JP2000309228A - Safety device for tractor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a front wheel double-speed unit and automatic breaking mechanism from operating while a sub-gear lever is shifted to be in a high-speed range by providing a shift lock device to control the shifting operation of the sub-gear lever to the high-speed position as well as to judge a gear position. SOLUTION: In a sub-gear lever 59, a shift lock device 61 is provided at the lower part of a guide opening 17a and electrically operated. When the sub-gear lever 59 is between a creep position C and second gear position 2, while a front wheel double-speed unit and automatic breaking mechanism of a tractor are ready to operate, the shift lock device 61 activates to control the sub-gear lever 59 not to shift to a third gear position 3. It is also possible to judge in what range the sub-gear lever 59 is. In this way, activation of the front wheel double-speed unit and automatic breaking mechanism while driving in a high-speed state can be prevented and warned.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tractor equipped with a front wheel speed-up device and an automatic brake mechanism which operate in conjunction with the steering operation of the front wheels. And a safety device for preventing an automatic brake mechanism from operating.

[0002]

2. Description of the Related Art Conventionally, some tractors have a front-wheel double-speed device and an automatic brake mechanism that operate in conjunction with the steering operation of the front wheels. For example, the front-wheel double-speed device is controlled by a hydraulic electric clutch. The automatic braking mechanism was hydraulically and electrically controlled. In such a tractor, an operation switch for switching the operation state of the front wheel double speed device and the automatic brake mechanism is provided, and a sensor for detecting a turning angle of the front wheel is provided. When the operation switch is on, the front wheel is turned off. When the angle exceeds a certain angle, the front wheel double speed device and the automatic brake mechanism are configured to operate.

[0003]

However, in the tractor as described above, when the vehicle is running at high speed by operating the sub-shift lever in the high-speed range, the steering operation is performed to keep the front wheel turning angle constant. When the angle exceeds the angle, the front wheel double speed device and the automatic brake mechanism are operated, and the running state changes rapidly, and the posture and behavior of the vehicle body may become unstable. Therefore,
The present invention provides a safety device for preventing the front wheel double speed device and the automatic brake mechanism from operating in a state where the sub-transmission lever is shifted to a high speed region.

[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, in a tractor provided with a front-wheel double-speed device operated in conjunction with a steering operation of a front wheel and controlled by a hydraulic electric clutch and an automatic brake mechanism hydraulically controlled, as set forth in claim 1, A shift lock device operated by electric means in a high-speed region within the shift range of
The shift operation of the sub shift lever to the high speed range can be restricted, and the shift position of the sub shift lever can be determined.

When an operation switch for switching the operation state of the front wheel double speed device and the automatic brake mechanism is turned on, and the front wheel double speed device and the automatic brake mechanism are in an operable state, the above-mentioned operation is performed. The shift lock device is actuated to restrict the shifting operation of the sub-shift lever to the high-speed range.

According to a third aspect of the present invention, when the shift position of the auxiliary shift lever is in a high speed region, an operation switch for switching an operation state of the front wheel double speed device and the automatic brake mechanism is switched to an ON state, and the front wheel is turned on. When the double-speed device and the automatic brake mechanism are made operable, the shift lock device is operated to detect that the shift position of the auxiliary transmission lever is in the high-speed range, and the alarm device is operated.

According to a fourth aspect of the present invention, when the auxiliary shift lever is shifted to a region other than the high-speed region or the operation switch is turned off during operation of the alarm device, the alarm device stops. It was configured as follows.

[0008]

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 view showing an instrument panel, and FIG. 4 is a connection showing an operating mechanism of a front wheel double speed device and an automatic brake mechanism. FIG. 5 is a circuit diagram, FIG. 5 is a hydraulic circuit diagram showing a front wheel double speed device and an automatic brake mechanism, FIG. 6 is a plan view showing an auxiliary transmission lever and a lever guide, FIG. 7 is a side view thereof, and FIG. FIG. 9 is a plan view showing the auxiliary transmission lever in a state, FIG. 9 is a circuit diagram showing an alarm device, and FIG.
0 is a side view showing the brake mechanism, FIG. 11 is a side view showing the inside of the brake device, and FIG. 12 is a plan sectional view showing the brake device.

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 disposed at the front of the machine which suspends the front wheels 2 and 2 and the rear wheels 3.3 before and after, and an engine 5 is built in the hood 4. A steering handle 51 is provided behind the hood 4, and a seat 52 is provided behind the steering handle 51. An instrument panel 18 is provided in front of the steering handle 51. Then, the steering handle 51, the seat 52, and the instrument panel 18
Are covered by a 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.
The shift operation is performed by 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 mechanism that automatically brakes the front wheels 2 inside the turning during 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 electrically 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 operating state of the front wheel double-speed device and the automatic brake mechanism. I have to.

Next, the switching mechanism between the two-wheel drive state and the four-wheel drive state and the operation mechanism of the front wheel double speed device and the automatic brake mechanism 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 vehicle is in the four-wheel drive state,
When the automatic brake on / off switch 32 is switched on from the off state and turned on, the safety relay 34 is operated to supply a current to the double speed / automatic brake relay 36, and the double speed / automatic brake relay 36 is operated and switched, so that the front wheel double speed device is switched. And the automatic brake mechanism becomes operable. As described above, when the front wheel double speed device and the automatic brake mechanism are in an operable state, the double speed mode indicator lamp 28a among the plurality of indicator lamps 28 shown in FIG. 3 is turned on.

As described above, for example, when the front wheel double speed device and the automatic brake mechanism are operable and the steering wheel 51 is used to make a left turn, the steering angle of the left front wheel 2 is constant. When the angle exceeds the angle, the left turning angle sensor 54a detects this and is turned on, the double speed relay 35 is operated, and a current flows through the double speed solenoid 39. When a current flows through the double-speed solenoid 39, the four-wheel drive / double-speed switching valve 21 operates to switch to the double-speed side,
Double-speed clutch 2 for turning on / off the drive rotation of front wheels 2
4, the pressure oil from the hydraulic pump 19 is pumped 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 27a 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 to brake the left rear wheel 3, that is, the rear wheel 3 inside the turning. That is, the automatic brake mechanism operates.

In the case where the steering wheel 51 is steered and turned rightward, when the turning angle of the right front wheel 2 exceeds a predetermined angle, the right turning angle 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 mechanism are operable, when the steering angle of the left and right front wheels 2 becomes greater than a certain angle by steering the steering handle 51, the front wheel double speed device is operated. And the automatic brake mechanism operates. In the present embodiment, switching between the two-wheel drive state and the four-wheel drive state is configured to be electrically performed by the four-wheel drive on / off switch 31. For example, the drive force is transmitted to the front wheels 2. A switching lever or a changeover switch may be connected to the clutch to be operated via a link mechanism or the like to mechanically switch between the two-wheel drive state and the four-wheel drive state.

Further, in the tractor, a safety device for preventing the front wheel double speed device and the automatic brake mechanism from operating when the auxiliary speed change lever 59 is shifted to a high speed range is configured. Next, the safety device will be described. As shown in FIGS. 7 and 8, the auxiliary speed change lever 59 is configured to be slidable in an elongated guide opening 17 a formed in the lever guide 17. The sub-shift lever 59 can be shifted to a low-speed first-speed position F1, a medium-speed second-speed position F2, a high-speed third-speed position F3, and a very low-speed creep position C. The neutral position N is arranged between the vehicle and the speed position F1.

The guide opening 17 of the auxiliary transmission lever 59
A shift lock device 61 is attached to a portion below a. The shift lock device 61 is electrically operated by a lock solenoid 40 shown in FIG. 4, and when a current flows through the lock solenoid 40, the shift lock device 61
When the lock piece 61a is actuated and extended, and the current does not flow through the lock solenoid 40, the lock piece 61a is not actuated and is in a contracted state. A lock guide 62 protruding downward from the lower surface of the lever guide 17 in the direction of the third speed position F3 from an intermediate position between the second speed position F2 and the third speed position F3 of the auxiliary transmission lever 59 is provided at the peripheral portion of the guide opening 17a. Are formed, and the lock guide 62 is
Are arranged on the side of the shift lock device 61 where the lock pieces 61a are provided.

When the lock piece 61a of the shift lock device 61 is in a contracted state, the sub-shift lever 59 is configured to be able to perform a shift operation in a range from the creep position C to the third speed position F3. When the lock piece 61a is in the extended state, when the sub-shift lever 59 is shifted from the range between the creep position C and the second speed position F2 to the third speed position F3, the second speed position F2 is set. The lock piece 61a is locked to the lock guide 62 at an intermediate position between the third speed position F3 and the third speed position F3 so that the gear can not be further shifted to the third speed position F3. That is, the shift lock device 6
When the first lock piece 61a is in a contracted state, the shift lock device 61 does not restrict the shift position of the sub-transmission lever 59, and in a state in which the lock piece 61a is extended, Third-speed position F3, which is a high-speed area
The shift operation to the gear is restricted by the shift lock device 61.

Further, as shown in FIG.
9 is located in the range from the creep position C to the second speed position F2 when the lock piece 61a of the shift lock device 61 is locked.
Is extended from the contracted state, the extension stroke of the lock piece 61a is the dimension D1. On the other hand, as shown in FIG. 8, when the lock piece 61a extends from the contracted state when the sub-transmission lever 59 is located at the third speed position F3,
Since the lock piece 61a abuts on the lock guide 62 during extension and cannot be further extended, the extension stroke of the lock piece 61a is a dimension D2 smaller than the dimension D1.

As described above, when the speed change operation position of the auxiliary speed change lever 59 provided with the shift lock device 61 is in the range from the creep position C to the second speed position F2, the four-wheel drive on / off switch 31 and the double speed When the automatic brake on / off switch 32 is turned on to make the front wheel double speed device and the automatic brake mechanism operable, an electric current flows through the lock solenoid 40, and the lock piece 61a of the shift lock device 61 extends by the dimension D1. The shift operation of the auxiliary shift lever 59 is restricted as described above, and the shift operation to the third speed position F3 cannot be performed.

As described above, when the shift operation position of the sub-transmission lever 59 is in the range from the creep position C to the second speed position F2, when the front wheel double speed device and the automatic brake mechanism of the tractor become operable. By activating the shift lock device 61 and restricting the speed change operation of the auxiliary speed change lever 59 to the third speed position F3 which is a high speed region, the front wheel double speed device and the automatic brake mechanism operate in a high speed running state. It is possible to prevent a situation in which the vehicle body suddenly changes and the posture and behavior of the vehicle body to become unstable.

On the other hand, when the sub-transmission lever 59 is operated to shift to the third speed position F3, the four-wheel drive on / off switch 31 is turned on.
Also, when the double speed / automatic brake on / off switch 32 is turned on and the front wheel double speed device and the automatic brake mechanism are made operable, the shift lock device 61 is also operated,
As described above, the lock piece 61a extends by the dimension D2. The lock solenoid 40 for extending and contracting the lock piece 61a is displaced in accordance with the degree of expansion and contraction of the lock piece 61a. As shown in FIG. A solenoid position detection sensor 63 for detection is provided, and a detection value of the solenoid position detection sensor 63 is input to a control unit 50 provided on the tractor. In the control unit 50, the input detection value is
If 1a has been extended by the dimension D1, it is determined that the shift operation position of the subtransmission lever 59 is in the range from the creep position C to the second speed position F2, and the input detection value is When the lock piece 61a is in the state of being extended by the dimension D2, it is determined that the shift operation position of the auxiliary shift lever 59 is at the third speed position F3.

Then, the auxiliary transmission lever 59 is moved to the third speed position F3.
When the gearshift operation is performed, the four-wheel drive on / off switch 3
When the 1 and double speed / automatic brake on / off switch 32 is turned on, the lock piece 61a of the shift lock device 61 extends by the dimension D2 as described above.
The position of the lock solenoid 40 extended by two is detected by the solenoid position detection sensor 63 and input to the control unit 50. Then, the control unit 50 determines that the sub-shift lever 59 is shifted to the third speed position F3, blinks the lit double speed mode indicator lamp 28a, and sounds the alarm buzzer 64 intermittently. Therefore, despite the fact that the sub-shift lever 59 is shifted to the high-speed region,
Assuming that the front wheel double speed device and the automatic brake mechanism are in an operable state, a warning is issued to the operator for erroneous operation.

As described above, when the speed change position of the auxiliary speed change lever 59 is in the high speed range, the double speed / automatic brake ON / OFF switch 32 is switched to the ON state, and the front wheel double speed device and the automatic brake mechanism can be operated. Then, the shift lock device 61 is operated to determine that the shift position of the sub-transmission lever 59 is in the high-speed range, and an alarm device such as the double speed mode indicator lamp 28a or the alarm buzzer 64 is operated. Warns the operator that the front wheel doubler and the automatic brake mechanism may operate during high-speed running, and warns the operator that the front wheel doubler and automatic brake mechanism are inadvertently operated during high-speed running. Can be prevented.

In the event that the operator ignores the warning and performs the steering operation until the turning angle of the front wheels 2.2 becomes a predetermined angle or more, and the front wheel double speed device and the automatic brake mechanism operate, The rotation speed of the engine 5 is configured to decrease at a preset rate, so that the traveling speed is reduced to enable stable turning.

As described above, when the double speed mode indicator lamp 28a is blinking and the alarm buzzer 64 is sounding intermittently, whether the shift position of the subtransmission lever 59 is operated to a position other than the third speed position F3 is determined. Alternatively, when the double speed / automatic brake ON / OFF switch 32 is turned off, the control unit 50 detects this and stops the blinking of the double speed mode indicator lamp 28a and the operation of the alarm buzzer 64. In this case, when the sub speed lever 59 is shifted to a position other than the third speed position F3, the double speed mode indicator lamp 28a switches from the blinking state to the lighting state, and when the double speed / automatic brake on / off switch 32 is switched off, the double speed mode The mode indicator lamp 28a turns off.

The warning buzzer 64 emits a warning sound intermittently when the tractor is moving backward, to alert the driver to the fact that the tractor is in reverse. Also,
With the sub-shift lever 59 shifted to the high-speed region,
The warning sound emitted from the alarm buzzer 64 when the front wheel double speed device and the automatic brake mechanism are made operable, and the warning sound emitted from the alarm buzzer 64 when the tractor moves backward may be distinguished between the two. The sound is not limited to this example.

As described above, while the alarm device such as the double speed mode indicator lamp 28a and the alarm buzzer 64 is operating, the sub-shift lever 59 is operated to shift to a region other than the high speed region, or the double speed / automatic brake is turned on. When the off switch 32 is switched to the off state, the warning device is configured to stop, so that the warning can be stopped by avoiding a state in which the front wheel double speed device and the automatic brake mechanism can be operated in a high-speed running state. , Can be easily performed by a simple operation.

As described above, the shift lock device 61 is attached to the sub-shift lever 59 so that the shift operation of the sub-shift lever 59 to the high speed region can be restricted by the shift lock device 61, and the shift of the sub-shift lever 59 can be controlled. By making it possible to determine the position, it is possible to prevent the front wheel double speed device and the automatic brake mechanism from operating in a high speed running state, or if the front wheel double speed device and the automatic brake mechanism become operable in the high speed running state It is possible to issue a warning and call attention to the worker with a simple and low-cost configuration in which only the shift lock device 61 is attached. Note that the shift lock device 61 may be provided on the lever guide 17 side so as to regulate the shift operation position of the sub-shift lever 59, and operate in a high-speed region within the shift range of the sub-shift lever 59. It is sufficient if they are provided.

As shown in FIG. 10, when the automatic brake mechanism operates, as described above, for example, the left brake piston 25a extends and abuts on the abutment portion 26b of the left brake cam 26a. The left brake device 29a is operated by rotating the brake cam 26a. However, the left brake device 29a can also be operated when the operator depresses the brake pedal 13.
That is, when the brake pedal 13 is depressed, the connecting rod 7
1 moves upward and the shaft 72 rotates rightward, whereby the brake rod 73 moves forward to rotate the left brake cam 26a and operate the left brake device 29a.

As shown in FIG. 11, the left brake cam 26
a, an arm 76 is fixedly mounted at the center of rotation so that the arm 76 can rotate integrally.
A stay 78 fixed to the brake shoe 79 of FIG. The brake shoe 79 is provided so as to face the support plate 80.
In addition, grooves 79a are formed in the support plate 80, and a ball member 81 is fitted between the grooves 79a.

When the left brake cam 26a is rotated forward by the brake rod 73 or the left brake piston 25a, the brake shoe 79 moves forward (see FIG. 12) through the arm 76, the link 77, and the stay 78. (In the direction of the arrow), and the brake shoe 79 is pushed out to the side opposite to the support plate 80 by the ball member 81 fitted into the groove portions 79a.
Is pressed by a brake disc 83 to brake the left rear wheel 3. Thus, the left brake device 29a is configured to be operable by both the depression pressure of the brake pedal 13 and the extension of the left brake piston 25a in the automatic braking mechanism.

As shown in FIGS. 10 and 11, the left brake piston 25a is 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, by moving the left brake piston 25a within the range of the elongated hole 92, the distance from the center of rotation of the left brake cam 26a to the contact position of the left brake piston 25a with the contact portion 26b can be adjusted. It is doing.
Thus, the contact portion 26b of the left brake piston 25a
Since the rotation torque of the left brake cam 26a by the left brake piston 25a is changed by adjusting the contact position to the rear wheel 3, the degree of braking of the rear wheel 3 by the automatic brake mechanism can be adjusted. Become.

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.

[0035]

As described above, the present invention has the following advantages. That is, as described in claim 1, a shift lock device which is operated by an electric means in a high-speed region within a shift range of the sub-transmission lever is provided, and the shift lock device controls a shift operation of the sub-transmission lever to a high-speed region. In addition to being able to regulate, the shift position of the sub-shift lever can be determined, so that the front wheel double speed device and the automatic brake mechanism are prevented from operating in a high-speed running state, or the front wheel double speed device and the automatic brake When the mechanism becomes operable, an alarm can be issued to alert the worker with a simple and low-cost configuration that simply requires the addition of a shift lock device.

When the operation switch for switching the operation state of the front wheel double speed device and the automatic brake mechanism is switched to the on state, and the front wheel double speed device and the automatic brake mechanism become operable, the above-mentioned state is obtained. The shift lock device is activated to restrict the speed change operation of the sub-shift lever to the high-speed range, so that the front double-speed device and the automatic brake mechanism are prevented from operating in the high-speed running state. It is possible to prevent the posture and behavior of the vehicle body from becoming unstable due to a sudden change in the state.

According to a third aspect of the present invention, when the shift position of the auxiliary shift lever is in a high speed range, an operation switch for switching an operation state of the front wheel double speed device and the automatic brake mechanism is switched to an on state, and the front wheel is turned on. When the double-speed device and the automatic brake mechanism are made operable, the shift lock device is operated to determine that the shift position of the auxiliary transmission lever is in the high-speed range, and the alarm device is operated. Warns the worker that there is a possibility that the front wheel speed doubler and the automatic brake mechanism may operate in the running state, and warns the operator, and prevents the front wheel doubler and the automatic brake mechanism from inadvertently operating in the high speed running state can do.

According to a fourth aspect of the present invention, when the sub-transmission lever is shifted to a region other than the high-speed region or the operation switch is turned off during operation of the alarm device, the alarm device stops. With such a configuration, it is possible to easily stop the warning by avoiding a state in which the front wheel double speed device and the automatic brake mechanism become operable in a high-speed running state by a simple operation.

[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 an operation mechanism of a front wheel double speed device and an automatic brake mechanism.

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

FIG. 6 is a plan view showing an auxiliary transmission lever and a lever guide.

FIG. 7 is a side view of the same.

FIG. 8 is a plan view showing the sub-transmission lever in a state where a shift operation is performed to a third speed position.

FIG. 9 is a circuit diagram showing an alarm device.

FIG. 10 is a side view showing a brake mechanism.

FIG. 11 is a side view showing the inside of the brake device.

FIG. 12 is a plan sectional view showing a brake device.

[Explanation of symbols]

 17 Lever guide 28a Double speed mode indicator lamp 29a / 29b Left / right brake device 32 Double speed / automatic brake ON / OFF switch 59 Secondary speed shift lever 61 Shift lock device 61a Lock piece 62 Lock guide F3 Third speed position (high speed area)

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) AA03 BA03 CB02 CB39 CD01 DA24

Claims (4)

[Claims] 1. A tractor having a front wheel double speed device which is operated in conjunction with a steering operation of a front wheel and is controlled by a hydraulic electric clutch and an automatic brake mechanism which is hydraulically controlled is provided within a speed range of a sub speed change lever. A shift lock device that is operated by electric means in a high-speed range is provided, and the shift lock device enables a shift operation of the sub-shift lever to a high-speed range to be restricted and a shift position of the sub-shift lever to be determined. A safety device for a tractor, characterized in that: 2. An operation switch for switching an operation state of the front wheel double speed device and the automatic brake mechanism is turned on, and when the front wheel double speed device and the automatic brake mechanism are in an operable state, the shift lock device is operated. hand,
The tractor safety device according to claim 1, wherein the auxiliary shift lever is configured to restrict a shift operation to a high-speed region. 3. When the shift position of the sub-transmission lever is in a high speed region, an operation switch for switching an operation state of the front wheel double speed device and the automatic brake mechanism is turned on, and the front wheel double speed device and the automatic brake mechanism are turned on. When the state is operable, the shift lock device is operated to determine that the shift position of the auxiliary shift lever is in the high speed region,
The tractor safety device according to claim 1, wherein the alarm device is configured to operate. 4. The system according to claim 1, wherein the alarm device is configured to stop when the sub-transmission lever is shifted to a region other than the high-speed region or the operation switch is turned off during the operation of the alarm device. The tractor safety device according to claim 3, characterized in that: