JP2000326741A - Front wheel speed increase/automatic brake device of tractor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an attitude and behavior of a car body from becoming unstable due to sudden changes in a traveling state by, when the sub- transmission is shifted to a high speed stage, reducing hydraulic fluid pressure of a hydraulic clutch more than when a sub-transmission is shifted to a low speed stage. SOLUTION: When a sub-transmission is shifted to a high speed stage by shifting a sub-shift lever to a third speed position, hydraulic fluid pressure of a double speed clutch 24 for controlling a front wheel double speed device is reduced more than when the sub-transmission is shifted to a low speed stage. Hydraulic fluid pressure of left/right brake pistons 25a, 25b for controlling an automatic brake device is also reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a front wheel double speed of a tractor which is constituted by a front wheel double speed device controlled by a hydraulic clutch and an automatic brake device controlled by hydraulic pressure, and which is activated when the steering angle of the front wheels exceeds a certain value. -It relates to the configuration of the automatic brake device.

[0002]

2. Description of the Related Art Conventionally, some tractors have a front wheel speed-increasing / automatic braking device including a front wheel double speed device and an automatic braking device that operate in conjunction with the steering operation of the front wheels. The front wheel double speed device is controlled by a hydraulic clutch, and the automatic brake device is hydraulically controlled. And in such a tractor
An operation switch for switching an operation state of the front wheel double speed / automatic brake device is provided, and a sensor for detecting a turning angle of the front wheel is provided. When the turning angle of the front wheel exceeds a predetermined angle when the operation switch is on, the front wheel is turned on. The double speed device and the automatic brake device were configured to operate.

[0003]

However, in the tractor as described above, when the steering angle of the front wheel is increased to a predetermined angle or more by the steering operation, the front wheel double speed device operates to transmit the driving force to the front wheels. And the automatic braking device is operated, and the rear wheel inside the turning is completely braked. When such front wheel speed doubling device and automatic brake device are operated during high-speed running with the sub-shift lever operated to shift to a high gear, the running state changes rapidly and the posture and behavior of the vehicle body change. Could become unstable.

[0004]

The problem to be solved by the present invention is as described above. Next, means for solving the problem will be described. That is, as set forth in claim 1, a front wheel speed-up / automatic braking device including a front wheel double speed device controlled by a hydraulic clutch and an automatic braking device controlled by hydraulic pressure is provided, and the steering angle of the front wheels is constant. In the tractor configured to operate the front wheel speed increasing / automatic braking device when the value becomes equal to or more than the value, when the auxiliary transmission is switched to the high gear, the traction is higher than when the auxiliary transmission is switched to the low gear. The hydraulic pressure of the hydraulic clutch is reduced.

According to a second aspect of the present invention, there is provided a front wheel speed-increasing / automatic braking device comprising a front wheel speed-up device controlled by a hydraulic clutch and an automatic braking device controlled by a hydraulic pressure. In a tractor configured so that the front wheel speed increasing / automatic braking device is activated when the value becomes equal to or more than a certain value, when the auxiliary transmission is switched to a high speed stage, the case where the auxiliary transmission is switched to a low speed stage is smaller than when the auxiliary transmission is switched to a low speed stage. Also, the operation hydraulic pressure of the automatic brake device is reduced.

According to a third aspect of the present invention, there is provided a front wheel speed-increasing / automatic braking device comprising a front wheel speed-up device controlled by a hydraulic clutch and an automatic braking device controlled by a hydraulic pressure. In a tractor configured so that the front wheel speed-increasing / automatic braking device is activated when a predetermined value or more is reached, when the automatic braking device is activated, the brake device is intermittently activated at a substantially constant cycle, and the sub-transmission is shifted to a high speed stage. When the gear is switched, the operating oil pressure of the brake device is reduced and the operating cycle of the brake device is shortened as compared with the case where the auxiliary transmission is switched to the low speed stage.

[0007]

Next, an embodiment of the present invention will be described. 1 is a side view showing a tractor on which the safety device of the present invention is mounted, FIG. 2 is a plan view of the same, FIG. 3 is a diagram showing an instrument panel, and FIG. 4 is a connection showing an operation mechanism of a front wheel double speed device and an automatic brake device. 5 is a circuit diagram, FIG. 5 is a hydraulic circuit diagram showing a front wheel double speed device and an automatic brake device, FIG. 6 is a side view showing a brake mechanism, FIG. 7 is a side view showing the inside of the brake device, and FIG. FIG. 9 is a side view, FIG. 10 is a diagram showing the change over time of the working oil pressure of the brake piston at low speed, and FIG. 11 is a diagram showing the change over time of the working oil pressure of the brake piston at high speed.

First, the overall configuration of a tractor equipped with a control device for a transmission according to the present invention will be described with reference to FIGS. A hood 4 is arranged in a part of the machine which suspends front wheels 2.2 and rear wheels 3.3 in front and back, and an engine 5 is built in the hood 4. A steering handle 51 is provided behind the hood 4 so that the steering handle 5
A seat 52 is provided behind the seat 1. An instrument panel 18 is provided in front of the steering handle 51. The steering handle 51, the seat 52, the instrument panel 18 and the like are covered by the cabin 12.

A transmission 53 is connected to the rear of the engine 5 to transmit power from the engine 5 to the rear wheels 3 for driving. Further, the driving force of the engine 5 drives the PTO shaft projecting rearward from the rear end of the machine body, and drives the work machine 57 connected to the work machine mounting device 56 at the rear end of the machine body. A main shift lever 58 is disposed on one side of the seat 52, and a sub shift lever 59 is disposed on the other side.
Thus, the shift operation of the main transmission and the sub transmission is performed respectively. Also, the front axle 2a supporting the left and right front wheels 2, 2 is provided with angle sensors 54a, 54b respectively near the left and right front wheels 2 so as to detect the angle of each front wheel 2 during steering. Make up.

In the tractor, the rear wheels 3.3
Only two wheels drive state, front wheels 2.2 and rear wheels 3.
3 and a four-wheel drive state for driving both. Further, a front wheel double speed device that increases the drive rotation of the front wheels 2 during turning and an automatic brake device that automatically brakes the rear wheel 3 inside the turning when turning are configured. FIG. 3 shows the instrument panel 18 provided with an engine tachometer 27, a plurality of indicator lamps 28, and the like. The instrument panel 18 is provided with a steering shaft 51a that supports the steering handle 51. A four-wheel drive on / off switch 31, a double speed / automatic brake on / off switch 32, and the like are disposed below the steering shaft 51a. The four-wheel drive ON / OFF switch 31 switches between the two-wheel drive state and the four-wheel drive state, and the double-speed / automatic brake ON / OFF switch 32 switches the operation state of the front wheel double speed device and the automatic brake device. .

Next, the switching mechanism between the two-wheel drive state and the four-wheel drive state and the operating mechanism of the front wheel double speed device and the automatic brake device will be described with reference to FIGS. First, when the tractor is in the two-wheel drive state and switches from the two-wheel drive state to the four-wheel drive state, when the four-wheel drive on / off switch 31 is switched from the off state to on, the four-wheel drive relay 33 operates. Electric current flows to the four-wheel drive solenoid 38. When a current flows to the four-wheel drive solenoid 38, the four-wheel drive / double speed switching valve 21 is operated to switch to the four-wheel drive side, and a four-wheel drive clutch for turning on and off transmission of the driving force to the front wheels 2.2. 23 is supplied with pressure oil from a hydraulic pump 19 driven by the engine 5 to be in a connected state, and the driving force is transmitted to the front wheels 2 to be in a four-wheel drive state.

When the double-speed / automatic brake on / off switch 32 is switched from the off state to the on state in the four-wheel drive state in which the four-wheel drive on / off switch 31 is turned on,
The front wheel speed increasing device and the automatic braking device, which constitute the front wheel speed increasing / automatic braking device, are in an operable state. When the front wheel double speed device and the automatic brake device are in an operable state, a double speed mode indicator lamp 28a among the plurality of indicator lamps 28 shown in FIG.

In the state where the front wheel double speed device and the automatic brake device are operable, for example, when the steering wheel 51 is used to make a left turn, the turning angle of the left front wheel 2 is equal to or more than a predetermined angle. Then, the left turning angle sensor 54a detects this and is turned on, and the double-speed relay 35 is operated to cause a current to flow through the double-speed solenoid 39. When current flows through the double-speed solenoid 39, four-wheel drive
The double-speed switching valve 21 is operated to switch to the double-speed side, and the double-speed clutch 24 for turning on / off the speed-up of the drive rotation of the front wheels 2.
Then, the pressure oil from the hydraulic pump 19 is pressure-fed to be in a connected state, and the front wheel double speed device operates to increase the drive rotation of the front wheels 2. Further, when the left turning angle sensor 54a is turned on, the front wheels 2.2 are accelerated, and at the same time, a current flows through the left brake solenoid 37a to switch the brake valve 22, and pressure oil flows through the left brake piston 25a. Thus, the left brake piston 25a extends. The left brake cam 26a is rotated by the extension of the left brake piston 25a, whereby the left brake device is operated and the left rear wheel 3,
That is, the rear wheel 3 inside the turning is braked. That is, the automatic brake device operates.

Similarly, when the steering wheel 51 is steered to turn right and the turning angle of the right front wheel 2 exceeds a predetermined angle, the right turning sensor 54b is similarly turned on and the front wheel is turned on. As the drive rotation of 2.2 is increased, a current flows through the right brake solenoid 37b to switch the brake valve 22, and the right brake piston 25b
And the right brake cam 26b is rotated to operate the right brake to brake the left rear wheel 3, that is, the rear wheel 3 inside the turn. In this manner, in a state where the front wheel double speed device and the automatic brake device are operable, when the steering angle of the left and right front wheels 2.2 becomes a predetermined angle or more by steering the steering handle 51, the front wheel double speed device is operated. And the automatic braking device operates.

As shown in FIG. 6, when the automatic brake device operates, as described above, the left brake piston 25a is extended and the left brake cam 26a is rotated to operate the left brake device 29a. Works, but
The left brake device 29a can also be operated by the operator depressing the brake pedal 13. That is, when the brake pedal 13 is depressed, the connecting rod 71 moves upward and the shaft 72 rotates to the right, whereby the brake rod 73 moves forward to rotate the left brake cam 26a, and the left brake device 29a is activated.

As shown in FIG. 7, the left brake cam 26a
Has an arm 76 fixed to the center of rotation so that the arm 76 can be integrally rotated.
Is connected to a stay 78 fixed to the brake shoe 79 by a link 77. A support plate 80 is provided facing the brake shoe 79.

When the left brake cam 26a is rotated forward by the brake rod 73 or the left brake piston 25a, the brake shoe 79 is moved forward via the arm 76, the link 77 and the stay 78. . When the brake shoe 79 is moved forward, the distance between the brake shoe 79 and the support plate 80 is increased by the ball member 81 interposed between the brake shoe 79 and the support plate 80, and The lining affixed to 79 is pressed by the brake disc 83 fixed to the rear axle of the left rear wheel 3, and the left rear wheel 3 is braked.

As described above, the left brake device 29a is operable by both the depression pressure of the brake pedal 13 and the extension of the left brake piston 25a in the automatic brake device. Note that the right brake device 29b is also configured to operate by the same mechanism as the left brake device 29a.

As shown in FIGS. 6 and 7, the left brake piston 25a is attached and fixed to the housing of the left brake device 29a by bolts 91. The fastening portion of the left brake piston 25a by the bolt 91 is formed in a long hole 92, and by loosening the bolts 91, the contact position of the left brake piston 25a with the contact portion 26b of the left brake cam 26a is adjusted. It is possible. That is, the front end (front end) of the left brake piston 25a is moved within the range of the long hole 92, and the left brake cam 26a
From the rotation center of the left brake piston 25a.
Thus, the distance to the contact position with respect to 6b can be adjusted. In this case, the movement within the long hole 92 of the left brake piston 25a is caused by the movement of the left brake piston 25a.
The rotation is performed by rotating the front end vertically about the rear end. Further, the contact surface of the contact portion 26b with the tip of the left brake piston 25a is
(a) It has an arc shape that matches the rotation locus of the tip. In this manner, the tip of the left brake piston 25a abutting on the abutting portion 26b formed in an arc shape is configured to rotate up and down around the rear end of the left brake piston 25a. Even when the position is changed, the pressing angle of the left brake piston 25a against the contact portion 26b can be kept constant by keeping the contact angle of the distal end portion with the contact portion 26b constant. And left brake piston 2
By configuring the contact position of the 5a to the contact portion 26b to be adjustable as described above, the distance from the rotation center of the left brake cam 26a to the pressing portion by the left brake piston 25a can be adjusted. Thus, the turning torque of the left brake cam 26a by the left brake piston 25a can be changed, and the degree of braking of the rear wheel 3 by the automatic brake mechanism can be adjusted.

The connecting portion between the left brake cam 26a and the brake rod 73 is formed in an elongated hole 26c to provide a play, and when the left brake cam 26a is rotated forward by the left brake piston 25a. The configuration is such that the force due to the turning operation of the left brake cam 26a is not transmitted to the brake pedal 13 side. In the right brake device, the left brake device 2 as described above is used.
It is configured and operated by the same structure and mechanism as 9a.

As shown in FIGS. 8 and 9, the auxiliary transmission lever 59 is slidable in a long guide opening 17a formed in the lever guide 17, and is provided at a low speed first speed position F1. The gears can be shifted to a middle-speed second-speed position F2, a high-speed third-speed position F3, and an ultra-low-speed creep position C, and a neutral position N is disposed between the creep position C and the first-speed position F1. ing. Below the lever guide 17,
A high speed gear detection switch 61 is provided,
Is shifted to the third speed position F3, which is the high gear,
The auxiliary shift lever 59 is configured to abut on the contact piece 61a of the high speed gear detection switch 61 to turn on the high speed gear detection switch 61.

As shown in FIGS. 4 and 5, when the high-speed gear detection switch 61 is turned on, the double-speed clutch interposed between the hydraulic circuit of the four-wheel drive / double-speed switching valve 21 and the double-speed clutch 24 is provided. Solenoid 6 of operating pressure switching valve 62
An electric current flows through 2a, the double speed clutch operating pressure switching valve 62 is switched, and the hydraulic oil after being depressurized through the double speed circuit pressure reducing valve 64 is supplied to the double speed clutch 24. That is, when the sub-shift lever 59 is shifted to the third speed position F3 of the high gear, the double speed clutch 24
Is actuated by the working oil depressurized by the double speed circuit pressure reducing valve 64 on the way.

Therefore, the sub-transmission lever 59 is moved to the third speed position F3.
When the speed change operation is performed, the operating oil pressure of the double speed clutch 24 becomes lower than when the speed change operation is performed to a low speed stage other than the third speed position F3, and the double speed clutch 24 slips in a half-clutch state, The degree of transmission of the driving force to the front wheels 2 is reduced. In this manner, by adjusting the operating oil pressure by the double speed circuit pressure reducing valve 64 to reduce the degree of transmission of the driving force to the front wheels 2, the speed increase of the front wheels 2 is also reduced. Even if the front wheel speed increasing device is operated while the vehicle is traveling at high speed with the gear shifting operation to the third speed position F3, the traveling state does not suddenly change, and the vehicle turns in a stable posture and state. It is possible to run.
The degree of pressure adjustment of the operating oil pressure by the double speed circuit pressure reducing valve 64 can be set arbitrarily.

On the other hand, as described above, the high speed stage detection switch 61
Is turned on, a current flows through the solenoid 63a of the brake operating pressure switching valve 63 interposed between the hydraulic circuit of the four-wheel drive / double speed switching valve 21 and the brake valve 22, and the brake operating pressure switching valve 63 Is switched,
Brake valve 22 and left and right brake pistons 25a
The working oil after the pressure has been reduced through the brake circuit pressure reducing valve 65 is supplied to 25b. That is, when the sub-shift lever 59 is shifted to the third gear position F3 of the high gear, the left and right brake pistons 25a and 25b are operated by the hydraulic oil depressurized by the brake circuit depressurizing valve 65 on the way. .

Therefore, the sub-transmission lever 59 is moved to the third speed position F3.
When the shift operation is performed at a speed other than the third speed position F3, the left and right brake pistons 2
The operating oil pressures of 5a and 25b are reduced, and the braking force of left and right brake devices 29a and 29b is reduced, so that the rear wheels 3 are not completely braked. In this way, by adjusting the operating oil pressure by the brake circuit pressure reducing valve 65 and reducing the braking force of the left and right brake devices 29a and 29b for braking the rear wheel 3, the sub-transmission lever 59 is moved to the third gear position F3 of the high gear.
Even if the automatic braking device is activated when the aircraft is moving at high speed with the gear shifting operation, the traveling state does not change suddenly, and the aircraft can turn and travel in a stable posture and state. Become. The brake circuit pressure reducing valve 65
Can be set arbitrarily.

When the steering operation is performed by the steering handle 51 to operate the automatic brake device, the left and right brake devices 29a and 29b are operated intermittently with a certain operating oil pressure to brake the rear wheel 3. It is configured to be. For example, when the sub shift lever 59 is in the creep position C
When the speed change operation is performed within the range from to the second speed position F2, as shown in FIG.
Left and right brake pistons 25a and 25 for operating 29b
The operation state b is turned on / off at a certain operating oil pressure P1 and at a certain cycle t1.

That is, the left and right brake pistons 25a and 25
b is repeated to stop the stop time t1 _off and actuation of the actuation time t1 _on, the time obtained by adding the between operating time t1 _on the stop time t1 _off, is set to the period t1 of the on and off states of the left and right brake piston 25a-25b . In this case, the steering angle of the front wheel becomes greater than a certain angle by steering operation of the steering handle 51, and the left and right brake pistons 25a and 25b
From the operation start time t _{0 at} which the brake valve 22 switches in the direction in which the hydraulic oil flows, after the brake valve 22 holds the state for a fixed operation time t 1 _on and operates the left and right brake pistons 25a and 25b. Then, the brake valve 22 is switched in a direction in which the hydraulic oil does not flow into the left and right brake pistons 25a and 25b, and then the state is maintained for a certain stop time t1 _{of f} to stop the left and right brake pistons 25a and 25b. After stopping the left and right brake pistons 25a and 25b for a fixed stop time t1 _{off, the} left and right brake pistons 25a and 25b are stopped.
The operation of the operation time t1 _on and the stop of the stop time t1 _off are repeatedly performed. By controlling the operation of the left and right brake pistons 25a and 25b in this manner, the braking force on the rear wheel 3 by the left and right brake devices 29a and 29b is changed over time.

As described above, when the automatic brake device operates, the left and right brake devices are intermittently operated to brake the rear wheel 3, so that the braking force of the brake device is adjusted. Thus, it is possible to prevent the rear wheel 3 from being locked. Thus, it is possible to prevent the occurrence of torque binding between the front and rear wheels 2 and 3 which is likely to occur when the steering handle 51 is steered during four-wheel drive. Further, wear of the rear wheel 3 can be suppressed and notching (hunting) near idling can be prevented.

On the other hand, when the auxiliary transmission lever 59 is operated to shift to the third speed position F3, as shown in FIG. 11, the left and right brake pistons 25a and 25b for operating the left and right brake devices 29a and 29b are in the operating state. It is configured to be turned on / off at a constant operating oil pressure P2 and at a constant period t2. That is, the left and right brake pistons 25
a.25b indicates the operation time t2 _on and the stop time t2 _off
The operation time t2 _on and the stop time t2
_off plus the left and right brake piston 25a
The on / off cycle t2 of 25b is set.

In this case, as in the case described above, the steering wheel 51 is steered and the turning angle of the front wheels becomes greater than a predetermined angle, and the left and right brake pistons 25a and 25b are turned.
From the operation start time t _{0 at} which the brake valve 22 switches in the direction in which the hydraulic oil flows, after the brake valve 22 holds the state for a certain operation time t2 _on and operates the left and right brake pistons 25a and 25b. Then, the brake valve 22 is switched in a direction in which the hydraulic oil does not flow into the left and right brake pistons 25a and 25b, and then the state is maintained for a certain stop time t2 _off to stop the left and right brake pistons 25a and 25b. After stopping the left and right brake pistons 25a and 25b for a fixed stop time t2 _{off, the} left and right brake pistons 25a and 25b are stopped.
The operation of the operation time t2 _on and the stop of the stop time t2 _off are repeated.

Then, the auxiliary transmission lever 59 is moved to the third speed position F3.
Left and right brake pistons 25 when gear shifting operation is performed
The operating oil pressure P2 of a · 25b is reduced by the brake circuit pressure reducing valve 65, and is lower than the operating oil pressure P1 when the sub shift lever 59 is shifted within the range from the creep position C to the second speed position F2. It is configured to have a small value. Further, the left and right brake pistons 2 when the sub shift lever 59 is operated to shift to the third speed position F3.
The ON / OFF cycle t2 of 5a and 25b is configured to be smaller than the cycle t1 when the sub-shift lever 59 is operated to shift within the range from the creep position C to the second speed position F2. I have. In this way, by controlling the operation of the left and right brake pistons 25a and 25b, the braking force of the rear wheels 3 by the left and right brake devices 29a and 29b is configured to be smaller than that in the case of the low speed described above, and the braking force is reduced over time. Is changing.

That is, when the sub-transmission lever 59 is shifted to the third speed position F3 and the vehicle is traveling at a high speed, the left and right brake pistons 25a and 25 are higher than when traveling at a low speed.
b, the on / off cycle of the left and right brake pistons 25a and 25b is shortened to reduce the braking force of the rear wheels 3 by the left and right brake devices 29a and 29b. Is more reliably prevented from being locked. As a result, it is possible to reliably prevent the occurrence of torque binding between the front and rear wheels 2 and 3 and the wear of the rear wheel 3 which are likely to occur when the steering handle 51 is steered during four-wheel drive, and particularly in a high-speed shift state. Notching (hunting) in the vicinity of idling, which is easy to perform, can be prevented, and the attitude and running state of the aircraft during turning at high speed can be stabilized.

[0033]

As described above, the present invention has the following advantages. That is, when the sub-transmission is switched to the high speed stage, the operating oil pressure of the hydraulic clutch is reduced as compared to when the sub-transmission is switched to the low speed stage. , The degree of transmission of the driving force to the front wheels can be reduced, and the speed increase of the front wheels is reduced. Therefore, when the aircraft is traveling at high speed with the sub-transmission being switched to the high speed stage. Even when the front wheel speed increasing device is activated, the running condition does not change suddenly, and the aircraft turns in a stable posture and state.
It is possible to run.

When the sub-transmission is switched to the high speed stage, the operating oil pressure of the automatic brake device is reduced as compared with the case where the sub-transmission is switched to the low speed stage. As a result, the braking force of the left and right brake devices for braking the rear wheels can be reduced, and the automatic brake device is operated when the vehicle is running at high speed with the sub-transmission set to the high speed stage. Even if it operates, the running state does not suddenly change, and the aircraft can turn and run in a stable posture and state.

According to a third aspect of the present invention, when the automatic brake device is operated, the brake device is operated intermittently at a substantially constant cycle, and when the sub-transmission is switched to a high speed stage,
Since the operating oil pressure of the brake device is reduced and the operating cycle of the brake device is shortened as compared with the case where the sub-transmission is switched to the lower gear, the braking force of the rear wheels by the left and right brake devices is reduced. Can be adjusted to be small, and the rear wheel can be more securely prevented from being locked. In addition, it reliably prevents the occurrence of torque binding between the front and rear wheels and wear of the rear wheels, which are likely to occur when steering the steering wheel during four-wheel drive. The occurrence of notching (hunting) can be prevented, and the attitude and traveling state of the aircraft can be stabilized when turning at high speed.

[Brief description of the drawings]

FIG. 1 is a side view showing a tractor equipped with a safety device of the present invention.

FIG. 2 is a plan view of the same.

FIG. 3 is a view showing an instrument panel.

FIG. 4 is a connection circuit diagram showing operation mechanisms of a front wheel double speed device and an automatic brake device.

FIG. 5 is a hydraulic circuit diagram showing a front wheel double speed device and an automatic brake device.

FIG. 6 is a side view showing a brake mechanism.

FIG. 7 is a side view showing the inside of the brake device.

FIG. 8 is a plan view showing an auxiliary transmission lever and a lever guide.

FIG. 9 is a side view of the same.

FIG. 10 is a diagram showing the change over time of the operating oil pressure of the brake piston at low speed.

FIG. 11 is a diagram showing a change over time of the operating oil pressure of the brake piston at a high speed.

[Explanation of symbols]

 Reference Signs List 17 lever guide 59 auxiliary transmission lever 21 four-wheel drive / double speed switching valve 22 brake valve 24 double speed clutch 25a / 25b left / right brake piston 62 double speed clutch operating pressure switching valve 63 brake operating pressure switching valve 64 double speed circuit pressure reducing valve 65 brake circuit pressure reducing valve F3 3rd gear position (high speed gear)

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (reference) B62D 11/08 B62D 11/08 EJ 49/49/00/00 EF term (reference) 3D036 AA04 GA15 GA45 GB13 GD01 GD04 GG17 GH12 GJ13 3D043 AA03 AA10 AB12 EA02 EA16 EA31 EA44 EB03 EB06 EB09 EB12 EB14 EF06 EF09 3D046 AA06 BB32 CC02 EE01 GG06 HH07 HH08 JJ11 0211 BB11 BB11 BB11 BB11 BB01 JJ00 JJ17 JJ19 JJ21 JJ22 JJ23 JJ25 JJ26

Claims (3)

[Claims] 1. A front wheel speed-increasing / automatic braking device comprising a front wheel double speed device controlled by a hydraulic clutch and an automatic braking device controlled by a hydraulic pressure. In a tractor configured to operate the front wheel speed increasing / automatic braking device, when the sub-transmission is switched to a high speed, the hydraulic clutch is operated more than when the sub-transmission is switched to a low speed. A tractor front wheel speed increasing / automatic braking device, characterized in that the operating oil pressure of the tractor is reduced. 2. A front wheel speed-increasing / automatic braking device comprising a front wheel double speed device controlled by a hydraulic clutch and a hydraulically controlled automatic braking device. In a tractor configured to operate the front wheel speed increasing / automatic braking device, when the auxiliary transmission is switched to a high speed stage, the automatic braking device is operated more than when the auxiliary transmission is switched to a low speed stage. A tractor front wheel speed increasing / automatic braking device, characterized in that the operating oil pressure of the tractor is reduced. 3. A front wheel speed-increasing / automatic braking device comprising a front wheel double speed device controlled by a hydraulic clutch and a hydraulically controlled automatic braking device, wherein when the steering angle of the front wheel exceeds a certain value, In a tractor configured to operate the front wheel speed increasing / automatic braking device, when the automatic braking device is operated, the brake device is operated intermittently at a substantially constant cycle, and when the auxiliary transmission is switched to a high speed stage. The tractor front wheel speed increase, wherein the operating oil pressure of the brake device is reduced and the operating cycle of the brake device is shortened as compared with the case where the auxiliary transmission is switched to a low speed stage.・ Automatic braking device.