not operated toward the braking side because the front wheel transmission 6 is not switched to the speed increasing state during turning.
This is the control valve for the front wheel transmission 6 and the side brake 1
The control valves for 1R and 11L may be separately provided, and the operation of the two control valves may be mechanically restrained by a stopper or the like according to the shift state of the transmission for traveling. Further, in the above-described embodiment, the above-mentioned three states are selected according to the shift position of the auxiliary transmission for traveling that is capable of shifting to high, medium, and low three speeds. The sixth speed and the fifth speed may be set as the high speed range, the fourth speed and the third speed may be set as the medium speed range, and the second speed and the first speed may be set as the low speed range, and the three states may be selected based on these. ..

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

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a linked state of left and right side brakes, a front wheel transmission, a control valve, a switching valve and a pressure regulating valve.

FIG. 2 is a vertical cross-sectional side view of a valve unit incorporating a control valve, a switching valve, and a pressure regulating valve.

3 is a cross-sectional view taken along the line CC of FIG.
View from the bottom to the top of the paper

FIG. 4 is a diagram showing a state of a switching valve, a pressure regulating valve and the like in a state where a shift lever is operated to a low speed position.

FIG. 5 is a diagram showing a state of a switching valve, a pressure regulating valve and the like in a state where a shift lever is operated to a medium speed position.

FIG. 6 is a diagram showing a state of a switching valve, a pressure regulating valve and the like in a state where a shift lever is operated to a high speed position.

FIG. 7 is a view showing the switching valve angle set to 180 in the state shown in FIG.
Figure showing the state of the switching valve and pressure regulating valve etc.

FIG. 8: The front wheel transmission is switched to the speed increasing state and the side
The first set pressure at which the brake is operated in the fine braking state, the second set pressure at which the front wheel transmission is operated at the speed increasing state and the side brake is operated at the weak braking state, and the operation at the front wheel transmission is switched to the speed increasing state. FIG. 3 is a diagram showing a relationship between three sets of pressures of a third set pressure at which the side brake is operated to a forced operation state and an operation position of a shift lever.

FIG. 9 is a state in which the front wheel transmission is switched to an accelerating state, and the side brakes are in a fine braking mode, a weak braking mode, and a forced braking mode.
Show the relationship between each operated state and the shift lever operating position.
Figure

FIG. 10 is a vertical sectional side view of a connection state of a side brake pedal and a side brake and a cylinder for connection.

FIG. 11 is an overall side view of an agricultural tractor.

[Explanation of reference numerals] 1 front wheel 2 rear wheel 6 front wheel transmission 11R, 11L side brake 16 first operating means, second operating means 18 steering angle detecting means 19, 24 first restraining means, second restraining means, third Checking mechanism H High speed range of the transmission for traveling M Medium speed range of the transmission for traveling L Low speed range of the transmission for traveling

[Procedure Amendment 2]

[Document name to be corrected] Drawing

[Correction target item name] Figure 8

[Correction method] Change

[Correction content]

[Figure 8]

[Procedure 3]

[Document name to be corrected] Drawing

[Correction target item name] Figure 9

[Correction method] Change

[Correction content]

[Figure 9]

Claims (1)

[Claims] 1. A switching operation between a normal state in which a front wheel (1) and a rear wheel (2) are driven at substantially the same speed and a speed-up state in which a front wheel (1) is driven at a higher speed than a rear wheel (2). A flexible front wheel transmission (6) and a pair of left and right side brakes (11) capable of braking selected one of the left and right rear wheels (2).
R), (11L) and steering angle detection means (18) for detecting the left and right steering angles of the front wheel (1) from the straight ahead position.
When the front wheel (1) is steered from the straight-ahead position to the right or left by a set angle or more, the front wheel transmission (6) is switched from the standard state to the speed-up state in conjunction with the steering operation. When the first operating means (16) and the front wheel (1) are steered from the straight-ahead position to one of the left and right over a set angle, the side brakes (11R),
2nd which operates the turning center side of (11L) to the braking side
A first operation means (16) for stopping the operation of the first and second operation means (16) in cooperation with the operation when the traveling transmission is operated in the high speed range (H). When the first restraint means (19) and (24) and the speed change device are operated in the medium speed range (M), the first operation is performed in conjunction with this operation.
The operation means (16) is allowed to operate, and the second operation means (1
Second restraint means (19), (2) for stopping the operation of 6)
4) and when the transmission is operated in the low speed range (L),
In conjunction with this operation, the first and second operating means (16)
Four-wheel drive work vehicle provided with third restraint means (19), (24) for permitting the operation of the.