JPH09194184A - Freight grasping maneuver operating method for hydraulic grab bucket and hydraulic control circuit for hydraulic grab bucket used for the method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the operating method for a hydraulic grab bucket and the control circuit, which restrains working oil in grasping operations from being increased in temperature, and makes the grasping operation of a freight efficient. SOLUTION: An unloading valve type relief valve 10 is used as a pressure control valve, after a bucket has been landed over a freight, a switching-over valve 6 is turned on to its closing side, let the bucket start a closing operation, and thereby let it start a freight grasping operation, and after the bucket has grasped the freight, let a crane start hoisting the bucket. Furthermore, the switching-over valve 6 is kept in a closed condition until the bucket is closed, and the unloading valve type relief valve 10 allows pump delivery oil to automatically go to an oil tank 1 when the pressure of a hydraulic cylinder is increased at its closing side, and when it reaches the set pressure value in a bucket closing operation from the time when the bucket starts grasping the freight to the time when the bucket closes its grasping operation, and the pressure of the hydraulic cylinder at the closing side is lowered to a specified value, let pump delivery oil automatically interact so as to be fed to the closing side of the hydraulic cylinder 9, so that the freight grasping operation is thereby completed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a load gripping operation method for a hydraulic grab bucket such as an electrohydraulic grab bucket. The temperature rise of the hydraulic oil for driving the hydraulic cylinder that controls the opening and closing of the bucket can be significantly and effectively suppressed during the gripping operation of the (load), and the gripping operation of the gripped object can be performed easily and reliably. The present invention relates to a load grab operation operation method for a hydraulic grab bucket that can be improved in efficiency, and a hydraulic control circuit for the hydraulic grab bucket used in the method.

[0002]

2. Description of the Related Art A hydraulic grab bucket, such as an electro-hydraulic type that uses an electric motor as a rotational drive source of a hydraulic pump that is a drive source of a hydraulic cylinder for opening and closing a bucket, or an engine hydraulic type that uses an engine, collects dust such as city dust. It is used for various grabs such as powder and granules, combustion ash, and sludge, and its application is also used for various applications. For example, in a garbage disposal site such as an urban garbage incinerator factory, the operation of moving the garbage from the garbage pit and putting it in the incineration hopper, mixing the combustible garbage such as paper and the incombustible garbage containing a lot of water in the garbage pit. For mixing / stirring work of the combined garbage, or for moving the dust that has been dropped to a certain point in the dust pit from the garbage collection truck to multiple points in the dust pit so that it can be spread and stored in the entire dust pit. It is used for mobile work.

For example, an electrohydraulic grab bucket as a hydraulic grab bucket is constituted by, for example, a pair of left and right buckets provided so as to be openable and closable by the operation of a hydraulic cylinder. It can be hoisted (lowered) by heavy equipment and positioned at a predetermined gripping place such as the garbage storage pit, and by operating the crane, the hydraulic grab bucket can be unwound as it is on the garbage Landing,
A switching valve (directional control valve) in which hydraulic oil of a hydraulic pump driven by an electric motor is attached to the pump discharge pipe and placed on the closed side
Through a hydraulic cylinder to close the bucket and grab dust. Then, by using the crane, the grab bucket is rolled up and moved to a predetermined unloading position such as the incineration hopper, and this time the switching valve is put on the opening side to operate the hydraulic cylinder in the opening direction to open the bucket. , Dump the garbage.

During the work of grasping a load by such a grab bucket, for example, when the load is too much to be grasped while the bucket is being closed, it becomes an overload and the pressure control provided in the hydraulic circuit. The relief valve as a valve relieves and the temperature of hydraulic oil (hereinafter, also referred to as oil temperature) rises. The oil temperature increases more and more when the gripping operation is repeated for a long time or many times until the gripping operation is almost or completely closed to such an extent that the load can be transferred. Then, the hydraulic pump, switching valve, pressure control valve,
The service life of hydraulic equipment such as hydraulic cylinders and hydraulic piping is significantly reduced. For example, if the oil temperature rises, a sealing member such as an oil seal, which is a rubber product, deteriorates significantly, which causes oil leakage and causes troubles in the pump and the like, which hinders continuous operation. Further, when the hydraulic grab bucket is an electric hydraulic grab bucket, if the relief is repeated for a long time or frequently, the heat generation of the electric motor becomes large, and the average output of the electric motor due to the heat generation becomes insufficient, so that a motor with a large output must be adopted. There is also the inconvenience.

Since the grab bucket is hung on a lifting device such as a crane, it is premised to have a lightweight and compact structure, and the capacity of the oil tank incorporated in the grab bucket should be increased. Is difficult and limited, and it is difficult to secure a space for installing a cooler such as an oil cooler, and the grab bucket does not have a practical cooler due to frequent impact loads. .

As described above, in a hydraulic grab bucket such as an electrohydraulic grab bucket, it is important to take a measure for suppressing a temperature rise of the hydraulic oil when gripping a load, and particularly in a hydraulic grab bucket that is continuously used for 24 hours, the oil temperature is reduced. It is necessary to make sure to prevent the rise of. The cause of the oil temperature rise is the heat generated by the compression action of the hydraulic pump, and the tandem center type switching valve is set to the neutral state when the bucket opening / closing operation is stopped. There is also a so-called so-called oil temperature rise due to the heat generation of the oil during idle circulation, but as described above, when the bucket is closed by applying a high pressure during the work of grasping the load with the bucket, the operation by the relief valve is applied. The effect of heat generation due to the relief operation of the pressure oil is the largest.

Therefore, the conventional method for preventing the oil temperature rise at the time of gripping the load will be described more specifically. First, a conventional hydraulic control circuit applied to an electrohydraulic grab bucket will be described. FIG. 8 shows a first conventional hydraulic control circuit, and FIG. 9 shows a second hydraulic control circuit.
FIG. 10 shows a third conventional example of the hydraulic control circuit.

The hydraulic control circuit of the first conventional example shown in FIG. 8 is used for a small electrohydraulic grab bucket.
In FIG. 8, 1 is an oil tank, 2 is a suction pipe, 3 is a hydraulic pump that is rotationally driven by an electric motor M, 4 is a discharge pipe connected to the hydraulic pump, 5 is a branch from the discharge pipe 4, and the end is the tank 1 It is a relief valve for circuit pressure setting that was communicated to. 6
Is a switching valve which is connected to the end of the discharge pipe 4 and supplies the switching oil to the closing side of the bucket opening / closing hydraulic cylinder 9, that is, the head side chamber 9a and the opening side, that is, the rod side chamber 9b. The center portion 6c is a tandem center type electromagnetic switching valve in which the pump port P and the tank port T are in communication with each other in the neutral position. Reference numeral 7 is a pressure oil supply pipe connected to the closing side 9a of the hydraulic cylinder 9, and 8 is a pressure oil supply pipe connected to the opening side 9b of the hydraulic cylinder 9.

The hydraulic control circuit of the second conventional example shown in FIG. 9 is applied to an electrohydraulic grab bucket for medium-sized vehicles.
In FIG. 9, the same or corresponding parts as those in FIG. 8 are designated by the same reference numerals. Compared to the first conventional example, a relief valve with a check valve 5A having a built-in check valve (check valve) 11A is used in place of the relief valve 5, and instead of the tandem center type electromagnetic switching valve 6. An electromagnetic pilot switching valve 6A is provided, and a pilot pressure supply pipe 4a branched from the pump discharge pipe 4 is connected to the valve 6A. The check valve 11A is for establishing a predetermined pilot pressure in the pilot pressure supply pipe 4a.

The hydraulic control circuit of the third conventional example shown in FIG. 10 is applied to a large electro-hydraulic grab bucket. In FIG. 10, the same or corresponding parts as those in FIG. 8 or 9 are designated by the same reference numerals. did. In this conventional example, the hydraulic pump has two
It is of a pump type (main pump 3, auxiliary pump 3a), the switching valve is an electromagnetic pilot switching valve 6A as in the second conventional example, and is branched from the discharge pipe 3b of the auxiliary pump with the check valve 3c interposed. The pilot pressure supply pipe 3d is connected to the switching valve 6A. The check valve 3c is for establishing a predetermined pilot pressure in the pilot pressure supply pipe 3d. In addition, the counterbalance modular valve 8 is connected to the pressure oil supply pipe 8.
A is installed. This valve 8A supplies hydraulic pressure to the head side chamber 9a of the cylinder 9 when closing the bucket from the open state, and provides resistance to the escape oil to the tank 1 when the oil in the rod side chamber 9b escapes to the tank 1 through the pipe 8. This is to prevent the bucket from suddenly closing due to its own weight even when the weight of the bucket is heavy. As the relief valve, the relief valve 5 similar to the first conventional example is used.

FIG. 11 shows the structure of a relief valve as a pressure control valve applied to the hydraulic control circuits of FIGS. FIG. 11 is a vertical sectional view showing the principle of the relief valve, which is a balance piston type relief valve (also called a pilot operated relief valve). 13 is an oil inlet port branched from the pump discharge pipe 4, 15 is a tank connection port, 20 is a pilot valve for setting the circuit pressure, 21 is a poppet attached to the tip thereof, and 22 is the poppet 21. A spring, which is pressed against the valve seat, is a set pressure adjusting handle. 30 is a balance piston, 31 is a spring that lightly presses the tip of the balance piston against the valve seat 34, and 32 is a pore (also called a choke or tankan) that connects the oil inlet 13 side of the piston 30 and the pilot valve 20 side. ) And 33 are oil escape holes penetrating the center of the piston 30, and are pores for allowing oil to escape from the pilot valve side to the tank connection port 15. The relief valve 5A of the hydraulic control circuit shown in FIG. 9 has a built-in check valve 11A. However, the structural principle of the circuit pressure setting unit including the pilot valve 20, the balance piston 30, etc. is completely the same as that shown in FIG. It is the same.

The operation of the hydraulic control circuits of the first to third conventional examples will be described. In the electric grab bucket of the circuit of the first conventional example, the bucket of the electrohydraulic grab bucket is fully opened and gripped by the crane. When the sol.b of the solenoid directional control valve 6 is excited to put the directional control valve 6 on the closing side 6a by hoisting it on the garbage as a load and landing it, the pressure oil of the hydraulic pump discharges the discharge pipe 4 and the directional control valve. 6 acting on the closing side (head side) 9a of the hydraulic cylinder 9 for opening and closing the bucket via the closing side 6a of 6 and the pressure oil supply pipe 7, and the piston rod of the hydraulic cylinder 9 extends to start closing the bucket, and the tip thereof Claws dig into the trash and grab the load and start.

Then, dust is caught by the bucket as the bucket closes. If the grasped amount is appropriate, the bucket is closed by the hydraulic pressure set by the relief valve 5, and the grab bucket is lifted by the crane and moved to a predetermined unloading point, and the solenoid switching valve 6 sol.a.
Is excited to cause the pressure oil of the pump 3 to act on the open side (rod side) 9b of the hydraulic cylinder 9 via the pressure oil supply pipe 8, and when the piston rod is contracted to open the bucket, dust is released. Dropped and unloading is complete. However, the crane operator often grabs the load with the grab bucket from a high place in a blind operation.
As described above, it is extremely rare to be able to grab an appropriate amount in the bucket at one time, and in most cases, the amount of grab will be excessive and the grab will be overgripped.

Then, the hydraulic pressure as the gripping force becomes overloaded, and the pressure oil discharged from the pump exceeds the set pressure range of the relief valve 5, so that the poppet 21 of the pilot valve 20 moves from the valve seat. The oil in the oil chamber W located in front of the poppet 21 starts to separate and the oil escape hole 33
Gradually begins to escape to the oil tank 1 through the passage, and the pressure of the balance piston 30 balances out due to the pressure drop in the oil pressure in the upper chamber Y of the balance piston 30 communicating with the oil chamber W due to the action of the pores (choke) 32. The piston 30 collapses and the piston 30 is lifted upward in the drawing, and the valve element under the piston slightly separates from the valve seat 34, whereby the pump discharge oil is relieved and the relief oil is returned from the tank connection port 15 to the oil tank 1. .

On the other hand, if an excessively grasped load is lifted by a crane with a small amount to drop dust little by little, the excessive grasping can be eliminated. Is rarely resolved in a short time, and the relief valve 5 continues relief for a long time. If this happens, the oil temperature will rise sharply and overheat. As described above, the hydraulic grab bucket is a hoisting tool for a crane, and therefore, it is desirable that it is compact, light in weight, and strong against impact load.
From this point of view, the volume of the oil tank 1 cannot be increased more than necessary, and there is a limit, and an oil cooler cannot be installed. In addition, too much grip is not solved well, and the bucket will be opened again and the load will be gripped again, which will increase the relief function of the relief valve further.
The oil temperature rises more severely.

In view of such a situation, the applicant has conventionally issued Japanese Patent No. 1203532 (Japanese Patent Publication No. 58-346).
The method disclosed in Japanese Patent No. 23) is further adopted. This method is a method of limiting the relief time of the relief valve 5 when an excessive load is grasped by an electric circuit. As an example of the operation in a municipal waste incineration plant, this method is shown in the circuit diagrams of FIGS. 8 to 9 and FIG. It will be described together with the graph showing the change in the hydraulic pump discharge pressure. The gripping operation is a remote operation on the garbage storage pit. Since the grab bucket opens and closes at a position 30 to 40 m (meters) below when viewed from directly above, it is difficult to see the grasped state and the operation depends on intuition. Operate the crane to open the bucket and wind it down to land on the garbage. The trick is to land on top of a mountain to improve grip. It is a grab operation than that.

As described above, when sol.b of the electromagnetic switching valve 6 is excited and the switching valve 6 is put on the closing side 6a and the bucket is closed to start gripping the load, in most cases, the grip is excessive. The pressure on the hydraulic cylinder closing side cannot be completely closed on the way, and the pressure becomes the set pressure of the relief valves 5 and 5A (for example, 175 kg / cm ² ), and the oil is relieved from the relief valve 5. That is, when the load gripping by the operation is started at the time t ₁ in the graph of FIG. 12, as the dust is gripped, the pump discharge pressure, that is, the cylinder closing side pressure gradually increases, and the dust is gripped too much and cannot be closed (time t 1). relief valve 5 is relief ₂₎ and at the set pressure P _S of the valve 5, 5A. Then, the overcurrent of the hydraulic pump driving electric motor M at that time is detected, and the time t when the timer is started and the relief is started is set to a predetermined time (for example, t =
2 to 5 seconds). When the timer has finished counting, the sol.b of the electromagnetic switching valve 6 is automatically de-energized to bring the electromagnetic switching valve 6 to the neutral state (state shown) (time t ₃ ).

When the electromagnetic switching valve 6 is neutralized, the pump discharge oil passes through the center bypass of the switching valve 6 and the oil tank 1
And returned to the idle circulation state. Then, at about the same time when the restriction on the relief operation is released and the electromagnetic switching valve 6 is neutralized, or slightly before, the grab bucket is inching-wound (lifted for a short distance) by the crane, and dust is gradually dropped from the bucket. The load applied to the bucket is reduced by lifting the bucket a little to remove the dust, or due to leakage from the spool of the switching valve 6 or the packing of the piston of the hydraulic cylinder 9, the switching valve 6 is neutralized. hydraulic held in the pipe 7 between the side chamber 9a closing of the switching valve 6 and the hydraulic cylinder 9 (hydraulic lock) gradually drops, the sol.b the electromagnetic switching valve 6 after a predetermined time (time t ₄₎ Energize and put it in the closing position to re-close the bucket.

When the electromagnetic switching valve 6 is closed, the hydraulic pressure of the hydraulic pump 3 enters the closing side chamber 9a of the hydraulic cylinder 9 and the hydraulic pressure of the hydraulic pump 3 becomes equal to the closing side pressure of the hydraulic cylinder 9 after a short time. The dotted line in the graph of FIG. 12 shows the change in the closing pressure of the hydraulic cylinder 9. Thereafter, the same gripping operation is performed until the bucket is movable to the unloading point and is almost or completely closed (time t _n ), and the load grabbing is completed. After the completion of grasping the load, the electromagnetic switching valve 6 is returned to the neutral state and brought into the idle circulation state. Thus, time t ₁
From the time t to the time t _n , re-grasping is performed many times due to excessive grasping of dust by the bucket.

When the load gripping is completed, the club bucket is lifted up a predetermined distance by a crane to escape from the garbage storage pit, and is moved to an unloading point such as an incineration hopper,
Or, it is moved to another point in the waste storage pit for mixing and stirring with other types of waste in the waste storage pit,
The sol. Of the electromagnetic switching valve 6 is excited to open the switching valve 6 on the open side 6
Put it in b and open the bucket to discharge dust and complete unloading.

[0021]

In the above-mentioned conventional hydraulic control circuit and the load gripping operation method using the same, the relief time of the relief valve 5 when the load is gripped too much is limited, and the heat generated by the relief, so-called oil. Although attempts have been made to suppress the temperature rise, it is difficult to stabilize the load-grabbing operation, that is, if the relief valve is relieved due to excessive load due to too much dust being caught, the inching hoisting operation of the crane will slightly raise the grab bucket. The load is adjusted by lifting and dropping the dust little by little from the bucket, but if you are not used to driving, you often drop dust and start over from the beginning, so the gripping operation is uncertain. Therefore, there is no choice but to repeat the relief operation as shown in FIG. 12 many times due to the re-gripping due to such over-gripping. As a result, the rise in oil temperature cannot be suppressed enough to hinder continuous operation.

In FIG. 12, at the time of relief, the energy of the oil in the portion hatched by the chain line in a rectangular shape is almost converted into heat. The relief valves 5 and 5A are in a state in which the valve body under the piston 30 is slightly separated from the valve seat (seat) 34 to the extent that the pressure in the oil inlet 13 chamber can be maintained at the set pressure during relief, and the pressurized oil is Since it is returned to the tank connection port 15 by receiving the throttling resistance, the energy of the oil is almost converted into heat and the oil temperature is raised. Such relief operation is the most important factor for raising the oil temperature.

Especially in an urban refuse incineration plant, 30 to 4
Since it is a bucket operation at a height of 0 m, it is difficult to see the gripping situation and the operation depends on intuition.
For example, one cycle from grasping the garbage, moving it to the unloading point, returning to the original grasping position and performing the grasping operation [eg 90
~ 150 seconds. In addition, this time is movement in the garbage pit,
It goes up and down in the process such as mixing and stirring. ] Between 1
There is no choice but to repeat it many times, such as 0 to 15 times, and moreover, the operation by such a gripping operation has to be performed continuously for 24 hours, so the oil temperature rises sharply and overheating may occur. Often happens. It should be noted that such overheating of hydraulic oil occurs even more frequently in an unfamiliar gripping operation. The heat generation of the hydraulic oil due to the relief operation occupies 60 to 70% of the generated heat amount, although it varies depending on the usage situation, model and the like.

In order to prevent heat generation due to the relief operation as described above, the vent port V of the relief valve 5, 5A is
Is provided with an electromagnetic switching valve for connecting or shutting off the oil tank 1 and the vent port V of the relief valve, and a pressure switch is provided for connection with the closing side 9a of the hydraulic cylinder. When the pressure exceeds a set value, an electromagnetic switching valve is inserted by the detection of the pressure switch to connect the vent port V to the oil tank 1 to open the atmosphere to release the valve body of the piston 30 of the relief valve from the valve seat. There is also a method of unloading, but this method is not preferable because there are problems such as electric wiring work, addition of electric wires, relief due to a time lag of operation, and reduction in reliability due to control by an electric circuit.

The present invention has been made in view of the problems of the conventional load gripping operation method as described above.
A hydraulic system that can significantly and effectively suppress the temperature rise of the hydraulic oil during the gripping operation of a gripped object (load) such as combustion ash, and that can easily and reliably and efficiently grip the gripped object. An object of the present invention is to provide a load gripping operation method for a grab bucket and a hydraulic control circuit for a hydraulic grab bucket used in the method.

[0026]

In order to achieve the above object, the present invention provides:

(1) As a load gripping operation method of a hydraulic grab bucket, a state in which a predetermined pressure is set by a pressure control valve via a switching valve connected to a discharge pipe of a hydraulic pump and switching the bucket between a closing side and an opening side. Is a load grab operation operation method of a hydraulic grab bucket in which hydraulic oil is applied to a hydraulic cylinder to close a bucket to grip a load such as dust, and an unload valve type pressure control valve is used as the pressure control valve. After landing the bucket on the load, put the switching valve on the closing side to start the closing operation of the bucket to start the load grasping, and after the bucket has grasped the load, start lifting the bucket with a lifting machine. And the directional control valve remains closed until the bucket is almost or completely closed, and the unload valve type pressure control valve allows the bucket to grab the load. During the bucket closing operation from the start to almost or completely closing, when the pressure on the hydraulic cylinder closing side rises and reaches the set pressure value of the valve, the pump discharge oil is automatically released to the oil tank and the hydraulic cylinder When the pressure on the closing side has decreased to a predetermined value, the pump discharge oil is automatically supplied to the closing side of the hydraulic cylinder to complete the gripping of the load.

(2) Further, as a hydraulic control circuit for carrying out the above method, the hydraulic pump and the discharge pipe of the hydraulic pump are connected to the hydraulic cylinder for opening and closing the bucket, and the hydraulic oil for discharging the hydraulic pump is supplied to the hydraulic cylinder. A hydraulic control circuit for a hydraulic grab bucket comprising a switching valve for switching and supplying the bucket to a closing side and a closing side, and a pressure control valve connected to a discharge pipe of the hydraulic pump and setting an operating pressure of the hydraulic cylinder. The check valve is provided so as to be interposed in the pump discharge pipe between the pressure control valve and the switching valve at a position downstream of the oil flow inlet, and the check valve prevents backflow of hydraulic oil on the hydraulic cylinder closing side. A valve, a pilot valve having a poppet valve at the tip to set the unloading pressure on the cylinder closing side, and an oil chamber at the end of the pore passage that communicates with the pump discharge pipe at one end side downstream of the check valve. Coming A plunger, which is arranged coaxially with the poppet valve so that the other end side thereof can contact the poppet valve and is slidably fitted to the valve body, and one end side of which faces the oil inflow port The other end is faced to the oil chamber communicating with the oil chamber between the poppet valve and the plunger, which has a valve portion for communicating or blocking the oil inlet and the tank connecting port, and the pilot valve and the tank connecting An oil passage provided through the center so as to communicate the mouth, and an oil chamber communicating with the oil chamber between the poppet valve and the plunger, and a pore communicating with the oil inlet, An unloading valve type pressure control valve composed of a balance piston slidably fitted to the valve body, the switching valve being on the bucket closing side until the bucket is almost or completely closed at the time of gripping. The unloading valve type pressure control is The valve automatically releases the pump discharge oil to the oil tank when the pressure on the hydraulic cylinder closing side rises to reach the set pressure, and automatically releases the pump discharge oil to the oil tank when the pressure on the hydraulic cylinder closing side drops to a specified value. It is configured to supply to the closed side.

[0029]

1 is a front view of an embodiment of an electro-hydraulic grab bucket applied to the present invention, FIG. 2 is a right side view of an electro-hydraulic grab bucket, and FIG. 3 is an electro-hydraulic grab bucket. First Embodiment of Applied Hydraulic Control Circuit, FIG.
Is the second embodiment of the hydraulic control circuit applied to the electro-hydraulic grab bucket, FIG. 5 is the third embodiment of the hydraulic control circuit applied to the electro-hydraulic grab bucket, and FIG. 6 is the circuit of FIGS. Longitudinal sectional view showing the principle and structure of an unload relief valve as an unload valve type pressure control valve applied to
FIG. 7 is a graph showing a pressure change state of the discharge oil of the hydraulic pump at the time of gripping a load by the load gripping operation method according to the present invention.

First, referring to FIGS. 1 and 2, the overall structure of an electro-hydraulic grab bucket as a hydraulic grab bucket applied to the present invention will be described. The electro-hydraulic grab bucket 50 is supported below a girder 51. Between a pair of left and right buckets 53 rotatably attached to the fixed shaft 52 with their upper ends rotatably supported, and between the left and right buckets at the upper end of the bucket 53 located above the shaft pivot point of the bucket 53. The main part is composed of a hydraulic cylinder 9 which is rotatably supported by pins at its both ends and hung around it, and a hydraulic pump unit 60 installed on the upper part of the girder 51. 61 is an oil level gauge with a thermometer attached to the oil tank, 5
Reference numeral 7 denotes a connecting bar which is pivotally supported by pins at both ends between the left and right buckets and is attached so as to open and close the pair of buckets symmetrically with respect to the center line CL. Bucket 5
3 has a plurality of claws 54 (four in this embodiment) provided at the bottom thereof at intervals and is formed into a substantially L-shaped outer shape in a front view, and an auxiliary claw (side) is provided outside the substantially intermediate height position thereof. Part stopper) 56
Have

A buffer 55 composed of an elastic body such as a tire is rotatably attached to both outer sides of the lower end of the bucket so that the shock can be absorbed even when the grab bucket 50 collides with a wall or the like. Has been done. Reference numeral 58 denotes a suspending member fixedly attached to the girder 51.
A chain is connected to the pin portion of 8 and the grab bucket 50 is hung or hung by a crane. Reference numeral 59 denotes a cabtire cable for supplying electricity to electric equipment such as a hydraulic pump built in the hydraulic pump unit 60 and a controller of other hydraulic equipment.

The glove bucket 50 constructed in this way
Is opened and closed by operating the hydraulic cylinder 9 so that the pair of left and right buckets 53, 53 are rotated symmetrically with respect to the center line CL about the shafts 52, 52 as rotation centers. In FIG. 1, the fully closed position (state) is shown by a solid line, and the fully opened position (state) is shown by a two-dot chain line. Bucket 5
In the state in which 3, 53 are completely closed, a required distance D is provided between the tips of the claws 54.

Next, the hydraulic control circuit for opening and closing the bucket 53 applied to the electrohydraulic grab bucket 50 will be described. FIG. 3 shows a first embodiment of the hydraulic control circuit, which is a circuit corresponding to the first conventional example of FIG. 8 and is applied to a small electrohydraulic grab bucket 50. In this figure, parts that are the same as or correspond to those in FIG. 8 are assigned the same reference numerals and explanations thereof are omitted.

In the hydraulic circuit of FIG. 3, the pump discharge pipe 4
In the portion between the connection point to the oil inflow port 13 of the pressure control valve main body portion 5 composed of the balance piston 30 and the pilot valve 20, which will be described later in detail in FIG. A stop valve (check valve) 11 is provided so as to be interposed, and further at a position downstream of the check valve 11, that is, the check valve 1
In the pump discharge pipe 4 between the solenoid valve 1 and the electromagnetic switching valve 6, circuit pressure is applied to the head (X chamber) on one end side of the unloading plunger 16 provided coaxially with the poppet 21 of the pilot valve 20. One end of a pilot line 12 for connecting is connected. In FIG. 3, a portion surrounded by a chain double-dashed line and denoted by reference numeral 5 constitutes the pressure control valve main body portion 5 and is a portion corresponding to the relief valve 5 in FIG.

Thus, the pressure control valve body 5, the check valve 11, and the pilot line 12 incorporating the unloading plunger 16 constitute an unload relief valve 10 as an unload valve type pressure control valve. . In FIG. 3, a portion corresponding to the unload relief valve 10 is shown surrounded by a one-dot chain line. FIG. 6 shows a configuration as a valve in which they are integrally combined. The embodiment of FIG. 3 has the same configuration as the hydraulic circuit of FIG. 8 except that the unload relief valve 10 is attached to the pump discharge pipe 4.

Now, the unload relief valve 10 will be described with reference to FIG. Incidentally, the same or corresponding parts as those of the relief valve 5 of FIG. The valve body of the unload relief valve 10 is provided with a pilot valve 20 having a poppet 21 at the tip and a balance piston 30 as a pressure control valve main body portion, and this portion has the same structure as the relief valve 5 in FIG. It is said that. Then, between the oil inlet 13 connected to the pump discharge pipe 4 and the hydraulic circuit connection port 14 connected to the pump discharge pipe 4 between the oil inlet 13 and the electromagnetic switching valve 6,
A check valve 11 (11A) having a spring 11a installed therein is provided, and the unloading plunger is arranged so as to face the poppet 21 at the tip of the pilot valve 20 and to be able to contact the poppet 21 in the oil chamber W. 16 is slidably mounted on the valve body coaxially with the poppet 21, and an oil chamber X is formed at one end of the plunger 16 opposite to the poppet 21. A pilot chamber is provided in the oil chamber X. The pressure introducing passage 12 (corresponding to the pilot line 12 in FIG. 3) is connected and connected. The valve body end portion of the pilot pressure introducing passage 12 serves as a pilot pressure introducing port 12A.

The unload relief valve 1 having such a configuration
To explain the operation of 0, the unloading pressure is set by adjusting the force that pushes the poppet 21 against the valve seat by rotating the handle 23 of the pilot valve 20. The state of FIG. 6 shows a state in which the circuit pressure has not yet reached the set pressure of the valve, so to speak, the bucket 53 is in the middle of grasping a load or opening the load normally, and when opening and closing normally. The check valve 11 is opened, and the circuit connection port 14 side (that is, the switching valve 6 side) from the oil inlet 13 (that is, the hydraulic pump 3) is opened.
It shows a state in which pressure oil is flowing into the hydraulic cylinder 9 side or the like). At this time, the pressures in the oil chambers X, Z, Y, W are equal, the poppet 21 of the pilot valve 20 and the balance piston 30 have their valve bodies seated on the valve seats, and the plunger 16 is in a pressure balanced state. And is located away from the poppet 21.

From this state, the load on the circuit side, that is, the load for gripping the bucket 53 increases, the pressure on the closing side of the hydraulic cylinder 9 increases, and the pressures in the Z chamber, the Y chamber, and the W chamber rise (still Y). When the pressure in the W chamber is equal to that in the W chamber and the control valve reaches the set pressure (cutout pressure), the poppet 21 is pushed away from the valve seat against the force of the spring 22, and the oil in the Z chamber passes through the choke 32. It flows into the Y chamber, further flows through the opening formed between the poppet 21 and its seat, through the small hole 33 in the central portion of the piston 30, to the tank connection port 15 side, and is returned to the oil tank 1. At this time, the piston 30 is pushed up above the Y chamber due to the pressure drop in the Y chamber due to the action of the choke 32, the valve body is separated from the seat 34, and the oil inlet 13 and the tank connection port 15 are communicated with each other. The oil at the inflow port 13 is made to flow to the tank connection port 15.

When this flow is generated, the pressure in the oil chamber Z (oil inlet 13) and the oil chamber Y (W) further decreases, and the pressure in the oil chamber X (that is, the pressure on the circuit connection port 14 side) becomes the oil chamber. Y (W)
When it becomes higher than the pressure of 1, the check valve 11 is closed and the pressure on the circuit side is maintained. At the same time, oil chamber X and oil chamber W
, The balance of the pressure acting on the end face of the plunger 16 is broken, and the thrust force in the right direction in the drawing acts on the plunger 16 so that the plunger 16 further pushes the poppet 21 against the force of the spring 22. Is further away from the seat. As a result, the pressure in the Y chamber is further reduced, and at the same time, the valve body of the piston 30 is largely separated from the seat 34, and the valve body is largely opened with respect to the seat 34. As a result, the pump discharge oil is returned to the oil tank 1 without resistance, and the pump 3 is brought into an unloading state (no-load operation).

In such an unload state, the oil chamber X
The pressure on the circuit side (pressure on the side of the circuit connection port 14 and the pilot pressure introduction port 12A) acting on is gradually decreased until the cut-in pressure is reached. The seat area of the poppet 21 and the cross-sectional area of the plunger 16 are determined so that the cut-in pressure is approximately 80 to 85% of the cut-out pressure. When the circuit side pressure drops to the cut-in pressure, the plunger 16 is pushed back to the left in the figure by the compression force of the spring 22 of the pilot valve 20, and the poppet 21 of the pilot valve 20 is also seated, so that the oil chamber Y,
The pressure of Z is made equal by the choke 32. The valve body of the piston 30 is operated by the spring 31 so that the valve seat 34
6 and the check valve 11 is opened to automatically return to the state shown in FIG.
3 to the circuit connection port 14 side, and the hydraulic pump 3 is brought into the on-load state. After that, the above operation is repeated.

As described above, since the unload relief valve 10 is internally provided with the unloading plunger 16 that pushes down the poppet 21 as compared with the relief valve 5, when the cutout pressure is reached, the valve body of the piston 30 is seated. 34
The oil inlet 13 is largely opened to the tank connection port 15 and the hydraulic pump 3 is in an unload state, and there is almost no resistance to return to the oil tank 1, and the relief valve 5
Since the pressurized oil is not returned from the valve body to the tank side due to the throttling resistance as in the case of the relief operation, the heat generation of the oil hardly occurs and the oil temperature rise is not a problem.

Therefore, the load grasping operation method by the electro-hydraulic grab bucket 50 using the hydraulic control circuit of the present embodiment as described above is shown in FIG. It will be described together with the graphs shown. Note that this operation method will be described in the same manner as in the conventional method described above, in the case of grasping dust in an urban refuse incinerator.

In the state of FIG. 3, the electromagnetic switching valve 6 is in a neutral state, and when the electric motor M is started and the hydraulic pump 3 is driven in this state, the oil discharged from the hydraulic pump passes through the discharge pipe 4 and the switching valve 6 to the tank. It returns to 1 and is idle-circulated. Then, the crane is operated on the dust storage pit having a height of 30 to 40 m to suspend the grab bucket 50 and land the bucket 53 on the dust in the dust storage pit in a fully opened state. Then, the tip of the pawl 54 of the bucket is sunk into the dust and the bucket is sunk. Then, the electromagnetic switching valve 6
sol.b is energized are placed in closing side 6a of the switching valve 6 (time t ₁ in the graph of FIG. 7), a pump discharge oil is sent to the tube 7 in the closed side chamber 9a street hydraulic cylinder 9 bucket 53
Begins to close and grabs garbage.

Then, the pump discharge pressure (closed side circuit pressure) rises, and in most cases, the bucket 53 is too grasped during the closing process and cannot be closed. At this time,
When the closed circuit pressure reaches the cutout pressure P _out (for example, 210 kg / cm ² ) of the set pressure of the unload relief valve 10 (time t ₂ ), the unload relief valve 10 cuts out as described above, that is, The valve element of the balance piston 30 is largely separated from the valve seat 34 thereof, and the discharge oil of the pump 3 is returned to the tank 1 without resistance and the pump 3 is unloaded. Then, the electromagnetic switching valve 6 is inserted into the closing side 6a at the start of the load gripping (time t ₁ ) and then the bucket 5
The state of being put on the closing side is maintained until the load gripping operation in which the items 3 and 53 are lifted up and can be moved to the trash dropping point until they are almost or completely closed (until time t _n ). Thereby, the closed side chamber 9 of the hydraulic cylinder 9
The pipelines 7 and 4 between the a and the check valve 11 are in a state in which pressure oil is retained, that is, in a hydraulic pressure locked state.

Then, after the buckets 53, 53 are closed and the dust gripping is started and the bucket grips the dust, time t
_During the period up to ₂ , the crane is hoisted to start lifting the grab bucket 50. Then, part of the trash that has been grasped too much falls from the buckets 53, 53. As a result, if the closing load of the bucket is reduced, or if there is a leak from the spool of the switching valve 6 or the packing of the piston of the hydraulic cylinder 6, as shown by the dotted line in the graph of FIG. The pressure of the hydraulic lock of the certain pipelines 7 and 4 is lowered to the cut-in pressure P _in (for example, 175 kg / cm ² ) of the unload relief valve 10 (time t ₃ ). Then, the valve 10 is automatically cut in by the above-mentioned operation, the hydraulic pump 3 is turned on, and the pump discharge oil is supplied to the closing side chamber 9a of the hydraulic cylinder 9 to flow in, so that the bucket 53 is closed again. And

When the closing operation still does not almost or completely close the unloading relief valve 10 again cuts the pump 3 into the unloading state, and the same operation is repeated automatically. During this period, the dust in the bucket 53 gradually decreases, and finally, at time t _n , the bucket 53 is in a state in which the bucket 53 can be lifted and moved, almost or completely.
It is closed and the grip is completed. After that, the grab bucket 50 is hoisted by a crane, the switching valve 6 is returned to the neutral position, and the gripping operation is finally completed. After returning the switching valve 6 to the neutral position, the discharge oil of the pump 3 is returned to the tank 1 through the center bypass of the neutral position 6c of the switching valve 6 and is circulated idle.

The hydraulic lock pressure of the pipelines 7 and 4 when the hydraulic pump 3 is unloaded, that is, the unload pressure, drops sharply or quickly without an accumulator (accumulator). Therefore, it is possible to prevent the unloading relief valve 10 from repeatedly turning on and off and causing hunting immediately after being cut down to the cut-in pressure of the unloading relief valve 10. That is, if the grasped object is dust as in the present embodiment or is combustion ash or the like, it has compressibility, and if the grasped object is heavy, the bucket 5 is used.
The reaction force acts on the claw 54 and the claw 54, so that it acts in the direction of opening the bucket. Therefore, the pressure oil locked on the cylinder closing side is compressed by the piston of the cylinder 9, so that it acts as a pressure accumulator and the pressure drop is reduced.

As described above, according to the hydraulic control circuit of the present embodiment and the dust gripping operation method using the hydraulic control circuit, the switching valve 6 is put in the closing side until the bucket 53 is almost or completely closed. By maintaining the closed state and utilizing the cut-out and cut-in operations of the unload relief valve 10, the dust gripping operation can be automatically performed. Therefore, the grasping operation becomes easy, the skill is not required so much, and the working efficiency is remarkably improved. That is, like the conventional gripping operation, instead of the step of limiting the relief operation time, the step of returning the switching valve to the neutral state, and the subsequent step of putting the switching valve in the closed position, the unloading relief valve is automatically gripped. Since the gripping operation is significantly facilitated, the gripping efficiency is improved and the gripping process is significantly shortened.

In the past, the relief function, which occupies 60 to 70% of the amount of heat generated during overheating, disappears, and the largest factor of oil temperature rise can be eliminated. Compared with the conventional gripping method using a relief valve. As a result, heat generation due to relief can be eliminated and the oil temperature rise can be greatly reduced, and continuous operation for 24 hours can be easily performed. In the conventional gripping operation, when the cycle time is about 80 seconds, the relief time t is 2 seconds, and the number of reliefs is repeated 10 times, an example of the oil temperature when the atmospheric temperature is 0 ° C is about 103 ° C. Become. On the other hand, in the case of the gripping operation without the relief operation of the present invention, the cycle time is about 60 seconds and the oil temperature is about 24 ° C., and the oil rising temperature is reduced to about a quarter as compared with the conventional operation method. Can be suppressed.

Further, the closing time is shortened by the relief time. Also, instead of using an electric circuit such as limiting the relief operation time or unloading and onloading the relief valve vent circuit with a solenoid valve on / off, hydraulic unloading and onloading Since it is a method of repeating, the apparatus is highly reliable. In addition, the grip is easier than the conventional method. Even when the electromagnetic switching valve 6 is closed, the pressure is about 15 to 20% at the cut-out pressure and cut-in pressure of the unload relief valve 10, cut out at 210 kg / cm ² , cut at about 175 kg / cm ² . Since it is in, it is not necessary to repeatedly perform the closing operation as in the conventional case, and it can be used almost in the same manner as the continuous relief operation.

Since the heat generated by the relief is eliminated, the inching hoisting operation of the crane at the time of gripping unlike the conventional case is not necessary, and the crane can be hoisted at the same time when the bucket is closed and the dust can be gripped by one operation.
This also improves gripping efficiency and shortens time.
Further, since the oil temperature is lowered, the life of hydraulic equipment is extended and oil leakage is eliminated, so that continuous use and operation can be sufficiently performed. Since the grab bucket 50 is hung on a crane, it is lightweight and compact, but it is not necessary to install a cooler such as an oil cooler, and the hydraulic tank can be made small. With respect to the bucket 53 as well, the conventional operation involves re-gripping several times for each grip, so that the number of times the load is applied to the bucket is increased and the fatigue limit is lowered. As a result, the thickness of the iron plate, etc. of the bucket constituent material becomes thicker and the weight becomes heavier. However, the present invention can eliminate this. As described above, the grab bucket 50 can be made compact and lightweight.

On the other hand, since there is no relief,
It can lead to energy saving. That is, the heat generation of the electric motor M of the hydraulic pump is reduced, the average output of the electric motor is also reduced, and the size of the electric motor can be further reduced. Also, it allows for a thinner cabtyre cable 59,
A small cable reel can be used.

The unload relief valve 10 itself is a conventionally known valve, but in the present invention, this valve 10 and
During the gripping operation, the switching valve 6 is kept closed and the gripping operation is continued. The cutout and cut-in operations of the valve 10 are automatically performed. It is characterized by a structure incorporated in the gripping operation, and the dust gripping operation method having the above-described excellent operational effects can be implemented with a hydraulic control circuit having a very simple structure.

In the circuit of FIG. 3 of this embodiment, the check valve 1 is added to the conventional hydraulic circuit having the relief valve 5 shown in FIG.
1. The present invention can be easily configured by attaching and modifying the pilot line 12 having the unloading plunger 16 therein. That is, as shown by the two-dot chain line in FIG. 6, the pilot pressure introducing passage is provided in the existing relief valve block R (5) including the pressure control valve main body portion 5 including the balance piston 30 portion and the pilot valve 20 portion. And the block P containing the plunger 16 is integrally mounted, and the check valve 11 is interposed in the pump discharge pipe 4, or the block C (11) is used as the block C,
This can be done by mounting it integrally with the block R.

Of course, when a new hydraulic circuit is constructed and manufactured, the unload relief valve 10 integrally formed as shown in FIG. 6 can be adopted. In addition, in the case of the integrated unload relief valve 10, FIG.
As shown by the two-dot chain line, the pilot pressure introducing passage 12 may have the pilot pressure introducing port 12A blind and the passage 12a or 12b formed inside the valve body.

FIG. 4 shows a second embodiment of the hydraulic control circuit,
The circuit corresponds to the second conventional example of FIG. 9 and is applied to a medium-sized electrohydraulic grab bucket 50. In this figure, parts that are the same as or correspond to those in FIG. 9 are assigned the same reference numerals and explanations thereof are omitted. In this embodiment, the check valve 11A of the existing relief valve 5A with a check valve, the pressure control valve body 5 including the balance piston 30 and the pilot valve 20 are used as they are, and the unloading plunger 16 is used. The unload relief valve 10 is configured by additionally installing only the pilot line 12 in which That is, in this embodiment, the block P containing the pilot pressure introducing passage and the plunger 16 is integrally attached to the pressure control valve main body 5 composed of the existing balance piston 30 and pilot valve 20 in FIG. Well, the invention can be easily implemented.

FIG. 5 shows a third embodiment of the hydraulic control circuit,
This circuit corresponds to the third conventional example of FIG. 10 and is applied to a large electrohydraulic grab bucket 50.
In this figure, parts that are the same as or correspond to those in FIG. 10 are assigned the same reference numerals and explanations thereof are omitted. In this embodiment, the unload relief valve 10 can implement the present invention by additionally installing the check valve 11 and the pilot line 12 to the existing relief valve 5 as in the embodiment of FIG. That is,
In FIG. 6, a block P in which a pilot pressure introducing passage and a plunger 16 are built in the existing pressure control valve main body 5,
Check valve block C may be attached.

In the above embodiments, the case where the unloading valve type pressure control valve is the unloading relief valve 10 has been described, but in the present invention, instead of the unloading relief valve 10, a general unloading valve, or A sequence valve can also be applied.

Further, in the above embodiment, the bucket type has been described as shown in FIGS. 1 and 2, but the present invention is not limited to this and can be applied to a hydraulic grab bucket provided with any type of bucket. it can. Further, although the case where the hydraulic grab bucket is an electrohydraulic grab bucket in which the prime mover for driving the hydraulic pump is an electric motor has been described, the present invention has an engine hydraulic grab using the prime mover as an engine such as a diesel engine or a gasoline engine. It may be a bucket. Furthermore, although city waste was explained as a grasped article (load), it is not limited to this grasped article, and combustion ash, powder particles, combustion ash,
It can be applied to various other grasped objects such as sludge.

[0060]

As is apparent from the above description, the present invention has the structure as described in the claims, so that the relief operation can be performed during the gripping operation of the gripping object (load) such as dust and combustion ash. Since the oil is eliminated, the oil does not overheat as in the conventional case, and the temperature rise of the hydraulic oil can be significantly and effectively suppressed. This gives 2
Even if the operation is continuous for 4 hours, or if the usage frequency is heavy, the load-grabbing operation can be performed without any trouble.

Further, the uncertainties of the grasping operation are eliminated, and the grasping work efficiency is remarkably improved, and the cycle time of the grasping operation is remarkably shortened. That is, since heat is not generated by relief as in the past, inching hoisting operation by a lifting device such as a crane at the time of gripping is performed, and the lifting device is blinded at the upper part of the garbage storage pit with a height of 30 to 40. Even if you have no choice but to grab dust by operating in the same way as driving, you can grab by hoisting with a lifting device at the same time as closing the bucket and operating it once (just put the switching valve in the operation position) and grab it. The usability of the bucket is significantly improved. Further, unlike the conventional operation, no special skill is required, and the grip operation is easily performed.

Since the oil temperature lowers, the life of hydraulic equipment such as an oil pump is extended, oil does not leak from the sealing portion such as a pipe connecting portion and a cylinder, and troubles such as the hydraulic pump are eliminated. Further, the oil tank can be downsized, a cooler such as an oil cooler is not required, and the hydraulic grab bucket can be configured to be lightweight and compact. Since the grab bucket is a hoisting device for a crane, it is desirable that it be compact, light in weight, and strong against impact loads.In the case of a hydraulic type, the hydraulic power source for opening and closing the bucket is an electric motor, the engine etc. is built in the grab bucket body and driven. Since it is rotated, its characteristics are especially required,
This can be fully satisfied.

Since the load gripping operation of the present invention is not electric control but hydraulic control by the unloading valve type pressure control valve itself, the control reliability is high, and the hydraulic control circuit configuration is very simple and simple. In addition, in the existing hydraulic circuit equipped with a relief valve, it is only necessary to install a check valve and a unloading plunger for modification, and in the existing hydraulic circuit equipped with a relief valve with a check valve, the unloading plan is used. The present invention can be easily implemented only by attaching and remodeling the jar, and as described above, the conventional drawbacks at the time of grasping a load can be improved and a great effect can be achieved. Therefore, the economic effect is great.

[Brief description of the drawings]

FIG. 1 is a front view of an embodiment of an electro-hydraulic grab bucket applied to the present invention.

FIG. 2 is a right side view of the electrohydraulic grab bucket.

FIG. 3 is a first embodiment of a hydraulic control circuit applied to an electrohydraulic grab bucket.

FIG. 4 is a second embodiment of a hydraulic control circuit applied to an electrohydraulic grab bucket.

FIG. 5 is a third embodiment of a hydraulic control circuit applied to an electrohydraulic grab bucket.

FIG. 6 is a vertical cross-sectional view showing the principle and structure of an unload relief valve as an unload valve type pressure control valve applied to the hydraulic control circuits of FIGS.

FIG. 7 is a graph showing a pressure change state of the hydraulic pump discharge oil in the load gripping operation method of the present invention.

FIG. 8 is a first conventional example of a hydraulic control circuit applied to an electrohydraulic grab bucket.

FIG. 9 is a second conventional example of a hydraulic control circuit applied to an electrohydraulic grab bucket.

FIG. 10 is a third conventional example of a hydraulic control circuit applied to an electrohydraulic grab bucket.

FIG. 11 is a vertical cross-sectional view showing the principle and structure of a relief valve as a pressure control valve applied to the hydraulic control circuits of FIGS. 8 to 10.

FIG. 12 is a graph showing a pressure change state of the hydraulic pump discharge oil in the conventional load gripping operation method.

[Explanation of symbols]

1 Oil Tank 3 Hydraulic Pump 4 Pump Discharge Pipe 5 Relief Valve 6, 6A Electromagnetic Changeover Valve 6a Electromagnetic Changeover Valve Closed Side 6b Electromagnetic Changeover Valve Open Side 9 Hydraulic Cylinder 9a Hydraulic Cylinder Closed Side Chamber 9b Hydraulic Cylinder Open Side Chamber 10 Unload Relief Valve 11 , 11A Check valve 12 Pilot line (pilot pressure introduction passage) 13 Oil inlet 14 Hydraulic circuit connection port 15 Tank connection port 16 Plunger 20 Pilot valve 21 Poppet 30 Balance piston 34 Valve seat (balance piston) W, X, Y , Z Oil chamber 50 Electro-hydraulic grab bucket 53 Bucket 54 Claw

Claims (2)

[Claims] 1. A bucket is closed by causing hydraulic oil to act on a hydraulic cylinder in a state where a predetermined pressure is set by a pressure control valve through a switching valve connected to a discharge pipe of a hydraulic pump and switching the bucket between a closing side and an opening side. A method for operating a load grasping operation of a hydraulic grab bucket for grasping a load such as dust by using an unload valve type pressure control valve as the pressure control valve, and after the bucket is landed on the load, the switching is performed. Put the valve on the closing side to start the closing operation of the bucket to start the load grasping, after the bucket has grasped the load, the lifting machine is started to lift the bucket, and the switching valve is such that The unloading valve type pressure control valve keeps the closed state until it is completely closed, and the unloading valve type pressure control valve moves the bucket closing motion until the bucket starts gripping the load and closes it almost or completely. During operation, when the pressure on the hydraulic cylinder closing side rises and reaches the set pressure value of the valve, the pump discharge oil is automatically released to the oil tank, and when the pressure on the hydraulic cylinder closing side drops to a predetermined value, the pump automatically pumps. A method for operating a gripping operation of a hydraulic grab bucket, characterized by causing discharged oil to be supplied to a closing side of a hydraulic cylinder to complete the gripping. 2. A hydraulic pump, and a switching valve which is connected to a discharge pipe of the hydraulic pump and supplies the discharge oil of the hydraulic pump to a bucket opening / closing hydraulic cylinder by switching between a bucket closing side and a bucket closing side of the hydraulic cylinder. A hydraulic control circuit for a hydraulic grab bucket, comprising: a pressure control valve connected to a discharge pipe of the hydraulic pump to set an operating pressure of the hydraulic cylinder, wherein the pressure control valve is located downstream of an oil inlet. Position check valve that is provided so as to be interposed in the pump discharge pipe between the switching valve and the switching valve, and that prevents backflow of hydraulic oil on the hydraulic cylinder closing side, and a poppet valve at the tip end of the check valve. A pilot valve for setting the load pressure and one end side of which is exposed to the oil chamber at the end of the pore passage communicating with the pump discharge pipe at a position downstream of the check valve, and the other end side of which can contact the poppet valve. Same as poppet valve A plunger axially arranged and slidably fitted to the valve body, and a valve portion having one end facing the oil inlet and connecting or shutting off the oil inlet and the tank connection opening at the end. The other end of the oil passage is exposed to an oil chamber communicating with the oil chamber between the poppet valve and the plunger, and an oil passage is formed through the center so as to communicate the pilot valve and the tank connection port. A balance piston slidably fitted to the valve body, the balance piston having an oil chamber communicating with an oil chamber between the poppet valve and the plunger, and a pore communicating with the oil inlet,
A pressure control valve of the unloading valve type composed of the switching valve, which holds the state of being put on the bucket closing side until the bucket is almost or completely closed at the time of gripping, and during the unloading period. The valve type pressure control valve automatically releases the pump discharge oil to the oil tank when the pressure on the hydraulic cylinder closing side rises to reach the set pressure, and automatically discharges the pump discharge oil when the pressure on the hydraulic cylinder closing side drops to a specified value. A hydraulic control circuit for a hydraulic grab bucket, which is characterized in that it is configured to supply to the hydraulic cylinder closing side.