Fluid pressure control apparatus

Abstract

To efficiently discharge air at a pilot chamber side to a drain chamber.SOLUTION: A gas extraction apparatus 80 includes: a discharge passage 81 formed in a piston 50 over a pilot chamber 23 and a drain chamber 51 to discharge fluid from the pilot chamber 23 to the drain chamber 51; a rod 82 movably supported by a pilot cap 58; a set screw 83 for moving the rod 82 forward in the discharge passage 81; a valve body 84 disposed in the discharge passage 81, and opening / closing the discharge passage 81; and a spring 85 disposed in the discharge passage 81 as an energization member for energizing the valve body 84 in the closing direction. By the rod 82 moving forward in the discharge passage 81 by the set screw 83, the rod 82 opens the valve body 84 against the energization force of the spring 85 so as to allow the fluid to flow from the pilot chamber 23 to the drain chamber 51.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a fluid pressure control device. [Background technology]

[0002] Patent Document 1 discloses a fluid pressure control device for controlling the operation of a work machine, which includes a control valve that switches the supply and discharge of hydraulic oil to a cylinder to control the extension and contraction movement of the cylinder, and a load holding mechanism installed in a main passage that connects the load side pressure chamber of the cylinder and the control valve.

[0003] The load holding mechanism includes an operated check valve and a meter-out control valve that operates by pilot pressure to switch the operation of the operated check valve. The meter-out control valve includes a spool, a pilot chamber to which the pilot pressure is introduced, and a piston that is slidably accommodated in the pilot chamber and receives the pilot pressure to move the spool. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2010-101400 A DISCLOSURE OF THEINVENTION [Problem to be solved by the invention]

[0005] In this type of fluid pressure control device, a drain chamber communicating with a tank is defined between the spool and the piston so that the thrust of the piston is efficiently transmitted to the spool when pilot pressure is introduced into the pilot chamber.

[0006] An annular gap is provided between the piston and the housing to allow air to be discharged from the pilot chamber to the drain chamber. However, because the cross-sectional area of ​​the annular gap is small, the air on the pilot chamber side cannot be efficiently discharged to the drain chamber. As a result, air remains in the pilot chamber, which may affect the operation of the fluid pressure control device.

[0007] The present invention has been made in consideration of the above problems, and has an object to efficiently exhaust air on the pilot chamber side. [Means for solving the problem]

[0008] The present invention is a fluid pressure control device that controls the expansion and contraction operation of a cylinder that drives a load, and includes a control valve that controls the supply of working fluid to the cylinder from a fluid pressure supply source, a pilot control valve that controls a pilot pressure led to the control valve from a pilot pressure supply source, a main passage that connects the control valve to a load side pressure chamber of the cylinder on which a load pressure due to a load acts when the control valve is in a neutral position, and a load holding mechanism provided in the main passage. The load holding mechanism has an operate check valve that allows the flow of working fluid from the control valve to the load side pressure chamber, while allowing the flow of working fluid from the load side pressure chamber to the control valve in response to a back pressure, and a switching valve that operates in conjunction with the control valve by pilot pressure led through the pilot control valve and switches the operation of the operate check valve. The switching valve has a pilot chamber to which pilot pressure is led through the pilot control valve, and a pilot pressure in the pilot chamber that moves in response to the pilot pressure in the pilot chamber. the gas venting device has a spool, a piston that receives pilot pressure and applies thrust to the spool, a drain chamber partitioned by the spool and the piston, a partition member provided opposite the piston and partitioning the pilot chamber, and a gas venting device provided on the piston and the partition member for discharging gas from the pilot chamber to the drain chamber, the gas venting device has a discharge passage formed in the piston across the pilot chamber and the drain chamber for discharging fluid from the pilot chamber to the drain chamber, a rod movably supported by the partition member, a rod drive unit that advances the rod within the discharge passage, a valve body provided in the discharge passage for opening and closing the discharge passage, and a biasing member provided in the discharge passage for biasing the valve body in a closing direction, and when the rod is advanced within the discharge passage by the rod drive unit, the rod opens the valve body against the biasing force of the biasing member, allowing fluid to flow from the pilot chamber to the drain chamber.

[0009] In this invention, by advancing the rod with the rod drive unit, the valve body provided in the exhaust passage is opened, and the pilot chamber and the drain chamber are connected through the exhaust passage. Therefore, when venting the air on the pilot chamber side, the air in the pilot chamber can be exhausted to the drain chamber through the exhaust passage having a large flow passage cross-sectional area, rather than through a passage having a small flow passage cross-sectional area such as the annular gap. Therefore, the air on the pilot chamber side can be efficiently exhausted to the drain chamber.

[0010] In addition, the present invention is characterized in that the switching valve further has a drain passage connected to the pilot chamber, and the drain passage is provided with a throttle for applying resistance to the working fluid passing therethrough.

[0011] In this invention, when the fluid is guided from the discharge passage to the drain passage during gas removal on the pilot chamber side, the pressure on the pilot chamber side increases due to the throttle, so the gas on the pilot chamber side is compressed and dissolved in the fluid, thereby allowing the air on the pilot chamber side to be efficiently discharged to the drain chamber.

[0012] In addition, the present invention is characterized in that, after the rod has opened the valve body, the rod is moved further forward by the rod drive portion, whereby the rod comes into contact with the piston and moves the piston and the spool.

[0013] In this invention, even in the event of an abnormality such as a failure of the pilot pressure supply source, the rod can be advanced by the rod drive unit to move the spool. Therefore, even in the event of an abnormality, the working fluid can be discharged from the cylinder to operate the cylinder. In this way, the gas venting device can perform two functions: venting the gas on the pilot chamber side and discharging the working fluid from the cylinder in the event of an abnormality.

[0014] In addition, the present invention is characterized in that the biasing force of the biasing member is set so that when the pilot pressure supply source is driven and pilot pressure is introduced into the pilot chamber, the valve body is not opened by the pilot pressure.

[0015] In this invention, the valve body is closed during normal operation of the cylinder, so that the gas venting device does not adversely affect the operation of the cylinder. Effect of the Invention

[0016] According to the present invention, the air on the pilot chamber side can be efficiently discharged to the drain chamber. [Brief description of the drawings]

[0017] [Figure 1] FIG. 2 is a diagram showing a portion of a hydraulic excavator. [Diagram 2] 1 is a fluid pressure circuit diagram of a fluid pressure control device according to an embodiment of the present invention. [Diagram 3] FIG. 2 is a cross-sectional view of a load holding mechanism of the fluid pressure control device according to the embodiment of the present invention. [Figure 4] FIG. 4 is an enlarged cross-sectional view of the gas removal device and its surroundings, showing a state in which the set screw is in the initial position and the valve body is closed. [Diagram 5] FIG. 4 is an enlarged cross-sectional view of the gas removal device and its surroundings, showing the valve body in an open state. [Figure 6] FIG. 11 is an enlarged cross-sectional view of the periphery of a gas removal device of a fluid pressure control device according to a fourth modified example of an embodiment of the present invention. [Figure 7] FIG. 13 is an enlarged cross-sectional view of the periphery of a gas removal device of a fluid pressure control device according to a fifth modified example of an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A fluid pressure control device according to an embodiment of the present invention will now be described with reference to the drawings.

[0019] A fluid pressure control device controls the operation of hydraulic work equipment such as a hydraulic excavator. In this embodiment, a hydraulic control device 100 is described that controls the extension and contraction operation of a cylinder 15 that drives a boom 14 (load) of a hydraulic excavator shown in Fig. 1. In the following, a case where hydraulic oil is used as the working fluid of the cylinder 15 will be described, but instead of hydraulic oil, for example, a water-soluble substitute liquid or the like may be used.

[0020] First, the hydraulic circuit of the hydraulic control device 100 will be described with reference to Fig. 2. The cylinder 15 includes a cylindrical cylinder tube 15c, a piston 15d slidably inserted into the cylinder tube 15c and dividing the inside of the cylinder tube 15c into a rod side chamber 15a and an anti-rod side chamber 15b, and a piston rod 15e having one end connected to the piston 15d and the other end extending outside the cylinder tube 15c and connected to the boom 14.

[0021] The hydraulic excavator is equipped with a power source such as an engine or an electric motor, and the power drives a pump 4 serving as a fluid pressure supply source and a pilot pump 5 serving as a pilot pressure supply source.

[0022] The hydraulic control device 100 includes a control valve 6 that controls the supply of hydraulic oil from the pump 4 to the cylinder 15 , and a pilot control valve 9 that controls the pilot pressure guided from the pilot pump 5 to the control valve 6 .

[0023] The control valve 6 and the anti-rod side chamber 15b of the cylinder 15 are connected by a first main passage 7, and the control valve 6 and the rod side chamber 15a of the cylinder 2 are connected by a second main passage 8.

[0024] The control valve 6 is operated by a pilot pressure that is guided from the pilot pump 5 through a pilot control valve 9 to pilot chambers 6a, 6b as the operator of the hydraulic excavator manually operates an operation lever 10.

[0025] Specifically, when pilot pressure is introduced into the pilot chamber 6a, the control valve 6 switches to position 6A, and hydraulic oil is supplied from the pump 4 through the first main passage 7 to the anti-rod side chamber 15b, while hydraulic oil in the rod side chamber 15a is discharged into the tank T through the second main passage 8. This causes the cylinder 15 to extend, and the boom 14 rises in the direction of the arrow 18 shown in FIG.

[0026] On the other hand, when pilot pressure is introduced into the pilot chamber 6b, the control valve 6 switches to position 6B, and hydraulic oil is supplied from the pump 4 through the second main passage 8 to the rod side chamber 15a, while hydraulic oil in the anti-rod side chamber 15b is discharged into the tank T through the first main passage 7. This causes the cylinder 15 to contract, and the boom 14 to move down in the direction of the arrow 19 shown in FIG.

[0027] When no pilot pressure is introduced to the pilot chambers 6a, 6b, the control valve 6 is in the position 6C, the supply and discharge of hydraulic oil to the cylinder 2 is cut off, and the boom 14 remains stopped.

[0028] In this way, the control valve 6 has three positions: an extension position 6A for extending the cylinder 15, a retraction position 6B for retracting the cylinder 15, and a neutral position 6C for holding the load on the cylinder 15. The control valve 6 switches between the supply and discharge of hydraulic oil in the cylinder 15 and controls the extension and retraction of the cylinder 15.

[0029] 1, when the control valve 6 is switched to the neutral position 6C to stop the movement of the boom 14 with the boom 14 lifting the arm 1, a force in the contracting direction acts on the cylinder 15 due to the weight of the boom 14, etc. In this way, in the cylinder 15 that drives the boom 14, the anti-rod side chamber 15b becomes a load side pressure chamber to which a load pressure acts when the control valve 6 is in the neutral position 6C.

[0030] A load holding mechanism 20 is provided in the first main passage 7 connected to the anti-rod side chamber 15b, which is the load side pressure chamber. The load holding mechanism 20 holds the load pressure in the rod side chamber 15a when the control valve 6 is in the neutral position 6C, and is fixed to the surface of the cylinder 15 as shown in FIG.

[0031] In the cylinder 2 that drives the arm 1 (see Figure 1), the rod side chamber 2a becomes the load side pressure chamber, so when a load holding mechanism 20 is provided in the arm 1, the load holding mechanism 20 is provided in the main passage connected to the rod side chamber 2a.

[0032] The load holding mechanism 20 has an operate check valve 21 provided in the first main passage 7, and a switching valve 22 that operates in conjunction with the control valve 6 by pilot pressure guided through the pilot control valve 9, and switches the operation of the operate check valve 21.

[0033] The operated check valve 21 has a valve element 24 that opens and closes the first main passage 7, a seat portion 28 on which the valve element 24 sits, a back pressure chamber 25 facing the back surface of the valve element 24, and a passage 26 formed in the valve element 24 and constantly directing hydraulic oil in the anti-rod side chamber 15b to the back pressure chamber 25. A throttle 26a that imparts resistance to the hydraulic oil passing through the passage 26 is provided.

[0034] The first main passage 7 has a cylinder side first main passage 7a connecting the anti-rod side chamber 15b and the operated check valve 21, and a control valve side first main passage 7b connecting the operated check valve 21 and the control valve 6.

[0035] The valve body 24 is formed with a first pressure-receiving surface 24a upon which the pressure of the control valve side first main passage 7b acts, and a second pressure-receiving surface 24b upon which the pressure of the anti-rod side chamber 15b acts through the cylinder side first main passage 7a.

[0036] A spring 27 serving as a biasing member that biases the valve body 24 in a closing direction is accommodated in the back pressure chamber 25. The pressure in the back pressure chamber 25 and the biasing force of the spring 27 act in a direction that causes the valve body 24 to seat on the seat portion 28.

[0037] With the valve body 24 seated on the seat portion 28, the operate check valve 21 functions as a check valve that blocks the flow of hydraulic oil from the anti-rod side chamber 15b to the control valve 6. In other words, the operate check valve 21 prevents leakage of hydraulic oil in the anti-rod side chamber 15b to maintain the load pressure and maintain the stopped state of the boom 14.

[0038] The switching valve 22 has a pilot chamber 23 to which pilot pressure is introduced via pilot control valve 9, a spool 56 (see Figure 3) that moves in response to the pilot pressure in the pilot chamber 23, a spring 36 as a biasing member that biases the spool 56 in the closing direction, a spring chamber 54 (see Figure 3) in which the spring 36 is housed, a drain chamber 51 (see Figure 3) provided on the opposite side of the spool 56 to the spring chamber 54, and a drain passage 76 that connects the spring chamber 54 and the drain chamber 51 to tank T.

[0039] A bypass passage 30 and a back pressure passage 31 are connected to the upstream side of the switching valve 22, and a downstream passage 38 is connected to the downstream side of the switching valve 22. The bypass passage 30 is a passage for guiding the hydraulic oil in the anti-rod side chamber 15b to the control valve side first main passage 7b, bypassing the operated check valve 21. The back pressure passage 31 is a passage for guiding the hydraulic oil in the back pressure chamber 25 to the control valve side first main passage 7b. The downstream passage 38 is a passage for guiding the hydraulic oil from the bypass passage 30 and the back pressure passage 31 to the control valve side first main passage 7b.

[0040] The switching valve 22 switches communication between the bypass passage 30 and the back pressure passage 31 and the downstream passage 38, and controls the flow of hydraulic oil in the first main passage 7 which is on the meter-out side when the cylinder 15 is extended.

[0041] The switching valve 22 has three ports: a first supply port 32 communicating with the bypass passage 30, a second supply port 33 communicating with the back pressure passage 31, and a discharge port 34 communicating with the downstream passage 38. The switching valve 22 also has three positions: a blocking position 22A, a first communicating position 22B, and a second communicating position 22C.

[0042] When the pilot pressure is introduced to the pilot chamber 6b of the control valve 6, the pilot pressure is also introduced to the pilot chamber 23. In other words, when the control valve 6 is switched to the contraction position 6B, the switching valve 22 is also switched to the first communication position 22B or the second communication position 22C.

[0043] More specifically, when no pilot pressure is introduced into the pilot chamber 23, the switching valve 22 is maintained in the shutoff position 22A by the biasing force of the spring 36. In the shutoff position 22A, both the first supply port 32 and the second supply port 33 are shut off.

[0044] When a pilot pressure equal to or greater than the first predetermined pressure and less than the second predetermined pressure is introduced to the pilot chamber 23, the switching valve 22 switches to the first communication position 22B. In the first communication position 22B, the first supply port 32 communicates with the discharge port 34. As a result, the hydraulic oil in the anti-rod side chamber 15b is introduced from the bypass passage 30 to the downstream passage 38 through the switching valve 22. In other words, the hydraulic oil in the anti-rod side chamber 15b bypasses the operated check valve 21 and is introduced to the control valve side first main passage 7b. At this time, the orifice 37 applies resistance to the flow of the hydraulic oil. The second supply port 33 remains blocked.

[0045] When a pilot pressure equal to or greater than the second predetermined pressure is introduced into the pilot chamber 23, the switching valve 22 switches to the second communication position 22C. In the second communication position 22C, the first supply port 32 communicates with the drain port 34, and the second supply port 33 also communicates with the drain port 34. As a result, the hydraulic oil in the back pressure chamber 25 is introduced from the back pressure passage 31 through the switching valve 22 to the downstream passage 38. At this time, the hydraulic oil in the back pressure chamber 25 bypasses the throttle 37 and is introduced into the control valve side first main passage 7b, and is discharged from the control valve 6 to the tank T. As a result, a pressure difference occurs before and after the throttle 26a, and the pressure in the back pressure chamber 25 decreases, so that the force acting on the valve body 24 in the closing direction decreases, and the valve body 24 moves away from the seat portion 28, and the function of the operated check valve 21 as a check valve is released.

[0046] The load holding mechanism 20 has a relief valve 41 that opens when the pressure in the anti-rod side chamber 15b reaches a predetermined pressure, and discharges the hydraulic oil in the anti-rod side chamber 15b to the tank T. The relief valve 41 is provided in a relief passage 40 that branches off from the bypass passage 30 upstream of the switching valve 22. The relief passage 40 may be provided by branching off from the cylinder side first main passage 7a, or may be directly connected to the anti-rod side chamber 15b.

[0047] The drain passage 76 includes a first drain passage 76a connected to the drain chamber 51, a second drain passage 76b connected to the spring chamber 54, and a joint drain passage 76c formed by joining the first drain passage 76a and the second drain passage 76b. The first drain passage 76a is joined to the relief passage 40. The first drain passage 76a is provided with an orifice 79 as a throttle that applies resistance to the working fluid passing through. The effect of the orifice 79 will be described later. The joint drain passage 76c is connected to a drain port 77 that opens on the outer surface of the body 60 (see FIG. 3) of the load holding mechanism 20. The drain port 77 is connected to the tank T through a drain hose 78. In this way, the drains of the drain chamber 51 and the spring chamber 54 are discharged to the tank T through the joint drain passage 76c, the drain port 77, and the drain hose 78. Since the drain chamber 51 and the spring chamber 54, respectively provided on either side of the spool 56 of the switching valve 22, are both connected to the tank T, when the switching valve 22 is in the shutoff position 22A, atmospheric pressure acts on both ends of the spool 56, preventing the spool 56 from moving unintentionally.

[0048] A relief valve 43 that opens when the pressure in the control valve side first main passage 7b reaches a predetermined pressure is connected to the control valve side first main passage 7b. A relief valve 44 that opens when the pressure in the second main passage 8 reaches a predetermined pressure is connected to the second main passage 8. The relief valves 43 and 44 are provided to release high pressure generated in the rod side chamber 15a and anti-rod side chamber 15b of the cylinder 15, respectively, when a large external force is applied to the boom 14.

[0049] Next, the switching valve 22 will be described in detail, mainly with reference to Fig. 3. Fig. 3 is a cross-sectional view of the load holding mechanism 20, showing a state in which the pilot pressure is not introduced to the pilot chamber 23 and the switching valve 22 is in the shutoff position 22A. In Fig. 3, the same reference numerals as those in Fig. 2 denote the same configuration as that shown in Fig. 2.

[0050] The switching valve 22 is incorporated into a body 60 of the load holding mechanism 20. A spool hole 60a is formed in the body 60, and a substantially cylindrical sleeve 61 is inserted into the spool hole 60a. The spool 56 is slidably incorporated into the sleeve 61.

[0051] A spring chamber 54 is defined by a cap 57 on the side of one end surface 56a of the spool 56. The spring chamber 54 is connected to a second drain passage 76b through a notch 61a formed in the end surface of the sleeve 61. Hydraulic oil that leaks into the spring chamber 54 is drained from the second drain passage 76b to the tank T.

[0052] The spring chamber 54 accommodates an annular first spring bearing member 45, the end face of which abuts against one end face 56a of the spool 56 and into which a pin portion 56c formed in the hollow portion and protruding from the one end face 56a of the spool 56 is inserted, and a second spring bearing member 46 disposed in the vicinity of the bottom of the cap 57. The spring 36 is interposed in a compressed state between the first spring bearing member 45 and the second spring bearing member 46, and biases the spool 56 in the closing direction via the first spring bearing member 45.

[0053] A pilot chamber 23 is defined on the side of the other end face 56b of the spool 56. The pilot chamber 23 is defined by a piston hole 60b formed in communication with the spool hole 60a, and a pilot cap 58 provided opposite the piston 50 and closing the piston hole 60b. The pilot cap 58 is a partitioning member that defines the pilot chamber 23. Pilot pressure oil (pilot fluid) is introduced to the pilot chamber 23 through a pilot passage 52 formed in the body 60. The piston 50 is slidably housed in the pilot chamber 23, and receives pilot pressure at its back surface to apply a thrust to the spool 56 against the biasing force of the spring 36.

[0054] Within the piston hole 60b, a drain chamber 51 is defined by the spool 56 and the piston 50. The drain chamber 51 is connected to a first drain passage 76a. The hydraulic oil that leaks into the drain chamber 51 is discharged from the first drain passage 76a to the tank T.

[0055] The piston 50 has a sliding portion 50a whose outer peripheral surface slides along the inner peripheral surface of the piston hole 60b, a tip portion 50b which is formed with a smaller diameter than the sliding portion 50a and faces the other end surface 56b of the spool 56, and a base end portion 50c which is formed with a smaller diameter than the sliding portion 50a and faces the tip surface of the pilot cap 58.

[0056] When pilot pressure oil is supplied into the pilot chamber 23 through the pilot passage 52, pilot pressure acts on the back surface of the base end 50c and the annular back surface of the sliding part 50a. As a result, the piston 50 advances, and the tip end 50b abuts against the other end surface 56b of the spool 56, moving the spool 56. In this manner, the spool 56 receives the thrust of the piston 50, which is generated based on the pilot pressure acting on the back surface of the piston 50, and moves against the biasing force of the spring 36. Even when the back surface of the base end 50c abuts against the tip surface of the pilot cap 58, the base end 50c has a smaller diameter than the sliding part 50a, and pilot pressure acts on the annular back surface of the sliding part 50a, so that the piston 50 can advance.

[0057] One end of the piston 50 faces the pilot chamber 23, and the other end faces the drain chamber 51 connected to the tank T, so that the thrust of the piston 50 generated based on the pilot pressure in the pilot chamber 23 is efficiently transmitted to the spool 56.

[0058] The spool 56 stops at a position where the biasing force of the spring 36 acting on one end face 56a and the thrust of the piston 50 acting on the other end face 56b are balanced, and the switching position of the switching valve 22 is set at the stopping position of the spool 56.

[0059] The piston 50 and the pilot cap 58 are provided with a gas venting device 80 for discharging air from the pilot chamber 23 to the drain chamber 51. The gas venting device 80 will be described in detail later.

[0060] The sleeve 61 is formed with three ports: a first supply port 32 communicating with the bypass passage 30 (see FIG. 2), a second supply port 33 communicating with the back pressure passage 31 (see FIG. 2), and a discharge port 34 communicating with the downstream passage 38 (see FIG. 2).

[0061] The outer peripheral surface of the spool 56 is partially cut out in an annular shape, and the cut out portion and the inner peripheral surface of the sleeve 61 form a first pressure chamber 64, a second pressure chamber 65, a third pressure chamber 66, and a fourth pressure chamber 67.

[0062] The first pressure chamber 64 is constantly connected to the exhaust port 34. The third pressure chamber 66 is constantly connected to the first supply port 32. A plurality of orifices 37 are formed on the outer circumferential surface of the land portion 72 of the spool 56, which communicate between the third pressure chamber 66 and the second pressure chamber 65 as the spool 56 moves against the biasing force of the spring 36. The fourth pressure chamber 67 is constantly connected to the second pressure chamber 65 through a pressure introducing passage 68 formed in the spool 56 in the axial direction.

[0063] When the operating lever 10 is not operated and pilot pressure is not introduced to the pilot chamber 23, the poppet valve 70 formed in the spool 56 is pressed against a valve seat 71 formed on the inner circumference of the sleeve 61 by the biasing force of the spring 36, and communication between the second pressure chamber 65 and the first pressure chamber 64 is blocked. Therefore, communication between the first supply port 32 and the exhaust port 34 is blocked. As a result, the hydraulic oil in the anti-rod side chamber 15b does not leak to the exhaust port 34. This state corresponds to the blocking position 22A of the switching valve 22. When the poppet valve 70 is seated on the valve seat 71 by the biasing force of the spring 36, a small gap exists between the end face of the first spring receiving member 45 and the end face of the sleeve 61, so that the poppet valve 70 is reliably seated against the valve seat 71 by the biasing force of the spring 36.

[0064] When the operating lever 10 is operated to introduce pilot pressure into the pilot chamber 23 and the thrust of the piston 50 acting on the spool 56 becomes greater than the biasing force of the spring 36, the spool 56 moves against the biasing force of the spring 36. As a result, the poppet valve 70 moves away from the valve seat 71 and the third pressure chamber 66 and the second pressure chamber 65 communicate with each other through the multiple throttles 37, so that the first supply port 32 communicates with the exhaust port 34 through the third pressure chamber 66, the second pressure chamber 65, and the first pressure chamber 64. The communication between the first supply port 32 and the exhaust port 34 causes the hydraulic oil in the anti-rod side chamber 15b to be introduced to the downstream passage 38 (see FIG. 2) through the throttle 37. This state corresponds to the first communication position 22B of the switching valve 22.

[0065] When the pilot pressure introduced to the pilot chamber 23 increases, the spool 56 moves further against the biasing force of the spring 36, and the second supply port 33 communicates with the fourth pressure chamber 67. As a result, the second supply port 33 communicates with the drain port 34 through the fourth pressure chamber 67, the pressure introducing passage 68, the second pressure chamber 65, and the first pressure chamber 64. Due to the communication between the second supply port 33 and the drain port 34, the hydraulic oil in the back pressure chamber 25 bypasses the throttle 37 and is introduced to the downstream passage 38 (see FIG. 2). This state corresponds to the second communication position 22C of the switching valve 22.

[0066] Next, the operation of the hydraulic control device 100 will be described with reference to FIGS.

[0067] When the control valve 6 is in the neutral position 6C, the hydraulic oil discharged by the pump 4 is not supplied to the cylinder 15. At this time, since no pilot pressure is introduced into the pilot chamber 23 of the switching valve 22, the switching valve 22 is in the shutoff position 22A.

[0068] For this reason, the back pressure chamber 25 of the operated check valve 21 is maintained at the pressure of the anti-rod side chamber 15b. Here, the pressure receiving area of ​​the valve element 24 in the closing direction (the area of ​​the back surface of the valve element 24) is larger than the area of ​​the second pressure receiving surface 24b, which is the pressure receiving area in the opening direction, so that the load acting on the back surface of the valve element 24 due to the pressure of the back pressure chamber 25 and the biasing force of the spring 27 cause the valve element 24 to be seated on the seat portion 28. In this way, the operated check valve 21 prevents leakage of hydraulic oil from the anti-rod side chamber 15b, and the stopped state of the boom 14 is maintained.

[0069] When the operating lever 10 is operated and pilot pressure is introduced from the pilot control valve 9 to the pilot chamber 6a of the control valve 6, the control valve 6 is switched to the extension position 6A by an amount corresponding to the pilot pressure. When the control valve 6 is switched to the extension position 6A, the discharge pressure of the pump 4 acts on the first pressure receiving surface 24a of the operated check valve 21. At this time, the switching valve 22 is in the shutoff position 22A without introducing pilot pressure to the pilot chamber 23, so that the back pressure chamber 25 of the operated check valve 21 is maintained at the pressure of the counter-rod side chamber 15b. When the load acting on the first pressure receiving surface 24a becomes larger than the total load of the load acting on the back surface of the valve body 24 due to the pressure of the back pressure chamber 25 and the biasing force of the spring 27, the valve body 24 moves away from the seat portion 28. When the operated check valve 21 opens in this way, the hydraulic oil discharged from the pump 4 is supplied to the counter-rod side chamber 15b, and the cylinder 15 is extended. This causes the boom 14 to rise in the direction of the arrow 18 shown in FIG.

[0070] When the operating lever 10 is operated and pilot pressure is introduced from the pilot control valve 9 to the pilot chamber 6b of the control valve 6, the control valve 6 switches to the contraction position 6B by an amount corresponding to the pilot pressure. At the same time, pilot pressure is also introduced to the pilot chamber 23, so that the switching valve 22 switches to the first communication position 22B or the second communication position 22C depending on the supplied pilot pressure.

[0071] When the pilot pressure introduced into the pilot chamber 23 is equal to or greater than the first predetermined pressure and less than the second predetermined pressure, the switching valve 22 switches to the first communication position 22B. In this case, since communication between the second supply port 33 and the discharge port 34 is blocked, the back pressure chamber 25 of the operated check valve 21 is maintained at the pressure of the anti-rod side chamber 15b, and the operated check valve 21 maintains the closed state.

[0072] On the other hand, since the first supply port 32 communicates with the discharge port 34, the hydraulic oil in the anti-rod side chamber 15b is guided from the bypass passage 30 through the throttle 37 to the downstream passage 38, and is discharged from the control valve side first main passage 7b through the control valve 6 to the tank T. In addition, since the hydraulic oil discharged from the pump 4 is supplied to the rod side chamber 15a, the cylinder 15 contracts. As a result, the boom 14 descends in the direction of the arrow 19 shown in FIG. 1.

[0073] Here, the switching valve 22 is mainly switched to the first communication position 22B when performing crane work to lower a load attached to the bucket 13 to a target position. In crane work, it is necessary to slowly lower the boom 14 in the direction of the arrow 19 by contracting the cylinder 15 at a low speed, so the pilot pressure introduced to the pilot chamber 6b of the control valve 6 is small and the control valve 6 is only slightly switched to the contraction position 6B. For this reason, the pilot pressure introduced to the pilot chamber 23 of the switching valve 22 is also small and is equal to or greater than the first predetermined pressure and less than the second predetermined pressure, and the switching valve 22 is only switched to the first communication position 22B. Therefore, the hydraulic oil in the counter-rod side chamber 15b is discharged through the throttle 37, and the boom 14 is lowered at a low speed suitable for crane work.

[0074] Furthermore, when switching valve 22 is in first communication position 22B, even if a situation occurs in which control valve side first main passage 7b ruptures or the like and hydraulic oil leaks to the outside, the flow rate of hydraulic oil discharged from anti-rod side chamber 15b is limited by orifice 37, so the falling speed of bucket 13 is suppressed. For this reason, switching valve 22 can be switched to shutoff position 22A before bucket 13 falls to the ground, and a sudden fall of bucket 13 can be prevented.

[0075] In this way, the restrictor 37 serves to suppress the descending speed of the cylinder 2 when the operate check valve 21 is closed, and also to suppress the falling speed of the bucket 13 when the control valve side first main passage 7b bursts.

[0076] When the pilot pressure led to the pilot chamber 23 is equal to or higher than the second predetermined pressure, the switching valve 22 is switched to the second communication position 22C. In this case, the second supply port 33 is connected to the discharge port 34, so that the hydraulic oil in the back pressure chamber 25 of the operated check valve 21 is led from the back pressure passage 31 to the downstream passage 38, bypassing the throttle 37, and is discharged from the control valve side first main passage 7b through the control valve 6 to the tank T. As a result, a pressure difference is generated before and after the throttle 26a, and the pressure in the back pressure chamber 25 decreases, so that the force acting on the valve element 24 in the closing direction decreases, and the valve element 24 moves away from the seat portion 28, and the function of the operated check valve 21 as a check valve is released.

[0077] In this way, the operate check valve 21 allows the flow of hydraulic oil from the control valve 6 to the anti-rod side chamber 15b, while operating to allow the flow of hydraulic oil from the anti-rod side chamber 15b to the control valve 6 in accordance with the back pressure, which is the pressure in the back pressure chamber 25.

[0078] When the operate check valve 21 opens, the hydraulic oil in the anti-rod side chamber 15b passes through the first main passage 7 and is discharged to the tank T, causing the cylinder 2 to quickly contract. In other words, when the switching valve 22 is switched to the second communication position 22C, the flow rate of hydraulic oil discharged from the anti-rod side chamber 15b increases, so the flow rate of hydraulic oil supplied to the rod side chamber 15a increases, and the contraction speed of the cylinder 2 increases. As a result, the boom 14 quickly descends in the direction of the arrow 19.

[0079] The switching valve 22 is switched to the second communication position 22C when excavation work or the like is performed, and the pilot pressure led to the pilot chamber 6b of the control valve 6 is high, so that the control valve 6 is switched largely to the contracted position 6B. Therefore, the pilot pressure led to the pilot chamber 23 of the switching valve 22 is also high and exceeds the second predetermined pressure, so that the switching valve 22 is switched to the second communication position 22C.

[0080] Next, the gas degassing device 80 will be described mainly with reference to Fig. 4. Fig. 4 is an enlarged cross-sectional view of the periphery of the gas degassing device 80 in Fig. 3. Below, a case will be described in which the gas degassing device 80 discharges air from the pilot chamber 23 to the drain chamber 51, but what is discharged by the gas degassing device 80 is not limited to air, and other gases may also be used.

[0081] The pilot cap 58 has a head 58a attached to the opening of the piston hole 60b in the body 60, and a main body 58b formed continuous with the head 58a and inserted into the piston hole 60b. A male thread 58c is formed on the outer circumferential surface of the main body 58b, and the male thread 58c and a female thread formed on the inner circumferential surface of the piston hole 60b are screwed together to attach the pilot cap 58 to the body 60. An insertion hole 58d is formed in the main body 58b, which opens to the pilot chamber 23 and through which a part of a rod 82 (described later) of the gas removal device 80 is inserted.

[0082] The gas venting device 80 is provided between the piston 50 and the pilot cap 58. The gas venting device 80 has a discharge passage 81 provided between the pilot chamber 23 and the drain chamber 51, a rod 82 movably supported by the pilot cap 58, a set screw 83 as a rod drive section that advances the rod 82 in the discharge passage 81, a valve body 84 provided in the discharge passage 81 for opening and closing the discharge passage 81, and a spring 85 provided in the discharge passage 81 as a biasing member that biases the valve body 84 in a closing direction. The discharge passage 81 is formed penetrating the piston 50 along the movement direction of the piston 50, and is formed coaxially with the insertion hole 58d of the pilot cap 58.

[0083] An annular valve seat 81a is provided in the discharge passage 81. The valve seat 81a has a hollow portion 81b having a diameter smaller than the inner circumferential surface of the discharge passage 81. The valve body 84 is a sphere and is seated on a T-shaped seating member 86. The valve body 84 may have a shape other than a sphere, for example, a poppet valve. The valve body 84 and the seating member 86 are provided on the drain chamber 51 side of the valve seat 81a in the discharge passage 81. The inner diameter of the valve seat 81a (hollow portion 81b) is smaller than the outer diameter of the valve body 84. Therefore, the valve body 84 can abut against the valve seat 81a, and when the valve body 84 is seated on the valve seat 81a, the discharge passage 81 is blocked. The spring 85 is compressed and provided between the seating member 86 and a support member 87 having a notch 87a and press-fitted into the drain chamber 51 side of the discharge passage 81. As a result, the spring 85 biases the valve body 84 toward the valve seat 81a via the seating member 86. In other words, the spring 85 biases the valve body 84 to block the discharge passage 81. The biasing force (initial set load) of the spring 85 is set so that when the pilot pump 5 is driven and pilot pressure is introduced into the pilot chamber 23, the valve body 84 does not open due to the pilot pressure. In other words, the biasing force of the spring 85 is set so that the valve body 84 closes during normal operation of the cylinder 15 and opens only when air is discharged from the pilot chamber 23 to the drain chamber 51 as described below.

[0084] The rod 82 is provided between the insertion hole 58d of the pilot cap 58 and the discharge passage 81. The rod 82 has a head 82a slidably supported on the inner circumferential surface of the insertion hole 58d, a shaft portion 82b extending from the head 82a in the axial direction, and a pressing portion 82c formed at the tip of the shaft portion 82b and capable of pressing the valve body 84. The head 82a is formed with a larger diameter than the shaft portion 82b, and a seal member 82d is provided on the outer circumferential surface of the head 82a to seal between the head 82a and the inner circumferential surface of the insertion hole 58d. The pilot cap 58 is held in the position shown in FIG. 4 by the head 82a being supported by the inner circumferential surface of the insertion hole 58d. A set screw 83 is provided in the head 82a so as to be able to abut against the head 82a. The shaft portion 82b is provided between the insertion hole 58d, the pilot chamber 23, and the discharge passage 81, and is formed with a smaller diameter than the discharge passage 81. The pressing portion 82c is formed with a smaller diameter than the shaft portion 82b and is provided facing the valve body 84. The pressing portion 82c is formed with a smaller diameter than the inner diameter of the valve seat 81a and can pass through the valve seat 81a. The axial length of the pressing portion 82c is formed longer than the axial length of the valve seat 81a. As a result, when the rod 82 advances in the discharge passage 81 as described below, the pressing portion 82c abuts against the valve body 84 before the shaft portion 82b abuts against the valve seat 81a.

[0085] The set screw 83 is provided in the pilot cap 58. The set screw 83 is provided so as to penetrate the head 58a of the pilot cap 58 and have a tip end (the end on the right side in FIG. 4) located in the insertion hole 58d and abutting against the head 82a of the rod 82. The set screw 83 can be moved in the axial direction by being manually rotated by an operator using a tool. When the set screw 83 moves, the rod 82 abutting against the set screw 83 moves together with the set screw 83. This causes the valve body 84 to open and close, and the air on the pilot chamber 23 side can be discharged as described later. During normal operation of the cylinder 15, the set screw 83 is held in the initial position as shown in FIG. 4. The set screw 83 may be moved electrically using an actuator or the like.

[0086] Next, the operation and function of the degassing device 80 will be described.

[0087] The gas venting device 80 is used to discharge air on the pilot chamber 23 side into the drain chamber 51, for example, after assembly work of the hydraulic excavator or when the hydraulic excavator is started after being stopped for a long period of time. If air remains on the pilot chamber 23 side, when the hydraulic excavator is started, the increase in pilot pressure in the pilot chamber 23 in response to an input operation by the operator is delayed. Therefore, the air on the pilot chamber 23 side causes a delay in the response of the cylinder 15 to an input operation by the operator. By using the gas venting device 80 to bleed air on the pilot chamber 23 side, the operation of the hydraulic control device 100 is stabilized.

[0088] When discharging air on the pilot chamber 23 side to the drain chamber 51, first, the operator rotates the set screw 83 from the initial position shown in Fig. 4 using a tool to move it to the right in Fig. 4. Then, the rod 82 moves to the right in Fig. 4 together with the set screw 83 and advances in the discharge passage 81. Then, the pressing portion 82c of the rod 82 contacts the valve body 84 and presses the valve body 84 against the biasing force of the spring 85. When the force of the rod 82 pressing the valve body 84 exceeds the biasing force of the spring 85, the valve body 84 leaves the valve seat 81a and opens as shown in Fig. 5. This allows the flow of fluid from the pilot chamber 23 to the drain chamber 51 through the discharge passage 81. Fluid is guided from the pilot chamber 23 to the drain chamber 51 between the outer circumferential surface of the shaft portion 82b of the rod 82 and the inner circumferential surface of the discharge passage 81, between the outer circumferential surface of the pressing portion 82c and the inner circumferential surface of the valve seat 81a, between the seating member 86 and the inner circumferential surface of the discharge passage 81, and through the notch 87a of the support member 87. In this way, when discharging air on the pilot chamber 23 side to the drain chamber 51, the operator operates the set screw 83 to move the rod 82 to a position where the pressing portion 82c opens the valve body 84 and the shaft portion 82b does not abut against the valve seat 81a.

[0089] Then, with the valve body 84 in an open state, the pilot pump 5 is driven to guide the fluid to the pilot chamber 23. The fluid supplied from the pilot pump 5 is guided to the pilot chamber 23 while pushing out any air remaining in the flow path after the assembly work of the hydraulic excavator, and is discharged to the drain chamber 51 through the discharge passage 81. The fluid discharged to the drain chamber 51 is discharged to the tank T through the first drain passage 76a, the junction drain passage 76c, and the drain port 77. In this manner, the gas on the pilot chamber 23 side is bled. When the gas bleed on the pilot chamber 23 side is completed, the set screw 83 is returned to the initial position shown in FIG. 4, and the discharge passage 81 is returned to a state in which it is blocked by the valve body 84. Note that the gas bleed on the pilot chamber 23 side may be performed using a pump dedicated to gas bleed, different from the pilot pump 5.

[0090] In this way, in the hydraulic control device 100, by advancing the rod 82 with the set screw 83, the valve element 84 provided in the discharge passage 81 is opened, and the pilot chamber 23 and the drain chamber 51 can be communicated through the discharge passage 81. Therefore, the air in the pilot chamber 23 can be discharged to the drain chamber 51 through the discharge passage 81, which has a large flow path cross-sectional area, rather than through a passage with a small flow path cross-sectional area such as the annular gap between the piston 50 and the piston hole 60b. Therefore, the air on the pilot chamber 23 side can be efficiently discharged to the drain chamber 51 in a short time.

[0091] Furthermore, in the hydraulic control device 100, the first drain passage 76a is provided with an orifice 79 that applies resistance to the working fluid passing therethrough. Therefore, when the fluid is guided from the discharge passage 81 to the first drain passage 76a during gas bleed on the pilot chamber 23 side, the pressure on the pilot chamber 23 side, which is upstream of the orifice 79, increases. This causes the air on the pilot chamber 23 side to be compressed, and the compressed high-pressure air can be dissolved in the fluid. Therefore, the air can be compressed and dissolved in the fluid and discharged, so that the air on the pilot chamber 23 side can be efficiently discharged to the drain chamber 51.

[0092] Furthermore, in the hydraulic control device 100, the biasing force of the spring 85 is set so that when the pilot pump 5 is driven and pilot pressure is introduced into the pilot chamber 23, the valve element 84 is not opened by the pilot pressure. Therefore, during normal operation of the cylinder 15 (in other words, when the pilot pump 5 mounted on the hydraulic excavator is in operation and the pilot pump 5 is driven), the valve element 84 is closed and the pilot chamber 23 and the drain chamber 51 do not communicate with each other through the discharge passage 81, so that the gas venting device 80 does not adversely affect the operation of the cylinder 15.

[0093] According to the above embodiment, the following effects are achieved.

[0094] In the hydraulic control device 100, when gas is bled from the pilot chamber 23 side, the air in the pilot chamber 23 can be discharged to the drain chamber 51 through the discharge passage 81 having a large flow path cross-sectional area, so that the air on the pilot chamber 23 side can be efficiently discharged to the drain chamber 51 in a short period of time.

[0095] In the hydraulic control device 100, when the fluid is guided from the discharge passage 81 to the first drain passage 76a during gas bleed on the pilot chamber 23 side, the pressure on the pilot chamber 23 side increases due to the orifice 79. This causes the air on the pilot chamber 23 side to be compressed and the compressed high-pressure air to be dissolved in the fluid, so that the air on the pilot chamber 23 side can be efficiently discharged to the drain chamber 51.

[0096] In the hydraulic control device 100, the valve body 84 is closed during normal operation of the cylinder 15 and is not opened by the pilot pressure led to the pilot chamber 23, so that the gas vent device 80 does not adversely affect the operation of the cylinder 15.

[0097] The following modified examples are also within the scope of the present invention, and it is possible to combine the configurations shown in the modified examples with the configurations described in the above-mentioned embodiments, to combine the configurations described in the different embodiments above, or to combine the configurations described in the different modified examples below.

[0098] <Variation 1> In the above embodiment, the hydraulic control device 100 controls the telescopic operation of the cylinder 15 that drives the boom 14 of the hydraulic excavator. However, the hydraulic control device 100 may also control the telescopic operation of the cylinder 2 that drives the arm 1 of the hydraulic excavator. In this configuration, the rod side chamber 2a of the cylinder 2 is connected to the first main passage 7, and the anti-rod side chamber 2b is connected to the second main passage 8. When the control valve 6 is switched to the position 6A, hydraulic oil is supplied from the pump 4 to the rod side chamber 2a through the first main passage 7, and hydraulic oil in the anti-rod side chamber 2b is discharged to the tank T through the second main passage 8, and the cylinder 2 is contracted. When the control valve 6 is switched to the position 6B, hydraulic oil is supplied from the pump 4 to the anti-rod side chamber 2b through the second main passage 8, and hydraulic oil in the rod side chamber 2a is discharged to the tank T through the first main passage 7, and the cylinder 2 is extended. When the control valve 6 is in position 6C, the supply and discharge of hydraulic oil to the cylinder 2 is cut off, and the arm 1 remains stopped. In the cylinder 2 that drives the arm 1, the rod side chamber 2a becomes a load side pressure chamber to which a load pressure acts when the control valve 6 is in the neutral position 6C. Even with this configuration, the same effects as those of the above embodiment can be achieved.

[0099] <Variation 2> In the above embodiment, when gas is vented from the pilot chamber 23 side, the set screw 83 serving as a rod drive unit is rotated, and the rod 82 advances within the discharge passage 81, thereby opening the valve body 84. However, the rod drive unit that moves the rod 82 is not limited to the set screw 83, and may be, for example, a solenoid. In this case, the solenoid is controlled so that the rod 82 advances within the discharge passage 81 when gas is vented from the pilot chamber 23 side, thereby opening the valve body 84. Even with this configuration, the same effects as those of the above embodiment can be achieved.

[0100] <Variation 3> In the above embodiment, the first drain passage 76a is provided with an orifice 79. As a result, when fluid is guided from the discharge passage 81 to the first drain passage 76a during gas bleed on the pilot chamber 23 side, the pressure on the pilot chamber 23 side increases due to the orifice 79, so that the air on the pilot chamber 23 side is compressed and the compressed high-pressure air can be dissolved in the fluid, and the air on the pilot chamber 23 side can be efficiently discharged to the drain chamber 51. However, the orifice 79 is not an essential component.

[0101] <Modification 4> In the above embodiment, the rod 82 has a head 82a, a shaft 82b, and a pressing portion 82c. In addition, as shown in FIG. 6, the rod 82 may have a notch 82e formed at the tip of the shaft 82b. The notch 82e is formed at a position on the shaft 82b facing the valve seat 81a. This allows the rod 82 to be pressed against the tip of the shaft 82b when the air on the pilot chamber 23 side is discharged to the drain chamber 51. Even when the pressing portion 82c opens the valve body 84 and the shaft portion 82b is in a position to abut against the valve seat 81a, a space is formed between the shaft portion 82b and the valve seat 81a by the cutout portion 82e, so that the flow of fluid from the pilot chamber 23 to the drain chamber 51 is permitted. Therefore, gas can be vented from the pilot chamber 23 side.

[0102] <Variation 5> In the above embodiment, the gas venting device 80 is used only for venting the gas on the pilot chamber 23 side. In addition, the gas venting device 80 may also be used to discharge the working fluid from the cylinder 15 in the event of an abnormality such as a failure of the pilot pump 5. Specifically, as shown in FIG. 7, after the valve body 84 is opened, the rod 82 is further advanced by the set screw 83, so that it abuts against the piston 50 and moves the piston 50 and the spool 56. This allows the spool 56 to be moved directly by the movement of the set screw 83, not by the pilot pressure. Therefore, even if pilot pressure is not supplied due to an abnormality such as a failure of the pilot pump 5, the spool 56 can be moved by the set screw 83 to switch the switching valve 22 from the shutoff position 22A to the first communication position 22B. This allows the working oil to be discharged from the counter-rod side chamber 15b of the cylinder 15, the cylinder 15 to be contracted, and the boom 14 to be lowered to a safe state.

[0103] The configuration, operation, and effects of the embodiment of the present invention will be described below.

[0104] The fluid pressure control device 100 for controlling the extension and retraction of the cylinders 15, 2 for driving a load (boom 14, arm 1) includes a control valve 6 for controlling the supply of hydraulic fluid from a pump 4 as a fluid pressure supply source to the cylinders 15, 2, a pilot control valve 9 for controlling pilot pressure introduced to the control valve 6 from a pilot pump 5 as a pilot pressure supply source, a main passage 7 for connecting the control valve 6 to a load side pressure chamber 15b, 2a of the cylinders 15, 2 on which a load pressure due to a load acts when the control valve 6 is in a neutral position 6C, and a load holding mechanism 20 provided in the main passage 7, The support mechanism 20 has an operate check valve 21 which allows the flow of the working fluid from the control valve 6 to the load side pressure chambers 15b, 2a while allowing the flow of the working fluid from the load side pressure chambers 15b, 2a to the control valve 6 in response to the back pressure, and a switching valve 22 which operates in conjunction with the control valve 6 by the pilot pressure introduced through the pilot control valve 9 and switches the operation of the operate check valve 21. The switching valve 22 has a pilot chamber 23 to which the pilot pressure is introduced through the pilot control valve 9, a spool 56 which moves in response to the pilot pressure of the pilot chamber 23, and a pilot pressure adjusting valve 56 which adjusts the operation of the pilot chamber 23. The piston 50 receives a thrust pressure and applies a thrust to a spool 56, a drain chamber 51 defined by the spool 56 and the piston 50, a pilot cap 58 disposed opposite the piston 50 as a partition member defining a pilot chamber 23, and a gas venting device 80 disposed on the piston 50 and the pilot cap 58 for discharging gas from the pilot chamber 23 to the drain chamber 51. The gas venting device 80 is formed in the piston 50 across the pilot chamber 23 and the drain chamber 51, and serves as a discharge passage for discharging fluid from the pilot chamber 23 to the drain chamber 51. The drain passage 81 has a rod 81, a rod 82 supported by pilot cap 58 for movement freely, a rod drive unit (set screw 83) for advancing the rod 82 within the drain passage 81, a valve body 84 provided in the drain passage 81 for opening and closing the drain passage 81, and a spring 85 provided in the drain passage 81 as a biasing member for biasing the valve body 84 in a closing direction, and as the rod 82 advances within the drain passage 81 by the rod drive unit, the rod 82 opens the valve body 84 against the biasing force of the spring 85, allowing the flow of fluid from the pilot chamber 23 to the drain chamber 51.

[0105] In this configuration, by advancing the rod 82 by the rod drive unit, the valve element 84 provided in the discharge passage 81 is opened, and the pilot chamber 23 and the drain chamber 51 can be communicated through the discharge passage 81. Therefore, when venting the air on the pilot chamber 23 side, the air in the pilot chamber 23 can be discharged to the drain chamber 51 through the discharge passage 81 having a large flow path cross-sectional area, rather than through a passage having a small flow path cross-sectional area such as the annular gap. Therefore, the air on the pilot chamber 23 side can be efficiently discharged to the drain chamber 51.

[0106] Moreover, the switching valve 22 further has a drain passage 76 connected to the pilot chamber 23, and the drain passage 76 is provided with an orifice 79 as a throttle that imparts resistance to the working fluid passing therethrough.

[0107] In this configuration, when the fluid is guided from the discharge passage 81 to the drain passage 76 during gas bleed on the pilot chamber 23 side, the pressure on the pilot chamber 23 side increases due to the orifice 79, so the gas on the pilot chamber 23 side can be compressed and dissolved in the fluid. Therefore, the air on the pilot chamber 23 side can be efficiently discharged to the drain chamber 51.

[0108] After opening the valve body 84, the rod 82 is further advanced by a rod drive portion (set screw 83) so as to come into contact with the piston 50 and move the piston 50 and the spool 56.

[0109] In this configuration, even in the event of an abnormality such as a breakdown in the pilot pump 5, the rod 82 can be advanced by the rod drive unit to move the spool 56. Therefore, even in the event of an abnormality, the working fluid can be discharged from the cylinder 15,2 to operate the cylinder 15,2. In this way, the gas venting device 80 can perform two functions: venting the gas on the pilot chamber 23 side, and discharging the working fluid from the cylinder 15,2 in the event of an abnormality.

[0110] The biasing force of the spring 85 is set so that when the pilot pump 5 is driven and pilot pressure is introduced into the pilot chamber 23, the valve body 84 is not opened by the pilot pressure.

[0111] In this configuration, the valve body 84 is closed during normal operation of the cylinders 15,2, so that the gas removal device 80 does not adversely affect the operation of the cylinders 15,2.

[0112] Although the embodiments of the present invention have been described above, the above-mentioned embodiments merely show some of the application examples of the present invention, and it is not intended that the technical scope of the present invention be limited to the specific configurations of the above-mentioned embodiments. [Explanation of symbols]

[0113] 100... hydraulic control device (fluid pressure control device), 1... arm (load), 2... cylinder, 2a... rod side chamber (load side pressure chamber), 4... pump (fluid pressure supply source), 5... pilot pump (pilot pressure supply source), 6... control valve, 6C... neutral position, 7... first main passage (main passage), 9... pilot control valve, 14... boom (load), 15... cylinder, 15b... anti-rod side chamber (load side pressure chamber), 20... load holding mechanism, 21... operate check valve, 22... switching valve, 23... pilot chamber, 50... piston, 51... drain chamber, 56... spool, 58... pilot cap (compartment member), 76... drain passage, 79... orifice (restriction), 80... gas vent device, 81... discharge passage, 82... rod, 83... set screw (rod drive section), 84... valve body, 85... spring (biasing member)

Claims

1. A fluid pressure control device that controls the extension and contraction operation of a cylinder that drives a load, a control valve that controls the supply of hydraulic fluid from a fluid pressure supply source to the cylinder; a pilot control valve for controlling a pilot pressure introduced from a pilot pressure supply source to the control valve; a main passage connecting the control valve to a load-side pressure chamber of the cylinder to which a load pressure due to a load acts when the control valve is in a neutral position; a load retaining mechanism provided in the main passage, The load holding mechanism includes: an operated check valve that allows the flow of hydraulic fluid from the control valve to the load side pressure chamber, and also allows the flow of hydraulic fluid from the load side pressure chamber to the control valve in response to a back pressure; a switching valve that operates in conjunction with the control valve by a pilot pressure introduced through the pilot control valve and switches the operation of the operated check valve; The switching valve is a pilot chamber to which a pilot pressure is introduced through the pilot control valve; A spool that moves in response to the pilot pressure in the pilot chamber; A piston that receives pilot pressure and applies thrust to the spool; a drain chamber defined by the spool and the piston; a partition member provided opposite the piston and partitioning the pilot chamber; a gas venting device provided on the piston and the partition member for discharging gas from the pilot chamber to the drain chamber, The gas removal device comprises: a drain passage formed in the piston across the pilot chamber and the drain chamber for discharging fluid from the pilot chamber to the drain chamber; A rod supported movably on the partition member; a rod drive portion that advances the rod within the discharge passage; a valve body provided in the discharge passage for opening and closing the discharge passage; a biasing member provided in the discharge passage and biasing the valve body in a closing direction, a rod driving portion that drives the rod forward within the drain passage, the rod opens the valve body against the biasing force of the biasing member, and allows fluid to flow from the pilot chamber to the drain chamber.

2. The fluid pressure control device according to claim 1, The switching valve further has a drain passage connected to the pilot chamber, 2. A fluid pressure control device, comprising: a throttle provided in the drain passage for applying resistance to the working fluid passing through the drain passage.

3. The fluid pressure control device according to claim 1, 2. The fluid pressure control device according to claim 1, wherein after the rod opens the valve body, the rod is further advanced by the rod drive portion to come into contact with the piston and move the piston and the spool.

4. The fluid pressure control device according to claim 1, A fluid pressure control device characterized in that the biasing force of the biasing member is set so that when the pilot pressure supply source is driven and pilot pressure is introduced to the pilot chamber, the pilot pressure does not cause the valve body to open.

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