JP2016133206A - Hydraulic circuit for construction machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydraulic circuit for a construction machine capable of assuring a requisite amount of pump oil for all three components of a boom, a bucket and an arm when these three components are operated simultaneously as a triple complex operation and further not producing any troubles such as poor matching in operations as well as energy loss caused by a metering action.SOLUTION: At a hydraulic circuit of triple circuit/triple pump system, a downstream side in a third circuit C is provided with a merging flow valve device D for controlling a flow of the third pump oil discharged out of a third pump 15. The merging flow valve device D is constituted by a confluence valve 22 and a confluence change-over valve 23. When a boom/bucket/arm combined operation is carried out in which the boom, bucket and arm are simultaneously operated, oil of a first pump 13 is supplied to a bucket cylinder 8, oil of a second pump 14 is supplied to an arm cylinder 7 and oil of the third pump is supplied to a boom cylinder 6 through a breed-off passage of a control valve 21 for a turning operation and the merging flow valve device, respectively, in a preferential manner.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a hydraulic circuit of a construction machine such as a hydraulic excavator employing a three-circuit / three-pump system.

  The background art will be described using a hydraulic excavator as an example.

  As shown in FIG. 4, the hydraulic excavator includes a crawler-type lower traveling body 1, an upper revolving body 2 mounted on the lower traveling body 1 so as to be rotatable about an axis X perpendicular to the ground, A front attachment 9 attached to the upper swing body 2 is provided.

  The front attachment 9 includes a boom 3 that moves up and down, an arm 4 that is pivotally attached to the tip of the boom 3, a work device 5 that is pivotally attached to the tip of the arm 4, and driving thereof. The boom, arm, and work device cylinders 6, 7, and 8 are used as a source.

  In addition, although the bucket as shown in figure is normally used as the working device 5, other working devices, such as a breaker, may be used. Hereinafter, in the case of a bucket, the working device cylinder 8 is referred to as a “bucket cylinder”.

  Further, as other hydraulic actuators, left and right traveling motors that drive the lower traveling body 1 (left and right crawlers) and a turning motor that turns the upper rotating body 2 (all not shown) are provided.

In this hydraulic excavator, as shown in Patent Documents 1 and 2, the entire hydraulic circuit is
i a first circuit to which one of the left and right side travel motors and the boom and bucket cylinders belong;
ii a second circuit to which the other travel motor and arm cylinder belong;
It is well known that a three-circuit / three-pump system is used in which the three circuits are basically driven by separate pumps (first to third pumps).

  In this known technique, a merging valve (speed increasing valve) is provided upstream of the third circuit for the purpose of promptly performing a boom raising operation during boom raising / turning combined operation in which the boom raising and turning are performed simultaneously. When the boom raising / turning combined operation is performed, the third pump oil discharged from the third pump is supplied to the boom cylinder in parallel with the turning motor by switching the joining valve from the neutral position to the joining position (first pump oil). To join).

  In addition, in the boom / arm combined operation in which the boom and the arm are operated simultaneously, the third pump oil supply destination is switched from the boom cylinder to the arm cylinder so that a favorable horizontal pull-in operation can be obtained with priority on the arm operation. Has been taken.

JP 2014-126103 A Japanese Patent Laid-Open No. 10-88627

  According to the configuration of the known technology, the above-described arm priority circuit configuration is used for a boom / bucket / arm combined operation in which the boom, bucket, and arm are operated simultaneously (hereinafter referred to as “three-component combined operation”). Three pump oils merge into the arm cylinder, and only the first pump oil is supplied to both the boom and bucket cylinders.

  However, in this case, most of the first pump oil flows into the lightly loaded bucket cylinder, and the amount of oil and pressure necessary for raising the boom cannot be obtained, so the boom does not rise.

  As a countermeasure against this point, in the known technology, a throttle is provided in a circuit that supplies pressure oil to the bucket cylinder, thereby increasing the flow rate and pressure of the first pump oil to the boom cylinder to ensure the boom raising operation. .

  However, there is a negative effect that energy loss occurs due to an increase in pressure caused by the throttle, and fuel consumption deteriorates.

  The arm cylinder receives a large amount of oil from both the second and third pumps and moves at a high speed. On the other hand, the boom and bucket cylinders to which only the first pump oil is supplied deteriorates, resulting in a speed difference between the three. This causes a problem that the operation cannot be matched.

  Therefore, the present invention can secure a necessary amount of pump oil in any of the boom, bucket, and arm cylinders during a three-way compound operation, and does not cause the adverse effects of energy loss due to throttling and malfunctions in operation matching. Is to provide.

  As means for solving the above-mentioned problems, in the present invention, a lower traveling body, an upper revolving body that is rotatably mounted on the lower traveling body and is driven to rotate by a revolving motor, and a front mounted on the upper revolving body. The front attachment is attached to the tip of a boom that is raised and lowered by a boom cylinder, and an arm that is pushed and pulled by an arm cylinder is rotatably attached. The front attachment is operated by a work device cylinder. The working device is pivotally mounted, and the hydraulic actuator circuit includes a first circuit to which the boom cylinder, the working device cylinder, and either the left or right travel motor belong, and the arm cylinder and the left or right travel. The second circuit to which the motor belongs and the swing motor to which the motor belongs 3 circuits, each of the first to third circuits has a control valve for controlling the operation of each hydraulic actuator, and a first pump as a hydraulic source of the first circuit, and the second circuit Valve for controlling the flow of the third pump oil discharged from the third pump in the hydraulic circuit of the construction machine having the second pump as the hydraulic source of the engine and the third pump as the hydraulic source of the third circuit A boom / bucket / arm combined operation in which the boom, bucket, and arm are operated simultaneously, the first pump oil to the bucket cylinder, the second pump oil to the arm cylinder, and the third pump oil. Is preferentially supplied to the boom cylinder through the bleed-off passage of the turning control valve and the merging valve device.

  Thus, during the boom / bucket / arm combined operation (three-party combined operation), the first pump oil is preferentially supplied to the bucket cylinder and the second pump oil is supplied to the arm cylinder, while the third pump oil is supplied. Is preferentially supplied to the boom cylinder, so that the normal driving of the boom during the three-way composite operation can be realized by a configuration without an aperture.

  For this reason, energy loss due to throttling is eliminated, speed differences due to unmatched supply flow rates of the boom, bucket, and arm cylinders can be eliminated, and operations can be matched during three-way composite operation.

  In this case, although the first pump communicates with the boom cylinder, in practice, the first pump oil is supplied exclusively to the bucket cylinder having a small load and does not flow into the boom cylinder. That is, as a matter of fact, it is preferentially supplied to the bucket cylinder.

  On the other hand, according to the present invention, since the merging valve device performs the speed increasing valve function, it is not necessary to add an independent speed increasing valve to the valve block, and there is no possibility of increasing the size and cost of the valve block.

  In the present invention, the merging valve device is preferably configured to supply the third pump oil to the arm cylinder through a bleed-off passage of the turning control valve when the boom and arm are combined. Item 2).

  By doing so, the third pump oil is joined only to the arm cylinder with priority on the arm during the boom / arm combined operation, which is advantageous particularly in the horizontal pull-in operation.

  Further, in the present invention, the merging valve device supplies the third pump oil to the boom cylinder through the bleed-off passage of the turning control valve during the boom raising single operation for performing only the boom raising operation. It is desirable that the third pump oil be returned to the tank through the bleed-off passage of the turning control valve when the boom lowering operation is performed alone.

  According to this configuration, the third pump oil is allowed to join the boom at the time of the boom raising single operation, so that a quick boom raising operation can be ensured. Thereby, the cycle time at the time of the operation | work which requires the boom operation | movement at high speed like the time of deep digging work can be shortened, and work efficiency can be improved.

  On the other hand, since the third pump oil is not merged with the boom cylinder during the boom lowering operation alone, it is possible to prevent the inconvenience that the boom lowering operation speeds up unnecessarily.

  In the present invention, the merging valve device includes a merging valve provided on the downstream side of the turning control valve, and a merging switching valve provided further downstream of the merging valve. The control valve is switched between a first position, which is a neutral position where the bleed-off passage is connected to the tank, and a second position, where the bleed-off passage is connected to the merging switching valve. It is configured to switch between a first position where the third pump oil that has passed through the merge valve at the second position of the merge valve is supplied to the boom cylinder and a second position where it is supplied to the arm cylinder. Desirable (claims 4 and 5).

  According to this configuration, since the merging valve device is composed of two valves, the merging valve and the merging switching valve, the merging valve device is configured as a single valve, and compared with the case of switching between a large number of positions, the valve configuration, circuit Configuration and control are simplified.

  In this case, the merging valve and the merging switching valve are each configured as a hydraulic pilot switching valve that is switched and operated by a pilot pressure, and the merging valve has a pilot pressure generated by either a boom raising operation or an arm operation. The switching is switched to the second position, and the merging switching valve is switched to the second position by the pilot pressure generated by the arm operation, while returning to the first position by the pilot pressure generated by the boom / arm combined operation. It is desirable to constitute (claim 5).

  According to this configuration, since the merging valve and the merging switching valve are switched using the pilot pressure generated by the actuator operation, for example, the boom raising operation or the arm operation is detected by the sensor, and based on this, the merging valve is detected by the controller. Compared with the case where the switching control is performed on the merging switching valve, the control configuration is simple and the cost is low, and the control reliability is high.

  Further, in the present invention, both the first and second circuits are connected to the first and second pumps with the traveling control valve as the most upstream side, and the merging valve device is configured to simultaneously perform the traveling operation and other actuator operations. It is desirable that the third pump oil is supplied to the other actuator during the combined traveling / other actuator operation.

  By so doing, it is possible to ensure a straight traveling function and actuator operation other than traveling during combined traveling / other actuator operations. Further, since the merging valve device also serves as a straight valve, the valve configuration is simplified.

  According to the present invention, a required amount of pump oil can be secured in any of the boom, bucket, and arm cylinders during the three-way combined operation, and there is no adverse effect such as energy loss due to throttling and poor matching of operation.

1 is a hydraulic circuit diagram showing an embodiment of the present invention. FIG. 2 is a partially enlarged view of FIG. 1. It is a matrix figure which shows the position of the confluence | merging valve and the confluence | merging switching valve with respect to each operation in embodiment, and the condition of the 3rd pump oil. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic side view of a hydraulic excavator that is one of application targets of the present invention.

  In the hydraulic circuit according to the embodiment, as shown in FIG. 1, as the hydraulic actuator circuit, the first circuit A to which the left traveling motor 10, the boom cylinder 6 and the bucket cylinder 8 belong, and the right traveling motor 11 and the arm cylinder 7 belong. A second circuit B and a third circuit C to which only the swing motor 12 belongs, a first pump 13 as a hydraulic source of the first circuit A, and a second pump 14 as a hydraulic source of the second circuit B, A third pump 15 is provided as a hydraulic pressure source of the third circuit C.

  Each circuit A, B, C is provided with a control valve (direction switching valve) that is a hydraulic pilot type spool valve that controls the actuator operation by operating the stroke by operating a remote control valve (not shown) for each hydraulic actuator. Yes.

  That is, the first circuit A includes control valves 16, 17, 18 for the boom cylinder, bucket cylinder, and left travel motor, and the second circuit B includes both control valves 19 for the arm cylinder and right travel motor. , 20 and the third circuit C are respectively provided with control valves 21 for the turning motor.

  For simplification of the drawing, illustration of elements and portions not directly related to the present invention such as relief valves provided in each pump line in FIG. 1 is omitted.

  In the actual machine, a spare actuator and its control valve are provided in the second circuit B, and a dozer cylinder and its control valve are provided in the third circuit, respectively, but they are not shown here.

  On the downstream side of the third circuit C, a merging valve device D that controls the flow of the third pump oil discharged from the third pump 15 is provided.

  The merging valve device D includes a merging valve 22 provided on the downstream side of the turning control valve 21 and a merging switching valve 23 provided further on the downstream side of the merging valve 22.

  The merging valve 22 and the merging switching valve 23 and their related configurations will be described in detail with reference to FIG. In addition, the code | symbol of the pilot port of the junction valve 22 and the junction switching valve 23 is attached | subjected only to FIG.

Junction Valve 22 and Related Configurations Junction valve 22 includes first and second pilot ports 22a and 22b on the opposite side of the spring chamber, and a neutral first valve is shut off / introduced to both pilot ports 22a and 22b. It is configured as a three-position hydraulic pilot switching valve that switches between the first position b, the second position b, and the third position c.

  That is, when pilot pressure is not introduced into either of the pilot ports 22a and 22b, the neutral position is set to the first position A, and when pilot pressure is introduced to the first pilot port 22a, the second position is reduced. When the pilot pressure is introduced into the second pilot port 22b, the position is switched to the third position c.

  The first pilot port 22a of the merging valve 22 is connected via a shuttle valve 24 to a boom raising pilot line 25 into which a boom raising pilot pressure is introduced, and an arm operating pilot pressure line 26 in which a pilot pressure is established when the arm is pushed / pulled. Connected, the merging valve 22 is switched to the second position B when the boom is raised or the arm is pushed / pulled.

  On the other hand, the second pilot port 22b is connected to a pilot primary pressure line 27 leading to a pilot hydraulic pressure source (not shown), and the merging valve 22 is switched to the third position C when the pilot primary pressure is introduced into the second pilot port 22b.

  Here, the first and second pilot lines 28 and 29 are connected to the pilot primary pressure line 27.

  The first pilot line 28 passes through the pilot pressure passages (passages closed during traveling operation) of the right and left traveling control valves 20 and 18 in series, and the second pilot line 29 is the pilot pressure passage of the bucket control valve 17. Each is connected to a tank T.

  Further, a branch pilot line 30 that branches from the upstream side of the traveling control valves 20 and 18 in the first pilot line 28 and a branch pilot line 31 that branches from the downstream side of the traveling control valves 20 and 18 are provided. The branched pilot lines 30 and 31 are connected to the tank T through the pilot pressure passages of the boom and bucket control valves 16 and 17 in series.

  Thus, the pilot primary pressure is introduced into the second pilot port 22b and the merging valve 22 is switched to the third position C only when traveling and other actuator operations are performed.

  The merging valve 22 includes both first and second input ports and first to third output ports (both of which are omitted).

  The first input port branches from the third pump line 32 that guides the third pump oil to the turning control valve 21 and passes to the unload passage 33 passing through the turning control valve 21. The second input port is the third pump line. The third pump branch line 34 branched from 32 is connected to each.

  A tank line 35 communicating with the tank T is connected to the first output port, and an input port of the merging switching valve 23 is connected to the second output port.

  The third output port includes a boom / bucket pressure oil supply line 36 that leads the third pump oil to both the boom and bucket control valves 16 and 17, and an arm that leads the third pump oil to the arm control valve 19. A pressure oil supply line 37 is connected.

Junction switching valve 23 and its related configuration The merging switching valve 23 is provided immediately downstream of the merging valve 22, and the third pump oil is supplied to the boom control valve in a state where the merging valve 22 is at the second position B or the third position C. 16 or the arm control valve 19 is switched.

  The merging switching valve 23 includes a first pilot port 23a on the side opposite to the spring chamber and a second pilot port 23b on the spring chamber side, and is neutral on the right side of the figure by blocking / introducing pilot pressure to both the pilot ports 23a and 23b. It is configured as a two-position hydraulic pilot switching valve that switches between a first position a that is a position and a second position b on the left side of the figure.

  That is, the merging switching valve 23 is held at the first position a in a state where the pilot pressure is not introduced into either of the pilot ports 23a and 23b and in a state where the pilot pressure is introduced into the second pilot port 23b. Then, the third pump oil passing through the junction valve 22 is supplied to the boom control valve 16 through the boom junction line 38.

  On the other hand, when the pilot pressure is introduced into the first pilot port 23a, the position is switched to the second position b, and in this state, the third pump oil passing through the merging valve 22 passes through the arm merging line 39 and the arm control valve 19. To be supplied.

  A pilot primary pressure line 27 is connected to the first pilot port 23a of the junction switching valve 23, and the second pilot line 29 is connected to the second pilot port 23b.

  The operation of this hydraulic circuit will be described.

  In the state where there is no actuator operation, as shown in FIGS. 1 and 2, the merging valve 22 and the merging switching valve 23 are both in the neutral first position a, a.

  That is, the merging valve device D as a whole is in the first state in which the pump line 32 of the third pump 15 is connected to the tank T through the bleed-off passage of the turning control valve.

(1) At the time of boom operation -1 At the time of boom independent operation When only the boom raising operation is performed from the state of FIG. 1 (the first state of the merging valve device D), as shown in FIG. While the valve 23 remains at the first position a, the merging valve 22 is introduced with the boom raising pilot pressure and switched to the second position B, and the merging valve device D as a whole enters the second state, and the third pump oil joins the boom. It is supplied only to the boom cylinder 6 through the line 38 and the boom control valve 16.

  Thereby, boom raising operation is performed at high speed.

  On the other hand, during the boom lowering operation alone, as shown in FIG. 3 (II), both the merging valve 22 and the merging switching valve 23 remain at the first position A, and the merging valve device D as a whole is supplied with the third pump oil in the tank. The first state falls to T (denoted as “unload” in FIG. 3). Therefore, the boom merge is not performed.

-2 Boom raising / turning operation When the boom raising operation and the turning operation are performed simultaneously from the state shown in FIG. 1 (first state), the merging valve 22 is moved to the second position as shown in FIG. On the other hand, the merging switching valve 23 remains at the first position a, and the merging valve device D as a whole is in the second state, that is, the third pump oil is supplied to the swing motor 12 and the boom cylinder 6 in tandem as described above. It becomes a state to do.

  In this case, since the turning pressure> the boom holding pressure, the boom is raised / turned in synchronization with the boom holding pressure on the low pressure side.

  During the boom lowering / turning operation, the merging valve 22 remains at the first position A, so that the third pump oil is not supplied (merged) to the boom cylinder 6.

  That is, when the boom is lowered / turned, merging is not performed unlike when the boom is raised / turned, so that the turning pressure does not decrease in synchronization with the boom lowering pressure. For this reason, favorable turning acceleration performance can be ensured.

(2) At the time of boom / arm operation When the arm operation is performed, the arm operation pilot pressure line 26 is shut off by the arm control valve 19 so that the pressure rises, so that the first pilot port 22a of the merging valve 22 is connected via the shuttle valve 24. Then, the pilot pressure is introduced, and the merging valve 22 is switched to the second position B.

  Further, the merging switching valve 23 is also switched to the second position b by introducing the pilot pressure into the first pilot port 23a.

  That is, as shown in FIG. 3 (IV), the merging valve 22 and the merging switching valve 23 are both in the second position b, and the third pump oil is supplied to the arm cylinder 7. That is, the arm merging action is performed.

  This gives priority to the arm during the combined boom / arm operation, and is particularly advantageous in terms of horizontal pull-in operation.

(3) Three-way combined operation When the boom, bucket, and arm are operated at the same time, pilot pressure is generated in the boom raising pilot line 25 or the arm operation pilot pressure line 26, so that the merging valve 22 is moved to the second position. Switch to.

  On the other hand, the merging switching valve 23 is switched to the first position a when the pilot pressure is established in the pilot line 29.

  That is, the entire merging valve device D is in the second state as shown in FIG. 3 (V), and the third pump oil is supplied to the boom cylinder 6 through the bleed-off passage of the turning control valve 21 and the merging valve device D. The

  Thus, the first pump oil is preferentially supplied to the bucket cylinder 8 and the second pump oil is preferentially supplied to the arm cylinder 7, while the third pump oil is preferentially supplied to the boom cylinder 6.

  In this case, the first pump 13 also communicates with the boom cylinder 6, but in practice, the first pump oil is supplied exclusively to the bucket cylinder 8 with a small load and does not flow into the boom cylinder 6. That is, as a matter of fact, it is preferentially supplied to the bucket cylinder.

  In this way, the boom, bucket, and arm cylinders 6, 8, and 7 are driven by separate pumps.

(4) When both traveling operations and other actuator operations are performed If both the left and right traveling control valves 18 and 20 are operated and the other control valves are not operated, the merging valve 22 and the merging switching valve 23 A pilot pressure is not introduced into one pilot port 22a, 23a.

  Further, since both the first and second pilot lines 28 and 29 communicate with the tank T, the pilot primary pressure is not introduced into the second pilot ports 22b and 23b.

  Therefore, both the merging valve 22 and the merging switching valve 23 are held at the first position a.

  When the combined operation of traveling and other actuators is performed from this state, the pilot primary pressure is introduced into the second pilot port 22b of the merging valve 22, and the merging valve 22 is switched to the third position c.

  On the other hand, the merging switching valve 23 is brought to the first position a when the pilot pressure is introduced into the second pilot port 23b.

  That is, as shown in FIG. 3 (VI), the merging valve 22 is in the third position C, the merging switching valve 23 is in the first position a, and the merging valve device D as a whole uses the third pump oil as an actuator other than the travel motor ( The fourth state is to be supplied to the operated actuator).

  Thus, the left traveling motor 10 is driven by the first pump 13, the right traveling motor 11 is driven by the second pump 14, and the other actuators are driven by the third pump 15. That is, the actuator operation other than traveling is ensured during both traveling.

  According to this hydraulic circuit, the following effects can be obtained.

  (i) During the three-way combined operation, the first pump oil is preferentially supplied to the bucket cylinder 8 and the second pump oil is preferentially supplied to the arm cylinder 7, while the third pump oil is preferentially supplied to the boom cylinder 6. Therefore, normal driving of the boom can be realized by a configuration in which no diaphragm is provided.

  For this reason, energy loss due to throttling is eliminated, speed differences due to unmatched supply flow rates of the boom, bucket, and arm cylinders 6, 8, and 7 are eliminated, and operations can be matched during three-way composite operation.

  (ii) During the combined boom / arm operation, the third pump oil is brought into a third state in which the arm is given priority and only the arm cylinder 7 is joined. This is particularly advantageous in the horizontal pull-in operation.

  (iii) Since the third pump oil joins the boom as the second state during the boom raising single operation, a quick boom raising operation can be ensured.

  For this reason, the cycle time at the time of the operation | work which requires the boom operation | movement at high speed like the time of deep digging work can be shortened, and work efficiency can be improved.

  (iv) Since the merging valve device D performs the speed increasing valve function, it is not necessary to add an independent speed increasing valve to the valve block, and there is no possibility of increasing the size and cost of the valve block.

  (v) Since the merging valve device D is constituted by the two valves of the merging valve 22 and the merging switching valve 23, the merging valve device D is configured as a single valve, and compared with the case of switching between a number of positions, Circuit configuration and control are simplified.

  (vi) The merging valve 22 and the merging switching valve 23 are each configured as a hydraulic pilot switching valve that is switched and operated by the pilot pressure, and the merging valve 22 and the merging switching valve 23 are switched using the pilot pressure generated by operating the actuator. Therefore, for example, the configuration for control is simpler and less costly than a configuration in which a boom raising operation or an arm operation is detected by a sensor, and a confluence valve and a confluence switching valve are controlled by a controller based on the sensor. However, it is cheap and the control reliability is high.

  (vii) Since the third pump oil is not merged into the boom cylinder 6 during the boom lowering operation alone, it is possible to prevent the inconvenience that the boom lowering operation speeds up unnecessarily.

  (viii) Since the booms are not joined at the time of the combined boom lowering / turning operation, the turning pressure is lowered in accordance with the boom lowering side where the pressure is low, and the turning acceleration is not deteriorated.

  (ix) Both the first and second circuits A and B are connected to the first and second pumps 13 and 14 with the traveling control valves 18 and 20 on the most upstream side, so that the traveling operation and other actuator operations can be performed simultaneously. Since the third pump oil is supplied to the other actuators during the combined travel / other actuator operation, it is possible to ensure the straight travel function and the actuator operation other than the travel during the combined travel / other actuator operation.

  Further, since the merging valve device D also serves as a straight valve, the valve configuration is simplified.

Other Embodiments In the present invention, when the traveling control valves 18 and 20 mentioned in the above embodiment have a circuit configuration other than the traveling priority circuit arranged on the most upstream side of the first and second circuits A and B, Can also be applied.

  Further, the present invention is not limited to a hydraulic excavator, and can be applied to a crusher, a dismantling machine, or the like that includes a hydraulic excavator as a base and a breaker or an open / close type crusher attached in place of a bucket.

DESCRIPTION OF SYMBOLS 1 Lower traveling body 2 Upper turning body 3 Boom 4 Arm 5 Working device (bucket)
6 Boom cylinder 7 Arm cylinder 8 Work device cylinder (bucket cylinder)
9 Front Attachment A 1st Circuit B 2nd Circuit C 3rd Circuit 10 Left Traveling Motor 11 Right Traveling Motor 12 Turning Motor 13 First Pump 14 Second Pump 15 Third Pump 16 Boom Control Valve 17 Bucket Control Valve 18 Left Control valve for traveling 19 Control valve for arm 20 Control valve for right traveling 21 Control valve for turning D Merge valve device 22 Merge valve constituting the merge valve device 22a, 22b Pilot port of merge valve 23 Merge switch valve 23a, 23b Merge switch Pilot port of valve 25 Pilot line 26 Arm operation pilot pressure line 27 Pilot primary pressure line 28, 29 Pilot line 30, 31 Branch pilot line 32 Pump line of first pump 33 Unload Road 34 pump branch line 35 tank line 36 joins line T tank confluence line 39 arm pressure oil supply line 38 for boom for pressure oil supply line 37 arm bucket

Claims (6)

  A lower traveling body, an upper revolving body that is rotatably mounted on the lower traveling body and is driven to rotate by a revolving motor, and a front attachment attached to the upper revolving body, the front attachment comprising a boom cylinder An arm that is pushed and pulled by an arm cylinder is pivotally attached to the tip of the boom that is raised and lowered by the above, and a work device that is actuated by the work device cylinder is pivotally attached to the tip of this arm. As a hydraulic actuator circuit, the first circuit to which the boom cylinder, the working device cylinder, and the left and right traveling motors belong, the second circuit to which the arm cylinder and the left and right traveling motors belong, and the swing motor belong to A third circuit, wherein each of the first to third circuits is a hydraulic actuator; A control valve for controlling the operation of each eta, and a first pump as a hydraulic source of the first circuit, a second pump as a hydraulic source of the second circuit, and a third circuit In a hydraulic circuit of a construction machine having a third pump as a hydraulic source, a merging valve device for controlling the flow of third pump oil discharged from the third pump is provided, and the boom, bucket, and arm are operated simultaneously. During combined boom / bucket / arm operation, the first pump oil is supplied to the bucket cylinder, the second pump oil is supplied to the arm cylinder, the third pump oil is supplied to the bleed-off passage of the turning control valve, and the merging valve device A hydraulic circuit for a construction machine, wherein the hydraulic circuit is preferentially supplied to the boom cylinder through the hydraulic circuit.   2. The merging valve device is configured to supply the third pump oil to the arm cylinder through a bleed-off passage of the turning control valve during combined operation of the boom and the arm. Hydraulic circuit of construction machinery.   The merging valve device supplies the third pump oil to the boom cylinder through the bleed-off passage of the turning control valve and performs only the boom lowering operation when the boom raising single operation for performing only the boom raising operation is performed. 3. The hydraulic circuit for a construction machine according to claim 1, wherein the third pump oil is returned to the tank through a bleed-off passage of the turning control valve during operation.   The merging valve device includes a merging valve provided on the downstream side of the turning control valve and a merging switching valve provided further on the downstream side of the merging valve. The merging switching valve is operated by switching between a first position that is a neutral position that connects the bleed-off passage to the tank and a second position that connects the bleed-off passage to the merging switching valve. It is configured to switch between a first position where the third pump oil that has passed through the merging valve at the second position is supplied to the boom cylinder and a second position where it is supplied to the arm cylinder. Item 4. The hydraulic circuit for a construction machine according to any one of Items 1 to 3.   The merging valve and the merging switching valve are each configured as a hydraulic pilot switching valve that is switched and operated by a pilot pressure, and the merging valve is a pilot pressure generated by either a boom raising operation or an arm operation. The merging switching valve is configured to switch to the second position with the pilot pressure generated by the arm operation and return to the first position with the pilot pressure generated by the boom / arm combined operation. The hydraulic circuit for a construction machine according to claim 4.   Both the first and second circuits are connected to the first and second pumps with the traveling control valve as the most upstream side, and the merging valve device is configured to travel / other where the traveling operation and other actuator operations are performed simultaneously. The hydraulic circuit for a construction machine according to any one of claims 1 to 5, wherein the third pump oil is supplied to the other actuator during combined actuator operation.

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