Hydraulic circuit

Abstract

To provide a hydraulic circuit capable of increasing an operation speed of an actuator.SOLUTION: A hydraulic circuit 1 comprises: a first pump 3, a second pump 4, and a third pump 6; a first unloading passage 41 and a first supply passage 42 connected to the first pump 3; a second unloading passage 43 and a second supply passage 44 connected to the second pump 4; a third unloading passage 61 and a third supply passage 62 connected to the third pump 6; and a plurality of control valves 15 to 17 provided in the middle of the first unloading passage 41 and the second unloading passage 43. Based on the operation of a boom control valve 15 selected from the plurality of control valves 15 to 17, hydraulic oil for the third pump 6 is supplied to the boom control valve 15 via the first supply passage 42 and the second supply passage 44.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a hydraulic circuit. [Background technology]

[0002] Some hydraulic circuits for construction machinery are known to have a detection mechanism for negative control installed at the most downstream of the unloading passage. The low pressure selection valve of the detection mechanism outputs the lower pressure of the working fluid in the unloading passage as the negative control pressure by operating a spool with hydraulic oil passing at the most downstream. The output negative control pressure is used by a pump regulator in the variable displacement pump to control the swash plate of the variable displacement pump, thereby changing the discharge volume of the variable displacement pump. When the spool of the low pressure selection valve operates, the hydraulic oil at the most downstream decreases, the negative control pressure falls, and the discharge volume of the variable displacement pump increases.

[0003] Also, among hydraulic circuits equipped with a detection mechanism for negative control, there are known ones that are equipped with a fixed displacement hydraulic pump in addition to a variable displacement pump. By providing a fixed displacement hydraulic pump in the hydraulic circuit, for example, it is possible to make up for a lack of flow rate when operating an actuator for a work machine with the fixed displacement hydraulic pump (for example, see Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-153399 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the above-mentioned hydraulic circuit, if the hydraulic oil discharged from the fixed displacement hydraulic pump is merged into the unloading passage, the negative control pressure increases and the low pressure selection valve does not operate normally. If the hydraulic oil discharged from the fixed displacement hydraulic pump is merged into the supply passage, the merged hydraulic oil has nowhere to go, and the fixed displacement hydraulic pump is relieved. For this reason, the entire amount of hydraulic oil discharged from the fixed displacement hydraulic pump cannot be supplied to the actuator for the work machine. Therefore, the operating speed of the actuator for the work machine is determined by the hydraulic oil discharged from the variable displacement pump, so there is a limit to the operating speed of the actuator for the work machine.

[0006] The present invention provides a hydraulic circuit that can increase the actuation speed of an actuator. [Means for solving the problem]

[0007] As a means for solving the above problems, the present invention has the following configuration. A hydraulic circuit according to one aspect of the present invention includes a first pump, a second pump, and a third pump each discharging a working fluid, a first unloading passage and a first supply passage connected to the first pump, a second unloading passage and a second supply passage connected to the second pump, a third unloading passage and a third supply passage connected to the third pump, and a plurality of control valves provided midway through the first unloading passage and the second unloading passage for controlling the drive of an actuator, and based on the operation of a desired control valve selected from the plurality of control valves, the working fluid discharged from the third pump is supplied to the desired control valve via the first supply passage and the second supply passage.

[0008] With this configuration, the working fluid discharged from the third pump can be supplied to the desired control valve through the first supply passage connected to the first pump and the second supply passage connected to the second pump based on the operation of the desired control valve. Therefore, the working fluid discharged from the third pump can be merged with the working fluid discharged from the first pump and the second pump to the actuator driven and controlled by the desired control valve. This allows the operating speed of the actuator to be increased by increasing the amount of working fluid supplied to the actuator.

[0009] In the above configuration, the control system may include a junction valve arranged downstream of the third unloading passage and in the third supply passage, the first supply passage, and the second supply passage, an operation unit that applies a pilot pressure to drive the junction valve, a pilot passage connected to the operation unit and in which the pilot pressure is generated, and a tank passage leading to a tank, wherein the junction valve has a first switching position and a second switching position that can be switched based on the pilot pressure, the first switching position having a first passage that communicates the third unloading passage with the tank passage, and a second passage that communicates the third supply passage with the first supply passage and the second supply passage, and the second switching position having a third passage that blocks the third unloading passage and communicates the third supply passage with the first supply passage and the second supply passage, the pilot passage is branched into the operation unit where the pilot pressure is applied to the junction valve and a second pilot passage connected to the tank, and an opening of the second pilot passage is changed based on an operation of the desired control valve.

[0010] A hydraulic circuit according to another aspect of the present invention includes a first pump, a second pump, and a third pump each discharging a working fluid, a first unloaded passage and a first supply passage connected to the first pump, a second unloaded passage and a second supply passage connected to the second pump, a third unloaded passage and a third supply passage connected to the third pump, a plurality of control valves provided midway between the first unloaded passage and the second unloaded passage for controlling the drive of an actuator, a tank passage leading to a tank, and a junction valve for switching between connection and disconnection of the third unloaded passage and the tank passage. the merging valve includes an operating unit which drives the merging valve, and a detection mechanism for negative control provided at the most downstream of the first unloading passage and the second unloading passage, wherein the detection mechanism has a first throttle provided at the most downstream of the first unloading passage, a second throttle provided at the most downstream of the second unloading passage, and a low pressure selection valve which outputs the lower of the pressure of the working fluid upstream of the first throttle and the pressure of the working fluid upstream of the second throttle as a negative control pressure, and applies the negative control pressure to a second operating unit on the opposite side of the operating unit of the merging valve.

[0011] In this way, the hydraulic circuit is provided with a detection mechanism for negative control, and negative control pressure is applied to the second operating part on the opposite side of the operating part of the merging valve. Therefore, the pilot pressure applied to the merging valve can be suppressed by the negative control pressure. This makes it possible to gradually switch the third unloading passage and the tank passage from a connected state to a blocked state based on the operation of a desired control valve selected from a plurality of control valves. Therefore, during switching of the desired control valve, a part of the working fluid discharged from the third pump can be distributed to the tank passage. As a result, the working fluid discharged from the third pump can be gradually merged with the working fluid discharged from the first pump and the second pump. Therefore, it is possible to suppress the operating speed of the actuator from suddenly increasing during switching of the desired control valve.

[0012] Furthermore, the tank passage is blocked by switching the desired control valve. This makes it possible to prevent a portion of the working fluid discharged from the third pump from being distributed to the tank passage. This makes it possible to suitably merge the working fluid discharged from the third pump with the working fluid discharged from the first pump and the second pump. This makes it possible to increase the amount of working fluid supplied to the actuator and increase the operating speed of the actuator. Effect of the Invention

[0013] According to the present invention, the operating speed of the actuator can be increased. [Brief description of the drawings]

[0014] [Figure 1] 1 is a schematic configuration diagram of a construction machine according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a circuit diagram showing a hydraulic circuit according to the embodiment of the present invention. [Diagram 3] FIG. 11 is a circuit diagram showing a hydraulic circuit according to a modified example of the embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Next, a hydraulic circuit according to an embodiment of the present invention will be described with reference to the drawings.

[0016] <Construction machinery> FIG. 1 is a schematic configuration diagram of a construction machine 100 according to this embodiment. 1, the construction machine 100 is, for example, a hydraulic excavator. The construction machine 100 includes a revolving body 101 and a running body 102 provided below the revolving body 101. The traveling body 102 includes a dozer 107 provided in front of the traveling direction. The dozer 107 swings up and down relative to the traveling body 102.

[0017] The rotating body 101 rotates relative to the traveling body 102. The rotating body 101 includes a drive unit 1. The rotating body 101 includes a cab 103, a boom 104 having one end connected to the cab 103, an arm 105 having one end connected to the other end of the boom 104, and a bucket 106 connected to the other end of the arm 105.

[0018] The cab 103 supports an operator riding on the rotating structure 101. The boom 104 swings relative to the main body of the rotating structure 101. The arm 105 swings relative to the boom 104. The bucket 106 swings relative to the arm 105. In other words, the boom 104, the arm 105, the bucket 106, and the dozer 107 configure a working device of the construction machine 100.

[0019] For example, a main part of the drive unit 1 is provided inside the revolving body 101. Hereinafter, the drive unit 1 may be referred to as a "hydraulic circuit (an example of a hydraulic circuit in the claims) 1." Hydraulic oil (an example of a working fluid in the claims) supplied from the hydraulic circuit 1 drives the revolving body 101, the traveling body 102, the boom 104, the arm 105, the bucket 106, and the dozer 107, for example.

[0020] <Hydraulic circuit> Fig. 2 is a circuit diagram showing the hydraulic circuit 1 in this embodiment. In Fig. 2, the left side of the paper is referred to as the "left side" and the right side of the paper is referred to as the "right side". 1 and 2, the hydraulic circuit 1 includes a control valve 2, a first pump (an example of the first pump in the claims) 3 that is connected to the control valve 2 and discharges hydraulic oil, a second pump (an example of the second pump in the claims) 4, a third pump (an example of the third pump in the claims) 6, and a pilot pump 7, and a tank (an example of the tank in the claims) 8 in which the hydraulic oil is stored by returning the hydraulic oil. Hereinafter, the upstream side and downstream side may be referred to based on the flow of the hydraulic oil.

[0021] <Control valve> The control valve 2 includes, arranged in order from the upstream side, a dozer control valve 14, a swing control valve 13, a junction valve (an example of a junction valve in the claims) 18, a pair of travel control valves 11, 12, a boom control valve (an example of a control valve in the claims) 15, an arm control valve (an example of a control valve in the claims) 16, a bucket control valve (an example of a control valve in the claims) 17, and a detection mechanism (an example of a detection mechanism in the claims) 20.

[0022] The dozer control valve 14 is connected to a dozer cylinder 34 that drives a dozer 107. The dozer control valve 14 controls the drive of the dozer cylinder 34. The swing control valve 13 is connected to a swing motor 33 that drives the swing body 101 to swing. The swing control valve 13 controls the drive of the swing motor 33. The pair of travel control valves 11, 12 are respectively connected to a pair of travel motors 31, 32 that drive left and right crawlers provided on the traveling body 102. The pair of travel control valves 11, 12 control the drive of the corresponding travel motors 31, 32, respectively.

[0023] The boom control valve 15 is connected to a boom cylinder (an example of an actuator in the claims) 35 that drives the boom 104. The boom control valve 15 controls the drive of the boom cylinder 35. The arm control valve 16 is connected to an arm cylinder (an example of an actuator in the claims) that drives the arm 105. The arm control valve 16 controls the drive of the arm cylinder . The bucket control valve 17 is connected to a bucket cylinder (an example of an actuator in the claims) 37 that drives the bucket 106. The bucket control valve 17 controls the drive of the bucket cylinder 37.

[0024] <Pump> The first pump 3 and the second pump 4 are so-called split-flow type variable displacement pumps that discharge hydraulic oil through two systems. Therefore, in this embodiment, the first pump 3 and the second pump 4 are configured as one pump, but they may be configured as separate pumps. Therefore, to make the following explanation easier to understand, separate names such as the first pump 3 and the second pump 4 are used.

[0025] The first pump 3 and the second pump 4 each have, for example, a built-in pump regulator 5. The pump regulator 5 is connected to a low pressure selection valve 23, which will be described later. The pump regulator 5 controls the discharge amount of the first pump 3 and the second pump 4 by changing the inclination angle of a movable swash plate 5a based on the negative control pressure applied from the low pressure selection valve 23.

[0026] The first pump 3 is connected to a first unloading passage (an example of a first unloading passage in the claims) 41 and a first supply passage (an example of a first supply passage in the claims) 42 via a junction valve 18. The first unloading passage 41 is connected to the first supply passage 42 via a first passage 46. The second pump 4 is connected to a second unloading passage (an example of a second unloading passage in the claims) 43 and a second supply passage (an example of a second supply passage in the claims) 44 via a junction valve 18. The second unloading passage 43 is connected to the second supply passage 44 via a second passage 47.

[0027] A plurality of control valves, namely, a boom control valve 15, an arm control valve 16, and a bucket control valve 17, are provided in the first unloading passage 41 and the second unloading passage 43. A first supply passage 42 is connected to the boom control valve 15, the arm control valve 16, and the bucket control valve 17 via first passages 51, 52, and 53. In addition, a second supply passage 44 is connected to the boom control valve 15, the arm control valve 16, and the bucket control valve 17 via second passages 54, 55, and 56.

[0028] The third pump 6 is a fixed displacement hydraulic pump. In this embodiment, the third pump 6 is described as a fixed displacement hydraulic pump, but the third pump 6 may be a variable displacement hydraulic pump. The third pump 6 is connected to a third unloading passage (an example of a third unloading passage in the claims) 61 via the dozer control valve 14 and the swing control valve 13. In addition, the third pump 6 is connected to a third supply passage (an example of a third supply passage in the claims) 62. The third unloading passage 61 and the third supply passage 62 are connected to the junction valve 18.

[0029] The pilot pump 7 is also a fixed displacement hydraulic pump. The pilot pump 7 is connected to a first pilot passage (an example of a pilot passage in the claims) 64. A filter 65 is provided in the first pilot passage 64. In the first pilot passage 64, pilot pressure is generated by the hydraulic oil discharged from the pilot pump 7.

[0030] The first pilot passage 64 branches into a first operating section (an example of an operating section in the claims) 66 of the junction valve 18 and a second pilot passage (an example of a second pilot passage in the claims) 68. That is, the first operating section 66 is connected to the first pilot passage 64. The first operating section 66 generates pilot pressure in the first pilot passage 64 and applies the pilot pressure to the junction valve 18. As a result, the first operating section 66 drives the spool 18a of the junction valve 18 to the left with the pilot pressure. The second pilot passage 68 is connected to the tank 8 via a pilot tank passage 69.

[0031] The second pilot passage 68 is connected to the boom control valve 15, the arm control valve 16, and the bucket control valve 17, and is connected to the tank 8 via a pilot tank passage 69. The second pilot passage 68 is supplied with hydraulic oil from the first pilot passage 64 in which pilot pressure is generated. Hereinafter, the hydraulic oil in which pilot pressure is generated may be referred to as pilot oil.

[0032] The second pilot passage 68 returns pilot oil from the second pilot passage 68 to the tank 8 via the pilot tank passage 69 when the spools 15a, 16a, 17a of the boom control valve 15, the arm control valve 16, and the bucket control valve 17 are positioned in neutral positions. 2 shows the neutral positions of the spools 15a, 16a, and 17a. When the spools 15a, 16a, and 17a are disposed in the neutral positions, pilot pressure of the first pilot passage 64 is not generated in the first operating portion 66. In this state, the spool 18a of the junction valve 18 is disposed in a first switching position 18a1 shown in FIG. 2. A detailed description of the first switching position 18a1 will be given later.

[0033] Meanwhile, the second pilot passage 68 varies based on the operation of the spool of the desired control valve selected from, for example, the boom control valve 15 , the arm control valve 16 , and the bucket control valve 17 . In the following, in this embodiment, the spool 15a of the boom control valve 15 will be described as an example of the spool of the desired control valve. The same applies when the arm control valve 16 or the bucket control valve 17 is operated instead of the boom control valve 15. The same applies when two or more control valves selected from the boom control valve 15, the arm control valve 16, and the bucket control valve 17 are operated simultaneously.

[0034] In a state in which the spool 15a of the boom control valve 15 is driven (actuated) leftward from the neutral position (position shown in FIG. 2) to supply hydraulic oil to the head 35a side of the boom cylinder 35, the second pilot passage 68 is blocked by the spool 15a of the boom control valve 15. Here, when the second pilot passage 68 is blocked by the spool 15a of the boom control valve 15, the opening degree of the second pilot passage 68 changes based on the operation of the spool 15a. When the second pilot passage 68 is opened by the spool 15a of the boom control valve 15, the opening degree of the second pilot passage 68 changes based on the operation of the spool 15a.

[0035] By blocking the second pilot passage 68, the pilot pressure generated in the first pilot passage 64 is applied to the first operating unit 66. As a result, the pilot pressure applied to the first operating unit 66 drives the spool 18a of the merging valve 18 to the left. In this state, the spool 18a of the merging valve 18 is disposed in the second switching position 18a2. A detailed description of the second switching position 18a2 will be given later.

[0036] <Confluence valve> The junction valve 18 is disposed (provided) downstream of the third unloading passage 61, in the third supply passage 62, the first supply passage 42, and the second supply passage 44. The spool 18a of the junction valve 18 has a first switching position 18a1 (an example of the first switching position in the claims) that can be switched based on a pilot pressure applied from a first operating unit 66, and a second switching position 18a2 (an example of the second switching position in the claims). Fig. 2 shows a state in which the spool 18a is positioned at the first switching position 18a1.

[0037] The junction valve 18 is provided with a second operating part (an example of the second operating part in the claims) 67 on the opposite side of the first operating part 66. The second operating part 67 is connected to the low pressure selection valve 23 described below. The second operating part 67 suppresses the pilot pressure applied from the first operating part 66 by the negative control pressure applied from the low pressure selection valve 23.

[0038] The first switching position 18a1 has a first passage (an example of a first passage in the claims) 74 that communicates the third unloading passage 61 with the second tank passage (an example of a tank passage in the claims) 72. Furthermore, the first switching position 18a1 has a second passage (an example of a first passage in the claims) 75 that communicates the third supply passage 62 with the first supply passage 42 and the second supply passage 44. That is, when the spool 18a of the junction valve 18 is switched to the first switching position 18a1, the third unloading passage 61 communicates with the second tank passage 72 via the first passage 74. Furthermore, the third supply passage 62 communicates with the first supply passage 42 and the second supply passage 44 via the second passage 75. The second tank passage 72 communicates with the tank 8 via the first tank passage 71.

[0039] The second switching position 18a2 blocks the third unloading passage 61 from the second tank passage 72. Furthermore, the second switching position 18a2 has a third passage (an example of a third passage in the claims) 76 that communicates the third supply passage 62 with the first supply passage 42 and the second supply passage 44. That is, when the spool 18a of the junction valve 18 is switched to the second switching position 18a2, the third unloading passage 61 is blocked from the second tank passage 72 by the spool 18a. Furthermore, the third supply passage 62 communicates with the first supply passage 42 and the second supply passage 44 via the third passage 76.

[0040] When the spools 15a, 16a, 17a of the boom control valve 15, the arm control valve 16, and the bucket control valve 17 are disposed in the neutral position, the spool 18a of the junction valve 18 is switched (maintained) to the first switching position 18a1. Therefore, the third unloading passage 61 is connected to the tank 8 via the first passage 74, the second tank passage 72, and the first tank passage 71. As a result, the hydraulic oil discharged from the third pump 6 is returned to the tank 8 via the third unloading passage 61, the first passage 74, the second tank passage 72, and the first tank passage 71.

[0041] For example, when the spool 15a of the boom control valve 15 is driven to the left from the neutral position to be positioned so as to supply hydraulic oil to the head 35a side of the boom cylinder 35, the spool 18a of the junction valve 18 is switched to the second switching position 18a2. Specifically, as a result of the spool 15a of the boom control valve 15 being driven leftward from the neutral position, the opening degree of the second pilot passage 68 changes based on the operation of the spool 15a, and the second pilot passage 68 is blocked by the spool 15a. As a result, the pilot pressure of the second pilot passage 68 is applied to the first operating unit 66, and the spool 18a of the junction valve 18 is switched to the second switching position 18a2.

[0042] In this manner, simply by switching the spool 15a of the boom control valve 15, the spool 18a of the junction valve 18 is switched between the first switching position 18a1 and the second switching position 18a2. When the spool 18a is switched to the second switching position 18a2, the third unloading passage 61 is blocked by the spool 18a from the second tank passage 72. At this time, the opening degree of the second tank passage 72 gradually changes in response to the switching operation of the spool 18a of the junction valve 18.

[0043] As the third unloading passage 61 is blocked from the second tank passage 72, the hydraulic oil discharged from the third pump 6 flows as shown by arrow A through the third supply passage 62 and the third passage 76 to the first supply passage 42 and the second supply passage 44. That is, the hydraulic oil discharged from the third pump 6 can be merged with the hydraulic oil in the first supply passage 42 discharged from the first pump 3 and the hydraulic oil in the second supply passage 44 discharged from the second pump 4.

[0044] The hydraulic oil discharged from the first pump 3 and the third pump 6 which join at the first supply passage 42 is supplied from the boom control valve 15 to the head 35a side of the boom cylinder 35 via a first passage 51 as indicated by arrow B. In addition, the hydraulic oil discharged from the second pump 4 and the third pump 6 which join at the second supply passage 44 is supplied from the boom control valve 15 to the head 35a side of the boom cylinder 35 via a second passage 54 as indicated by arrow B. In this way, by providing the junction valve 18 in the hydraulic circuit 1, the hydraulic oil discharged from the third pump 6 can be supplied to the boom control valve 15 via the first supply passage 42 and the second supply passage 44 based on the operation of the boom control valve 15.

[0045] <Detection mechanism> A detection mechanism 20 for negative control is provided at the most downstream of the first unloading passage 41 and the second unloading passage 43. The detection mechanism 20 has a first throttle (an example of the first throttle in the claims) 21 provided at the most downstream of the first unloading passage 41, a second throttle (an example of the second throttle in the claims) 22 provided at the most downstream of the second unloading passage 43, and a low pressure selection valve (an example of the low pressure selection valve in the claims) 23 provided upstream of the first throttle 21 and the second throttle 22. A first relief valve 24 is provided upstream of the first throttle 21. A second relief valve 25 is provided upstream of the second throttle 22.

[0046] The low pressure selection valve 23 outputs the lower of the pressure of the hydraulic oil on the upstream side of the first orifice 21 and the pressure of the hydraulic oil on the upstream side of the second orifice 22 as the negative control pressure. For this reason, the negative control pressure becomes zero (0), for example, when the spool 15a of the boom control valve 15 is at a full stroke. Also, the negative control pressure becomes high when the spools 15a, 16a, 17a of the boom control valve 15, arm control valve 16, and bucket control valve 17 are in neutral positions.

[0047] The low pressure selection valve 23 is connected to the pump regulators 5 of the first pump 3 and the second pump 4, and to a second operating unit 67 on the opposite side of the first operating unit 66 of the junction valve 18. That is, the low pressure selection valve 23 applies a negative control pressure to the pump regulator 5 and the second operating unit 67. By applying the negative control pressure to the second operating unit 67, the pilot pressure applied from the first operating unit 66 is suppressed by the negative control pressure.

[0048] For example, when the negative control pressure is zero (0), the pump regulator 5 changes the inclination angle of the movable swash plate 5a so that the discharge rates of the first pump 3 and the second pump 4 are maximized. In addition, when the negative control pressure is high, the pump regulator 5 changes the inclination angle of the movable swash plate 5a so that the discharge rates of the first pump 3 and the second pump 4 are minimized.

[0049] As described above, according to the hydraulic circuit 1 in the embodiment described above, the hydraulic oil discharged from the third pump 6 can be supplied to the boom control valve 15 via the first supply passage 42 and the second supply passage 44 based on the operation of the boom control valve 15. The first pump 3 is connected to the first supply passage 42. The second supply passage 44 is connected to the second pump 4. For this reason, in addition to the hydraulic oil discharged from the first pump 3 and the second pump 4, the hydraulic oil discharged from the third pump 6 can be merged on the head 35a side of the boom cylinder 35 whose drive is controlled by the boom control valve 15. Thereby, by increasing the amount of hydraulic oil supplied to the head 35a side of the boom cylinder 35, the operating speed of the boom cylinder 35 (that is, the actuator) can be increased.

[0050] In the above-described embodiment, the opening degree of the second pilot passage 68 is changed based on the operation of the spool 15a provided in the boom control valve 15, and the opening degree of the second tank passage 72 is changed by switching the spool 18a of the junction valve 18. Specifically, for example, while the spool 18a of the merging valve 18 is being switched from the first switching position 18a1 to the second switching position 18a2, the opening of the second tank passage 72 can be gradually reduced. This allows the hydraulic oil released (flowing) to the second tank passage 72 to be gradually reduced. This allows the hydraulic oil discharged from the third pump 6 to be smoothly merged and distributed (supplied and distributed) into the hydraulic fluid in the first supply passage 42 connected to the first pump 3 and the hydraulic oil in the second supply passage 44 connected to the second pump 4.

[0051] The hydraulic circuit 1 includes a detection mechanism 20 for negative control. In the junction valve 18, a negative control pressure is applied from the low pressure selection valve 23 of the detection mechanism 20 to a second operation part 67 on the opposite side to the first operation part 66. Therefore, the pilot pressure applied to the first operation part 66 of the junction valve 18 can be suppressed by the negative control pressure applied to the second operation part 67. This allows the spool 18a of the junction valve 18 to be gradually switched from the first switching position 18a1 to the second switching position 18a2 based on the operation of the spool 15a of the boom control valve 15. That is, the third unloading passage 61 and the second tank passage 72 can be gradually switched from a connected state to a blocked state. Therefore, the opening degree of the second tank passage 72 can be gradually reduced.

[0052] As a result, while the boom control valve 15 is being switched, a portion of the hydraulic oil discharged from the third pump 6 can be distributed to the second tank passage 72. Therefore, the hydraulic oil discharged from the third pump 6 can be gradually merged with the hydraulic oil discharged from the first pump 3 and the second pump 4. Therefore, while the boom control valve 15 is being switched, it is possible to prevent the operating speed of the boom cylinder 35 from suddenly increasing.

[0053] Furthermore, by switching the spool 18a of the junction valve 18 to the second switching position 18a2, the second tank passage 72 is blocked by the spool 18a. This makes it possible to prevent a portion of the hydraulic oil discharged from the third pump 6 from being distributed to the second tank passage 72. This makes it possible to suitably merge the hydraulic oil discharged from the third pump 6 with the hydraulic oil discharged from the first pump 3 and the second pump 4. Therefore, the amount of hydraulic oil supplied to the head 35a side of the boom cylinder 35 can be increased, thereby making it possible to increase the operating speed of the boom cylinder 35.

[0054] [Variations] Next, a hydraulic circuit 80 (one example of a hydraulic circuit in the claims) according to a modification of the present embodiment will be described with reference to Fig. 3. In the hydraulic circuit 80 according to the modification, the same or similar members as those in the hydraulic circuit 1 of the above-described embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted. FIG. 3 is a circuit diagram showing a hydraulic circuit 80 according to a modified example of the present embodiment. 3, a hydraulic circuit 80 of the modified example is configured such that the merging valve 18 provided in the hydraulic circuit 1 of the above-described embodiment is replaced with another merging valve (an example of the merging valve in the claims) 82. The other configurations of the hydraulic circuit 80 of the modified example are similar to those of the hydraulic circuit 1 of the above-described embodiment.

[0055] The spool 82a of the junction valve 82 has a first switching position 82a1 (an example of the first switching position in the claims) that can be switched based on the pilot pressure applied from the first operating unit 66, and a second switching position 82a2 (an example of the second switching position in the claims). The first switching position 82a1 is similar to the first switching position 18a1 in the above-mentioned embodiment. The second switching position 82a2 is obtained by providing a fourth passage 84 in the second switching position 18a2 in the above-mentioned embodiment.

[0056] In the junction valve 82, when the spool 82a is switched to the second switch position 82a2, the third unloading passage 61 is blocked from the second tank passage 72 by the spool 82a. Furthermore, the third supply passage 62 communicates with the first supply passage 42 and the second supply passage 44 via a third passage 76. In addition, the first pump 3 and the second pump 4 communicate with the first supply passage 42 via a fourth passage 84. Therefore, the hydraulic circuit 80 of the modified example provides the same functions and effects as the hydraulic circuit 1 of the above-described embodiment.

[0057] The present invention is not limited to the above-described embodiment and modifications, but includes various modifications to the above-described embodiment and modifications without departing from the spirit of the present invention.

[0058] For example, in the above embodiment, the construction machine 100 has been described as being, for example, a hydraulic excavator. An example has been described in which the above-described hydraulic circuit 1 is applied to the construction machine 100. However, the present invention is not limited to this, and the above-described hydraulic circuit 1 can be applied to various construction machines, or to machines other than construction machines.

[0059] In the above embodiment, the boom control valve 15, the arm control valve 16, and the bucket control valve 17 are used as examples of the multiple control valves, but the hydraulic circuit 1 may be applied to other control valves. The control valve 2 has been described as including, in order from the upstream side, a dozer control valve 14, a swing control valve 13, a junction valve 18, a pair of travel control valves 11 and 12, a boom control valve 15, an arm control valve 16, a bucket control valve 17, and a detection mechanism 20. However, the order of each part can be changed as appropriate. Also, each of the control valves 11 to 17 may be used for other driving purposes.

[0060] In the above embodiment, hydraulic oil is exemplified as the working fluid. However, the present invention is not limited to this, and may be applied to a working fluid other than hydraulic oil. The working fluid is not limited to a liquid, and may be a gas.

[0061] In addition, the components of the above-described embodiment may be replaced with well-known components without departing from the spirit of the present invention. Also, the above-described modified examples may be combined.

[0062] Among the embodiments disclosed in this specification, those that are composed of multiple objects may be integrated, and conversely, those that are composed of one object may be divided into multiple objects. Regardless of whether they are integrated or not, it is sufficient that they are configured to achieve the object of the invention. [Explanation of symbols]

[0063] 1,80...hydraulic circuit, 2...control valve, 3...first pump, 4...second pump, 6...third pump, 8...tank, 15...boom control valve (one of a plurality of control valves), 16...arm control valve (one of a plurality of control valves), 17...bucket control valve (one of a plurality of control valves), 18,82...junction valve, 18a1,82a1...first switching position, 18a2,82a2...second switching position, 20...detection mechanism, 21...first throttle, 22...second throttle, 23...low pressure selection valve, 35...boom cylinder (actuator ), 36... arm cylinder (actuator), 37... bucket cylinder (actuator), 41... first unloading passage, 42... first supply passage, 43... second unloading passage, 44... second supply passage, 61... third unloading passage, 62... third supply passage, 64... first pilot passage (pilot passage), 66... ​​first operating section (operating section), 67... second operating section, 68... second pilot passage, 72... second tank passage (tank passage), 74... first passage, 75... second passage, 76... third passage

Claims

1. a first pump, a second pump, and a third pump each discharging a working fluid; a first unloading passage and a first supply passage connected to the first pump; a second unloading passage and a second supply passage connected to the second pump; a third unloading passage and a third supply passage connected to the third pump; a plurality of control valves provided in the first unloading passage and the second unloading passage for controlling the actuation of the actuator; Equipped with supplying the working fluid discharged from the third pump to a desired control valve via the first supply passage and the second supply passage based on an operation of a desired control valve selected from the plurality of control valves. Hydraulic circuit.

2. a merging valve disposed downstream of the third unloading passage and in the third supply passage, the first supply passage, and the second supply passage; An operation unit that applies a pilot pressure to drive the junction valve; a pilot passage connected to the operation unit and through which the pilot pressure is generated; a tank passageway leading to the tank; Equipped with the junction valve has a first switching position and a second switching position that can be switched based on the pilot pressure, the first switching position has a first passageway that communicates the third unloading passageway and the tank passageway, and a second passageway that communicates the third supply passageway with the first supply passageway and the second supply passageway, the second switching position has a third passage that blocks the third unloading passage and communicates the third supply passage with the first supply passage and the second supply passage, the pilot passage is branched into the operation section where the pilot pressure is applied to the junction valve and a second pilot passage connected to the tank, The opening of the second pilot passage is changed based on the desired operation of the control valve.

2. The hydraulic circuit of claim 1.

3. a first pump, a second pump, and a third pump each discharging a working fluid; a first unloading passage and a first supply passage connected to the first pump; a second unloading passage and a second supply passage connected to the second pump; a third unloading passage and a third supply passage connected to the third pump; a plurality of control valves provided in the first unloading passage and the second unloading passage for controlling the actuation of the actuator; a tank passageway leading to the tank; a merging valve that switches between connecting and blocking the third unloading passage and the tank passage; An operation unit that drives the junction valve; a detection mechanism for a negative control provided at the most downstream of the first unloading passage and the second unloading passage; Equipped with The detection mechanism includes: a first throttle provided at the most downstream position of the first unloading passage; a second throttle provided at the most downstream side of the second unloading passage; a low pressure selection valve that outputs a lower pressure of the working fluid on the upstream side of the first throttle and the working fluid on the upstream side of the second throttle as a negative control pressure; having The negative control pressure is applied to a second operating part on the opposite side to the operating part of the junction valve. Hydraulic circuit.

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