JP6857571B2 - Fluid pressure controller - Google Patents

Description

The present invention relates to a fluid pressure control device.

As a fluid pressure control device for controlling the operation of work equipment, Patent Document 1 includes a control valve for switching the supply and discharge of hydraulic oil to the cylinder to control the expansion and contraction operation of the cylinder, and a load side pressure chamber and a control valve for the cylinder. Those provided with a load holding mechanism interposed in the main passage to be connected are disclosed.

The load holding mechanism includes an operating check valve and a meter-out control valve that operates by pilot pressure to switch the operation of the operating check valve. The meter-out control valve includes a spool, a pilot chamber to which the pilot pressure is guided, and a piston that is slidably housed in the pilot chamber and receives the pilot pressure to move the spool.

Japanese Unexamined Patent Publication No. 2010-101400

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

An annular gap is provided between the piston and the housing to ensure the slidability of the piston and to discharge air from the pilot chamber to the drain chamber. If the work equipment continues to be stopped, the air contained in the hydraulic oil on the drain chamber side will move 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 rise of the pilot pressure in the pilot chamber in response to the operator's input operation, and the air on the pilot chamber side drains through the annular gap between the piston and the housing. After being discharged to the chamber, the increase in the pilot pressure in the pilot chamber is completed.

As described above, the air on the pilot room side causes a delay in response to the input operation of the operator when the work equipment is started.

The present invention has been made in view of the above problems, and an object of the present invention is to suppress a response delay due to the influence of air.

The first invention is a fluid pressure control device that controls the expansion and contraction operation of the cylinder that drives the load, and the load side pressure chamber and the control valve of the cylinder on which the load pressure due to the load acts when the control valve is in the neutral position. The load holding mechanism is provided with a main passage for connecting the above and a load holding mechanism provided in the main passage, and the load holding mechanism operates in conjunction with the control valve by the pilot pressure guided through the pilot control valve to switch the operation of the operation check valve. The switching valve is equipped with a switching valve for guiding the pilot pressure through the pilot control valve, a piston that receives the pilot pressure and applies a thrust to the spool against the urging force of the urging member, and a piston. In the housing in which the piston accommodating hole is formed, the drain chamber in the piston accommodating hole divided by the spool and the piston, and the annular groove formed on the outer peripheral surface of the piston or the inner peripheral surface of the piston accommodating hole. It is equipped with a housed seal ring, which throttles the air flow from the drain chamber to the pilot chamber and guides the piston pressure to the pilot chamber when the pilot pressure is not guided to the pilot chamber. The condition is characterized by allowing the flow of working fluid from the pilot chamber to the drain chamber.

In the first invention, when the pilot pressure is not guided to the pilot chamber, the seal ring throttles the air flow from the drain chamber to the pilot chamber, so that the movement of air from the drain chamber side to the pilot chamber side is suppressed. Will be done. Further, when the pilot pressure is guided to the pilot chamber, the seal ring allows the flow of the working fluid from the pilot chamber to the drain chamber, so that the air on the pilot chamber side is discharged to the drain chamber.

In the second invention, the seal ring is housed in an annular groove formed on the outer peripheral surface of the piston, and the radial length of the gap between the outer peripheral surface of the seal ring and the inner peripheral surface of the piston accommodating hole and the inner circumference of the seal ring. The sum of the sum of the surface and the radial length of the gap between the bottom surface of the annular groove is smaller than the radial length of the gap between the outer peripheral surface of the piston and the inner peripheral surface of the piston accommodating hole.

In the third invention, the seal ring is housed in an annular groove formed on the inner peripheral surface of the piston accommodating hole, and the radial length of the gap between the inner peripheral surface of the seal ring and the outer peripheral surface of the piston and the outer circumference of the seal ring. The sum of the sum of the surface and the radial length of the gap between the bottom surface of the annular groove is smaller than the radial length of the gap between the outer peripheral surface of the piston and the inner peripheral surface of the piston accommodating hole.

In the second and third inventions, the movement of air from the drain chamber side to the pilot chamber side is suppressed in a state where the pilot pressure is not guided to the pilot chamber.

In the fourth invention, a slit is formed on the end surface of the seal ring that contacts the inner surface of the annular groove in a state where the pilot pressure is guided to the pilot chamber to allow the flow of the working fluid from the pilot chamber to the drain chamber. It is characterized by that.

In the fourth invention, even if air is present on the pilot chamber side, air is discharged from the pilot chamber to the drain chamber through the slit when the work equipment is started.

The fifth invention is characterized in that the seal ring is made of resin.

In the fifth invention, since the seal ring is made of resin, it is possible to prevent the flow of the working fluid from the pilot chamber to the drain chamber from being blocked due to deformation even when the pilot pressure is guided to the pilot chamber.

In the sixth invention, the seal ring is housed in an annular groove formed on the outer peripheral surface of the piston, the piston has a sliding portion that slides along the inner peripheral surface of the piston housing hole, and the ring groove is formed. , The outer peripheral surface of the sliding portion is formed, and no annular groove other than the annular groove is formed on the outer peripheral surface of the sliding portion.

In the sixth invention, since the annular groove also exerts the function of the labyrinth groove, it is not necessary to provide the labyrinth groove on the outer peripheral surface of the sliding portion of the piston.

According to the present invention, the response delay due to the influence of air can be suppressed.

It is a figure which shows a part of the hydraulic excavator. It is a hydraulic circuit diagram of the fluid pressure control device which concerns on embodiment of this invention. It is sectional drawing of the load holding mechanism of the fluid pressure control device which concerns on embodiment of this invention. It is a partially enlarged sectional view of the load holding mechanism of the fluid pressure control device which concerns on embodiment of this invention. It is a partially enlarged sectional view of the load holding mechanism of the fluid pressure control device which concerns on the modification of embodiment of this invention. It is a hydraulic circuit diagram of the fluid pressure control device which concerns on the modification of embodiment of this invention.

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

The fluid pressure control device controls the operation of a hydraulic work device such as a hydraulic excavator, and in the present embodiment, controls the expansion / contraction operation of the cylinder 2 that drives the arm (load) 1 of the hydraulic excavator shown in FIG. The hydraulic control device 100 will be described.

First, the hydraulic circuit of the hydraulic control device 100 will be described with reference to FIG.

The cylinder 2 is connected to 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 one end connected to the piston 2d. A rod 2e whose other end 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 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 is operated by the pilot pressure guided from the pilot pump 5 to the pilot chambers 6a and 6b through the pilot control valve 9 as the operator of the hydraulic excavator manually operates the operating lever 10.

Specifically, when the pilot pressure is guided to the pilot chamber 6a, the control valve 6 switches to the position 6A, hydraulic oil is supplied from the pump 4 to the rod side chamber 2a through the first main passage 7, and the hydraulic oil is supplied. 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 contracts and the arm 1 rises in the direction of arrow 98 shown in FIG.

On the other hand, when the pilot pressure is guided to the pilot chamber 6b, the control valve 6 switches to the position 6B, hydraulic oil is supplied from the pump 4 to the anti-rod side chamber 2b through the second main passage 8, and the rod side chamber The hydraulic oil of 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 99 shown in FIG.

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

As described above, 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 of the cylinder 2, with respect to the cylinder 2. The supply and discharge of hydraulic oil is switched to control the expansion and 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 while the bucket 13 is lifted, the cylinder 2 is caused 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 for driving the arm 1, the rod side chamber 2a is 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 tube 2c as shown in FIG.

In the cylinder 15 that drives the boom 14, the anti-rod side chamber 15b serves as the load side pressure chamber. Therefore, when the load holding mechanism 20 is provided on the boom 14, a 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 conjunction 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 of the load holding mechanism 20 operates in conjunction with the control valve 6. A switching valve 22 for switching the operation is provided.

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

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

The back pressure chamber 25 accommodates a spring 27 as an urging member that urges the valve body 24 in the valve closing direction. The pressure of the back pressure chamber 25 and the urging 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 operating check valve 21 functions as a check valve that shuts off the flow of hydraulic oil from the rod side chamber 2a to the control valve 6. That is, the operating check valve 21 prevents leakage of hydraulic oil in the rod side chamber 2a, holds the load pressure, and holds the stopped state of the arm 1.

The load holding mechanism 20 further includes a bypass passage 30 for guiding the hydraulic oil in the rod side chamber 2a to the control valve side main passage 7b by bypassing the operating check valve 21, and a back pressure chamber 25 for the hydraulic oil in the control valve side main passage. A back pressure passage 31 leading to 7b is provided.

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

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

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

Specifically, when the pilot pressure is not guided to the pilot chamber 23, the switching valve 22 keeps the shutoff position 22A by the urging force of the spring 36. At the cutoff position 22A, both the first supply port 32 and the second supply port 33 are cut off.

When a pilot pressure equal to or higher than the first predetermined pressure and lower than the second predetermined pressure is induced in 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 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 main passage 7b. At this time, the throttle 37 imparts resistance to the flow of hydraulic oil. At the first communication position 22B, the second supply port 33 remains shut off.

When a pilot pressure equal to or higher than the second predetermined pressure is guided to 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 main passage 7b through the switching valve 22. At this time, the hydraulic oil in the back pressure chamber 25 is guided to the control valve side main passage 7b by bypassing the throttle 37, 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, so that the force acting on the valve body 24 in the valve closing direction is reduced, and the valve body 24 is moved from the seat portion 28. After leaving, the function of the operating check valve 21 as a check valve is released.

A relief passage 40 is branched and connected to the 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 the passage of hydraulic oil and allows the hydraulic 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.

A relief valve 43 that opens when the pressure of the control valve side main passage 7b reaches a predetermined pressure is connected to the control valve side main passage 7b. A relief valve 44 that opens when the pressure of the second main passage 8 reaches a predetermined pressure is connected to the second main passage 8. The relief valve 43 and the relief valve 44 are for releasing the high pressure generated in the rod side chamber 2a and the anti-rod side chamber 2b of the cylinder 2 when a large external force acts on the arm 1.

Next, the switching valve 22 will be described in detail mainly with reference to FIG. FIG. 3 is a cross-sectional view of the load holding mechanism 20 and shows a state in which the pilot pressure is not guided to the pilot chamber 23 and the switching valve 22 is at the shutoff position 22A. In FIG. 3, the one having the same reference numeral as that shown in FIG. 2 has the same configuration as that shown in FIG.

The switching valve 22 is incorporated in the housing 80. A spool accommodating hole 81 is formed in the housing 80, and a substantially cylindrical sleeve 61 is inserted into the spool accommodating hole 81. The spool 56 is slidably incorporated in the sleeve 61.

A spring chamber 54 is partitioned by a cap 57 on the side of 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 76a is connected to the tank T. Therefore, the hydraulic oil leaked into the spring chamber 54 is discharged to the tank T.

The spring chamber 54 accommodates a spring 36 as an urging member for urging the spool 56. A first spring receiving member 45 and a second spring receiving member 46 are housed in the spring chamber 54, and the spring 36 is provided between the first spring receiving member 45 and the second spring receiving member 46 in a compressed state. The first spring receiving member 45 is an annular member in which an end surface abuts on one end surface 56a of the spool 56 and a pin portion 56c formed so as to project from one end surface 56a of the spool 56 is inserted into a hollow portion. The second spring receiving member 46 is a disc-shaped member arranged near the bottom of the cap 57. The spring 36 urges the spool 56 in the valve closing direction via the first spring receiving member 45.

An adjusting bolt 47 penetrates and is screwed to the bottom of the cap 57. The axial position of the second spring receiving member 46 in the spring chamber 54 is set by the adjusting bolt 47 whose tip abuts on the back surface of the second spring receiving member 46. By screwing the adjusting bolt 47, the second spring receiving member 46 moves in the 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 the nut 48.

The housing 80 is formed with a piston accommodating hole 82 that communicates with the spool accommodating hole 81. The opening of the piston accommodating hole 82 is closed by the plug 58. The piston 50 is slidably accommodated in the piston accommodating hole 82. A small diameter portion 82a having a smaller diameter than other portions is formed in the piston accommodating hole 82, and the piston 50 slides along the inner peripheral surface of the small diameter portion 82a. A piston chamber 23 and a drain chamber 51 are formed in the piston accommodating hole 82 by the piston 50. The pilot chamber 23 is partitioned by the piston 50 and the plug 58, and the drain chamber 51 is partitioned by the piston 50 and the spool 56.

Pilot pressure is guided to the pilot chamber 23 through a pilot passage 52 formed in the housing 80. The piston 50 receives the pilot pressure of the pilot chamber 23 on the back surface and applies a thrust to the spool 56 against the urging force of the spring 36. The pilot passage 52 opens as a pilot port 52a on the outer surface of the housing 80. The pilot port 52a and the pilot control valve 9 are connected via a pilot hose 53 (see FIG. 1).

The drain chamber 51 is connected to a second drain passage 76b formed in the housing 80. The second drain passage 76b is connected to the tank T. Therefore, the hydraulic oil leaked into the drain chamber 51 is discharged to the tank T.

The first drain passage 76a and the second drain passage 76b merge to form a merging drain passage 77, and the merging drain passage 77 is connected to the tank T. The merging drain passage 77 opens as a drain port 77a on the outer surface of the housing 80. The drain port 77a and the tank T are connected via a drain hose 78 (see FIG. 1).

Each of the spring chamber 54 and the drain chamber 51 is connected to the tank T through the first drain passage 76a and the second drain passage 76b. Therefore, when the switching valve 22 is at the shutoff position 22A, atmospheric pressure acts on both ends of the spool 56, and a situation in which the spool 56 unintentionally moves is prevented.

The piston 50 has a sliding portion 50a whose outer peripheral surface slides along the inner peripheral surface of the piston accommodating hole 82 and a tip having a smaller diameter than the sliding portion 50a and facing the other end surface 56b of the spool 56. A portion 50b and a base end portion 50c formed having a smaller diameter than the sliding portion 50a and facing the tip surface of the plug 58 are provided.

A plurality of annular labyrinth grooves 59 are formed on the outer peripheral surface of the sliding portion 50a. Since the piston 50 is held concentrically with respect to the piston accommodating hole 82 by the hydraulic pressure guided into the labyrinth groove 59, galling between the outer peripheral surface of the sliding portion 50a and the inner peripheral surface of the piston accommodating hole 82 is prevented. .. A seal ring 96 is provided on the outer peripheral surface of the sliding portion 50a on the drain chamber 51 side of the labyrinth groove 59. The seal ring 96 will be described in detail later.

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 comes into contact with 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 urging force of the spring 36. Even when the back surface of the base end portion 50c is in contact with the tip surface of the plug 58, the piston 50 can move forward because the pilot pressure acts on the annular back surface of the sliding portion 50a.

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

The spool 56 moves in a balance between the urging force of the spring 36 acting on the one end surface 56a and the thrust force of the piston 50 acting on the other end surface 56b. The switching position of the switching valve 22 is set by the movement of the spool 56.

The sleeve 61 communicates with the first supply port 32 communicating with the bypass passage 30 (see FIG. 2), the second supply port 33 communicating with the back pressure passage 31 (see FIG. 2), and the control valve side main passage 7b. Three ports of the discharge port 34 are formed.

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 third pressure chamber 66. A 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 connected to the first supply port 32. A plurality of throttles 37 communicating with the third pressure chamber 66 and the second pressure chamber 65 are formed on the outer circumference of the land portion 72 of the spool 56 by moving the spool 56 against the urging force of the spring 36. ..

The fourth pressure chamber 67 always communicates 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 by the urging force of the spring 36 is pressed against the valve seat 71 formed on the inner circumference of the sleeve 61, 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 cut off. As a result, the hydraulic oil in the rod side chamber 2a does not leak 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 face of the first spring receiving member 45 and the end face of the sleeve 61, so that the poppet valve 70 is a spring. The urging force of 36 ensures that the seat is seated against the valve seat 71.

When the pilot pressure is guided to the pilot chamber 23 and the thrust of the piston 50 acting on the spool 56 becomes larger than the urging force of the spring 36, the spool 56 moves against the urging force of the spring 36. As a result, the poppet valve 70 is separated 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 has the third pressure chamber 66 and the second pressure. It communicates with the discharge port 34 through the chamber 65 and the first pressure chamber 64. By communicating 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 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 further moves against the urging 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. The hydraulic oil in the back pressure chamber 25 is guided to the control valve side main passage 7b by the communication between the second supply port 33 and the discharge port 34. This state corresponds to the second communication position 22C of the switching valve 22.

Next, the operation of the hydraulic control device 100 will be described mainly with reference to FIG.

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 guided to 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 operating check valve 21 is maintained at the pressure of the rod side chamber 2a. Here, since the pressure receiving area in the valve closing direction (the area of the back surface of the valve body 24) in 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 in the back pressure chamber 25 The valve body 24 is seated on the seat portion 28 due to the load acting on the back surface of the valve body 24 and the urging force of the spring 27. In this way, the operating check valve 21 prevents the hydraulic oil from leaking into the rod side chamber 2a, and keeps the arm 1 stopped.

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 switches to the contraction position 6A by an amount corresponding to the pilot pressure. When the control valve 6 is switched to the contraction position 6A, the discharge pressure of the pump 4 acts on the first pressure receiving surface 24a of the operation check valve 21. At this time, since the switching valve 22 is in the state of the shutoff position 22A without the pilot pressure being guided to the pilot chamber 23, the back pressure chamber 25 of the operating check valve 21 is maintained at the pressure of the rod side chamber 2a. When the load acting on the first pressure receiving surface 24a becomes larger than the total load 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 Separate from the seat portion 28. When the operating check valve 21 is opened 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 arrow 98 shown in FIG.

When the operating 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 corresponding to the pilot pressure. At the same time, since the pilot pressure is also guided 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 greater than the first predetermined pressure and less than the second predetermined pressure, the switching valve 22 switches to the first communication position 22B. In this case, since the communication between the second supply port 33 and the discharge port 34 is cut off, the back pressure chamber 25 of the operating check valve 21 is maintained at the pressure of the rod side chamber 2a, and the operating 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 is guided from the bypass passage 30 through the throttle 37 to the control valve side main passage 7b, and from the control valve 6 to the tank. It is discharged to T. Further, since the hydraulic oil discharged from the pump 4 is supplied to the anti-rod side chamber 2b, the cylinder 2 extends. As a result, the arm 1 descends in the direction of arrow 99 shown in FIG.

Here, the switching valve 22 is switched to the first communication position 22B mainly in the case of performing a crane operation of lowering the transported object attached to the bucket 13 to a target position. In the crane operation, since it is necessary to extend the cylinder 2 at a low speed and slowly lower the arm 1 in the direction of arrow 99, the control valve 6 is only slightly switched to the extension 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 equal to or more than the first predetermined pressure and less than the second predetermined pressure, and the switching valve 22 communicates with the first communication. It only switches to position 22B. Therefore, the hydraulic oil in the rod side chamber 2a is discharged through the throttle 37, and the arm 1 descends at a low speed suitable for crane work.

Further, when the switching valve 22 is in the first communication position 22B, even if a situation occurs in which the main passage 7b on the control valve side bursts and the hydraulic oil leaks to the outside, the operation is discharged from the rod side chamber 2a. Since the flow rate of oil 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 shutoff position 22A before the bucket 13 falls to the ground, and the bucket 13 can be prevented from suddenly falling.

As described above, the throttle 37 is for suppressing the lowering 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 main passage 7b bursts.

When the pilot pressure guided to the pilot chamber 23 is equal to or higher than the second predetermined pressure, the switching valve 22 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 operation check valve 21 is guided to the control valve side main passage 7b through the back pressure passage 31, and the control valve 6 Is discharged 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 becomes small. Therefore, the force acting on the valve body 24 in the valve closing direction becomes small, and the valve body 24 separates from the seat portion 28. , The function of the operating check valve 21 as a check valve is released.

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

When the operating 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 is rapidly extended. That is, when the switching valve 22 is switched to the second communication position 22C, the flow rate of the hydraulic oil discharged from the rod side chamber 2a increases, so that the flow rate of the hydraulic oil supplied to the anti-rod side chamber 2b increases, and the flow rate of the hydraulic oil supplied to the anti-rod side chamber 2b increases. The elongation rate becomes faster. As a result, the arm 1 quickly descends in the direction of arrow 99.

The switching valve 22 is switched to the second communication position 22C when excavation work or the like 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 seal ring 96 provided on the outer peripheral surface of the piston 50 will be described mainly with reference to FIG. FIG. 4 is a cross-sectional view of the periphery of the seal ring 96.

An annular shape is formed between the piston 50 and the housing 80, specifically, between the outer peripheral surface of the sliding portion 50a of the piston 50 and the inner peripheral surface of the piston accommodating hole 82 to ensure the slidability of the piston 50. A gap 90 is provided. The gap 90 also functions as a passage for discharging the air contained in the pilot pressure oil from the pilot chamber 23 to the drain chamber 51 during the operation of the hydraulic control device 100.

When the hydraulic excavator continues to be stopped by providing the gap 90 between the piston 50 and the housing 80, the air contained in the hydraulic oil on the drain chamber 51 side moves to the pilot chamber 23 side through the gap 90. It ends up. Specifically, as shown in FIG. 1, the load holding mechanism 20 provided in the cylinder 2 for driving the arm 1 is provided at the highest position in the hydraulic excavator. Therefore, if the state in which the hydraulic excavator is stopped continues, air is accumulated in the drain chamber 51, the second drain passage 76b, the merging drain passage 77, and the drain hose 78. The accumulated air moves to the pilot chamber 23, the pilot passage 52, and the pilot hose 53 through the gap 90.

When the air moves from the drain chamber 51 side to the pilot chamber 23 side in this way, when the hydraulic excavator is started, the pilot chamber is affected by the air moved to the pilot chamber 23 side in response to the operator's input operation. The increase in the pilot pressure of the pilot chamber 23 is delayed, and the air on the pilot chamber 23 side is discharged to the drain chamber 51 through the gap 90, and then the boost of the pilot pressure in the pilot chamber 23 is completed. As described above, the air on the pilot chamber 23 side causes a delay in response to the input operation of the operator when the hydraulic excavator is started.

As a countermeasure, in order to suppress the movement of air from the drain chamber 51 side to the pilot chamber 23 side through the gap 90, the outer diameter of the sliding portion 50a of the piston 50 or the inner diameter of the piston accommodating hole 82 is adjusted to adjust the gap. It is conceivable to reduce the radial dimension of 90. However, this method adversely affects the slidability of the piston 50, and there is a possibility that the switching valve 22 may not be switched to the first communication position 22B or the second communication position 22C as set.

Therefore, in the present embodiment, an annular seal ring 96 is provided on the outer peripheral surface of the sliding portion 50a of the piston 50 in order to suppress the movement of air from the drain chamber 51 side to the pilot chamber 23 side through the gap 90.

An annular groove 91 is formed on the outer peripheral surface of the sliding portion 50a of the piston 50 over the entire circumference. The seal ring 96 is housed in the annular groove 91. The seal ring 96 is made of a resin such as Teflon or nylon and has no elasticity. A cut surface (not shown) is formed on the seal ring 96 so that the diameter can be expanded in a C shape in consideration of the mountability to the annular groove 91.

The seal ring 96 is provided so as to face the inner peripheral surface of the small diameter portion 82a of the piston accommodating hole 82 over the entire moving range of the piston 50. That is, the seal ring 96 does not deviate from the small diameter portion 82a over the entire moving range of the piston 50.

Tapered portions 96e are formed on both sides of the outer peripheral surface 96a of the seal ring 96 in the axial direction in order to reduce the sliding resistance between the seal ring 96 and the inner peripheral surface of the small diameter portion 82a of the piston accommodating hole 82.

In FIG. 3, the seal ring 96 is provided on the drain chamber 51 side of the labyrinth groove 59. However, the seal ring 96 may be provided closer to the pilot chamber 23 than the labyrinth groove 59.

The axial length L1 of the seal ring 96 is smaller than the axial length M1 of the annular groove 91 (L1 <M1). Further, the radial length L2 of the seal ring 96 is smaller than the radial length M2 between the bottom surface 91a of the annular groove 91 and the inner peripheral surface of the piston accommodating hole 82 (L2 <M2). Therefore, the seal ring 96 can move slightly in the axial direction and the radial direction when it is housed in the annular groove 91. There is a gap 92 between the outer peripheral surface 96a of the seal ring 96 and the inner peripheral surface of the piston accommodating hole 82, and there is a gap 93 between the inner peripheral surface 96b of the seal ring 96 and the bottom surface 91a of the annular groove 91. There is a gap 94 between the end surface 96c of the seal ring 96 on the drain chamber 51 side and one inner side surface 91b of the annular groove 91, and the end surface 96d of the seal ring 96 on the pilot chamber 23 side and the annular groove 91. There is a gap 95 with the other inner surface 91c of the above. In this way, the seal ring 96 does not block the gap 90.

The radial length L2 of the seal ring 96 is larger than the depth M3 of the annular groove 91 (L2> M3). Therefore, when the seal ring 96 is housed in the annular groove 91, its outer peripheral edge protrudes from the annular groove 91 to narrow the gap 90. Specifically, the sum of the radial length G1 of the gap 92 and the radial length G2 of the gap 93 is smaller than the radial length G3 of the gap 90 (G1 + G2 <G3). More specifically, the sum of the radial length G1 of the gap 92 and the radial length G2 of the gap 93 is about half of the radial length G3 of the gap 90.

In this way, since the seal ring 96 narrows the gap 90, it acts to throttle the air flow from the drain chamber 51 to the pilot chamber 23 when the pilot pressure is not guided to the pilot chamber 23. Therefore, the seal ring 96 acts to suppress the movement of air from the drain chamber 51 side to the pilot chamber 23 side through the gap 90 when the hydraulic excavator is stopped. Therefore, even if the hydraulic excavator is stopped for a long time, the movement of air from the drain chamber 51 side to the pilot chamber 23 side can be suppressed as much as possible.

A slit 97 extending in the radial direction is formed on the end surface 96c of the seal ring 96 on the drain chamber 51 side. The slit 97 is formed over the outer peripheral surface 96a and the inner peripheral surface 96b of the seal ring 96. A plurality of slits 97 may be formed on the end face 96c of the seal ring 96.

In a state where the pilot pressure is guided to the pilot chamber 23, the seal ring 96 receives the pilot pressure on the end surface 96d, and the end surface 96c is pressed against the inner surface 91b of the annular groove 91. However, since the seal ring 96 is made of resin, it does not deform in the radial direction and close the gaps 92 and 93. Further, the gap 94 is closed when the end surface 96c of the seal ring 96 abuts on the inner surface 91b of the annular groove 91, but since the slit 97 is formed in the end surface 96c, the gap 93 and the gap 90 cannot communicate with each other. Maintained through slit 97. Therefore, when the pilot pressure is guided to the pilot chamber 23, the seal ring 96 allows the hydraulic oil to flow from the pilot chamber 23 to the drain chamber 51. Specifically, the path flowing from the pilot chamber 23 to the drain chamber 51 through the gap 90, the gap 92, and the gap 90, and the drain chamber from the pilot chamber 23 through the gap 90, the gap 95, the gap 93, the slit 97, and the gap 90. The flow path to 51 allows the flow of hydraulic oil from the pilot chamber 23 to the drain chamber 51.

In this way, since the seal ring 96 allows the flow of hydraulic oil from the pilot chamber 23 to the drain chamber 51, even if air is present on the pilot chamber 23 side, the above two paths are taken when the hydraulic excavator is started. Air is discharged from the pilot chamber 23 to the drain chamber 51.

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

As described above, in the state where the pilot pressure is not guided to the pilot chamber 23, the seal ring 96 narrows the air flow from the drain chamber 51 to the pilot chamber 23, so that the seal ring 96 moves from the drain chamber 51 side to the pilot chamber 23 side. The movement of air is suppressed. Further, in a state where the pilot pressure is guided to the pilot chamber 23, the seal ring 96 allows the hydraulic oil 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. To. Therefore, even if the hydraulic excavator is stopped for a long time, the movement of air from the drain chamber 51 side to the pilot chamber 23 side can be suppressed as much as possible. Further, even if air is present on the pilot chamber 23 side, air can be discharged from the pilot chamber 23 to the drain chamber 51 when the hydraulic excavator is started. Therefore, when the hydraulic excavator is started, it is possible to suppress a delay in response to an operator's input operation due to the influence of air.

Hereinafter, modifications of the present embodiment will be described with reference to FIGS. 5 and 6. In the following description of the modified example, the same components as those in the above embodiment are designated by the same reference numerals in FIGS. 5 and 6, and the description thereof will be omitted.

(1) In the above embodiment, there is a gap 92 between the outer peripheral surface 96a of the seal ring 96 and the inner peripheral surface of the piston accommodating hole 82, and the inner peripheral surface 96b of the seal ring 96 and the bottom surface 91a of the annular groove 91. The form in which the seal ring 96 is housed in the annular groove 91 has been described so that the gap 93 exists between the two. Alternatively, the seal ring 96 may be housed in the annular groove 91 so that the inner peripheral surface 96b contacts the bottom surface 91a of the annular groove 91. In this case, in a state where the pilot pressure is guided to the pilot chamber 23, in order to allow the flow of hydraulic oil from the pilot chamber 23 to the drain chamber 51 through the slit 97, the inner peripheral surface 96b of the seal ring 96 is formed. However, it is necessary to form a slit in the axial direction so as to communicate the gap 95 and the gap 94. Further, the seal ring 96 may be accommodated in the annular groove 91 so that the outer peripheral surface 96a is in contact with the inner peripheral surface of the piston accommodating hole 82. In this case, the communication between the pilot chamber 23 and the drain chamber 51 through the gap 92 is cut off.

(2) In the above embodiment, a mode in which the seal ring 96 is provided on the outer peripheral surface of the piston has been described. Instead, in this modification, the seal ring 96 is provided on the inner peripheral surface of the housing 80, as shown in FIG. Specifically, the annular groove 91 in which the seal ring 96 is accommodated is formed on the inner peripheral surface of the small diameter portion 82a of the piston accommodating hole 82. The axial length L1 of the seal ring 96 is smaller than the axial length M1 of the annular groove 91 (L1 <M1). Further, the radial length L2 of the seal ring 96 is smaller than the radial length M2 between the bottom surface 91a of the annular groove 91 and the outer peripheral surface of the sliding portion 50a of the piston 50 (L2 <M2). There is a gap 92 between the inner peripheral surface 96b of the seal ring 96 and the outer peripheral surface of the sliding portion 50a of the piston 50, and there is a gap between the outer peripheral surface 96a of the seal ring 96 and the bottom surface 91a of the annular groove 91. 93 exists, and a gap 94 exists between the end surface 96c of the seal ring 96 on the drain chamber 51 side and one inner side surface 91b of the annular groove 91, and is annular with the end surface 96d of the seal ring 96 on the pilot chamber 23 side. There is a gap 95 between the groove 91 and the other inner surface 91c. The radial length L2 of the seal ring 96 is larger than the depth M3 of the annular groove 91 (L2> M3). Therefore, when the seal ring 96 is housed in the annular groove 91, its outer peripheral edge protrudes from the annular groove 91 to narrow the gap 90. Specifically, the sum of the radial length G1 of the gap 92 and the radial length G2 of the gap 93 is smaller than the radial length G3 of the gap 90 (G1 + G2 <G3). Tapered portions 96e are formed on both sides of the inner peripheral surface 96b of the seal ring 96 in the axial direction in order to reduce the sliding resistance between the seal ring 96 and the outer peripheral surface of the sliding portion 50a of the piston 50. Also in the above modified examples, the same action and effect as those of the above-described embodiment can be obtained. Further, a tubular sleeve may be inserted into the inner peripheral surface of the piston accommodating hole 82, and a seal ring 96 may be provided on the inner peripheral surface of the sleeve.

(3) In the above embodiment, the relief pressure oil discharged from the relief valve 41 is discharged to the tank T, and the relief pressure oil does not affect the operation of the switching valve 22. Instead of this, in this modification, as shown in FIG. 6, an orifice 42 is provided downstream of the relief valve 41 in the relief passage 40, and the relief pressure oil discharged upstream of the orifice 42 discharged from the relief valve 41 is the pilot chamber 23. The switching valve 22 is configured to switch to the second communication position 22C by the pressure of the relief pressure oil. In this configuration, the first drain passage 76a is connected to the downstream of the orifice 42 of the relief passage 40 and connected to the tank T, and the second drain passage 76b is connected to the upstream of the orifice 42 of the relief passage 40 and is connected to the tank T. Will be done.

(4) In the above embodiment, an annular groove 91 and a labyrinth groove 59 in which the seal ring 96 is housed are formed on the outer peripheral surface of the sliding portion 50a of the piston 50. Instead of this, the labyrinth groove 59 may be abolished so that an annular groove other than the annular groove 91 is not formed on the outer peripheral surface of the sliding portion 50a. That is, the outer peripheral surface of the sliding portion 50a has a constant outer diameter except for the annular groove 91. In this configuration, the piston 50 is held concentrically with respect to the piston accommodating hole 82 by the hydraulic pressure guided to the gaps 94 and 95 in the annular groove 91, so that the outer peripheral surface of the sliding portion 50a and the inside of the piston accommodating hole 82 Galing with the peripheral surface is prevented. As described above, since the annular groove 91 also exerts the function of the labyrinth groove 59, the labyrinth groove 59 can be abolished.

Hereinafter, the configurations, actions, and effects of the embodiments of the present invention will be collectively described.

A fluid pressure control device 100 that controls the expansion and contraction operation of the cylinder 2 that drives the load 1, from the control valve 6 that controls the supply of the working fluid from the fluid pressure supply source 4 to the cylinder 2, and the pilot pressure supply source 5. The pilot control valve 9 that controls the pilot pressure guided to the control valve 6 is connected to the load side pressure chamber 2a and the control valve 6 of the cylinder 2 on which the load pressure by the load 1 acts when the control valve 6 is in the neutral position 6C. The main passage 7 and the load holding mechanism 20 provided in the main passage 7 are provided, and the load holding mechanism 20 allows the flow of the working fluid from the control valve 6 to the load side pressure chamber 2a while allowing the back pressure to flow. The operating check valve 21 that allows the flow of working fluid from the load side pressure chamber 2a to the control valve 6 accordingly, and the operating check valve 21 that operates in conjunction with the control valve 6 by the pilot pressure guided through the pilot control valve 9. The switching valve 22 includes a switching valve 22 for switching the operation of the above, and the switching valve 22 includes a pilot chamber 23 in which a pilot pressure is guided through a pilot control valve 9, a spool 56 that moves according to the pilot pressure in the pilot chamber 23, and a spool. An urging member 36 that urges the 56 in the valve closing direction, a piston 50 that receives pilot pressure and applies a thrust to the spool 56 against the urging force of the urging member 36, and a piston accommodating hole in which the piston 50 is accommodated. An annular shape formed on the outer peripheral surface of the piston 50 or the inner peripheral surface of the piston accommodating hole 82, the housing 80 in which the 82 is formed, the drain chamber 51 in the piston accommodating hole 82 and partitioned by the spool 56 and the piston 50. A seal ring 96 housed in the groove 91 is provided, and the seal ring 96 throttles the air flow from the drain chamber 51 to the pilot chamber 23 and the pilot in a state where the pilot pressure is not guided to the pilot chamber 23. When the pilot pressure is guided to the chamber 23, the flow of the working fluid from the pilot chamber 23 to the drain chamber 51 is allowed.

In this configuration, when the pilot pressure is not guided to the pilot chamber 23, the seal ring 96 throttles the air flow from the drain chamber 51 to the pilot chamber 23, so that the air from the drain chamber 51 side to the pilot chamber 23 side Movement is suppressed. Further, in a state where the pilot pressure is guided to the pilot chamber 23, the seal ring 96 allows the flow of the working 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. To. Therefore, the response delay due to the influence of air can be suppressed.

Further, the seal ring 96 is accommodated in an annular groove 91 formed on the outer peripheral surface of the piston 50, and has a radial length G1 of a gap 92 between the outer peripheral surface 96a of the seal ring 96 and the inner peripheral surface of the piston accommodating hole 82. The sum of the radial length G2 of the gap 93 between the inner peripheral surface 96b of the seal ring 96 and the bottom surface 91a of the annular groove 91 is the diameter of the gap 90 between the outer peripheral surface of the piston 50 and the inner peripheral surface of the piston accommodating hole 82. It is smaller than the directional length G3.

The seal ring 96 is housed in an annular groove 91 formed on the inner peripheral surface of the piston accommodating hole 82, and the radial length G1 of the gap 92 between the inner peripheral surface 96b of the seal ring 96 and the outer peripheral surface of the piston 50. The sum of the radial length G2 of the gap 93 between the outer peripheral surface 96a of the seal ring 96 and the bottom surface 91a of the annular groove 91 is the diameter of the gap 90 between the outer peripheral surface of the piston 50 and the inner peripheral surface of the piston accommodating hole 82. It is smaller than the directional length G3.

In these configurations, the movement of air from the drain chamber 51 side to the pilot chamber 23 side is suppressed in a state where the pilot pressure is not guided to the pilot chamber 23.

Further, the end surface 96c of the seal ring 96 that contacts the inner surface 91b of the annular groove 91 with the pilot pressure guided to the pilot chamber 23 has a slit 97 that allows the flow of the working fluid from the pilot chamber 23 to the drain chamber 51. Is formed.

In this configuration, even if air is present on the pilot chamber 23 side, air is discharged from the pilot chamber 23 to the drain chamber 51 through the slit 97 when the work equipment is started.

The seal ring 96 is made of resin.

In this configuration, since the seal ring 96 is made of resin, it is possible to prevent the flow of the working fluid from the pilot chamber 23 to the drain chamber 51 from being blocked due to deformation even when the pilot pressure is guided to the pilot chamber 23. ..

Further, the seal ring 96 is housed in an annular groove 91 formed on the outer peripheral surface of the piston 50, and the piston 50 has a sliding portion 50a that slides along the inner peripheral surface of the piston housing hole 82 and is annular. The groove 91 is formed on the outer peripheral surface of the sliding portion 50a, and no annular groove other than the annular groove 91 is formed on the outer peripheral surface of the sliding portion 50a.

In this configuration, since the annular groove 91 also exerts the function of the labyrinth groove, it is not necessary to provide the labyrinth groove on the outer peripheral surface of the sliding portion 50a of the piston 50.

Although the embodiments of the present invention have been described above, the above embodiments are only a part of the application examples of the present invention, and the technical scope of the present invention is limited to the specific configurations of the above embodiments. Absent.

100 ... Fluid pressure control device (hydraulic control device), 1 ... Arm (load), 2 ... Cylinder, 2a ... Rod side pressure chamber (load side pressure chamber), 4 ... Pump ( Fluid pressure supply source), 5 ... Piston pump (piston pressure supply source), 6 ... Control valve, 7 ... 1st main passage, 9 ... Piston control valve, 20 ... Load holding mechanism , 21 ... Operate check valve, 22 ... Switching valve, 23 ... Piston chamber, 50 ... Piston, 50a ... Sliding part, 51 ... Drain chamber, 52 ... Piston passage , 56 ... Spool, 59 ... Labyrinth groove, 80 ... Housing, 82 ... Piston accommodating hole, 82a ... Small diameter part, 90, 92, 93, 94, 95 ... Gap, 91・ ・ ・ Circular groove, 96 ・ ・ ・ Seal ring, 97 ・ ・ ・ Slit

Claims (6)

A fluid pressure control device that controls the expansion and contraction of the cylinder that drives the load.
A control valve that controls the supply of working fluid from the fluid pressure supply source to the cylinder,
A pilot control valve that controls the pilot pressure guided from the pilot pressure supply source to the control valve,
When the control valve is in the neutral position, the load pressure due to the load acts on the load side pressure chamber of the cylinder and the main passage connecting the control valve.
A load holding mechanism provided in the main passage is provided.
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.
It is provided with a switching valve that operates in conjunction with the control valve by the pilot pressure guided through the pilot control valve and for switching the operation of the operated check valve.
The switching valve is
A pilot chamber in which the pilot pressure is guided through the pilot control valve, and
A spool that moves according to the pilot pressure in the pilot chamber,
An urging member that urges the spool in the valve closing direction, and
A piston that receives pilot pressure and applies thrust to the spool against the urging force of the urging member, and
A housing in which a piston accommodating hole for accommodating the piston is formed, and
A drain chamber in the piston accommodating hole and partitioned by the spool and the piston,
A seal ring accommodated in an annular groove formed on the outer peripheral surface of the piston or the inner peripheral surface of the piston accommodating hole is provided.
The seal ring throttles the flow of air from the drain chamber to the pilot chamber when the pilot pressure is not guided to the pilot chamber, and the pilot pressure is guided to the pilot chamber. A fluid pressure control device characterized in that the flow of a working fluid from a chamber to the drain chamber is allowed. The fluid pressure control device according to claim 1.
The seal ring is housed in the annular groove formed on the outer peripheral surface of the piston.
The sum of the radial length of the gap between the outer peripheral surface of the seal ring and the inner peripheral surface of the piston accommodating hole and the radial length of the gap between the inner peripheral surface of the seal ring and the bottom surface of the annular groove is the piston. A fluid pressure control device characterized in that it is smaller than the radial length of the gap between the outer peripheral surface of the piston and the inner peripheral surface of the piston accommodating hole. The fluid pressure control device according to claim 1.
The seal ring is housed in the annular groove formed on the inner peripheral surface of the piston housing hole.
The sum of the radial length of the gap between the inner peripheral surface of the seal ring and the outer peripheral surface of the piston and the radial length of the gap between the outer peripheral surface of the seal ring and the bottom surface of the annular groove is the outer peripheral surface of the piston. A fluid pressure control device characterized in that it is smaller than the radial length of the gap between the piston and the inner peripheral surface of the piston accommodating hole. The fluid pressure control device according to any one of claims 1 to 3.
A slit that allows the flow of the working fluid from the pilot chamber to the drain chamber is formed on the end surface of the seal ring that comes into contact with the inner surface of the annular groove while the pilot pressure is guided to the pilot chamber. A fluid pressure control device characterized by. The fluid pressure control device according to any one of claims 1 to 4.
A fluid pressure control device characterized in that the seal ring is made of resin. The fluid pressure control device according to claim 1 or 2.
The seal ring is housed in the annular groove formed on the outer peripheral surface of the piston.
The piston has a sliding portion that slides along the inner peripheral surface of the piston accommodating hole.
The annular groove is formed on the outer peripheral surface of the sliding portion.
A fluid pressure control device characterized in that an annular groove other than the annular groove is not formed on the outer peripheral surface of the sliding portion.

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