Fluid Pressure Control Device

Abstract

A load holding mechanism 20 has a switch valve (22) that switches operation of an operation check valve (21). The switch valve (22) is provided in a first drain passage (76a) connected to a pilot chamber (23), and has a gas release valve (80) for discharging gas from the pilot chamber (23) to the drain side. The gas release valve (80) has a valve body (82) that opens and closes a passage (81). When a pilot pressure supply source (5) is stopped, the valve body (82) is brought into contact with a first seat portion (81b) by a bias force of a biasing member (83), and blocks the passage (81). When the pilot pressure supply source (5) is driven and a pilot pressure of the pilot chamber (23) is less than a predetermined pressure lower than a pilot pressure at which a spool (56) moves, the valve body (82) moves against the bias force of the biasing member (83) and separates from the first seat portion (81b) to allow a flow of fluid from the pilot chamber (23) to the drain side.

Description

[Technical field]

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

[0002] Japanese Patent Application Laid-Open No. 2010-101400 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 a cylinder to control the extension and contraction movement of the cylinder, and a load holding mechanism installed in a main passage connecting the load side pressure chamber of the cylinder and the control valve.

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

[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. When the working equipment is stopped, the air on the drain chamber side moves to the pilot chamber side through the annular gap between the piston and the housing. When the working equipment is started, the air that has moved to the pilot chamber side causes a delay in the rise in pilot pressure in the pilot chamber in response to the operator's input operation, and the increase in pilot pressure in the pilot chamber is completed only after the air on the pilot chamber side has been discharged to the drain chamber through the annular gap between the piston and the housing.

[0006] In this way, the gas on the pilot chamber side causes a delay in response to an input operation by the operator when starting up the working equipment.

[0007] 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 caused by the influence of gas.

[0008] 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 which drives a load, the fluid pressure control device comprising: a control valve which controls the supply of hydraulic fluid to the cylinder; a pilot control valve which controls a pilot pressure which is led to the control valve from a pilot pressure supply source; a main passage which 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 which is provided in the main passage, the load holding mechanism being an operated check valve which allows the hydraulic fluid to flow from the control valve to the load side pressure chamber, while allowing the hydraulic fluid to flow from the load side pressure chamber to the control valve in response to a back pressure. and a switching valve which operates in conjunction with the control valve by a pilot pressure introduced through the pilot control valve and switches the operation of the operated check valve, the switching valve having a pilot chamber to which pilot pressure is introduced through the pilot control valve, a spool which moves in response to the pilot pressure in the pilot chamber, a drain passage connected to the pilot chamber, and a gas vent valve which is provided in the drain passage and which discharges gas from the pilot chamber to a drain side, the gas vent valve having a passage provided between the pilot chamber side and the drain side, a valve body which opens and closes the passage, and a biasing member which biases the valve body, The initial load of the biasing member is The valve body but When the pilot pressure supply source is stopped, the biasing force of the biasing member causes the biasing member to contact the first seat portion and block the passage, and when the pilot pressure in the pilot chamber is driven and is less than a predetermined pressure lower than the pilot pressure at which the spool moves, the biasing member moves against the biasing force of the biasing member and separates from the first seat, allowing the flow of fluid from the pilot chamber to the drain side. It is set as follows: . [Brief description of the drawings]

[0009] [Figure 1] FIG. 2 is a diagram showing a portion of a hydraulic excavator. [Diagram 2] 1 is a fluid pressure circuit diagram of a fluid pressure control device according to an embodiment of the present invention. [Diagram 3] FIG. 2 is a cross-sectional view of a load holding mechanism of the fluid pressure control device according to the embodiment of the present invention. [Figure 4] FIG. 4 is a cross-sectional view of the periphery of the gas release valve. [Diagram 5] 10 is a graph 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 side. FIG. [Figure 6] FIG. 11 is a cross-sectional view of the periphery of a gas bleed valve in a load holding mechanism of a fluid pressure control device according to a modified example of an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A fluid pressure control device according to an embodiment of the present invention will now be described with reference to the drawings.

[0011] 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 extension and retraction 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 also be one that controls the extension and retraction 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 hydraulic oil, for example, a water-soluble substitute liquid or the like may be used.

[0012] 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 slidably inserted into the cylinder tube 2c and dividing the inside of the cylinder tube 2c into a rod side chamber 2a and an anti-rod side chamber 2b, and a rod 2e having one end connected to the piston 2d and the other end extending outside the cylinder tube 2c and connected to the arm 1.

[0013] The hydraulic excavator is equipped with a power source such as an engine or an electric motor, and the power of the engine drives a pump 4 serving as a fluid pressure supply source and a pilot pump 5 serving as a pilot pressure supply source. The pilot pump 5 may be eliminated, and the pump 4 may also be used as the pilot pressure supply source. In other words, the pump 4 may be used as both the fluid pressure supply source and the pilot pressure supply source.

[0014] 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 the pilot pressure guided from the pilot pump 5 to the control valve 6 .

[0015] The control valve 6 and the rod side chamber 2 a of the cylinder 2 are connected by a first main passage 7 , and the control valve 6 and the anti-rod side chamber 2 b of the cylinder 2 are connected by a second main passage 8 .

[0016] The control valve 6 is operated by a pilot pressure that is guided from the pilot pump 5 through a pilot control valve 9 to pilot chambers 6a, 6b as the operator of the hydraulic excavator manually operates an operation lever 10.

[0017] 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 rod side chamber 2a, while hydraulic oil in the anti-rod side chamber 2b is discharged into the tank T through the second main passage 8. As a result, the cylinder 2 contracts, and the arm 1 rises in the direction of the arrow 18 shown in FIG.

[0018] On the other hand, when pilot pressure is introduced into the pilot chamber 6b, the control valve 6 switches to position 6B, and hydraulic oil is supplied from the pump 4 through the second main passage 8 to the anti-rod side chamber 2b, while hydraulic oil in the rod side chamber 2a is discharged into the tank T through the first main passage 7. This causes the cylinder 2 to extend, and the arm 1 to move down in the direction of the arrow 19 shown in FIG.

[0019] When no pilot pressure is introduced into the pilot chambers 6a, 6b, the control valve 6 is in the position 6C, the supply and discharge of hydraulic oil to the cylinder 2 is cut off, and the arm 1 remains stopped.

[0020] In this way, the control valve 6 has three positions: a contraction position 6A for contracting the cylinder 2, an extension position 6B for extending the cylinder 2, and a neutral position 6C for holding the load on the cylinder 2. The control valve 6 switches between the supply and discharge of hydraulic oil in the cylinder 2 and controls the extension and retraction of the cylinder 2.

[0021] 1, when the control valve 6 is switched to the neutral position 6C to stop the movement of the arm 1 with the bucket 13 raised, a force acts on the cylinder 2 in the extending direction due to the weight of the bucket 13 and the arm 1, etc. Thus, in the cylinder 2 that drives the arm 1, the rod side chamber 2a becomes a load side pressure chamber to which a load pressure acts when the control valve 6 is in the neutral position 6C.

[0022] A load holding mechanism 20 is provided in the first main passage 7 connected to the rod side chamber 2a, which is the 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.

[0023] 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 a load holding mechanism 20 is provided on the boom 14, the load holding mechanism 20 is provided in the main passage connected to the anti-rod side chamber 15b.

[0024] The load holding mechanism 20 has an operate check valve 21 provided in the first main passage 7, and a switching valve 22 that operates in conjunction with the control valve 6 by pilot pressure guided through the pilot control valve 9, and switches the operation of the operate check valve 21.

[0025] The operated check valve 21 has a valve element 24 that opens and closes the first main passage 7, a seat portion 28 on which the valve element 24 sits, a back pressure chamber 25 facing the back surface of the valve element 24, and a passage 26 formed in the valve element 24 for constantly directing hydraulic oil in the rod side chamber 2a to the back pressure chamber 25. A throttle 26a that imparts resistance to the hydraulic oil passing through the passage 26 is provided.

[0026] The first main passage 7 has a cylinder side first main passage 7a connecting the rod side chamber 2a and the operated check valve 21, and a control valve side first main passage 7b connecting the operated check valve 21 and the control valve 6.

[0027] 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 rod side chamber 2a acts through the cylinder side first main passage 7a.

[0028] A spring 27 serving as a biasing member that biases the valve body 24 in a closing direction is accommodated in the back pressure chamber 25. The pressure in the back pressure chamber 25 and the biasing force of the spring 27 act in a direction that causes the valve body 24 to seat on the seat portion 28.

[0029] When the valve body 24 is 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 rod side chamber 2a to the control valve 6. In other words, the operate check valve 21 prevents leakage of hydraulic oil in the rod side chamber 2a to maintain the load pressure and maintains the stopped state of the arm 1.

[0030] The switching valve 22 has a pilot chamber 23 to which pilot pressure is introduced via pilot control valve 9, a spool 56 (see Figure 3) that moves in response to the pilot pressure in the pilot chamber 23, a spring 36 as a biasing member that biases the spool 56 in the closing direction, a spring chamber 54 (see Figure 3) in which the spring 36 is accommodated, and a drain passage 76 connected to the pilot chamber 23 and the spring chamber 54.

[0031] 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 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.

[0032] The switching valve 22 switches communication between the bypass passage 30 and the back pressure passage 31 and the downstream passage 38, and controls the flow of hydraulic oil in the first main passage 7 which is on the meter-out side when the cylinder 2 is extended.

[0033] The switching valve 22 has three ports: a first supply port 32 communicating with the bypass passage 30, a second supply port 33 communicating with the back pressure passage 31, and a discharge port 34 communicating with the downstream passage 38. The switching valve 22 also has three positions: a blocking position 22A, a first communicating position 22B, and a second communicating position 22C.

[0034] When the pilot pressure is introduced to the pilot chamber 6b of the control valve 6, the pilot pressure is also introduced to the pilot chamber 23. That is, when the control valve 6 is switched to the extension position 6B, the switching valve 22 is also switched to the first communication position 22B or the second communication position 22C.

[0035] More specifically, when no pilot pressure is introduced into the pilot chamber 23, the switching valve 22 is maintained in the shutoff position 22A by the biasing force of the spring 36. In the shutoff position 22A, both the first supply port 32 and the second supply port 33 are shut off.

[0036] When a pilot pressure equal to or greater than the first predetermined pressure and less than the second predetermined pressure is introduced to the pilot chamber 23, the switching valve 22 switches to the first communication position 22B. In the first communication position 22B, the first supply port 32 communicates with the discharge port 34. As a result, the hydraulic oil in the rod side chamber 2a 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 rod side chamber 2a bypasses the operated check valve 21 and is introduced to the control valve side first main passage 7b. At this time, the orifice 37 applies resistance to the flow of the hydraulic oil. The second supply port 33 remains blocked.

[0037] When a pilot pressure equal to or greater than the second predetermined pressure is introduced into the pilot chamber 23, the switching valve 22 switches to the second communication position 22C. In the second communication position 22C, the first supply port 32 communicates with the drain port 34, and the second supply port 33 also communicates with the drain port 34. As a result, the hydraulic oil in the back pressure chamber 25 is introduced from the back pressure passage 31 through the switching valve 22 to the downstream passage 38. At this time, the hydraulic oil in the back pressure chamber 25 bypasses the throttle 37 and is introduced into the control valve side first main passage 7b, and is discharged from the control valve 6 to the tank T. As a result, a pressure difference occurs before and after the throttle 26a, and the pressure in the back pressure chamber 25 decreases, so that the force acting on the valve body 24 in the closing direction decreases, and the valve body 24 moves away from the seat portion 28, and the function of the operated check valve 21 as a check valve is released.

[0038] 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 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 rod side chamber 2a.

[0039] The drain passage 76 has a first drain passage 76a connected to the pilot chamber 23, a second drain passage 76b connected to the spring chamber 54, and a joint drain passage 76c formed by the joining of the first drain passage 76a and the second drain passage 76b. The joint 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.

[0040] 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 2a and anti-rod side chamber 2b of the cylinder 2, respectively, when a large external force is applied to the arm 1.

[0041] Next, the switching valve 22 will be described in detail, mainly with reference to Fig. 3. Fig. 3 is a cross-sectional view of the load holding mechanism 20, showing a state in which the pilot pressure is not introduced to the pilot chamber 23 and the switching valve 22 is in the shutoff position 22A. In Fig. 3, the same reference numerals as those in Fig. 2 denote the same configuration as that shown in Fig. 2.

[0042] 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.

[0043] 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.

[0044] The spring chamber 54 accommodates an annular first spring bearing member 45, the end face of which abuts against one end face 56a of the spool 56 and into which a pin portion 56c formed in the hollow portion and protruding from the one end face 56a of the spool 56 is inserted, and a second spring bearing member 46 disposed in the vicinity of the bottom of the cap 57. The spring 36 is interposed in a compressed state between the first spring bearing member 45 and the second spring bearing member 46, and biases the spool 56 in the closing direction via the first spring bearing member 45.

[0045] 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 pilot hole 60b formed in communication with a spool hole 60a of the body 60, a cap 58 closing the pilot hole 60b, and the other end surface 56b of the spool 56. A pilot passage 52 formed in the body 60 is connected to the pilot chamber 23, and pilot pressure oil (pilot fluid) is introduced through the pilot passage 52. The pilot pressure of the pilot chamber 23 acts on the other end surface 56b of the spool 56, and the spool 56 moves against the biasing force of the spring 36. The spool 56 stops at a position where the biasing force of the spring 36 acting on the one end surface 56a and the load due to the pilot pressure 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.

[0046] A first drain passage 76a formed in the body 60 is also connected to the pilot chamber 23. A gas vent valve 80 is provided in the first drain passage 76a to discharge air from the pilot chamber 23 to the drain side (tank T side). When the pilot pressure in the pilot chamber 23 exceeds a predetermined pressure, the gas vent valve 80 blocks the flow of pilot pressure oil from the pilot chamber 23 to the drain side, and therefore does not adversely affect the operation of the spool 56. The gas vent valve 80 will be described in detail later. Note that the gas vent valve 80 is not shown in FIG. 2.

[0047] The sleeve 61 is formed with three ports: a first supply port 32 communicating with the bypass passage 30 (see FIG. 2), a second supply port 33 communicating with the back pressure passage 31 (see FIG. 2), and a discharge port 34 communicating with the downstream passage 38 (see FIG. 2).

[0048] 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.

[0049] The first pressure chamber 64 is constantly connected to the exhaust port 34. The third pressure chamber 66 is constantly connected to the first supply port 32. A plurality of orifices 37 are formed on the outer circumferential surface of the land portion 72 of the spool 56, which communicate between the third pressure chamber 66 and the second pressure chamber 65 as the spool 56 moves against the biasing force of the spring 36. The fourth pressure chamber 67 is constantly connected to the second pressure chamber 65 through a pressure introducing passage 68 formed in the spool 56 in the axial direction.

[0050] When the operating lever 10 is not operated and pilot pressure is not introduced to the pilot chamber 23, the poppet valve 70 formed in the spool 56 is pressed against a valve seat 71 formed on the inner circumference of the sleeve 61 by the biasing force of the spring 36, and communication between the second pressure chamber 65 and the first pressure chamber 64 is blocked. Therefore, communication between the first supply port 32 and the exhaust port 34 is blocked. As a result, the hydraulic oil in the rod side chamber 2a does not leak to the exhaust port 34. This state corresponds to the blocking position 22A of the switching valve 22. When the poppet valve 70 is seated on the valve seat 71 by the biasing force of the spring 36, a small gap exists between the end face of the first spring receiving member 45 and the end face of the sleeve 61, so that the poppet valve 70 is reliably seated against the valve seat 71 by the biasing force of the spring 36.

[0051] When the operating lever 10 is operated to introduce pilot pressure into the pilot chamber 23, and the load of the pilot pressure acting on the spool 56 becomes greater than the biasing force of the spring 36, the spool 56 moves against the biasing force of the spring 36. As a result, the poppet valve 70 moves away from the valve seat 71, and the third pressure chamber 66 and the second pressure chamber 65 communicate with each other through the multiple throttles 37, so that the first supply port 32 communicates with the exhaust port 34 through the third pressure chamber 66, the second pressure chamber 65, and the first pressure chamber 64. The communication between the first supply port 32 and the exhaust port 34 allows the hydraulic oil in the rod side chamber 2a to be introduced to the downstream passage 38 (see FIG. 2) through the throttle 37. This state corresponds to the first communication position 22B of the switching valve 22.

[0052] When the pilot pressure introduced to the pilot chamber 23 increases, the spool 56 moves further against the biasing force of the spring 36, and the second supply port 33 communicates with the fourth pressure chamber 67. As a result, the second supply port 33 communicates with the drain port 34 through the fourth pressure chamber 67, the pressure introducing passage 68, the second pressure chamber 65, and the first pressure chamber 64. Due to the communication between the second supply port 33 and the drain port 34, the hydraulic oil in the back pressure chamber 25 bypasses the throttle 37 and is introduced to the downstream passage 38 (see FIG. 2). This state corresponds to the second communication position 22C of the switching valve 22.

[0053] Next, the operation of the hydraulic control device 100 will be described with reference to FIGS.

[0054] 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 no pilot pressure is introduced into the pilot chamber 23 of the switching valve 22, the switching valve 22 is in the shutoff position 22A.

[0055] 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 element 24 in the closing direction (the area of ​​the back surface of the valve element 24) is larger than the area of ​​the second pressure receiving surface 24b, which is the pressure receiving area in the opening direction, so that the load acting on the back surface of the valve element 24 due to the pressure of the back pressure chamber 25 and the biasing force of the spring 27 cause the valve element 24 to be seated on the seat portion 28. In this way, the operated check valve 21 prevents leakage of hydraulic oil from the rod side chamber 2a, and the stopped state of the arm 1 is maintained.

[0056] When the operating lever 10 is operated and pilot pressure is introduced from the pilot control valve 9 to the pilot chamber 6a of the control valve 6, the control valve 6 is switched to the contraction position 6A by an amount corresponding to the pilot pressure. When the control valve 6 is switched to the contraction position 6A, the discharge pressure of the pump 4 acts on the first pressure receiving surface 24a of the operated check valve 21. At this time, the switching valve 22 is in the shutoff position 22A without introducing pilot pressure to the pilot chamber 23, so that the back pressure chamber 25 of the operated check valve 21 is maintained at the pressure of the 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 moves away from the seat portion 28. When the operated check valve 21 opens in this way, the hydraulic oil discharged from the pump 4 is supplied to the rod side chamber 2a, and the cylinder 2 contracts. As a result, the arm 1 moves upward in the direction of the arrow 18 shown in FIG.

[0057] 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 extension position 6B by an amount corresponding to the pilot pressure. At the same time, pilot pressure is also introduced to the pilot chamber 23, so that the switching valve 22 switches to the first communication position 22B or the second communication position 22C depending on the supplied pilot pressure.

[0058] When the pilot pressure introduced into the pilot chamber 23 is equal to or greater than the first predetermined pressure and less than the second predetermined pressure, the switching valve 22 switches to the first communication position 22B. In this case, since communication between the second supply port 33 and the discharge port 34 is blocked, the back pressure chamber 25 of the operated check valve 21 is maintained at the pressure of the rod side chamber 2a, and the operated check valve 21 maintains the closed state.

[0059] 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 through the throttle 37 to the downstream passage 38, and is discharged from the control valve side first main passage 7b through the control valve 6 to the tank T. In addition, since the hydraulic oil discharged from the pump 4 is supplied to the anti-rod side chamber 2b, the cylinder 2 extends. As a result, the arm 1 descends in the direction of the arrow 19 shown in FIG. 1.

[0060] Here, the switching valve 22 is mainly switched to the first communication position 22B when performing crane work to lower a load attached to the bucket 13 to a target position. In crane work, it is necessary to extend the cylinder 2 at a low speed to slowly lower the arm 1 in the direction of the arrow 19, so the pilot pressure led to the pilot chamber 6b of the control valve 6 is small and the control valve 6 is only slightly switched to the extension position 6B. For this reason, the pilot pressure led 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 rod side chamber 2a is discharged through the throttle 37, and the arm 1 is lowered at a low speed suitable for crane work.

[0061] Furthermore, when switching valve 22 is in first communication position 22B, even if a situation occurs in which control valve side first main passage 7b ruptures or the like and hydraulic oil leaks to the outside, the flow rate of hydraulic oil discharged from rod side chamber 2a is limited by orifice 37, so the falling speed of bucket 13 is suppressed. For this reason, switching valve 22 can be switched to shutoff position 22A before bucket 13 falls to the ground, and a sudden fall of bucket 13 can be prevented.

[0062] In this way, the restrictor 37 serves to suppress the descending speed of the cylinder 2 when the operate check valve 21 is closed, and also to suppress the falling speed of the bucket 13 when the control valve side first main passage 7b bursts.

[0063] When the pilot pressure led to the pilot chamber 23 is equal to or higher than the second predetermined pressure, the switching valve 22 is switched to the second communication position 22C. In this case, the second supply port 33 is connected to the discharge port 34, so that the hydraulic oil in the back pressure chamber 25 of the operated check valve 21 is led from the back pressure passage 31 to the downstream passage 38, bypassing the throttle 37, and is discharged from the control valve side first main passage 7b through the control valve 6 to the tank T. As a result, a pressure difference is generated before and after the throttle 26a, and the pressure in the back pressure chamber 25 decreases, so that the force acting on the valve element 24 in the closing direction decreases, and the valve element 24 moves away from the seat portion 28, and the function of the operated check valve 21 as a check valve is released.

[0064] In this way, the operated check valve 21 allows the flow of hydraulic oil from the control valve 6 to the rod side chamber 2a, while also operating to allow the flow of hydraulic oil from the rod side chamber 2a to the control valve 6 in accordance with the back pressure, which is the pressure in the back pressure chamber 25.

[0065] When the operate 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, causing the cylinder 2 to extend quickly. 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 anti-rod side chamber 2b increases, and the extension speed of the cylinder 2 increases. As a result, the arm 1 quickly descends in the direction of the arrow 19.

[0066] The switching valve 22 is switched to the second communication position 22C when excavation work or the like is performed, and the pilot pressure introduced to the pilot chamber 6b of the control valve 6 is high, so that the control valve 6 is switched largely to the extension position 6B. Therefore, the pilot pressure introduced to the pilot chamber 23 of the switching valve 22 is also high and exceeds the second predetermined pressure, so that the switching valve 22 is switched to the second communication position 22C.

[0067] Next, the gas vent valve 80 will be described, mainly with reference to Fig. 4. Fig. 4 is a cross-sectional view of the periphery of the gas vent valve 80. Below, a case will be described in which the gas vent valve 80 discharges air from the pilot chamber 23 to the drain chamber 51, however, what is discharged by the gas vent valve 80 is not limited to air and may be other gases.

[0068] In the conventional hydraulic control device, there was a problem that air on the drain side moves to the pilot chamber 23 side when the hydraulic excavator is stopped. Specifically, when the hydraulic excavator is stopped, 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 air sucked from the tank T into the joint drain passage 76c and the first drain passage 76a moves to the pilot chamber 23 and the pilot passage 52. In addition, 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. 1. Therefore, if the hydraulic excavator is stopped for a long time, air accumulates in the first drain passage 76a, the second drain passage 76b, the joint drain passage 76c, and the drain hose 78. The accumulated air moves to the pilot chamber 23 and the pilot passage 52.

[0069] If air moves from the drain side to the pilot chamber 23 side in this way, when the hydraulic excavator starts from a stopped state, the increase in pilot pressure in the pilot chamber 23 in response to the operator's input operation is delayed due to the influence of the air that has moved to the pilot chamber 23 side. In this way, the air on the pilot chamber 23 side causes a delay in the response of the cylinder 2 to the operator's input operation when the hydraulic excavator starts.

[0070] As a countermeasure against this, in this embodiment, the gas vent valve 80 provided in the first drain passage 76a exhausts air from the pilot chamber 23 to the drain side, and blocks the flow of air from the drain side to the pilot chamber 23. This will be described in detail below.

[0071] The gas vent valve 80 has a housing 90, a passage 81 formed in the housing 90 and extending between the pilot chamber 23 side and the drain side, a valve element 82 for opening and closing the passage 81, and a spring 83 as a biasing member for biasing the valve element 82. The passage 81 is formed penetrating the housing 90 along the longitudinal direction of the first drain passage 76a. The valve element 82 is a sphere, and is provided midway through the passage 81. The spring 83 is provided in a compressed state between the valve element 82 and the housing 90.

[0072] 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. One end of the spring 83 is accommodated in the valve body accommodating portion 81a and contacts the valve body 82, and the other end is provided outside the valve body accommodating portion 81a and contacts a step portion 90a formed in the housing 90. As a result, the valve body accommodating portion 81a is formed with an annular first seat portion 81b with which the valve body 82 comes into contact due to the biasing force of the spring 83, and a second seat portion 81c with which the valve body 82 comes into contact due to the pressure of the pilot chamber 23. The valve body 82 moves between the first seat portion 81b and the second seat portion 81c in the valve body accommodating portion 81a.

[0073] The housing 90 includes a first housing 91 mounted in the first drain passage 76a and a second housing 92 attached to the first housing 91. A hole 91a is formed in the end surface of the first housing 91 facing the pilot chamber 23, and the second housing 92 is attached in the hole 91a. An O-ring 99 is provided as a seal member between the inner surface of the first drain passage 76a and the outer circumferential surface of the first housing 91 to prevent leakage of pilot pressure oil through the two. Instead of providing the O-ring 99, the first housing 91 may be press-fitted into the first drain passage 76a. Also, an O-ring 98 is provided as a seal member between the outer circumferential surface of the second housing 92 and the inner circumferential surface of the hole 91a to prevent leakage of pilot pressure oil through the two. Instead of providing the O-ring 98, the second housing 92 may be press-fitted into the hole 91a. The first housing 91 may be formed integrally with the body 60.

[0074] The second housing 92 is formed with a small diameter hole 92a communicating with the pilot chamber 23 side, and a large diameter hole 92b communicating with the small diameter hole 92a and having an inner diameter larger than that of the small diameter hole 92a. The small diameter hole 92a and the large diameter hole 92b form a part of the passage 81. The large diameter hole 92b defines the valve body accommodating portion 81a. A step portion formed between the small diameter hole 92a and the large diameter hole 92b forms a first seat portion 81b. The opening edge of the passage 81 formed on the bottom surface of the hole 91a forms a second seat portion 81c.

[0075] When installing the gas vent valve 80 in the first drain passage 76a, first, with the valve body 82 accommodated in the large diameter hole 92b of the second housing 92, the second housing 92 is inserted and attached into the hole 91a of the first housing 91 so that the spring 83 is interposed between the valve body 82 and the step portion 90a. Then, the integrated first housing 91 and second housing 92 are installed in the first drain passage 76a.

[0076] Next, the operation and function of the gas vent valve 80 will be described.

[0077] 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, and therefore the valve body 82 comes into contact with the first seat portion 81b by the biasing force of the spring 83 to block the passage 81 (the state shown in FIG. 4). As a result, even when the hydraulic excavator is stopped, the movement of air from the drain side to the pilot chamber 23 side through the passage 81 is prevented.

[0078] 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 contacts the second seat portion 81c when the pilot pressure in the pilot chamber 23 is equal to or greater than the predetermined pressure. This will be described in detail with reference to Fig. 5. Fig. 5 is a graph 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 side.

[0079] When the pilot pump 5 is driven and the operator is not operating the operation lever 10, the pilot pressure oil discharged from the pilot pump 5 is discharged to the tank T through the pilot control valve 9 and is hardly led to the pilot chamber 23. However, even in this state, when the pilot pump 5 is driven, a minimum pilot pressure, specifically, a pilot pressure of about 0.05 to 0.2 MPa, acts on the pilot passage 52 and the pilot chamber 23. In this state, the valve body 82 moves against the biasing force of the spring 83 and moves away from the first seat portion 81b, but does not contact the second seat portion 81c. In other words, 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. 5, air is permitted to flow from the pilot chamber 23 to the drain side through the passage 81, and the air on the pilot chamber 23 side is discharged to the drain side. Therefore, when the hydraulic excavator is started from a stopped state, the air on the pilot chamber 23 side is naturally discharged to the drain side before the operator operates the control lever 10, so that when the operator starts to operate the control lever 10, a delay in the response of the cylinder 2 to the operation is suppressed.

[0080] When an operator operates the operating lever 10 to perform 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 contacts 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 side 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 that the passage 81 does not adversely affect the operation of the cylinder 2.

[0081] 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 about 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, etc. Then, the initial load of the spring 83 is set so that the valve body 82 contacts the second seat portion 81c at the set predetermined pressure or higher.

[0082] As described above, the gas vent valve 80 prevents air from moving from the drain side to the pilot chamber 23 side when the pilot pump 5 is stopped, and when the pilot pump 5 is driven, the air on the pilot chamber 23 side is naturally discharged to the drain side before the operator operates the control lever 10, thereby suppressing a delay in the response of the cylinder 2 to the operator's input operation. Furthermore, when the operator is operating the control lever 10, the flow of pilot pressure oil from the pilot chamber 23 to the drain side is blocked, so the gas vent valve 80 does not adversely affect the operation of the switching valve 22 and the cylinder 2.

[0083] When the hydraulic excavator is started from a stopped state, the operator may operate the control lever 10 to bleed air from the pilot chamber 23 to the drain side through the passage 81. In this case, however, it is necessary to operate the control lever 10 so that the valve body 82 does not come into contact with the second seat portion 81c (so that the pilot pressure in the pilot chamber 23 does not become 0.3 MPa or more in this embodiment). In other words, it is necessary to operate the control lever 10 so that the spool 56 does not move.

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

[0085] When the pilot pump 5 is stopped, the valve element 82 of the gas vent valve 80 comes into contact with the first seat portion 81b by the biasing force of the spring 83 to block the passage 81, thereby preventing the movement of air from the drain side to the pilot chamber 23 side. Furthermore, when the pilot pump 5 is operating and the pilot pressure in the pilot chamber 23 is less than a predetermined pressure, the valve element 82 moves against the biasing force of the spring 83 and separates from the first seat portion 81b to allow air to flow from the pilot chamber 23 to the drain side, so that the air on the pilot chamber 23 side is discharged to the drain side and a response delay in the cylinder 2 caused by the influence of the air is suppressed.

[0086] In addition, when the operator operates the operating lever 10, the flow of pilot pressure oil from the pilot chamber 23 to the drain side through the passage 81 is blocked, so that the gas bleed valve 80 does not adversely affect the operation of the cylinder 2.

[0087] <Variation 1> A modified example of the above embodiment will be described below with reference to Fig. 6. Fig. 6 corresponds to Fig. 4 and is a cross-sectional view of the periphery of the gas release valve 80. In Fig. 6, components having the same functions as those in the above embodiment are given the same reference numerals. In this modified example, the configuration of the gas release valve 80 differs from that of the above embodiment.

[0088] In this modified example as well, when the pilot pump 5 is stopped, the valve element 82 comes into contact with the first seat portion 81b by the biasing force of the spring 83 to block the passage 81, thereby preventing the movement of air from the drain side to the pilot chamber 23 side. Moreover, when the pilot pump 5 is driven and the pilot pressure in the pilot chamber 23 is less than a predetermined pressure, the valve element 82 moves against the biasing force of the spring 83 and separates from the first seat portion 81b to allow the flow of air from the pilot chamber 23 to the drain side, so that the air on the pilot chamber 23 side is discharged to the drain side, and a response delay of the cylinder 2 due to the influence of the air is suppressed. In this respect, this modified example is the same as the above embodiment.

[0089] However, in the gas vent valve 80 of this modified example, even when the pilot pressure in the pilot chamber 23 is equal to or higher than a predetermined pressure, the valve element 82 moves against the biasing force of the spring 83 but does not come into contact with 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 side through the passage 81. This is because, unlike the above embodiment, the entire spring 83 is accommodated in the valve element accommodating portion 81a. Specifically, the spring 83 is provided in a compressed state between the valve element 82 and the bottom surface of a hole 91a formed in the first housing 91.

[0090] In this modified example, even when the pilot pressure in the pilot chamber 23 is equal to or higher than a predetermined pressure, the valve element 82 does not come into contact with the second seat portion 81c (see FIG. 4), and therefore allows the flow of pilot pressure oil from the pilot chamber 23 to the drain side through the passage 81. However, the gas vent valve 80 has an orifice 85 provided in the passage 81 as a throttle that applies resistance to the flow of pilot pressure oil from the pilot chamber 23 to the drain side. Therefore, when the operator operates the control lever 10, the orifice 85 applies resistance to the flow of pilot pressure oil from the pilot chamber 23 to the drain side, and the desired pilot pressure acts on the pilot chamber 23, and therefore the gas vent valve 80 does not adversely affect the operation of the cylinder 2.

[0091] In this modification, the orifice 85 is formed in the second housing 92. However, the position where the orifice 85 is formed is not limited as long as the orifice 85 is provided in the passage 81. For example, the orifice 85 may be provided in the passage 81 of the first housing 91.

[0092] <Variation 2> In the above embodiment and the above modified example 1, a configuration in which a piston is not provided in the pilot chamber 23 has been described. However, a piston (not shown) may be slidably accommodated in the pilot chamber 23. In this configuration, the pilot chamber 23 is defined between the cap 58 and the piston, and a drain chamber is defined between the piston and the spool 56. The piston receives the pilot pressure of the pilot chamber 23 and applies a thrust to the spool 56 against the biasing force of the spring 36. In the modified example 2, when the pilot pump 5 is driven and the pilot pressure of the pilot chamber 23 is less than a predetermined pressure, the air in the pilot chamber 23 flows through the gap between the outer circumferential surface of the piston and the inner circumferential surface of the pilot hole 60b, and is then discharged from the gas vent valve 80 to the drain side.

[0093] The configuration, operation, and effects of the embodiment of the present invention will be described below.

[0094] A hydraulic control device 100 (fluid pressure control device) for controlling the expansion and contraction operation of a cylinder 2 for driving a load 1 includes a control valve 6 for controlling the supply of working fluid from a pump 4 (fluid pressure supply source) to the cylinder 2, a pilot control valve 9 for controlling the pilot pressure led to the control valve 6 from a pilot pump 5 (pilot pressure supply source), a main passage 7 for connecting the control valve 6 to a load side pressure chamber 2a of the cylinder 2 on which a load pressure from the load 1 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 load holding mechanism 20 has an operate check valve 21 for allowing the flow of working fluid from the control valve 6 to the load side pressure chamber 2a, while allowing the flow of working fluid from the load side pressure chamber 2a to the control valve 6 in response to a back pressure, and a switching valve 22 for operating in conjunction with the control valve 6 by the pilot pressure led through the pilot control valve 9 and for switching the operation of the operate check valve 21. The switching valve 22 is connected to the pilot control valve 9 via the pilot control valve 9. the pilot chamber 23 to which the pilot pressure is introduced, a spool 56 that moves in response to the pilot pressure of the pilot chamber 23, a first drain passage 76a (drain passage) connected to the pilot chamber 23, and a gas vent valve 80 that is provided in the first drain passage 76a and discharges air (gas) from the pilot chamber 23 to the drain side. The gas vent valve 80 has a passage 81 that is provided across the pilot chamber 23 side and the drain side, a valve body 82 that opens and closes the passage 81, and a spring 83 (biasing member) that biases the valve body 82. 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 to block the passage 81, and when the pilot pump 5 is driven and the pilot pressure in the pilot chamber 23 is less than a predetermined pressure that is lower than the pilot pressure at which the spool 56 moves, the valve body 82 moves against the biasing force of the spring 83 and separates from the first seat portion 81b to allow the flow of fluid from the pilot chamber 23 to the drain side.

[0095] In this configuration, a gas vent valve 80 for discharging air from the pilot chamber 23 to the drain side is provided in the first drain passage 76a, and 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 biasing force of the spring 83 to block the passage 81, thereby preventing air from moving from the drain side to the pilot chamber 23 side. 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, allowing the flow of fluid from the pilot chamber 23 to the drain side, so that the air on the pilot chamber 23 side is discharged to the drain side, and a response delay of the cylinder 2 due to the influence of the air is suppressed. Thus, the movement of air from the drain side to the pilot chamber 23 side can be prevented, and a response delay due to the influence of the air can be suppressed.

[0096] In addition, when the pilot pump 5 is operating and the pilot pressure in the pilot chamber 23 is equal to or higher than a predetermined pressure, the valve body 82 moves against the biasing force of the spring 83 and contacts the second seat portion 81c, blocking the passage 81 and blocking the flow of pilot pressure oil from the pilot chamber 23 to the drain side.

[0097] In this configuration, when the pilot pump 5 is operating and the pilot pressure in the pilot chamber 23 is equal to or higher than a predetermined pressure, the valve body 82 blocks the flow of pilot pressure oil from the pilot chamber 23 to the drain side through the passage 81, so that the gas vent valve 80 does not adversely affect the operation of the cylinder 2.

[0098] In addition, the valve body 82 allows the flow of pilot pressure oil from the pilot chamber 23 to the drain side even when the pilot pressure in the pilot chamber 23 is equal to or higher than the specified pressure, and the gas bleed valve 80 further has an orifice 85 (restriction) that is provided in the passage 81 and applies resistance to the flow of pilot pressure oil from the pilot chamber 23 to the drain side.

[0099] In this configuration, when the pilot pump 5 is operating and the pilot pressure in the pilot chamber 23 is equal to or 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 side, so that the gas vent valve 80 does not adversely affect the operation of the cylinder 2.

[0100] Although the embodiments of the present invention have been described above, the above-mentioned embodiments merely show some of the application examples of the present invention, and it is not intended that the technical scope of the present invention be limited to the specific configurations of the above-mentioned embodiments.

[0101] This application claims priority based on Patent Application No. 2022-41677, filed with the Japan Patent Office on March 16, 2022, the entire contents of which are incorporated herein by reference.

Claims

1. A fluid pressure control device that controls the extension and contraction operation of a cylinder that drives a load, a control valve for controlling the supply of hydraulic fluid to the cylinder; a pilot control valve for controlling a pilot pressure introduced from a pilot pressure supply source to the control valve; a main passage connecting the control valve to a load-side pressure chamber of the cylinder to which a load pressure due to a load acts when the control valve is in a neutral position; a load retaining mechanism provided in the main passage, The load holding mechanism includes: an operated check valve that allows the flow of hydraulic fluid from the control valve to the load side pressure chamber, and also allows the flow of hydraulic fluid from the load side pressure chamber to the control valve in response to a back pressure; a switching valve that operates in conjunction with the control valve by a pilot pressure introduced through the pilot control valve and switches the operation of the operated check valve; The switching valve is a pilot chamber to which a pilot pressure is introduced through the pilot control valve; A spool that moves in response to the pilot pressure in the pilot chamber; A drain passage connected to the pilot chamber; a gas vent valve provided in the drain passage for discharging gas from the pilot chamber to the drain side, The gas vent valve is A passage provided between the pilot chamber side and the drain side; a valve body for opening and closing the passage; and a biasing member for biasing the valve body, The initial load of the biasing member is set so that, when the pilot pressure supply source is stopped, the valve body comes into contact with the first seat portion by the biasing force of the biasing member to block the passage, and, when the pilot pressure supply source is driven and the pilot pressure in the pilot chamber is less than a predetermined pressure lower than the pilot pressure at which the spool moves, the valve body moves against the biasing force of the biasing member and separates from the first seat portion to allow the flow of fluid from the pilot chamber to the drain side. Fluid pressure control device.

2. 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 a predetermined pressure, the valve body moves against the biasing force of the biasing member to come into contact with the second seat portion, blocking the passage and blocking the flow of pilot fluid from the pilot chamber to the drain side. Fluid pressure control device.

3. The fluid pressure control device according to claim 1, the valve body allows the pilot fluid to flow from the pilot chamber to the drain side even when the pilot pressure in the pilot chamber is equal to or higher than the predetermined pressure, The gas vent valve further has a throttle provided in the passage for providing resistance to the flow of pilot fluid from the pilot chamber to the drain side. Fluid pressure control device.

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