Hydraulic circuit

Abstract

The invention relates to a hydraulic circuit. The hydraulic circuit has a first pump, a second pump, a third pump, a first unloading passage, a first supply passage, a second unloading passage, a second supply passage, a third unloading passage, a third supply passage, and a plurality of control valves. On the basis of the operation of a desired control valve selected from the plurality of control valves, the hydraulic circuit supplies the working fluid discharged from the third pump to the desired control valve via the first supply passage and the second supply passage.

Description

Technical Field

[0001] The present invention relates to hydraulic circuits. Background Art

[0002] As a hydraulic circuit used in construction machinery, there is a known hydraulic circuit in which a detection mechanism for negative control is set at the most downstream of the unloading passage. The low-pressure selection valve of the detection mechanism operates the sliding column by using the working oil passing through the most downstream, and outputs the lower pressure of the working fluid in the unloading passage as the negative control pressure. The output negative control pressure is used to control the inclined plate of the variable capacity pump by using the pump regulator in the variable capacity pump, thereby changing the discharge volume of the variable capacity pump. If the sliding column of the low-pressure selection valve is operated, the working oil at the most downstream is reduced, the negative control pressure drops, and the discharge volume of the variable capacity pump increases.

[0003] In addition, as a hydraulic circuit having a detection mechanism for negative control, a hydraulic circuit having a fixed capacity hydraulic pump in addition to a variable capacity pump is also known. By having a fixed capacity hydraulic pump in a hydraulic circuit, for example, insufficient flow when operating an actuator for a working machine can be supplemented by the fixed capacity hydraulic pump (for example, refer to Patent Document 1).

[0004] Patent Document 1: Japanese Patent Application Publication No. 2020-153399

[0005] However, in the above hydraulic circuit, if the working oil ejected from the fixed capacity hydraulic pump is merged into the unloading passage, the negative control pressure increases and the low pressure selector valve cannot work normally. If the working oil ejected from the fixed capacity hydraulic pump is merged into the supply passage, the merged working oil has nowhere to go and the fixed capacity hydraulic pump will overflow. Therefore, the full amount of working oil ejected from the fixed capacity hydraulic pump cannot be supplied to the working machine actuator. Therefore, the working speed of the working machine actuator is determined by the working oil ejected from the variable capacity pump, so the working speed of the working machine actuator is limited. Summary of the invention

[0006] The present invention provides a hydraulic circuit capable of increasing the operating speed of an actuator.

[0007] As a means for solving the above-mentioned problems, the present invention has the following configuration.

[0008] A hydraulic circuit of one embodiment of the present invention comprises: a first pump; a second pump; a third pump; 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 disposed midway between the first unloading passage and the second unloading passage to perform drive control of an actuator. The first pump, the second pump, and the third pump respectively eject working fluids. Based on the action of a desired control valve selected from the plurality of control valves, the working fluid ejected from the third pump is supplied to the desired control valve via the first supply passage and the second supply passage.

[0009] With such a structure, the working fluid ejected from the third pump can be supplied to the desired control valve via the first supply passage connected to the first pump and the second supply passage connected to the second pump based on the desired control valve action. Therefore, in the actuator driven and controlled by the desired control valve, in addition to the working fluid ejected from the first pump and the second pump, the working fluid ejected from the third pump can also be merged. Thus, by increasing the working fluid supplied to the actuator, the operating speed of the actuator can be increased.

[0010] In the above structure, there may be: a merging valve disposed on the downstream side of the third unloading passage and disposed on the third supply passage, the first supply passage, and the second supply passage; an operating unit that applies a pilot pressure to the merging valve for driving the merging valve; a pilot passage that is connected to the operating unit and generates the pilot pressure; and a tank passage that is connected to the tank. The merging valve may also have a first switching position and a second switching position that can be switched based on the pilot pressure. The first switching position may also have a first passage that connects the third unloading passage with the tank passage, and a second passage that connects the third supply passage with the first supply passage and the second supply passage. The second switching position may also have a third passage that blocks the third unloading passage and connects the third supply passage with the first supply passage and the second supply passage. The pilot passage may also be branched into the operating unit that applies the pilot pressure to the merging valve and the second pilot passage connected to the tank. The opening degree of the second pilot passage may also be changed based on the desired action of the control valve.

[0011] A hydraulic circuit according to another embodiment of the present invention comprises: a first pump; a second pump; a third pump; 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 disposed in the middle of the first unloading passage and the second unloading passage to control the driving of an actuator; a tank passage connected to a tank; a merging valve to switch the connection and interruption between the third unloading passage and the tank passage; an operating unit to drive the merging valve; and a negative control detection mechanism disposed at the most downstream of the first unloading passage and the second unloading passage. The first pump, the second pump, and the third pump eject working fluids respectively. The detection mechanism comprises: a first throttle disposed at the most downstream of the first unloading passage; a second throttle disposed at the most downstream of the second unloading passage; and a low pressure selector valve to output the lower pressure of the working fluid pressure on the upstream side of the first throttle and the working fluid pressure on the upstream side of the second throttle as a negative control pressure. The negative control pressure is applied to a second operating portion of the merging valve on the side opposite to the operating portion.

[0012] In this way, the hydraulic circuit is constructed to have a detection mechanism for negative control, and a negative control pressure is applied to the second operating part on the side opposite to the operating part in the merging valve. Therefore, the pilot pressure applied to the merging valve can be suppressed by the negative control pressure. Thus, based on the action of the desired control valve selected from the plurality of control valves, the connection state between the third unloading passage and the tank passage can be gradually switched to the blocked state. Therefore, during the switching process of the desired control valve, a part of the working fluid ejected from the third pump can be distributed to the tank passage. As a result, the working fluid ejected from the third pump can be gradually merged with the working fluid ejected from the first pump and the second pump. Thus, during the switching process of the desired control valve, the working speed of the actuator can be suppressed from accelerating sharply.

[0013] Furthermore, by switching the desired control valve, the tank passage is blocked. Therefore, a part of the working fluid ejected from the third pump can be not distributed to the tank passage. Thus, the working fluid ejected from the third pump can be appropriately merged with the working fluid ejected from the first pump and the second pump. Therefore, the working fluid supplied to the actuator can be increased, and the operating speed of the actuator can be improved.

[0014] According to the aspect of the present invention, the operating speed of the actuator can be increased. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic structural diagram of a construction machine according to an embodiment of the present invention.

[0016] Figure 2 This is a circuit diagram showing a hydraulic circuit according to an embodiment of the present invention.

[0017] Figure 3 This is a circuit diagram showing a modified example of the hydraulic circuit according to the embodiment of the present invention.

[0018] Description of Reference Numerals

[0019] 1, 80: hydraulic circuit; 2: control valve; 3: first pump; 4: second pump; 6: third pump; 8: tank; 15: boom control valve (one of the plurality of control valves); 16: arm control valve (one of the plurality of control valves); 17: bucket control valve (one of the plurality of control valves); 18, 82: confluence 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 part (operating part); 67: second operating part; 68: second pilot passage; 72: second tank passage (tank passage); 74: first passage; 75: second passage; 76: third passage. DETAILED DESCRIPTION

[0020] Next, a hydraulic circuit according to an embodiment of the present invention will be described with reference to the drawings.

[0021] <Construction machinery>

[0022] Figure 1 It is a schematic configuration diagram of a construction machine 100 according to the present embodiment.

[0023] like Figure 1 As shown, the construction machine 100 is, for example, a hydraulic excavator. The construction machine 100 includes a revolving body 101 and a traveling body 102 provided below the revolving body 101. The traveling body 102 includes a bulldozer 107 provided forward in the traveling direction. The bulldozer 107 swings vertically relative to the traveling body 102.

[0024] The revolving body 101 revolves relative to the traveling body 102. The revolving body 101 has a driving device 1. The revolving body 101 has a cab 103, a boom 104 connected to the cab 103 at one end, an arm 105 connected to the other end of the boom 104 at one end, and a bucket 106 connected to the other end of the arm 105.

[0025] The operator's cab 103 supports an operator riding on the revolving structure 101. The boom 104 swings relative to the main body of the revolving structure 101. The arm 105 swings relative to the boom 104. The bucket 106 swings relative to the arm 105. That is, the boom 104, the arm 105, the bucket 106, and the dozer 107 constitute a working device of the construction machine 100.

[0026] The driving device 1 is mainly provided in the revolving body 101. Hereinafter, the driving device 1 is sometimes referred to as a "hydraulic circuit (an example of a hydraulic circuit in the claims) 1". The hydraulic oil (an example of a working fluid in the claims) supplied from the hydraulic circuit 1 drives, for example, the revolving body 101, the traveling body 102, the boom 104, the arm 105, the bucket 106, and the bulldozer 107.

[0027] <Hydraulic circuit>

[0028] Figure 2 is a circuit diagram showing a hydraulic circuit 1 according to this embodiment. Figure 2 In the description, 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”.

[0029] like Figure 1 , Figure 2 As shown, the hydraulic circuit 1 has a control valve 2, a first pump (an example of the first pump in the claim) 3, a second pump (an example of the second pump in the claim) 4, a third pump (an example of the third pump in the claim) 6, a pilot pump 7 and a tank (an example of the tank in the claim) 8.

[0030] The first pump 3, the second pump 4, and the third pump 6 are connected to the control valve 2. The first pump 3, the second pump 4, and the third pump 6 respectively discharge hydraulic oil. The hydraulic oil is refluxed and stored in the tank 8. Hereinafter, the upstream side and the downstream side may be referred to according to the flow of the hydraulic oil.

[0031] <Control valve>

[0032] The control valve 2 has a bulldozer control valve 14, a swing control valve 13, a merging valve (an example of a merging 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, a dipper 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, which are arranged in sequence from the upstream side.

[0033] The blade control valve 14 is connected to the blade cylinder 34 that drives the blade 107. The blade control valve 14 controls the driving of the blade cylinder 34.

[0034] The swing control valve 13 is connected to a swing motor 33 that swing-drives the swing body 101. The swing control valve 13 controls the driving of the swing motor 33.

[0035] The pair of travel control valves 11 and 12 are connected to a pair of travel motors 31 and 32 for driving left and right crawlers of the travel body 102. The pair of travel control valves 11 and 12 perform drive control of the corresponding travel motors 31 and 32, respectively.

[0036] 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 driving of the boom cylinder 35.

[0037] The arm control valve 16 is connected to an arm cylinder (an example of an actuator in the claims) 36 that drives the arm 105. The arm control valve 16 controls the driving of the arm cylinder 36.

[0038] 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 driving of the bucket cylinder 37.

[0039] <Pump>

[0040] The first pump 3 and the second pump 4 eject working oil from two systems, and are so-called split-flow variable capacity pumps. Therefore, in the present embodiment, the first pump 3 and the second pump 4 are composed of one pump, but they may also be composed of different pumps. Therefore, in order to facilitate the understanding of the following description, different names such as the first pump 3 and the second pump 4 are used.

[0041] For example, a pump regulator 5 is built into the first pump 3 and the second pump 4. The pump regulator 5 is connected to a low-pressure selector valve 23 described later. The pump regulator 5 changes the inclination angle of the movable swash plate 5a based on the negative control pressure applied from the low-pressure selector valve 23. Thus, the pump regulator 5 controls the discharge amount of the first pump 3 and the second pump 4.

[0042] 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 merging valve 18. The first unloading passage 41 is connected to the first supply passage 42 via a first passage 46.

[0043] 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 merging valve 18. The second unloading passage 43 is connected to the second supply passage 44 via a second passage 47.

[0044] A plurality of control valves, namely, the boom control valve 15, the arm control valve 16, and the bucket control valve 17, are provided in the middle of the first unloading passage 41 and the second unloading passage 43. The 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, the 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.

[0045] The third pump 6 is a fixed capacity hydraulic pump. In the present embodiment, the third pump 6 is described as a fixed capacity hydraulic pump, but the third pump 6 may also be a variable capacity 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 a bulldozer control valve 14 and a 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 a confluence valve 18.

[0046] 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 middle of the first pilot passage 64. The first pilot passage 64 generates a pilot pressure using hydraulic oil discharged from the pilot pump 7.

[0047] The first pilot passage 64 branches into a first operating portion (an example of an operating portion in the claims) 66 of the merging valve 18 and a second pilot passage (an example of a second pilot passage in the claims) 68. That is, the first pilot passage 64 is connected to the first operating portion 66. The first operating portion 66 generates a pilot pressure in the first pilot passage 64 and applies the pilot pressure to the merging valve 18. Thus, the first operating portion 66 drives the spool 18a of the merging valve 18 to the left side by the pilot pressure. The second pilot passage 68 is connected to the tank 8 via the pilot tank passage 69.

[0048] The second pilot passage 68 is connected to the boom control valve 15, the arm control valve 16, and the bucket control valve 17. The second pilot passage 68 is connected to the tank 8 via the pilot tank passage 69. The hydraulic oil of the first pilot passage 64 that generates the pilot pressure is supplied to the second pilot passage 68. Hereinafter, the hydraulic oil that generates the pilot pressure may be referred to as pilot oil.

[0049] When the spools 15a, 16a, 17a of the boom control valve 15, the arm control valve 16, and the bucket control valve 17 are arranged in the neutral position, the second pilot passage 68 returns the pilot oil of the second pilot passage 68 from the pilot tank passage 69 to the tank 8. Figure 21 shows the neutral position of the spools 15a, 16a, 17a. When the spools 15a, 16a, 17a are arranged in the neutral position, the 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 confluence valve 18 is arranged in the neutral position. Figure 2 The first switching position 18a1 is shown. The first switching position 18a1 will be described in detail later.

[0050] On the other hand, the second pilot passage 68 changes based on the action 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. Hereinafter, in the present embodiment, the spool 15a of the boom control valve 15 is described as an example of the desired control valve spool. The same applies to the case where the arm control valve 16 and the bucket control valve 17 are operated instead of the boom control valve 15. The same applies to the case where 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.

[0051] The spool 15a of the boom control valve 15 is moved from the neutral position ( Figure 2 The state in which the second pilot passage 68 is driven (operated) to the left side and the working oil is supplied to the head 35a side of the boom cylinder 35 (shown in the position shown in the figure) is described. In this state, the second pilot passage 68 is blocked by the spool 15a of the passive arm control valve 15. Here, when the second pilot passage 68 is blocked by the spool 15a of the passive arm control valve 15, the opening degree of the second pilot passage 68 changes based on the action of the spool 15a. When the second pilot passage 68 is opened by the spool 15a of the passive arm control valve 15, the opening degree of the second pilot passage 68 changes based on the action of the spool 15a.

[0052] The pilot pressure generated in the first pilot passage 64 is applied to the first operating portion 66 by blocking the second pilot passage 68. Therefore, the spool 18a of the merging valve 18 is driven to the left by the pilot pressure applied to the first operating portion 66. In this state, the spool 18a of the merging valve 18 is arranged in the second switching position 18a2. The details of the second switching position 18a2 will be described later.

[0053] <Merging valve>

[0054] The merging valve 18 is arranged (set) on the downstream side of the third unloading passage 61 and is arranged (set) in the third supply passage 62, the first supply passage 42, and the second supply passage 44. The spool 18a of the merging valve 18 has a first switching position (an example of the first switching position in the claims) 18a1 and a second switching position (an example of the second switching position in the claims) 18a2. In the first switching position, switching can be performed based on the pilot pressure applied from the first operating part 66. Figure 22 shows a state where the slide rod 18 a is located at the first switching position 18 a 1 .

[0055] In the confluence valve 18, a second operating part (an example of a second operating part in the claims) 67 is provided on the opposite side to the first operating part 66. The second operating part 67 is connected to the low pressure selector valve 23 described later. 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 selector valve 23.

[0056] The first switching position 18a1 has a first passage (an example of the first passage in the claims) 74 that connects the third unloading passage 61 with the second tank passage (an example of the tank passage in the claims) 72. Furthermore, the first switching position 18a1 has a second passage (an example of the first passage in the claims) 75 that connects 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 confluence valve 18 is switched to the first switching position 18a1, the third unloading passage 61 is connected to the second tank passage 72 via the first passage 74. Furthermore, the third supply passage 62 is connected to the first supply passage 42 and the second supply passage 44 via the second passage 75. The second tank passage 72 is connected to the tank 8 via the first tank passage 71.

[0057] 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 the third passage in the claims) 76 that connects 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 confluence 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 is connected to the first supply passage 42 and the second supply passage 44 via the third passage 76.

[0058] When the spools 15a, 16a, 17a of the boom control valve 15, the arm control valve 16, and the bucket control valve 17 are arranged in the neutral position, the spool 18a of the confluence valve 18 is switched (maintained) in 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 ejected from the third pump 6 flows back 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.

[0059] For example, when the spool 15a of the boom control valve 15 is driven leftward from the neutral position to be disposed at a position for supplying hydraulic oil to the head 35a side of the boom cylinder 35, the spool 18a of the merging valve 18 switches to the second switching position 18a2.

[0060] Specifically, the spool 15a of the boom control valve 15 is driven to the left from the neutral position, so that the opening of the second pilot passage 68 changes based on the movement of the spool 15a, and the second pilot passage 68 is blocked by the spool 15a. Therefore, the pilot pressure of the second pilot passage 68 is applied to the first operating part 66, and the spool 18a of the confluence valve 18 is switched to the second switching position 18a2.

[0061] In this way, only by switching the spool 15 a of the boom control valve 15 , the spool 18 a of the merging valve 18 is switched between the first switching position 18 a 1 and the second switching position 18 a 2 .

[0062] When the spool 18a 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. At this time, the opening degree of the second tank passage 72 gradually changes in accordance with the switching operation of the spool 18a of the merging valve 18.

[0063] Since the third unloading passage 61 is blocked from the second tank passage 72 , the hydraulic oil discharged from the third pump 6 flows to the first supply passage 42 and the second supply passage 44 as indicated by arrows A via the third supply passage 62 and the third passage 76 .

[0064] 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 .

[0065] The hydraulic oil ejected from the first pump 3 and the third pump 6 that merge in the first supply passage 42 is supplied from the boom control valve 15 to the head 35a side of the boom cylinder 35 via the first passage 51 as indicated by the arrow B. In addition, the hydraulic oil ejected from the second pump 4 and the third pump 6 that merge in the second supply passage 44 is supplied from the boom control valve 15 to the head 35a side of the boom cylinder 35 via the second passage 54 as indicated by the arrow B.

[0066] By providing the merging valve 18 in the hydraulic circuit 1 in this manner, 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 .

[0067] <Testing Agency>

[0068] A negative control detection mechanism 20 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, a second throttle (an example of the second throttle in the claims) 22, and a low-pressure selection valve (an example of the low-pressure selection valve in the claims) 23. The first throttle 21 is provided at the most downstream of the first unloading passage 41. The second throttle 22 is provided at the most downstream of the second unloading passage 43. The low-pressure selection valve 23 is provided on the upstream side of the first throttle 21 and the second throttle 22. A first overflow valve 24 is provided on the upstream side of the first throttle 21. A second overflow valve 25 is provided on the upstream side of the second throttle 22.

[0069] The low pressure selector valve 23 outputs the lower pressure of the working oil pressure on the upstream side of the first throttle valve 21 and the working oil pressure on the upstream side of the second throttle valve 22 as the negative control pressure. Therefore, the negative control pressure is zero (0) when the spool 15a of the boom control valve 15 is in full stroke, for example. In addition, the negative control pressure becomes high when the spools 15a, 16a, 17a of the boom control valve 15, the arm control valve 16, and the bucket control valve 17 are in the neutral position.

[0070] The low pressure selector valve 23 is connected to the pump regulators 5 of the first pump 3 and the second pump 4, and the second operating portion 67 of the confluence valve 18 on the side opposite to the first operating portion 66. That is, the low pressure selector valve 23 applies a negative control pressure to the pump regulators 5 and the second operating portion 67. By applying the negative control pressure to the second operating portion 67, the pilot pressure applied from the first operating portion 66 is suppressed by the negative control pressure.

[0071] The pump regulator 5 changes the inclination angle of the movable swash plate 5a when the negative control pressure is zero (0), for example, so that the discharge amount of the first pump 3 and the second pump 4 becomes maximum. 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 amount of the first pump 3 and the second pump 4 becomes minimum.

[0072] In this way, according to the hydraulic circuit 1 of the above-mentioned embodiment, the working oil ejected 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 action of the boom control valve 15. The first pump 3 is connected to the first supply passage 42. The second pump 4 is connected to the second supply passage 44. Therefore, in addition to the working oil ejected from the first pump 3 and the second pump 4, the working oil ejected from the third pump 6 can also be merged at the head 35a side of the boom cylinder 35 driven and controlled by the boom control valve 15.

[0073] Thus, by increasing the amount of hydraulic oil supplied to the head portion 35 a side of the boom cylinder 35 , the operating speed of the boom cylinder 35 (ie, the actuator) can be increased.

[0074] In the above embodiment, the opening degree of the second pilot passage 68 is changed based on the operation of the spool 15 a of the boom control valve 15 , and the opening degree of the second tank passage 72 is changed by switching the spool 18 a of the merging valve 18 .

[0075] Specifically, for example, in the process of switching the spool 18a of the merging valve 18 from the first switching position 18a1 to the second switching position 18a2, the opening of the second tank passage 72 can be gradually reduced. Therefore, the working oil released to (flowing to) the second tank passage 72 can be gradually reduced. As a result, the working oil ejected from the third pump 6 can be smoothly merged and distributed (supply distributed) to the working fluid of the first supply passage 42 connected to the first pump 3 and the working oil of the second supply passage 44 connected to the second pump 4.

[0076] The hydraulic circuit 1 has a detection mechanism 20 for negative control. In the merging valve 18, a negative control pressure is applied from the low pressure selector valve 23 of the detection mechanism 20 to the second operating part 67 on the side opposite to the first operating part 66. Therefore, the pilot pressure applied to the first operating part 66 of the merging valve 18 can be suppressed by the negative control pressure applied to the second operating part 67. Thus, the spool 18a of the merging valve 18 can be gradually switched from the first switching position 18a1 to the second switching position 18a2 based on the action of the spool 15a of the boom control valve 15. That is, the connection state of the third unloading passage 61 and the second tank passage 72 can be gradually switched to the blocked state. Therefore, the opening of the second tank passage 72 can be gradually reduced.

[0077] As a result, during the switching process of the boom control valve 15, a part of the working oil ejected from the third pump 6 can be distributed to the second tank passage 72. Therefore, the working oil ejected from the third pump 6 can be gradually merged with the working oil ejected from the first pump 3 and the second pump 4. Thus, during the switching process of the boom control valve 15, the working speed of the boom cylinder 35 can be suppressed from increasing rapidly.

[0078] Furthermore, by switching the spool 18a of the confluence valve 18 to the second switching position 18a2, the second tank passage 72 is blocked by the spool 18a. Therefore, a part of the working oil ejected from the third pump 6 can be not distributed to the second tank passage 72. Thus, the working oil ejected from the third pump 6 can be appropriately merged with the working oil ejected from the first pump 3 and the second pump 4. Therefore, the working oil supplied to the head 35a side of the boom cylinder 35 can be increased and the working speed of the boom cylinder 35 can be improved.

[0079] [Modifications]

[0080] Next, based on Figure 3A modified example (an example of a hydraulic circuit in the claims) 80 of the hydraulic circuit of the present embodiment will be described. In the modified example hydraulic circuit 80, components identical or similar to those of the hydraulic circuit 1 of the above embodiment are denoted by the same reference numerals and detailed descriptions thereof will be omitted.

[0081] Figure 3 It is a circuit diagram showing a modified example of the hydraulic circuit 80 of the present embodiment.

[0082] like Figure 3 As shown, the hydraulic circuit 80 has a structure in which the merging valve 18 provided in the hydraulic circuit 1 of the above embodiment is replaced with another merging valve (an example of a merging valve in the claims) 82. The other structures of the hydraulic circuit 80 are the same as those of the hydraulic circuit 1 of the above embodiment.

[0083] The spool 82a of the confluence valve 82 has a first switching position (an example of the first switching position in the claims) 82a1 and a second switching position (an example of the second switching position in the claims) 82a2. In the first switching position 82a1, switching is possible based on the pilot pressure applied from the first operating portion 66. The first switching position 82a1 is the same as the first switching position 18a1 of the above-mentioned embodiment. The second switching position 82a2 is a position where the fourth passage 84 is set at the second switching position 18a2 of the above-mentioned embodiment.

[0084] In the confluence valve 82, when the spool 82a is switched to the second switching 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 the third passage 76. In addition, the first pump 3 and the second pump 4 communicate with the first supply passage 42 via the fourth passage 84.

[0085] Therefore, the hydraulic circuit 80 achieves the same operation and effects as the hydraulic circuit 1 of the above-described embodiment.

[0086] The present invention is not limited to the above-described embodiment and modified examples. The present invention also includes various changes added to the above-described embodiment and modified examples without departing from the gist of the present invention.

[0087] For example, in the above-mentioned embodiment, the case where the construction machine 100 is a hydraulic excavator is described. The example in which the hydraulic circuit 1 is applied to the construction machine 100 is described. However, the present invention is not limited thereto. The hydraulic circuit 1 can be applied to various construction machines or the hydraulic circuit 1 can be applied to machines other than construction machines.

[0088] In the above embodiment, the boom control valve 15 , the arm control valve 16 , and the bucket control valve 17 are described as examples of the plurality of control valves, but the hydraulic circuit 1 may be applied to other control valves.

[0089] In the above example, the control valve 2 includes a bulldozer control valve 14, a swing control valve 13, a confluence 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, which are arranged in order from the upstream side. However, the order of the plurality of components constituting the control valve 2 can be changed appropriately. In addition, each control valve 11 to 17 can also be used to drive other components.

[0090] In the above embodiment, working oil is exemplified as the working fluid. However, the present invention is not limited thereto. The present invention can also be applied to working fluids other than working oil. The working fluid is not limited to liquids, but may also be gas.

[0091] Furthermore, the components of the above-described embodiments may be replaced with known components without departing from the spirit of the present invention.

[0092] The components composed of a plurality of objects in the embodiments disclosed in this specification may be integrated into the plurality of objects, or conversely, a component composed of one object may be divided into a plurality of objects. Regardless of whether they are integrated or not, they may be constructed so as to achieve the purpose of the invention.

Claims

1. A hydraulic circuit, wherein: have: First pump; Second pump; The third pump; 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 are provided in the middle of the first unloading passage and the second unloading passage to control the driving of the actuator; The first pump, the second pump and the third pump respectively eject working fluid. 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.

2. The hydraulic circuit according to claim 1, wherein: have: a merging valve disposed on a downstream side of the third unloading passage and disposed in the third supply passage, the first supply passage, and the second supply passage; an operating unit for applying a pilot pressure to the merging valve for driving the merging valve; A pilot passage connected to the operating part and generating the pilot pressure; as well as a tank passage, connected to the tank; The merging 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 passage that connects the third unloading passage with the tank passage, and has a second passage that connects the third supply passage with the first supply passage and the second supply passage. The second switching position has a third passage that blocks the third unloading passage and connects the third supply passage with the first supply passage and the second supply passage. The pilot passage is branched into the operating portion for applying the pilot pressure to the merging valve and a second pilot passage connected to the tank. The opening degree of the second pilot passage changes based on the desired operation of the control valve.

3. A hydraulic circuit, wherein: have: First pump; Second pump; The third pump; 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 are provided in the middle of the first unloading passage and the second unloading passage to control the driving of the actuator; a tank passage, connected to the tank; a merging valve for switching connection and disconnection between the third unloading passage and the tank passage; An operating unit, driving the confluence valve; as well as A negative control detection mechanism is arranged at the most downstream of the first unloading passage and the second unloading passage; The first pump, the second pump and the third pump respectively eject working fluid. The detection mechanism has: A first throttling member is arranged at the most downstream of the first unloading passage; a second throttling member, disposed at the most downstream of the second unloading passage; as well as a low pressure selector valve that outputs a lower pressure of a pressure of the working fluid on the upstream side of the first throttle member and a pressure of the working fluid on the upstream side of the second throttle member as a negative control pressure; The negative control pressure is applied to a second operating portion of the merging valve on the side opposite to the operating portion.

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