JPH08276758A - Four-wheel drive work vehicle - Google Patents

Abstract

PURPOSE: To prevent damage of the ground by a drag due to stopping a right or left rear wheel in the turn center side, in a four-wheel drive work vehicle constituted in such a manner that a front wheel transmission is automatically switched to be operated in an accelerating condition at turn operating time to automatically operate to a braking side a right or left side brake in the turn center side by a right or left actuator. CONSTITUTION: In this constitution, right/left rotational speed sensors 18R, 18L of detecting a rotational speed of right/left rear wheels 2 are provided, in a condition that a right or left side brake 11R, 11L in the turn center side is operated to a braking side at turn operating time, when a rotational speed of the right or left rear wheel 2 on the turn center side is decreased to a preset value or less, so as to automatically weaken operating force to a braking side of the right or left side brake 11R, 11L on the turn center side by a right or left actuator 13R, 13L.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure for automatically braking the right and left rear wheels in a four-wheel drive work vehicle.

[0002]

2. Description of the Related Art An agricultural tractor, which is an example of a four-wheel drive type work vehicle, has a structure as disclosed in, for example, Japanese Unexamined Patent Publication No. 5-16833. In this structure, the front wheels (5 in FIG. 1 of the publication) and the rear wheels (3 in FIG. 1 of the publication) are driven at substantially the same speed, and the front wheels are driven faster than the rear wheels. Front wheel transmission (6 in FIG. 1 of the above publication) which can be freely switched to the increased speed state
And a right side brake capable of braking the right rear wheel (8R in FIG. 1 of the publication) and a right actuator capable of operating the right side brake to the braking side (see FIGS. 1 and 3 of the publication). 9R), a left side brake capable of braking the left rear wheel (8L in FIG. 1 of the publication), and a left actuator capable of operating the left side brake to the braking side (see FIGS. 1 and 3 of the publication). 9L).

As a result, when the front wheels are steered from the straight-ahead position to the right or left by a set angle or more to perform the turning operation of the body, the front wheel transmission is automatically changed from the standard state to the speed-increasing state by the operating means. Switching is performed, and the right or left side brake on the turning center side is automatically operated to the braking side by the right or left actuator. As described above, the small turn of the airframe can be performed by the speed increasing action of the front wheels and the braking action on the rear wheels on the turning center side.

[0004]

As described above, if the structure is such that the right or left side brake on the turning center side is automatically operated to the braking side during the turning operation of the airframe, the turning center is particularly effective when the ground is soft. The operating force to the braking side of the right or left actuator on the left side may be too strong, and the right or left rear wheel on the turning center side may stop. As a result, the right or left rear wheel on the side of the stopped turning center may be dragged, and the ground may be damaged. In the above-mentioned structure, the right or left actuator is used only for operating the right or left side brake to the braking side at the time of turning operation of the airframe, so improvement in terms of multipurpose use of this right or left actuator is also possible. There is room.

According to the present invention, the front wheel transmission is automatically switched from the standard state to the speed increasing state during the turning operation of the machine body, and the right or left side brake on the turning center side is automatically set to the braking side by the right or left actuator. An object of the present invention is to provide a four-wheel drive type work vehicle configured to be operated so as to eliminate a state in which a rear wheel on a turning center side is stopped and dragged so that the right and left actuators can be used for multiple purposes.

[0006]

A feature of the present invention is that the four-wheel drive type working vehicle as described above is configured as follows. [1] A front wheel transmission capable of switching between a standard state in which the front wheels and the rear wheels are driven at substantially the same speed and an increased state in which the front wheels are driven at a higher speed than the rear wheels, and the right rear wheel is braked With a possible right side brake, a right actuator that can operate the right side brake on the braking side, a left side brake that can brake the left rear wheel, and a left actuator that can operate the left side brake on the braking side. When the front wheels are steered by more than the right or left set angle from the straight ahead position, the front wheel transmission is switched from the standard state to the speed increasing state, and the right or left actuator is operated to the right or left of the turning center side. A rear wheel differential device for distributing power from the engine to the right and left rear wheels, and a right rotation speed sensor for detecting the rotation speed of the right rear wheel, together with an operating means for operating the side brake on the braking side. Rotation of the left rear wheel In the state where the front wheel is steered from the straight ahead position to the right or left at a set angle or more from the straight ahead position, and the right or left side brake on the turning center side is operated to the braking side by the operating means, When the number of rotations of the right or left rear wheel on the turning center side becomes equal to or less than a set value, an operating force control means for weakening the operating force on the braking side of the right or left side brake on the turning center side by the right or left actuator is provided. is there.

[2] A front wheel transmission capable of switching between a standard state in which the front wheels and the rear wheels are driven at substantially the same speed and an increased state in which the front wheels are driven at a higher speed than the rear wheels, and a right rear A right side brake that can brake the wheels, a right actuator that can operate the right side brake on the braking side, a left side brake that can brake the left rear wheel, and a left actuator that can operate the left side brake on the braking side. When the front wheels are steered from the straight ahead position to the right or left at a set angle or more,
The front wheel transmission is operated to switch from the standard state to the speed increasing state, and the operating means for operating the right or left side brake on the turning center side to the braking side by the right or left actuator is provided. The rear wheel differential device that distributes to the left rear wheel, the right rotation speed sensor that detects the rotation speed of the right rear wheel, the left rotation speed sensor that detects the rotation speed of the left rear wheel, and the straight position of the front wheel With a steering angle sensor that detects the steering angle to the right or left of the, the front wheel is located within the set angle of right or left from the straight ahead position based on the detection of the steering angle sensor. And when the difference in the number of rotations detected by the left rotation speed sensor exceeds the set value,
There is provided automatic braking means for operating the right or left side brake to the braking side by the right or left actuator so that the right or left rear wheel on the high rotation side is braked.

[3] A front wheel transmission capable of switching between a standard state in which the front wheels and the rear wheels are driven at substantially the same speed and a speed-up state in which the front wheels are driven at a higher speed than the rear wheels, and a right rear A right side brake that can brake the wheels, a right actuator that can operate the right side brake on the braking side, a left side brake that can brake the left rear wheel, and a left actuator that can operate the left side brake on the braking side. When the front wheels are steered from the straight ahead position to the right or left at a set angle or more,
The front wheel transmission is switched from the standard state to the speed increasing state, and the right or left actuator is provided with an operating means for operating the right or left side brake on the turning center side to the braking side. The right side brake pedal that can be operated to the braking side, the right operation sensor that detects that the right side brake pedal is stepped on the braking side, and the left side brake pedal that can artificially operate the left side brake to the braking side And a left operation sensor that detects that the left side brake pedal is stepped on the braking side, and a steering angle sensor that detects the steering angle to the right or left from the straight position of the front wheels. Based on the detection of the angle sensor, when the front wheel is located within the set angle to the right or left from the straight ahead position, the right side brake pedal is activated by the right operation sensor. If it is detected that only the steering wheel is stepped on the braking side, the left actuator operates the left side brake to the braking side by the left actuator, and based on the detection of the steering angle sensor, the front wheels move to the right or When the left operation sensor detects that only the left side brake pedal has been depressed to the braking side while the vehicle is positioned within the set angle on the left, the right actuator operates the right side brake to the braking side. And control means.

[0009]

[Action]

[I] With the configuration as described in [1] above, for example, as shown in FIG. 1, the front wheel transmission 6 is in the standard state during the turning operation of the aircraft in which the front wheels 1 are steered to the right or the left set angle A or more. Is switched to the speed increasing state, and the right or left actuator 13R, 13L automatically operates the right or left side brake 11R, 11L on the turning center side to the braking side.

In this case, the right or left rotation speed sensor 18
The rotation speed of the rear wheel 2 on the turning center side is detected by R and 18L, and when the rotation speed of the right or left rear wheel 2 on the turning center side falls below the set value, the right or left of the turning center side is detected. Rear wheel 2
Is judged to be stopping. As a result, the operating force on the braking side of the right or left side brakes 11R, 11L on the turning center side by the right or left actuators 13R, 13L is automatically weakened, and the rear wheel 2 on the right or left side on the turning center side is reduced. The stopping condition is prevented.

[II] When configured as in the above [2], for example, as shown in FIG. 1, the front wheel 1 is set to the right or left set angle A.
During the turning operation of the aircraft which has been steered as described above, the front wheel transmission 6 is switched from the standard state to the speed increasing state, and the right or left actuator 13R, 13L causes the right or left side brake 11R, 11L on the turning center side. Is automatically operated to the braking side.

When the front wheel 1 is steered within the set angle A of the right or left or in a straight traveling state or in a gentle turning state, the rotation speeds of the right and left rear wheels 2 are controlled by the right and left rotation speed sensors 18R and 18L. The difference between the rotational speeds of the right and left rear wheels 2 is detected. In this case, when the difference between the rotational speeds of the right and left rear wheels 2 becomes equal to or greater than the set value, one rear wheel 2 rides on a particularly soft part of the ground and starts idling at a high speed by the action of the rear wheel differential device 5. , It is determined that the aircraft has begun to face in a direction different from the direction of the front wheels 1. As a result, the right or left actuator 13R, 13L automatically operates the right or left side brake 11R, 11L of the rear wheel 2 on the high rotation side to the braking side, and the rotational speed of the rear wheel 2 on the high rotation side is reduced. Therefore, it is possible to suppress the state in which the vehicle body starts to face in a direction different from the direction of the front wheels 1.

As described above, the right and left actuators for the right and left side brakes, which are used during the turning operation of the airframe, reduce the difference in the rotational speeds of the right and left rear wheels in the straight traveling state and the gentle turning state. It will have a function to hold down (locking function of the rear wheel differential device). This eliminates the need for the lock mechanism of the rear wheel differential device.

[III] When configured as in the above item [3], for example, as shown in FIG. 1, the front wheel transmission device 6 is operated during turning operation of the machine body in which the front wheel 1 is steered to the right or left at the set angle A or more. Is switched from the standard state to the speed increasing state, and the right or left actuator 13R, 13L automatically operates the right or left side brake 11R, 11L on the turning center side to the braking side.

When the front wheel 1 is steered within the right or left set angle A in a straight traveling state or in a gentle turning state, an operator accidentally depresses only the right side brake pedal 12R or the left side brake pedal. If you step on 12L only, the aircraft will suddenly change direction,
It can damage the ground.

In this case, with the construction of the above [3], when the operator depresses the right side brake pedal 12R to operate the right side brake 11R to the braking side, the left actuator 13L causes the left side brake to act. 1
1L is automatically operated to the braking side. Conversely, when the operator depresses the left side brake pedal 12L to operate the left side brake 11L to the braking side, the right actuator 13R automatically operates the right side brake 11R to the braking side. As a result, even if the operator accidentally depresses the right or left side brake pedal in the straight traveling state or the gentle turning state, the other right or left side brake is automatically operated to the braking side, and as a result, Both the right and left side brakes are operated to the braking side, and the aircraft does not suddenly change direction.

[0017]

According to the present invention, the front wheel transmission is automatically switched from the standard state to the speed increasing state during the turning operation of the machine body, and the right or left side of the turning center side is turned by the right or left actuator. In a four-wheel drive work vehicle configured so that the brake is automatically operated to the braking side, when the right or left rear wheel on the turning center side is about to stop, the right or left on the turning center side is automatically The operation force on the braking side of the side brake is weakened to prevent the right or left rear wheel on the turning center side from stopping. As a result, it is possible to prevent the right or left rear wheel on the side of the stopped turning center from being dragged and roughening the ground during the turning operation of the machine body, thereby improving the turning performance of the four-wheel drive work vehicle. I was able to.

According to the present invention, the front wheel transmission is automatically switched from the standard state to the speed increasing state during the turning operation of the machine body, and the right or left side brake on the turning center side is operated by the right or left actuator. In a four-wheel drive work vehicle that is configured to be automatically operated on the braking side, the right and left actuators for the right and left side brakes that are used during turning operation of the aircraft are operated in a straight traveling state and a gentle turning state. It will also have a function of suppressing the difference in the rotational speed between the right and left rear wheels. As a result, the right and left actuators can be used for multiple purposes, and the lock mechanism of the rear wheel differential device is not required, which is advantageous in terms of simplification of the structure.

According to the third aspect of the present invention, the front wheel transmission is automatically switched from the standard state to the speed increasing state during the turning operation of the airframe, and the right or left side brake on the turning center side is operated by the right or left actuator. In a four-wheel drive work vehicle that is configured to be automatically operated on the braking side, the right and left actuators for the right and left side brakes that are used during turning operation of the machine are operated in a straight traveling state or a gentle turning state. Will also be provided with a function of suppressing a sudden change in the direction of the machine body due to an erroneous operation by the operator (stepping operation of the right or left side brake pedal). As a result, the right and left actuators can be used for multiple purposes, which is advantageous in terms of simplification of the structure.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. (1) FIG. 1 shows an outline of an agricultural tractor which is an example of a four-wheel drive type work vehicle, and an engine ( (Not shown), an agricultural tractor is configured with a mission case 4 at the rear. Power from the engine is transmitted from the rear wheel differential device 5 to the right and left rear wheels 2 via a main transmission device (not shown) and an auxiliary transmission device (not shown) in the mission case 4. The power branched from immediately before the rear wheel differential device 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 device 8.

As shown in FIG. 1, the front wheel transmission 6 has a normal state in which the front wheels 1 and the rear wheels 2 are driven at substantially the same speed, and an increased state in which the front wheels 1 are driven at a higher speed than the rear wheels 2. The shift member 9 for switching operation is urged by the spring 10 toward the occlusal side with the standard gear 20, so that the shift member 9 is normally engaged with the standard gear 20. It is in a state. An electromagnetically controllable first control valve 15 that is switchable is provided at two positions, a hydraulic oil supply position and a hydraulic oil drain position, and the hydraulic oil from the first control valve 15 is transferred to the shift member 9 When the oil is supplied into the oil chamber (not shown) formed between the gear and the standard gear 20, the shift member 9 is slid to the left side of the drawing, and the friction clutch 21
Is pressed and operated to obtain a speed-up state.

As shown in FIGS. 1 and 2, a right side brake 11R capable of braking the right rear wheel 2 and a left side brake 11L capable of braking the left rear wheel 2 are provided. The right side brake pedal 12R and the left side brake pedal 12L are arranged side by side on the right side of the floor surface of the control section, and the right and left side brake pedals 12R and 12L and the right and left side brakes 11R and 11L are connected to the right cylinder 13R.
(Corresponding to the right actuator), the left cylinder 13L (corresponding to the left actuator), and the linkage rod 14 are interlockingly connected.

A right braking position for supplying hydraulic oil to the right cylinder 13R and draining hydraulic oil from the left cylinder 13L, the left cylinder 1
Left braking position where hydraulic oil is supplied to 3L and hydraulic oil is drained from the right cylinder 13R, and right and left cylinders 13R and 13L
The second control valve 16 of the electromagnetic operation type which can be freely switched to the three positions of the release position for draining the hydraulic oil from the right and left cylinders 13R,
An electromagnetically operated pressure reducing valve 17 capable of controlling the pressure of the hydraulic oil supplied to 13L to be high or low is provided.

As shown in FIG. 2, right and left cylinders 13
R and 13L are urged toward the extension side by springs 13a, and when the second control valve 16 is operated to the release position, the right and left side brake pedals 12R and 12L are depressed to operate the right and left sides. The brakes 11R and 11L can be independently and independently operated to the braking side. next,
By operating the second control valve 16 to the right braking position or the left braking position and contracting the right or left cylinders 13R and 13L, the right or left side brakes 11R and 11L can be operated to the braking side. Therefore, the pressure reducing valve 17 can change the operating force applied to the braking side by the right and left cylinders 13R and 13L to strong or weak.

As shown in FIG. 1, a right rotation speed sensor 18R for detecting the rotation speed of the right rear wheel 2, a left rotation speed sensor 18L for detecting the rotation speed of the left rear wheel 2, and an input to the rear wheel differential device 5. A rotation speed sensor 19 for detecting the rotation speed of the power immediately before the operation is provided, and the right and left rotation speed sensors 18 are provided.
The detection values of the R, 18L and the rotation speed sensor 19 are the control device 2
It is entered in 2. Pitman arm 2 for steering operation of front wheel 1 and swinging left and right by steering handle 3
3 is provided with a steering angle sensor 24 that detects the steering angle of the front wheel 1 from the straight-ahead position to the right or left by detecting the angle of the pitman arm 23. The detected value is input to the control device 22.

As shown in FIGS. 1 and 2, the limit switch type right operation sensor 25R for detecting that the right side brake pedal 12R is depressed and the fact that the left side brake pedal 12L is depressed are detected. A limit switch type left operation sensor 25L is provided, and signals from the right and left operation sensors 25R and 25L are input to the control device 22.

(2) Next, the state of the turning operation of the machine body will be described with reference to FIG. The operator controls the steering wheel 3
When the front wheel 1 is steered from the straight ahead position to the right or left by a set angle A or more and the turning operation of the machine body is started, this is detected by the detection value of the steering angle sensor 24 (step S1). ), The first changeover switch 2 shown in FIG.
When 6 is operated to the OFF position (step S2), the front wheel transmission 6 is not switched to the speed increasing state and is maintained in the standard state. The brakes 11R and 11L are not automatically operated to the braking side. When the operator turns the first changeover switch 26 to the OFF position to turn the vehicle, if the operator depresses the right or left side brake pedal 12R or 12L on the turning center side, the turning operation is performed. Center side right or left side brake 11R, 11
L is operated to the braking side.

Next, when the first changeover switch 26 is operated to the first turning position D during the turning operation of the machine body (step S2), when the detected value N3 of the rotation speed sensor 19 is less than or equal to the set value N4 (the machine body When the traveling speed of is relatively low)
(Steps S3 and S4), the first control valve 15 is operated from the oil discharge position to the supply position, and the front wheel transmission 6 is switched from the standard state to the speed increasing state (step S5). On the other hand, the right or left side brake 11R, 1 on the turning center side
1L is not automatically operated on the braking side.

As described above, when the vehicle body is being turned while the first changeover switch 26 is being operated to the first turning position D, the operator depresses the right or left side brake pedals 12R, 12L on the turning center side. When operated, the right or left side brakes 11R and 11L on the turning center side are operated to the braking side. Then, the operator operates the steering wheel 3 to move the front wheel 1
When the steering operation is performed within the set angle A of the right or the left to complete the turning operation of the machine body (step S1), the first control valve 15 is operated from the supply position to the oil draining position, and the front wheel transmission 6 is accelerated. The state is switched to the standard state (step S1)
3).

On the contrary, during the turning operation of the machine body by operating the first changeover switch 26 to the first turning position D (step S2), the detected value N3 of the rotation speed sensor 19 is set to the set value N4.
Is greater than (the traveling speed of the aircraft is relatively high) (steps S3 and S4), the front wheel transmission 6 is not switched to the speed increasing state and is maintained in the standard state. Side right or left side brake 11R,
The 11L is not automatically operated on the braking side.

Next, when the first changeover switch 26 is operated to the second turning position AD during the turning operation of the machine body, when the detected value N3 of the rotation speed sensor 19 is less than the set value N4 (the traveling speed of the machine body is When the speed is relatively low) (Step S
6, S7), the first control valve 15 is operated from the oil discharge position to the supply position, the front wheel transmission 6 is switched from the standard state to the speed increasing state (step S8), and the second control valve 16 is in the release position. To the right or left braking position, and the right or left cylinders 13R, 13L automatically operate the right or left side brakes 11R, 11L on the turning center side to the braking side (step S9) (in operation means). Equivalent).

The right or left side brake 11 on the turning center side
The braking force of R, 11L is set to be slightly weak by the pressure reducing valve 17 so that the right or left rear wheel 2 on the turning center side does not stop, and the right or left rotation speed sensor 18R, The rotational speed N1 of the right or left rear wheel 2 on the turning center side is detected by 18L (step S10). In this case, when the rotation speed N1 of the right or left rear wheel 2 on the turning center side falls below the set value N5 and the right or left rear wheel 2 on the turning center side almost stops (step S11), the pressure is reduced. The pressure of the hydraulic oil supplied to the right or left cylinder 13R, 13L is automatically reduced by the valve 17, and the operating force to the braking side of the right or left side brake 11R, 11L on the turning center side is automatically weakened. As a result (step S12), the state in which the right or left rear wheel 2 on the turning center side is stopped is prevented (corresponding to operating force control means).

When the operator operates the steering wheel 3 to steer the front wheels 1 within the set angle A of right or left, and the turning operation of the machine body is completed (step S1), the first control valve 15
Is operated from the supply position to the oil drain position, and the front wheel transmission 6
Is switched from the speed-up state to the standard state (step S1
3), the second control valve 16 is operated from the right or left braking position to the release position, and the right or left side brake 1 on the turning center side is
Release operations of 1R and 11L are performed (step S14).

On the contrary, during the turning operation of the machine body by operating the first changeover switch 26 to the second turning position AD (step S2), the detected value N3 of the rotation speed sensor 19 is the set value N4.
If it is larger than (the traveling speed of the aircraft is relatively high) (steps S6, S7), the front wheel transmission 6 is not switched to the speed increasing state and is maintained in the standard state. Side right or left side brake 11R,
The 11L is not automatically operated on the braking side.

(3) Next, a state in which the front wheel 1 is steered within the right or left set angle A will be described with reference to FIG. When the second selector switch 27 shown in FIG. 1 is operated to the ON position in the straight traveling state in which the front wheels 1 are steered within the set angle A of the right or the left, or in the gentle turning state (step S15), Right and left rotation speed sensor 1
8R and 18L detect the rotational speed N1 of the right and left rear wheels 2 (steps S16 and S17), and detect the difference N2 between the rotational speeds N1 of the right and left rear wheels 2 (step S1).
8).

In this case, the rotation speed N of the right and left rear wheels 2
When the difference N2 of 1 exceeds the set value N6 (step S1
9) On the other hand, it is determined that the one rear wheel 2 rides on a particularly soft portion of the ground and starts idling at a high speed by the action of the rear wheel differential device 5, and the second control valve 16 moves from the release position to the right or left braking position. The left or right side brake 11 of the rear wheel 2 on the high rotation side is operated by the right or left cylinder 13R, 13L.
R and 11L are automatically operated to the braking side (step S
20). The operation force to the braking side of the right or left side brake 11R, 11L is set to be weak by the pressure reducing valve 17, and the difference N2 between the rotation speeds N1 of the right and left rear wheels 2 returns to less than the set value N6. (Corresponding to automatic braking means).

Next, when the detected value N3 of the rotation speed sensor 19 is equal to or greater than the set value N7 while the front wheel 1 is being steered within the set angle A of the right or left (the traveling speed of the machine is relatively high. In the case of high speed (steps S21 and S22), when the operator depresses the right side brake pedal 12R to operate the right side brake 11R to the braking side (step S23), based on the signal from the right operation sensor 25R. , The second control valve 16 is operated from the release position to the left braking position,
The left side brake 11L is automatically operated to the braking side by the left cylinder 13L (step S25) (corresponding to left control means).

On the contrary, when the operator has left side brake pedal 1
When the left side brake 11L is operated to the braking side by stepping on 2L (step S24), the left operation sensor 2
Based on the 5L signal, the second control valve 16 is operated from the release position to the right braking position, and the right side brake 11R is automatically operated to the braking side by the right cylinder 13R (step S26) (to the right control means). Equivalent).

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 configuration of the accompanying drawings by the entry.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a linked state of a front wheel transmission, right and left side brakes, right and left side brake pedals, right and left cylinders, and the like.

FIG. 2 is a side view showing a linked state of the right and left side brakes, the right and left side brake pedals, and the right and left cylinders.

FIG. 3 is a diagram showing a front half flow of control of a front wheel transmission and right and left side brakes.

FIG. 4 is a diagram showing the flow of the latter half of the control of the front wheel transmission and the right and left side brakes.

[Explanation of symbols]

 1 Front Wheel 2 Rear Wheel 5 Rear Wheel Diff Device 6 Front Wheel Transmission 11R Right Side Brake 11L Left Side Brake 12R Right Side Brake Pedal 12L Left Side Brake Pedal 13R Right Actuator 13L Left Actuator 18R Right Speed Sensor 18L Left Speed Sensor 24 Manipulation Angle sensor 25R Right operation sensor 25L Left operation sensor N1 Right and left rear wheel speed N2 Difference between right and left rear wheel speed N5, N6 Set value A Set angle

Claims (3)

[Claims] 1. A standard state in which the front wheels (1) and the rear wheels (2) are driven at substantially the same speed, and a speed-up state in which the front wheels (1) are driven at a higher speed than the rear wheels (2). Operable front wheel transmission (6) and right side brake (11) that can brake the right rear wheel (2)
R), a right actuator (13R) capable of operating the right side brake (11R) to the braking side, a left side brake (11L) capable of braking the left rear wheel (2), and the left side brake (11L). ) Is operated to the braking side, and the front wheel (1) is steered from the straight ahead position to a right or left set angle (A) or more, the front wheel transmission ( 6) is switched from the standard state to the speed increasing state, and the right or left actuator (13R), (13L) is used to turn the right or left side brake (11R) on the turning center side,
(11L) is provided with an operating means for operating to the braking side, and a rear wheel differential device (5) for distributing the power from the engine to the right and left rear wheels (2) and the right rear wheel (2). A right rotation speed sensor (18R) for detecting the rotation speed (N1) of
A left rotation speed sensor (18L) for detecting the rotation speed (N1) of the left rear wheel (2) is provided, and the front wheel (1) is steered from a straight ahead position to a right or left set angle (A) or more. The right or left side brakes (11R), (11L) on the turning center side are operated by the operating means.
When the rotational speed (N1) of the right or left rear wheel (2) on the turning center side becomes less than or equal to the set value (N5) in the state where the is operated to the braking side, the right or left actuator (13R),
A four-wheel drive work vehicle provided with operation force control means for weakening the operation force to the braking side of the right or left side brake (11R), (11L) on the turning center side by (13L). 2. A normal state in which the front wheels (1) and the rear wheels (2) are driven at substantially the same speed, and a speed increasing state in which the front wheels (1) are driven at a higher speed than the rear wheels (2). Operable front wheel transmission (6) and right side brake (11) that can brake the right rear wheel (2)
R), a right actuator (13R) capable of operating the right side brake (11R) to the braking side, a left side brake (11L) capable of braking the left rear wheel (2), and the left side brake (11L). ) Is operated to the braking side, and the front wheel (1) is steered from the straight ahead position to a right or left set angle (A) or more, the front wheel transmission ( 6) is switched from the standard state to the speed increasing state, and the right or left actuator (13R), (13L) is used to turn the right or left side brake (11R) on the turning center side,
(11L) is provided with an operating means for operating to the braking side, and a rear wheel differential device (5) for distributing the power from the engine to the right and left rear wheels (2) and the right rear wheel (2). A right rotation speed sensor (18R) for detecting the rotation speed (N1) of
A left rotation speed sensor (18L) for detecting the rotation speed (N1) of the left rear wheel (2), and a steering angle for detecting the steering angle of the front wheel (1) to the right or left from the straight traveling position. A sensor (24), and based on the detection of the steering angle sensor (24), in the state where the front wheel (1) is located within the set angle (A) on the right or left from the straight ahead position, And the rotation speed (N1) detected by the left rotation speed sensors (18R) and (18L)
When the difference (N2) becomes equal to or more than the set value (N6), the right or left actuator (13R), (13L) is operated by the right or left actuator so that the right or left rear wheel (2) on the high rotation side is braked. A four-wheel drive work vehicle equipped with automatic braking means for operating the left side brakes (11R) and (11L) to the braking side. 3. A normal state in which the front wheels (1) and the rear wheels (2) are driven at substantially the same speed, and a speed-up state in which the front wheels (1) are driven at a higher speed than the rear wheels (2). Operable front wheel transmission (6) and right side brake (11) that can brake the right rear wheel (2)
R), a right actuator (13R) capable of operating the right side brake (11R) to the braking side, a left side brake (11L) capable of braking the left rear wheel (2), and the left side brake (11L). ) Is operated to the braking side, and the front wheel (1) is steered from the straight ahead position to a right or left set angle (A) or more, the front wheel transmission ( 6) is switched from the standard state to the speed increasing state, and the right or left actuator (13R), (13L) is used to turn the right or left side brake (11R) on the turning center side,
The right side brake pedal (12R) and the right side brake pedal (12R) are provided with an operating means for operating the (11L) to the braking side and capable of artificially operating the right side brake (11R) to the braking side. A right operation sensor (25R) that detects that the brake pedal is depressed, a left side brake pedal (12L) that can artificially operate the left side brake (11L) to the braking side, and the left side brake pedal. A left operation sensor (25L) that detects that (12L) is stepped on the braking side, and a steering angle sensor (24) that detects the steering angle of the front wheel (1) to the right or left from the straight traveling position. ) And based on the detection of the steering angle sensor (24), the front wheel (1) is located in the set angle (A) of the right or left from the straight ahead position, Serial right operation sensor (25
R) detects that only the right side brake pedal (12R) is stepped on the braking side, the left actuator (13L) causes the left side brake (1R) to operate.
1L) to the braking side, and the front wheel (1) is located within the set angle (A) to the right or left from the straight-ahead position based on the detection of the steering angle sensor (24). In the state, the left operation sensor (25
L) detects that only the left side brake pedal (12L) is stepped on the braking side, the right actuator (13L) causes the right side brake (1L) to operate.
A four-wheel drive work vehicle including a right control means for operating 1L) to a braking side.