Fluid pressure control device

Abstract

A degassing device (80) includes: a discharge passage (81) that is formed in a piston (50) across a pilot chamber (23) and a drain chamber (51) and that is for discharging fluid from the pilot chamber (23) to the drain chamber (51); a rod (82) that is movably supported by a pilot cap (58); a set screw (83) that advances the rod (82) in the discharge passage (81); a valve body (84) that is provided in the discharge passage (81) and opens / closes the discharge passage (81); and a spring (85) provided in the discharge passage (81) and serving as an urging member for urging the valve body (84) in the closing direction. The rod (82) is advanced within the discharge passage (81) by the set screw (83), whereby the rod (82) opens a valve by advancing the valve body (84) against the urging force of the spring (85), and the flow of the fluid from the pilot chamber (23) to the drain chamber (51) is permitted.

Description

Fluid Pressure Control Device

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

[0002] JP2010-101400A discloses a fluid pressure control device for controlling the operation of work equipment, which includes a control valve that switches the supply and discharge of hydraulic oil to and from a cylinder to control the extension and contraction operation of the cylinder, and a load holding mechanism that is installed in a main passage that connects the load side pressure chamber of the cylinder to the control valve.

[0003] The load holding mechanism includes a pilot operated check valve and a meter-out control valve that operates in response to pilot pressure to switch the operation of the pilot 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.

[0004] 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.

[0005] 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 may remain in the pilot chamber, which could affect the operation of the fluid pressure control device.

[0006] An object of the present invention is to efficiently exhaust air on the pilot chamber side.

[0007] According to one aspect of the present invention, there is provided a fluid pressure control device for controlling the extension and retraction of a cylinder that drives a load, the device comprising: 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 introduced 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, wherein 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 accordance with a back pressure; and 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 operate check valve, wherein the switching valve has a pilot chamber to which pilot pressure is introduced through the pilot control valve, and a spool that moves in accordance with the pilot pressure in the pilot chamber. a piston that applies thrust to the spool by receiving pilot pressure; a drain chamber partitioned by the spool and the piston; a partition member that is provided opposite the piston and partitions the pilot chamber; and a gas venting device that is provided on the piston and the partition member and discharges gas from the pilot chamber to the drain chamber. The gas venting device has: a discharge passage that is formed in the piston across the pilot chamber and the drain chamber and is for discharging fluid from the pilot chamber to the drain chamber; a rod that is movably supported by the partition member; a rod driving unit that moves the rod forward within the discharge passage; a valve body that is provided in the discharge passage and opens and closes the discharge passage; and a biasing member that is provided in the discharge passage and biases the valve body in a closing direction. When the rod is moved forward within the discharge passage by the rod driving unit, the rod opens the valve body against the biasing force of the biasing member, and fluid is allowed to flow from the pilot chamber to the drain chamber.

[0008] FIG. 1 is a diagram showing a portion of a hydraulic excavator. FIG. 2 is a fluid pressure circuit diagram of a fluid pressure control device according to an embodiment of the present invention. FIG. 3 is a cross-sectional view of a load holding mechanism of a fluid pressure control device according to an embodiment of the present invention. FIG. 4 is an enlarged cross-sectional view of the periphery of a gas vent device, showing a state in which the set screw is in an initial position and the valve body is closed. FIG. 5 is an enlarged cross-sectional view of the periphery of a gas vent device, showing a state in which the valve body is open. FIG. 6 is an enlarged cross-sectional view of the periphery of a gas vent device of a fluid pressure control device according to a fourth modification of the embodiment of the present invention. FIG. 7 is an enlarged cross-sectional view of the periphery of a gas vent device of a fluid pressure control device according to a fifth modification of the embodiment of the present invention.

[0009] Hereinafter, a fluid pressure control device according to an embodiment of the present invention will be described with reference to the drawings.

[0010] 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 will be described that controls the extension and retraction operation of a cylinder 15 that drives a boom 14 (load) of a hydraulic excavator shown in Fig. 1. In the following, a case will be described in which hydraulic oil is used as the working fluid of the cylinder 15, but instead of hydraulic oil, for example, a water-soluble substitute liquid or the like may be used.

[0011] First, the hydraulic circuit of the hydraulic control device 100 will be described with reference to Figure 2. The cylinder 15 includes a cylindrical cylinder tube 15c, a piston 15d that is slidably inserted into the cylinder tube 15c and divides the interior of the cylinder tube 15c into a rod-side chamber 15a and an anti-rod-side chamber 15b, and a piston rod 15e that has one end connected to the piston 15d and the other end extending outside the cylinder tube 15c and connected to the boom 14.

[0012] The hydraulic excavator is equipped with a power source such as an engine or an electric motor, and the power drives a pump 4 as a fluid pressure supply source and a pilot pump 5 as a pilot pressure supply source.

[0013] 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 .

[0014] The control valve 6 and the anti-rod side chamber 15 b of the cylinder 15 are connected by a first main passage 7 , and the control valve 6 and the rod side chamber 15 a of the cylinder 2 are connected by a second main passage 8 .

[0015] The control valve 6 is operated by a pilot pressure that is guided from the pilot pump 5 through the pilot control valve 9 to the pilot chambers 6 a and 6 b when the operator of the hydraulic excavator manually operates the control lever 10 .

[0016] 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 to 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 arrow 18 shown in FIG.

[0017] 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 to the rod side chamber 15a through the second main passage 8, while hydraulic oil in the anti-rod side chamber 15b is discharged to the tank T through the first main passage 7. This causes the cylinder 15 to contract, and the boom 14 moves down in the direction of arrow 19 shown in FIG.

[0018] When no pilot pressure is introduced into the pilot chambers 6a and 6b, the control valve 6 is in position 6C, the supply and discharge of hydraulic oil to the cylinder 2 is cut off, and the boom 14 remains stopped.

[0019] 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 the supply and discharge of hydraulic oil in the cylinder 15 and controls the extension and retraction of the cylinder 15.

[0020] 1, when the control valve 6 is switched to the neutral position 6C to stop the movement of the boom 14 while the boom 14 is 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 load pressure acts when the control valve 6 is in the neutral position 6C.

[0021] A load holding mechanism 20 is provided in the first main passage 7 connected to the anti-rod side chamber 15b, which is a 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.

[0022] In the cylinder 2 that drives the arm 1 (see Figure 1), the rod side chamber 2a serves as a 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 a main passage connected to the rod side chamber 2a.

[0023] The load holding mechanism 20 has an operated 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 operated check valve 21.

[0024] Operated check valve 21 has a valve element 24 that opens and closes first main passage 7, a seat portion 28 on which valve element 24 seats, a back pressure chamber 25 facing the back surface of valve element 24, and a passage 26 formed in valve element 24 that constantly guides hydraulic oil in anti-rod side chamber 15b to back pressure chamber 25. Passage 26 is provided with a throttle 26a that applies resistance to hydraulic oil passing through it.

[0025] The first main passage 7 has a cylinder side first main passage 7 a connecting the anti-rod side chamber 15 b and the operated check valve 21 , and a control valve side first main passage 7 b connecting the operated check valve 21 and the control valve 6 .

[0026] The valve body 24 is formed with a first pressure-receiving surface 24a on which the pressure of the control valve side first main passage 7b acts, and a second pressure-receiving surface 24b on which the pressure of the anti-rod side chamber 15b acts through the cylinder side first main passage 7a.

[0027] A spring 27 serving as a biasing member that biases the valve body 24 in the 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.

[0028] With the valve element 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 from the anti-rod side chamber 15b, maintains the load pressure, and maintains the stopped state of the boom 14.

[0029] The switching valve 22 has a pilot chamber 23 to which pilot pressure is introduced via the pilot control valve 9, a spool 56 (see FIG. 3) that moves according 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 FIG. 3) that accommodates the spring 36, a drain chamber 51 (see FIG. 3) that is provided on the opposite side of the spool 56 from the spring chamber 54, and a drain passage 76 that connects the spring chamber 54 and the drain chamber 51 to the tank T.

[0030] 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.

[0031] The switching valve 22 switches the 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.

[0032] 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 shutoff position 22A, a first communicating position 22B, and a second communicating position 22C.

[0033] When the pilot pressure is introduced into the pilot chamber 6b of the control valve 6, the pilot pressure is also introduced into 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.

[0034] 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.

[0035] When a pilot pressure equal to or greater than a first predetermined pressure and less than a second predetermined pressure is introduced into 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 through the switching valve 22 to the downstream passage 38. In other words, the hydraulic oil in the anti-rod-side chamber 15b bypasses the operated check valve 21 and is introduced into the control valve-side first main passage 7b. At this time, resistance is applied to the flow of hydraulic oil by the orifice 37. The second supply port 33 remains blocked.

[0036] 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 discharge port 34, and the second supply port 33 also communicates with the discharge 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 across the throttle 26a, and the pressure in the back pressure chamber 25 decreases. As a result, the force acting on the valve element 24 in the closing direction decreases, 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.

[0037] 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.

[0038] 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 combined drain passage 76c formed by the combination of the first drain passage 76a and the second drain passage 76b. The first drain passage 76a is combined with 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 combined 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 from the drain chamber 51 and the spring chamber 54 are discharged to the tank T through the combined drain passage 76c, the drain port 77, and the drain hose 78. The drain chamber 51 and the spring chamber 54 provided on both sides of the spool 56 of the switching valve 22 are both connected to the tank T, so that 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.

[0039] 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 acts on the boom 14.

[0040] 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 pilot pressure is not introduced to the pilot chamber 23 and the switching valve 22 is in the shut-off position 22A. In Fig. 3, components that are assigned the same reference numerals as those shown in Fig. 2 have the same configuration as those shown in Fig. 2.

[0041] 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.

[0042] 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.

[0043] 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 whose hollow portion a pin portion 56c formed to protrude from the one end face 56a of the spool 56 is inserted, and a second spring bearing member 46 disposed near 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.

[0044] A pilot chamber 23 is defined to the side of the other end surface 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 within the pilot chamber 23. The piston 50 receives pilot pressure at its back surface and applies a thrust to the spool 56 against the biasing force of the spring 36.

[0045] Within the piston bore 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. Hydraulic oil that leaks into the drain chamber 51 is discharged from the first drain passage 76a to the tank T.

[0046] The piston 50 has a sliding portion 50a whose outer surface slides along the inner surface of the piston hole 60b, a tip portion 50b formed with a smaller diameter than the sliding portion 50a and facing the other end surface 56b of the spool 56, and a base end portion 50c formed with a smaller diameter than the sliding portion 50a and facing the tip surface of the pilot cap 58.

[0047] 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 portion 50a. As a result, the piston 50 moves forward, and the tip end 50b abuts against the other end surface 56b of the spool 56, moving the spool 56. In this way, 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 portion 50a, and pilot pressure acts on the annular back surface of the sliding portion 50a, allowing the piston 50 to move forward.

[0048] 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.

[0049] The spool 56 stops at a position where the biasing force of the spring 36 acting on one end surface 56a and the thrust of the piston 50 acting on the other end surface 56b are balanced, and the switching position of the switching valve 22 is set at the stopping position of the spool 56.

[0050] 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.

[0051] The sleeve 61 has three ports formed therein: 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).

[0052] 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.

[0053] 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 peripheral 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.

[0054] When the operating lever 10 is not operated and pilot pressure is not introduced into the pilot chamber 23, the biasing force of the spring 36 presses the poppet valve 70 formed in the spool 56 against a valve seat 71 formed on the inner periphery of the sleeve 61, blocking communication between the second pressure chamber 65 and the first pressure chamber 64. Therefore, communication between the first supply port 32 and the exhaust port 34 is blocked. This prevents hydraulic oil from leaking from the anti-rod-side chamber 15b 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 bearing member 45 and the end face of the sleeve 61, so the poppet valve 70 is reliably seated against the valve seat 71 by the biasing force of the spring 36.

[0055] 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 orifices 37. Therefore, 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. Due to the communication between the first supply port 32 and the exhaust port 34, the hydraulic oil in the anti-rod-side chamber 15b is introduced into the downstream passage 38 (see FIG. 2 ) through the orifice 37. This state corresponds to the first communicating position 22B of the switching valve 22.

[0056] When the pilot pressure introduced into 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 discharge 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 discharge 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.

[0057] Next, the operation of the hydraulic control device 100 will be described with reference to FIGS.

[0058] 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, no pilot pressure is introduced into the pilot chamber 23 of the switching valve 22, so the switching valve 22 is in the shut-off position 22A.

[0059] 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, and therefore the load acting on the back surface of the valve element 24 due to the pressure in 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.

[0060] 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 switches to the extension position 6A by an amount corresponding to the pilot pressure. When the control valve 6 switches 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 shut-off position 22A without introducing pilot pressure to the pilot chamber 23, so the back pressure chamber 25 of the operated check valve 21 is maintained at the pressure of the anti-rod side chamber 15b. When the load acting on the first pressure-receiving surface 24a becomes greater than the total load of the load acting on the back surface of the valve disc 24 due to the pressure in the back pressure chamber 25 and the biasing force of the spring 27, the valve disc 24 moves away from the seat portion 28. When the operated check valve 21 opens in this manner, hydraulic oil discharged from the pump 4 is supplied to the anti-rod side chamber 15b, and the cylinder 15 extends. This causes the boom 14 to rise in the direction of the arrow 18 shown in FIG.

[0061] 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 the switching valve 22 switches to the first communication position 22B or the second communication position 22C depending on the supplied pilot pressure.

[0062] 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, communication between the second supply port 33 and the discharge port 34 is blocked, so 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 its closed state.

[0063] Meanwhile, because 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. Furthermore, because 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 .

[0064] Here, the switching valve 22 is switched to the first communication position 22B mainly when performing crane work to lower an object attached to the bucket 13 to a target position. During crane work, it is necessary to slowly lower the boom 14 in the direction of arrow 19 by retracting the cylinder 15 at a low speed. Therefore, the pilot pressure introduced to the pilot chamber 6b of the control valve 6 is small, and the control valve 6 is only switched slightly to the retracted 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 anti-rod-side chamber 15b is discharged through the orifice 37, and the boom 14 is lowered at a low speed suitable for crane work.

[0065] Furthermore, when selector valve 22 is in first communicating position 22B, even if an incident 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, thereby suppressing the falling speed of bucket 13. For this reason, selector valve 22 can be switched to shut-off position 22A before bucket 13 falls to the ground, preventing bucket 13 from falling suddenly.

[0066] In this way, the throttle 37 serves to suppress the descending speed of the cylinder 2 when the operated 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.

[0067] When the pilot pressure introduced into 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 introduced from the back pressure passage 31 to the downstream passage 38, bypassing the throttle 37, and is then discharged from the control valve-side first main passage 7b through the control valve 6 to the tank T. This generates a pressure difference across the throttle 26a, reducing the pressure in the back pressure chamber 25. This reduces the force acting on the valve element 24 in the closing direction, causing the valve element 24 to move away from the seat portion 28, and the function of the operated check valve 21 as a check valve is released.

[0068] 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 also 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.

[0069] When the operate check valve 21 opens, the hydraulic oil in the anti-rod side chamber 15b is discharged to the tank T through the first main passage 7, causing the cylinder 2 to quickly retract. In other words, when the switching valve 22 is switched to the second communicating 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 retraction speed of the cylinder 2 increases. As a result, the boom 14 quickly descends in the direction of arrow 19.

[0070] The switching valve 22 is switched to the second communication position 22C when excavation work or the like is being performed, and the pilot pressure introduced to the pilot chamber 6b of the control valve 6 is large, so that the control valve 6 is switched largely to the contracted position 6B. Therefore, the pilot pressure introduced to the pilot chamber 23 of the switching valve 22 is also large and exceeds the second predetermined pressure, so that the switching valve 22 is switched to the second communication position 22C.

[0071] Next, the gas depletion 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 depletion device 80 in Fig. 3. Below, a case will be described in which the gas depletion device 80 discharges air from the pilot chamber 23 to the drain chamber 51, but what is discharged by the gas depletion device 80 is not limited to air and may be other gases.

[0072] 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 peripheral surface of the main body 58b, and the male thread 58c and a female thread formed on the inner peripheral surface of the piston hole 60b are threadedly coupled 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 portion of a rod 82 (described later) of the gas venting device 80 is inserted.

[0073] 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 in the pilot cap 58, a set screw 83 serving as a rod drive unit that moves the rod 82 forward within 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 to pass through the piston 50 in the direction of movement of the piston 50, and is formed coaxially with the insertion hole 58d of the pilot cap 58.

[0074] The discharge passage 81 is provided with an annular valve seat 81a. The valve seat 81a has a hollow portion 81b whose diameter is smaller than the inner circumferential surface of the discharge passage 81. The valve element 84 is a sphere and is seated on a T-shaped seating member 86. The valve element 84 may have a shape other than a sphere, such as a poppet valve. The valve element 84 and seating member 86 are located 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 element 84. Therefore, the valve element 84 can abut against the valve seat 81a, and when the valve element 84 seats on the valve seat 81a, the discharge passage 81 is blocked. The spring 85 is compressed and located 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 element 84 toward the valve seat 81a via the seating member 86. In other words, the spring 85 biases the valve element 84 so as 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 element 84 will not open due to the pilot pressure. In other words, the biasing force of the spring 85 is set so that the valve element 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 will be described later.

[0075] The rod 82 is disposed between the insertion hole 58d of the pilot cap 58 and the discharge passage 81. The rod 82 includes a head 82a slidably supported on the inner circumferential surface of the insertion hole 58d, a shaft 82b extending axially from the head 82a, and a pressing portion 82c formed at the tip of the shaft 82b and capable of pressing the valve body 84. The head 82a has a larger diameter than the shaft 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 disposed in contact with the head 82a. The shaft 82b is disposed between the insertion hole 58d, the pilot chamber 23, and the discharge passage 81 and has 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 be inserted 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 within 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.

[0076] The set screw 83 is provided in the pilot cap 58. The set screw 83 passes through the head 58a of the pilot cap 58, and its tip (the end on the right side in FIG. 4 ) is positioned within the insertion hole 58d and abuts against the head 82a of the rod 82. The set screw 83 can be moved axially by being manually rotated using a tool by an operator. When the set screw 83 moves, the rod 82 abutting against the set screw 83 moves together with the set screw 83. This opens and closes the valve body 84, enabling air to be discharged from the pilot chamber 23 side, as described below. During normal operation of the cylinder 15, the set screw 83 is held in its initial position as shown in FIG. 4. The set screw 83 may be moved electrically using an actuator or the like.

[0077] Next, the operation and function of the degassing device 80 will be described.

[0078] The gas vent device 80 is used to discharge air on the pilot chamber 23 side into the drain chamber 51, for example, after assembly of the hydraulic excavator or when starting the hydraulic excavator after being stopped for a long period of time. If air remains on the pilot chamber 23 side, when starting the hydraulic excavator, the increase in pilot pressure in the pilot chamber 23 in response to input operations by the operator will be delayed. Therefore, the air on the pilot chamber 23 side will cause a delay in the response of the cylinder 15 to input operations by the operator. By using the gas vent device 80 to vent air on the pilot chamber 23 side, the operation of the hydraulic control device 100 will be stable.

[0079] When discharging air from the pilot chamber 23 side into the drain chamber 51, the operator first uses a tool to rotate the setscrew 83 from the initial position shown in FIG. 4 to move it to the right in FIG. 4. This causes the rod 82 to move to the right in FIG. 4 together with the setscrew 83 and advance within the discharge passage 81. The pressing portion 82c of the rod 82 then contacts the valve element 84 and presses the valve element 84 against the biasing force of the spring 85. When the force with which the rod 82 presses the valve element 84 exceeds the biasing force of the spring 85, the valve element 84 lifts off the valve seat 81a and opens, as shown in FIG. 5. This allows fluid to flow 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 element 84 and the shaft portion 82b does not abut against the valve seat 81a.

[0080] Then, with the valve element 84 in an open state, the pilot pump 5 is driven to introduce fluid into the pilot chamber 23. The fluid supplied from the pilot pump 5 is introduced into the pilot chamber 23 while pushing out any air remaining in the flow path after the assembly of the hydraulic excavator, and is then discharged into the drain chamber 51 through the discharge passage 81. The fluid discharged into the drain chamber 51 is then discharged into the tank T through the first drain passage 76a, the combined drain passage 76c, and the drain port 77. In this manner, gas is vented from the pilot chamber 23 side. Once gas venting from the pilot chamber 23 side is complete, the set screw 83 is returned to its initial position shown in FIG. 4 , and the discharge passage 81 is returned to a state in which it is blocked by the valve element 84. Note that gas venting from the pilot chamber 23 side may be performed using a pump dedicated to gas venting that is different from the pilot pump 5.

[0081] 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.

[0082] 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 through. Therefore, 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, which is upstream of the orifice 79, increases. This compresses the air on the pilot chamber 23 side, and allows the compressed, high-pressure air to be dissolved in the fluid. Therefore, the air can be compressed and dissolved in the fluid before being discharged, allowing the air on the pilot chamber 23 side to be efficiently discharged to the drain chamber 51.

[0083] 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 will not open due to 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, and therefore the gas vent device 80 does not adversely affect the operation of the cylinder 15.

[0084] According to the above embodiment, the following effects are achieved.

[0085] In the hydraulic control device 100, when the air 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, which has 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 time.

[0086] 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 compresses the air on the pilot chamber 23 side and allows 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.

[0087] 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 guided to the pilot chamber 23, so the gas vent device 80 does not adversely affect the operation of the cylinder 15.

[0088] The following modified examples are also within the scope of the present invention, and it is possible to combine the configuration shown in the modified example with the configuration described in the above embodiment, to combine the configurations described in the different embodiments above, or to combine the configurations described in the different modified examples below.

[0089] <Modification 1> In the above embodiment, the hydraulic control device 100 controls the extension and retraction of the cylinder 15 that drives the boom 14 of the hydraulic excavator. However, the hydraulic control device 100 may also control the extension and retraction 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 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, causing the cylinder 2 to contract. When the control valve 6 is switched to 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, causing the cylinder 2 to extend. 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 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.

[0090] <Modification 2> In the above embodiment, when gas is vented from the pilot chamber 23 side, the set screw 83 serving as the rod drive unit is rotated, and the rod 82 moves forward within the discharge passage 81, thereby opening the valve element 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, by controlling the solenoid, the rod 82 moves forward within the discharge passage 81 when gas is vented from the pilot chamber 23 side, thereby opening the valve element 84. Even with this configuration, the same effects as those of the above embodiment can be achieved.

[0091] <Modification 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 venting on the pilot chamber 23 side, the orifice 79 increases the pressure on the pilot chamber 23 side, compressing the air on the pilot chamber 23 side and dissolving the compressed high-pressure air into the fluid, thereby enabling the air on the pilot chamber 23 side to be efficiently discharged to the drain chamber 51. However, the orifice 79 is not an essential component.

[0092] <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 in a position on the shaft 82b facing the valve seat 81a. As a result, when air on the pilot chamber 23 side is discharged to the drain chamber 51, even if the pressing portion 82c of the rod 82 opens the valve body 84 and the shaft 82b is in a position abutting the valve seat 81a, a space is formed between the shaft 82b and the valve seat 81a by the notch 82e, allowing fluid to flow from the pilot chamber 23 to the drain chamber 51. This allows gas to be vented from the pilot chamber 23 side.

[0093] <Modification 5> In the above embodiment, the gas vent device 80 is used only to vent the gas on the pilot chamber 23 side. In addition, the gas vent device 80 may also be used to discharge hydraulic 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 setscrew 83, thereby contacting the piston 50 and moving the piston 50 and the spool 56. This allows the spool 56 to be moved directly by the movement of the setscrew 83, rather than by 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 using the setscrew 83 to switch the switching valve 22 from the shut-off position 22A to the first communicating position 22B. This allows hydraulic fluid to be discharged from the anti-rod-side chamber 15b of the cylinder 15, causing the cylinder 15 to retract, and the boom 14 to be lowered to a safe state.

[0094] The configuration, operation, and effects of the embodiment of the present invention will be described below.

[0095] The fluid pressure control device 100 for controlling the extension and retraction of the cylinders 15, 2 that drive the load (boom 14, arm 1) includes a control valve 6 that controls 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 that controls the pilot pressure introduced to the control valve 6 from a pilot pump 5 as a pilot pressure supply source, a main passage 7 that connects the control valve 6 to load-side pressure chambers 15b, 2a of the cylinders 15, 2 on which load pressure due to the 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 operated check valve 21 that allows the flow of working fluid from the control valve 6 to the load side pressure chambers 15b and 2a, while allowing the flow of working fluid from the load side pressure chambers 15b and 2a to the control valve 6 in accordance with the back pressure, and a switching valve 22 that operates in conjunction with the control valve 6 by pilot pressure introduced through the pilot control valve 9 and switches the operation of the operated check valve 21. The switching valve 22 has a pilot chamber 23 to which pilot pressure is introduced through the pilot control valve 9, a spool 56 that moves in accordance with the pilot pressure in the pilot chamber 23, and a pilot valve 22. a piston 50 that applies thrust to a spool 56 by receiving a thrust pressure; a drain chamber 51 that is partitioned by the spool 56 and the piston 50; a pilot cap 58 that is provided opposite the piston 50 and serves as a partitioning member that partitions the pilot chamber 23; and a gas venting device 80 that is provided on the piston 50 and the pilot cap 58 and that discharges 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 51 has a rod 81, a rod 82 supported by the pilot cap 58 so as to be freely movable, a rod drive unit (set screw 83) that moves the rod 82 forward within the drain passage 81, a valve body 84 that is provided in the drain passage 81 and opens and closes the drain passage 81, and a spring 85 that is provided in the drain passage 81 as a biasing member that biases the valve body 84 in the closing direction, and when the rod 82 moves forward 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 fluid to flow from the pilot chamber 23 to the drain chamber 51.

[0096] In this configuration, by advancing the rod 82 with 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, 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. Therefore, the air on the pilot chamber 23 side can be efficiently discharged to the drain chamber 51.

[0097] 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 applies resistance to the working fluid passing through.

[0098] In this configuration, when the fluid is guided from the discharge passage 81 to the drain passage 76 during gas venting 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 into the fluid. Therefore, the air on the pilot chamber 23 side can be efficiently discharged to the drain chamber 51.

[0099] After opening the valve body 84 , the rod 82 is further advanced by the rod drive unit (set screw 83 ), and comes into contact with the piston 50 , moving the piston 50 and the spool 56 .

[0100] With this configuration, even in the event of an abnormality such as a breakdown of 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 cylinders 15, 2 to operate the cylinders 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 cylinders 15, 2 in the event of an abnormality.

[0101] 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 does not open due to the pilot pressure.

[0102] 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.

[0103] Although the embodiments of the present invention have been described above, the above embodiments merely illustrate 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 embodiments.

[0104] This application claims priority based on Japanese Patent Application No. 2023-145842, filed with the Japan Patent Office on September 8, 2023, the entire contents of which are incorporated herein by reference.

Claims

1. A fluid pressure control device for controlling the extension and retraction of a cylinder that drives a load, comprising: a control valve for controlling the supply of working fluid to the cylinder from a fluid pressure supply source; a pilot control valve for controlling pilot pressure led to the control valve from a pilot pressure supply source; a main passage connecting the control valve to a load side pressure chamber of the cylinder on which 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, wherein the load holding mechanism has: an operate check valve for allowing 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 back pressure; and a switching valve for operating in conjunction with the control valve by pilot pressure led through the pilot control valve and for switching the operation of the operate check valve, wherein the switching valve has: a pilot chamber to which pilot pressure is led through the pilot control valve; a spool that moves in response to the pilot pressure in the pilot chamber; and 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 defining 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, wherein the gas venting device comprises: a discharge passage formed in the piston spanning the pilot chamber and the drain chamber, for discharging fluid from the pilot chamber to the drain chamber; a rod supported movably in the partition member; a rod drive unit for advancing 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, wherein the rod is advanced within the discharge passage by the rod drive unit, so that the rod opens the valve body against the biasing force of the biasing member, thereby allowing a flow of fluid from the pilot chamber to the drain chamber.

2. A fluid pressure control device as claimed in claim 1, wherein the switching valve further has a drain passage connected to the pilot chamber, and the drain passage is provided with a restriction that provides resistance to the working fluid passing through.

3. A fluid pressure control device as claimed in claim 1, wherein after the valve body is opened, the rod is moved further forward by the rod drive section, thereby abutting against the piston and moving the piston and the spool.

4. A fluid pressure control device as claimed in claim 1, wherein 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 pilot pressure does not cause the valve body to open.

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