JP7612944B2 - Fluid Pressure Control Device - Google Patents

Description

The present invention relates to a fluid pressure control device.

Japanese Patent Application Laid-Open No. 2010-101400 discloses a fluid pressure control device for controlling the operation of a work machine, which includes a control valve that switches the supply and discharge of hydraulic oil to and from a cylinder, thereby controlling the extension and contraction movement of the cylinder, and a load holding mechanism that is installed in a main passage that connects the load side pressure chamber of the cylinder and the control valve.

The load holding mechanism includes an operated check valve and a meter-out control valve that operates with 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.

In this type of fluid pressure control device, a drain chamber connected to the 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.

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 work 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 work equipment is started, the air that has moved to the pilot chamber side delays the increase 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.

In this way, gas on the pilot chamber side can cause a delayed response to the operator's input operations when starting up the work equipment.

The present invention aims to prevent gas from moving from the drain side to the pilot chamber side and to suppress response delays caused by the influence of gas.

According to one aspect of the present invention, there is provided a fluid pressure control device for controlling the extension and retraction of a cylinder that drives a load, the device comprising: a control valve for controlling the supply of hydraulic fluid to the cylinder; a pilot control valve for controlling the pilot pressure led to the control valve from a pilot pressure supply source; a main passage connecting the control valve to a load side pressure chamber of the cylinder on which a load pressure due to a load acts when the control valve is in a neutral position; and a load holding mechanism provided in the main passage. The load holding mechanism comprises an operate check valve that 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 that operates in conjunction with the control valve by the pilot pressure led through the pilot control valve and switches the operation of the operate check valve. The switching valve is a pilot pressure-driven valve to which the pilot pressure is led through the pilot control valve. a pilot chamber, a spool that moves in response to pilot pressure in the pilot chamber, a piston that receives pilot pressure and applies thrust to the spool, a drain chamber partitioned by the spool and the piston, and a gas vent valve provided on the piston for discharging gas from the pilot chamber to the drain chamber, the gas vent valve having a passage provided between 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, when the pilot pressure supply source is stopped, the valve body comes into contact with a 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 that is 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 a flow of fluid from the pilot chamber to the drain chamber.

FIG. 2 is a diagram showing a portion 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. 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. FIG. 4 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 chamber. FIG. 13 is a cross-sectional view of the periphery of a piston in a load holding mechanism of a fluid pressure control device according to a modified example of an embodiment of the present invention. FIG.

Below, with reference to the drawings, we will explain the fluid pressure control device according to an embodiment of the present invention.

A fluid pressure control device controls the operation of hydraulic work equipment such as a hydraulic excavator. In this embodiment, a hydraulic control device 100 is described that controls the extension and retraction operation of a cylinder 2 that drives the arm (load) 1 of a hydraulic excavator shown in Figures 1 and 2. The fluid pressure control device may also control the extension and retraction operation of a lift cylinder mounted on a forklift or the like. Below, a case where hydraulic oil is used as the working fluid of the cylinder 2 is described, but instead of hydraulic oil, for example, a water-soluble substitute liquid may be used.

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

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

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.

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 anti-rod side chamber 2b of the cylinder 2 are connected by a second main passage 8.

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

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

On the other hand, when pilot pressure is introduced into the pilot chamber 6b, the control valve 6 switches to position 6B, hydraulic oil is supplied from the pump 4 through the second main passage 8 to the anti-rod side chamber 2b, and 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. 1.

When pilot pressure is not supplied to the pilot chambers 6a and 6b, the control valve 6 is in position 6C, the supply and discharge of hydraulic oil to the cylinder 2 is cut off, and the arm 1 remains stopped.

Thus, 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, and switches the supply and discharge of hydraulic oil in the cylinder 2 to control the extension and retraction of the cylinder 2.

Now, as shown in Figure 1, when the bucket 13 is lifted and the control valve 6 is switched to the neutral position 6C to stop the movement of the arm 1, 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 the load side pressure chamber to which the 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 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.

In the cylinder 15 that drives the boom 14 (see Figure 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.

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

The operated check valve 21 has a valve body 24 that opens and closes the first main passage 7, a seat portion 28 on which the valve body 24 sits, a back pressure chamber 25 facing the back surface of the valve body 24, and a passage 26 formed in the valve body 24 that constantly guides hydraulic oil in the rod side chamber 2a to the back pressure chamber 25. A throttle 26a is provided in the passage 26 to provide 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 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.

The back pressure chamber 25 contains a spring 27 as a biasing member that biases the valve body 24 in the closing direction. 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. In other words, the operated check valve 21 prevents leakage of hydraulic oil from the rod side chamber 2a, maintains the load pressure, and maintains the stopped state of the arm 1.

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

The bypass passage 30 and the back pressure passage 31 are connected to the upstream side of the switching valve 22, and the downstream passage 38 is connected to the downstream side of the switching valve 22. The bypass passage 30 is a passage for leading 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 leading 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 leading 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 the communication between the bypass passage 30 and the back pressure passage 31 and the downstream passage 38, thereby controlling the flow of hydraulic oil in the first main passage 7, which is 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. The switching valve 22 also has three positions: a shutoff position 22A, a first communication position 22B, and a second communication position 22C.

When pilot pressure is introduced to the pilot chamber 6b of the control valve 6, pilot pressure is also introduced to the pilot chamber 23 at the same time. In other words, 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.

Specifically, when pilot pressure is not 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.

When a pilot pressure equal to or greater than the first predetermined pressure and less than the second predetermined pressure is introduced into the pilot chamber 23, the switching valve 22 switches to the first communication position 22B. In the first communication position 22B, the first supply port 32 communicates with the discharge port 34. As a result, the hydraulic oil in the rod side chamber 2a is led 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 led 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 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 exhaust port 34, and the second supply port 33 also communicates with the exhaust port 34. As a result, the hydraulic oil in the back pressure chamber 25 is led 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 led 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 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, 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.

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.

The drain passage 76 has a first drain passage 76a connected to the drain chamber 51, a second drain passage 76b connected to the spring chamber 54, and a junction drain passage 76c formed by the junction of the first drain passage 76a and the second drain passage 76b. The junction drain passage 76c is connected to a drain port 77 that opens on the outer surface of the body 60 (see FIG. 3) of the load holding mechanism 20. The drain port 77 is connected to the tank T through a drain hose 78. In this way, the drains of the drain chamber 51 and the spring chamber 54 are discharged to the tank T through the junction drain passage 76c, the drain port 77, and the drain hose 78. Since the drain chamber 51 and the spring chamber 54 provided on either side of the spool 56 of the switching valve 22 are both connected to the tank T, when the switching valve 22 is in the shutoff position 22A, atmospheric pressure acts on both ends of the spool 56, preventing the spool 56 from moving unintentionally.

A relief valve 43 is connected to the control valve side first main passage 7b, which opens when the pressure in the control valve side first main passage 7b reaches a predetermined pressure. A relief valve 44 is connected to the second main passage 8, which opens when the pressure in the second main passage 8 reaches a predetermined pressure. The relief valves 43 and 44 are intended 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 acts on the arm 1.

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

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 generally cylindrical sleeve 61 is inserted into the spool hole 60a. The 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 face 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 face of the sleeve 61. Hydraulic oil that has leaked into the spring chamber 54 is drained from the second drain passage 76b to the tank T.

The spring chamber 54 contains a first annular 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 protruding from the one end face 56a of the spool 56 is inserted in the hollow portion, and a second spring bearing member 46 disposed near the bottom of the cap 57. The spring 36 is interposed in a compressed state between the first spring bearing member 45 and the second spring bearing member 46, and biases the spool 56 in the closing direction via the first spring bearing member 45.

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 to the pilot chamber 23 through a pilot passage 52 formed in the body 60. A piston 50 is slidably housed in the pilot chamber 23, which receives pilot pressure on its back surface and applies a thrust to the spool 56 against the biasing force of the spring 36.

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

The piston 50 has a sliding portion 50a whose outer peripheral surface slides along the inner peripheral surface of the piston hole 60b, a tip portion 50b which is formed with a smaller diameter than the sliding portion 50a and faces the other end surface 56b of the spool 56, and a base portion 50c which is formed with a smaller diameter than the sliding portion 50a and faces the tip 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 50c and the annular back surface of the sliding part 50a. As a result, the piston 50 advances, and the tip end 50b abuts against the other end surface 56b of the spool 56, moving the spool 56. In this 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 base end 50c abuts against the tip surface of the cap 58, the base end 50c has a smaller diameter than the sliding part 50a, and pilot pressure acts on the annular back surface of the sliding part 50a, so the piston 50 can advance.

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

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

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 described in detail later. Note that the gas vent valve 80 is not shown in FIG. 2.

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

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.

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

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 the 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, there is a small gap 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.

When the operating lever 10 is operated to introduce pilot pressure into the pilot chamber 23, and the thrust of the piston 50 acting on the spool 56 becomes greater than the biasing force of the spring 36, the spool 56 moves against the biasing force of the spring 36. As a result, the poppet valve 70 moves away from the valve seat 71, and the third pressure chamber 66 and the second pressure chamber 65 communicate with each other through a plurality of orifices 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 leads the hydraulic oil in the rod side chamber 2a to the downstream passage 38 (see FIG. 2) through the orifices 37. This state corresponds to the first communication position 22B of the switching valve 22.

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 is connected to the fourth pressure chamber 67. As a result, the second supply port 33 is connected to the exhaust port 34 through the fourth pressure chamber 67, the pressure guide passage 68, the second pressure chamber 65, and the first pressure chamber 64. By connecting the second supply port 33 to the exhaust port 34, the hydraulic oil in the back pressure chamber 25 bypasses the throttle 37 and is led to the downstream passage 38 (see FIG. 2). 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 explained with reference to Figures 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 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.

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 (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, so 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 causes the valve body 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.

When the operating lever 10 is operated and pilot pressure is introduced from the pilot control valve 9 to the pilot chamber 6a of the control valve 6, the control valve 6 switches to the contraction position 6A by an amount corresponding to the pilot pressure. When the control valve 6 switches 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 cut-off position 22A without introducing pilot pressure to the pilot chamber 23, so the back pressure chamber 25 of the operated check valve 21 is maintained at the pressure of the 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 leaves 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 rises in the direction of the arrow 18 shown in FIG.

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.

When the pilot pressure introduced into the pilot chamber 23 is equal to or greater than the first predetermined pressure and less than the second predetermined pressure, the switching valve 22 switches to the first communication position 22B. In this case, communication between the second supply port 33 and the exhaust port 34 is blocked, so 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 its closed state.

On the other hand, because the first supply port 32 is connected to 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, because 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.

Here, the switching valve 22 is mainly switched to the first communication position 22B when performing crane work to lower the load attached to the bucket 13 to the 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 extended 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.

In addition, when the switching valve 22 is in the first communication position 22B, even if the control valve side first main passage 7b were to burst or otherwise cause hydraulic oil to leak to the outside, the flow rate of hydraulic oil discharged from the rod side chamber 2a is restricted by the orifice 37, so the falling speed of the bucket 13 is suppressed. Therefore, before the bucket 13 falls to the ground, the switching valve 22 can be switched to the shutoff position 22A, and the sudden fall of the bucket 13 can be prevented.

In this way, the throttle 37 is intended to suppress the descent speed of the cylinder 2 when the operate check valve 21 is closed, and to suppress the fall speed of the bucket 13 when the control valve side first main passage 7b ruptures.

When the pilot pressure introduced into the pilot chamber 23 is equal to or greater 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 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, 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.

In this way, the operated check valve 21 operates to allow hydraulic oil to flow from the control valve 6 to the rod side chamber 2a, while also allowing hydraulic oil to flow from the rod side chamber 2a to the control valve 6 in response to the back pressure, which is the pressure in the back pressure chamber 25.

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 into 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.

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

Next, the gas vent valve 80 provided on the piston 50 will be described, mainly with reference to Figure 4. Figure 4 is a cross-sectional view of the piston 50 and its surroundings. Note that the gas vent valve 80 is not shown in Figure 3. 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, but the gas discharged by the gas vent valve 80 is not limited to air and may be other gases.

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, an annular gap 69 is provided. In the conventional switching valve, this gap 69 functions as a passage for discharging air on the pilot chamber 23 side to the drain chamber 51 side. However, by providing the gap 69 between the piston 50 and the body 60, when the hydraulic excavator is stopped, the air on the drain chamber 51 side moves to the pilot chamber 23 side through the gap 69. To be more specific, 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 through the gap 69. 1, the load holding mechanism 20 provided on the cylinder 2 that drives the arm 1 is provided at the highest position in the hydraulic excavator. Therefore, if the hydraulic excavator remains stopped for a long period of time, air will accumulate in the drain chamber 51, the first drain passage 76a, the second drain passage 76b, the joint drain passage 76c, and the drain hose 78. The accumulated air moves through the gap 69 to the pilot chamber 23 and the pilot passage 52.

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 air that has moved to the pilot chamber 23 side causes a delay in the increase in pilot pressure in the pilot chamber 23 in response to the operator's input operation, and the increase in pilot pressure in the pilot chamber 23 is completed only 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 on the pilot chamber 23 side causes a delay in the response of cylinder 2 to the operator's input operation when the hydraulic excavator starts.

As a countermeasure, in this embodiment, the gap 69 between the piston 50 and the body 60 is sealed by an O-ring 99 as a sealing member, and the flow of air through the gap 69 is blocked. In addition, the gas vent valve 80 provided in the piston 50 exhausts 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 release valve 80 has a passage 81 extending between 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 by passing through the piston 50 along the direction of movement of the piston 50. The valve body 82 is a sphere and is provided midway through the passage 81. The spring 83 is provided in a compressed state 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. 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 50f formed on the piston 50. 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.

A slit 50d is formed in the end face of the tip 50b of the piston 50 facing the spool 56. The slit 50d communicates with the passage 81 and opens to the outer circumferential surface of the tip 50b. By forming the slit 50d in the end face 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 part of the piston 50. A hole 50e is formed in the end face of the base end 50c of the piston 50 that faces the pilot chamber 23, and the housing 84 is attached in the hole 50e. An O-ring 98 is provided as a seal member between the outer circumferential surface of the housing 84 and the inner circumferential surface of the hole 50e to prevent leakage of pilot pressure oil between the two. Instead of providing an 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 that communicates with the pilot chamber 23, and a large diameter hole 84b that communicates with the small diameter hole 84a and has a larger inner diameter than the small diameter hole 84a. The small diameter hole 84a and the large diameter hole 84b form 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 forms the first seat portion 81b. The opening edge of the passage 81 formed on the bottom surface of the hole 50e forms the 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 housing 84 is inserted into the hole 50e of the piston 50 so that the spring 83 is interposed between the valve body 82 and the step portion 50f of the piston 50.

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

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

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 explained in more detail with reference to Figure 5. Figure 5 is a graph showing the relationship between the pilot pressure in the pilot chamber 23 and the air flow rate flowing from the pilot chamber 23 to the drain chamber 51.

When the pilot pump 5 is in operation and the operator is not operating the control 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 in operation, 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 chamber 51 through the passage 81, and the air on 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 on the pilot chamber 23 side is naturally discharged to the drain chamber 51 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.

When the 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 chamber 51 through the passage 81 is blocked, and the flow of pilot pressure oil is also blocked. Therefore, the 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 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.

As described above, the gas vent valve 80 prevents air from moving from the drain chamber 51 to the pilot chamber 23 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 chamber 51 side before the operator operates the control lever 10, suppressing a delay in the response of the cylinder 2 to the operator's input operation. 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 does not adversely affect the operation of the switching valve 22 and the cylinder 2.

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 chamber 51 through the passage 81. In this case, however, the control lever 10 must be operated 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 exceed 0.3 MPa in this embodiment). In other words, the control lever 10 must be operated 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 release valve 80 comes into contact with the first seat portion 81b by the biasing force of the spring 83 to block the passage 81, preventing the movement of air from the drain chamber 51 side to the pilot chamber 23 side. Also, 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 air from the pilot chamber 23 to the drain chamber 51, so that the air on the pilot chamber 23 side is discharged to the drain chamber 51 side, and the response delay of the cylinder 2 due to the influence of air is suppressed.

In addition, when the operator operates the operating 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 that the gas bleed valve 80 does not adversely affect the operation of the cylinder 2.

Below, a modified example of the above embodiment will be described with reference to Figure 6. Figure 6 corresponds to Figure 4 and is a cross-sectional view of the piston 50 and its surroundings. In Figure 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 vent valve 80 differs from that of the above embodiment.

In this modified example, when the pilot pump 5 is stopped, the valve body 82 comes into contact with the first seat portion 81b due to the biasing force of the spring 83 to block the passage 81, preventing air from moving from the drain chamber 51 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 air to flow from the pilot chamber 23 to the drain chamber 51, so that the air on the pilot chamber 23 side is discharged to the drain chamber 51 side, and the 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.

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 body 82 moves against the biasing force of the spring 83 but does not contact 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 modified example, even if the pilot pressure in the pilot chamber 23 is equal to or higher than a predetermined pressure, the valve body 82 does not contact the second seat portion 81c (see FIG. 4), so that the flow of pilot pressure oil from the pilot chamber 23 to the drain chamber 51 through the passage 81 is permitted. However, the gas bleed 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 chamber 51. Therefore, when the operator operates the operating lever 10, the orifice 85 applies 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, so that the gas bleed valve 80 does not adversely affect the operation of the cylinder 2.

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

The configuration, operation, and effects of the embodiments of the present invention are summarized below.

A hydraulic control device 100 (fluid pressure control device) that controls the expansion and contraction operation of a cylinder 2 that drives a load 1 includes a control valve 6 that controls the supply of hydraulic fluid from a pump 4 (fluid pressure supply source) to the cylinder 2, a pilot control valve 9 that controls the pilot pressure led to the control valve 6 from a pilot pump 5 (pilot pressure supply source), a main passage 7 that connects the load side pressure chamber 2a 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, to the control valve 6, and a load holding mechanism 20 provided in the main passage 7. The load holding mechanism 20 has an operate check valve 21 that allows the flow of hydraulic fluid from the control valve 6 to the load side pressure chamber 2a, while allowing the flow of hydraulic fluid from the load side pressure chamber 2a to the control valve 6 in response to a back pressure, and a switching valve 22 that operates in conjunction with the control valve 6 by the pilot pressure led through the pilot control valve 9 and switches the operation of the operate check valve 21. The switching valve 22 connects the pilot chamber 2 to which the pilot pressure is led through the pilot control valve 9. 3, a spool 56 that moves in response to the pilot pressure in the pilot chamber 23, a piston 50 that receives the pilot pressure and applies a thrust to the spool 56, a drain chamber 51 defined by the spool 56 and the piston 50, and a gas vent valve 80 that is provided in the piston 50 and that discharges air (gas) from the pilot chamber 23 to the drain chamber 51. The gas vent valve 80 has a passage 81 provided between the pilot chamber 23 and the drain chamber 51, a valve element 82 that opens and closes the passage 81, and a valve element 82 that opens and closes the passage 81. When the pilot pump 5 is stopped, the valve body 82 comes into contact with the first seat portion 81b due to the biasing force of the spring 83, thereby blocking the passage 81. 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 away from the first seat portion 81b, thereby allowing the flow of fluid from the pilot chamber 23 to the drain chamber 51.

In this configuration, the piston 50 is provided with a gas vent valve 80 for discharging air from the pilot chamber 23 to the drain side, and the valve body 82 of the gas vent valve 80 contacts the first seat portion 81b by the biasing force of the spring 83 to block the passage 81 when the pilot pump 5 is stopped, preventing air from moving from the drain chamber 51 side to the pilot chamber 23 side. In addition, when the pilot pump 5 is driven and the pilot pressure of 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 chamber 51, so that the air on the pilot chamber 23 side is discharged to the drain chamber 51 side, and the response delay of the cylinder 2 due to the influence of air is suppressed. Therefore, the movement of air from the drain side to the pilot chamber 23 side can be prevented, and the response delay due to the influence of air can be suppressed.

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 chamber 51.

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 chamber 51 through the passage 81, so that the gas vent valve 80 does not adversely affect the operation of the cylinder 2.

In addition, the valve body 82 allows the flow of pilot pressure oil from the pilot chamber 23 to the drain chamber 51 even when the pilot pressure in the pilot chamber 23 is equal to or higher than the specified pressure, and the gas vent valve 80 further has an orifice 85 (restriction) provided in the passage 81 which provides resistance to the flow of pilot pressure oil from the pilot chamber 23 to the drain chamber 51.

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 chamber 51, so that the gas bleed valve 80 does not adversely affect the operation of the cylinder 2.

The above describes embodiments of the present invention, but the above embodiments merely illustrate some 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.

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

Claims (4)

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 piston that receives pilot pressure and applies thrust to the spool;
a drain chamber defined by the spool and the piston;
a gas vent valve provided in the piston for discharging gas from the pilot chamber to the drain chamber,
The gas vent valve is
a passage provided between the pilot chamber and the drain chamber;
a valve body for opening and closing the passage;
and a biasing member for biasing the valve body,
The fluid pressure control device is set so that, when the pilot pressure supply source is stopped, the valve body contacts the first seat portion due to 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 that is 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 fluid to flow from the pilot chamber to 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 to contact a second seat portion, blocking the passage and blocking 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 when 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 for providing resistance to the flow of pilot fluid from the pilot chamber to the drain chamber. The fluid pressure control device according to claim 1,
A fluid pressure control device, wherein the passage of the gas vent valve is formed through the piston along the direction of movement of the piston.

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