JP6860400B2 - Hydraulic control device for construction machinery - Google Patents

Description

The present invention relates to a hydraulic control device for construction machinery such as a hydraulic excavator.

A typical example of a construction machine is a hydraulic excavator, which has a self-propelled lower traveling body, an upper rotating body mounted on the lower traveling body so as to be able to turn, and a front mounted on the front side of the upper turning body so as to be able to move up and down. It is equipped with a device, and the upper swing body is equipped with an engine, a hydraulic pump using the engine as a drive source, and the like.

The front device is used for excavation work, etc., and has a boom rotatably attached to the upper swivel body, an arm rotatably attached to the tip of the boom, and a rotatable arm tip. By the attached bucket, the boom cylinder provided between the upper swing body and the boom, the arm cylinder provided between the boom and the arm, the bucket cylinder provided between the arm and the bucket, and the like. It is configured. Then, the operator who got into the operation chamber provided in the upper swing body operates various operation levers, and the pressure oil is supplied from the hydraulic pump to each cylinder (hydraulic actuator) corresponding to the operation levers, so that the front device Each work element (boom, arm, bucket) is operated.

Generally, in a construction machine such as a hydraulic excavator, hydraulic oil is supplied from a hydraulic pump to a hydraulic actuator via a throttle by a direction switching valve, and the hydraulic actuator is driven to perform a predetermined work. It is the mainstream to use a hydraulic circuit called an open circuit (open) that discharges the water to the hydraulic oil tank. In such an open circuit, it is possible to connect and control a plurality of hydraulic actuators with one hydraulic pump, but there is a drawback that the pressure loss is large because the throttle by the direction switching valve is used.

Therefore, in recent years, the hydraulic oil discharged by the hydraulic pump is directly supplied to the hydraulic actuator, and the hydraulic oil after driving the hydraulic actuator to perform a predetermined work is directly returned to the hydraulic pump without going through the hydraulic oil tank. A construction machine using a hydraulic circuit called a closed circuit (closed) connected to is proposed. Such a closed circuit has an advantage that the pressure loss due to the throttle is small and the energy of the return hydraulic oil from the hydraulic actuator can be regenerated by the hydraulic pump, so that the fuel efficiency is excellent.

In the prior art disclosed in Patent Document 1, a variable displacement hydraulic pump, a hydraulic actuator driven by a pressure oil supply from the hydraulic pump, and two ports of a hydraulic pump discharge port, a suction port, and a hydraulic actuator. A closed circuit connecting the spaces and a logic valve having at least two poppets provided in the closed circuit are provided, and the closed circuit is connected and disconnected by opening and closing these poppets.

In the hydraulically closed circuit configured in this way, when the electromagnetic switching valve provided in the logic valve is in the neutral position, the maximum pressure of the front-rear pressure of each poppet acts on the back surface of the poppet, so that this maximum pressure is obtained. The poppet is pushed down by the force of the spring provided on the back of the poppet, so that the logic valve is in the closed state. When the electromagnetic switching valve is switched from the neutral position to the switching position, the lowest pressure among the front and rear pressures of each poppet acts on the back surface of each poppet, so that the front and rear pressure of each poppet is more than the force of the spring. When it gets bigger, the poppet is pushed up and the logic valve opens. As a result, the hydraulic actuator operates according to the discharge direction and discharge amount of the hydraulic pump.

Japanese Unexamined Patent Publication No. 56-14670

However, in the prior art disclosed in Patent Document 1, when the leakage of hydraulic oil from the hydraulic pump to the tank is promoted due to foreign matter contamination (contamination) or the like, the hydraulic oil flowing out from the hydraulic actuator flows out to the tank via the hydraulic pump. There was a concern that the work equipment would sink against the intention of the operator.

The present invention has been made to solve the above problems, and an object of the present invention is to construct a construction machine capable of suppressing the sinking of a working machine even when the leakage of hydraulic oil from a hydraulic pump to a tank is promoted. The purpose is to provide a hydraulic control device for a machine.

In order to achieve the above object, the present invention typically includes a variable displacement hydraulic pump, a hydraulic actuator driven by a pressure oil supply from the hydraulic pump, a discharge port and a suction port of the hydraulic pump, and the above. A construction in which a closed circuit connecting between two ports of a hydraulic actuator and a logic valve having at least two poppets provided in the closed circuit are provided, and the closed circuit is connected and disconnected by opening and closing the poppet. In the hydraulic control device of the machine, the maximum pressure selection unit that selects the maximum pressure among the front-rear pressures of each poppet, the low-pressure selection unit that selects the lower pressure among the front-rear pressures of each poppet, and the neutral position. An electromagnetic switching valve that guides the maximum pressure selected by the maximum pressure selection unit to the back surface of each poppet, and guides the lower pressure selected by the low pressure selection unit to the back surface of each poppet at the switching position, and the hydraulic pump. A charge pump connected to the discharge port pipeline and the suction port pipeline, a charge boosting sensitive valve that switches from a neutral position to a switching position when the pressure in the suction port pipeline of the hydraulic pump exceeds a threshold, and the charge boosting. A maximum pressure forced introduction circuit having a plurality of switching valves including a sensitive valve is provided, and the maximum pressure forced introduction circuit switches the charge boosting sensitive valve to a neutral position when the electromagnetic switching valve is in the switching position. by,-out guide the maximum pressure selected by the maximum pressure selection unit regardless switching position of the electromagnetic switching valve at the back of each poppet, the highest pressure force introduction circuit, the output port of the low pressure selector A first shuttle valve provided between the back of each poppet, the first input port is connected to the output port of the electromagnetic switching valve, and the output port is connected to the back of the poppet, and the low pressure selection. The output port of the unit is provided between the output port of the unit and the second input port of the first shuttle valve, the second input port is connected to the output port of the low pressure selection unit, and the output port is the first shuttle. It is provided between the second shuttle valve connected to the second input port of the valve and the output port of the maximum pressure selection unit and the tank, and in the neutral position, the output port of the maximum pressure selection unit and the second Load check that connects the first input port of the shuttle valve of the above, shuts off the output port of the maximum pressure selection unit at the switching position, and connects the first input port of the second shuttle valve and the tank. Provided between the function valve, the front and rear ports of each poppet, and the spring-side switching chamber and the opposite-side switching chamber of the load check function valve. In the neutral position, the front port of each poppet is connected to the opposite side switching chamber of the load check function valve, and the rear port of each poppet is connected to the spring side switching chamber of the load check function valve for switching. At the position, the front port of each poppet is connected to the spring side switching chamber of the load check function valve, and the rear port of each poppet is connected to the opposite side switching chamber of the load check function valve. The electromagnetic switching valve is provided with the output port of the maximum pressure selection unit connected to the first input port of the first shuttle valve in the neutral position, and the first shuttle valve of the first shuttle valve in the switching position. The input port of 1 is communicated with the tank, and the directional valve is switched from the neutral position to the switching position when the pressure of the front port of each poppet is higher than the pressure of the rear port. It is provided between the opposite side switching chamber of the direction sensitive valve and the tank, and at the neutral position, the opposite side switching chamber of the direction sensitive valve and the tank are connected, and at the switching position, the opposite side switching chamber of the direction sensitive valve is connected. It is characterized in that and the front port of each poppet are connected.

According to the present invention, even when the leakage of hydraulic oil from the hydraulic pump to the tank is promoted, the sinking of the working machine can be suppressed. Issues, configurations, and effects other than those described above will be clarified by the following description of the embodiments.

It is a side view of the hydraulic excavator to which the hydraulic control device which concerns on embodiment of this invention is applied. It is a hydraulic circuit diagram of the hydraulic control device which concerns on embodiment of this invention.

Hereinafter, a case where the construction machine according to the embodiment of the present invention is applied to a hydraulic excavator provided with a front device for work will be taken as an example, and the hydraulic control device will be described with reference to the drawings. FIG. 1 is a side view of a large hydraulic excavator to which the hydraulic control device according to the embodiment of the present invention is applied. As shown in FIG. 1, the hydraulic excavator 100 includes a lower traveling body 103 provided with crawler-type traveling devices 108a and 108b on both sides in the left-right direction, and an upper rotating body 102 rotatably mounted on the lower traveling body 103. And have. A cab 101 on which the operator is boarded is provided on the upper swivel body 102.

On the front side of the upper swivel body 102, for example, a front work device 104 for performing excavation work or the like is attached so as to be able to move up and down. The front working device 104 includes a boom 105, a pair of left and right boom cylinders (hydraulic actuators) 2a and 2b for driving the boom 105, an arm 106, an arm cylinder 109 for driving the arm 106, a bucket 107, and a bucket 107. It includes a pair of left and right bucket cylinders 110a and 110b to be driven.

The cab 101 is provided with a plurality of operating levers (not shown) for traveling / turning operations and operating the boom 105, the arm 106, and the bucket 107. By operating these operating levers, the hydraulic excavator 100 is driven / turned and excavated.

FIG. 2 is a hydraulic circuit diagram showing the overall configuration of the hydraulic control device according to the embodiment of the present invention. In FIG. 2, 1 is a hydraulic pump, 2a and 2b are boom cylinders driven by the hydraulic pump 1, 3a and 3b are logic valves provided between the hydraulic pump 1 and boom cylinders 2a and 2b, and 4 is a logic valve. It is a flushing valve provided between the pipelines connecting 3a and 3b and the boom cylinders 2a and 2b, and the output port of the flushing valve 4 is connected to the charge pipeline 5.

Reference numeral 6 denotes a charge pump, and the charge pump 6 is connected to both discharge pipes of the hydraulic pump 1 via check valves 7 and 8. 9a is a poppet provided between the conduit 10a and the conduit 11a, 9b is a poppet provided between the conduit 10b and the conduit 11b, and 12a and 12b are springs that push the back surfaces of the poppets 9a and 9b. Reference numeral 15 is an electromagnetic switching valve, 16a is a shuttle valve that selects the higher pressure of the pipelines 10a and 11a, and 16b is a shuttle valve that selects the higher pressure of the pipelines 10b and 11b. These shuttle valves 16a and 16b form a maximum pressure selection section. 17a is a low pressure selection valve that selects the lower pressure among the pressures of the pipelines 10a and 11a, and 17b is a low pressure selection valve that selects the lower pressure among the pressures of the pipelines 10b and 11b.

18a, 18b, 19a, 19b, 20a, 20b are switching valves, the switching valve 18a is switched via the switching valve 19a by the pressure difference of the pipelines 10a, 11a, and when the switching valve 18a is in the C position, the second is The first input port of the shuttle valve 13a and the output port of the maximum pressure selection unit are connected, and when the switching valve 18a is in the D position, the first input port of the second shuttle valve 13a and the tank 21 are connected.

The switching valve 19a is switched via the switching valve 20b by the pressure difference between the pipelines 10b and 11b, and when the switching valve 19a is in the E position, the spring side switching chamber of the switching valve 18a and the conduit 11a are connected and The switching chamber on the opposite side of the switching valve 18a is connected to the pipeline 10a. When the switching valve 19a is in the F position, the spring side switching chamber of the switching valve 18a and the pipeline 10a are connected, and the opposite side switching chamber of the switching valve 18a and the pipeline 11a are connected.

The switching valve 19b is switched via the switching valve 20a by the pressure difference between the pipelines 10a and 11a, and when the switching valve 19b is in the E position, the spring side switching chamber of the switching valve 18b and the conduit 11b are connected and The switching chamber on the opposite side of the switching valve 18b is connected to the pipeline 10b. When the switching valve 19b is in the F position, the spring side switching chamber of the switching valve 18b and the pipeline 10b are connected, and the opposite side switching chamber of the switching valve 18b and the pipeline 11b are connected.

The switching valve 20a is switched by the charge pressure boosted by the hydraulic pump 1 and the charge pump 6, and when the switching valve 20a is in the G position, the switching chamber on the opposite side of the switching valve 19b and the tank 21 are connected, and the switching valve 20a is When in the H position, the switching chamber on the opposite side of the switching valve 19b and the pipeline 10a are connected.

The switching valve 20b is switched by the charge pressure boosted by the hydraulic pump 1 and the charge pump 6, and when the switching valve 20b is in the G position, the switching chamber on the opposite side of the switching valve 19a and the tank 21 are connected, and the switching valve 20b is When in the H position, the switching chamber on the opposite side of the switching valve 19a and the pipeline 10b are connected.

13a is a second shuttle valve that selects the higher pressure of the output port pressure of the low pressure selection valve 17a and the pressure of the output port of the switching valve 18a, and 13b is the pressure of the output port of the low pressure selection valve 17b and the switching valve 18b. The second shuttle valve that selects the higher pressure of the output port pressure of 14a is the pressure of the output port of the electromagnetic switching valve 15 and the pressure of the output port of the second shuttle valve 13a, whichever is higher. The first shuttle valve 14b to be selected is the first shuttle valve that selects the higher pressure of the pressure of the output port of the electromagnetic switching valve 15 and the pressure of the output port of the second shuttle valve 13b.

When the electromagnetic switching valve 15 is in the A position (neutral position), the first input port of the first shuttle valve 14a and the output port of the maximum pressure selection unit are connected, and the electromagnetic switching valve 15 is in the B position (switching). Position), the first input port of the first shuttle valve 14a and the first input port of the first shuttle valve 14b are connected to the tank 21.

Next, the operation of the hydraulic control device configured as described above will be described.

First, the boom lowering operation in a normal state where there is no leakage of hydraulic oil from the hydraulic pump 1 to the tank 21 will be described. Here, during the boom lowering operation, the electromagnetic switching valve 15 is in the switching position B, the charge line 5 is boosted to the charge pressure (for example, 2 MPa) by the charge pump 6, and the switching valve 20b on the right side of the drawing is in the switching position by the charge pressure. Switch to H. As a result, the pressure of the pipeline 11b is guided to the spring-side switching chamber of the switching valve 19a, and the pressure of the pipeline 10b is guided to the switching chamber on the opposite side of the switching valve 19a via the switching valve 20b. At this time, since the pressure (2 MPa) of the pipeline 10b connected to the charge pipeline 5 is lower than the pressure (for example, 17 MPa) of the pipeline 11b connected to the bottom side of the boom cylinders 2a and 2b, the switching valve 19a is neutral. Hold position E.

Next, the pressure of the pipeline 11a is guided to the spring-side switching chamber of the switching valve 18a via the switching valve 19a, and the pressure of the pipeline 10a is guided to the switching chamber on the opposite side of the switching valve 18a via the switching valve 19a. .. At this time, the pressure of the pipe line 10a connected to the discharge port side of the hydraulic pump 1 (for example, 4 MPa) is higher than the pressure of the pipe line 11a connected to the rod side of the boom cylinders 2a and 2b (for example, 2 MPa). The valve 18a switches to the switching position D. As a result, the first input port of the second shuttle valve 13a is connected to the tank 21 via the switching valve 18a, and the second input port of the second shuttle valve 13a is low-pressure selected by the low-pressure selection valve 17a. The pressure of the conduit 11a is guided. At this time, since the pressure in the pipeline 11a is higher than the pressure in the tank 21 (0.5 MPa), the output port of the second shuttle valve 13a selects the pressure in the pipeline 11a (2 MPa).

Next, the first input port of the first shuttle valve 14a is connected to the tank 21 via the electromagnetic switching valve 15, and the second shuttle valve 13a is connected to the second input port of the first shuttle valve 14a. The pressure (2 MPa) of the conduit 11a is guided through the pipe. At this time, since the pressure in the conduit 11a is higher than the pressure in the tank 21, the output port of the first shuttle valve 14a selects the pressure in the conduit 11a. As a result, the pressure of the conduit 11a is guided to the back surface of the poppet 9a, and at this time, the pressure of the conduit 10a (4 MPa) is higher than the pressure of the conduit 11a (2 MPa), so that the poppet 9a is opened.

Similarly, the switching valve 20a on the left side of the drawing switches to the switching position H by the charge pressure. As a result, the pressure of the pipeline 11a is guided to the spring-side switching chamber of the switching valve 19b, and the pressure of the pipeline 10a is guided to the switching chamber on the opposite side of the switching valve 19b via the switching valve 20a. At this time, since the pressure (4 MPa) of the pipeline 10a connected to the discharge port side of the hydraulic pump 1 is higher than the pressure (2 MPa) of the pipeline 11a connected to the rod side of the boom cylinders 2a and 2b, the switching valve 19b Switches to the switching position F.

Next, the pressure of the pipeline 10b is guided to the spring-side switching chamber of the switching valve 18b via the switching valve 19b, and the pressure of the pipeline 11b is guided to the switching chamber on the opposite side of the switching valve 18b via the switching valve 19b. .. At this time, since the pressure (2 MPa) of the pipeline 10b is lower than the pressure (17 MPa) of the pipeline 11b, the switching valve 18b is switched to the switching position D. As a result, the first input port of the second shuttle valve 13b is connected to the tank 21 via the switching valve 18b, and the second input port of the second shuttle valve 13b is low-pressure selected by the low-pressure selection valve 17b. The pressure of the conduit 10b is introduced. At this time, since the pressure in the pipeline 10b is higher than the pressure in the tank 21 (0.5 MPa), the output port of the second shuttle valve 13b selects the pressure in the pipeline 10b (2 MPa).

Next, the first input port of the first shuttle valve 14b is connected to the tank 21 via the electromagnetic switching valve 15, and the second shuttle valve 13b is connected to the second input port of the first shuttle valve 14b. The pressure in the pipeline 10b is guided through the pipe. At this time, since the pressure in the pipeline 10b is higher than the pressure in the tank 21, the output port of the first shuttle valve 14b selects the pressure in the pipeline 10b. As a result, the pressure of the conduit 10b is guided to the back surface of the poppet 9b, and at this time, the pressure of the conduit 10b (2 MPa) is lower than the pressure of the conduit 11b (17 MPa), so that the poppet 9b is opened.

Therefore, the hydraulic oil is supplied from the discharge port side of the hydraulic pump 1 to the rod side of the boom cylinders 2a and 2b via the poppet 9a, and after performing a predetermined work, the hydraulic oil is supplied to the hydraulic pump 1 via the poppet 9b. The return and boom lowering operation can be performed normally.

The above is the description of the operation when the boom is normally lowered. Next, the boom lowering operation when the hydraulic oil leaks from the hydraulic pump 1 via the tank 21 occurs will be described.

When the hydraulic oil leaks from the hydraulic pump 1 to the tank 21 during the boom lowering operation, the charge line 5 is connected to the tank 21 via the hydraulic pump 1, so that the pressure in the charge line 5 is charged. The pressure is lower than the pressure (0.5 MPa). As a result, the switching chamber on the opposite side of the switching valve 20b is connected to the tank 21 via the hydraulic pump 1, and the switching valve 20b is switched to the neutral position G. As a result, the pressure of the pipeline 11b is guided to the spring-side switching chamber of the switching valve 19a, and the opposite-side switching chamber of the switching valve 19a is connected to the tank 21 via the switching valve 20b. At this time, since the pressure of the tank 21 is lower than the pressure of the pipeline 11b (17 MPa), the switching valve 19a holds the neutral position E.

Next, the pressure of the pipeline 11a is guided to the spring-side switching chamber of the switching valve 18a via the switching valve 19a, and the pressure of the pipeline 10a is guided to the switching chamber on the opposite side of the switching valve 18a via the switching valve 19a. .. At this time, the pressure of the pipe line 10a is the tank pressure (0.5 MPa) due to the leakage of hydraulic oil, and the pressure of the pipe line 10a is the pressure of the pipe line 11a connected to the rod side of the boom cylinders 2a and 2b (for example). Since it is lower than 3 MPa), the switching valve 18a switches to the neutral position C. As a result, the pressure of the pipeline 11b selected by the maximum pressure selection unit is guided to the first input port of the second shuttle valve 13a via the switching valve 18a, and the second input of the second shuttle valve 13a is introduced. The low pressure selection valve 17a guides the pressure of the low pressure selected pipeline 10b to the port. At this time, since the pressure (0.5 MPa) of the pipeline 10b is lower than the pressure of the pipeline 11b, the output port of the second shuttle valve 13a selects the pressure (17 MPa) of the pipeline 11b.

Next, the first input port of the first shuttle valve 14a is connected to the tank 21 via the electromagnetic switching valve 15, and the second shuttle valve 13a is connected to the second input port of the first shuttle valve 14a. The pressure in the pipeline 11b is guided through the pipe. At this time, since the pressure in the pipeline 11b is higher than the pressure in the tank 21, the output port of the first shuttle valve 14a selects the pressure in the pipeline 11b. As a result, the pressure of the conduit 11b is guided to the back surface of the poppet 9a, and at this time, the pressure of the conduit 10a (0.5 MPa) is lower than the pressure of the conduit 11b (17 MPa), so that the poppet 9a is closed. To.

Similarly, the switching chamber on the opposite side of the switching valve 20a is connected to the tank 21 via the hydraulic pump 1, and the switching valve 20b switches to the neutral position G. As a result, the pressure of the pipeline 11a is guided to the spring-side switching chamber of the switching valve 19a, and the opposite-side switching chamber of the switching valve 19a is connected to the tank 21 via the switching valve 20a. At this time, since the pressure of the tank 21 is lower than the pressure of the pipeline 11a (3 MPa), the switching valve 19b holds the neutral position E.

Next, the pressure of the pipeline 11b is guided to the spring-side switching chamber of the switching valve 18b via the switching valve 19b, and the pressure of the pipeline 10b is guided to the switching chamber on the opposite side of the switching valve 18b via the switching valve 19b. .. At this time, since the pressure (0.5 MPa) of the pipeline 10b is lower than the pressure (17 MPa) of the pipeline 11b, the switching valve 18b is switched to the neutral position C. As a result, the pressure of the pipeline 11b selected by the maximum pressure selection unit is guided to the first input port of the second shuttle valve 13b via the switching valve 18b, and the second input of the second shuttle valve 13b is introduced. The low pressure selection valve 17b guides the pressure of the low pressure selected pipeline 10b to the port. At this time, since the pressure in the pipeline 10b is lower than the pressure in the pipeline 11b, the output port of the second shuttle valve 13b selects the pressure in the pipeline 11b (17 MPa).

Next, the first input port of the first shuttle valve 14b is connected to the tank 21 via the electromagnetic switching valve 15, and the second shuttle valve 13b is connected to the second input port of the first shuttle valve 14b. The pressure in the pipeline 11b is guided through the pipe. At this time, since the pressure in the pipeline 11b is higher than the pressure in the tank 21, the output port of the first shuttle valve 14b selects the pressure in the pipeline 11b. As a result, the pressure of the conduit 11b is guided to the back surface of the poppet 9b, and at this time, the pressure of the conduit 10b (0.5 MPa) is lower than the pressure of the conduit 11b (17 MPa), so that the poppet 9b is closed. To.

Therefore, even when the leakage of hydraulic oil from the hydraulic pump 1 to the tank 21 is promoted during the boom lowering operation, the hydraulic pump 1 and the boom cylinders 2a and 2b are connected by closing the poppets 9a and 9b. Since the space is cut off, it is possible to prevent the boom from sinking against the intention of the operator.

As described above, in the flood control device according to the embodiment of the present invention, switching valves 18a and 18b having a load check function are provided between the boom cylinders (hydraulic actuators) 2a and 2b and the logic valves 3a and 3b. When the leakage of hydraulic oil from the hydraulic pump 1 to the tank 21 is promoted, the switching valves 20a and 20b, which are charge boost-sensitive valves, are switched to the neutral position G, so that the switching valves 19a, which are direction-sensitive valves, The 19b is held in the neutral position E to connect the spring side switching chambers of the switching valves 18a and 18b to the rear ports of the poppets 9a and 9b, and the opposite side switching chambers of the switching valves 18a and 18b and the poppets 9a and 9b. It is configured to connect to the front port. Even when the leakage of hydraulic oil from the hydraulic pump 1 through the tank 21 is promoted in this way, the switching valves 18a and 18b, which are load check function valves, hold the neutral position C and enter the spring chambers of the poppets 9a and 9b. Since the pressure of the rear port of the poppet is guided, the poppet 9b is closed to close the return circuit of the hydraulic oil from the boom cylinders 2a and 2b even though the electromagnetic switching valve 15 is in the switching position B. This makes it possible to prevent the work equipment from sinking against the intention of the operator.

In the present embodiment, the switching valves 18a and 18b which are load check function valves, the switching valves 19a and 19b which are direction sensitive valves, the switching valves 20a and 20b which are charge boosting sensitive valves, and the first shuttle valve. The maximum pressure forced introduction circuit is composed of 14a and 14b and the second shuttle valves 13a and 13b, and this maximum pressure forced introduction circuit is a charge boost sensitive valve when the electromagnetic switching valve 15 is in the switching position B. By switching the (switching valves 20a and 20b) to the neutral position G, the maximum pressure selected by the maximum pressure selection unit is guided to the back surface of the poppets 9a and 9b regardless of the switching position of the electromagnetic switching valve 15. ..

The above-described embodiments are examples for the purpose of explaining the present invention, and the scope of the present invention is not limited to those embodiments. One of ordinary skill in the art can practice the present invention in various other aspects without departing from the gist of the present invention. For example, in the above-described embodiment, the case where a boom cylinder for driving a boom is used as the hydraulic actuator has been described, but a hydraulic cylinder other than the boom cylinder (for example, arm cylinder 109, bucket cylinders 110a, 110b, etc.), a hydraulic motor, etc. The present invention can also be applied to the hydraulic actuators of the above, and the present invention may be applied to construction machines such as wheel loaders other than the hydraulic excavators.

1 Hydraulic pump 2a, 2b Boom cylinder (hydraulic actuator)
3a, 3b Logic valve 4 Flushing valve 5 Charge line 6 Charge pump 7,8 Check valve 9a, 9b Poppet 10a, 10b, 11a, 11b Line 12a, 12b Spring 13a, 13b Second shuttle valve 14a, 14b First Shuttle valve 15 Electromagnetic switching valve 16a, 16b Shuttle valve (maximum pressure selection part)
17a, 17b Low-voltage selection valve (low-voltage selection unit)
18a, 18b switching valve (load check function valve)
19a, 19b switching valve (direction sensitive valve)
20a, 20b switching valve (charge boost sensitive valve)
21 tank

Claims (1)

A variable displacement hydraulic pump, a hydraulic actuator driven by a pressure oil supply from the hydraulic pump, and a closed circuit connecting between the discharge port and suction port of the hydraulic pump and the two ports of the hydraulic actuator. In a construction machine hydraulic control device that includes a logic valve having at least two poppets provided in the closed circuit and connects and disconnects the closed circuit by opening and closing the poppet.
A maximum pressure selection unit that selects the maximum pressure among the front and rear pressures of each poppet,
A low-pressure selection unit that selects the lower of the front-rear pressures of each poppet,
In the neutral position, the maximum pressure selected by the maximum pressure selection unit is guided to the back surface of each poppet, and in the switching position, the lower pressure selected by the low pressure selection unit is guided to the back surface of each poppet.
A charge pump connected to the discharge port line and the suction port line of the hydraulic pump,
A charge boosting sensitive valve that switches from the neutral position to the switching position when the pressure in the suction port pipeline of the hydraulic pump exceeds the threshold value.
A maximum pressure forced introduction circuit having a plurality of switching valves including the charge boost sensitive valve, and
With
The maximum pressure forced introduction circuit is selected by the maximum pressure selection unit regardless of the switching position of the electromagnetic switching valve by switching the charge boost sensitive valve to the neutral position when the electromagnetic switching valve is in the switching position. -out guide the maximum pressure that the back of each poppet,
The maximum pressure forced introduction circuit is
A first input port provided between the output port of the low pressure selection unit and the back surface of each poppet, the first input port is connected to the output port of the electromagnetic switching valve, and the output port is connected to the back surface of the poppet. 1 shuttle valve and
It is provided between the output port of the low pressure selection unit and the second input port of the first shuttle valve, the second input port is connected to the output port of the low pressure selection unit, and the output port is the first. A second shuttle valve connected to the second input port of one shuttle valve,
It is provided between the output port of the maximum pressure selection unit and the tank, and in the neutral position, the output port of the maximum pressure selection unit and the first input port of the second shuttle valve are connected, and in the switching position, the above. A load check function valve that shuts off the output port of the maximum pressure selection unit and connects the first input port of the second shuttle valve to the tank.
It is provided between the front and rear ports of each poppet and the spring-side switching chamber and the opposite-side switching chamber of the load check function valve, and in the neutral position, the front port of each poppet and the opposite-side switching chamber of the load check function valve. And the rear port of each poppet and the spring side switching chamber of the load check function valve are connected, and at the switching position, the front port of each poppet and the spring side switching chamber of the load check function valve are connected. And a direction-sensitive valve that connects the rear port of each poppet to the opposite side switching chamber of the load check function valve.
Is equipped with
The electromagnetic switching valve connects the output port of the maximum pressure selection unit and the first input port of the first shuttle valve at the neutral position, and the first input port of the first shuttle valve at the switching position. To the tank,
The directional valve is switched from the neutral position to the switching position when the pressure at the front port of each poppet is higher than the pressure at the rear port.
The charge boost-sensitive valve is provided between the opposite-side switching chamber of the direction-sensitive valve and the tank, and is connected to the opposite-side switching chamber of the direction-sensitive valve and the tank in the neutral position, and the direction in the switching position. A hydraulic control device for construction machinery, characterized in that a switching chamber on the opposite side of a sensitive valve is connected to a front port of each poppet.

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