JP2018150744A - Hydraulic circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inhibit reduction of an excavation speed of a bucket during excavation work including arm drawing and bucket excavation.SOLUTION: A hydraulic circuit comprises: a first confluent line L14 that merges hydraulic oil from a third pump 15 with a discharge line of a first pump 13; a second confluent line L13 that merges hydraulic oil from the third pump 15 with a discharge line of a second pump 14; and an opening adjustment valve 23 that limits an opening area of the first confluent line L14 to a preset limited opening area in order to guide hydraulic oil from the third pump 15 to the discharge line of the second pump 14 preferentially compared with the discharge line of the first pump 13 when pressure inside a head side chamber of an arm cylinder 9 is less than or equal to a preset pressure P1, and operates so as to expand the opening area of the first confluent line L14 more than the limited opening area when the pressure inside the head side chamber of the arm cylinder 9 exceeds the preset pressure P1.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a hydraulic circuit provided in a construction machine such as a hydraulic excavator.

  For example, a hydraulic excavator having a lower traveling body, an upper revolving body that is turnable with respect to the lower traveling body, and an attachment that is attached to the upper revolving body so as to be raised and lowered is known.

  The attachment is pivotally attached to the upper swing body, an arm pivotably attached to the tip of the boom, and pivotally attached to the tip of the arm. And a bucket.

  The hydraulic excavator includes a hydraulic circuit described in Patent Document 1, for example.

  The hydraulic circuit includes a swing motor that rotates the upper swing body, a boom cylinder that rotates the boom relative to the upper swing body, an arm cylinder that rotates the arm relative to the boom, and a bucket that rotates the bucket relative to the arm. A bucket cylinder to be moved.

  The hydraulic circuit includes, for example, a first pump for supplying hydraulic oil to the boom cylinder and the bucket cylinder, and a second pump for supplying hydraulic oil to the arm cylinder, as disclosed in Patent Document 1. And a third pump for supplying hydraulic oil to the turning motor, and an engine for driving the first to third pumps.

  Furthermore, the hydraulic circuit described in Patent Document 1 includes a first merging line for joining hydraulic oil from the third pump to a discharge line of the first pump, and a hydraulic oil from the third pump being discharged from the second pump. A second merging line for merging with the line.

  Accordingly, the hydraulic oil from the third pump can be added to the hydraulic oil from the first pump and the second pump, and the hydraulic actuator to be driven by the first pump and the second pump can be reliably operated.

  Further, the hydraulic circuit (merging valve) described in Patent Document 1 preferentially supplies hydraulic oil to the second merging line when merging hydraulic oil from the third pump to the discharge lines of the first pump and the second pump. In order to guide, a restriction for limiting the opening area of the first merge line is provided.

  Thus, for example, when the boom lowering and the arm operation are performed simultaneously, the arm can be accelerated by flowing the hydraulic oil preferentially through the arm cylinder, and workability can be improved.

JP 2013-147864 A

  In the construction machine having the hydraulic circuit as described above, torque control for controlling the capacities of the first pump and the second pump is executed so that the load torque required for the engine is lower than the output torque of the engine.

  Further, the hydraulic circuit has a relief valve that is opened when the pressure of the hydraulic oil in the hydraulic circuit becomes equal to or higher than a preset relief pressure to prevent the hydraulic equipment in the hydraulic circuit from being damaged. .

  Here, when arm excavation and bucket excavation are performed simultaneously to perform excavation work for excavating earth and sand, a load on the arm cylinder increases due to a reaction force that the arm receives from the ground. Moreover, the hydraulic oil discharged from the third pump is preferentially supplied to the discharge line (arm cylinder) of the second pump by the above-described throttle.

  Therefore, during excavation work, the pressure in the hydraulic circuit rises and the relief valve opens, and the load on the first pump and the second pump that discharges hydraulic oil in such a high pressure state increases. Torque control is executed as the pump load increases.

  As a result, as the capacity of the first pump decreases, the excavation speed of the bucket decreases, and the workability of excavation work may decrease.

  The objective of this invention is providing the hydraulic circuit which can suppress the fall of the excavation speed of the bucket in the excavation work which involves arm pulling and bucket excavation.

  In order to solve the above-described problems, the present invention provides a boom, an arm that is rotatably attached to the tip of the boom, and a bucket that is rotatably attached to the tip of the arm. A hydraulic circuit provided in a construction machine having an arm cylinder for rotating the arm with respect to the boom, a bucket cylinder for rotating the bucket with respect to the arm, and an operation on the bucket cylinder A first pump for supplying oil, a second pump for supplying hydraulic oil to the arm cylinder, a third pump, the first pump, the second pump, and the third pump are driven. An engine, a first merging line for merging hydraulic oil from the third pump to a discharge line of the first pump, and hydraulic oil from the third pump to the second pump A second merge line for merging with the discharge line, and a discharge of the second pump in comparison with the discharge line of the first pump when the pressure in the head side chamber of the arm cylinder is equal to or lower than a preset set pressure. In order to preferentially guide hydraulic oil from the third pump to the line, the opening area of the first merging line is limited to a preset limiting opening area, and the pressure in the head side chamber of the arm cylinder is There is provided a hydraulic circuit comprising: an opening adjusting valve that operates so that an opening area of the first merge line is larger than the limited opening area when the set pressure is exceeded.

  According to the present invention, a situation in which the combined operation of the arm and bucket is performed and the load on the arm cylinder is relatively low (for example, arm pulling and bucket excavation operations are performed and a reaction force is received from the ground. In a situation where there is not, the opening adjustment valve limits the opening area of the first merging line to the limited opening area. As a result, the hydraulic oil from the third pump is guided preferentially to the arm cylinder as compared to the bucket cylinder, so that the speed of the arm can be increased and workability can be improved.

  On the other hand, a situation where the combined operation of the arm and bucket is performed and the load on the arm cylinder is high (for example, during an excavation operation in which arm pulling and bucket excavation operations are performed and a reaction force from the ground is received) ), The opening area of the first merging line is wider than the limited opening area by the opening adjusting valve. As a result, the pressure in the hydraulic circuit increases as the relief valve in the hydraulic circuit is opened, as in the case where the priority supply of hydraulic oil from the third pump is continued to the arm cylinder in a high load state. Can be suppressed. Therefore, it is possible to suppress the load of the first pump and the second pump from increasing as the pressure in the hydraulic circuit increases, and to limit the torque of the first pump. It is possible to improve the excavation speed of the bucket by effectively utilizing the hydraulic oil that is joined to the discharge line of one pump.

  Therefore, according to the present invention, it is possible to suppress a decrease in bucket excavation speed during excavation work involving arm pulling and bucket excavation.

  The “set pressure” in the present invention is lower than the relief pressure set in the hydraulic circuit in the merged state where the hydraulic oil of the third pump is led to the discharge line of the first pump and the discharge line of the second pump. It is preset as a value. That is, the “set pressure” is set lower than the relief pressure set in the relief valve provided in the hydraulic circuit so that the relief is possible by the discharge pressures of the first to third pumps in the merged state. If it does in this way, execution of torque control by the load of an arm cylinder becoming high in a merging state can be controlled.

  Here, when the pressure in the head side chamber of the arm cylinder changes from a value equal to or lower than the set pressure to a value exceeding the set pressure, the opening adjusting valve can also rapidly increase the opening area of the first merge line. . However, in this case, when the amount of hydraulic oil supplied from the third pump to the arm cylinder rapidly decreases, the arm cylinder rapidly decelerates, and workability may be deteriorated.

  Therefore, in the hydraulic circuit, the opening adjusting valve opens the first merge line as the pressure in the head side chamber of the arm cylinder increases in a state where the pressure in the head side chamber of the arm cylinder exceeds the set pressure. It is preferable to operate so as to increase the area.

  According to this aspect, it is possible to keep the pressure in the hydraulic circuit low to such an extent that torque control is not performed while maintaining the acceleration period of the arm cylinder as much as possible in a situation where the load on the arm cylinder is relatively small.

  Therefore, it is possible to suppress the deterioration of workability by suppressing the deceleration of the arm cylinder.

  The hydraulic circuit includes a boom cylinder for rotating the boom with respect to a machine body of the construction machine that rotatably supports the boom, and a boom for guiding hydraulic oil from the first merging line to the boom cylinder. And a side line.

  In this configuration, a boom raising operation may be further performed during excavation work. In this case, if the hydraulic oil from the third pump is supplied unconditionally to the boom cylinder, the bucket moves in a direction away from the ground with the boom raising operation, and it is difficult to efficiently perform the excavation work. .

  Therefore, the hydraulic circuit compares the reference pressure in the head side chamber of the arm cylinder with the reference area compared to the opening area of the boom side line when the pressure in the head side chamber of the arm cylinder is equal to or lower than a preset reference pressure. It is preferable to further include an opening change valve that operates so as to limit the opening area of the boom-side line when the pressure is exceeded.

  According to this aspect, when the boom raising operation is performed, during excavation work, that is, in a situation where the load on the arm cylinder is high, the amount of hydraulic oil supplied from the third pump to the boom cylinder is suppressed and relative In addition, the amount of hydraulic oil supplied from the third pump to the bucket cylinder can be increased.

  Therefore, according to the said aspect, excavation work can be performed more efficiently by accelerating bucket excavation, suppressing the speed | rate of boom raising operation | movement at the time of excavation work.

  In the above aspect, the “reference pressure” is set in the hydraulic circuit in the merged state in which the hydraulic oil of the third pump is led to the discharge line of the first pump and the discharge line of the second pump, similarly to the set pressure. Is set in advance as a value lower than the relief pressure.

  Here, when the pressure in the head side chamber of the arm cylinder changes from a value equal to or lower than the reference pressure to a value exceeding the reference pressure, the opening change valve can also rapidly limit the opening area of the boom side line. . However, in this case, the amount of hydraulic oil supplied from the third pump to the boom cylinder rapidly decreases, so that the boom cylinder rapidly decelerates and workability may be deteriorated.

  Therefore, in the hydraulic circuit, the opening change valve has an opening area of the boom side line as the pressure in the head side chamber of the arm cylinder increases in a state where the pressure in the head side chamber of the arm cylinder exceeds the reference pressure. It is preferable to operate so that becomes smaller.

  According to this aspect, it is possible to prevent the bucket from moving away from the ground in a situation where the load of the arm cylinder is large, while speeding up the boom in a situation where the load of the arm cylinder is relatively small.

  Therefore, workability at the time of excavation work can be further improved.

  Here, a sensor that detects the pressure of the hydraulic oil in the head side chamber of the arm cylinder, and a controller that outputs a command to the opening adjustment valve and the opening change valve based on the detection value of the sensor, the opening adjustment valve and The opening change valve may be configured by an electromagnetic switching valve that operates in accordance with a command from the controller.

  On the other hand, in the hydraulic circuit, it is preferable that the opening adjustment valve and the opening change valve are respectively configured by pilot-type switching valves that operate according to the pressure of the hydraulic oil in the head side chamber of the arm cylinder.

  According to this aspect, compared to the case where the circuit adjustment valve and the opening change valve are configured by electromagnetic switching valves, the configuration of the sensor, the controller, and the like can be omitted, which is advantageous in terms of cost. .

  ADVANTAGE OF THE INVENTION According to this invention, the fall of the excavation speed of the bucket during excavation work with arm pulling and bucket excavation can be suppressed.

1 is a side view showing an overall configuration of a hydraulic excavator that is an example of a construction machine of the present invention. It is a circuit diagram of the hydraulic circuit which concerns on 1st Embodiment provided in the hydraulic shovel of FIG. It is a graph which shows the opening characteristic of the opening adjustment valve of FIG. It is a graph which shows the opening characteristic of the opening change valve of FIG. It is a circuit diagram of the hydraulic circuit which concerns on 2nd Embodiment.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. The following embodiments are examples embodying the present invention, and are not of a nature that limits the technical scope of the present invention.

<First Embodiment>
Referring to FIG. 1, a hydraulic excavator 1 which is an example of a construction machine includes a lower traveling body 2, an upper swinging body 3 provided so as to be pivotable with respect to the lower traveling body 2, and an upper swinging body 3. And an attachment 4 that can be raised and lowered. The lower traveling body 2 and the upper swing body 3 correspond to a machine body that rotatably supports the attachment 4 (boom 5).

  The attachment 4 has a boom 5 having a base end portion rotatably attached to the upper swing body 3, and an arm 6 having a base end portion rotatably attached to the distal end portion of the boom 5. , And a bucket 7 that is rotatably attached to the tip of the arm 6.

  Further, the excavator 1 includes a hydraulic circuit shown in FIG.

  The hydraulic circuit includes a boom cylinder 8 that rotates the boom 5 relative to the upper swing body 3, an arm cylinder 9 that rotates the arm 6 relative to the boom 5, and a bucket that rotates the bucket 7 relative to the arm 6. A cylinder 10 and a turning motor 11 that drives the upper turning body 3 to turn relative to the lower traveling body 2 are provided.

  The hydraulic circuit includes a variable displacement first pump 13 for supplying hydraulic oil to the bucket cylinder 10 and the boom cylinder 8, and a variable displacement second pump 14 for supplying hydraulic oil to the arm cylinder 9. And a third pump 15 for supplying hydraulic oil to the swing motor 11, a pilot pump 16 for supplying pilot pressure to control valves 17 to 19 and 21, which will be described later, and these pumps 13 to 16 are driven. And an engine 12.

  Hereinafter, the structure provided between the 1st pump 13 in the hydraulic circuit, the bucket cylinder 10, and the boom cylinder 8 is demonstrated.

  The hydraulic circuit includes a boom control valve 17 provided between the first pump 13 and the boom cylinder 8, and a bucket control valve 18 provided between the first pump 13 and the bucket cylinder 10. ing.

  Both control valves 17 and 18 are connected to each other in series via a tandem line L1 connected to the first pump 13. The tandem line L1 is connected to the tank line LT on the downstream side of the bucket control valve 18.

  Both control valves 17 and 18 are connected in parallel via lines L2 to L4.

  Specifically, the supply side port of the boom control valve 17 is connected to the supply line L3 connected to the middle part of the branch line L2 that branches from the upstream side of the boom control valve 17 of the tandem line L1. Yes. A check valve that allows the flow of hydraulic oil from the tandem line L1 to the supply line L3 side, while restricting the flow in the opposite direction, to the tandem line L1 side from the connection point of the supply line L3 in the branch line L2. Is omitted). The supply line L3 is provided with a check valve (not shown) that permits the flow of hydraulic oil from the branch line L2 to the boom control valve 17 while restricting the flow in the opposite direction.

  On the other hand, a supply line L4 branched from a portion between the boom control valve 17 and the bucket control valve 18 in the tandem line L1 is connected to the supply side port of the bucket control valve 18. The supply line L4 is provided with a pair of check valves (not shown) that allow the flow of hydraulic oil from the tandem line L1 to the bucket control valve 18 while restricting the flow in the opposite direction. A branch line L2 is connected between the check valves of the supply line L4. A stop (reference numeral omitted) is provided at a position downstream of the supply line L3 in the branch line L2. This throttle is provided in order to improve operability by guiding hydraulic oil in preference to the boom cylinder 8 when the combined operation of raising the boom 5 and excavating the bucket 7 is performed.

  Further, a lead-out line L5 connected to the tank line LT is connected to the tank side port of the boom control valve 17. Similarly, the tank side port of the bucket control valve 18 is connected to a lead-out line L6 connected to the tank line LT.

  In addition, a relief line (not shown) is provided between a portion of the tandem line L1 between the first pump 13 and the boom control valve 17 and the tank line LT, and a relief valve 27 is provided in the middle of the relief line. Is provided. The relief valve 27 opens the relief line when the pressure in the tandem line L1 is equal to or higher than a preset relief pressure, and guides the hydraulic oil in the tandem line L1 to the tank line LT. Thereby, when the load of the first pump 13 (the load of the boom cylinder 8 and the bucket cylinder 10) becomes high, the hydraulic circuit can be protected.

  The boom control valve 17 has a neutral position that is biased when the operation lever (not shown) is not operated, and a boom raising that is operated by hydraulic oil (pilot pressure) from the pilot pump 16 according to the operation of the operation lever. A position (right side position in FIG. 2) and a boom lowering position (left side position in FIG. 2). The boom control valve 17 in the neutral position stops the supply and discharge of hydraulic oil to and from the boom cylinder 8 and opens the tandem line L1. The boom control valve 17 at the boom raising position closes the tandem line L1, guides hydraulic fluid from the supply line L3 to the head side chamber of the boom cylinder 8, and guides hydraulic fluid in the rod side chamber of the boom cylinder 8 to the lead-out line L5. . The boom control valve 17 in the boom lowered position closes the tandem line L1, guides hydraulic oil from the supply line L3 to the rod side chamber of the boom cylinder 8, and guides hydraulic oil in the head side chamber of the boom cylinder 8 to the lead-out line L5. .

  The bucket control valve 18 is a bucket excavation that is operated by a neutral position that is energized when the operation lever (not shown) is not operated, and hydraulic oil (pilot pressure) from the pilot pump 16 according to the operation of the operation lever. A position (right side position in FIG. 2) and a bucket dump position (left side position in FIG. 2). The bucket control valve 18 in the neutral position stops the supply and discharge of hydraulic oil to and from the bucket cylinder 10 and opens the tandem line L1. The bucket control valve 18 in the bucket excavation position closes the tandem line L1, guides hydraulic oil from the supply line L4 to the head side chamber of the bucket cylinder 10, and guides hydraulic oil in the rod side chamber of the bucket cylinder 10 to the outlet line L6. . The bucket control valve 18 at the bucket dump position closes the tandem line L1, guides hydraulic oil from the supply line L4 to the rod side chamber of the bucket cylinder 10, and guides hydraulic oil in the head side chamber of the bucket cylinder 10 to the outlet line L6. .

  Next, a configuration provided between the second pump 14 and the arm cylinder 9 in the hydraulic circuit will be described.

  The hydraulic circuit includes an arm control valve 19 provided between the second pump 14 and the arm cylinder 9.

  The arm control valve 19 is provided in the middle of the pump line L7 extending from the second pump 14 to the tank line LT.

  Further, a supply line L8 branched from a portion between the second pump 14 and the arm control valve 19 in the pump line L7 is connected to the supply side port of the arm control valve 19. The supply line L8 is provided with a check valve (not shown) that permits the flow of hydraulic oil from the pump line L7 toward the arm control valve 19 while restricting the flow in the opposite direction.

  Furthermore, a relief line (not shown) is provided between a portion of the pump line L7 between the second pump 14 and the arm control valve 19 and the tank line LT, and a relief valve 20 is provided in the middle of the relief line. Is provided. The relief valve 20 closes the relief line when the pressure in the pump line L7 is lower than a preset relief pressure, and opens the relief line when the pressure in the pump line L7 is equal to or higher than the relief pressure to open the relief line 20 in the pump line L7. To the tank line LT. Thereby, the hydraulic circuit can be protected when the load of the second pump 14 (the load of the arm cylinder 9) becomes high.

  On the other hand, a lead-out line L9 connected to the tank line LT is connected to the tank side port of the arm control valve 19.

  The arm control valve 19 has a neutral position that is biased when the operation lever (not shown) is not operated, and an arm pusher that is operated by hydraulic oil (pilot pressure) from the pilot pump 16 according to the operation of the operation lever. A position (right side position in FIG. 2) and an arm pulling position (left side position in FIG. 2). The arm control valve 19 in the neutral position stops the supply and discharge of the hydraulic oil to and from the arm cylinder 9 and opens the pump line L7. The arm control valve 19 in the arm pushing position closes the pump line L7, guides hydraulic oil from the supply line L8 to the rod side chamber of the arm cylinder 9, and guides hydraulic oil from the head side chamber of the arm cylinder to the outlet line L9. The arm control valve 19 in the arm pulling position closes the pump line L7, guides hydraulic oil from the supply line L8 to the head side chamber of the arm cylinder 9, and guides hydraulic oil from the rod side chamber of the arm cylinder 9 to the outlet line L9.

  Next, the structure provided between the 3rd pump 15 and the turning motor 11 in a hydraulic circuit is demonstrated.

  The hydraulic circuit includes a turning control valve 21 provided between the third pump 15 and the turning motor 11.

  The turning control valve 21 is provided in the middle of a pump line L10 extending from the third pump 15 to a first merging line L14 and a second merging line L13, which will be described later.

  A supply line L11 that branches from a portion of the pump line L10 between the third pump 15 and the turning control valve 21 is connected to the supply side port of the turning control valve 21. The supply line L11 is provided with a check valve (not shown) that permits the flow of hydraulic oil from the pump line L10 to the turning control valve 21 while restricting the flow in the opposite direction.

  Furthermore, a relief line (not shown) is provided between a portion of the pump line L10 between the third pump 15 and the turning control valve 21 and the tank line LT, and a relief valve 22 is provided in the middle of the relief line. Is provided. The relief valve 22 closes the relief line when the pressure in the pump line L10 is lower than a preset relief pressure, while opening the relief line when the pressure in the pump line L10 is equal to or higher than the relief pressure to open the relief line 22 in the pump line L10. To the tank line LT. Thereby, the hydraulic circuit can be protected when the load of the third pump 15 (the load of the turning motor 11) becomes high.

  On the other hand, a lead-out line L12 connected to the tank line LT is connected to the tank side port of the turning control valve 21.

  The turning control valve 21 has a neutral position that is biased when the operation lever (not shown) is not operated, and a right-hand rotation that is operated by hydraulic oil (pilot pressure) from the pilot pump 16 according to the operation of the operation lever. A turning position (right position in FIG. 2) and a left turn position (left position in FIG. 2). The turning control valve 21 in the neutral position stops the supply and discharge of hydraulic oil to and from the turning motor 11 and opens the pump line L10. The turning control valve 21 in the right turning position and the left turning position closes the pump line L10, guides hydraulic oil from the supply line L11 to one port of the turning motor 11, and leads out from the other port of the turning motor. Lead hydraulic fluid to line L12.

  Hereinafter, a configuration for joining the hydraulic oil discharged from the third pump 15 to the discharge lines of the first pump 13 and the second pump 14 will be described.

  The hydraulic circuit joins the first joining line L14 for joining the working oil from the third pump 15 to the discharge line of the first pump 13, and the working oil from the third pump 15 to the discharge line of the second pump 14. A second merging line L13. Here, the discharge line of the first pump 13 includes a portion of the tandem line L1 between the first pump 13 and the boom control valve 17, and a branch line L2. The discharge line of the second pump 14 has a portion between the second pump 14 and the arm control valve 19 in the pump line L7.

  Specifically, the first merging line L14 and the second merging line L13 are lines branched from the downstream end of the turning control valve 21 of the pump line L10 connected to the third pump 15. The first merge line L14 is connected to a connection point with the supply line L3 in the branch line L2. On the other hand, the 2nd merge line L13 is connected to the connection point with the supply line L8 in the pump line L7.

  As a result, in a state where the turning control valve 21 is switched to a position other than the neutral position, the hydraulic oil from the third pump 15 flows into the branch line L2 (the discharge line of the first pump 13) and the supply line L8 (the second line). To the discharge line of the pump 14.

  Here, the first merging line L14 is provided with an opening adjusting valve 23 for adjusting the opening area of the first merging line L14.

  FIG. 3 is a graph showing the opening characteristics of the opening adjusting valve 23.

  Referring to FIGS. 2 and 3, the opening adjustment valve 23 is second in comparison with the discharge line of the first pump 13 when the pressure in the head side chamber of the arm cylinder 9 is equal to or lower than a preset pressure P <b> 1. In order to lead hydraulic oil from the third pump 15 preferentially to the discharge line of the pump 14, the opening area of the first merging line L14 is set in advance and limited to the limited opening area. On the other hand, when the pressure in the head side chamber of the arm cylinder 9 exceeds the set pressure P1, the opening adjusting valve 23 increases the opening area of the first merging line L14 beyond the limit opening area.

  The set pressure P1 is a value lower than the relief pressure set in the hydraulic circuit in the merged state where the hydraulic oil of the third pump 15 is led to the discharge line of the first pump 13 and the discharge line of the second pump 14. Is preset. That is, the “set pressure” is higher than the relief pressure set in the relief valves 20, 22, and 27 provided in the hydraulic circuit so that relief is possible by the discharge pressures of the first to third pumps 13 to 15 in the merged state. It is set low.

  Specifically, the opening adjustment valve 23 has a restriction position that restricts the opening area by a diaphragm and a non-limit position that does not have a diaphragm. The pilot port of the opening adjustment valve 23 is connected to the head side chamber of the arm cylinder 9. The opening adjusting valve 23 is urged to the restriction position when the pressure in the head side chamber of the arm cylinder 9 is equal to or lower than the set pressure P1, while the pressure in the head side chamber of the arm cylinder 9 exceeds the set pressure P1. In this case, the restriction position is continuously switched to the non-restriction position so that the larger the pressure is, the larger the opening area becomes.

  Therefore, for example, when the combined operation of the arm cylinder 9 and the bucket cylinder 10 is performed and the load on the arm cylinder 9 is relatively small, the opening adjustment valve 23 is biased to the restriction position. As a result, the hydraulic oil from the third pump 15 is supplied to the arm cylinder 9 in preference to the bucket cylinder 10, so that the speed of the arm 6 can be increased.

  On the other hand, when the combined operation of the arm 6 and the bucket 7 is performed and the load on the arm cylinder 9 is high, the opening adjustment valve 23 operates to the non-restricted position, and the opening area of the first merging line L14 is limited. It is wider than the opening area. As a result, the pressure in the hydraulic circuit is increased as the relief valves 20, 22, 27 are opened as in the case where the priority supply of the hydraulic oil from the third pump 15 is continued to the arm cylinder 9 in the high load state. The rise can be suppressed. Here, when the relief valves 20, 22, and 27 are opened, torque control is performed in which the capacities of the first pump 13 and the second pump 14 are limited by a controller (not shown). In this situation, the capacity of the first pump 13 is limited, so that the speed of the bucket 7 decreases. On the other hand, as described above, it is possible to effectively increase the speed of the bucket 7 by suppressing the relief valves 20, 22, and 27 from being opened.

  Furthermore, since the opening area of the first merging line L14 is continuously expanded according to the pressure in the head side chamber of the arm cylinder 9, the arm cylinder 9 increases in a situation where the load on the arm cylinder 9 is relatively small. The pressure in the hydraulic circuit can be kept low while maintaining the speed period as much as possible.

  Further, the hydraulic circuit further includes an opening change valve 24 provided in a supply line L3 (boom side line) for guiding hydraulic oil from the first merging line L14 to the boom cylinder 8.

  FIG. 4 is a graph showing the opening characteristics of the opening change valve 24.

  Referring to FIGS. 2 and 4, the opening change valve 24 is compared with the opening area of the supply line L3 when the pressure in the head side chamber of the arm cylinder 9 is equal to or lower than a preset reference pressure P2. It operates so that the opening area of the supply line L3 is limited when the pressure in the head side chamber exceeds the reference pressure P2. The reference pressure P2 is set in the hydraulic circuit in the merged state where the hydraulic oil of the third pump 15 is guided to the discharge line of the first pump 13 and the discharge line of the second pump 14 as in the case of the set pressure. It is preset as a value lower than the relief pressure. That is, the “reference pressure” is higher than the relief pressure set in the relief valves 20, 22, and 27 provided in the hydraulic circuit so that relief can be performed by the discharge pressures of the first to third pumps 13 to 15 in the merged state. It is set low.

  The reference pressure P2 of the opening change valve 24 is set lower than the set pressure P1 of the opening adjustment valve 23.

  Specifically, the opening change valve 24 has a restriction position that restricts the opening area by a diaphragm and a non-restricted position that does not have a diaphragm. The pilot port of the opening change valve 24 is connected to the head side chamber of the arm cylinder 9. The opening change valve 24 is biased to the non-restricted position when the pressure in the head side chamber of the arm cylinder 9 is equal to or lower than the reference pressure P2, while the pressure in the head side chamber of the arm cylinder 9 reduces the reference pressure P2. When the pressure exceeds the non-restricted position, the opening area is reduced as the pressure increases.

  Therefore, when the combined operation of the boom 5, the arm 6, and the bucket 7 is performed and the load of the arm cylinder 9 is relatively low, the opening change valve 24 is held at the non-restricted position, and the third pump 15 Can be effectively utilized by the boom 5, the arm 6, and the bucket 7.

  On the other hand, when the combined operation of the boom 5, the arm 6, and the bucket 7 is performed and the load on the arm cylinder 9 is relatively high, the opening change valve 24 is switched to the limit position, and the third pump 15 The hydraulic oil can be preferentially supplied to the bucket 7 as compared with the boom 5. Therefore, even if the boom raising operation is performed during excavation work, the bucket 7 can be accelerated.

  As described above, the combined operation of the arm 6 and the bucket 7 is performed and the load on the arm cylinder 9 is relatively low (for example, the arm pulling and bucket excavation operations are performed, and the reaction force is applied from the ground. In a situation where the opening is not received, the opening adjustment valve 23 limits the opening area of the first merging line L14 to the limited opening area. As a result, hydraulic oil from the third pump 15 is preferentially guided to the arm cylinder 9 as compared with the bucket cylinder 10, so that the arm 6 can be accelerated and workability can be improved.

  On the other hand, a situation where the combined operation of the arm 6 and the bucket 7 is performed and the load on the arm cylinder 9 is high (for example, arm pulling and bucket excavation operations are performed and a reaction force from the ground is received. At the time of excavation work, the opening area of the first merging line L14 is expanded by the opening adjusting valve 23 beyond the limited opening area. As a result, as the relief valves 20 and 22 in the hydraulic circuit are opened as in the case where the priority supply of the hydraulic oil from the third pump 15 is continued to the arm cylinder 9 in a high load state, It is possible to suppress an increase in pressure. Therefore, as the pressure in the hydraulic circuit increases, the load on the first pump 13 and the second pump 14 increases, and the torque of the first pump 13 can be suppressed from being restricted. It is possible to improve the excavation speed of the bucket 7 by effectively utilizing the hydraulic oil that is merged from the pump 15 to the discharge line of the first pump 13.

  Therefore, it is possible to suppress a decrease in excavation speed of the bucket 7 during excavation work involving arm pulling and bucket excavation.

  Moreover, according to 1st Embodiment, there can exist the following effects.

  As the pressure in the head side chamber of the arm cylinder 9 increases, the opening area of the first merging line L14 increases, so that the acceleration period of the arm cylinder 9 is maintained as much as possible in a situation where the load on the arm cylinder 9 is relatively small. However, the pressure in the hydraulic circuit can be kept low to such an extent that torque control is not performed.

  Accordingly, it is possible to suppress the deceleration of the arm cylinder 9 and to suppress the workability.

  When the boom raising operation is performed, during excavation work, that is, when the load on the arm cylinder 9 is high, the opening change valve 24 suppresses the amount of hydraulic oil supplied from the third pump 15 to the boom cylinder 8. The supply amount of hydraulic oil from the third pump 15 to the bucket cylinder 10 can be relatively increased.

  Therefore, the excavation work can be performed more efficiently by increasing the speed of the bucket excavation while suppressing the speed of the boom raising operation during the excavation work.

  The opening change valve 24 operates so that the opening area of the supply line L3 increases as the pressure in the head side chamber of the arm cylinder 9 increases. Thereby, it is possible to prevent the bucket 7 from moving away from the ground in a situation where the load of the arm cylinder 9 is high while the speed of the boom 5 is increased in a situation where the load of the arm cylinder 9 is relatively small.

  Therefore, workability at the time of excavation work can be further improved.

  The opening adjusting valve 23 and the opening changing valve 24 are respectively constituted by pilot-type switching valves that operate according to the pressure of the hydraulic oil in the head side chamber of the arm cylinder 9.

  Thereby, compared with the case where the opening adjustment valve 23 and the opening change valve 24 are comprised by the electromagnetic switching valve, since structures, such as a sensor and a controller, can be omitted, it becomes advantageous in terms of cost.

Second Embodiment
Although 1st Embodiment demonstrated the example which employ | adopted the hydraulic pilot type opening adjustment valve 23 and the opening change valve 24, these valves 23 and 24 are not limited to a hydraulic pilot type.

  Hereinafter, with reference to FIG. 5, only the portions of the hydraulic circuit different from the first embodiment will be described.

  The hydraulic circuit according to the second embodiment shown in FIG. 5 includes an electromagnetic opening adjusting valve 23, an electromagnetic opening changing valve 24, a pressure sensor 25 capable of detecting the pressure in the head side chamber of the arm cylinder 9, And a controller 26 that controls both valves 23 and 24 based on a detection signal from the pressure sensor 25.

  The controller 26 outputs an electrical command to the solenoid of the opening adjustment valve 23 when the pressure detected by the pressure sensor 25 exceeds the set pressure P1. Thereby, the opening adjustment valve 23 operates continuously from the restriction position toward the non-restriction position according to the magnitude of the pressure detected by the pressure sensor 25.

  According to the second embodiment, since both valves 23 and 24 can be controlled by an electrical command, the degree of freedom of switching timing and the like of both valves 23 and 24 is increased.

  In addition, this invention is not limited to the said embodiment, For example, the following aspects can also be employ | adopted.

  Although the boom cylinder 8 is supplied with hydraulic oil from the first pump 13, the supply source of hydraulic oil to the boom cylinder 8 is not limited to the first pump 13.

  The third pump 15 supplies the hydraulic oil to the swing motor 11, but the supply destination of the hydraulic oil of the third pump 15 is not limited to the swing motor 11.

  The configuration in which the first merging line L14 and the second merging line L13 are branched from the pump line L10 has been described as an example, but hydraulic oil from the third pump 15 is discharged from the first pump 13 and the second pump 14. A merging valve (for example, a merging valve of Patent Document 1) having a switching position for leading to the line may be provided in the pump line L10. In this case, the merging valve and the line connecting the discharge line of the first pump correspond to the first merging line, and the line connecting the merging valve and the discharge line of the second pump is the second merging line. Equivalent to. Further, in this case, the merging valve may adjust the opening area of the first merging line, that is, may have a function of an opening adjusting valve.

  Although the example in which the opening adjustment valve 23 can continuously adjust the opening area has been described, the adjustment is instantaneously performed from the restriction position (left position in FIG. 2) to the non-restriction position (right position in FIG. 2) with the set pressure as a boundary. Possible opening adjustment valve 23 can also be employed.

  The construction machine is not limited to a hydraulic type, and may be a hybrid type.

L1 Tandem line (discharge line of the first pump 13)
L2 branch line (discharge line of the first pump 13)
L3 supply line (boom side line)
L7 pump line (discharge line of the second pump 13)
L13 2nd merge line L14 1st merge line P1 Set pressure P2 Reference pressure 1 Hydraulic excavator (construction machine)
2 Lower traveling body (airframe)
3 Upper swing body (airframe)
5 Boom 6 Arm 7 Bucket 8 Boom Cylinder 9 Arm Cylinder 10 Bucket Cylinder 12 Engine 13 First Pump 14 Second Pump 15 Third Pump 23 Opening Adjustment Valve 24 Opening Change Valve

Claims (5)

A hydraulic circuit provided in a construction machine having a boom, an arm rotatably attached to the tip of the boom, and a bucket rotatably attached to the tip of the arm There,
An arm cylinder for rotating the arm with respect to the boom;
A bucket cylinder for rotating the bucket relative to the arm;
A first pump for supplying hydraulic oil to the bucket cylinder;
A second pump for supplying hydraulic oil to the arm cylinder;
A third pump;
An engine for driving the first pump, the second pump, and the third pump;
A first merging line for merging hydraulic oil from the third pump to a discharge line of the first pump;
A second merging line for merging the hydraulic oil from the third pump to the discharge line of the second pump;
When the pressure in the head side chamber of the arm cylinder is equal to or lower than a preset set pressure, the discharge from the third pump is preferentially performed with respect to the discharge line of the second pump as compared with the discharge line of the first pump. In order to guide the hydraulic oil, the opening area of the first merging line is limited to a preset limiting opening area, and when the pressure in the head side chamber of the arm cylinder exceeds the set pressure, the first merging line And an opening adjusting valve that operates so that the opening area of the opening is wider than the limited opening area. The hydraulic circuit according to claim 1,
The opening adjusting valve operates such that the opening area of the first merge line increases as the pressure in the head side chamber of the arm cylinder increases in a state where the pressure in the head side chamber of the arm cylinder exceeds the set pressure. Hydraulic circuit. The hydraulic circuit according to claim 1 or 2,
A boom cylinder for rotating the boom relative to the machine body of the construction machine that rotatably supports the boom;
A boom side line for guiding hydraulic oil from the first merging line to the boom cylinder;
The pressure when the pressure in the head side chamber of the arm cylinder exceeds the reference pressure compared to the opening area of the boom side line when the pressure in the head side chamber of the arm cylinder is equal to or lower than a preset reference pressure. And an opening change valve operable to limit an opening area of the boom side line. The hydraulic circuit according to claim 3,
The opening change valve operates so that the opening area of the boom side line becomes smaller as the pressure in the head side chamber of the arm cylinder increases in a state where the pressure in the head side chamber of the arm cylinder exceeds the reference pressure. , Hydraulic circuit. The hydraulic circuit according to claim 3 or 4,
The opening adjustment valve and the opening changing valve are hydraulic circuits each constituted by a pilot-type switching valve that operates according to the pressure of hydraulic oil in the head side chamber of the arm cylinder.

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