KR102542812B1 - Hydraulic circuit - Google Patents

Abstract

A hydraulic circuit capable of performing an operation (particularly a lowering operation) of a supporting member such as a boom with high energy efficiency is provided.
The hydraulic circuit 10 includes a selector valve 40 that communicates with the head side chamber 84 and switches the flow path 11 according to the pressure of hydraulic fluid from the head side chamber 84, and the head side chamber 84. and a connection passage 23 communicating the rod-side chamber 83. The selector valve 40 blocks communication between the hydraulic pressure source 12 and the rod-side chamber 83 when the pressure of hydraulic oil from the head-side chamber 84 is equal to or higher than the switching pressure.

Description

Hydraulic circuit {HYDRAULIC CIRCUIT}

The present invention relates to a hydraulic circuit connected to a hydraulic cylinder.

The boom of the hydraulic excavator is driven up and down in a substantially vertical direction under the influence of gravity. In consideration of the driving characteristics of such a boom, various types of hydraulic circuits have been proposed as hydraulic circuits connected to hydraulic cylinders for driving the boom.

For example, in the energy saving device for construction machinery described in Patent Document 1, a control valve (direction selector valve) for controlling the supply of pressurized oil to a boom cylinder is provided, and a negative control orifice is provided in the flow path leading to the tank. , a sensor is provided on the upstream side of the negative control orifice. In this energy saving device, based on the negative control pressure detected by the sensor, the number of revolutions of an engine that drives a hydraulic pump is controlled, and energy saving is achieved.

Further, in the boom regeneration circuit of a hydraulic excavator described in Patent Document 2, at the boom lowering position of the direction control valve, an orifice is provided in the tank return passage on the boom bottom side, and an orifice is provided in the supply passage to the boom rod side. It is installed. Further, a regeneration flow path that communicates the tank return flow path and the supply flow path is provided, and a check valve is interposed in the regeneration flow path. According to this regeneration circuit, during the boom lowering operation, since the return oil from the boom bottom side can be returned to the boom rod side through the regeneration flow passage by increasing the pressure by the orifice, the supply oil from the hydraulic pump can be reduced. .

Further, in the hydraulic circuit described in Patent Literature 3, when the boom is lowered in a state in which a force resisting the lowering of the boom is not acting, the first switching valve opens the first center bypass flow path to operate the first hydraulic pump. While reducing the discharge amount, discharged oil from the extension-side oil chamber is supplied to the cylinder contraction-side oil chamber via the regeneration circuit. On the other hand, when a force resisting the descending of the boom is acting, the first center bypass passage is closed by the first switching valve and the pump discharge amount increases.

Japanese Unexamined Patent Publication No. 2007-333017 Japanese Unexamined Patent Publication No. 10-089317 Japanese Unexamined Patent Publication No. 11-247236

In the conventional hydraulic circuit described above, devises such as suppressing the supply amount of hydraulic oil supplied from a hydraulic source (hydraulic pump) during the lowering operation of the boom have been made, but further improvements for simplifying the configuration, reducing cost, and saving energy there is room for

For example, in a device that controls the output of hydraulic oil of a hydraulic pump based on a detection result of a sensor, such as the energy saving device of Patent Document 1, the installation of the sensor is essential, so the device configuration is complicated and the cost is high. In addition, in the regeneration circuit of Patent Document 2, even when the boom can be lowered using its own weight, for example, when the boom is lowered while the bucket is in the air, the boom cylinder (especially the boom rod side) from the hydraulic pump Oil is supplied to In this way, since supplying unnecessary hydraulic oil from the hydraulic pump to the boom cylinder causes loss of energy, optimum energy saving is not always achieved. Also in the hydraulic circuit of Patent Literature 3, when the boom is lowered in a state in which the force resisting the lowering of the boom is not acting, the hydraulic oil from the hydraulic pump is supplied to the boom cylinder, resulting in loss of energy.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a hydraulic circuit capable of performing an operation (particularly a lowering operation) of a support member such as a boom with high energy efficiency.

One aspect of the present invention is a hydraulic circuit connected to a hydraulic cylinder having a hydraulic source for supplying hydraulic oil to a flow path, a piston rod supporting a support member driven in the vertical direction, a head side chamber and a rod side chamber, the head side A selector valve communicating with the chamber and switching a flow path according to the pressure of the hydraulic fluid from the head chamber, and a connection path communicating the head chamber and the rod chamber, the selector valve comprising: the pressure of the hydraulic fluid from the head chamber It relates to a hydraulic circuit that cuts off communication between a hydraulic pressure source and a rod-side chamber when the pressure is equal to or higher than the switching pressure.

The selector valve may communicate the hydraulic pressure source and the rod-side chamber when the hydraulic oil pressure from the head-side chamber is lower than the switching pressure.

The connecting path may communicate the head side chamber with the tank passage, the rod side chamber may communicate with the tank passage, and communicate with the head side chamber via the tank passage and the connecting passage.

The selector valve may communicate a hydraulic pressure source to the bypass passage when the pressure of hydraulic fluid from the head side chamber is equal to or higher than the switching pressure.

The hydraulic pressure source may be a negative control type hydraulic pump that changes the supply amount of hydraulic oil according to the pressure of the hydraulic oil in the bypass passage.

The hydraulic circuit may further include a directional selector valve for switching a flow path between the hydraulic source and the hydraulic cylinder, and the selector valve may be provided inside the directional selector valve.

The support member may be a boom.

ADVANTAGE OF THE INVENTION According to this invention, the operation|movement (especially lowering operation|movement) of support members, such as a boom, can be performed with high energy efficiency.

1 is a circuit diagram showing an example of a circuit configuration of a hydraulic circuit, and shows a state in which the directional control valve for booms is disposed in a neutral position and the directional control valve for arms is disposed in a neutral position.
2 is a circuit diagram showing a circuit configuration example of a hydraulic circuit, showing a state in which the directional control valve for a boom is disposed in a reverse driving position and the directional control valve for an arm is disposed in a neutral position, and the boom is in an airborne state. show the case
Fig. 3 is a circuit diagram showing an example of the circuit configuration of the hydraulic circuit, showing a state in which the directional control valve for booms is disposed in the reverse driving position and the directional control valve for arms is disposed in the reverse driving position.
4 is a circuit diagram showing an example of the circuit configuration of the hydraulic circuit, showing a state in which the directional control valve for the boom is disposed in the reverse drive position and the directional control valve for the arm is disposed in the neutral position, and the boom is in a grounded state. show the case
Fig. 5 is a partial cross-sectional view showing an example of a directional control valve and a selector valve for a boom, showing a state in which the boom is in a grounded state and the directional control valve for a boom is disposed in a neutral position.
Fig. 6 is a partial cross-sectional view showing an example of a directional control valve and a selector valve for a boom, showing a state in which the boom is in an airborne state and the directional control valve for the boom is disposed in a reverse drive position.
Fig. 7 is a partial cross-sectional view showing an example of a directional control valve and a selector valve for a boom, showing a state in which the boom is in a grounded state and the directional control valve for a boom is disposed in a reverse drive position.
Fig. 8 is a partial sectional view showing an example of a directional control valve for a boom and a selector valve, showing a state in which the directional control valve for a boom is disposed at a forward drive position.

EMBODIMENT OF THE INVENTION Embodiment of this invention is described with reference to drawings. In addition, elements shown in each drawing may include elements whose sizes and scales are different from actual ones for ease of understanding.

Hereinafter, a case in which the present invention is applied to a hydraulic circuit for driving control of a hydraulic excavator (particularly, a boom) will be described. However, the present invention can be effectively applied to a hydraulic circuit for driving control of a hydraulic cylinder having a piston rod supporting a support member driven in a vertical direction other than the boom, and the application target of the present invention is boom driving control It is not limited to the hydraulic circuit for.

1 to 4 are circuit diagrams showing an example of a circuit configuration of a hydraulic circuit 10 according to an embodiment of the present invention. 1 shows a state in which the directional control valve 30 for booms is disposed at the neutral position b and the directional control valve 31 for arms is disposed at the neutral position b. 2 and 4 show a state in which the directional control valve 30 for the boom is disposed in the reverse drive position c and the directional control valve 31 for the arm is disposed in the neutral position b, and FIG. 2 shows the boom 71 ) shows the case where the bucket 73 and the arm 72 are in a state away from the ground (hereinafter also referred to as "in the air"), and FIG. 4 shows the boom 71 with the bucket 73 and the arm A case in a state of being in contact with the ground through (72) (hereinafter also referred to as a "grounded state") is shown. 3 shows a state where the directional control valve 30 for booms is disposed at the reverse drive position c and the directional control valve 31 for arms is disposed at the reverse drive position c.

1 to 4, the flow path configuration is shown as a circuit diagram, while the hydraulic excavator 70 (especially the boom 71, arm 72 and bucket 73, etc.) is shown as an external view. Therefore, in FIGS. 1-4, although the hydraulic cylinder 75 for arms is shown in both a circuit diagram and an external view, these point out the same hydraulic cylinder 75 for arms.

The hydraulic circuit 10 shown in FIGS. 1 to 4 is connected to the hydraulic source 12, the hydraulic cylinder 74 for booms, and the hydraulic cylinder 75 for arms, and the hydraulic source 12 and the hydraulic cylinder 74 for booms. ) and a directional selector valve 30 for a boom that switches the flow path 11 between the arms, and a direction selector valve 31 for arms that switches the flow path 11 between the oil pressure source 12 and the hydraulic cylinder 75 for arms. . In this specification, the term flow passage 11 is a generic term for passages through which hydraulic oil flows, and for example, branch passages 11b and 11c described later, a tank passage 21, a bypass passage 22, and a connecting passage ( 23), the negative control flow path 24, and passages for hydraulic oil in the directional control valves 30 and 31 also constitute the flow path 11.

The directional selector valve 30 for booms and the directional selector valve 31 for arms are comprised by the spool valve. The directional selector valves 30 and 31 shown in FIGS. 1 to 4 switch the flow path 11 according to the pilot hydraulic pressure applied to the spool, but may be configured with other valve elements (such as an electromagnetic drive type spool valve). . In addition, although a directional control valve for a bucket is installed between the hydraulic source 12 and the hydraulic cylinder 76 for a bucket, the directional control valve for a bucket is omitted in FIGS. 1 to 4 in order to simplify the overall configuration and facilitate understanding. In the following, a detailed description of driving control of the directional control valve for buckets and the hydraulic cylinder 76 for buckets will be omitted. However, the way of connecting the directional control valve for buckets and the hydraulic cylinder 76 for buckets to the oil passage 11 and the way of supplying hydraulic oil can be made similar to those of the directional control valve 31 for arms and the hydraulic cylinder 75 for arms.

The hydraulic source 12 is constituted by a variable displacement hydraulic pump that supplies hydraulic oil to the oil passage 11, and can increase or decrease the amount of hydraulic oil supplied to the oil passage 11 under the control of the regulator 13. The hydraulic pressure source 12 of the present embodiment is the pressure of the hydraulic oil in the negative control flow passage 24 connected to the bypass passage 22 (in particular, the second bypass passage 22b) communicating with the tank 14 (that is, the second bypass passage 22b). , the pressure of the hydraulic oil in the second bypass flow path 22b) is configured by a negative control type hydraulic pump that changes the supply amount of the hydraulic oil. For example, as the pressure of the hydraulic oil in the second bypass passage 22b and the negative control passage 24 increases due to an increase in the flow rate of the hydraulic oil flowing through the second bypass passage 22b, the regulator 13 operates as a hydraulic source ( 12) to reduce the supply of hydraulic oil. Meanwhile, as the pressure of the hydraulic oil in the bypass passage 22 and the negative control passage 24 decreases due to the decrease in the flow rate of the hydraulic oil flowing through the second bypass passage 22b, the regulator 13 operates from the hydraulic pressure source 12. Increases the supply of hydraulic oil.

The flow path 11 extending from the hydraulic source 12 is a flow path 11a (hereinafter also referred to as “main flow path”) extending toward the directional control valve 30 for a boom, and diverging from this main flow path 11a. It includes two oil passages (hereinafter also referred to as "branch oil passages") 11b and 11c, and the main oil passage 11a and the branch oil passages 11b and 11c are connected in parallel to the hydraulic pressure source 12. One branch passage 11b is intended to communicate with the bypass passage 22 (particularly the first bypass passage 22a) through the directional control valve 30 for the boom, and the operation of the directional control valve 30 for the boom Depending on the state, communication between the branch flow path 11b and the bypass passage 22 and blocking are controlled. In addition, the other branch oil passage 11c is intended to communicate with the hydraulic cylinder 75 for arms via the directional control valve 31 for arms, and according to the operating state of the directional control valve 31 for arms, the branch oil passage 11c Communication and blocking between the and the arm hydraulic cylinder 75 are controlled.

The hydraulic cylinder 74 for the boom has a piston rod 81 and a cylinder tube 82. The piston rod 81 includes a piston portion 81a disposed in the cylinder tube 82 and a rod portion 81b integrally provided with the piston portion 81a and extending from the inside to the outside of the cylinder tube 82. ) has A boom 71 is rotatably connected to one end of the rod portion 81b, and the piston rod 81 supports the boom 71 from below in the vertical direction. By increasing the protruding amount of the piston rod 81 from the cylinder tube 82, the boom 71 is driven upward, and by reducing the protruding amount of the piston rod 81 from the cylinder tube 82, the boom 71 is drive down The inner space of the cylinder tube 82 is partitioned into a rod-side chamber 83 and a head-side chamber 84 via the piston portion 81a. The piston portion 81a is formed between the rod side chamber 83 and the head side chamber 84 so that hydraulic oil does not leak between the rod side chamber 83 and the head side chamber 84 in the cylinder tube 82. It is installed so that the inside of the cylinder tube 82 is movable, sealing each.

The hydraulic cylinder 75 for arms is basically configured similarly to the hydraulic cylinder 74 for booms described above, and includes a movably installed piston rod 75a, a variable capacity rod side chamber 75b and a head side chamber 75c have In addition, the hydraulic cylinder 76 for a bucket is basically configured similarly to the hydraulic cylinder 74 for a boom and the hydraulic cylinder 75 for an arm described above, although illustration as a circuit diagram is omitted. It has a rod-side chamber and a head-side chamber of

The hydraulic circuit 10 (particularly, the directional control valve 30 for booms) of the present embodiment is provided with a connecting path 23, and the head side in a state where the directional control valve 30 for booms is disposed at the reverse driving position c The chamber 84 and the rod-side chamber 83 communicate with each other through a connecting passage 23 . That is, the head side chamber 84 communicates with the tank passage 21 connected to the tank 14 via the connecting passage 23 formed in the directional control valve 30 for booms. On the other hand, the rod-side chamber 83 communicates with the tank passage 21 without passing through the direction change valve 30 for the boom. Therefore, the rod-side chamber 83 and the head-side chamber 84 communicate with each other or are blocked from each other through the tank passage 21 and the connecting passage 23 according to the driving state of the direction change valve 30 for the boom.

A line relief makeup valve 43 is installed in the flow path 11 between the tank passage 21 and the rod-side chamber 83. The line relief make-up valve 43 includes a check valve 41 and a pressure control valve 45 installed in parallel to the flow path 11 on the tank passage 21 side and the flow path 11 on the rod side chamber 83 side. ). The check valve 41 of the line relief make-up valve 43 permits the flow of hydraulic oil from the tank passage 21 side toward the rod-side chamber 83 side, but from the rod-side chamber 83 side to the tank passage 21 side. ) side is not allowed to flow. The pressure control valve 45 of the line relief make-up valve 43 operates on the rod-side chamber 83 side when the hydraulic fluid pressure in the flow path 11 on the rod-side chamber 83 side is greater than a predetermined valve opening pressure. Although the oil passage 11 and the oil passage 11 on the tank passage 21 side are communicated, when the hydraulic oil pressure in the oil passage 11 on the rod side chamber 83 side is equal to or less than the predetermined valve opening pressure, the rod side chamber 83 The communication between the flow path 11 on the ) side and the flow path 11 on the tank passage 21 side is interrupted.

When the hydraulic oil pressure in the oil passage 11 on the tank passage 21 side is greater than the hydraulic oil pressure in the oil passage 11 on the rod side chamber 83 side, the check valve 41 of the line relief makeup valve 43 is turned on. Through this, hydraulic oil flows from the flow path 11 on the tank passage 21 side to the flow path 11 on the rod side chamber 83 side. On the other hand, the pressure of the hydraulic oil in the oil passage 11 on the rod-side chamber 83 side is greater than the pressure of the hydraulic oil in the oil passage 11 on the tank passage 21 side, and the pressure control valve 45 of the line relief makeup valve 43 ), flow of hydraulic fluid between the flow path 11 on the rod side chamber 83 side and the flow path 11 on the tank passage 21 side is performed by the line relief make-up valve 43. Blocked. And the pressure of the hydraulic oil in the oil passage 11 on the rod side chamber 83 side is higher than the pressure of the hydraulic oil in the oil passage 11 on the tank passage 21 side, and the pressure control valve 45 of the line relief makeup valve 43 When it is greater than the valve opening pressure of , the pressure control valve 45 opens, and hydraulic oil flows from the flow path 11 on the side of the rod side chamber 83 to the flow path 11 on the side of the tank passage 21 .

In this way, the line relief make-up valve 43 has a function of supplying hydraulic oil from the flow path 11 on the tank passage 21 side to the flow path 11 on the rod side chamber 83 side while preventing reverse flow, and When the pressure of the hydraulic oil in the oil passage 11 on the (83) side becomes excessive, the hydraulic oil is allowed to escape from the oil passage 11 on the rod side chamber 83 side to the oil passage 11 on the tank passage 21 side, and the rod side It also has a function of preventing the pressure of the hydraulic fluid in the chamber 83 from becoming excessive. Therefore, the valve opening pressure of the pressure control valve 45 of the line relief make-up valve 43 is within the upper limit of the allowable pressure of the working oil in the rod-side chamber 83 and the flow path 11 on the rod-side chamber 83 side. determined on the basis of

As described above, the rod side chamber 83 communicates with the tank passage 21 through the line relief makeup valve 43 . On the other hand, when the directional control valve 30 for the boom is disposed at the reverse driving position c, the connecting passage 23 communicates the head side chamber 84 with the tank passage 21. Therefore, when the directional control valve 30 for the boom is disposed at the reverse drive position c, the head side chamber 84 and the rod side chamber 83 form a flow path including the connecting passage 23 and the tank passage 21. 11 and the line relief make-up valve 43 communicate with each other. In particular, by providing the line relief make-up valve 43, the pressure of the hydraulic oil discharged from the head side chamber 84 to the tank passage 21 via the connecting passage 23 and the pressure of the hydraulic oil in the rod side chamber 83 are reduced. The flow of hydraulic fluid between the tank passage 21 (and hence the head chamber 84) and the rod chamber 83 is appropriately adjusted according to the size relationship and the pressure of the hydraulic fluid in the rod-side chamber 83. can

The hydraulic circuit 10 also has a selector valve 40 . In the hydraulic circuit 10 shown in FIGS. 1-4, the selector valve 40 is provided in the inside of the directional control valve 30 for booms. In a state where the directional control valve 30 for the boom is disposed at the reverse driving position c, the selector valve 40 communicates with the head side chamber 84 via the flow passage 11 (particularly the connecting passage 23), and the head The oil passage 11 is switched according to the pressure of the hydraulic fluid from the side chamber 84 (in Figs. 1 to 4, the pressure of the hydraulic fluid in the connecting passage 23). For example, when the pressure of hydraulic oil supplied from the head side chamber 84 to the selector valve 40 (that is, the pressure of the hydraulic oil in the connecting passage 23) is equal to or higher than a predetermined switching pressure, the selector valve 40 operates as a hydraulic pressure source. Communication between (12) and the rod-side chamber 83 is cut off (see reference sign "e" in Fig. 2). On the other hand, when the pressure of the hydraulic oil supplied from the head side chamber 84 to the selector valve 40 (that is, the pressure of the hydraulic oil in the connecting passage 23) is lower than the switching pressure, the selector valve 40 is operated by the hydraulic pressure source 12 ) and the rod-side chamber 83 are brought into communication (refer to symbol “f” in FIG. 4).

In addition, the selector valve 40 directs the hydraulic source 12 to the bypass passage 22 (particularly, when the pressure of the hydraulic oil from the head side chamber 84 is equal to or higher than the switching pressure (see reference numeral “e” in FIG. 2). 1 bypass passage 22a), and when the pressure of the hydraulic oil from the head side chamber 84 is lower than the switching pressure, the communication between the hydraulic source 12 and the bypass passage 22 is cut off (FIG. See the symbol “f” in 4). The bypass passage 22 is a flow path 11 communicating with the tank 14 . The tank 14 connected to the bypass passage 22 and the tank 14 connected to the tank passage 21 described above are constituted by the same tank. A directional control valve 31 for arms is provided in the bypass passage 22 shown in FIGS. 1 to 4 , and the bypass passage 22 is a first bypass upstream of the directional control valve 31 for arms. It divides into the passage 22a and the 2nd bypass flow path 22b on the downstream side rather than the directional control valve 31 for arms. Both ends of the first bypass passage 22a are opened and closed by the direction change valve 30 for the boom and the direction change valve 31 for the arm, respectively. Moreover, one end of the 2nd bypass flow path 22b is connected to the directional control valve 31 for arms, and the other end is connected to the tank 14. One end of the second bypass passage 22b is opened and closed by the female direction change valve 31 .

In the hydraulic circuit 10 shown in Figs. 1 to 4, a check valve 41, an orifice 42, a pressure control valve 45 and other mechanisms are further provided as appropriate. For example, check valves 41 are provided in the main flow passage 11a and the branch passage 11c. Further, an orifice 42 is provided in the connecting passage 23, and this orifice 42 is on the downstream side of the connecting passage 23 to be connected to the selector valve 40 (that is, on the tank 14 side). is installed on Therefore, when the selector valve 40 switches the flow path 11 (see reference numerals “e” and “f” shown in FIGS. 1 to 4), the pressure is increased by the orifice 42 provided in the connecting passage 23. It is performed according to the pressure of the working oil of the connection path 23 raised. Further, a discharge control valve 44 having an orifice 42 and a pressure control valve 45 is provided in the second bypass flow path 22b. The orifice 42 of the discharge control valve 44 is provided on the downstream side (that is, on the tank 14 side) of the portion connected to the negative control flow path 24 in the second bypass flow path 22b. Therefore, the control of the hydraulic pressure source 12 by the regulator 13 is performed according to the pressure of the hydraulic fluid in the negative control passage 24 whose pressure is increased by the orifice 42 provided in the second bypass passage 22b. The pressure control valve 45 of the discharge control valve 44 is opened and closed according to the pressure of the hydraulic fluid in the second bypass passage 22b, and the pressure of the hydraulic fluid in the second bypass passage 22b is higher than the predetermined valve opening pressure. It opens in the large case, increasing the flow rate of hydraulic oil towards the tank 14.

Next, the operation of the hydraulic circuit 10 described above will be described.

First, as shown in FIG. 1, the case where both the directional selector valve 30 for booms and the directional selector valve 31 for arms are arrange|positioned at the neutral position b is demonstrated. In this case, the communication between the hydraulic source 12 and the hydraulic cylinder 74 for the boom is blocked by the direction change valve 30 for the boom, and the communication between the hydraulic source 12 and the hydraulic cylinder 75 for the arm changes the direction for the arm It is blocked by valve 31. That is, the direction change valve 30 for the boom blocks communication between the head side chamber 84 and the tank passage 21, and between the rod side chamber 83 and the hydraulic source 12 (especially the main flow path 11a). is blocked, and the branch passage 11b and the first bypass passage 22a are brought into communication. In addition, the directional control valve 31 for arms blocks the communication between the rod side chamber 75b of the hydraulic cylinder 75 for arms and the tank passage 21, and diverges from the head side chamber 75c of the hydraulic cylinder 75 for arms. Communication between the flow passages 11c is cut off, and the first bypass passage 22a and the second bypass passage 22b are brought into communication.

In this case, the hydraulic source 12 is connected to the first bypass passage 22a via the branch oil passage 11b, and the first bypass passage 22a is connected to the second bypass via the female directional control valve 31. It is connected to the flow path 22b. Therefore, the oil pressure source 12 communicates with the tank 14 and the negative control oil passage 24 via the branch oil passage 11b and the bypass passage 22 . Therefore, when the directional control valve 30 for the boom and the directional control valve 31 for the arm are originally disposed at the neutral position b, the amount of hydraulic oil flowing through the bypass passage 22 increases, and the pressure of the hydraulic oil in the negative control passage 24 increases. it rises Therefore, the hydraulic source 12 suppresses the supply amount of hydraulic oil under the control of the regulator 13 . As a result, the amount of hydraulic oil flowing through the bypass passage 22 is reduced, the pressure of the hydraulic oil in the negative control passage 24 is lowered, and energy saving is achieved.

Next, as shown in FIG. 2, the directional control valve 30 for the boom is disposed at the reverse drive position c, the directional control valve 31 for the arm is disposed at the neutral position b, and the boom 71 is disposed at the bucket 73 And the case of being in the air with the arm 72 will be described. In this case, the head side chamber 84 communicates with the connecting passage 23 and communicates with the tank passage 21 through the connecting passage 23 . In addition, under the influence of gravity, the piston rod 81 is lowered by the weight of the boom 71 and the like, and the pressure of the hydraulic oil in the head chamber 84 increases, and the connection passage 23 communicating with the head chamber 84 The pressure of the hydraulic fluid becomes higher than the switching pressure of the selector valve 40. Therefore, the selector valve 40 takes the state indicated by reference numeral "e" in Figs. Also, the hydraulic pressure source 12 is communicated with the first bypass passage 22a via the branch oil passage 11b. On the other hand, the arm directional control valve 31 blocks the communication between the rod side chamber 75b of the arm hydraulic cylinder 75 and the tank passage 21, and the head side chamber 75c of the arm hydraulic cylinder 75 and Communication between the branch passages 11c is cut off, and the first bypass passage 22a and the second bypass passage 22b are brought into communication.

In this case, the high-pressure hydraulic oil discharged from the head side chamber 84 flows toward the tank 14 via the connecting passage 23 and the tank passage 21, and the connecting passage 23 and the tank passage 21 and is supplied (ie, regenerated) to the hydraulic cylinder 74 for the boom via the line relief make-up valve 43 (particularly the check valve 41). By this, the shortage of the amount of hydraulic oil and the pressure in the rod-side chamber 83, whose volume increases as the piston portion 81a descends, is compensated for, and the boom 71 can descend using its own weight. . On the other hand, the hydraulic oil discharged from the hydraulic source 12 is sent toward the tank 14 via the bypass passage 22, and the supply amount of the hydraulic oil from the negative control type hydraulic source 12 is suppressed to a low level to save energy. can promote

Next, as shown in FIG. 3, the directional control valve 30 for the boom is disposed at the reverse drive position c, the directional control valve 31 for the arm is also disposed at the reverse drive position c, and the boom 71 is disposed at the bucket 73 ) and the case in the air with the arm 72 will be described. In this case, similarly to the case shown in FIG. 2 described above, the head side chamber 84 communicates with the tank passage 21 through the connecting passage 23, and the pressure of the hydraulic fluid in the connecting passage 23 is applied to the selector valve ( 40), the selector valve 40 assumes a state indicated by reference numeral "e" in FIGS. 1 to 4. Therefore, the directional control valve 30 for the boom blocks the communication between the rod side chamber 83 and the hydraulic source 12 (particularly the main oil passage 11a), and also provides the hydraulic pressure source 12 through the branch oil passage 11b. It communicates with the bypass passage 22. On the other hand, the directional control valve 31 for arms communicates the rod-side chamber 75b and the tank passage 21, and communicates the head-side chamber 75c and the hydraulic pressure source 12 (particularly the branch oil passage 11c), Communication between the first bypass passage 22a and the second bypass passage 22b is blocked.

In this case, the high-pressure hydraulic oil discharged from the head side chamber 84 passes through the connecting path 23, the tank passage 21, and the line relief make-up valve 43, similarly to the case shown in FIG. It is supplied to the cylinder 74, and the boom 71 descends using its own weight. On the other hand, part of the hydraulic fluid discharged from the hydraulic source 12 is supplied to the head side chamber 75c through the branch oil passage 11c. In addition, the hydraulic fluid discharged from the rod side chamber 75b is sent to the tank passage 21, and then discharged to the tank 14 or supplied to the rod side chamber 83 via the line relief make-up valve 43. . In this way, while the dead weight of the boom 71 or the like is used to drive the hydraulic cylinder 74 for the boom, the high-pressure hydraulic oil discharged from the head side chamber 84 and the rod side chamber 75b is used, so that the hydraulic pressure source 12 ) does not need to be used for driving the hydraulic cylinder 75 for arms. Therefore, the hydraulic oil newly supplied from the hydraulic source 12 can be used efficiently with respect to the drive of the hydraulic cylinder 75 for arms, and energy saving can be achieved. In addition, since the second bypass flow path 22b is blocked by the female directional control valve 31, the amount of hydraulic oil flowing through the second bypass flow path 22b is reduced and the pressure of the hydraulic oil in the negative control flow path 24 increases. Lowered, the negative control hydraulic pressure source 12 increases the supply of hydraulic oil. In this way, the hydraulic fluid in a sufficient amount and at a sufficient pressure can be supplied to the head side chamber 75c via the branch oil passage 11c.

Next, as shown in FIG. 4, the directional control valve 30 for the boom is disposed at the reverse driving position c, the directional control valve 31 for the arm is disposed at the neutral position b, and the boom 71 is disposed at the bucket 73 And the case of being in a grounded state through the arm 72 will be described. In this case, the head side chamber 84 communicates with the connecting passage 23 and communicates with the tank passage 21 through the connecting passage 23 . However, since the boom 71 is in a grounded state, the weight of the boom 71 or the like cannot be used basically in driving the piston rod 81 down. Therefore, the pressure of the hydraulic oil in the head side chamber 84 is relatively small, and the pressure of the hydraulic oil in the connecting passage 23 communicating with the head side chamber 84 is smaller than the switching pressure of the selector valve 40. Therefore, the selector valve 40 takes the state indicated by the reference numeral "f" in FIG. 4 to make the hydraulic source 12 communicate with the rod-side chamber 83 via the main oil passage 11a, and furthermore, the hydraulic source 12 ) (particularly the branch passage 11b) and the bypass passage 22 (particularly the first bypass passage 22a). On the other hand, the arm directional control valve 31 blocks the communication between the rod side chamber 75b of the arm hydraulic cylinder 75 and the tank passage 21, and the head side chamber 75c of the arm hydraulic cylinder 75 and Communication between the branch passages 11c is cut off, and the first bypass passage 22a and the second bypass passage 22b are brought into communication.

When the hydraulic circuit 10 assumes the state shown in FIG. 4 described above, the hydraulic oil discharged from the hydraulic source 12 is supplied to the rod-side chamber 83, and the pressure of the hydraulic oil in the rod-side chamber 83 increases to the head. The pressure of the hydraulic oil in the side chamber 84 is greater, and the piston portion 81a receives a downward force, and the boom 71 is lowered. The head side chamber 84 communicates with the tank passage 21 through the connection passage 23, but since the pressure of the hydraulic oil discharged from the head side chamber 84 is smaller than the pressure of the hydraulic oil in the rod side chamber 83, the head side chamber 84 Hydraulic oil is not sent from the side chamber 84 to the rod side chamber 83. Therefore, the hydraulic fluid discharged from the head side chamber 84 is sent toward the tank 14 via the connecting path 23 and the tank passage 21. In addition, the check valve 41 of the line relief make-up valve 43 prevents the hydraulic oil from flowing backward from the rod side chamber 83 toward the tank 14, the tank passage 21 and the head side chamber 84. . Also, the hydraulic source 12 is blocked from the bypass passage 22 (particularly, the first bypass passage 22a) by the directional control valve 30 for the boom. Therefore, the amount of hydraulic oil flowing through the second bypass flow path 22b decreases, the pressure of the hydraulic oil in the negative control flow path 24 decreases, and the negative control hydraulic pressure source 12 increases the supply amount of hydraulic oil. As a result, hydraulic oil in a sufficient amount and at a sufficient pressure can be supplied to the rod-side chamber 83 via the main oil passage 11a.

In addition, detailed description is omitted, but when the directional control valve 30 for the boom is disposed at the forward drive position a, the hydraulic pressure source 12 communicates with the head side chamber 84 of the hydraulic cylinder 74 for the boom via the main oil passage 11a And, the rod-side chamber 83 of the boom hydraulic cylinder 74 communicates with the tank passage 21, and communication between the branch passage 11b and the first bypass passage 22a is blocked. In this case, the hydraulic oil discharged from the hydraulic source 12 is supplied to the head side chamber 84, and the hydraulic oil discharged from the rod side chamber 83 flows out into the tank passage 21, so that the boom 71 is driven by a piston rod It rises with (81). On the other hand, when the directional control valve 31 for arms is disposed at the forward drive position a, the hydraulic pressure source 12 communicates with the rod side chamber 75b of the hydraulic cylinder 75 for arms via the branch oil passage 11c, and the hydraulic cylinder for arms The head side chamber 75c of 75 communicates with the tank passage 21, and communication between the first bypass passage 22a and the second bypass passage 22b is blocked. In this case, the hydraulic oil discharged from the hydraulic source 12 is supplied to the rod-side chamber 75b, and the hydraulic oil discharged from the head-side chamber 75c flows out into the tank passage 21, causing the piston rod 75a to protrude. The amount is reduced, and the arm 72 swings in the upward direction using the connection point with the boom 71 as a fulcrum. In addition, the bypass passage 22 is blocked by the directional control valve 30 for the boom and/or the directional control valve 31 for the arm, and the negative control hydraulic pressure source 12 increases the supply of hydraulic oil to provide a sufficient amount and Hydraulic oil of sufficient pressure can be supplied to the head side chamber 84 and/or the rod side chamber 75b.

Next, specific configuration examples of the directional control valve 30 for booms and the selector valve 40 are described.

5 to 8 are partial cross-sectional views showing examples of the directional control valve 30 and selector valve 40 for booms. 5 shows a state in which the boom 71 is in the grounded state and the directional control valve 30 for the boom is disposed in the neutral position b. Fig. 6 shows a state in which the boom 71 is in the air and the directional control valve 30 for the boom is disposed in the reverse drive position c. 7 shows a state in which the boom 71 is in the grounded state and the directional control valve 30 for the boom is disposed in the reverse drive position c. Fig. 8 shows a state in which the directional control valve 30 for booms is disposed at the forward driving position a. In addition, the directional control valve 30 and selector valve 40 for booms shown in FIGS. 5 to 8 are exactly the same as the directional control valve 30 and selector valve 40 for booms shown in FIGS. 1 to 4 described above. Although they do not coincide structurally and functionally, they roughly correspond to the boom directional control valve 30 and selector valve 40 shown in FIGS. 1 to 4 . Therefore, those skilled in the art can fully understand the structures and functions of the directional control valve 30 for booms and the selector valve 40 shown in Figs. 5 to 8 based on the following description.

The directional control valve 30 for booms shown in FIGS. 5 to 8 includes a spool 50 and a body portion 51 that holds the spool 50 on the inside so as to be slidable. Inside the spool 50, the selector valve 40 is slidably installed. The spool 50 is formed with a plurality of land portions and a plurality of cutouts (including a groove portion in the spool 50 in which the selector valve 40 is accommodated and a hole portion connecting the outside of the spool 50). Depending on the slide position of the spool 50 relative to the part 51, the passage 11 is switched. A plurality of land portions and a plurality of cutouts are also formed in the selector valve 40 , and the flow path 11 is switched according to the slide position of the selector valve 40 relative to the spool 50 .

In the body portion 51, a tank communication passage 52 communicating with the tank passage 21, a first actuator passage 53 communicating with the rod side chamber 83, and a bridge passage communicating with the hydraulic source 12 ( 58), the first upstream unloading passage 54 communicating with the branch passage 11b, the second upstream unloading passage 56, and the first downstream unloading passage 55 communicating with the first bypass passage 22a ), the second downstream unloading passage 57, and the second actuator passage 59 communicating with the head chamber 84 are formed. Although not shown, in the main body portion 51, via the second actuator passage 59, there is a tank that communicates with the tank 14 on the opposite side to the bridge passage 58 (rightward side in FIGS. 5 to 8). A communication channel is also formed.

The spool 50 is further formed with a connecting path 23 . One end of the connecting passage 23 (left end in FIGS. 5 to 8 ) communicates with one end of the selector valve 40 (right end in FIGS. 5 to 8 ), and the other end of the connecting passage 23 (Right ends of FIGS. 5 to 8 ) communicate with the cutout formed in the spool 50 . A switching spring 60 (elastic body) is provided at the other end of the selector valve 40 (the left end in Figs. 5 to 8). As will be described later, the slide position of the selector valve 40 is determined by the force of the hydraulic fluid from the connecting passage 23 acting on one end of the selector valve 40 and the other end of the selector valve 40. , is determined according to the elastic force of the switching spring 60. Therefore, the state in which hydraulic oil is not supplied from the connecting passage 23 to one end of the selector valve 40 or the force of the hydraulic oil from the connecting passage 23 acting on one end of the selector valve 40 is In a state where the elastic force of the switching spring 60 applied to the other end of the valve 40 is smaller, the selector valve 40 is pushed by the switching spring 60 and is disposed in the rightward position in FIGS. 5 to 8 .

For example, when the directional control valve 30 for a boom is disposed at the neutral position b (see FIG. 1 ), the directional control valve 30 for a boom and the selector valve 40 are disposed as shown in FIG. 5 . That is, through the land portion of the spool 50, the rod side chamber 83 is blocked from the bridge passage 58 and the tank communication passage 52, and the second actuator passage 59 communicates with the bridge passage 58 and the tank. furnace (not shown). On the other hand, the first upstream unload passage 54 and the first downstream unload passage 55 communicate with each other through the cutout portion of the spool 50 and the cutout portion of the selector valve 40, and the second upstream unload passageway 56 and the second downstream unloading passage 57 communicate with each other through the cutout of the spool 50. Therefore, hydraulic oil from the hydraulic source 12 is not supplied to either the rod-side chamber 83 or the head-side chamber 84, and the first upstream unloading passage 54 and the second upstream passage 54 pass through the branch passage 11b. It flows into the upstream unload passage 56 and flows out into the first bypass passage 22a via the first downstream unload passage 55 and the second downstream unload passage 57.

Also, when the directional control valve 30 for the boom is disposed in the neutral position b, the connecting passage 23 communicates with the head side chamber 84 via the second actuator passage 59. Therefore, the hydraulic oil from the head side chamber 84 flows into the connecting path 23 through the second actuator passage 59, and the selector valve 40 slides according to the pressure of the hydraulic oil in the connecting path 23. all. 5, the boom 71 is in a grounded state, the pressure of the hydraulic oil flowing from the head side chamber 84 to the connecting passage 23 is low, and the selector valve 40 is pressed by the switching spring 60 to move in the right direction. A case in which it is disposed is shown. However, when the boom 71 is in an air state and the pressure of the hydraulic oil flowing from the head side chamber 84 into the connecting passage 23 is high, the selector valve 40 operates on the hydraulic oil from the connecting passage 23. It is pushed and placed in the left direction. Also in this case, the rod-side chamber 83 is blocked from the bridge passage 58 and the tank communication passage 52, and the second actuator passage 59 is blocked from the bridge passage 58 and the tank communication passage (not shown). , The first upstream unload passage 54 and the first downstream unload passage 55 communicate with each other through the cutout of the spool 50 and the cutout of the selector valve 40, and the second upstream unload passage ( 56) and the second downstream unload passage 57 communicate with each other through the cutout of the spool 50.

On the other hand, when the boom 71 is in the air and the directional control valve 30 for the boom is disposed in the reverse drive position c (see Figs. 2 and 3), the directional control valve 30 and the spool 50 for the boom It is arranged as shown in FIG. 6 . That is, the spool 50 is disposed to the right of the position shown in FIG. 5 by the pilot pressure. In addition, hydraulic fluid from the head side chamber 84 flows into the connecting passage 23 via the second actuator passage 59, presses the selector valve 40 to compress the switching spring 60, and the selector valve 40 is placed at a position in the left direction of FIG. 6 . As a result, the first actuator passage 53 is blocked from the bridge passage 58 through the land portion of the spool 50 . In addition, the second actuator passage 59 is blocked from the bridge passage 58 through the land portion of the spool 50, and the tank communication passage (not shown) through the cutout portion of the spool 50 and the connecting passage 23 ) is connected to On the other hand, the first upstream unload passage 54 and the first downstream unload passage 55 communicate with each other through the cutout portion of the spool 50 and the cutout portion of the selector valve 40, and the second upstream unload passageway 56 and the second downstream unloading passage 57 communicate with each other through the cutout of the spool 50. Therefore, the hydraulic oil from the hydraulic source 12 is not supplied to either the rod-side chamber 83 or the head-side chamber 84, and the first upstream unloading passage 54 and the second upstream from the branch passage 11b. It flows into the side unloading passage 56 and flows out into the first bypass passage 22a through the first downstream unloading passage 55 and the second downstream unloading passage 57. On the other hand, the hydraulic fluid discharged from the head side chamber 84 flows into a tank communication passage (not shown) through the connecting passage 23, and flows into the tank communication passage indicated by reference numeral 52 in FIG. 6 from the tank communication passage. and is supplied (regenerated) to the rod-side chamber 83 from the tank communication passage 52 through the first actuator passage 53.

Further, when the boom 71 is in the grounded state and the directional control valve 30 for the boom is disposed in the reverse drive position c (see FIG. 4), the directional control valve 30 and the spool 50 for the boom are shown in FIG. 7 are placed as That is, the spool 50 is arranged at the position basically the same as the position shown in FIG. 6 with respect to the body part 51 by the pilot pressure. However, the force applied to the selector valve 40 by the hydraulic oil flowing into the connecting passage 23 from the head side chamber 84 through the second actuator passage 59 is ), the selector valve 40 is pushed down by the switching spring 60 and is disposed in the rightward position in FIG. 7 . As a result, the first actuator passage 53 communicates with the bridge passage 58 through the cutout portion of the spool 50 and the cutout portion of the selector valve 40 . In addition, the second actuator passage 59 is blocked from the bridge passage 58 through the land portion of the spool 50, and the tank communication passage (not shown) through the cutout portion of the spool 50 and the connection passage 23 connected to Meanwhile, the first upstream unload passage 54 and the first downstream unload passage 55 are blocked from each other through the land portion of the spool 50 and the land portion of the selector valve 40, and the second upstream unload passage ( 56) and the second downstream unload passage 57 are blocked from each other through the land portion of the spool 50. Therefore, hydraulic oil from the hydraulic source 12 is supplied to the rod-side chamber 83 through the bridge passage 58 and the first actuator passage 53, and the branch passage 11b is supplied from the first bypass passage 22a. Blocked. On the other hand, the hydraulic fluid discharged from the head side chamber 84 flows into a tank communication passage (not shown) through the connecting passage 23, and flows from the tank communication passage to a tank (not shown) (reference numeral 14 in FIGS. 1 to 4). 」 reference) flows toward.

Further, when the directional control valve 30 for booms is disposed at the positive drive position a, the directional control valve 30 for booms and the spool 50 are arranged as shown in FIG. 8 . That is, the spool 50 is disposed leftward from the position shown in FIG. 5 by the pilot pressure. Thereby, the rod-side chamber 83 communicates with the tank passage 21 via the first actuator passage 53 and the tank communication passage 52, and the head-side chamber 84 communicates with the bridge passage 58 and the second The first upstream unloading passage 54 and the second upstream unloading passage 56 communicate with the hydraulic power source 12 through the two actuator passages 59, respectively, the first downstream unloading passage 55 and the second It is blocked from the downstream unloading passage 57.

As described above, according to the hydraulic circuit 10, the directional control valve 30 for the boom, and the selector valve 40 described above, when the boom 71 in the air is driven down, the head side chamber 84 The high-pressure hydraulic oil discharged from is supplied to the rod-side chamber 83, and no new hydraulic oil is supplied from the hydraulic source 12 to the hydraulic cylinder 74 for the boom. Therefore, potential energy of the boom 71 or the like can be effectively used to lower the boom with high energy efficiency.

Further, the selector valve 40 brings the hydraulic pressure source 12 and the rod-side chamber 83 into communication with each other when the hydraulic oil pressure from the head-side chamber 84 is lower than the switching pressure of the selector valve 40 (FIG. 4). reference). In this case, even if the weight of the boom 71 or the like cannot be used to lower the piston rod 81, hydraulic oil (pressure oil) is supplied from the hydraulic source 12 to the rod-side chamber 83, so that the piston portion 81a The included piston rod 81 can be lowered. Therefore, for example, even when the bucket 73 of the hydraulic excavator 70 descends and grounds, and the pressure of the hydraulic oil from the head side chamber 84 is lower than the switching pressure of the selector valve 40, the hydraulic source 12 Since the piston rod 81 can be lowered by the hydraulic oil supplied to the rod-side chamber 83 from), the work of compacting the ground by the bucket 73 or lifting the gas of the hydraulic excavator 70 can be done efficiently.

In addition, this invention is not limited to the above-mentioned embodiment and modified example.

For example, in the embodiment described above, the selector valve 40 is provided inside the directional control valve 30 for booms, and the directional control valve 30 for booms and the selector valve 40 are integrally configured, but the boom direction The selector valve 40 may be installed outside the selector valve 30, and the boom directional selector valve 30 and the selector valve 40 may be configured separately from each other.

1 to 4 show a hydraulic circuit 10 mainly connected to the hydraulic cylinder 74 for booms and the hydraulic cylinder 75 for arms, but the hydraulic cylinder 76 for buckets and the hydraulic excavator 70 are shown. Other constituting hydraulic actuators (for example, hydraulic motors for driving that drive wheels (crawlers) and hydraulic motors for swings that swing and drive a structure above the crawler) may be connected to the hydraulic circuit 10. The connection aspect with respect to the hydraulic circuit 10 of these hydraulic actuators is not specifically limited. For example, even if a flow path extending from the hydraulic source 12 is branched and these branched flow paths connected in parallel to each other with respect to the hydraulic source 12 are connected to respective hydraulic actuators through a directional control valve such as a spool valve. do. Alternatively, a flow path branching from a bypass passage (refer to reference numeral 22 in FIGS. 1 to 4 ) communicating with the tank 14 may be connected to each hydraulic actuator via a directional control valve.

In addition, various modifications may be applied to each element of the above-described embodiments and modified examples. In addition, forms including components other than the above-described components may also be included in the embodiments of the present invention. In addition, a form in which some of the above-described components are not included may also be included in the embodiment of the present invention. In addition, a form including some constituent elements included in one embodiment of the present invention and some constituent elements included in other embodiments of the present invention may also be included in the embodiment of the present invention. Therefore, components included in each of the above-described embodiments and modified examples and embodiments of the present invention other than those described above may be combined, and forms according to such combinations may also be included in the embodiments of the present invention. In addition, the effects exhibited by the present invention are not limited to the above-mentioned effects, and unique effects according to the specific configuration of each embodiment can also be exhibited. In this way, various additions, changes, and partial deletions to each element described in the claims, specification, abstract, and drawings are possible without departing from the technical spirit and spirit of the present invention.

10: hydraulic circuit
11: Euro
11a: Main Euro
11b: quarter euro
11c: quarter euro
12: hydraulic source
13: regulator
14: tank
21: tank passage
22: bypass passage
22a: first bypass passage
22b: second bypass flow path
23: with connection
24: negative control euro
30: directional valve for boom
31: directional seated valve for arm
40: selector valve
41: check valve
42: orifice
43: line relief make-up valve
44: discharge control valve
45: pressure control valve
50: spool
51: body part
52: tank communication path
53: first actuator passage
54: first upstream unload passage
55: first downstream unload passage
56: second upstream unload passage
57: second downstream unload passage
58 Bridge passage
59: second actuator passage
60: transition spring
70: hydraulic excavator
71: boom
72 cancer
73 bucket
74: hydraulic cylinder for boom
75: hydraulic cylinder for arm
75a: piston rod
75b: rod-side chamber
75c: head side chamber
76: hydraulic cylinder for bucket
81: piston rod
81a: piston part
81b: loading part
82 cylinder tube
83: rod-side chamber
84: head side chamber
a: Jeonggu-dong location
b: neutral position
c: reverse drive position

Claims (7)

A hydraulic circuit connected to a hydraulic cylinder having a hydraulic source for supplying hydraulic fluid to a flow path, a piston rod supporting a support member driven in the vertical direction, a head side chamber and a rod side chamber,
a selector valve communicating with the head-side chamber and switching the flow path according to the pressure of the hydraulic fluid from the head-side chamber;
A connection path communicating the head-side chamber and the rod-side chamber is provided;
The hydraulic circuit according to claim 1 , wherein the selector valve cuts off communication between the hydraulic pressure source and the rod-side chamber when the pressure of the hydraulic oil from the head-side chamber is equal to or higher than the switching pressure. According to claim 1,
The hydraulic circuit according to claim 1 , wherein the selector valve communicates the hydraulic pressure source and the rod-side chamber when a pressure of the hydraulic oil from the head-side chamber is lower than the switching pressure. According to claim 1 or 2,
The connecting passage communicates the head side chamber with the tank passage,
The hydraulic circuit according to claim 1 , wherein the rod-side chamber communicates with the tank passage, and communicates with the head-side chamber through the tank passage and the connecting passage. According to claim 1 or 2,
The hydraulic circuit according to claim 1 , wherein the selector valve communicates the hydraulic pressure source to a bypass passage when a pressure of the hydraulic oil from the head side chamber is equal to or higher than the switching pressure. According to claim 4,
The hydraulic circuit according to claim 1 , wherein the hydraulic source is a negative control type hydraulic pump that changes the supply amount of the hydraulic oil according to the pressure of the hydraulic oil in the bypass passage. According to claim 1 or 2,
Further comprising a directional switching valve for switching the flow path between the hydraulic source and the hydraulic cylinder,
The hydraulic circuit, wherein the selector valve is installed inside the directional control valve. According to claim 1 or 2,
and the support member is a boom.

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