JPH0689535B2 - Automatic control device for snowplow - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic control system for a snow removal vehicle for automating a part of snow removal work.

[0002]

2. Description of the Related Art In recent years, from the viewpoint of improving the efficiency of snow removal work, high-speed snow removal has become popular, in which snow removal is performed while running a snow removal vehicle at a high speed of 40 km / h or more.

However, in the conventional snow plow, the operator is required to perform various blade operations required during snow pruning work, such as adjusting the ground contact pressure of the blade, avoiding the blade from an obstacle, and reducing the width of the blade when approaching a narrow road. Since it had to be done by one person, many operations had to be performed in a short time as the speed of the snow removal vehicle increased, which caused an excessive burden and hindered safe driving. It was.

[0004]

Therefore, it is a technical object of the present invention to make it possible to easily perform a complicated blade operation even during high-speed snow removal.

[0005]

[Means for Solving the Problems] In the present invention,
Means adopted for solving the above problems will be described.

While the blades are independently hung on the two hydraulic cylinders for lifting and lowering via a clearance mechanism, the number of revolutions of the engine per unit time is measured, and the number of revolutions to output a signal based on the measurement result. A detector, an accelerator sensor that detects the amount of depression of the accelerator and outputs a signal based on the detection result, a braking sensor that detects the operation of the anti-locking brake system and outputs a signal based on the detection, and a limited A grip sensor that detects the operation of the slipping differential and outputs a signal based on the detection is provided as an input device with an automatic mode switch that outputs a signal when selected, and the grip sensor is provided in each fluid conduit of the pair of fluid pressure cylinders. Output the installed solenoid valve and the pressure control valve arranged in each fluid pipe of the pair of fluid pressure cylinders The device with a built-in microcomputer having as, when the automatic mode switch is a signal input is selected the microcomputer,
The engine speed detected by the rotation speed detector is above a specified value or the accelerator pedal depression amount detected by the accelerator sensor is below a specified value, and the anti-locking brake system operation detection signal is not input by the braking sensor. , When there is no limited slipping differential actuation detection signal input by the grip sensor,
Applying a predetermined fluid pressure in the lifting fluid pressure cylinder,
When the blade edge is grounded at a predetermined pressure and the engine speed detected by the rotation speed detector is less than a predetermined value and the accelerator pedal depression amount detected by the accelerator sensor is more than the predetermined value, or by the rotation speed detector The engine speed is equal to or higher than a predetermined value, or the accelerator pedal depression amount detected by the accelerator sensor is equal to or lower than a predetermined value, and the anti-locking brake system operation detection signal is input by the braking sensor or the grip sensor limited When the operation detection signal of the ripping differential is input, a fluid pressure which is a certain amount subtracted from the above-mentioned predetermined fluid pressure to be applied is applied to the lifting fluid pressure cylinder so that the edge of the blade is kept at a constant pressure. Select the automatic mode switch by adopting the means of grounding with In, can various blade operations automatically, it had provided an automatic control device which greatly simplified the blade operation in snow removal.

[0007]

EXAMPLES The present invention will be described below based on examples.

On the lower surface of the chassis of the truck that employs the automatic transmission, a pair of main brackets 46, 46 are fixedly installed side by side in the front right and rear left directions, and the first fluid pressure cylinders 44, 44 are mounted on the brackets. It is pivotally installed. Also, this bracket has parallel links
The clearance cylinders 47, 47 are connected via 48, 48, ... And the rod ends of the first fluid pressure cylinders 44, 44 are also connected to the cylinders 47, 47. When the fluid pressure cylinder expands and contracts, the cylinders 47, 47 also move up and down. And, to this cylindrical body 47, 47, through the bracket, the pivot 45
・ 45 are arranged horizontally and in a one-way manner. Furthermore, this axis
A composite blade bracket 42 is pivotally installed at 45 and 45. This composite blade bracket 42 has a slide guide on the front surface, and two divided blades 41 having a slide guide on the rear surface are arranged in a stepwise manner with the divided blade located on the right side in front of each other to form a composite blade. Constitute. In addition, the composite blade bracket 42 and the split blades 41, 41
Second fluid pressure cylinders 43, 43 are respectively installed between and, and when the second fluid pressure cylinders 43, 43 extend, both split blades project laterally to widen the overall width of the composite blade, On the contrary, when the second fluid pressure cylinders 43, 43 contract, the divided blades 41, 41 approach the center so as to overlap with each other and narrow the width of the entire composite blade.

Further, on the upper portion of the rear surface of the composite blade bracket 42 pivotally mounted on the shaft 45, there is a triangle plate member 53.
The rod ends of the third fluid pressure cylinders 54, 54 are connected to each other via a link constituted by the arc plate material 55 and a separable joint described later. Since the bottom end of the third fluid pressure cylinder 54, 54 is pivotally supported by the frame carried out from the shaft, when the third fluid pressure cylinder 54, 54 extends, the entire composite blade falls forward and the third fluid pressure cylinder 54. Pressure cylinder 54 ・
When 54 shrinks, the entire composite blade rises. The separable joint includes a male meshing member 51 fixed to the composite blade bracket 42, and a third fluid pressure cylinder.
It is composed of a female mating member 52 fixed to a link pivotally provided at the rod end of 54, 54, and the concave and convex portions of both mating members 51, 52 mesh with each other to connect the composite blade bracket 42 and the link. This meshing is made by strip-shaped teeth extending parallel to the blade surface of the composite blade and extending in a direction perpendicular to the link when the blade is upright.
Therefore, this tooth engagement is due to the combined blade bracket
Strong in the direction that separates 42 from the link. Also, the link is
Since not only the fluid pressure cylinder but also the shaft 45 is pivotally installed, even if the separable joint is separated into two, the female mating member 52 can be kept at a predetermined distance from the shaft 45. There is. Therefore, after separating the separable joint, it is only necessary to extend the third fluid pressure cylinders 54, 54 and
The 51 and the female mesh member 52 meet again and mesh with each other.

Above the composite blade, a frame 66 having rails is arranged. A shutter bracket 64 is held on this rail in a state in which it can be moved back and forth due to the expansion and contraction of the fifth fluid pressure cylinder 65. The bracket 64 is arranged so as to be taken out to the left end side of the blade, and the parallel links 63, 63 are attached to the taken out tip.
Is rotatably provided. Parallel links 63 and 63 are 2 each
It has a shape that the rods of the book are reinforced with a cauldron,
The shutter blade 61 is supported at the end of the link opposite to the bracket, and the direction of the blade surface is expanded and contracted by the expansion and contraction of the fourth fluid pressure cylinders 62, 62 provided between the shutter bracket 64 and the shutter blade 61. Swings up and down while being kept constant.

The first to fifth fluid pressure cylinders described above have independent fluid supply conduits and fluid discharge conduits, and electromagnetic operation valves 3a, 3a, ... Are provided in the respective conduits. However, by opening and closing this solenoid operated valve, it is possible to expand and contract independently. Further, in the first fluid pressure cylinder, a pressure control valve 3b is also provided in the pipeline so that the pressure of the fluid in the cylinder can be maintained at a desired value.

The solenoid operated valve and the pressure control valve related to the expansion and contraction of the fluid pressure cylinder are operated by the snow removal automatic control device 1 provided in the cab of the truck. The automatic snow removal control device 1 has a microcomputer (trade name; FA-2J, manufactured by Izumi Electric Co., Ltd.) built in a box-shaped main body, and appropriately operates a valve based on information input to the microcomputer. By controlling the expansion and contraction of the fluid pressure cylinder, the blade operation necessary for snow removal work is performed. Further, various switches and photographing are arranged on the upper surface of the main body of the automatic control device 1.

The input device of the microcomputer incorporated in the automatic control device 1 includes eight push-button type switches (automatic mode switch 2a, forwarding mode switch 2b, work standby mode switch) provided on the upper surface of the automatic control device 1. 2c, grounding mode switch 2d, pressing mode switch 2e, temporary avoidance mode switch 2f, side shutter opening switch 2g and side shutter closing switch 2h) and 3 types of slide type setting shooting (pressing pressure setting shooting 2i, left and right) Balance setting shot 2j, blade width setting shot 2k), and two types of marker detectors (shutter marker detector 2l, temporary avoidance marker detector 2m) provided on the lower part of the front of the truck, front lower surface of the truck, rear portion Ultrasonic receiving elements 2n and 2n provided one by one on the bottom surface, photoelectric receiving element 2o provided only one on the bottom surface of the rear part of the track, composite breaker The blade sensor 2p and the snow removal width detector 2q arranged on the bracket 42, the rotation speed detector 2r connected to the tachometer of the engine, the speed detector 2s connected to the speedometer, and the antilocking brake system of the truck. A braking sensor 2t that outputs a signal in conjunction with it, a grip sensor 2u that outputs a signal in conjunction with a limited slipping differential, and an accelerator sensor 2v that monitors the amount of depression of the accelerator are adopted. Further, in the output device of the microcomputer, in addition to the solenoid operated valves 3a, 3a, ..., The pressure control valve 3b, a work status indicator 3c disposed in the cab, a front lower surface of the truck, and a lower rear surface of the truck are provided. The ultrasonic wave oscillating elements 3d and 3d and the probe light oscillating element 3e on the lower surface of the rear part of the track are adopted.

Of the above input devices, an automatic mode switch button, a forwarding mode switch button, a work standby mode switch button, a grounding mode switch button, a pressing mode switch button, a temporary avoidance mode switch button, etc. are pressed to push the switch. When a signal is input to the microcomputer, the microcomputer responds to the input by performing a process 1 described later.
~ 4, X, 0, 00, 000, 0000, 0000 is set.

First of all, the basic blade operation performed by the microcomputer will be briefly described. The blade operation is each operation of raising and lowering the blade, pressing and adjusting the left and right balance, rotating, expanding and contracting the width, and raising and lowering the shutter blade. Among these operations, the raising and lowering of the blade is performed by the expansion and contraction of the first fluid pressure cylinder, and the pressing of the blade is performed while the first fluid pressure cylinder is extended and the blade is lowered. This is done by keeping the fluid pressure in the cylinder at a predetermined value. At the time of this pressing, the left and right balance of the blade pressing is adjusted depending on whether the two first fluid pressure cylinders have the same fluid pressure or the two fluid pressures are left and right separately.

Further, the microcomputer realizes the work modes of the five kinds of composite blades by the above blade operation. The first working mode is the forwarding mode,
This is accomplished by retracting the first fluid cylinder of the book together and extending the third fluid pressure cylinder to lay down the blades and float the entire surface off the road. The second work mode is a work standby mode and is achieved by retracting the two first fluid cylinders together and retracting the third fluid pressure cylinder so that the edge is lifted from the road surface while the blade is standing upright. To be done. The third working mode is the grounding mode, in which the two first fluid pressure cylinders are extended to a predetermined length and the third fluid pressure cylinders are retracted so that the blade is raised and the edge is slid on the road surface. Achieved by keeping in. The fourth work mode is the pressing mode, in which the third fluid pressure cylinder is retracted,
This is achieved by applying a predetermined fluid pressure to the inside of each of the two first fluid pressure cylinders to extend the cylinders, and pressing the edge of the blade against the road surface with a predetermined ground pressure. At this time, if the fluid pressures inside the two first fluid pressure cylinders are changed, the pressing state in which the ground pressure is different between the left and right is achieved. Finally, the fifth work mode is the temporary avoidance mode, in which the third fluid pressure cylinder is retracted and the two first work modes are used.
From the state in which the predetermined fluid pressure is applied to each inside of the fluid pressure cylinder and the fluid pressure cylinder is extended, only the first fluid pressure cylinder on the right side is retracted by a predetermined amount, and the left end of the blade is grounded,
This is accomplished by slightly lifting the right edge of the blade above the ground.

The realization of these five work modes is selected according to which of the six work mode selection switches is selected.

First, when selecting the automatic mode switch,
Based on the information from other input devices, the microcomputer selects the most suitable mode from the above-mentioned five working modes, namely, the pressing mode, the grounding mode, and the temporary avoidance mode, and realizes that mode. The selection and realization of this mode are the most important processes (see processes 1 to 4 below) performed by the microcomputer. The information that serves as the basis for this selection is detection information of the temporary avoidance marker, track speed information, engine speed information, accelerator depression amount information, anti-locking brake system operation information,
It is operation information of the limited slipping differential, road surface state information, ground pressure setting value information, and left and right balance setting value information.

#. Process 1 Of these information, the detection information of the temporary avoidance marker is
It has the highest priority as a judgment criterion, and whenever the temporary avoidance marker is detected, the blade is temporarily moved to the avoidance state. This temporary avoidance marker detection information is
The temporary avoidance marker detector detects the temporary avoidance marker that is pre-embedded before the location of the obstacle caught by the blade such as the bridge joint. The temporary avoidance marker needs to be, for example, an oscillator that oscillates an electromagnetic wave of a specific frequency in order to distinguish it from other types of markers. Alternatively, a marker is constructed by embedding a ferrite magnetic material in a specific pattern such as a bar code that is identified by its width and number, and the marker detector is composed of an electromagnetic coil and a ferrite sensor. A method of recognizing that the road surface is magnetized by the ferrite sensor may be adopted. In addition, the microcomputer is set in advance for the time required to pass a location with an obstacle from the standard traveling speed of the snowplow, and after the temporary avoidance marker is detected and the temporary avoidance mode is entered, After waiting for the passage of the required time, the snow removal mode is always restored.

#. Process 2 Track speed information, information that combines engine speed information and accelerator depression amount information, anti-locking brake system operation information, and limited slipping differential operation information is next to the temporary avoidance marker detection information. Moreover, it has a high priority as a criterion. These pieces of information are input to the microcomputer from the speed detector, the rotation speed detector and the accelerator sensor, the braking sensor, and the grip sensor, respectively. Then, the microcomputer shifts the blade to the ground mode if the speed of the track input from the speed detector is equal to or lower than a predetermined value. Efficient snow removal requires a certain amount of speed, and a state where the speed is below a certain value is a transient state that is either trying to stop or accelerating from now on. If so, pressing the blade against the road surface is a major obstacle to acceleration. Further, the microcomputer reduces the ground pressure of the blade when the engine speed input from the rotation speed detector is equal to or lower than a predetermined value and the depression amount input from the accelerator sensor is equal to or higher than the predetermined value. . In order to accelerate by depressing the accelerator while pressing the blade against the road surface, a considerable amount of engine torque is required, and when acceleration is required but the engine speed drops below a certain value, the engine load is lightened. This is because it is necessary to increase the number of rotations. The accelerator sensor detects the amount of depression by monitoring the amount of movement of the wire end connected to the accelerator. Furthermore, when the detection information of the operation of the anti-locking brake system is input from the braking sensor, the microcomputer reduces the ground pressure of the blade by a predetermined amount. The operation of the anti-locking brake system generally occurs when the tire is about to slip during sudden braking, and in such a case, the contact pressure of the one-sided blade is relaxed to increase the grip force of the tire and also from the road surface. This is because it is necessary to prevent the track from skidding due to the force applied to the blade. Further, when the limited slipping differential is activated, the microcomputer reduces the ground pressure of the blade by a predetermined amount. This is because the operation of the limited slipping differential is caused by the slip of the tire, and in such a case, it is necessary to reduce the ground contact pressure of the blade to enhance the grip force of the tire. In addition, the sum of the pressing pressure of the blade and the load applied to each tire is almost equal to the weight of the entire snow removal vehicle,
Therefore, when the pressing pressure is reduced, the load applied to the tire is increased and the grip force is increased.

#. Process 3 The road surface condition information is used as a criterion for determining the working mode: temporary avoidance marker detection information, truck speed information, engine speed information and accelerator pedal depression amount information, anti-locking brake system operation information, limited slipping. It is inferior to the differential operation information. And
Only when the blade operation conditions based on the priority information are not satisfied, the blade operation determination criterion is obtained. The road surface state information has priority over the ground contact pressure setting value information and the left-right balance setting value information, but like the ground pressure setting value information and the left-right balance setting value information, keeps the blade in the snow removal mode. This road surface state information will be described in detail. This information can be obtained from the ultrasonic wave receiving element and the photoelectric receiving element on the lower surface of the track. The ultrasonic wave receiving element receives the ultrasonic wave emitted by the ultrasonic wave oscillating element whose output is controlled by the microcomputer, which is reflected back on the road surface or snow surface, and returns an electric signal corresponding to the amount of energy. Input to microcomputer. The amount of energy of the reflected wave is
It is proportional to the amount of ultrasonic waves reflected from the road surface or the snow surface on the road surface. As a result of the test, the greater the amount of snow, the greater the ratio of the amount of ultrasonic waves absorbed by the snow than the amount reflected by the snow surface, and the harder the snow,
Since it was found that the ultrasonic reflectivity increased in proportion to it, by comparing the actual received amount with the empirical value, from the energy amount of the reflected wave captured by the receiving element on the front side of the track, You can know the state of snow on the road before snow removal. Further, it is possible to monitor whether the road surface is exposed by completely removing snow behind the blade from the amount of energy of the reflected wave captured by the vibration receiving element on the rear side of the track. When it is determined that the amount of snow on the road surface before snow removal is large or the snow surface is hard, the microcomputer increases the ground contact pressure of the blade above the current value. Further, when the snow is completely removed behind the blade and the road surface is not exposed, the ground contact pressure of the blade is increased. Actually, when the snowplow travels, the chassis of the truck vibrates, and the distance of the oscillation element or the vibration receiving element from the road surface changes. Therefore, in order to determine the snow accumulation state before snow removal and the road surface exposure after snow removal, it is necessary to temporally average the amounts of energy of the reflected waves obtained by the vibration receiving element before making the determination. However, depending on the road surface condition, the vibration of the chassis may become so large that it may be difficult to make a judgment even if time averaging is performed. Only the road condition will be judged. Since the paved road surface has a lower light reflectance than the snow surface, it can be judged that snow can be completely removed and the road surface is exposed only when the amount of reflected energy of the exploratory light emitted by the oscillation element falls below a specified value. . When it is determined that the road surface is not exposed, the microcomputer increases the ground contact pressure of the blade.

#. Process 4 Prioritized information such as temporary avoidance marker detection information, truck speed information, engine speed information and accelerator depression amount information, anti-locking brake system operation information, limited slipping differential operation information, When the condition for blade operation determined by the microcomputer is not satisfied, the microcomputer causes the blade to enter the snow removal mode. At this time,
The ground pressure of the blade follows the ground pressure setting value information and the left-right balance setting value information. The ground pressure setting value information is input by pressing pressure setting shooting, and the left and right balance setting value information is input by left and right balance setting shooting. The microcomputer corrects the ground pressure setting value information based on the left-right balance setting information, loads predetermined fluid pressures inside the left and right first fluid pressure cylinders, and presses the blades according to the shooting settings. Of.

#. Processing X Further, the microcomputer selects one of five types of work mode selection switches (forwarding mode switch, work standby mode switch, grounding mode switch, pressing mode switch, temporary avoidance mode switch) other than the automatic mode switch. Occasionally, the blade is moved to a work mode corresponding to each switch. After this selection, the same work mode is maintained until one of the other work mode switches including the automatic mode switch is selected.

#. Process 0 In addition, regardless of which one of the five modes the blade is in, and whether any of the six work mode selection switches is selected, the microcomputer determines the current blade width. According to, control the slide of the shutter bracket. First, a snow removal width detector that employs a rotary encoder measures the current amount of overhang of the divided blades, and the microcomputer calculates the current blade width. At the same time, the microcomputer calculates the position of the left end of the blade and slides the shutter bracket so that when the shutter blade is closed, the shutter blade is positioned slightly left of the left end position of the blade.

#. Process 00 In addition, the blade width is basically the blade width regardless of which of the six kinds of work mode selection switches is selected, regardless of which of the five kinds of modes the blade is in. The microcomputer expands and contracts according to the width set in the set shooting. Therefore, when the blade width setting shot is moved, the blade width and the shutter position change simultaneously.

#. Process 000 Further, in principle, the shutter blade is opened and closed by the microcomputer when the side shutter open switch and the side shutter close switch are selected. However, when the automatic mode switch is selected and a marker is detected by the shutter marker detector, the shutter blade is opened and closed. This shutter marker can have a structure similar to that of the temporary avoidance marker, and must be placed at both ends of a section where snowfall should be stopped, such as an intersection. When the snow removal vehicle approaches this section with the shutter blade open, the shutter marker detector detects the first shutter marker, the microcomputer closes the shutter blade, and the snow removal vehicle concerned. When passing the section, the shutter marker detector detects the second shutter marker, and the microcomputer closes the shutter blade.

#. Processing 0000 In addition, regardless of which of the six work mode selection switches is selected, the microcomputer uses the proximity switch blade when the edge of the blade is caught by an obstacle and flips over. This is detected by the sensor, and after sufficient time has passed for the blade to pass over the obstacle, the third fluid pressure cylinder is extended and retracted to return the blade to the standing state.

#. Processing 00000 The microcomputer displays the current blade mode and the energy of the reflected wave detected by the vibration receiving element on the work status indicator in the cab regardless of which of the six work mode selection switches is selected. By displaying the snow cover information before snow removal, which is determined based on the amount of snow, the presence or absence of road surface exposure after snow removal, and the opening or closing of the shutter blade, the operator can see the blade condition without directly observing the blade at the rear of the driver Make sure that it helps to judge the blade operation.

[0029]

INDUSTRIAL APPLICABILITY As described above, the automatic control device of the present invention reduces the burden on the operator by automating the blade operation during snow removal work, and has a high industrial utility value.

[Brief description of drawings]

FIG. 1 is a side view of an embodiment.

FIG. 2 is a plan view of the embodiment.

FIG. 3 is a side view of the embodiment with the shutter blade omitted.

FIG. 4 is a plan view of the embodiment with the shutter blade omitted.

FIG. 5 is a plan view of a composite blade (standing state) in the example.

FIG. 6 is a side view of the composite blade in the example.

FIG. 7 is a rear view of the composite blade in the embodiment in which the first fluid pressure cylinder and the third fluid pressure cylinder are omitted.

FIG. 8 is a cross-sectional view of the composite blade (standing state) in the embodiment, with the upper part omitted.

FIG. 9 is a cross-sectional view of the composite blade (with the joints separated) in the embodiment, with the upper part omitted.

FIG. 10 is a sectional view of a separable joint (connected state) in the example.

FIG. 11 is a cross-sectional view of a separable joint (transitional state) in the example.

FIG. 12 is a sectional view of a separable joint (separated state) in the example.

FIG. 13 is a rear view of the shutter blade in the embodiment.

FIG. 14 is a plan view of the shutter blade in the embodiment.

FIG. 15 is a plan view of the snow removal controller in the embodiment.

FIG. 16 is a block diagram illustrating a configuration of a fluid conduit and an operation of a microcomputer in the embodiment.

FIG. 17 is a side view illustrating the temporary avoidance mode of the blade in the embodiment with the shutter blade omitted.

[Explanation of symbols]

 41 Split blade 61 Shutter blade

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Shigeo Iwasaki 1-35-3, Bunkyo, Fukui City, Fukui Prefecture Iwasaki Industry Co., Ltd. (72) Inventor Ken Kai Kai, Ishimori Town, Fukui Prefecture

Claims (1)

[Claims] 1. A snow plow equipped with blades independently suspended by a pair of left and right fluid pressure cylinders via a clearance mechanism, and the left and right ends thereof are individually lifted and pressed against the ground. A device with a built-in microcomputer that measures the engine speed per unit time as an input device of the microcomputer, and outputs the signal based on the measurement result and the accelerator pedal depression amount. Detects the accelerator sensor that outputs a signal based on the detection result and the operation of the anti-locking brake system,
It is equipped with a braking sensor that outputs a signal based on the detection, a grip sensor that detects the operation of the limited slipping differential, and outputs a signal based on the detection, and an automatic mode switch that outputs a signal when selected. As a container, an electromagnetic valve provided in each fluid pipeline of the pair of fluid pressure cylinders, and a pressure control valve provided in each fluid pipeline of the pair of fluid pressure cylinders, When the automatic mode switch is selected and a signal is input to the microcomputer, the engine speed detected by the rotation speed detector is equal to or higher than a predetermined value, or the accelerator depression amount detected by the accelerator sensor is equal to or lower than a predetermined value. Also, the operation detection signal of the anti-locking brake system is not input by the braking sensor. In addition, when there is no operation detection signal input of the limited slipping differential with the grip sensor, a predetermined fluid pressure is applied to the lifting fluid pressure cylinder,
When the blade edge is grounded at a predetermined pressure, the engine speed detected by the rotation speed detector is less than a predetermined value, and the accelerator depression amount detected by the accelerator sensor is more than a predetermined value, the lifting hydraulic cylinder is lifted. A fluid pressure that is a certain amount less than the above-mentioned predetermined fluid pressure to be applied is applied, the edge of the blade is grounded at a certain pressure, and the engine speed detected by the rotation speed detector is above a predetermined value. Or the amount of depression of the accelerator detected by the accelerator sensor is less than a predetermined value, and there is an operation detection signal input of the anti-locking brake system by the braking sensor, or there is an operation detection signal input of the limited slipping differential by the grip sensor. In this case, the predetermined fluid pressure to be applied to the lifting fluid pressure cylinder is An automatic control device for a snow plow, characterized in that the blade edge is grounded at a constant pressure by applying a fluid pressure that has been reduced by a certain amount.