JP6706170B2 - Fluid pressure controller - Google Patents

Description

The present invention relates to a fluid pressure control device that controls the operation of hydraulic working equipment.

As a hydraulic control device that controls the operation of a hydraulic working device, Patent Document 1 discloses a cylinder device, a control valve that controls expansion and contraction operation of the cylinder device, and a load holding valve provided between the cylinder device and the control valve. , Are disclosed. The load holding valve includes a pilot check valve, a switching valve for canceling the check function of the pilot check valve, and a relief valve that opens when the load pressure in the bottom side pressure chamber of the cylinder device rises.

The switching valve includes a pilot chamber into which the pilot pressure is guided, and a spool that moves according to the pilot pressure in the pilot chamber. The end of the spool does not directly face the pilot chamber, but the end of a sub-spool provided adjacent to the spool faces.

When the load pressure in the bottom side pressure chamber of the cylinder device rises and the relief valve opens, a relief back pressure occurs upstream of the orifice provided downstream of the relief valve, and the relief back pressure is the pilot chamber of the switching valve. Between the spool and the sub spool at. As a result, the spool moves, the switching valve switches, the check function of the pilot check valve is released, and the pressure in the bottom side pressure chamber decreases.

JP 2000-220603 A

In the hydraulic control device disclosed in Patent Document 1, when the cylinder device is contracted, the operator of the hydraulic excavator manually operates the operation lever to guide the pilot pressure to the pilot chamber of the switching valve. The pilot pressure acts on the sub-spool, and the sub-spool applies thrust to the spool to open the spool, the check function of the pilot check valve is released, and the cylinder device contracts. On the other hand, when the load pressure in the bottom side pressure chamber of the cylinder device rises and the relief valve opens, the relief back pressure generated upstream of the orifice provided downstream of the relief valve is introduced between the spool and the sub spool. Acting on the spool, and thrust is applied to the spool. As described above, when the pilot pressure is introduced into the pilot chamber by the operator's operation to move the spool, thrust is applied to the spool via the sub spool, while the relief back pressure is directly spooled when the relief valve is opened. Act on.

If the relief valve opens when the pilot pressure is introduced to the pilot chamber by the operator's operation and the spool is open, the relief back pressure is introduced between the spool and the sub-spool, so the sub-spool is Therefore, the thrust force by the pilot pressure is difficult to be transmitted from the sub spool to the spool. Further, when the pressure receiving area of the spool on which the relief back pressure acts is smaller than the pressure receiving area of the sub spool, the spool moves in the closing direction depending on the relief back pressure.

Therefore, if the relief valve is opened while the operator is operating the operating lever to cause the cylinder device to contract, the spool moves in the closing direction and the cylinder device intended by the operator is removed. A situation may occur in which the contraction speed cannot be obtained.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a fluid pressure control device that enables stable operation of a cylinder.

A first aspect of the present invention is a fluid pressure control device that controls expansion and contraction operations of a cylinder that drives a load, the control valve controlling a supply of a working fluid from a fluid pressure supply source to a cylinder, and a control from a pilot pressure supply source. Provided in the main passage, a pilot control valve that controls the pilot pressure guided to the valve, a main passage that connects the load side pressure chamber of the cylinder where the load pressure from the load acts when the control valve is in the neutral position, and the control valve The load holding mechanism allows the flow of the working fluid from the control valve to the load side pressure chamber, while the load holding mechanism allows the flow of the working fluid from the load side pressure chamber to the control valve according to the back pressure. Operate check valve that allows the operating pressure and the pilot valve guided through the pilot control valve to operate in conjunction with the control valve, and the switching valve for switching the operation of the operate check valve and the pressure in the load side pressure chamber reach the specified pressure. A relief valve which is opened in the case of, and a relief discharge passage for guiding the relief fluid discharged from the relief valve to the tank, the switching valve, the pilot chamber through which the pilot pressure is guided from the pilot passage through the pilot control valve, A spool that moves according to the pilot pressure in the pilot chamber, a spring chamber that stores a biasing member that biases the spool in the valve closing direction, and a pilot pressure on the back surface that receives the pilot pressure and resists the biasing force of the biasing member on the spool. A piston for applying a thrust force, a drain chamber defined by the spool and the piston, and a drain passage that connects the drain chamber and the spring chamber to the relief discharge passage.The pilot passage and the pilot chamber form a pilot line. The return line is constituted by the relief discharge passage, the drain chamber, and the drain passage, and the load holding mechanism includes a connection passage connecting the pilot line and the return line, and a working fluid from the return line to the pilot line provided in the connection passage. And a check valve which allows only passage of the check valve.

In the first aspect, the relief fluid discharged from the relief valve is discharged to the tank through the relief discharge passage, so that the relief fluid does not operate the switching valve. Further, since the pilot line and the return line communicate with each other through the connection passage, even if the relief fluid pressure is guided to the drain chamber of the switching valve through the relief discharge passage and the drain passage, the relief fluid pressure also flows through the connection passage to the pilot chamber. Is guided. As a result, the thrusts acting on the piston due to the relief fluid pressure cancel each other out, so that the relief fluid pressure does not affect the operation of the switching valve. Therefore, even if the relief valve is opened while the operator is operating the operation lever to extend and retract the cylinder, the spool does not move in the closing direction, and the cylinder intended by the operator is not moved. The expansion and contraction speed of is obtained.

A second invention is characterized in that a connection passage is formed in the piston to connect the drain chamber and the pilot chamber.

According to the second aspect of the present invention, it is possible to easily process the connection passage and improve the space efficiency.

A third invention is characterized in that the connection passage connects the relief discharge passage and the pilot passage.

A fourth invention is characterized in that the connection passage connects the drain passage and the pilot passage.

According to the present invention, stable operation of the cylinder is possible.

It is a figure showing a part of hydraulic excavator. It is a hydraulic circuit diagram of the fluid pressure control device concerning the embodiment of the present invention. It is sectional drawing of the load holding mechanism of the fluid pressure control apparatus which concerns on embodiment of this invention. It is an expanded sectional view of the A section in FIG. It is a top view of the load retention mechanism of the fluid pressure control device concerning the embodiment of the present invention. It is sectional drawing of the load holding mechanism of the fluid pressure control apparatus which concerns on the 1st modification of embodiment of this invention. It is a hydraulic circuit diagram of the fluid pressure control device concerning the 2nd modification of the embodiment of the present invention. It is a top view of the load retention mechanism of the fluid pressure control device concerning the 2nd modification of the embodiment of the present invention. It is a hydraulic circuit diagram of the fluid pressure control device which concerns on the 1st comparative example of this invention. It is sectional drawing of the load holding mechanism of the fluid pressure control apparatus which concerns on the 1st comparative example of this invention. It is a hydraulic circuit diagram of the fluid pressure control device which concerns on the 2nd comparative example of this invention.

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

The fluid pressure control device controls the operation of hydraulic working equipment such as a hydraulic excavator, and in the present embodiment, controls the expansion and contraction operation of a cylinder 2 that drives an arm (load) 1 of the hydraulic excavator shown in FIG. 1. The hydraulic control device will be described.

First, the hydraulic circuit of the hydraulic control device will be described with reference to FIG.

The cylinder 2 has 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 a non-rod side chamber 2b, and one end thereof is connected to the piston 2d. A rod 2e, the other end of which extends to the outside of the cylinder tube 2c and is connected to the arm 1, is provided.

An engine is mounted on the hydraulic excavator, and the power of the engine drives a pump 4 as a fluid pressure supply source and a pilot pump 5 as a pilot pressure supply source.

The hydraulic control device 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 introduced 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 non-rod-side chamber 2b of the cylinder 2 are connected by a second main passage 8.

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

Specifically, when the pilot pressure is introduced into the pilot chamber 6a, the control valve 6 switches to the position 6A, and the hydraulic oil is supplied from the pump 4 to the rod side chamber 2a through the first main passage 7 and The hydraulic oil in the anti-rod side chamber 2b is discharged to the tank T through the second main passage 8. As a result, the cylinder 2 is contracted, and the arm 1 rises in the direction of the arrow 80 shown in FIG.

On the other hand, when the pilot pressure is introduced to the pilot chamber 6b, the control valve 6 is switched to the position 6B, the working oil is supplied from the pump 4 to the non-rod side chamber 2b through the second main passage 8, and the rod side chamber 2b is supplied. The hydraulic oil 2a is discharged to the tank T through the first main passage 7. As a result, the cylinder 2 is extended and the arm 1 is lowered in the direction of the arrow 81 shown in FIG.

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

As described above, the control valve 6 has three positions, that is, the contracted position 6A for contracting the cylinder 2, the expanded position 6B for expanding the cylinder 2, and the neutral position 6C for holding the load of the cylinder 2. The supply/discharge of hydraulic oil is switched to control the expansion/contraction operation of the cylinder 2.

Here, as shown in FIG. 1, when the control valve 6 is switched to the neutral position 6C and the movement of the arm 1 is stopped in a state where the bucket 13 is lifted, the cylinder 2 is moved by the weight of the bucket 13 and the arm 1 and the like. A force in the extending direction acts on the. As described above, in the cylinder 2 that drives the arm 1, the rod-side chamber 2a serves as a load-side pressure chamber on 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 of 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, the anti-rod side chamber 15b serves as a load side pressure chamber. Therefore, when the load holding mechanism 20 is provided on the boom 14, the load is applied to the main passage connected to the anti rod side chamber 15b. A holding mechanism 20 is provided (see FIG. 1).

The load holding mechanism 20 operates in cooperation with the control valve 6 by the operation check valve 21 provided in the first main passage 7 and the pilot pressure guided to the pilot chamber 23 through the pilot control valve 9, and the operation check valve 21 is operated. A switching valve 22 for switching the operation.

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

The first main passage 7 has a cylinder-side first main passage 7a connecting the rod-side chamber 2a and the operating check valve 21, and a control valve-side first main passage 7b connecting the operating check valve 21 and the control valve 6. ..

The valve body 24 includes a first pressure receiving surface 24a on which the pressure of the control valve side first main passage 7b acts and a second pressure receiving surface 24b on which the pressure of the rod side chamber 2a acts through the cylinder side first main passage 7a. It is formed.

The back pressure chamber 25 accommodates a spring 27 as a biasing member that biases the valve element 24 in the valve closing direction. The pressure of the back pressure chamber 25 and the biasing force of the spring 27 act in the direction in which the valve body 24 is seated on the seat portion 28.

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. That is, the operate check valve 21 prevents the hydraulic oil from leaking in the rod side chamber 2a, holds the load pressure, and holds the arm 1 in the stopped state.

The load holding mechanism 20 further includes a bypass passage 30 that guides the hydraulic oil in the rod side chamber 2a to the control valve side first main passage 7b bypassing the operation check valve 21, and the hydraulic oil in the back pressure chamber 25 to the control valve side. And a back pressure passage 31 leading to the first main passage 7b.

The switching valve 22 is provided in the bypass passage 30 and the back pressure passage 31, switches communication between the bypass passage 30 and the back pressure passage 31 with respect to the control valve-side first main passage 7b, and a meter-out side when the cylinder 2 is extended. The flow of hydraulic oil in the first main passage 7 is controlled.

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 control valve side first main passage 7b. Have. Further, the switching valve 22 has three positions of a shutoff position 22A, a first communication position 22B, and a second communication position 22C.

When the pilot pressure is introduced into the pilot chamber 6b of the control valve 6, the pilot pressure of the same pressure is introduced into the pilot chamber 23 at the same time. 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.

More specifically, when the pilot pressure is not guided to the pilot chamber 23, the switching valve 22 maintains the cutoff position 22A by the urging force of the spring 36. At the blocking position 22A, both the first supply port 32 and the second supply port 33 are blocked.

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

When the pilot pressure higher than the second predetermined pressure is introduced into the pilot chamber 23, the switching valve 22 switches to the second communication position 22C. At the second communication position 22C, the first supply port 32 communicates with the discharge port 34, and the second supply port 33 also communicates with the discharge port 34. As a result, the hydraulic oil in the back pressure chamber 25 is guided from the back pressure passage 31 to the control valve side first main passage 7b through the switching valve 22. At this time, the hydraulic oil in the back pressure chamber 25 bypasses the throttle 37, is guided to the control valve side first main passage 7b, and is discharged from the control valve 6 to the tank T. As a result, a differential pressure is generated before and after the throttle 26a, and the pressure in the back pressure chamber 25 is reduced. Therefore, the force in the valve closing direction that acts on the valve body 24 is reduced, and the valve body 24 is removed from the seat portion 28. Then, the function of the operating check valve 21 as a check valve is released.

A relief passage 40 is branched and connected upstream of the switching valve 22 in the bypass passage 30. The relief passage 40 is provided with a relief valve 41 that opens when the pressure in the rod-side chamber 2a reaches a predetermined pressure to allow passage of the working oil and allows the working oil in the rod-side chamber 2a to escape. The relief pressure oil discharged from the relief valve 41 is discharged to the tank T through a relief discharge passage 77 connecting the relief valve 41 and the tank T.

The relief discharge passage 77 has a main discharge passage 77a connected to the relief valve 41, and a first branch passage 77b and a second branch passage 77c branched from the main discharge passage 77a into two. The first branch passage 77b is connected to the first drain port 53, and the second branch passage 77c is connected to the second drain port 86. The first drain port 53 and the second drain port 86 each open to the outer surface of the body 60 described below. The first drain port 53 has a smaller diameter than the second drain port 86, and is configured to be connectable to a pipe having a smaller diameter. In the present embodiment, the pipe 55 communicating with the tank T is connected to the first drain port 53, and the second drain port 86 is sealed by the plug 88 (see FIG. 5). Therefore, in the present embodiment, the relief pressure oil discharged from the relief valve 41 is guided to the pipe 55 through the main discharge passage 77a, the first branch passage 77b, and the first drain port 53, and is discharged to the tank T.

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.

Next, the switching valve 22 will be described in detail mainly with reference to FIGS. 3 to 5. FIG. 3 is a cross-sectional view of the load holding mechanism 20, showing a state in which the pilot pressure is not introduced into the pilot chamber 23 and the switching valve 22 is in the cutoff position 22A. FIG. 4 is an enlarged view of the portion A in FIG. 3, and shows a state in which a check valve 90 described later is closed. FIG. 5 is a plan view of the load holding mechanism 20. In FIGS. 3 to 5, the components denoted by the same reference numerals as those shown in FIG. 2 have the same configurations as those shown in FIG.

As shown in FIG. 3, the switching valve 22 is incorporated in the body 60. A spool hole 60a is formed in the body 60, and a substantially cylindrical sleeve 61 is inserted into the spool hole 60a. A spool 56 is slidably incorporated in the sleeve 61.

A spring chamber 54 is defined by a cap 57 beside the one end surface 56a of the spool 56. The spring chamber 54 is connected to the first drain passage 76a through a notch 61a formed in the end surface of the sleeve 61. The first drain passage 76 a is connected to the first branch passage 77 b of the relief discharge passage 77. Therefore, the hydraulic oil that has leaked into the spring chamber 54 is discharged to the tank T through the first drain passage 76a and the first branch passage 77b.

The spring 36 is accommodated in the spring chamber 54 as a biasing member that biases the spool 56. Further, in the spring chamber 54, an annular first spring receiving member 45 in which an end surface abuts on the one end surface 56a of the spool 56 and a pin portion 56c formed so as to project from the one end surface 56a of the spool 56 into the hollow portion is inserted. And the second spring receiving member 46 arranged near the bottom of the cap 57 are accommodated. The spring 36 is interposed between the first spring receiving member 45 and the second spring receiving member 46 in a compressed state, and biases the spool 56 in the valve closing direction via the first spring receiving member 45.

The axial position of the second spring receiving member 46 in the spring chamber 54 is set by the tip of the adjusting bolt 47 penetrating the bottom of the cap 57 and screwed into contact with the back surface of the second spring receiving member 46. To be done. By screwing the adjustment bolt 47, the second spring receiving member 46 moves in a direction approaching the first spring receiving member 45. Therefore, the initial spring load of the spring 36 can be adjusted by adjusting the screwing amount of the adjusting bolt 47. The adjusting bolt 47 is fixed by a nut 48.

The pilot chamber 23 is defined on the side of the other end surface 56b of the spool 56 by a piston hole 60b formed in communication with the spool hole 60a and a cap 58 closing the piston hole 60b. Pilot pressure is introduced into the pilot chamber 23 through a pilot passage 52 formed in the body 60. In the pilot chamber 23, a piston 50 that receives a pilot pressure on the back surface and applies a thrust force against the urging force of the spring 36 to the spool 56 is slidably accommodated.

A drain chamber 51 is defined in the piston hole 60b by the spool 56 and the piston 50. The drain chamber 51 is connected to the second drain passage 76b, and the second drain passage 76b is connected to the first branch passage 77b of the relief discharge passage 77. Therefore, the hydraulic oil that has leaked into the drain chamber 51 is discharged to the tank T through the second drain passage 76b and the first branch passage 77b.

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

As shown in FIGS. 3 and 4, the piston 50 is provided with a connection passage 78 that connects the drain chamber 51 and the pilot chamber 23. The connection passage 78 is provided with a check valve 90 that allows only the flow of hydraulic oil from the drain chamber 51 to the pilot chamber 23. The piston 50 is formed so that the pressure receiving area of the drain chamber 51 that receives the pressure is equal to the pressure receiving area of the pilot chamber 23 that receives the pressure.

The connection passage 78 is formed so as to open at both axial end surfaces at the axial center position of the piston 50.

The check valve 90 includes a ball 91 that is seated on and off a valve seat 78 a formed in the connection passage 78, and a cap member 92 that is provided on the opposite side of the ball 91 from the valve seat 78 a.

The cap member 92 is formed with a through hole 93 penetrating in the axial direction and a slit 94 extending in the radial direction on the end face on the ball 91 side (right side in FIG. 4) so as to communicate with the through hole 93. It

When the pressure in the pilot chamber 23 is higher than the pressure in the drain chamber 51, the check valve 90 is closed. Specifically, the ball 91 is seated on the valve seat 78a, and the communication between the drain chamber 51 and the pilot chamber 23 is cut off. When the pressure in the drain chamber 51 is higher than the pressure in the pilot chamber 23, the check valve 90 opens (state shown in FIG. 4). Specifically, the ball 91 separates from the valve seat 78 a and contacts the end surface of the cap member 92, and the hydraulic oil in the drain chamber 51 is guided to the pilot chamber 23 through the slit 94 and the through hole 93. By opening the check valve 90 in this manner, the drain chamber 51 and the pilot chamber 23 communicate with each other through the connection passage 78.

In addition, in the present embodiment, the check valve 90 has a structure that does not have a biasing member (for example, a spring) that biases the ball 91 in the closing direction. You may urge. The check valve 90 is not limited to the structure shown in FIG. 3 and may have a known configuration.

When the pilot pressure oil is supplied into the pilot chamber 23 through the pilot passage 52, the pilot pressure acts on the back surface of the base end portion 50c and the annular back surface of the sliding portion 50a. As a result, the piston 50 moves forward, and the tip portion 50b contacts the other end surface 56b of the spool 56 to move the spool 56. In this way, the spool 56 receives the thrust of the piston 50 generated based on the pilot pressure acting on the back surface of the piston 50, and moves against the biasing force of the spring 36. Even when the back surface of the base end portion 50c is in contact with the tip end surface of the cap 58, the base end portion 50c has a smaller diameter than the sliding portion 50a, and the pilot pressure is applied to the annular back surface of the sliding portion 50a. , The piston 50 can move forward.

Since one end of the piston 50 faces the pilot chamber 23 and the other end faces the drain chamber 51 connected to the tank T, the thrust of the piston 50 generated based on the pilot pressure of the pilot chamber 23 is efficiently spooled. 56 is transmitted.

Each of the drain chamber 51 and the spring chamber 54 communicates with the first branch passage 77b of the relief discharge passage 77 through the first drain passage 76a and the second drain passage 76b. The first branch passage 77b is formed in communication with the first drain port 53 opening to the outer surface of the body 60. The first drain port 53 is connected to the tank T through a pipe 55 (see FIG. 2). Since both the drain chamber 51 and the spring chamber 54 communicate with the tank T, when the switching valve 22 is in the shut-off position 22A, atmospheric pressure acts on both ends of the spool 56, and the spool 56 moves unintentionally. Such a situation is prevented.

In this way, the relief pressure oil discharged from the relief valve 41 and the drain of the drain chamber 51 and the spring chamber 54 join together and are discharged to the tank T through the first drain port 53 and the pipe 55.

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

The sleeve 61 includes 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 control valve side first main passage 7b. Three ports of the discharge port 34 that communicate with each other are formed.

The outer peripheral surface of the spool 56 is partially cut out in an annular shape, and the cutout 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 The fourth pressure chamber 67 is formed.

The first pressure chamber 64 always communicates with the discharge port 34.

The third pressure chamber 66 is always in communication with the first supply port 32. A plurality of throttles 37 that connect the third pressure chamber 66 and the second pressure chamber 65 are formed on the outer periphery of the land portion 72 of the spool 56 as the spool 56 moves against the biasing force of the spring 36. ..

The fourth pressure chamber 67 is always in communication with the second pressure chamber 65 through a pressure guiding passage 68 formed in the spool 56 in the axial direction.

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

When the pilot pressure is introduced into the pilot chamber 23 and the thrust of the piston 50 acting on the spool 56 becomes larger 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 separates from the valve seat 71, and the third pressure chamber 66 and the second pressure chamber 65 communicate with each other through the plurality of throttles 37, so that the first supply port 32 is connected to the third pressure chamber 66 and the second pressure chamber 66. It communicates with the exhaust port 34 through the chamber 65 and the first pressure chamber 64. Due to the communication between the first supply port 32 and the discharge port 34, the hydraulic oil in the rod side chamber 2a is guided to the control valve side first main passage 7b through the throttle 37. This state corresponds to the first communication position 22B of the switching valve 22.

When the pilot pressure guided to the pilot chamber 23 increases, the spool 56 moves further against the biasing force of the spring 36, and the fourth pressure chamber 67 communicates with the second supply port 33. As a result, the second supply port 33 communicates with the discharge port 34 through the fourth pressure chamber 67, the pressure guiding passage 68, the second pressure chamber 65, and the first pressure chamber 64. Due to the communication between the second supply port 33 and the discharge port 34, the hydraulic oil in the back pressure chamber 25 is guided to the control valve side first main passage 7b. This state corresponds to the second communication position 22C of the switching valve 22.

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

When the control valve 6 is in the neutral position 6C, the hydraulic oil discharged by the pump 4 is not supplied to the cylinder 2. At this time, since the pilot pressure is not introduced into the pilot chamber 23 of the switching valve 22, the switching valve 22 is also in the shutoff position 22A.

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

When the operating lever 10 is operated and the pilot pressure is guided from the pilot control valve 9 to the pilot chamber 6a of the control valve 6, the control valve 6 is switched to the contracted position 6A by an amount according to the pilot pressure. When the control valve 6 is switched to the contracted position 6A, the discharge pressure of the pump 4 acts on the first pressure receiving surface 24a of the operating check valve 21. At this time, since the switching valve 22 is in the shut-off position 22A without the pilot pressure being guided to the pilot chamber 23, the back pressure chamber 25 of the operate 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 urging force of the spring 27, the valve body 24 is Separate from the seat portion 28. When the operate 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 80 shown in FIG.

When the operation lever 10 is operated and the pilot pressure is guided 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 according to the pilot pressure. At the same time, since the pilot pressure is also introduced to the pilot chamber 23, the switching valve 22 switches to the first communication position 22B or the second communication position 22C according to the supplied pilot pressure.

When the pilot pressure guided to the pilot chamber 23 is equal to or higher than the first predetermined pressure and lower than the second predetermined pressure, the switching valve 22 switches to the first communication position 22B. In this case, since the communication between the second supply port 33 and the discharge port 34 is cut off, the back pressure chamber 25 of the operate check valve 21 is maintained at the pressure of the rod side chamber 2a, and the operate check valve 21 is closed. It becomes a state.

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 passes from the bypass passage 30 through the throttle 37 to the control valve-side first main passage 7b, and the control valve 6 Is discharged from the tank to the tank T. Further, since the working oil discharged from the pump 4 is supplied to the non-rod side chamber 2b, the cylinder 2 extends. As a result, the arm 1 descends in the direction of the arrow 81 shown in FIG.

Here, switching the switching valve 22 to the first communication position 22B is performed, for example, when performing a crane operation for lowering a transported object attached to the bucket 13 to a target position, or moving the arm 1 and the boom 14 at the same time, This is a case where a horizontal pulling operation is performed in which the bucket 13 is moved horizontally. In the crane work, since it is necessary to extend the cylinder 2 at a low speed to slowly move the arm 1 downward in the direction of the arrow 81, the control valve 6 is only slightly switched to the extended position 6B. Further, since the horizontal pulling work is an advanced work in which the arm 1 and the boom 14 are simultaneously moved so that the bucket 13 moves horizontally, the arm 1 and the boom 14 are slowly moved. Therefore, even in the horizontal pulling operation, the control valve 6 is only slightly switched to the extended position 6B. Therefore, the pilot pressure guided to the pilot chamber 6b of the control valve 6 is small, the pilot pressure guided to the pilot chamber 23 of the switching valve 22 is not less than the first predetermined pressure and less than the second predetermined pressure, and the switching valve 22 is at the first communication position. It only switches to 22B. Therefore, the hydraulic oil in the rod side chamber 2a is discharged through the throttle 37, and the arm 1 moves at a low speed suitable for crane work and horizontal pulling work.

Further, when the switching valve 22 is in the first communication position 22B, even if a situation occurs in which the control valve-side first main passage 7b ruptures and the hydraulic oil leaks to the outside, it is discharged from the rod-side chamber 2a. Since the flow rate of the hydraulic oil to be supplied is limited by the throttle 37, the falling speed of the bucket 13 is suppressed. This function is called metering control. Therefore, the switching valve 22 can be switched to the shut-off position 22A before the bucket 13 falls to the ground, and the bucket 13 can be prevented from being suddenly dropped.

Thus, the throttle 37 is for suppressing the descending speed of the cylinder 2 when the operation check valve 21 is closed, and for suppressing the falling speed of the bucket 13 when the control valve side first main passage 7b is ruptured. ..

When the pilot pressure guided to the pilot chamber 23 is equal to or higher than the second predetermined pressure, the switching valve 22 switches to the second communication position 22C. In this case, since the second supply port 33 communicates with the discharge port 34, the hydraulic oil in the back pressure chamber 25 of the operating check valve 21 is guided to the control valve side first main passage 7b through the back pressure passage 31 and is controlled. It is discharged from the valve 6 to the tank T. As a result, a differential pressure is generated before and after the throttle 26a, and the pressure in the back pressure chamber 25 is reduced, so that the force in the valve closing direction acting on the valve body 24 is reduced and the valve body 24 is separated from the seat portion 28. The function of the operating check valve 21 as a check valve is released.

As described above, the operation check valve 21 allows the flow of the hydraulic oil from the control valve 6 to the rod side chamber 2a, while the flow of the hydraulic oil from the rod side chamber 2a to the control valve 6 according to the pressure of the back pressure chamber 25. To act to allow.

When the operation check valve 21 is opened, the hydraulic oil in the rod side chamber 2a is discharged to the tank T through the first main passage 7, so that the cylinder 2 quickly extends. That is, when the switching valve 22 is switched to the second communication position 22C, the flow rate of the working oil discharged from the rod side chamber 2a increases, so that the flow rate of the working oil supplied to the non-rod side chamber 2b increases and the cylinder 2 The extension speed becomes faster. As a result, the arm 1 quickly descends in the direction of arrow 81.

The switching valve 22 is switched to the second communication position 22C when excavation work is performed, and the control valve 6 is largely switched to the extension position 6B. Therefore, the pilot pressure guided to the pilot chamber 6b of the control valve 6 is large, the pilot pressure guided to the pilot chamber 23 of the switching valve 22 becomes equal to or higher than the second predetermined pressure, and the switching valve 22 switches to the second communication position 22C. ..

Next, the operation of this embodiment will be described.

First, a comparative example of this embodiment will be described with reference to FIGS. 9 to 11. 9 and 10 are diagrams showing a first comparative example, and FIG. 11 is a diagram showing a second comparative example. 9 to 11, the same components as those in the above embodiment are denoted by the same reference numerals as those in FIGS.

In the first comparative example shown in FIGS. 9 and 10, the relief passage 40 is provided with a relief valve 110 that opens when the pressure in the rod-side chamber 2a reaches a predetermined pressure and releases the working oil in the rod-side chamber 2a. An orifice 111 is provided in the relief discharge passage 77 that connects the relief valve 110 and the tank T. When the pressure in the rod side chamber 2a reaches a predetermined pressure and the relief valve 110 opens, the relief pressure oil on the upstream side of the orifice 111 discharged from the relief valve 110 is guided to the drain chamber 51 through the second drain passage 76b. As a result, the switching valve 22 is switched to the second communication position 22C, so that the operate check valve 21 is opened and the pressure of the hydraulic oil in the rod side chamber 2a is reduced.

In the first comparative example as described above, the pilot valve 23 is moved by the operator's operation to move the spool 56, and the cylinder 2 is extended so that the pressure in the rod side chamber 2a increases and the relief valve 110 operates. Is opened, the relief pressure oil on the upstream side of the orifice 111 discharged from the relief valve 110 is guided to the drain chamber 51. Since the relief back pressure on the upstream side of the orifice 111 guided to the drain chamber 51 is larger than the pilot pressure guided to the pilot chamber 23, the piston 50 moves away from the spool 56. Therefore, the thrust of the piston 50 generated by the pilot pressure is not transmitted to the spool 56. Further, since the pressure receiving area of the spool 56 on which the pressure of the drain chamber 51 acts is smaller than the pressure receiving area of the piston 50, depending on the magnitude of the relief back pressure on the upstream side of the orifice 111 guided to the drain chamber 51, the spool 56 may have a different pressure. There is a possibility that 56 is moved in the closing direction by the urging force of the spring 36.

As described above, in the first comparative example, when the relief valve 110 opens while the operator operates the operation lever to extend the cylinder 2, the spool 56 moves in the closing direction. As a result, a situation may occur in which the extension speed of the cylinder 2 intended by the operator cannot be obtained.

In the second comparative example shown in FIG. 11, the relief discharge passage 77 that connects the relief valve 41 and the tank T is not provided with an orifice, and the piston 50 has a connection passage 78 that connects the drain chamber 51 and the pilot chamber 23. Not provided.

In the second comparative example, the relief pressure oil discharged from the relief valve 41 is discharged to the tank T through the relief discharge passage 77, and high pressure hardly acts on the drain chamber 51. However, when the relief valve 41 is opened, some relief pressure oil is introduced into the drain chamber 51 through the second drain passage 76b. The relief pressure oil guided to the drain chamber 51 acts so as to resist the thrust of the piston 50 generated by the pilot pressure.

If the relief valve 41 is opened when the amount of operation of the operation lever by the operator is relatively small and the pilot pressure guided to the pilot chamber 23 is also relatively small, relief pressure oil having a pressure higher than the pilot pressure is discharged to the drain chamber 51. May be led to. In such a case, the piston 50 is pushed back by the pressure in the drain chamber 51 in the direction away from the spool 56 against the thrust of the pilot pressure.

Therefore, in the second comparative example, if the relief valve 41 is opened while the operator is operating the operation lever to extend the cylinder 2, the spool 56 is unintentionally caused by the pressure in the drain chamber 51. May move in the closing direction. Further, when the relief valve 41 is closed from the opened state, the relief pressure oil in the drain chamber 51 is discharged to the tank T through the relief discharge passage 77, so that the spool 56 moves in the opening direction and the speed of the cylinder 2 increases. Is unintentionally faster. Thus, even in the second comparative example, the extension speed of the cylinder 2 intended by the operator may not be obtained.

On the other hand, in the present embodiment, the drain chamber 51 and the pilot chamber 23 are connected by the connection passage 78 formed in the piston 50. Therefore, when the relief valve 41 is opened and the relief pressure oil having a pressure higher than the pilot pressure is guided to the drain chamber 51, the check valve 90 is opened by the relief pressure oil, and at the same time, the relief pressure is also applied to the pilot chamber 23. Oil is guided. Since the pressure receiving area of the piston 50 receiving the pressure of the drain chamber 51 and the pressure receiving area of the piston 50 receiving the pressure of the pilot chamber 23 are substantially equal to each other, the thrusts acting on the piston 50 by the relief pressure oil cancel each other out.

Therefore, the relief valve 41 is opened while the operator is operating the operation lever to extend the cylinder 2, and relief pressure oil having a pressure larger than the pilot pressure is introduced into the drain chamber 51. However, the relief pressure oil does not move the piston 50. Therefore, the spool 56 does not move in the closing direction. As described above, in the present embodiment, the spool 56 moves in the closing direction even when the relief valve 41 is opened while the operator is operating the operation lever to extend and retract the cylinder 2. Therefore, the expansion/contraction speed of the cylinder 2 intended by the operator can be obtained.

Note that most of the relief pressure oil discharged from the relief valve 41 is discharged to the tank T through the relief discharge passage 77, and the flow rate introduced to the drain chamber 51 is small. Therefore, the relief pressure oil guided to the pilot chamber 23 through the connection passage 78 is not guided to the pilot chamber 6b of the control valve 6 and does not affect the operation of the control valve 6.

Next, a modified example of the present embodiment will be described.

In the above-described embodiment, the connection passage 78 that connects the drain chamber 51 and the pilot chamber 23 is formed in the piston 50. As a result, even if the relief valve 41 is opened and the relief pressure oil whose pressure is higher than the pilot pressure is introduced into the drain chamber 51, the relief pressure oil is also introduced into the pilot chamber 23 at the same time. Therefore, the thrust force acting on the piston 50 is canceled by the relief pressure oil, and the expansion/contraction speed of the cylinder 2 intended by the operator is obtained. On the other hand, the connection passage 78 may be one that connects the pilot line through which the pilot pressure from the pilot control valve 9 is guided and the return line through which the relief pressure from the relief valve 41 is guided. The pilot line includes the pilot passage 52 and the pilot chamber 23. Relief discharge passage 77, first and second drain passages 76a. 76b and the drain chamber 51 are included. The details will be described below.

In the first modification shown in FIG. 6, the connection passage 78 is formed in the body 60 and connects the pilot passage 52 and the second drain passage 76b. Even in such a first modification, when the relief valve 41 is opened, the relief pressure oil is guided to the drain chamber 51 through the second drain passage 76b, and at the same time, the second drain passage 76b and the connection passage 78 are provided. , And to the pilot chamber 23 through the pilot passage 52. Therefore, according to the first modified example, the same effect as that of the above-described embodiment is obtained.

In the above embodiment, the pipe 55 is connected to the first drain port 53, and the first drain port 53 and the tank T are connected via the pipe 55. On the other hand, the first drain port 53 may be sealed by a plug, the pipe 55a may be connected to the second drain port 86, and the second drain port 86 and the tank T may be connected via the pipe 55a.

In such a case, the connection passage 78 may be formed in the body 60 to connect the second branch passage 77c and the pilot passage 52, as in the second modification shown in FIGS. 7 and 8. The pipe 55 a connected to the second drain port 86 can be connected to a pipe having a larger diameter than the pipe 55 connected to the first drain port 53. Therefore, by connecting the pipe 55a having a relatively large diameter, although the cost is increased, the flow path resistance can be reduced and the magnitude of the relief pressure introduced to the drain chamber 51 can be reduced. As a result, the movement of the spool 56 due to the relief pressure oil can be prevented more reliably.

Note that pipes may be connected to both the first drain port 53 and the second drain port 86, and the relief pressure oil may be discharged to the tank T through the first branch passage 77b and the second branch passage 77c. In this case, the connection passage 78 may be connected to the first branch passage 77b or the second branch passage 77c. According to this, the flow rate of the relief pressure oil guided to the drain chamber 51 can be reduced. However, in order to reduce the piping that connects the body 60 of the load holding mechanism 20 and the tank T, the piping is not connected to the second drain port 86 and the second drain port 86 is connected to the plug 88 as in the above embodiment. It is preferable to seal with.

Further, although not shown, a connection passage connecting any one of the main discharge passage 77a, the first branch passage 77b, and the first drain passage 76a in the relief discharge passage 77 to one of the pilot chamber 23 and the pilot passage 52 is provided. It may be provided.

As described above, the connection passage 78 includes one of the pilot passage 52 and the pilot chamber 23 forming the pilot line, the relief discharge passage 77 forming the return line, the first and second drain passages 76a and 76b, and the drain chamber. Any one that connects any one of 51 and 51 may be used.

Since the piston 50 is smaller than the body 60, it is easy to process, and conventionally, since no other oil passage or the like is formed in the piston 50, space efficiency can be improved. As in the embodiment, it is preferable to form the piston 50.

According to this embodiment described above, the following effects can be obtained.

Since the relief pressure oil discharged from the relief valve 41 is discharged to the tank T through the relief discharge passage 77, the relief fluid does not operate the switching valve 22. Further, since the pilot chamber 23 and the drain chamber 51 are connected by the connection passage 78, even if the relief pressure oil is guided to the drain chamber 51 through the relief discharge passage 77 and the drain passage 76b, at the same time, the pilot chamber is connected through the connection passage 78. The relief pressure oil is also introduced to 23. As a result, the thrusts exerted on the piston 50 by the relief pressure oil cancel each other out, so that the relief pressure oil does not affect the operation of the switching valve. Therefore, even if the relief valve 41 is opened while the operator is operating the operation lever to extend and retract the cylinder 2, the spool 56 does not move in the closing direction, and the operator does not move. The intended expansion/contraction speed of the cylinder 2 is obtained. Therefore, stable operation of the cylinder 2 is possible.

Further, in the present embodiment, the connection passage 78 that connects the drain chamber 51 and the pilot chamber 23 is formed in the piston 50. Therefore, the processing of the connection passage 78 can be facilitated and the space efficiency can be improved.

Further, in the present embodiment, the relief pressure oil discharged from the relief valve 41 merges with the drain of the drain chamber 51 and the spring chamber 54 and is discharged to the tank T through the first drain port 53 and the pipe 55. Therefore, since it is not necessary to provide a dedicated pipe for guiding the relief pressure oil discharged from the relief valve 41 to the tank T, the number of pipes can be reduced.

Further, since the relief pressure oil discharged from the relief valve 41 is discharged to the tank T through the relief discharge passage 77 and is hardly guided to the drain chamber 51, the relief back pressure pulsates when the relief valve 41 is opened. However, the pulsation is prevented from propagating to the spool 56. Therefore, generation of vibration is suppressed.

Further, the relief valve 110 of the first comparative example in which the switching valve 22 is switched by the discharged relief pressure oil to open the operation check valve 21 is the pressure enough to switch the spool 56 of the switching valve 22 to the second communication position 22C. Need only be introduced into the drain chamber 51, so a small capacity relief valve with a small discharge flow rate is used. On the other hand, the relief valve 41 of the present embodiment opens when the pressure in the rod side chamber 2a reaches a predetermined pressure, allows the hydraulic oil in the rod side chamber 2a to escape to the tank T, and reduces the pressure in the rod side chamber 2a. Since it is necessary to have a function of lowering the pressure, a large capacity type relief valve having a larger discharge flow rate than the relief valve 110 of the first comparative example is used. As described above, since the relief valve 41 of the present embodiment is of a large capacity type, the degree of freedom in design is improved. Further, since the relief valve 41 is of a large capacity type, the pressure in the rod side chamber 2a can be maintained at a predetermined pressure even when a surge pressure is generated in which the pressure in the rod side chamber 2a sharply rises. Therefore, damage to the cylinder 2 due to surge pressure can be prevented.

Hereinafter, the configuration, operation, and effect of the embodiment of the present invention will be collectively described.

In the present embodiment, a fluid pressure control device that controls the expansion and contraction operation of the cylinder 2 that drives the arm 1 is controlled by a control valve 6 that controls the supply of hydraulic oil from the pump 4 to the cylinder 2 and a pilot pump 5. A pilot control valve 9 for controlling the pilot pressure guided to the valve 6, and a main passage connecting the rod side chamber 2a of the cylinder 2 on which the load pressure by the arm 1 acts when the control valve 6 is in the neutral position 6C and the control valve 6. 7 and a load holding mechanism 20 provided in the main passage 7, the load holding mechanism 20 allows the flow of the hydraulic oil from the control valve 6 to the rod side chamber 2a, while the rod side chamber 2a depending on the back pressure. From the operating check valve 21 that allows the flow of hydraulic oil from the control valve 6 to the control valve 6, and a switching for switching the operation of the operating check valve 21 that operates in cooperation with the control valve 6 by the pilot pressure introduced through the pilot control valve 9. The switching valve includes a valve 22, a relief valve 41 that opens when the pressure in the rod-side chamber 2a reaches a predetermined pressure, and a relief discharge passage 77 that guides the relief fluid discharged from the relief valve 41 to the tank T. Reference numeral 22 denotes a pilot chamber 23 in which pilot pressure is guided from the pilot control valve 9 through a pilot passage 52, a spool 56 that moves according to the pilot pressure in the pilot chamber 23, and a spring 36 that biases the spool 56 in the valve closing direction. A spring chamber 54 accommodated therein, a piston 50 for applying a thrust against the biasing force of the spring 36 to the spool 56 by receiving pilot pressure on the back surface, a drain chamber 51 partitioned by the spool 56 and the piston 50, and a drain chamber. 51 and the spring chamber 54 and the first and second drain passages 76a and 76b for communicating with the relief discharge passage 77, the pilot passage 52 and the pilot chamber 23 constitute a pilot line, and the relief discharge passage 77 and the drain chamber are provided. 51 and the first and second drain passages 76a and 76b form a return line, and the load holding mechanism 20 includes a connection passage 78 that connects the pilot line and the return line, and a pilot line from the return line provided in the connection passage 78. And a check valve 90 that only allows passage of hydraulic oil to the line.

In this configuration, the relief pressure oil discharged from the relief valve 41 is discharged to the tank T through the relief discharge passage 77, so that the relief pressure oil does not operate the switching valve 22. Further, since the pilot line and the return line communicate with each other through the connection passage 78, even if the relief pressure oil is guided to the drain chamber 51 of the switching valve 22 through the relief discharge passage 77 and the drain passage 76b, the pilot line is also transmitted through the connection passage 78 at the same time. The relief pressure oil is also introduced into the chamber 23. As a result, the thrusts acting on the piston 50 due to the relief pressure oil cancel each other out, so that the relief pressure oil does not affect the operation of the switching valve 22. Therefore, even if the relief valve 41 is opened while the operator is operating the operation lever to extend and retract the cylinder 2, the spool 56 does not move in the closing direction, and the operator does not move. The intended expansion/contraction speed of the cylinder 2 is obtained. Therefore, stable operation of the cylinder 2 is possible.

Further, in the present embodiment, the connection passage 78 is formed in the piston 50 and connects the drain chamber 51 and the pilot chamber 23.

With this configuration, the connection passage 78 can be easily processed, and the space efficiency can be improved.

Further, in the first modified example of the present embodiment, the connection passage 78 connects the relief discharge passage 77 and the pilot passage 52.

Further, in the second modification of the present embodiment, the connection passage 78 connects the drain passage 76b and the pilot passage 52.

Although the embodiment of the present invention has been described above, the above embodiment merely shows a part of the application example of the present invention, and the technical scope of the present invention is limited to the specific configuration of the above embodiment. Absent.

1... Arm (load), 2... Cylinder, 2a... Rod side pressure chamber (load side pressure chamber), 4... Pump (fluid pressure supply source), 5... Pilot pump (Pilot) Pressure supply source), 6... Control valve, 7... First main passage, 9... Pilot control valve, 20... Load holding mechanism, 21... Operate check valve, 22... Switching Valve, 23... Pilot chamber, 41... Relief valve, 50... Piston, 51... Drain chamber, 53... Drain port, 54... Spring chamber, 56... Spool, 76a ...First drain passage, 76b...second drain passage, 77...relief discharge passage, 78...connection passage, 90...check valve

Claims (4)

A fluid pressure control device for controlling expansion and contraction of a cylinder for driving a load,
A control valve for controlling the supply of working fluid from a fluid pressure supply source to the cylinder;
A pilot control valve for controlling pilot pressure guided from the pilot pressure supply source to the control valve;
A main passage that connects the control valve with the load side pressure chamber of the cylinder on which the load pressure acts when the control valve is in the neutral position;
A load holding mechanism provided in the main passage,
The load holding mechanism is
An operating check valve that allows the flow of the working fluid from the control valve to the load side pressure chamber while allowing the flow of the working fluid from the load side pressure chamber to the control valve according to the back pressure,
A switching valve that operates in conjunction with the control valve by the pilot pressure guided through the pilot control valve and switches the operation of the operate check valve;
A relief valve that opens when the pressure of the load side pressure chamber reaches a predetermined pressure,
A relief discharge passage for guiding the relief fluid discharged from the relief valve to the tank,
The switching valve is
A pilot chamber in which the pilot pressure is guided from the pilot control valve through a pilot passage,
A spool that moves according to the pilot pressure in the pilot chamber,
A spring chamber accommodating a biasing member that biases the spool in the valve closing direction;
A piston which receives the pilot pressure on the back surface and applies a thrust force against the biasing force of the biasing member to the spool;
A drain chamber partitioned by the spool and the piston,
A drain passage that connects the drain chamber and the spring chamber to the relief discharge passage,
A pilot line is configured by the pilot passage and the pilot chamber,
A return line is configured by the relief discharge passage, the drain chamber, and the drain passage,
The load holding mechanism further includes a connection passage that connects the pilot line and the return line, and a check valve that is provided in the connection passage and allows only the passage of the working fluid from the return line to the pilot line. A fluid pressure control device comprising. The fluid pressure control device according to claim 1, wherein the connection passage is formed in the piston to connect the drain chamber and the pilot chamber. The fluid pressure control device according to claim 1, wherein the connection passage connects the relief discharge passage and the pilot passage. The fluid pressure control device according to claim 1, wherein the connection passage connects the drain passage and the pilot passage.

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