JP2014122654A - Hydraulic circuit of construction machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent generation of rotation shock due to switchover of a confluence valve during boom raising/rotation in a hydraulic circuit of a three circuit-three pump system.SOLUTION: The hydraulic circuit includes a first circuit A to which a boom cylinder 6 belongs; a second circuit B to which an arm cylinder 7 belongs; and a third circuit C to which a rotation motor 12 belongs. The hydraulic circuit also includes first to third pumps 13 to 15 as hydraulic power sources of the circuits A to C, respectively; and a confluence valve 22 for merging third pump oil discharged from the third pump 15 with the first circuit A or second circuit B. At a first position (a) that is a neutral position of this confluence valve 22, the third pump oil is supplied to the boom cylinder 6 in parallel to the rotation motor 12. At this first position (a) of the confluence valve 22, boom raising/rotation operation and only the boom raising operation are performed. During only the rotation operation, the merge is cut off.

Description

  The present invention relates to a hydraulic circuit of a construction machine that employs a three-circuit / three-pump system.

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

  As shown in FIG. 3, the excavator is mounted on a crawler type lower traveling body 1 so that an upper swing body 2 can swing around an axis X that is perpendicular to the ground. 3, an arm 4, a bucket 5, and a front attachment 9 including cylinders 6, 7, and 8 for booms, arms, and buckets that operate these are mounted.

  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 Document 1, in order to ensure the independence of the turning operation and other actuator operations, the entire circuit is
a first circuit to which one of the left and right side travel motors and the boom cylinder belong;
ii a second circuit to which the other travel motor and arm cylinder belong;
It is well known to use a three-circuit / three-pump system in which the three circuits are basically driven by separate pumps (first to third pumps).

  In this known technique, a merging valve is provided on the upstream side of the third circuit for the purpose of promptly performing a boom raising operation during a boom raising / turning operation in which the boom raising and turning are performed simultaneously.

  The merging valve has a neutral first position and a second position, and is switched from the first position to the second position when the boom is raised / turned, and at this second position, the third pump discharged from the third pump. Pump oil is supplied to the boom cylinder in parallel with the swing motor (joins with the first pump oil).

Japanese Patent No. 3681833

  However, a time lag occurs due to a response delay of the merging valve between the boom raising / turning operation point and the merging valve switching point from the first position to the second position.

  When this is viewed from the swing motor, the state in which the third pump oil is supplied alone changes to a state in which it is supplied in parallel to the boom cylinder, and the maximum pressure (swing pressure) of the swing motor suddenly changes from the relief pressure to the boom operating pressure. For this reason, a turning shock occurs, and the operability is poor.

  Accordingly, the present invention provides a hydraulic circuit for a construction machine that can prevent the occurrence of a swing shock due to switching of a merging valve during boom raising / turning.

  As means for solving the above problems, the present invention has all the following requirements (A) to (G).

  (A) It has 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.

  (B) This front attachment has a boom operated by a boom cylinder and an arm operated by an arm cylinder.

  (C) The hydraulic actuator circuit includes a first circuit to which the boom cylinder belongs, a second circuit to which the arm cylinder belongs, and a third circuit to which the swing motor belongs, and each circuit controls operation for each hydraulic actuator. To have control valves for boom, arm, and swivel.

  (D) having 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 pump as a hydraulic source of the third circuit.

  (E) having a merging valve for sending the third pump oil discharged from the third pump to the first circuit and joining the oil from the first pump;

  (F) The merging valve has a neutral first position and a second position. In the first position, the third pump oil is merged with the first circuit, and the merging valve is merged with the second position. Configured to block.

  (G) The merging valve is configured to be held at the first position during a boom raising / turning operation in which a boom raising operation and a turning operation are performed simultaneously and in a boom raising single operation in which only a boom raising operation is performed.

  (H) The merging valve is configured to be switched to the second position at the time of a single turn operation in which only a turn operation is performed.

  According to this configuration, the third pump oil can be merged with the first circuit (boom cylinder) at the neutral position (first position) of the merging valve, and the boom can be raised / turned at this first position. Thus, when the boom is raised / turned, the switching of the merging valve (merge) is delayed, so that the turning pressure suddenly changes, that is, the turning shock does not occur.

  Further, the boom raising operation is performed at a high speed by performing the merging action with respect to the boom cylinder even during the boom raising single operation.

  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.

  In addition, since the merging valve 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 addition, the switching valve is switched to the second position at the time of the single swing operation, and the third pump oil falls into the tank through the boom control valve in the neutral position in order to block the merge of the third pump oil to the boom cylinder. The situation can be prevented and the turning motion can be secured.

  In the present invention, the control valve and the merging valve are each configured as a hydraulic pilot switching valve that is switched and operated by the pilot pressure, and the boom raising pilot pressure applied to the boom control valve is guided to the pilot port of the merging valve. It is desirable that the merging valve is configured to be held in the first position (claim 2).

  According to this configuration, the boom raising pilot pressure is used to hold the merging valve at the first position. For example, the boom raising operation is detected by the sensor, and based on this, the merging valve is held at the first position by the controller. Compared to the configuration, the configuration for control is simple and the cost is low, and the reliability of the control is high.

  Further, in the configuration of claim 1 or 2, the control valve and the merging valve are each configured as a hydraulic pilot switching valve that is switched and operated by a pilot pressure, and based on the switching to the swing position of the swing control valve during the swing operation. Preferably, the pilot port of the merging valve is configured to introduce a pilot pressure in a direction for switching the merging valve to the second position.

  According to this configuration, the switching of the merging valve to the second position at the time of the single turning operation can be reliably performed in conjunction with the turning operation by the pilot pressure.

  On the other hand, on the premise of the configuration according to any one of claims 1 to 3, the third pump oil is joined to the head side of the arm cylinder of the second circuit at the second position of the junction valve, and the boom is raised. It is desirable that the merging valve is switched to the second position during the boom raising / arm pulling operation in which the operation and the arm pulling operation are performed simultaneously (claims 4 and 5).

  According to this configuration, when the boom is raised and the arm is pulled, that is, when the horizontal is pulled, the third pump oil is joined to the arm cylinder, so that the arm is prioritized and horizontal pulling is facilitated.

  In this case, the control valve and the merging valve are each configured as a hydraulic pilot switching valve that is switched and operated by the pilot pressure, and the boom raising pilot pressure applied to the boom control valve is guided to the spring chamber of the merging valve, The merging valve is configured to be held at the first position, and at the time of the boom raising / arm pulling operation, the arm pulling pilot pressure is canceled, the boom raising pilot pressure is canceled, and the merging valve is switched to the second position. It is desirable to make it act as a force for this purpose (claim 5).

  As described above, by adopting a configuration in which the boom raising pilot pressure is canceled by the arm pulling pilot pressure, control using a control means such as a controller becomes unnecessary, and the configuration becomes simple.

  In the present invention, it is desirable that the merging valve is switched to the second position during the boom lowering operation.

  According to this configuration, the boom lowering operation does not merge and the boom lowering is not accelerated, so that it can be operated with the same feeling and movement as usual without any sense of incongruity. Further, there is no possibility that the turning performance is lowered in synchronism with the low pressure of lowering the boom when the boom is lowered / turned.

  According to the present invention, it is possible to prevent the occurrence of a turning shock due to the switching of the merging valve during boom raising / turning.

1 is a hydraulic circuit diagram showing an embodiment of the present invention. FIG. 2 is a partially enlarged view of FIG. 1. 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 a hydraulic actuator circuit, a first circuit A to which the left traveling motor 10, the boom cylinder 6 and the bucket cylinder 8 belong, a right traveling motor 11 and an arm cylinder 7 A second circuit B to which 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. And a third pump 15 as a hydraulic pressure source of the third circuit C is provided.

  For simplification of the drawing, the relief valve provided in each pump line is not shown.

  Each circuit A, B, C is provided with a control valve (direction switching valve) which is a hydraulic pilot type spool valve for controlling the operation of each hydraulic actuator.

  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.

  These control valves 16 to 21 are individually controlled by operating a remote control valve (not shown). In FIG. 1, “boom raising Pi”, “boom lowering Pi”, and “arm pulling Pi” respectively represent boom raising pilot pressure, boom lowering pilot pressure, and arm pulling pilot pressure from the remote control valve for boom.

  Here, in both the first and second circuits A and B, the traveling control valves 18 and 20 are arranged on the most upstream side of the flow of pump oil as shown in the figure, and are discharged from the first pump 13 during the traveling operation. The first pump oil is preferentially supplied to the left traveling motor 10, and the second pump oil discharged from the second pump 14 is preferentially supplied to the right traveling motor 11.

  Therefore, when both the travel motors 10 and 11 are driven simultaneously, and an operation for supplying the entire pump flow rate to the travel motors 10 and 11 is performed, the travel motors in the first and second circuits A and B are used. No pump flow rate is supplied to other hydraulic actuators.

  Therefore, a merging valve 22 is provided as means for securing other actuator operations during both travelings, and the third pump oil discharged from the third pump 15 toward the third circuit C (swing motor 12) during both travelings. The first and second circuits A and B are configured to merge with the third circuit C in a tandem or parallel flow.

  The merging valve 22 and its related configuration will be described in detail with reference to FIG.

  The merging valve 22 has both first and second pilot ports 22a and 22b on the opposite side of the spring chamber, and the neutral first position A, second position B, It is configured as a three-position hydraulic pilot switching valve that switches between three positions.

  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.

  This junction valve 22 has two input ports and an output port.

  One input port branches from the pump line 23 of the third pump 15 to the unload passage 24 passing through the bleed-off passage of the turning control valve 21, and the other connects to the parallel passage 25 branched from the pump line 23. Has been.

  Of the two output ports, the first output port is connected to the first circuit A via the first merge line 26, and the second output port is connected to the second circuit B via the second merge line 27. Has been.

  In FIG. 1, 28 is a tank line that leads to the tank T.

  The junction valve 22 switches the flow of the third pump oil at the first to third positions a, b, and c as follows.

  First position a: The unload and parallel passages 24 and 25 are joined together and connected to the first joining line 26.

  Second position B: The parallel passage 25 is blocked while the unload passage 24 is connected to the second merging line 27.

  Third position c: The parallel passage 25 is blocked, while the unload passage 24 is connected to both the first and second merge lines 26 and 27.

  The pilot configuration of the junction valve 22 is as follows.

  The first pilot port 22 a of the merging valve 22 is connected to a boom lowering pilot line 30 for guiding a boom lowering pilot pressure from the boom remote control valve via a shuttle valve 29 and a pilot primary pressure line 32 leading to the pilot hydraulic power source 31. It is connected.

  On the other hand, the second pilot port 22 b is directly connected to the pilot primary pressure line 32.

  The pilot primary pressure line 32 is connected to first and second side bypass lines 33 and 34.

  The first side bypass line 33 is connected to a drain passage 35 communicating with the tank T through the side bypass portion 21 a of the turning control valve 21 and the side bypass portion 19 a of the arm control valve 19.

  The second side bypass line 34 includes side bypass portions 20a of other control valves (control valves for right travel, left travel, boom, and bucket in order from the top of FIG. 1) 20, 18, 16, and 17. 18a, 16a and 17a are connected in series to the drain passage 35.

  In addition, throttles 36 and 37 are provided in the most upstream part of both side bypass lines 33 and 34, and even if one of both side bypass lines 33 and 34 is in communication with the tank T by the throttles 36 and 37, the other The pilot pressure is maintained.

  Each side bypass part 16a-20a has a position corresponding to the three positions of each control valve 16-20, and the position is switched in conjunction with the switching operation of the control valves 16-20.

  Among the side bypass portions 16a to 20a, the side bypass portions 20a and 18a of the right travel and left travel control valves 20 and 18 are always the second side bypass line 34 regardless of the positions of the control valves 20 and 18. Is opened.

  When both control valves 20 and 18 are in the neutral position, the second side bypass line 34 is directly communicated with the tank line 35.

  On the other hand, the side bypass portions 19a, 16a, and 17a of the control valves 19, 16, and 17 for the arm, boom, and bucket use the first side when the control valves 19, 16, and 17 are in the neutral position. The bypass line 33 is opened, and the first side bypass line 33 is blocked when the control valves 19, 16, 17 are in the operating position.

  In this way, the supply of the pilot primary pressure to the first and second pilot ports 22a, 22b of the merging valve 22 according to the operating state of the control valves 19, 20, 18, 16, 17 other than the turning control valve 21, and Supply cut-off is performed.

  On the other hand, a spring chamber of the merging valve 22 is connected to a boom raising pilot line 39 that guides a boom raising pilot pressure via a pilot pressure control valve 38 that is a hydraulic pilot valve.

  The pilot pressure control valve 38 has a pressurizing position A as a neutral position for connecting the spring chamber to the boom raising pilot line 39, and a tank position B for communicating the spring chamber with the tank T. When pilot pressure is introduced, the tank position is switched to B.

  Due to the action of the pilot pressure control valve 38, during the boom raising operation, the boom raising pilot pressure in the spring chamber of the merging valve 22 opposes the pilot pressure introduced into the first and second pilot ports 22a and 22b on the opposite side. On the other hand, when the arm pulling operation is performed in this state, the boom raising pilot pressure is canceled.

  The operation of this hydraulic circuit will be described.

  In a state where there is no actuator operation, the pilot pressure is not supplied to any of the pilot ports 22a and 22b of the merging valve 22, so that the merging valve 22 is in the illustrated first position A.

  At this first position (a), the third pump oil can be supplied to both the boom and bucket control valves 16 and 17 of the first circuit A via the first merge line 26.

  However, if there is no boom operation or bucket operation at this first position A, the first merging line 26 is connected to the tank line 28 via both boom and bucket control valves 16 and 17, so the third pump 15 The pump pressure does not increase.

(1) At the time of boom raising / turning operation When the boom raising / turning operation is performed in the state of FIG. 1, the first bypass line 33 is connected to the side of the control valve 21 based on the switching of the turning control valve 21 to the turning position. Since it is blocked by the bypass portion 21 a, the pilot primary pressure is supplied to the first pilot port 22 a of the merging valve 22.

  At this time, the boom raising pilot pressure is introduced into the spring chamber of the junction valve 22, and the total force of the boom raising pilot pressure and the spring force acts on the spring chamber side.

here,
Since (spring force + boom raising pilot pressure)> pilot primary pressure is set, the merging valve 22 is held at the first position (a).

  Accordingly, the third pump oil is supplied to the boom cylinder 6 in parallel with the swing motor 12.

  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.

  As a result, the amount of boom lifting during boom raising / turning is increased, and dump loading is improved.

  In this case, only the swivel and boom control valves 21 and 16 are stroked, and the merging valve 22 does not operate (switch), so that the swing relief pressure due to the response delay of the merging valve 22 is changed to the boom operating pressure. There is no turning shock due to sudden change.

(2) During boom raising single operation When only the boom raising operation is performed in the state shown in FIG. 1, pilot pressure is not supplied to both pilot ports 22a and 22b of the merging valve 22, while boom raising pilot pressure acts on the spring chamber. Therefore, the merging valve 22 is held at the first position a.

  Accordingly, the third pump oil is supplied to the first circuit A and joins the boom cylinder 6 in the same manner as when the boom is raised / turned. Thereby, boom raising operation is performed at high speed.

(3) At the time of single turning operation When the boom raising operation is not performed in the state shown in FIG. 1, the third pump oil falls into the tank T as described above, and the third pump pressure does not increase.

  If only the turning operation is performed in this state, the first bypass line 33 is blocked by the side bypass portion 21a of the turning control valve 21, so that the pilot primary pressure is supplied to the first pilot port of the merging valve 22 via the shuttle valve 29. 22a.

  On the other hand, the boom raising pilot pressure is not introduced into the spring chamber of the junction valve 22 at this time.

  For this reason, the merging valve 22 is switched to the second position B.

  At the second position B, the first merging line 26 is cut off, so that the third pump oil is prevented from falling into the tank T through the boom control valve 16 in the neutral position, and the turning operation is ensured. be able to.

(4) During boom lowering operation When the boom lowering operation is performed in the state shown in FIG. 1, the boom lowering pilot pressure is supplied to the first pilot port 22a of the merging valve 22, so that the merging valve 22 is turned to the second position B. Change.

  In the second position B, the unload passage 24 is connected to the second merging line 27, and the third pump oil flows into the tank T if the arm is not operated.

  That is, if there is a boom lowering operation, the third pump oil is not supplied to the boom cylinder 6.

  Therefore, since the boom lowering is not accelerated, the same feeling and movement as usual can be operated without a sense of incongruity.

  Further, when the boom is lowered / turned, the turning pressure is synchronized with the low pressure at which the boom is lowered and there is no fear that the turning performance is lowered, and a good turning acceleration performance can be ensured.

(5) During boom raising / arm pulling operation When the arm pulling operation is performed, the arm pulling pilot pressure is introduced into the pilot port 38a of the pilot pressure control valve 38, and the pilot pressure control valve 38 is moved from the pressurizing position a to the tank position. And the spring chamber of the merging valve 22 is in a tank communication state.

  That is, the introduction of the boom raising pilot pressure into the spring chamber is blocked (cancelled).

  On the other hand, the first bypass line 33 is blocked by the side bypass portion 19 a of the arm control valve 19, and the pilot primary pressure is introduced into the first pilot port 22 a of the merging valve 22.

  As a result, the merging valve 22 is switched to the second position B, and the third pump oil is supplied to the head side of the arm cylinder 7 via the second merging line 27 and the arm control valve 19.

  Thus, the third pump oil is joined to the arm cylinder 7 at the time of boom raising / arm pulling operation, that is, at the time of horizontal pulling, so that it becomes easy to perform the horizontal pulling because of the arm priority movement.

(6) 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, both side bypass lines 33 and 34 are both In order to communicate with the tank T through the drain passage 35, the pilot primary pressure is not introduced into either of the pilot ports 22a and 22b of the merging valve 22, and the merging valve 22 is in the first position (a).

  When another actuator operation is performed in this state, the side bypass lines 33 and 34 are blocked from the drain passage 35 by the operated side bypass portion of the control valve, so that the pilot primary pressure is the second pilot of the merging valve 22. Introduced into the port 22b, the merging valve 22 is switched to the third position c.

  In the third position C, the third pump oil flows to both the first and second circuits A and B via the first and second merge lines 26 and 27.

  Thereby, the actuator operation other than traveling can be ensured during both traveling.

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

  (1) As described above, the boom is raised / turned at the first position A of the merging valve 22, and switching is performed only by both the boom and turning control valves 16 and 21, and the merging valve 22 does not move. Thus, when the boom is raised / turned, the switching of the merging valve (merge) is delayed, so that the turning pressure suddenly changes, that is, the turning shock does not occur.

  (2) The boom raising operation is performed at a high speed by performing the merging action with respect to the boom cylinder 6 even during the boom raising single operation. 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.

  (3) Since the merging valve 22 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.

  (4) At the time of the single swing operation, the merging valve 22 is switched to the second position B, and the third pump oil shuts off the boom control valve 16 in the neutral position in order to block the merging of the third pump oil to the boom cylinder 6. It is possible to prevent the situation from passing through and falling into the tank, and to ensure the turning motion.

  (5) A configuration in which, for example, a boom raising operation is detected by a sensor, and based on this, the confluence valve is held in the first position in order to hold the confluence valve 22 in the first position a using the boom raising pilot pressure. Compared with the case of taking control, the configuration for control is simple and the cost is low, and the control reliability is high.

  (6) During the turning operation, the pilot pressure (pilot primary) in the direction of switching the merging valve 22 to the second position B is switched to the first pilot port 22a of the merging valve 22 based on the switching of the turning control valve 21 to the turning position. Therefore, the switching of the merging valve 22 to the second position B at the time of the single turning operation can be reliably performed in conjunction with the turning operation by the pilot pressure.

  (7) A configuration in which the third pump oil is merged to the head side of the arm cylinder 7 at the second position B of the merging valve 22, and the merging valve 22 is switched to the second position B during the boom raising / arm pulling operation. Therefore, when the boom is raised or the arm is pulled, that is, when the horizontal is retracted, the arm is prioritized and the horizontal retracting is facilitated.

  (8) By guiding the boom raising pilot pressure to the spring chamber of the merging valve 22, the merging valve 22 is configured to be held at the first position A, and the arm pulling pilot pressure is increased during the boom raising / arm pulling operation. Since the configuration is such that the boom raising pilot pressure is canceled and the merging valve 22 acts as a force for switching to the second position B, control using a control means such as a controller becomes unnecessary, and the configuration becomes simple.

  (9) During the boom lowering operation, the merging valve 22 is switched to the second position B to block the merging, so the boom lowering is not accelerated and can be operated with the same feeling and movement as usual. . Further, there is no possibility that the turning performance is lowered in synchronism with the low pressure of lowering the boom when the boom is lowered / turned.

Other embodiments
(a) During excavation work, it is desirable to increase the speed by merging the third pump oil to the arm cylinder 7 during the arm pulling operation on the arm cylinder extending side, while in the arm pushing operation on the arm cylinder contracting side, the merging is performed. As a result, the return side flow rate increases due to the difference in cylinder cross-sectional area, and the pressure loss increases.

  Therefore, the side bypass portion 19a of the arm control valve 19 may be configured to open both when the valve is neutral and when the arm is pushed, and the third pump oil may not be merged with the arm cylinder 7 when the arm is pushed. Good.

  In this way, the pressure loss on the return side during the arm pushing operation can be reduced.

  (b) The excavation work is a cooperative work of the arm 4 and the bucket 5 in FIG. 3. At this excavation, the merge valve 22 is switched to the second position B only by operating the arm, and the third pump oil is supplied to the arm cylinder 7. When the combined oil is relieved, the supply flow rate to the bucket cylinder 8 is reduced and the movement of the bucket becomes worse when the combined oil is relieved.

  Therefore, as a circuit configuration of the side bypass lines 33 and 34, the pilot primary pressure falls to the tank T when the bucket is operated, and the merging valve 22 is held at the first position (the merging of the third pump oil to the arm cylinder 7 is performed). (Do not perform).

  By doing so, even when the excavation ground is hard and the arm cylinder flow rate is relieved, the bucket cylinder flow rate is ensured, so that a good movement of the bucket 5 is secured.

  (c) Another actuator (for example, a spare service actuator or a swing cylinder that swings the boom 3 in the left-right direction) may be added to the second circuit B, or a dozer cylinder may be added to the third circuit C.

  (d) The present invention is also applicable to the case where the traveling motors 10 and 11 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 do.

  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.

A 1st circuit B 2nd circuit C 3rd circuit T Tank 1 Lower traveling body 2 Upper turning body 3 Boom 4 Arm 6 Boom cylinder 7 Arm cylinder 9 Front attachment 10 Left traveling motor 11 Right traveling motor 12 Turning motor 13 First pump 14 Second pump 15 Third pump 16 Boom control valve 18 Left travel control valve 19 Arm control valve 20 Right travel control valve 16a, 17a, 18a, 19a, 20a, 21a Side bypass portion 21 Turning control valve 22 Merge valve 22a Merge pilot valve first pilot port 22b Same as above, second pilot port 23 Third pump pump line 24 Same as above Unload passage 25 Same as parallel passage 26 First merge line 27 Second merge line 28 Tanker Down 29 shuttle valve 30 boom lowering pilot line 31 the pilot hydraulic source 32 pilot primary pressure line 33 first side bypass line 34 the second side bypass line 35 drain passage 38 pilot pressure control valve 39 boom raising pilot line

Claims (6)

A hydraulic circuit for a construction machine characterized by satisfying all the following requirements (A) to (G):
(A) It has 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.
(B) This front attachment has a boom operated by a boom cylinder and an arm operated by an arm cylinder.
(C) The hydraulic actuator circuit includes a first circuit to which the boom cylinder belongs, a second circuit to which the arm cylinder belongs, and a third circuit to which the swing motor belongs, and each circuit controls operation for each hydraulic actuator. To have control valves for boom, arm, and swivel.
(D) having 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 pump as a hydraulic source of the third circuit.
(E) having a merging valve for sending the third pump oil discharged from the third pump to the first circuit and joining the oil from the first pump;
(F) The merging valve has a neutral first position and a second position. In the first position, the third pump oil is merged with the first circuit, and the merging valve is merged with the second position. Configured to block.
(G) The merging valve is configured to be held at the first position during a boom raising / turning operation in which a boom raising operation and a turning operation are performed simultaneously and in a boom raising single operation in which only a boom raising operation is performed.
(H) The merging valve is configured to be switched to the second position at the time of a single turn operation in which only a turn operation is performed.   The control valve and the merging valve are each configured as a hydraulic pilot switching valve that is switched and operated by a pilot pressure, and the boom raising pilot pressure applied to the boom control valve is guided to the pilot port of the merging valve, thereby 2. The hydraulic circuit for a construction machine according to claim 1, wherein the hydraulic circuit is held at the first position.   The control valve and the merging valve are each configured as a hydraulic pilot switching valve that is switched and operated according to the pilot pressure, and the merging valve is joined to the pilot port of the merging valve based on the switching to the turning position of the turning control valve during turning operation. 3. The hydraulic circuit for a construction machine according to claim 1, wherein a pilot pressure in a direction for switching the valve to the second position is introduced.   The third pump oil is joined to the head side of the arm cylinder of the second circuit at the second position of the merging valve, and the boom raising / arm pulling operation is performed at the same time when the boom raising operation and the arm pulling operation are performed. The hydraulic circuit for a construction machine according to any one of claims 1 to 3, wherein the junction valve is configured to be switched to the second position.   The control valve and the merging valve are each configured as a hydraulic pilot switching valve that is switched and operated by a pilot pressure, and the boom raising pilot pressure applied to the boom control valve is guided to the spring chamber of the merging valve, thereby At the time of the boom raising / arm pulling operation, the arm pulling pilot pressure is a force for canceling the boom raising pilot pressure and switching the merging valve to the second position. The hydraulic circuit for a construction machine according to claim 4, wherein the hydraulic circuit is configured to act as   The hydraulic circuit for a construction machine according to any one of claims 1 to 5, wherein the merging valve is switched to the second position during a boom lowering operation.

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