WO2023176685A1

WO2023176685A1 - Fluid pressure control device

Info

Publication number: WO2023176685A1
Application number: PCT/JP2023/009044
Authority: WO
Inventors: 俊輔久保
Original assignee: Ｋｙｂ株式会社
Priority date: 2022-03-16
Filing date: 2023-03-09
Publication date: 2023-09-21

Abstract

A load retention mechanism (20) has a switching valve (22) for switching the operation of an operation check valve (21). The switching valve (22) has a piston (50) that, upon reception of pilot pressure, imparts thrust to a spool (56); and a gas releasing valve (80) that is provided to the piston (50) and that discharges gas from the pilot chamber (23) to a drain side. The gas releasing valve (80) has a valve body (82) for opening/closing a passage (81). The valve body (82) comes into contact with a first sheet part (81b) by a biasing force of a biasing member (83) and blocks the passage (81) during stoppage of a pilot pressure supply source (5), and moves against the biasing force of the biasing member (83) to be separated from the first sheet part (81b) and allows a fluid to flow from the pilot chamber (23) to a drain chamber (51) while the pilot pressure supply source (5) is driving and when the pilot pressure of the pilot chamber (23) is less than a prescribed pressure level which is lower than the pilot pressure for moving the spool (56).

Description

Fluid pressure control device

The present invention relates to a fluid pressure control device.

As a fluid pressure control device that controls the operation of work equipment, Japanese Patent Application Publication No. 2010-101400 discloses a control valve that switches the supply and discharge of hydraulic oil to and from a cylinder and controls the expansion and contraction operation of the cylinder, and a load side pressure chamber of the cylinder. A device is disclosed that includes a load holding mechanism interposed in a main passage connecting the control valve.

The load holding mechanism includes an operated check valve and a meter-out control valve that is operated 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 pilot pressure is introduced, and a piston that is slidably accommodated in the pilot chamber and receives the pilot pressure to move the spool.

In this type of fluid pressure control device, a drain chamber that communicates with the tank is divided between the spool and the piston so that when pilot pressure is introduced into the pilot chamber, the thrust of the piston is efficiently transmitted to the spool. There is.

An annular gap is provided between the piston and the housing for discharging air from the pilot chamber to the drain chamber. When the work equipment is stopped, air in the drain chamber moves to the pilot chamber through the annular gap between the piston and the housing. When the work equipment is started, the increase in pilot pressure in the pilot room is delayed in response to the operator's input operation due to the influence of the air that has moved to the pilot room side, and the air from the pilot room side drains through the annular gap between the piston and the housing. The increase in pilot pressure in the pilot room is completed after it is discharged into the pilot room.

In this way, the gas on the pilot room side causes a delay in response to operator input operations when starting the work equipment.

An object of the present invention is to prevent the movement of gas from the drain side to the pilot chamber side, and to suppress response delays due to the influence of the gas.

According to an aspect of the present invention, there is provided a fluid pressure control device for controlling the expansion and contraction operation of a cylinder that drives a load, comprising: a control valve that controls supply of working fluid to the cylinder; and a control valve that controls the supply of working fluid to the cylinder; a pilot control valve that controls pilot pressure guided to the valve; a main passage connecting the control valve and 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; a load holding mechanism provided in the main passage, the load holding mechanism 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 in accordance with back pressure. an operated check valve that allows a flow of working fluid to the control valve; and a switching valve that operates in conjunction with the control valve by pilot pressure guided through the pilot control valve and switches the operation of the operated check valve. The switching valve has a pilot chamber to which pilot pressure is introduced through the pilot control valve, a spool that moves according to the pilot pressure in the pilot chamber, and a thrust force applied to the spool in response to the pilot pressure. It has a piston, a drain chamber defined by the spool and the piston, and a gas vent valve provided in the piston for discharging gas from the pilot chamber to the drain chamber, the gas vent valve being , a passage provided across the pilot chamber and the drain chamber, a valve body that opens and closes the passage, and a biasing member that biases the valve body, the valve body being connected to the pilot pressure supply source. When stopped, the biasing force of the biasing member contacts the first seat portion to block the passage, and when the pilot pressure supply source is driven, the pilot pressure in the pilot chamber is applied to the pilot chamber in which the spool moves. When the pressure is lower than the predetermined pressure, the fluid moves against the biasing force of the biasing member and leaves the first seat portion, allowing fluid to flow from the pilot chamber to the drain chamber.

It is a figure showing a part of a hydraulic excavator. 1 is a fluid pressure circuit diagram of a fluid pressure control device according to an embodiment of the present invention. FIG. 3 is a sectional view of a load holding mechanism of a fluid pressure control device according to an embodiment of the present invention. FIG. 3 is a sectional view of the vicinity of the piston. FIG. 3 is a graph diagram showing the relationship between the pilot pressure in the pilot chamber and the flow rate of air flowing from the pilot chamber to the drain chamber. FIG. 7 is a sectional view of the vicinity of a piston in a load holding mechanism of a fluid pressure control device according to a modification of the embodiment of the present invention.

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

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 that controls the expansion and contraction operation of a cylinder 2 that drives an arm (load) 1 of a hydraulic excavator shown in FIGS. 1 and 2 will be described. The fluid pressure control device may control the expansion and contraction operation of a lift cylinder mounted on a forklift or the like. In the following, a case will be described in which hydraulic oil is used as the working fluid of the cylinder 2, but instead of the hydraulic oil, for example, a water-soluble substitute liquid or the like may be used.

First, the hydraulic circuit of the hydraulic control device 100 will be described with reference to FIG. 2. The cylinder 2 includes a cylindrical cylinder tube 2c, a piston 2d that is slidably inserted into the cylinder tube 2c and partitions the inside of the cylinder tube 2c into a rod side chamber 2a and an anti-rod side chamber 2b, and one end is connected to the piston 2d. A rod 2e whose other end extends outside the cylinder tube 2c and is connected to the arm 1 is provided.

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. The pilot pump 5 may be eliminated and the pump 4 may also be used as a pilot pressure supply source. That is, the pump 4 may be used as a fluid pressure supply source and a pilot pressure supply source.

The hydraulic control device 100 includes a control valve 6 that controls the supply of hydraulic oil from the pump 4 to the cylinder 2, and a pilot control valve 9 that controls pilot pressure guided from the pilot pump 5 to the control valve 6.

The control valve 6 and the rod side chamber 2a of the cylinder 2 are connected by a first main passage 7, and the control valve 6 and the opposite rod side chamber 2b of the cylinder 2 are connected by a second main passage 8.

The control valve 6 is operated by pilot pressure guided from the pilot pump 5 to the

pilot chambers

6a, 6b through the pilot control valve 9 when the operator of the hydraulic excavator manually operates the control lever 10.

Specifically, when pilot pressure is introduced into the pilot chamber 6a, the control valve 6 is switched to the position 6A, and hydraulic oil is supplied from the pump 4 to the rod side chamber 2a through the first main passage 7. The hydraulic oil in the opposite-rod side chamber 2b is discharged to the tank T through the second main passage 8. This causes the cylinder 2 to contract and the arm 1 to rise in the direction of the arrow 18 shown in FIG.

On the other hand, when the pilot pressure is introduced into the pilot chamber 6b, the control valve 6 is switched to the position 6B, and hydraulic oil is supplied from the pump 4 to the anti-rod side chamber 2b through the second main passage 8, and the rod side chamber The hydraulic oil 2a is discharged into the tank T through the first main passage 7. As a result, the cylinder 2 is extended and the arm 1 is lowered in the direction of the arrow 19 shown in FIG.

When pilot pressure is not guided to the

pilot chambers

6a, 6b, the control valve 6 is in position 6C, supply and discharge of hydraulic oil to and from the cylinder 2 is cut off, and the arm 1 remains in a stopped state.

In this way, the control valve 6 has three positions: a retracted position 6A where the cylinder 2 is contracted, an extended position 6B where the cylinder 2 is extended, and a neutral position 6C where the load on the cylinder 2 is maintained. It switches the supply and discharge of hydraulic oil and controls the expansion and contraction operation of the cylinder 2.

Here, as shown in FIG. 1, if the control valve 6 is switched to the neutral position 6C and the movement of the arm 1 is stopped with the bucket 13 lifted, the weight of the bucket 13, arm 1, etc. will cause the cylinder 2 to A force in the direction of elongation acts on . In this way, in the cylinder 2 that drives the arm 1, the rod side chamber 2a becomes a load side pressure chamber on which load pressure acts when the control valve 6 is in the neutral position 6C.

A load holding mechanism 20 is provided in the first main passage 7 connected to the rod side chamber 2a, which is a load side pressure chamber. The load holding mechanism 20 holds the load pressure in the rod side chamber 2a when the control valve 6 is in the neutral position 6C, and is fixed to the surface of the cylinder 2, as shown in FIG.

In addition, in the cylinder 15 that drives the boom 14 (see FIG. 1), the anti-rod side chamber 15b becomes the load side pressure chamber, so when the boom 14 is provided with the load holding mechanism 20, it is connected to the anti-rod side chamber 15b. A load holding mechanism 20 is provided in the main passage.

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

The operated check valve 21 includes a valve body 24 that opens and closes the first main passage 7, a seat portion 28 on which the valve body 24 is seated, a back pressure chamber 25 facing the back side of the valve body 24, and a rod formed in the valve body 24. It has a passage 26 that always guides the hydraulic oil in the side chamber 2a to the back pressure chamber 25. The passage 26 is provided with a restriction 26a that provides resistance to the hydraulic oil passing therethrough.

The first main passage 7 has a cylinder side first main passage 7a that connects the rod side chamber 2a and the operated check valve 21, and a control valve side first main passage 7b that connects the operated check valve 21 and the control valve 6. .

The valve body 24 has 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 rod side chamber 2a acts through the cylinder side first main passage 7a. It is formed.

A spring 27 as a biasing member that biases the valve body 24 in the closing direction is housed 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 to seat the valve body 24 on the seat portion 28 .

When the valve body 24 is seated on the seat portion 28, the operated check valve 21 functions as a check valve that blocks the flow of hydraulic oil from the rod side chamber 2a to the control valve 6. That is, the operating check valve 21 prevents leakage of the hydraulic oil in the rod side chamber 2a, maintains the load pressure, and maintains the stopped state of the arm 1.

The switching valve 22 includes a pilot chamber 23 to which pilot pressure is introduced through the pilot control valve 9, a spool 56 (see FIG. 3) that moves according to the pilot pressure in the pilot chamber 23, and an energizer that biases the spool 56 in the closing direction. A spring 36 as a biasing member, a spring chamber 54 (see FIG. 3) housing the spring 36, a drain chamber 51 (see FIG. 3) provided on the opposite side of the spring chamber 54 across the spool 56, and a spring chamber 54 (see FIG. 3) that accommodates the spring 36. It has a drain passage 76 that connects the chamber 54 and the drain chamber 51 to the tank T.

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 rod side chamber 2a to the control valve side first main passage 7b, bypassing the operating 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.

The switching valve 22 switches communication between the bypass passage 30 and the back pressure passage 31 with respect to 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 2 is extended.

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. Moreover, the switching valve 22 has three positions: a cutoff position 22A, a first communication position 22B, and a second communication position 22C.

When pilot pressure is introduced into the pilot chamber 6b of the control valve 6, pilot pressure is also introduced into the pilot chamber 23 at the same time. That is, when the control valve 6 is switched to the extended position 6B, the switching valve 22 is also switched to the first communication position 22B or the second communication position 22C.

Specifically, when pilot pressure is not introduced into the pilot chamber 23, the switching valve 22 is maintained at the shutoff position 22A by the biasing force of the spring 36. At the blocking position 22A, both the first supply port 32 and the second supply port 33 are blocked.

When a pilot pressure equal to or higher than the first predetermined pressure and lower than the second predetermined pressure is introduced into the pilot chamber 23, the switching valve 22 is switched to the first communication position 22B. At the first communication position 22B, the first supply port 32 communicates with the discharge port 34. Thereby, the hydraulic oil in the rod side chamber 2a is guided from the bypass passage 30 to the downstream passage 38 through the switching valve 22. That is, the hydraulic oil in the rod side chamber 2a bypasses the operated check valve 21 and is guided to the control valve side first main passage 7b. At this time, the throttle 37 provides resistance to the flow of the hydraulic oil. The second supply port 33 remains blocked.

When a pilot pressure equal to or higher than the second predetermined pressure is introduced into the pilot chamber 23, the switching valve 22 is switched to the second communication position 22C. At 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. Thereby, the hydraulic oil in the back pressure chamber 25 is guided from the back pressure passage 31 to the downstream passage 38 through the switching valve 22. At this time, the hydraulic oil in the back pressure chamber 25 bypasses the throttle 37, is guided to 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 is generated before and after the throttle 26a, and the pressure in the back pressure chamber 25 is reduced, so the force in the closing direction acting on the valve body 24 is reduced, and the valve body 24 is separated from the seat portion 28. , the function of the operated check valve 21 as a check valve is canceled.

The load holding mechanism 20 has a relief valve 41 that opens when the pressure in the rod side chamber 2a reaches a predetermined pressure and discharges the hydraulic oil in the rod side chamber 2a to the tank T. The relief valve 41 is provided in a relief passage 40 that branches from the upstream side of the switching valve 22 in the bypass passage 30 . Note that the relief passage 40 may be provided branching off from the cylinder side first main passage 7a, or may be directly connected to the rod side chamber 2a.

The drain passage 76 is formed by a first drain passage 76a connected to the drain chamber 51, a second drain passage 76b connected to the spring chamber 54, and a confluence of the first drain passage 76a and the second drain passage 76b. It has a confluence drain passage 76c. The combined drain passage 76c communicates with 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 drain in the drain chamber 51 and the spring chamber 54 is discharged to the tank T through the combined drain passage 76c, the drain port 77, and the drain hose 78. Since the drain chamber 51 and the spring chamber 54, which are provided on both sides of the spool 56 of the switching valve 22, both communicate with the tank T, when the switching valve 22 is in the cutoff position 22A, atmospheric pressure is present at both ends of the spool 56. This prevents the spool 56 from moving unintentionally.

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 valve 43 and the relief valve 44 are for releasing the high pressure generated in the rod side chamber 2a and the anti-rod side chamber 2b of the cylinder 2, respectively, when a large external force is applied to the arm 1.

Next, the switching valve 22 will be described in detail, mainly with reference to FIG. 3. FIG. 3 is a 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 cutoff position 22A. In FIG. 3, components denoted by the same reference numerals as those shown in FIG. 2 have the same configurations as those shown in FIG.

The switching valve 22 is incorporated into the 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. A spool 56 is slidably incorporated into the sleeve 61.

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 the second drain passage 76b through a notch 61a formed in the end surface of the sleeve 61. The hydraulic oil that has leaked into the spring chamber 54 is discharged to the tank T from the second drain passage 76b.

The spring chamber 54 includes a first annular spring receiving member 45 whose end surface abuts the one end surface 56a of the spool 56 and into which a pin portion 56c formed to protrude from the one end surface 56a of the spool 56 is inserted into the hollow portion; A second spring receiving member 46 disposed near the bottom of the cap 57 is housed. The spring 36 is interposed in a compressed state between the first spring receiving member 45 and the second spring receiving member 46, and urges the spool 56 in the closing direction via the first spring receiving member 45.

A pilot chamber 23 is defined on 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 cap 58 that closes the piston hole 60b. Pilot pressure oil (pilot fluid) is introduced into the pilot chamber 23 through a pilot passage 52 formed in the body 60 . Inside the pilot chamber 23, a piston 50 is slidably housed, which receives pilot pressure on the back surface and applies a thrust to the spool 56 against the biasing force of the spring 36.

A drain chamber 51 is defined within the piston hole 60b by the spool 56 and the piston 50. Drain chamber 51 is connected to first drain passage 76a. The hydraulic oil that has leaked into the drain chamber 51 is discharged to the tank T from the first drain passage 76a.

The piston 50 includes a sliding portion 50a whose outer peripheral surface slides along the inner peripheral surface of the piston hole 60b, and a tip portion that is formed to have a smaller diameter than the sliding portion 50a and faces the other end surface 56b of the spool 56. 50b, and a base end portion 50c that is formed to have a smaller diameter than the sliding portion 50a and faces the distal end surface of the cap 58.

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 portion 50c and the annular back surface of the sliding portion 50a. As a result, the piston 50 moves forward, and the tip portion 50b abuts the other end surface 56b of the spool 56 to move the spool 56. In this way, the spool 56 receives the thrust of the piston 50 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 proximal end 50c is in contact with the distal end surface of the cap 58, the proximal end 50c has a smaller diameter than the sliding portion 50a, and pilot pressure is applied to the annular back surface of the sliding portion 50a. acts, so the piston 50 can move forward.

Since 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, the thrust of the piston 50 generated based on the pilot pressure in the pilot chamber 23 is efficiently transferred to the spool. 56.

The spool 56 stops at a position where the urging force of the spring 36 acting on one end surface 56a and the thrust force 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. Set.

The piston 50 is provided with a gas vent valve 80 (see FIG. 4) for discharging air from the pilot chamber 23 to the drain chamber 51. The gas vent valve 80 will be explained in detail later. Note that in FIG. 2, illustration of the gas vent valve 80 is omitted.

The sleeve 61 has 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 downstream passage 38 (see FIG. 2). Three communicating discharge ports 34 are formed.

The outer circumferential surface of the spool 56 is partially annularly cut out, and the cutout portion and the inner circumferential 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 is formed.

The first pressure chamber 64 is always in communication with the discharge port 34. The third pressure chamber 66 is always in communication with the first supply port 32. A plurality of throttles 37 are formed on the outer peripheral surface of the land portion 72 of the spool 56 as the spool 56 moves against the biasing force of the spring 36 to communicate the third pressure chamber 66 and the second pressure chamber 65. Ru. The fourth pressure chamber 67 is constantly in communication with the second pressure chamber 65 through a pressure guiding passage 68 formed in the spool 56 in the axial direction.

When the operating lever 10 is not operated and pilot pressure is not guided to the pilot chamber 23, the poppet valve 70 formed on the spool 56 is moved by the urging force of the spring 36 to the valve seat 71 formed on the inner periphery of the sleeve 61. , and communication between the second pressure chamber 65 and the first pressure chamber 64 is cut off. Therefore, communication between the first supply port 32 and the discharge port 34 is cut off. This prevents the hydraulic oil in the rod side chamber 2a from leaking to the discharge port 34. This state corresponds to the cutoff position 22A of the switching valve 22. When the poppet valve 70 is seated on the valve seat 71 due to the biasing force of the spring 36, there is a slight gap between the end face of the first spring receiving member 45 and the end face of the sleeve 61, so the poppet valve 70 is seated on the valve seat 71. The seat 71 is reliably seated by the biasing force of the spring 36.

When the operating lever 10 is operated and pilot pressure is introduced into the pilot chamber 23 and the thrust of the piston 50 acting on the spool 56 becomes greater than the urging force of the spring 36, the spool 56 resists the urging force of the spring 36. and move. As a result, the poppet valve 70 separates from the valve seat 71 and the third pressure chamber 66 and the second pressure chamber 65 communicate with each other through the plurality of throttles 37. It communicates with the discharge port 34 through the chamber 65 and the first pressure chamber 64 . Due to the communication between the first supply port 32 and the discharge port 34, the hydraulic oil in the rod side chamber 2a is guided 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.

When the pilot pressure guided to the pilot chamber 23 increases, the spool 56 moves further against the urging force of the spring 36, and the fourth pressure chamber 67 communicates with the second supply port 33. Thereby, the second supply port 33 communicates with the discharge port 34 through the fourth pressure chamber 67, the pressure guiding 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 is guided to the downstream passage 38 (see FIG. 2), bypassing the throttle 37. This state corresponds to the second communication position 22C of the switching valve 22.

Next, the operation of the hydraulic control device 100 will be described with reference to FIGS. 2 and 3.

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 2. At this time, since pilot pressure is not introduced into the pilot chamber 23 of the switching valve 22, the switching valve 22 is in the shutoff position 22A.

Therefore, the back pressure chamber 25 of the operated check valve 21 is maintained at the pressure of the rod side chamber 2a. Here, the pressure receiving area of the valve body 24 in the closing direction (the area of the back surface of the valve body 24) is larger than the area of the second pressure receiving surface 24b, which is the pressure receiving area in the opening direction. Due to the load acting on the back surface of the body 24 and the biasing force of the spring 27, the valve body 24 is placed in a seated state on the seat portion 28. In this way, the operating check valve 21 prevents the hydraulic oil from leaking in the rod side chamber 2a, and the arm 1 is maintained in a stopped state.

When the operating lever 10 is operated and pilot pressure is guided from the pilot control valve 9 to the pilot chamber 6a of the control valve 6, the control valve 6 is switched to the retracted position 6A by an amount corresponding to the pilot pressure. When the control valve 6 is switched to the retracted position 6A, the discharge pressure of the pump 4 acts on the first pressure receiving surface 24a of the operating check valve 21. At this time, the switching valve 22 is in the cutoff position 22A with no pilot pressure introduced into the pilot chamber 23, so the back pressure chamber 25 of the operating check valve 21 is maintained at the pressure of the rod side chamber 2a. 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 It leaves the seat part 28. When the operating check valve 21 is opened in this manner, the hydraulic oil discharged from the pump 4 is supplied to the rod side chamber 2a, and the cylinder 2 is contracted. As a result, arm 1 rises in the direction of arrow 18 shown in FIG.

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

When the pilot pressure guided to the pilot chamber 23 is greater than or equal to the first predetermined pressure and less than the second predetermined pressure, the switching valve 22 is switched to the first communication position 22B. In this case, since the communication between the second supply port 33 and the discharge port 34 is cut off, the back pressure chamber 25 of the operated check valve 21 is maintained at the pressure of the rod side chamber 2a, and the operated check valve 21 is closed. maintain the condition.

On the other hand, since the first supply port 32 communicates with the discharge port 34, the hydraulic oil in the rod side chamber 2a is guided from the bypass passage 30 to the downstream passage 38 through the throttle 37, and from the control valve side first main passage 7b to the control valve 6. It is discharged into tank T through. Moreover, since the hydraulic oil discharged from the pump 4 is supplied to the opposite-rod side chamber 2b, the cylinder 2 expands. As a result, arm 1 descends in the direction of arrow 19 shown in FIG.

Here, the switching valve 22 is switched to the first communication position 22B mainly when a crane operation is performed to lower the transported object attached to the bucket 13 to a target position. In crane work, it is necessary to extend the cylinder 2 at low speed and slowly lower the arm 1 in the direction of the arrow 19. Therefore, the pilot pressure introduced into the pilot chamber 6b of the control valve 6 is small, and the control valve 6 is It is only slightly switched to the extended position 6B. For this reason, the pilot pressure guided to the pilot chamber 23 of the switching valve 22 is also small, being greater than or equal to 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 rod side chamber 2a passes through the throttle 37 and is discharged, and the arm 1 descends at a low speed suitable for crane work.

Further, when the switching valve 22 is in the first communication position 22B, even if the control valve side first main passage 7b ruptures and the hydraulic oil leaks to the outside, the hydraulic oil will not be discharged from the rod side chamber 2a. Since the flow rate of the hydraulic oil is restricted by the throttle 37, the falling speed of the bucket 13 is suppressed. Therefore, the switching valve 22 can be switched to the cutoff position 22A before the bucket 13 falls to the ground, and the bucket 13 can be prevented from falling suddenly.

In this way, the throttle 37 is intended to suppress the descending speed of the cylinder 2 when the operating 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. .

When the pilot pressure guided 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, since the second supply port 33 communicates with the discharge port 34, the hydraulic oil in the back pressure chamber 25 of the operated check valve 21 is guided from the back pressure passage 31 to the downstream passage 38, bypassing the throttle 37, and is controlled. It is discharged from the valve-side first main passage 7b to the tank T through the control valve 6. As a result, a pressure difference is generated before and after the throttle 26a, and the pressure in the back pressure chamber 25 is reduced, so that the force in the closing direction acting on the valve body 24 is reduced, and the valve body 24 is separated from the seat portion 28. The function of the operating check valve 21 as a check valve is canceled.

In this way, the operating check valve 21 allows the flow of hydraulic oil from the control valve 6 to the rod side chamber 2a, while allowing the flow of hydraulic oil from the rod side chamber 2a to the control valve 6 according to the back pressure, which is the pressure in the back pressure chamber 25. Operates to allow flow of hydraulic oil.

When the operating check valve 21 opens, the hydraulic oil in the rod side chamber 2a passes through the first main passage 7 and is discharged to the tank T, so the cylinder 2 quickly expands. 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 rod side chamber 2a increases, so the flow rate of hydraulic oil supplied to the non-rod side chamber 2b increases, and the flow rate of the hydraulic oil discharged from the rod side chamber 2a increases. The elongation speed becomes faster. As a result, arm 1 quickly descends in the direction of arrow 19.

The switching valve 22 is switched to the second communication position 22C when performing excavation work, etc., and the pilot pressure guided to the pilot chamber 6b of the control valve 6 is large, and the control valve 6 is switched to the extended position 6B. For this reason, the pilot pressure guided to the pilot chamber 23 of the switching valve 22 is also large and becomes equal to or higher than the second predetermined pressure, so the switching valve 22 is switched to the second communication position 22C.

Next, the gas vent valve 80 provided in the piston 50 will be explained with reference mainly to FIG. 4. FIG. 4 is a sectional view of the vicinity of the piston 50. Note that in FIG. 3, illustration of the gas vent valve 80 is omitted. Although a case will be described below in which the gas vent valve 80 discharges air from the pilot chamber 23 to the drain chamber 51, what the gas vent valve 80 discharges is not limited to air, and may discharge other gases.

An annular gap 69 is provided between the piston 50 and the body 60, specifically, between the outer peripheral surface of the sliding portion 50a of the piston 50 and the inner peripheral surface of the piston hole 60b of the body 60. In the conventional switching valve, this gap 69 functions as a passage for discharging air from the pilot chamber 23 side to the drain chamber 51 side. However, because the gap 69 is provided between the piston 50 and the body 60, when the hydraulic excavator is stopped, air from the drain chamber 51 side moves through the gap 69 to the pilot chamber 23 side. Specifically, when the hydraulic excavator stops, the hydraulic oil in the pilot chamber 23 and the pilot passage 52 flows down to the tank T by gravity, so that the pilot chamber 23 and the pilot passage 52 become negative pressure, and as a result, the hydraulic oil in the pilot chamber 23 and the pilot passage 52 flows down from the tank T. Air sucked into the combined drain passage 76c and the first drain passage 76a moves to the pilot chamber 23 and the pilot passage 52 through the gap 69. Further, the load holding mechanism 20 provided in the cylinder 2 that drives the arm 1 is provided at the highest position in the hydraulic excavator, as shown in FIG. Therefore, when the hydraulic excavator remains stopped for a long time, air accumulates in the drain chamber 51, the first drain passage 76a, the second drain passage 76b, the combined drain passage 76c, and the drain hose 78. The accumulated air moves to the pilot chamber 23 and the pilot passage 52 through the gap 69.

If air moves from the drain chamber 51 side to the pilot chamber 23 side in this way, when the hydraulic excavator starts from a stopped state, the operator's input The increase in the pilot pressure in the pilot chamber 23 is delayed with respect to the operation, and the increase in the pilot pressure in the pilot chamber 23 is completed after the air on the pilot chamber 23 side is discharged to the drain chamber 51 through the gap 69. In this way, the air in the pilot chamber 23 causes a delay in the response of the cylinder 2 to the operator's input operation when the hydraulic excavator is started.

As a countermeasure against this, in this embodiment, the gap 69 between the piston 50 and the body 60 is sealed with an O-ring 99 as a sealing member, and the flow of air through the gap 69 is blocked. Further, the gas vent valve 80 provided in the piston 50 discharges air from the pilot chamber 23 to the drain chamber 51 and blocks the flow of air from the drain chamber 51 to the pilot chamber 23. This will be explained in detail below.

The gas vent valve 80 has a passage 81 provided across the pilot chamber 23 and the drain chamber 51, a valve body 82 that opens and closes the passage 81, and a spring 83 as a biasing member that biases the valve body 82. The passage 81 is formed through the piston 50 along the direction of movement of the piston 50. The valve body 82 is a spherical body, and is provided in the middle of the passage 81. The spring 83 is compressed and provided between the valve body 82 and the piston 50.

The passage 81 has a valve body accommodating portion 81a that accommodates the valve body 82. The inner diameter of the valve body accommodating portion 81a is larger than the outer diameter of the valve body 82. In the passage 81, the inner diameter of the portion other than the valve body accommodating portion 81a is smaller than the outer diameter of the valve body 82. The spring 83 has one end housed in the valve body accommodating portion 81 a and in contact with the valve body 82 , and the other end side provided outside the valve body accommodating portion 81 a and in contact with a stepped portion 50 f formed on the piston 50 . As a result, the valve body housing portion 81a has an annular first seat portion 81b with which the valve body 82 contacts due to the biasing force of the spring 83, and a second seat portion 81c with which the valve body 82 contacts due to the pressure of the pilot chamber 23. , is formed. The valve body 82 moves between the first seat portion 81b and the second seat portion 81c within the valve body housing portion 81a.

A slit 50d is formed on the end surface of the tip 50b of the piston 50 facing the spool 56. The slit 50d communicates with the passage 81 and opens on the outer peripheral surface of the tip portion 50b. By forming the slit 50d on the end surface of the piston 50, the passage 81 is not blocked by the spool 56 even when the tip 50b of the piston 50 is in contact with the spool 56.

The gas vent valve 80 has a cylindrical housing 84 that is attached to the piston 50 and forms a part of the piston 50. A hole 50e is formed in the end surface of the base end 50c of the piston 50 facing the pilot chamber 23, and the housing 84 is installed in the hole 50e. An O-ring 98 serving as a sealing member is provided between the outer peripheral surface of the housing 84 and the inner peripheral surface of the hole 50e to prevent leakage of pilot pressure oil between the two. Instead of providing the O-ring 98, the housing 84 may be press-fitted into the hole 50e.

The housing 84 is formed with a small diameter hole 84a communicating with the pilot chamber 23, and a large diameter hole 84b communicating with the small diameter hole 84a and having a larger inner diameter than the small diameter hole 84a. The small diameter hole 84a and the large diameter hole 84b constitute a part of the passage 81. The large diameter hole 84b defines the valve body accommodating portion 81a. The step portion formed between the small diameter hole 84a and the large diameter hole 84b constitutes the first seat portion 81b. The opening edge of the passage 81 formed on the bottom surface of the hole 50e constitutes a second seat portion 81c.

When attaching the gas vent valve 80 to the piston 50, the valve body 82 is accommodated in the large diameter hole 84b of the housing 84, and the spring 83 is interposed between the valve body 82 and the stepped portion 50f of the piston 50. Then, the housing 84 is inserted into the hole 50e of the piston 50 and attached.

Next, the operation and function of the gas vent valve 80 will be explained.

When the power source mounted on the hydraulic excavator is in a stopped state and the pilot pump 5 is stopped, the pilot pressure in the pilot chamber 23 is zero, so the valve body 82 is pushed against the first seat portion 81b by the biasing force of the spring 83. They make contact and block the passage 81 (the state shown in FIG. 4). This prevents air from moving from the drain chamber 51 side to the pilot chamber 23 side through the passage 81 even when the hydraulic excavator is stopped. Furthermore, since an O-ring 99 is provided between the piston 50 and the body 60, air movement from the drain chamber 51 side to the pilot chamber 23 side through the gap 69 between the piston 50 and the body 60 is also prevented. Ru.

On the other hand, when the power source mounted on the hydraulic excavator is in operation and the pilot pump 5 is driven, the valve body 82 moves against the biasing force of the spring 83 and separates from the first seat portion 81b. At this time, the valve body 82 does not contact the second seat portion 81c when the pilot pressure in the pilot chamber 23 is less than a predetermined pressure, and the valve body 82 does not contact the second seat portion 81c when the pilot pressure in the pilot chamber 23 is higher than the predetermined pressure. Contact 81c. This will be explained in detail with reference to FIG. 5 as well. FIG. 5 is a graph diagram showing the relationship between the pilot pressure in the pilot chamber 23 and the flow rate of air flowing from the pilot chamber 23 to the drain chamber 51.

When the pilot pump 5 is being driven and the operator is not operating the operating lever 10, the pilot pressure oil discharged from the pilot pump 5 is discharged into the tank T through the pilot control valve 9 and into the pilot chamber 23. There is almost no guidance. However, even in such a state, when the pilot pump 5 is driven, the pilot passage 52 and the pilot chamber 23 have a minimum pilot pressure, specifically, a pilot pressure of about 0.05 to 0.2 MPa. acts. In this state, the valve body 82 moves against the biasing force of the spring 83 and separates from the first seat portion 81b, but does not contact the second seat portion 81c. That is, the valve body 82 is located between the first seat portion 81b and the second seat portion 81c due to the balance between the pilot pressure in the pilot chamber 23 and the biasing force of the spring 83. This state is when the pilot pressure in the pilot chamber 23 is less than a predetermined pressure. In this state, as shown in FIG. 5, air flow from the pilot chamber 23 to the drain chamber 51 through the passage 81 is allowed, and air from the pilot chamber 23 side is discharged to the drain chamber 51 side. Therefore, when the hydraulic excavator is started from a stopped state, the air in the pilot chamber 23 is naturally discharged to the drain chamber 51 before the operator operates the operating lever 10. When the operation is started, the response delay of the cylinder 2 to the operation is suppressed.

When the operator operates the control lever 10 to work, a pilot pressure of 0.3 MPa or more acts on the pilot chamber 23. In this state, the valve body 82 moves against the biasing force of the spring 83 and comes into contact with the second seat portion 81c. This state is when the pilot pressure in the pilot chamber 23 is equal to or higher than a predetermined pressure. In this state, as shown in FIG. 5, the flow of air from the pilot chamber 23 to the drain chamber 51 through the passage 81 is blocked, and the flow of pilot pressure oil is also blocked. Therefore, a desired pilot pressure acts on the pilot chamber 23, and the movement of the piston 50 allows the spool 56 to move, so the passage 81 does not adversely affect the operation of the cylinder 2.

The predetermined pressure, which is the pilot pressure at which the valve body 82 contacts the second seat portion 81c, is set to a pressure lower than the pilot pressure at which the spool 56 moves, and is approximately 0.3 PMa in this embodiment. This predetermined pressure is set according to the capacity of the pilot pump 5, the inner diameter and length of the pilot passage 52, and the like. The initial load of the spring 83 is set so that the valve body 82 contacts the second seat portion 81c at a pressure equal to or higher than the set predetermined pressure.

As described above, the gas vent valve 80 prevents air from moving from the drain chamber 51 side to the pilot chamber 23 side when the pilot pump 5 is stopped, and when the pilot pump 5 is driven, the operator operates the control lever 10. Since the air in the pilot chamber 23 side is naturally discharged to the drain chamber 51 side before the operation, a delay in the response of the cylinder 2 to the operator's input operation is suppressed. Furthermore, when the operator operates the control lever 10, the flow of pilot pressure oil from the pilot chamber 23 to the drain chamber 51 is blocked, so the gas vent valve 80 adversely affects the operation of the switching valve 22 and the cylinder 2. Never.

Note that when the hydraulic excavator is started from a stopped state, the operator may operate the operating lever 10 to bleed air from the pilot chamber 23 to the drain chamber 51 through the passage 81. However, in this case, it is necessary to operate the operating lever 10 so that the valve body 82 does not come into contact with the second seat portion 81c (in this embodiment, so that the pilot pressure in the pilot chamber 23 does not exceed 0.3 MPa). There is. In other words, it is necessary to operate the operating lever 10 so that the spool 56 does not move.

According to the above embodiment, the following effects are achieved.

When the pilot pump 5 is stopped, the valve body 82 of the gas vent valve 80 comes into contact with the first seat portion 81b by the urging force of the spring 83 and blocks the passage 81, so that air does not flow from the drain chamber 51 side to the pilot chamber 23 side. movement is prevented. Furthermore, when the pilot pump 5 is driven and the pilot pressure in the pilot chamber 23 is less than a predetermined pressure, the valve body 82 moves against the biasing force of the spring 83 and separates from the first seat portion 81b. In order to allow air to flow from the pilot chamber 23 to the drain chamber 51, the air from the pilot chamber 23 side is discharged to the drain chamber 51 side, thereby suppressing the response delay of the cylinder 2 due to the influence of air.

Furthermore, when the operator operates the control lever 10, the flow of pilot pressure oil from the pilot chamber 23 to the drain chamber 51 through the passage 81 is blocked, so the gas vent valve 80 has a negative effect on the operation of the cylinder 2. Never.

A modification of the above embodiment will be described below with reference to FIG. FIG. 6 is a diagram corresponding to FIG. 4, and is a sectional view of the vicinity of the piston 50. In FIG. 6, components having the same functions as those in the above embodiment are denoted by the same reference numerals. In this modification, the configuration of the gas vent valve 80 is different from the above embodiment.

Also in this modification, when the pilot pump 5 is stopped, the valve body 82 contacts the first seat portion 81b and blocks the passage 81 due to the biasing force of the spring 83, so that the valve body 82 blocks the passage 81 from the drain chamber 51 side to the pilot chamber 23 side. Air movement is prevented. Furthermore, when the pilot pump 5 is driven and the pilot pressure in the pilot chamber 23 is less than a predetermined pressure, the valve body 82 moves against the biasing force of the spring 83 and separates from the first seat portion 81b. In order to allow air to flow from the pilot chamber 23 to the drain chamber 51, the air from the pilot chamber 23 side is discharged to the drain chamber 51 side, thereby suppressing the response delay of the cylinder 2 due to the influence of air. In this respect, this modification is the same as the above embodiment.

However, in the gas vent valve 80 of this modification, even if the pilot pressure in the pilot chamber 23 is higher than a predetermined pressure, the valve body 82 moves against the biasing force of the spring 83, but the second seat portion 81c (see FIG. 4), and does not block the flow of pilot pressure oil from the pilot chamber 23 to the drain chamber 51 through the passage 81. This is because, unlike the above embodiment, the entire spring 83 is accommodated in the valve body accommodating portion 81a. Specifically, the spring 83 is compressed and provided between the valve body 82 and the bottom surface of the hole 50e formed in the piston 50.

In this modification, even if the pilot pressure in the pilot chamber 23 is higher than a predetermined pressure, the valve body 82 does not come into contact with the second seat portion 81c (see FIG. 4). Pilot pressure oil is allowed to flow into the drain chamber 51. However, the gas vent valve 80 has an orifice 85 that is provided in the passage 81 and serves as a throttle that provides resistance to the flow of pilot pressure oil from the pilot chamber 23 to the drain chamber 51. Therefore, when the operator operates the control lever 10, the orifice 85 provides resistance to the flow of pilot pressure oil from the pilot chamber 23 to the drain chamber 51, and the desired pilot pressure acts on the pilot chamber 23. The gas vent valve 80 does not adversely affect the operation of the cylinder 2.

In this modification, the orifice 85 is formed in the housing 84. However, the orifice 85 only needs to be provided in the passage 81, and the position where it is formed is not limited. For example, an orifice 85 may be provided in the passage 81 between the bottom surface of the hole 50e and the slit 50d.

Hereinafter, the configuration, operation, and effects of the embodiments of the present invention will be collectively described.

A hydraulic control device 100 (fluid pressure control device) that controls the expansion and contraction operation of the cylinder 2 that drives the load 1 includes a control valve 6 that controls the supply of working fluid from the pump 4 (fluid pressure supply source) to the cylinder 2; A pilot control valve 9 that controls the pilot pressure guided from the pilot pump 5 (pilot pressure supply source) to the control valve 6, and the load side of the cylinder 2 on which the load pressure from the load 1 acts when the control valve 6 is in the neutral position 6C. The load holding mechanism 20 includes a main passage 7 that connects the pressure chamber 2a and the control valve 6, and a load holding mechanism 20 provided in the main passage 7. and an operating check valve 21 that allows the flow of working fluid from the load-side pressure chamber 2a to the control valve 6 according to the back pressure, and a pilot pressure led through the pilot control valve 9 to control the control valve 6 and the control valve 6. It has a switching valve 22 that operates in conjunction with the operating check valve 21 to switch the operation of the operating check valve 21. A spool 56 that moves according to pressure; a piston 50 that applies thrust to the spool 56 in response to pilot pressure; a drain chamber 51 that is partitioned by the spool 56 and the piston 50; It has a gas vent valve 80 for discharging air (gas) to the drain chamber 51, and the gas vent valve 80 includes a passage 81 provided across the pilot chamber 23 and the drain chamber 51, and a valve body that opens and closes the passage 81. 82, and a spring 83 (biasing member) that biases the valve body 82, and when the pilot pump 5 is stopped, the valve body 82 comes into contact with the first seat portion 81b by the biasing force of the spring 83. The passage 81 is shut off, and when the pilot pump 5 is driven and the pilot pressure in the pilot chamber 23 is less than a predetermined pressure lower than the pilot pressure at which the spool 56 moves, It moves away from the first seat portion 81b and allows fluid to flow from the pilot chamber 23 to the drain chamber 51.

In this configuration, a gas vent valve 80 for discharging air from the pilot chamber 23 to the drain side is provided on the piston 50, and the valve body 82 of the gas vent valve 80 is moved by the biasing force of the spring 83 when the pilot pump 5 is stopped. Since the passage 81 is blocked by contacting the first seat portion 81b, movement of air from the drain chamber 51 side to the pilot chamber 23 side is prevented. Furthermore, when the pilot pump 5 is driven and the pilot pressure in the pilot chamber 23 is less than a predetermined pressure, the valve body 82 moves against the biasing force of the spring 83 and separates from the first seat portion 81b. In order to allow fluid to flow from the pilot chamber 23 to the drain chamber 51, air from the pilot chamber 23 side is discharged to the drain chamber 51 side, and response delay of the cylinder 2 due to the influence of air is suppressed. Therefore, it is possible to prevent air from moving from the drain side to the pilot chamber 23 side, and to suppress response delays due to the influence of air.

Further, when the pilot pump 5 is driven and the pilot pressure in the pilot chamber 23 is higher than a predetermined pressure, the valve body 82 moves against the biasing force of the spring 83 and comes into contact with the second seat portion 81c. The passage 81 is blocked, and the flow of pilot pressure oil from the pilot chamber 23 to the drain chamber 51 is blocked.

In this configuration, the valve body 82 allows pilot pressure oil to flow from the pilot chamber 23 to the drain chamber 51 through the passage 81 when the pilot pressure in the pilot chamber 23 is higher than a predetermined pressure when the pilot pump 5 is driven. Since the flow is blocked, the gas vent valve 80 does not adversely affect the operation of the cylinder 2.

Further, the valve body 82 allows pilot pressure oil to flow from the pilot chamber 23 to the drain chamber 51 even when the pilot pressure in the pilot chamber 23 is higher than the predetermined pressure, and the gas vent valve 80 allows the pilot pressure oil to flow from the pilot chamber 23 to the drain chamber 51. It further includes an orifice 85 (restriction) provided at 81 to provide resistance to the flow of pilot pressure oil from pilot chamber 23 to drain chamber 51 .

In this configuration, when the pilot pump 5 is driven and the pilot pressure in the pilot chamber 23 is higher than a predetermined pressure, the orifice 85 provides resistance to the flow of pilot pressure oil from the pilot chamber 23 to the drain chamber 51. Therefore, the gas vent valve 80 does not adversely affect the operation of the cylinder 2.

Although the embodiments of the present invention have been described above, the above embodiments merely show a part of the application examples of the present invention, and are not intended to limit the technical scope of the present invention to the specific configurations of the above embodiments. do not have.

This application claims priority based on Japanese Patent Application No. 2022-41672 filed with the Japan Patent Office on March 16, 2022, and the entire contents of this application are incorporated herein by reference.

Claims

A fluid pressure control device that controls the expansion and contraction operation of a cylinder that drives a load,
a control valve that controls supply of working fluid to the cylinder;
a pilot control valve that controls pilot pressure guided from a pilot pressure supply source to the control valve;
a main passage connecting the control valve and 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;
A load holding mechanism provided in the main passage,
The load holding mechanism is
an operated check valve that allows a flow of working fluid from the control valve to the load-side pressure chamber, and also allows a flow of working fluid from the load-side pressure chamber to the control valve depending on back pressure;
a switching valve that operates in conjunction with the control valve by pilot pressure guided through the pilot control valve to switch the operation of the operating check valve;
The switching valve is
a pilot chamber into which pilot pressure is introduced through the pilot control valve;
a spool that moves according to pilot pressure in the pilot chamber;
a piston that applies thrust to the spool in response to pilot pressure;
a drain chamber defined by the spool and the piston;
a gas vent valve provided on the piston for discharging gas from the pilot chamber to the drain chamber;
The gas vent valve is
a passageway provided across the pilot chamber and the drain chamber;
a valve body that opens and closes the passage;
a biasing member that biases the valve body;
When the pilot pressure supply source is stopped, the valve body contacts the first seat part to block the passage by the biasing force of the biasing member, and when the pilot pressure supply source is driven, the valve body closes the passage. If the pilot pressure of the spool is less than a predetermined pressure lower than the pilot pressure at which the spool moves, the spool moves against the biasing force of the biasing member and moves away from the first seat portion, and the spool moves from the pilot chamber to the predetermined pressure. A fluid pressure control device that allows fluid to flow into the drain chamber.
The fluid pressure control device according to claim 1,
When the pilot pressure supply source is driven and the pilot pressure in the pilot chamber is equal to or higher than the predetermined pressure, the valve body moves against the biasing force of the biasing member and closes the second seat portion. A fluid pressure control device that contacts and blocks the passage to block the flow of pilot fluid from the pilot chamber to the drain chamber.
The fluid pressure control device according to claim 1,
The valve body allows pilot fluid to flow from the pilot chamber to the drain chamber even if the pilot pressure in the pilot chamber is equal to or higher than the predetermined pressure,
The gas vent valve further includes a throttle provided in the passage and providing resistance to the flow of pilot fluid from the pilot chamber to the drain chamber.