JPH11130375A - Hydraulic control circuit for hydraulic grab bucket - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydraulic control circuit for a hydraulic grab bucket, which is run continuously for a long time by suppressing a temperature increase by the heating of hydraulic oil caused by a relief operation or the like with the set pressure of a pressure control valve for setting a hydraulic cylinder operation pressure when a bucket is closed to grab a load or the like. SOLUTION: A plurality of hydraulic pumps 3 composed of large and small capacity pumps 3a and 3b are provided for driving a hydraulic cylinder 15, a small capacity pump discharge pipe 7 is connected to a large capacity discharge pipe 5 in a downstream side lower than a check valve 18, solenoid unloading relief valves 16 and 17 are respectively provided as pressure control valves in the large and small capacity pump discharge pipes 5 and 7, a pressure control valve 16 for the large capacity pump 3a is set as a pressure control valve for constituting a non-load circuit, and by unloading the large capacity pump 3a during the operation of the pressure control valve 16 for a large capacity pump with a set pressure while a bucket is closed or opened, the hydraulic cylinder 15 is pressurized only by the small capacity pump 3b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic control circuit for a hydraulic grab bucket such as an electrohydraulic grab bucket, and more particularly to a bucket for opening and closing a load such as garbage such as municipal garbage and combustion ash by a hydraulic cylinder for opening and closing the bucket. When closing and gripping, or opening the bucket to release the gripped load, the hydraulic pressure is controlled by suppressing the temperature rise etc. due to the heat generation of the hydraulic oil due to the relief operation of the pressure control valve for setting the operating pressure of the hydraulic cylinder. The present invention relates to a hydraulic control circuit for a hydraulic grab bucket capable of continuously operating a grab bucket.

[0002]

2. Description of the Related Art Conventionally, for example, in a cleaning plant, a hydraulic pump, a pressure control valve, a directional control valve, etc., which are driven by a motor such as an electric motor, are mounted on a girder of a glove bucket body for transporting waste such as municipal waste and incinerated ash. A hydraulic grab bucket for opening and closing a grab bucket by incorporating an electric hydraulic pump unit having the above hydraulic equipment is used.

[0003] This type of hydraulic grab bucket has, for example, a pair of left and right buckets openably and closably mounted by a hydraulic cylinder on a girder that can be suspended by a lifting device such as a crane, and the hydraulic cylinder is mounted on the girder. A hydraulic pump to be driven, a prime mover such as an electric motor to drive the hydraulic pump, an electromagnetic switching valve for sending hydraulic oil discharged from the hydraulic pump to the hydraulic cylinder and switching a driving (operating) direction of the hydraulic cylinder, and a hydraulic cylinder operation A pressure adjusting valve for setting pressure and a hydraulic pump unit having a built-in hydraulic pipe for connecting the respective devices and an oil tank are provided.

[0004] When the hydraulic pump unit of the grab bucket is taken in and immersed in garbage or incineration ash which is a grasped object or in water, the incineration ash, water and the like enter the unit. In some cases, the periphery of a hydraulic device including a motor such as an electric motor, a hydraulic pump, or the like is covered with a panel and sealed so as to be sealed against the external atmosphere.

The hydraulic control circuit of such a hydraulic pump unit will be described with reference to FIG. 8. 1 is an oil tank, 2 is a suction pipe, 3 is a hydraulic pump that is rotated by an electric motor 4 as a prime mover, and is a large capacity pump. The pump 3a is configured as a multiple pump in which the small capacity pump 3b is integrated. Reference numeral 5 denotes a discharge pipe connected to the oil discharge port of the large capacity pump 3a, and 6 denotes a circuit pressure setting for branch pressure connection to the discharge pipe 5 and an end connected to the oil tank 1, that is, a hydraulic cylinder 15 for opening and closing the bucket. A relief valve of a balance piston type or the like as a pressure control valve for setting an operating pressure, 7 is a discharge pipe connected to an oil discharge port of the small capacity pump 3b, 8 is a communication between the discharge pipe 7 and the tank line 10. This is a bypass line in which a check valve (check valve) 9 is interposed. The check valve 9 acts to raise a predetermined pilot pressure and supply it to a pilot switching valve 11B described later.

Reference numeral 11 designates an electromagnetic switching valve for switching and supplying the hydraulic oil discharged from the large-capacity hydraulic pump 3a and sent to the discharge pipe 5 to the head side chamber 15a and the rod side chamber 15b of the hydraulic cylinder 15 to switch the operating direction of the hydraulic cylinder 15. The electromagnetic pilot switching valve, the electromagnetic pilot switching valve 11
Is composed of a main switching valve 11A and a pilot switching valve 11B. The main switching valve 11A has a center portion at a neutral position shown in the figure, a pump port P to which the end of the large-capacity hydraulic pump discharge pipe 5 is connected, and the tank line 10
Is connected to the tank port T to which the end of
A tandem center type switching valve in which ports A and B are blocked is provided.

On the other hand, the pilot switching valve 11B has a center portion at a neutral position shown in the drawing, and a pump port connected to an end of the small-capacity hydraulic pump discharge pipe 7 is blocked, and an end of the tank line 12 is connected. A pressure port block type solenoid-operated directional control valve in which the tank port T, the A port, and the B port are in communication with each other. One end of each of the pressure oil supply pipes 13 and 14 is connected to the A port and the B port of the main switching valve 11A, and the other end of the pressure oil supply pipe 13 is connected to the rod side chamber 1 of the hydraulic cylinder 15.
5b, and the other end of the pressure oil supply pipe 14 is connected to the head side chamber 15a of the hydraulic cylinder 15.

A port of the pilot switching valve 11B and one end of the main switching valve 11A are connected to a pilot pressure supply pipe 11
a port B of the pilot switching valve 11B is connected to the pilot pressure supply pipe 1 at the other end of the main switching valve 11A.
1b.

In the hydraulic control circuit of the hydraulic grab bucket configured as described above, when the electric motor 4 is started in the state shown in FIG. 8, the hydraulic pump 3 is driven and the oil discharged from the large capacity pump 3a passes through the discharge pipe 5. Then, the electromagnetic pilot switching valve 11 is bypassed at the center of the main switching valve 11A, returned to the tank line 10, and circulated idle. The oil discharged from the small-capacity pump 3b flows through the discharge pipe 7 and further returns to the tank line 10 through the bypass line 8 with the check valve 9 interposed therebetween, and is circulated idle.

In this state, when the garbage, which is a grasping object, is grasped by the hydraulic grab bucket, the garbage is suspended with the hydraulic grab bucket suspended by a crane as a lifting device, positioned above the garbage, and opened. , And the bucket is closed. At this time, SOL.b of the pilot switching valve 11B of the electromagnetic pilot switching valve 11 is excited. Then, the pressure oil discharged from the small capacity pump 3b flows into the pilot pressure supply pipe 11b through the discharge pipe 7 and the B port of the pilot switching valve 11B, and flows into the main switching valve 1b.
It is supplied to the other end of 1A, the main switching valve 11A is switched, and its pump port P and B port are communicated.

Then, the oil discharged from the large-capacity pump 3a flows from the pump port P of the main switching valve 11A to the B port via the discharge pipe 5 and passes through the hydraulic oil supply pipe 14 to the hydraulic cylinder 15 for opening and closing the bucket. The air is supplied to the head side chamber 15a, the piston rod is extended, the grab bucket is closed, and dust is grasped. At this time, the oil in the rod side chamber 15b of the hydraulic cylinder 15 flows from the A port of the main switching valve 11A to the tank line 10 via the tank port T via the pressure oil supply pipe 13, and is returned to the oil tank 1.

After the dust is thus grasped by the bucket, the SOL.b of the pilot switching valve 11B is de-energized, the pilot switching valve 11B is neutralized as shown, and the main switching valve 11A is returned to the neutral state. After lifting the hydraulic grab bucket with a crane, it is transported by moving it to the unloading point, opening the bucket and dropping the grabbed garbage to unload. At this time, SOL.a of the pilot switching valve 11B of the electromagnetic pilot switching valve 11 is excited. Then, the pressure oil discharged from the small-capacity pump 3b flows through the discharge pipe 7 into the pilot pressure supply pipe 11a via the A port of the pilot switching valve 11B, and is supplied to one end of the main switching valve 11A. Is switched so that the pump port P and the A port communicate with each other.

Then, the oil discharged from the large-capacity pump 3a flows through the discharge pipe 5 from the pump port P of the main switching valve 11A to the A port, and passes through the hydraulic oil supply pipe 13 to the hydraulic cylinder 15 for opening and closing the bucket. The piston rod is supplied to the rod side chamber 15b, the piston rod is retracted, the grab bucket is opened, and dust is unloaded. At this time, the oil in the head side chamber 15a of the hydraulic cylinder 15 flows from the B port of the main switching valve 11A to the tank line 10 via the tank port T via the pressure oil supply pipe 14, and is returned to the oil tank 1.

The hydraulic pressure of the pressure oil supplied to the hydraulic cylinder 15 necessary for closing the bucket for grasping the debris with the bucket and for opening the bucket when unloading the debris which has been grasped is controlled by a pressure control valve. The pressure is set within the pressure set by the relief valve 6.

[0015]

When a load such as dust is grasped by a hydraulic grab bucket using a hydraulic control circuit as shown in FIG. 8 described above, the bucket is closed or
When a load is caught between the buckets and cannot be closed any more, the pressure of the discharge oil discharged from the large-capacity pump 3a of the hydraulic pump 3 increases and the relief valve 6
, The entire discharge oil of the large-capacity pump 3 a is relieved from the relief valve 6, passed through the tank line 10 and returned to the oil tank 1. By this relief operation, the entire energy of the hydraulic oil is converted into heat, the hydraulic oil is heated, and the temperature of the hydraulic oil rises.

Further, the closing operation of the bucket when the load is grasped by the bucket is rarely completed by one operation. For example, if the load is grasped too much, the bucket is not completely closed. In such a case, when the first closing operation is completed, the hydraulic grab bucket is slightly lifted by the crane and the main switching valve 11A of the electromagnetic pilot switching valve 11 is lifted.
To a neutral state, the pressurization of the head chamber side 15a is stopped, and the load is gradually dropped from the bucket while the pressure oil of the head chamber side 15a and the rod chamber side 15b of the hydraulic cylinder 15 is held, and then, again. The SOL.b of the pilot switching valve 11B of the electromagnetic pilot switching valve 11 is excited to put the main switching valve 11A into the bucket closed state, pressurize the closing side (the head chamber 15a side) of the hydraulic cylinder 15, and complete the bucket. Or lifted so that it can be transported.

Such an additional pressurizing operation, that is, an operation called “grabbing”, usually needs to be repeated several times, such as three times. Each time such a catching operation is performed, the relief operation of the discharge oil of the large-capacity pump 3a by the relief valve 6 is performed, and the oil temperature is further increased. The relief operation of the relief valve 6 increases the power consumption of the electric motor 4 as the driving motor of the hydraulic pump 3 and causes heat generation.

When the hydraulic pump unit has a hermetic structure as described above, heat is not satisfactorily dissipated due to ventilation, so that the release of the relief valve 6 causes the generation of hydraulic oil and the operation of the hydraulic pump 3. Heat of the motor 4 cannot be released to the outside, and the hydraulic oil such as hydraulic oil, the hydraulic pump 3, the electromagnetic pilot switching valve 11, the piping, and the hydraulic motor 4 and the temperature of the motor 4 are excessively increased. Had trouble.

With the recent increase in the amount of municipal solid waste in waste management plants and the introduction of continuous combustion of waste incinerators as a measure against dioxins, the frequency of use of grab buckets in waste treatment plants is increasing, and these severe conditions are increasing. There is a demand for a grab bucket that can be operated continuously for a long time even under various use conditions.

The present invention has been made in order to eliminate the above-mentioned drawbacks of the conventional hydraulic control circuit of a hydraulic grab bucket, in which a load such as municipal waste or combustion ash is transferred to a bucket by a bucket opening / closing hydraulic cylinder. When the hydraulic cylinder is closed and gripped, or when the bucket is opened to release the load, the temperature rise due to the heat generated by the hydraulic oil due to the relief operation of the pressure control valve for setting the operating pressure of the hydraulic cylinder and the hydraulic pump driven by the relief operation It is an object of the present invention to provide a hydraulic control circuit for a hydraulic grab bucket capable of suppressing heat generation and the like of a prime mover such as an electric motor so that the hydraulic grab bucket can be operated continuously for a long time.

[0021]

In order to achieve the above object, a hydraulic control circuit for a hydraulic grab bucket according to the present invention comprises:

(1) A hydraulic cylinder for opening and closing the bucket, a hydraulic pump for driving the hydraulic cylinder, and a hydraulic oil connected to a discharge pipe of the hydraulic pump for switching and supplying pressure oil to the head side chamber and the rod side chamber of the hydraulic cylinder. In a hydraulic control circuit of a hydraulic grab bucket having an electromagnetic switching valve for switching an operation direction, and a pressure adjusting valve connected to a discharge pipe of the hydraulic pump and setting a hydraulic cylinder operating pressure, the hydraulic pump is connected to at least a large capacity side. And a plurality of hydraulic pumps comprising two small-capacity pumps, and a discharge pipe of the small-capacity pump is connected to a discharge pipe of the large-capacity pump at a point downstream of the check valve. A pressure control valve is attached to each of the discharge pipe of the displacement pump and the discharge pipe of the small displacement pump, and the pressure control valve for the large displacement pump is a pressure control valve that can constitute a no-load circuit. The hydraulic cylinder is pressurized only by the small-capacity pump by unloading the large-capacity pump during operation of the pressure control valve for the large-capacity pump at the set pressure when the bucket is closed and / or opened. The configuration was adopted.

(2) In the hydraulic control circuit of the hydraulic grab bucket according to the above (1), the pressure control valve for the small displacement pump is a balance piston type relief valve, and the pressure control valve for the large displacement pump. Is a solenoid valve type unload relief valve comprising a balance piston type relief valve and an electromagnetic switching valve connected to a vent connection port of the balance piston type relief valve.

(3) In the hydraulic control circuit of the hydraulic grab bucket according to the above (1), the pressure control valve for the small displacement pump is a balance piston type relief valve, and the pressure control valve for the large displacement pump. Is a hydraulic pilot type unload relief valve.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a front view of an embodiment of an electro-hydraulic grab bucket as a hydraulic grab bucket applied to the present invention, FIG. 2 is a right side view of the electro-hydraulic grab bucket, and FIG. First Embodiment of a Hydraulic Control Circuit Applied to an Electro-hydraulic Grab Bucket, FIG. 4 is a longitudinal sectional view showing the structure of an electromagnetic unload relief valve which is a pressure control valve applied to the hydraulic control circuit of FIG. FIG. 5 is a graph showing the pressure change state of the discharge oil of the hydraulic pump during the unloading operation by gripping the bucket and opening the bucket based on the hydraulic control circuit configuration of FIG. 3, and FIG. 6 is applied to the electrohydraulic grab bucket. FIG. 7 is a longitudinal sectional view showing the structure of a hydraulic pilot type unload relief valve which is a pressure control valve applied to the hydraulic control circuit of FIG.

First, the overall structure of an electrohydraulic grab bucket as a hydraulic grab bucket applied to the present invention will be described with reference to FIGS. The electrohydraulic grab bucket 50 has a pair of left and right buckets 52 that are rotatably supported on the shaft 51a that is supported and fixed to the lower part of the girder 51 and that is rotatably supported at the upper part. A hydraulic cylinder 15 for opening and closing the bucket, which is rotatably supported by a pin at both ends at the upper end of the bucket 52 at the upper position between the left and right buckets and rotatably supported by pins, and a hydraulic pressure installed on the upper part of the girder 51. The main part is constituted by the pump unit PN.

1 is an oil tank, 53 is left and right buckets 52
A connection bar is mounted between the two ends and pivotally supported by pins so as to open and close a pair of buckets symmetrically with respect to a vertical center line. 52a is a claw provided at the bottom of the bucket 52, and 54 is a buffer made of an elastic body such as a tire attached to both side surfaces of the bucket 52 and capable of absorbing shock even when the bucket 50 collides with a wall or the like.

Reference numeral 55 denotes a suspension member fixed to the girder 51. A pin is attached to the suspension member 55, and a chain is connected to the suspension member.
Is suspended or suspended. Reference numeral 57 denotes a cabtire cable for supplying electricity to a hydraulic pump driving motor, an electromagnetic switching valve, an operation panel, and a control panel incorporated in the hydraulic pump unit PN. Hydraulic pump unit P
N is hermetically enclosed by a panel PNP so that a load such as dust or the like, water, dust, or the like as a grasped object does not enter from outside. Reference numeral 56 denotes a protector (cover) for protecting the hydraulic pump unit PN and the like from the surroundings.

With such a configuration, the grab bucket 5
The reference numeral 0 indicates that the pair of left and right buckets 52, 52 are opened and closed by rotating the pair of left and right buckets symmetrically with respect to the vertical center line about the shafts 51a, 51a, respectively, by operating the hydraulic cylinder 15. In FIG. 1, the fully closed position (state) is indicated by a solid line, and the fully open position (state) is indicated by a two-dot chain line. When the buckets 52, 52 are completely closed, the claws 52a at the tips of the left and right buckets are engaged with each other.

Next, a hydraulic control circuit for opening and closing the bucket 52 applied to the electrohydraulic grab bucket 50 will be described. First, a first embodiment of the hydraulic control circuit will be described with reference to FIG. FIG. 3 shows a hydraulic control circuit corresponding to the conventional example of FIG. In FIG. 3, the same or corresponding portions as those in FIG. 8 are denoted by the same reference numerals, and description thereof will be omitted.

Also in the hydraulic control circuit of this embodiment, a multiple pump in which a large capacity pump 3a and a small capacity pump 3b are integrated is used as the hydraulic pump 3. However, in the circuit of this embodiment, the discharge oil of both the large-capacity pump 3a and the small-capacity pump 3b is supplied to the hydraulic cylinder 15 and used for opening and closing the bucket 52. An electromagnetic unload relief valve 16 as a pressure control valve is connected to and attached to the discharge pipe 5 of the large-capacity pump 3a, and is located at a position downstream of the mounting point of the electromagnetic unload relief valve 16 of the discharge pipe 5. Is provided with a check valve 18.
The check valve 18 is for preventing and preventing the backflow of the pressure oil acting on the head chamber side 15a or the rod chamber side 15b of the hydraulic cylinder 15 when the electromagnetic unload relief valve 16 is unloaded. It is.

The discharge pipe 7 of the small-capacity pump 3b is connected at its end to a pilot switching valve 11B of the electromagnetic pilot switching valve 11, similarly to the circuit of FIG. In the present embodiment, another discharge pipe 19 is branched and connected in the middle of the discharge pipe 7 to
9 is provided with a check valve 20 and the end of the discharge pipe 19 is connected to the discharge pipe 5 of the large-capacity pump 3a at a point downstream from the check valve 18 provided in the discharge pipe 5. The pressure oil discharged from the large-capacity pump 3a and the oil discharged from the small-capacity pump 3b merge. The balance pipe type relief valve 17 is provided between the discharge pipe 7 of the small capacity pump 3b and the tank line 10 by the check valve 20.
It is provided in a branch connection at an upstream position.

The check valve 20 is an electromagnetic pilot switching valve 11
This is for establishing a predetermined pilot pressure for operating the main spool of the main switching valve 11A.
As shown in FIG. 4 in detail, the electromagnetic unload relief valve 16 includes a relief valve body composed of a balance piston type relief valve 16a, and a balance piston type relief valve 16a.
And the electromagnetic switching valve 16b connected to the vent connection port v. That is, the electromagnetic unload relief valve 16 on the large-capacity pump 3a side is a pressure control valve that can form a no-load circuit. Other configurations are the same as those of the circuit of FIG.

Here, the structure of the balance piston type relief valve 16a will be described with reference to FIG. 4. An oil inlet 30 branched from the large capacity pump discharge pipe 5 and connected thereto, and 31 is connected to the tank line 10 A tank connection port, 32 is a pilot valve for setting a circuit pressure, 33 is a poppet attached to the tip thereof, 34 is a spring pressing the poppet 33 against a valve seat, and 35 is a set pressure adjusting handle. 36 is a balance piston, 37 is a spring for lightly pressing the tip of the balance piston 36 against the valve seat 40, and 38 is a fine hole (both choke or tanker) communicating the oil inlet 30 side of the piston 36 and the pilot valve 32 side. , 39) is an oil escape hole provided through the center of the piston 36, and is a small hole for allowing oil to escape from the pilot valve side to the tank connection port 31.

In the balance piston type relief valve 16a having such a structure, when the bucket is closed and the load is gripped, or when the bucket is opened and unloaded, the electromagnetic switching valve 16b connected to the vent connection port v is operated as shown in FIG. As shown in FIG. 4, the SOL.R excitation is released and the relief valve 16a is released.
The vent connection port v is blocked, the so-called vent connection port v is closed, and the relief valve 16a acts as a normal pressure control valve based on the set pressure (set value). That is, pressure oil based on the set pressure of the relief valve 16a is supplied to the hydraulic cylinder 15, and the hydraulic cylinder 15 is operated to open and close the bucket.

When the bucket is fully closed, the load is excessively grasped, or the load is caught between the buckets and cannot be closed any more, resulting in an overload (overload). The discharged pressure oil rises and reaches the set value (pressure) of the relief valve 16a, at which time the poppet 33 of the pilot valve 32 starts to separate from the valve seat, and the oil in the oil chamber w located in front of the poppet 33 escapes. The pressure in the upper chamber y of the balance piston 36 communicating with the oil chamber w is reduced by the action of the fine holes 38 due to the action of the small holes 38, and the pressure of the balance piston 36 begins to gradually escape through the hole 39 to the oil tank 1 through the tank connection port 31. Pressure balance is lost, the balance piston 36 is lifted upward in the figure, and the valve body below the balance piston 36 is slightly separated from the valve seat 39, so that the pump discharge oil is recovered. And-safe, relief and oil is returned through the tank connection port 31 to the oil tank 1.

At the time of this relief, the valve body below the balance piston 36 is slightly separated from the valve seat 39 as described above, and the pressurized oil is returned to the tank connection port 31 by receiving the throttle resistance here. Most of the energy it has is turned into heat and raises the oil temperature. Such a relief operation is the biggest factor in raising the oil temperature.

On the other hand, when the pressure oil discharged from the large-capacity pump 3a exceeds the set value (pressure) of the relief valve 16a as described above, the electromagnetic switching valve 16b is switched off.
When the SOL.R is excited, the vent connection port v of the relief valve 16a is communicated with the oil tank 1 to be substantially at atmospheric pressure, so-called,
The vent connection port v is opened, and the hydraulic pressure in the upper chamber y of the balance piston 36 is set to substantially the atmospheric pressure, so that the pressure balance of the balance piston 36 is largely disturbed, and the piston 36 is largely lifted upward. The valve body is moved so as to be largely separated from the valve seat 39, and the oil inlet 30 and the tank connection port 31 communicate with each other. That is, the relief valve 16a is in the unloaded state, and does not operate as a normal relief valve.
As a result, the entire amount of oil discharged from the large-capacity pump 3a is returned to the oil tank 1 at a very small pressure of only the pipe resistance. At this time, heat generation of the oil hardly occurs.

In this embodiment, the balance piston type relief valve 17 connected to the discharge pipe 7 of the small capacity pump 3b has the same structure as the balance piston type relief valve 16a of the electromagnetic unload relief valve 16. ing.

The operation of the hydraulic control circuit of the electrohydraulic grab bucket having the structure shown in FIG. 3 will be described with reference to the graph shown in FIG. In this embodiment, the set pressure of the balance piston type relief valve 16a of the electromagnetic unload relief valve 16 for the large capacity pump 3a and the set pressure of the balance piston type relief valve 17 for the small capacity pump 3b are the same. You. In addition, both the relief valves 1
Actually, the set values of 6a and 17 are set so that the pressure of the pipe 19 downstream of the check valve 20 and the pressure of the pipe 5 downstream of the check valve 18 become equal, that is, via the main switching valve 11A. The check valve 2 is supplied to the hydraulic cylinder 15 so that the hydraulic pressure becomes equal.
It is determined in consideration of a difference between 0 and the cracking pressure of the check valve 18 and the like.

In this embodiment, the cracking pressure is controlled by the check valve 20.
Is set to, for example, about 3 to 5 kg / cm ² higher than that of the check valve 18 from the necessity of supplying the pilot pressure for the main spool switching operation to the main switching valve 11A. The difference in the cracking pressure of the valve 17 is higher than that of the relief valve 16a. However, in the present embodiment, the description will be made assuming that the set values of both the relief valves 16a and 17 are the same. In this embodiment, the oil discharge amount ratio between the large capacity pump 3a and the small capacity pump 3b is 9: 1.

At the start of operation, the electromagnetic pilot switching valve 11
3 and the electromagnetic switching valve 16b is in the state shown in FIG. 3, and when the electric motor 4 is started, the large and small pumps 3a, 3
b is driven, and oil flows from the respective pumps to the respective discharge pipes 5 and 7. The oil discharged from the large-capacity pump 3a and flowing through the discharge pipe 5 is discharged from the small-capacity pump 3b when passing through the check valve 18, and is discharged from the small-capacity pump 3b and the discharge pipe 19
Flows through the center line of the main switching valve 11A of the electromagnetic pilot switching valve 11, and the tank line 1
It is returned to 0 and is circulated idlely.

During this idle circulation, the solenoid valve 16b of the electromagnetic unload relief valve 16 is excited to excite the SOL.R to open the vent connection port v of the relief valve 16a to bring the relief valve 16a into the unloaded state. For example, the pressure loss due to the cracking pressure of the check valve 18 of the oil flow is eliminated, and the oil temperature rise can be further suppressed.

When the bucket 52 is closed from the idle circulation state to grab garbage as a load, the grab bucket 50 is suspended by a crane, positioned above the garbage, and lands on the garbage with the bucket open. At this time, SOL.b of the pilot switching valve 11B of the electromagnetic pilot switching valve 11 is excited. Then, the pressure oil discharged from the small capacity pump 3b passes through the discharge pipe 7 and flows into the pilot pressure supply pipe 11b through the B port of the pilot switching valve 11B, and is supplied to the other end side of the main switching valve 11A. 11A is switched to connect the pump port P and the B port.

Then, the oil discharged from the large capacity pump 3a and flowing through the discharge pipe 5 and the oil discharged from the small capacity pump 3b and flowing through the discharge pipe 7 and the discharge pipe 19 are downstream of the check valve 18 of the discharge pipe 5. At the point, they flow from the P port to the B port of the main switching valve 11A, pass through the pressure oil supply pipe 14, and the head side chamber 15a of the hydraulic cylinder 15 for opening and closing the bucket.
, The piston rod is extended, the grab bucket is closed and debris is caught. At this time, both the discharge oil of the large-capacity pump and the discharge oil of the small-capacity pump act on the hydraulic cylinder 15 as compared with the conventional circuit, so that the operation of the hydraulic cylinder 15 is performed earlier. At this time, the oil in the rod-side chamber 15b of the hydraulic cylinder 15 flows from the port A of the main switching valve 11A to the tank line 10 via the tank port T via the pressure oil supply pipe 13, and is returned to the oil tank 1.

When the bucket 52 begins to close at time t1 in FIG. 5 and begins to grab debris, as shown in FIG. 5, the pressure (discharge oil pressure) of the discharge oil of the large capacity pump 3a and the small capacity pump 3b of the hydraulic pump 3 is increased. Rise. Then, at time t2, when the bucket 52 grasps the dust and closes it, or the bucket 52 grasps the dust too much and cannot be further closed, the discharge hydraulic pressure of the hydraulic pump 3 is increased by the solenoid valve type unload relief valve. When the set pressures of the relief valves 16a and 17 (for example, 17.5 MPa (175 kg / cm ² )) are reached and the oil discharged from the respective pumps is totally released from the respective relief valves 16a and 17, the tank line 10 Then, the oil is returned to the oil tank 1. At the time of this relief operation, almost all the energy of the hydraulic oil is converted into heat.

At the time of this relief operation, that is, when the relief valve is operating at the set pressure, when a time T1 has elapsed from the time t2 when the relief was started (U in FIG. 5).
At point P), SOL.R of the electromagnetic switching valve 16b of the solenoid valve type unload relief valve 16 on the large capacity pump side is excited to put the relief valve 16a in a no-load state (a state in which the vent connection port v is opened to the tank). Unload the displacement pump 3a. Even after the unloading is started, the head-side chamber 15a (closed-side chamber) of the hydraulic cylinder 15 is set at a set pressure (for example, 1
The discharge oil discharged at 7.5MPa) acts on the head side chamber 1
5a is pressurized, and the closing force of the bucket is maintained.

Then, a time T2 from the start of the unloading
At time t3 when the time has elapsed, the excitation of the pilot switching valve 11B of the electromagnetic pilot switching valve 11 is released, and the main switching valve 1
1A to the neutral state, and the head side chamber 1 of the hydraulic cylinder 15
The pressurization of 5a is stopped, and the discharge oil of the large and small hydraulic pumps 3a, 3b is circulated idle. At this time, the main switching valve 11A
Are blocked, the hydraulic pressure in the head side chamber 15a and the rod side chamber 15b is maintained.
As described above, in FIG. 5, time T1 is a relief operation time by the relief valves of the large capacity pump and the small capacity pump, and time T2 is an unload time of the large capacity pump, and
This is the relief operation time by the relief valve of only the small capacity pump.

T is the total time of T1 and T2, and is the pressurizing time of the head side chamber or the rod side chamber of the hydraulic cylinder 15. In this embodiment, for example, the time T1 is 0.5 seconds, and the time T2 is
1.5 seconds T is set to 2 seconds, which significantly shortens the time during which the relief operation of the relief valve 16a of the large capacity pump 3a is closed among the relief operation times of both relief valves. And T
The times T1 and T2 are both set by the timer. The start of the timer counting for the T1 time is performed by detecting an overload current value which is a current value corresponding to a set pressure of the relief valve 16a or 17 of the electric motor 4 for driving the hydraulic pump 3 by the current sensor.

It is rare that the above-mentioned grasping of the dust by closing the bucket is completed only by the first grasping operation. In most cases, the bucket is not completely closed due to excessive grasping of the dust and the bucket is lifted. It cannot be transported. In such a case, the grab bucket 50 is slightly lifted by a crane to drop garbage little by little, for example, at the same time as the start of the idle circulation at the time t3 when the first gripping operation is completed. Adjusts the grip load so that it can be fully closed, and the bucket closing operation, that is,
The pressurization of the head side chamber 15a of the hydraulic cylinder 15 is performed again.

Also, even if the fully closed state can be achieved by the first gripping operation, the crane operator (grab bucket operator) may not be able to completely confirm the distant bucket. In order to complete the closing of the bucket, it is necessary to repeatedly pressurize the closing side chamber of the cylinder. Such an operation is also called catching.

That is, at time t4, this first catching is started, and the SOL.b of the pilot switching valve 11B of the solenoid-operated pilot switching valve 11 is excited as described above, and the large capacity pump is connected. Both small-capacity pumps discharge at a set pressure (for example, 17.5 MPa) with the relief operation of the respective relief valves 16a and 17 and pressurize the head-side chamber (closed-side chamber) 15a of the hydraulic cylinder 15 in the direction of closing the bucket. . Then, after the start of pressurization, T1 time (for example, 0.5
Seconds) At the UP point, the SOL.R of the electromagnetic switching valve 16b of the solenoid valve type unload relief valve 16 is excited to release the relief valve 16 in the same manner as in the above-described relief operation immediately after the start of gripping.
Open the tank at the vent connection port v of the large capacity pump 3a
And the pressurization of the head side chamber (closed side chamber) 15a of the hydraulic cylinder 15 is continued only by the small capacity pump 3b.

When a time T2 (for example, 1.5 seconds) has elapsed from the start of unloading of the large capacity pump, that is, at time t4
The pilot switching valve 11 of the electromagnetic pilot switching valve 11
The excitation of B is released, and the main switching valve 11A is set to the neutral state.
The pressurization of the head side chamber 15a of the hydraulic cylinder 15 is stopped,
The oil discharged from the large and small hydraulic pumps 3a and 3b is circulated in an idle state. Thereafter, the same pressurizing operation of the closing side chamber 15a of the hydraulic cylinder 15 as that of the first time is performed twice at time t6 and time t8. When the three catching operations are completed at time t9, the hydraulic circuit is put into an idle circulation state, and the grab bucket 50 is lifted by the crane and transported to a predetermined unloading position. Open and unloading starts.

When the bucket is opened for unloading, the pilot switching valve 11 of the electromagnetic pilot switching valve 11
Excite B SOL.a. Then small capacity pump 3b
The pressure oil discharged from the tank flows through the discharge pipe 7 through the A port of the pilot switching valve 11B into the pilot pressure supply pipe 11a, is supplied to one end of the main switching valve 11A, and the main switching valve 11 is switched. The pump port P communicates with the A port.

Then, the oil discharged from the large-capacity pump 3a and flowing through the discharge pipe 5 and the oil discharged from the small-capacity pump 3b and flowing through the discharge pipe 7 and the discharge pipe 19 are located downstream of the check valve 18 of the discharge pipe 5. And is passed from the pump port P of the main switching valve 11A to the A port, passes through the pressure oil supply pipe 13, and the rod side chamber 1 of the hydraulic cylinder 15 for opening and closing the bucket.
5b, the piston rod is retracted, the grab bucket is opened, and refuse is unloaded. At this time, the oil in the head side chamber 15a of the hydraulic cylinder 15 is
4 and flows from the B port of the main switching valve 11A to the tank line 10 via the tank port T and returns to the oil tank 1.

At time t11 in the bucket opening operation by such an operation, the bucket 52 is fully opened, and the oil discharged from the large-capacity pump and the small-capacity pump is adjusted to the set pressures of the respective relief valves 16a and 17. At this point, the respective relief valves 16a and 17 are relieved. And
Similarly to the operation at the time of the above-described relief at the time of closing the bucket, the electromagnetic switching valve 16b of the solenoid-operated unload relief valve 16 of the large-capacity pump 3a is excited at the UP point when T1 time has elapsed after the start of the relief, and the relief valve 16a Is opened, the large capacity pump 3a is unloaded, and the small capacity pump 3a is unloaded.
b, the relief operation of the relief valve 17 is continued, and the pressurization of the open side chamber (rod side chamber) 15b of the hydraulic cylinder 15 is continued.

At time t12 after time T2 from the start of the unloading operation of the large capacity pump 3a, the main switching valve 11A is returned to the neutral state by the pilot switching valve 11B, and the large and small pumps 3a, 3b are set in the idle circulation state. Unloading ends. Thereafter, the grab bucket 50 is returned to the load gripping position by the crane, and at time t13, the same load gripping operation is performed, and thereafter, the similar bucket opening and closing operations are repeatedly performed.

As described above, since the relief operation time of the relief valve 16a of the large capacity pump 3a is greatly reduced when the bucket 52 is closed and opened, the amount of heat generated by the relief operation of the relief valve 16a is increased. Can be reduced. In other words, the calorific value obtained by subtracting the calorific value by the relief operation by the relief valve 17 of the small capacity pump from the calorific value corresponding to the area of the hatched portion in FIG. 5 [(the discharge oil of the large capacity pump 3a) Difference between the discharge pressure in the relief state and the discharge pressure in the unload state)
X (heat generation amount for (unload time T2)).

In this embodiment, the discharge amount of the large-capacity pump 3a and the small-capacity pump 3b is 9: 1, so that the small-capacity pump 3b generates a small amount of heat in the relief operation of the relief valve 17. It only needs things. By reducing the relief oil discharge operation time of the large-capacity pump 3a, the load on the electric motor 4 for driving the hydraulic pump 3 can be reduced, the heat generated by the electric motor itself can be reduced, and the power consumption of the electric motor can be reduced. Can be done.

As described above, in the circuit of this embodiment, during operation of the relief valve 16a, which is a pressure control valve of the large capacity pump 3a, at the set pressure, that is, during the relief operation, the relief valve 1
6a constitutes a no-load circuit by the electromagnetic switching valve 16b,
Since the large-capacity pump 3a having a large discharge amount is unloaded, an increase in the oil temperature due to the relief operation can be reduced by that amount, and therefore, an excessive increase in the temperature of the electric motor 4 for driving the hydraulic pump 3 can be prevented. Power consumption can be reduced. Therefore, even if the hydraulic pump unit PN has a closed structure, continuous operation of the hydraulic unit becomes possible, and continuous operation of the electrohydraulic grab bucket 1 becomes possible.

Next, a second embodiment of the hydraulic control circuit of the electrohydraulic grab bucket according to the present invention will be described with reference to FIG. 6, the same reference numerals are given to the same or corresponding parts as the circuit of FIG. 3 of the first embodiment, and the description thereof will be omitted. In this embodiment, a hydraulic pilot type unload relief valve 21 is connected to the discharge pipe 5 and used as a pressure control valve of the large capacity pump 3a. The pressure control valve of the small capacity pump 3b is a balance piston type relief valve 17 as in the first embodiment of FIG. Other configurations are the same as those of the first embodiment in FIG.

Here, the hydraulic pilot type unload relief valve 21 will be described with reference to FIG. 7. The pilot valve 32 having a poppet 33 at the tip and the balance piston 36 are provided at the valve body of the unload relief valve 21. It is provided as a control valve main body, and this part has the same configuration as the relief valve 16 in FIG. And between the oil inlet 30 connected to the large capacity pump discharge pipe 5 and the hydraulic circuit connection port 41 connected to the large capacity pump discharge pipe 5 between the oil inlet 30 and the main switching valve 11A. Is provided with a check valve 23 having a spring 23a therein.

Further, an unloading plunger 43 slides on the valve body coaxially with the poppet 33 so as to face the poppet 33 at the tip of the pilot valve 32 and contact the poppet 33 in the oil chamber W. An oil chamber X is movably mounted on one end of the plunger 43 opposite to the poppet 33, and a pilot pressure introduction passage 42 (corresponding to the pilot line 22 in FIG. 6) is formed in the oil chamber X. Are connected to each other. An end of the valve element of the pilot pressure introduction passage 42 is a pilot pressure introduction port 42A. The tank connection port 31 is connected to the tank line 10 in FIG.

The operation of the hydraulic pilot type unload relief valve 21 having such a configuration will be described. The unload pressure is set by adjusting the force of the pilot valve 32 pressing the poppet 33 against the valve seat by the rotation of the handle 35. Is done. The state of FIG. 7 shows a state in which the circuit pressure has not yet reached the set pressure of the valve, that is, a state in which the bucket 52 normally opens and closes while gripping a load or releasing a load. The stop valve 23 is opened and the oil inlet 30 is opened.
This shows a state where pressure oil is flowing from the large-capacity hydraulic pump 3a to the circuit connection port 41 side (that is, the main switching valve 11A side, the hydraulic cylinder 15 side, and the like). At this time, the pressures in the oil chambers X, Z, Y, and W are equal, and the poppet 33 and the balance piston 36 of the pilot valve 32 each have their valve bodies seated on valve seats.
3 is in a pressure equilibrium state and is located away from the poppet 33.

In this state, when the bucket 52 begins to close and begins to grab dust, the load on the circuit side, that is, the load on the bucket 52, increases, and the pressure in the closing chamber 15a of the hydraulic cylinder 15 increases. Small capacity pump 3b
Discharge pressure rises. Then, when the bucket 52 grasps the dust and closes, or the bucket 52 grasps the garbage too much and cannot be closed any more, the hydraulic pilot type unload relief valve 2 on the side of the large capacity pump 3a.
The pressures in the Z chamber, Y chamber and W chamber of No. 1 rise (the Y chamber and
When the pressure of the control valve is equal to the set pressure (cut-out pressure) of the control valve, the poppet 33 is pushed away from the valve seat against the force of the spring 34, and the oil in the Z chamber passes through the choke 38 to the Y chamber. It flows into the tank 31 through the opening formed between the poppet 33 and its valve seat, flows through the small hole 39 at the center of the piston 36, and returns to the oil tank 1.

At this time, the piston 36 is pushed upward above the Y chamber due to the pressure drop in the Y chamber due to the action of the choke 38, and the valve body is separated from the valve seat 40, so that the oil inlet 30 and the tank connection port 31 are opened. And the oil at the oil inlet 30 flows to the tank connection port 31. When this flow occurs, the pressures in the oil chamber Z (oil inlet 30) and the oil chamber Y (W) further decrease, and the pressure in the oil chamber X (that is, the pressure on the circuit connection port 41 side) decreases. The check valve 23 is closed at the point of time when the pressure becomes higher than the pressure on the circuit side, and the pressure on the circuit side is maintained.

At the same time, the equilibrium state of the pressures acting on the end faces of the plungers 43 in the oil chambers X and W is broken, and a rightward thrust acts on the plungers 43 as shown in the drawing, so that the plungers 43 are further spring-loaded. Pushing the poppet 33 against the force of 34 causes the poppet 33 to be further separated from the valve seat. As a result, the pressure in the Y chamber further decreases, and at the same time, the piston 36 has its valve body largely separated from the seat 40,
The valve body opens largely with respect to the valve seat 40. As a result, the oil discharged from the large-capacity pump 3a can be transferred to the oil tank
The large-capacity pump 3a is returned to the unloaded state (no-load operation).

The unloading state is in the oil chamber X
The pressure on the circuit side (pressure on the circuit connection port 41 and the pilot pressure introduction port 42A side) acting on the main switching valve 11A is neutralized from the pressurized state of the hydraulic cylinder 15 in the present embodiment, for example. Continue until the cut-in pressure is reached, such as when returning. Note that the seat area of the poppet 33, the cross-sectional area of the plunger 43, and the like 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 43 is pushed back in the left direction in the figure by the compressive force of the spring 34 of the pilot valve 32, and the poppet 33 of the pilot valve 32 also sits down, and the oil chamber Y , Z
Are equalized by the choke 38. The piston 36 has its valve body seated on the valve seat 40 by the action of the spring 37 and the check valve 23 is opened to automatically return to the state shown in FIG. 7, and the large-capacity hydraulic pump discharges oil. The oil is supplied from the inflow port 30 to the circuit connection port 41 side, and pressure oil is discharged from the large capacity hydraulic pump 3a at a pressure equal to or lower than the set pressure (cutout pressure) of the hydraulic pilot type unload relief valve 21.

As described above, the hydraulic pilot type unload relief valve 21 is provided with the unload plunger 43 for pushing down the poppet 33, so that the cut-out pressure of the set pressure of the unload relief valve 21 (in this embodiment, For example, when the pressure reaches 17.5 MPa, the valve body of the piston 36 is largely separated from the valve seat 40, and the oil inlet 30 is greatly opened to the tank connection port 31 so that the large capacity hydraulic pump 3a
3, the large capacity pump 3a is automatically unloaded without the necessity of electrically configuring a no-load circuit of the control valve using the electromagnetic switching valve 16b as in the embodiment of FIG. State. As described above, the no-load circuit of the hydraulic pilot type unload relief valve 21 is automatically configured at the set pressure (cutout pressure).

During the unloading operation of the large capacity pump 3a by the hydraulic pilot type unload relief valve 21, there is almost no resistance of the large capacity pump discharge oil to the oil tank 1, and the relief valve of the balanced piston type is released. Since the pressurized oil does not receive the throttle resistance and is returned from the valve body to the tank as in the case of the operation, the heat generated by the oil is only the resistance of the pipe, and the oil temperature rise is extremely small.

Thus, also in the hydraulic control circuit of the second embodiment, the bucket 52 performs a dust-gripping operation based on a change in pump discharge pressure similar to the graph shown in FIG. That is, during the operation of grasping dust by closing the bucket or unloading the dust by opening the bucket, the hydraulic pressure of the discharge oil of the large-capacity and small-capacity pumps is controlled by the hydraulic pilot type unload relief valve 21 which is the respective pressure control valve. When the set pressure (set value) of the balance piston type relief valve 17 has been reached, the unloading of the large capacity pump 3a is automatically started by the action of the unloading relief valve 21. The small-volume pump 3b is operated for a predetermined time T with the relief operation of the balance piston type relief valve 17,
When the bucket is closed, pressurization of the head side chamber (closed side chamber) 15a of the hydraulic cylinder 15 is continued, and when the bucket is opened, pressurization of the rod side chamber 15b of the hydraulic cylinder 15 is continued.

When the main switching valve 11A is set to the neutral state and idle circulation is started before the pursuing operation after the pressurizing time T is completed, the hydraulic pilot type unload relief valve 21 is moved to the check valve 23. Thereafter, the pressure of the discharge pipe 5 decreases, reaches the cut-in pressure, and returns to the pressure control state at or below the set pressure.

As described above, also in the circuit of the second embodiment,
Hydraulic cylinder 1 at the set pressure at their pressure control valves 21, 17 by large capacity pump 3a and small capacity pump 3b
At the time of pressurizing 5, the large-capacity pump 3a is unloaded, so that the heat generation of the oil and the rise in the oil temperature can be suppressed accordingly.

In the above embodiment, the unloading operation of the large-capacity pump 3a by the unload relief valve 21 of the large-capacity pump 3a is performed when closing the bucket (when grasping dust) and when opening the bucket (unloading the dust). ), But this may be performed only when the bucket is closed.

Further, in the above embodiment, two hydraulic pumps, that is, a large-capacity hydraulic pump 3a and a small-capacity hydraulic pump 3b, have been described. For example, when the three hydraulic pumps are used, the pressure control valves of the large-capacity hydraulic pump and the medium-capacity hydraulic pump may constitute a no-load circuit. The large-capacity hydraulic pump and the medium-capacity hydraulic pump are unloaded during operation at the set pressure of the pressure control valve, which can constitute these no-load circuits when the bucket is closed and / or when the bucket is opened. The configuration may be such that the hydraulic cylinder 15 is pressurized only by the hydraulic pump.

In the above embodiment, the case where the hydraulic pump unit PN is hermetically enclosed by the panel PNP has been described. However, the present invention is applicable even if the hydraulic pump unit PN is open to the atmosphere. It is possible.

In the above embodiment, the case where the hydraulic grab bucket is an electro-hydraulic grab bucket in which the prime mover for driving the hydraulic pump is an electric motor has been described. However, the present invention relates to a case where the prime mover is a diesel engine or a gasoline engine. The present invention can be applied to a case where the engine is an engine hydraulic grab bucket.

Further, in the above embodiment, the bucket type shown in FIGS. 1 and 2 has been described. However, the present invention is not limited to this, and may be applied to a hydraulic grab bucket having any type of bucket. Can be.

Further, in the above embodiment, the garbage such as municipal garbage is described as the load (grabbed object). However, the present invention is not limited to this, and the ash, powder, granulated ash, sludge, etc. It can be applied to various grips.

[0081]

As is apparent from the above description, the present invention has the following advantages because it is configured as described in the claims.

According to the first aspect of the present invention, during operation of the pressure control valve such as the relief valve of the large-capacity side pump at the set pressure, the pressure control valve forms a no-load circuit to provide a large discharge amount. Since the side pump is unloaded and the hydraulic cylinder for opening and closing the bucket can be pressurized only by the small-capacity pump after the unloading starts, the oil temperature rise can be largely suppressed by unloading the large-capacity pump. When the prime mover for driving the hydraulic pump is an electric motor, excessive temperature rise and power consumption can be greatly suppressed. Further, when the prime mover is an engine such as a diesel engine, the fuel consumption can be suppressed.

Therefore, even if the hydraulic pump unit, that is, the hydraulic control circuit has a closed structure, or if the hydraulic grab bucket performs a catching operation, Continuous operation of the hydraulic control circuit becomes possible, and continuous operation of the hydraulic grab bucket becomes possible.

According to the second aspect of the present invention, the pressure control valve for the large-capacity side pump is a solenoid valve type relief valve comprising a balance piston type relief valve and an electromagnetic switching valve connected to the vent connection port of the balance piston type relief valve. Since the load relief valve is used, the unloading start time and unloading end time of the large-capacity side pump are determined during the operation of the relief valve as the pressure control valve of the large-capacity side pump at the set pressure, that is, during the relief operation. By changing the timing at which the switching valve is excited or the excitation is released, the unload time of the large-capacity pump can be changed according to the operating conditions, and the suppression of the temperature rise of the hydraulic oil can be adjusted. .

According to the third aspect of the present invention, since the pressure control valve for the large-capacity side pump is a hydraulic pilot type unload relief valve, a no-load circuit is automatically formed at the set pressure (cutout pressure). Since the large capacity pump can be automatically unloaded, the operation is simplified, and the no-load circuit of the pressure control valve is formed not by electrical control but by hydraulic control by the pressure control valve itself. High control reliability. In addition, an electric circuit for forming the no-load circuit, such as an electromagnetic switching valve, is not required, and the equipment is simplified.

[Brief description of the drawings]

FIG. 1 is a front view of an embodiment of an electro-hydraulic grab bucket as a 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 the electrohydraulic grab bucket.

4 is a longitudinal sectional view showing a structure of an electromagnetic unload relief valve which is a pressure control valve applied to the hydraulic control circuit of FIG.

FIG. 5 is a graph showing a pressure change state of the discharge oil of the hydraulic pump during a load grasping operation by closing the bucket and an unloading operation by opening the bucket based on the hydraulic control circuit configuration of FIG. 3;

FIG. 6 is a second embodiment of the hydraulic control circuit applied to the electrohydraulic grab bucket.

7 is a longitudinal sectional view showing a structure of a hydraulic pilot type unload relief valve which is a pressure control valve applied to the hydraulic control circuit of FIG.

FIG. 8 is a conventional hydraulic control circuit applied to an electro-hydraulic grab bucket.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Oil tank 3 Hydraulic pump 3a Large capacity pump 3b Small capacity pump 4 Electric motor 5 Large capacity pump oil discharge pipe 6 Relief valve 7 Small capacity pump oil discharge pipe 10 Tank line 11 Electromagnetic pilot switching valve 11a Main switching valve 11b Pilot switching valve 15 Hydraulic cylinder 16 Solenoid valve type unload relief valve (pressure control valve) 16a Balanced piston type relief valve 16b Solenoid switching valve 17 Balanced piston type relief valve (pressure control valve for small capacity pump) 18, 20 Check valve (check valve) 21 Hydraulic Pilot Type Unload Relief Valve 23 Check Valve (Check Valve) PN Hydraulic Pump Unit 50 Electric Hydraulic Grab Bucket 51 Girder 52 Bucket

Continued on the front page (72) Inventor Kazumi Miura 9-80 Mikawakita-cho, Fukushima City, Fukushima Prefecture Inside Fukushima Mfg. Co., Ltd.

Claims (3)

[Claims] 1. A hydraulic cylinder for opening and closing a bucket, a hydraulic pump for driving the hydraulic cylinder, and a hydraulic oil connected to a discharge pipe of the hydraulic pump for switching and supplying pressure oil to a head side chamber and a rod side chamber of the hydraulic cylinder to operate the hydraulic cylinder. In a hydraulic control circuit of a hydraulic grab bucket provided with an electromagnetic switching valve for switching the direction, and a pressure adjusting valve connected to a discharge pipe of the hydraulic pump and setting a hydraulic cylinder operating pressure, the hydraulic pump is connected to at least the large capacity side. A plurality of hydraulic pumps each composed of two small-capacity pumps, wherein a discharge pipe of the small-capacity pump is connected to a discharge pipe of the large-capacity pump at a point downstream of the check valve; A pressure control valve is attached to each of the discharge pipe of the side pump and the discharge pipe of the small capacity side pump. By unloading the large-capacity pump while the pressure control valve for the large-capacity pump is operating at the set pressure when the unit is closed and / or opened, the hydraulic cylinder is applied only by the small-capacity pump. A hydraulic control circuit for a hydraulic grab bucket, characterized in that it is configured to press. 2. The pressure control valve for the small capacity side pump is a balance piston type relief valve, and the pressure control valve for the large capacity side pump is a vent connection between the balance piston type relief valve and the balance piston type relief valve. 2. The hydraulic control circuit for a hydraulic grab bucket according to claim 1, wherein the hydraulic control circuit is an electromagnetic valve type unload relief valve including an electromagnetic switching valve connected to a port. 3. The pressure control valve for the small capacity side pump is a balance piston type relief valve, and the pressure control valve for the large capacity side pump is a hydraulic pilot type unload relief valve. The hydraulic control circuit for a hydraulic grab bucket according to claim 1.