Fluid pressure control device

Abstract

The load holding mechanism (20) has a switching valve (22) that switches the operation of a one-way valve (21), and a relief valve (41) that opens the valve when the pressure in a load-side pressure chamber (2a) reaches a predetermined pressure. The switching valve (22) has a drain chamber (51) provided on the side opposite to a spring chamber (54) with a spool (56) interposed therebetween, a drain passage (76) connected to the relief valve (41) and to at least one of the drain chamber (51) and the spring chamber (54), a pilot passage (90) connecting the drain passage (76) and a downstream side of the spool (56), and a one-way valve (91) provided in the pilot passage (90) and allowing the flow of working fluid only from the drain passage (76) to the downstream side of the spool (56).

Description

Technical Field

[0001] This invention relates to a fluid pressure control device. Background Technology

[0002] The fluid pressure control device described in Japanese Patent Application Publication No. 2017-62010 includes: an overflow valve that opens when the pressure in the load-side pressure chamber of the cylinder reaches a predetermined pressure; an overflow discharge passage that guides the overflow fluid discharged from the overflow valve to the fluid tank; and a drainage passage that connects the drainage chamber and the spring chamber of the switching valve to the overflow discharge passage. Summary of the Invention

[0003] In the fluid pressure control device described in Japanese Patent Application Publication No. 2017-62010, during the process of the operator extending the cylinder by operating a handle, if the overflow valve is open, the overflow fluid is discharged into the fluid tank through the overflow discharge passage, and also flows into the drain chamber and spring chamber through the drain passage. If the spool valve of the switching valve moves to the closed direction, the cylinder extension speed desired by the operator may not be achieved. In this case, when the operator operates the handle to increase the pilot pressure acting on the spool valve in order to obtain the desired extension speed, the spool valve moves to the open direction, and the working fluid flows forcefully to the downstream side of the spool valve, where the pressure has decreased due to the spool valve moving to the closed direction, causing the cylinder to temporarily accelerate rapidly.

[0004] The purpose of this invention is to provide a fluid pressure control device for preventing rapid acceleration of a cylinder.

[0005] According to one aspect of the present invention, a fluid pressure control device controls the extension and retraction of a cylinder driving a load, comprising: 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 a pilot pressure guided from a pilot pressure supply source to the control valve; a main passage connecting the load-side pressure chamber of the cylinder, which operates under load pressure generated by the load when the control valve is in a neutral position, to the control valve; and a load holding mechanism disposed in the main passage, the load holding mechanism having: an actuating check valve that allows the flow of working fluid from the control valve to the load-side pressure chamber, and on the other hand, allows the flow of working fluid from the load-side pressure chamber to the control valve based on back pressure; and a switching valve that is guided via the pilot control valve. The switching valve is operated in conjunction with the control valve by a pilot pressure and is used to switch the operation of the operating check valve; an overflow valve that opens when the pressure in the load-side pressure chamber reaches a predetermined pressure; the switching valve having: a pilot chamber guided by the pilot control valve to a pilot pressure; a spool valve that moves according to the pilot pressure of the pilot chamber; a spring chamber housing a force-applying component that applies force to the spool valve in the closing direction; a drain chamber sandwiching the spool valve and disposed on the opposite side of the spring chamber; a drain passage connected to the overflow valve and connected to at least one of the drain chamber and the spring chamber; a pressure-conducting passage connecting the drain passage and the downstream side of the spool valve; and a check valve disposed in the pressure-conducting passage and allowing only the flow of working fluid from the drain passage to the downstream side of the spool valve. Attached Figure Description

[0006] Figure 1 A diagram showing a portion of a hydraulic excavator.

[0007] Figure 2 This is a fluid pressure circuit diagram of a fluid pressure control device according to an embodiment of the present invention.

[0008] Figure 3 This is a cross-sectional view of the load holding mechanism of the fluid pressure control device according to an embodiment of the present invention.

[0009] Figure 4 A fluid pressure loop diagram illustrating a variation of the drainage path.

[0010] Figure 5 A fluid pressure loop diagram illustrating a variation of the drainage path.

[0011] Figure 6 A fluid pressure loop diagram illustrating a variation of the drainage path.

[0012] Figure 7A fluid pressure circuit diagram of a fluid pressure control device according to a variation of an embodiment of the present invention.

[0013] Figure 8 This is a cross-sectional view of the load holding mechanism of a fluid pressure control device according to a variation of an embodiment of the present invention.

[0014] Figure 9 A fluid pressure loop diagram illustrating a variation of the drainage path. Detailed Implementation

[0015] Hereinafter, with reference to the accompanying drawings, the fluid pressure control device according to the embodiments of the present invention will be described.

[0016] The fluid pressure control device controls the operation of hydraulic work equipment such as hydraulic excavators. In this embodiment, regarding the drive... Figure 1 The hydraulic control device 100 shown is used to control the extension and retraction of cylinder 2 of the boom (load) 1 of the hydraulic excavator. Hereinafter, the use of a working fluid as the working fluid for cylinder 2 will be explained; however, a water-soluble alternative fluid may also be used instead of the working fluid.

[0017] First, refer to Figure 2 The hydraulic circuit of the hydraulic control device 100 will be described.

[0018] The cylinder 2 includes: a cylindrical cylinder 2c; a piston 2d, which is inserted into the cylinder 2c in a free sliding manner and divides the cylinder 2c into a rod-side chamber 2a and a rod-opposite-side chamber 2b; and a rod 2e, one end of which is connected to the piston 2d, and the other end extends laterally to the outside of the cylinder 2c and is connected to the boom 1.

[0019] The hydraulic excavator is equipped with a power source consisting of an engine and an electric motor, which in turn drives a pump 4, which serves as a fluid pressure supply source, and a pilot pump 5, which serves as a pilot pressure supply source.

[0020] The hydraulic control device 100 includes: a control valve 6, which controls the supply of working fluid from the pump 4 to the cylinder 2; and a pilot control valve 9, which controls the pilot pressure guided from the pilot pump 5 to the control valve 6.

[0021] The rod-side chamber 2a of control valve 6 and cylinder 2 is connected through the first main passage 7, and the rod-side chamber 2b of control valve 6 and cylinder 2 is connected through the second main passage 8.

[0022] The control valve 6 is operated by the pilot pressure, which is the pilot pressure that is guided from the pilot pump 5 to the pilot chambers 6a and 6b via the pilot control valve 9 as the operator of the hydraulic excavator manually operates the control lever 10.

[0023] Specifically, when pilot pressure is directed to pilot chamber 6a, control valve 6 switches to position 6A, supplying working fluid from pump 4 to rod-side chamber 2a via first main passage 7, while working fluid in the opposite-side chamber 2b is discharged to fluid tank T via second main passage 8. This causes cylinder 2 to retract, and stick 1 to... Figure 1 The direction of arrow 80 shown is upward.

[0024] On the other hand, when the pilot pressure is directed to the pilot chamber 6b, the control valve 6 switches to position 6B, supplying working fluid from the pump 4 to the opposite side chamber 2b of the boom via the second main passage 8, and the working fluid in the boom-side chamber 2a is discharged to the fluid tank T via the first main passage 7. This causes the cylinder 2 to extend, and the boom 1 extends... Figure 1 The direction of arrow 81 shown is downward.

[0025] When the pilot pressure is not guided to the pilot chambers 6a and 6b, the control valve 6 is in position 6C, the supply and discharge of the working fluid relative to the cylinder 2 is blocked, and the boom 1 remains in a stopped state.

[0026] Thus, the control valve 6 has three positions: a contracted position 6A for the cylinder 2 to contract, an extended position 6B for the cylinder 2 to extend, and a neutral position 6C for maintaining the load on the cylinder 2. By switching the supply and discharge of the working fluid relative to the cylinder 2, the extension and retraction of the cylinder 2 can be controlled.

[0027] Here, as Figure 1 As shown, when the bucket 13 is raised, and the control valve 6 is switched to the neutral position 6C and the stick 1 is stopped, the force in the extension direction is applied to the cylinder 2 due to the weight of the bucket 13 and the stick 1. Thus, in the cylinder 2 that drives the stick 1, the stick-side chamber 2a becomes a load-side pressure chamber where the load pressure is applied when the control valve 6 is in the neutral position 6C.

[0028] A load holding mechanism 20 is provided on the first main passage 7, which is connected to the rod-side chamber 2a, which serves as the load-side pressure chamber. The load holding mechanism 20 maintains the load pressure of the rod-side chamber 2a when the control valve 6 is in the neutral position 6C, such as... Figure 1 As shown, it is fixed to the surface of cylinder 2.

[0029] Additionally, in the drive boom 14 (refer to...) Figure 1 In cylinder 15, the opposite side chamber 15b of the rod becomes the load-side pressure chamber. Therefore, when the load holding mechanism 20 is provided on the boom 14, the load holding mechanism 20 is provided on the main passage connected to the opposite side chamber 15b of the rod.

[0030] The load holding mechanism 20 includes: an operating check valve 21 disposed in the first main passage 7; and a switching valve 22 that is operated in conjunction with the control valve 6 by a pilot pressure guided via the pilot control valve 9 and is used to switch the operation of the operating check valve 21.

[0031] The one-way valve 21 includes: a valve core 24 for opening and closing the first main passage 7; a seat 28 for the valve core 24 to sit on; a back pressure chamber 25 facing the back of the valve core 24; and a passage 26 formed in the valve core 24, which always guides the working fluid from the rod-side chamber 2a to the back pressure chamber 25. A throttling section 26a is provided in the passage 26 to resist the flow of the working fluid.

[0032] The first main passage 7 has: a cylinder-side first main passage 7a, which connects the rod-side chamber 2a and the operating check valve 21; and a control valve-side first main passage 7b, which connects the operating check valve 21 and the control valve 6.

[0033] On the valve core 24, there are a first pressure-receiving surface 24a that is subjected to pressure from the first main passage 7b on the control valve side, and a second pressure-receiving surface 24b that is subjected to pressure from the rod-side chamber 2a via the first main passage 7a on the cylinder side.

[0034] The back pressure chamber 25 houses a spring 27, which acts as a force-applying component to apply force to the valve core 24 in the valve-closing direction. The pressure in the back pressure chamber 25 and the force of the spring 27 work in the direction that causes the valve core 24 to sit on the seat portion 28.

[0035] With the valve core 24 seated in the seat portion 28, the one-way valve 21 functions as a check valve to block the flow of working fluid from the rod-side chamber 2a to the control valve 6. That is, the one-way valve 21 prevents leakage of working fluid in the rod-side chamber 2a, maintains the load pressure, and keeps the boom 1 in a stopped state.

[0036] Switching valve 22 includes: a pilot chamber 23, which is guided by pilot control valve 9 to pilot pressure; and a spool valve 56 (see reference). Figure 3 The pilot chamber 23 moves according to the pilot pressure; the spring chamber 54 houses the spring 36, which is a force-applying component that applies force to the slide valve 56 in the closing direction; the drain chamber 51 is located on the opposite side of the spring chamber 54, sandwiching the slide valve 56; and the drain passage 76 connects the spring chamber 54 and the drain chamber 51 to the fluid tank T.

[0037] A bypass passage 30 and a back pressure passage 31 are connected upstream of the switching valve 22, and a downstream passage 38 is connected downstream of the switching valve 22. The bypass passage 30 is used to guide the working fluid of the rod-side chamber 2a to the first main passage 7b of the control valve side by bypassing the one-way valve 21. The back pressure passage 31 is used to guide the working fluid of the back pressure chamber 25 to the first main passage 7b of the control valve side. The downstream passage 38 is used to guide the working fluid from the bypass passage 30 and the back pressure chamber 30 to the first main passage 7b of the control valve side.

[0038] The switching valve 22 switches the connection between the bypass passage 30 and the back pressure passage 31 relative to the downstream passage 38, and controls the flow of the working fluid in the first main passage 7, which becomes the instrument output side, when the cylinder 2 is extended.

[0039] The switching valve 22 has three ports: a first supply port 32 connected to the bypass passage 30, a second supply port 33 connected to the back pressure passage 31, and a discharge port 34 connected to the downstream passage 38. Additionally, the switching valve 22 has three positions: a blocking position 22A, a first connecting position 22B, and a second connecting position 22C.

[0040] When pilot pressure is directed to pilot chamber 6b of control valve 6, pilot pressure is also directed to pilot chamber 23 simultaneously. That is, when control valve 6 is switched to the extended position 6B, switching valve 22 is also switched to the first connected position 22B or the second connected position 22C.

[0041] In a more specific context, when the pilot pressure is not directed to the pilot chamber 23, the switching valve 22 is held in the blocked position 22A by the force of the spring 36. In the blocked position 22A, both the first supply port 32 and the second supply port 33 are blocked.

[0042] When a pilot pressure above the first predetermined pressure and below the second predetermined pressure is guided to the pilot chamber 23, the switching valve 22 switches to the first connection position 22B. In the first connection position 22B, the first supply port 32 is connected to the discharge port 34. Here, the working fluid in the rod-side chamber 2a is guided from the bypass passage 30 to the downstream passage 38 via the switching valve 22. That is, the working fluid in the rod-side chamber 2a is guided to the first main passage 7b on the control valve side by means of the bypass operation check valve 21. At this time, resistance is applied to the flow of the working fluid through the throttling section 37. The second supply port 33 remains blocked.

[0043] When a pilot pressure exceeding the second predetermined pressure is guided to the pilot chamber 23, the switching valve 22 switches to the second connection position 22C. In the second connection position 22C, the first supply port 32 is connected to the discharge port 34, and the second supply port 33 is also connected to the discharge port 34. Here, the working fluid in the back pressure chamber 25 is guided from the back pressure passage 31 to the downstream passage 38 via the switching valve 22. At this time, the working fluid in the back pressure chamber 25 is guided to the first main passage 7b on the control valve side via the bypass throttling section 37, and discharged from the control valve 6 to the fluid tank T. Here, a pressure difference is generated before and after the throttling section 26a, the pressure in the back pressure chamber 25 decreases, and therefore, the force acting on the valve core 24 in the valve-closing direction decreases, causing the valve core 24 to separate from the seat section 28, thereby disabling the function of the one-way valve 21 as a check valve.

[0044] The load holding mechanism 20 has an overflow valve 41, which opens to allow the flow of working fluid and releases the working fluid from the rod-side chamber 2a when the pressure in the rod-side chamber 2a reaches a predetermined pressure. The overflow valve 41 is located in the overflow passage 40, which branches off upstream of the switching valve 22 in the bypass passage 30. The overflow fluid discharged from the overflow valve 41 is discharged to the fluid tank T via the drain passage 76. Alternatively, the overflow passage 40 can be configured to branch off from the cylinder-side first main passage 7a or to be directly connected to the rod-side chamber 2a.

[0045] The drainage passage 76 includes: a first drainage passage 76a connected to the drainage chamber 51; a second drainage passage 76b connected to the spring chamber 54; a third drainage passage 76c connected to the overflow valve 41; and a fourth drainage passage 76d connecting the first drainage passage 76a, the second drainage passage 76b, and the third drainage passage 76c. The first drainage passage 76a and the second drainage passage 76b are configured to be directly connected.

[0046] The drain chamber 51 is connected to the third drain passage 76c downstream of the overflow valve 41 via the first drain passage 76a and the fourth drain passage 76d. The spring chamber 54 is connected to the third drain passage 76c downstream of the overflow valve 41 via the second drain passage 76b and the fourth drain passage 76d. The third drain passage 76c is connected to the main body 60 of the load holding mechanism 20 (see reference). Figure 3 The drain port 86, which has an opening on the outer surface of the pipe, is connected to the drain port 86. The drain port 86 is connected via pipe 55 (see reference). Figure 2It is connected to the fluid tank T. Thus, the overflow pressure discharged from the overflow valve 41, and the drainage from the drain chamber 51 and spring 54 are discharged to the fluid tank T via the drain port 86 and the piping 55. Since both the drain chamber 51 and the spring chamber 54, respectively located on both sides of the slide valve 56 of the switching valve 22, are connected to the fluid tank T, atmospheric pressure acts on both ends of the slide valve 56 when the switching valve 22 is in the blocked position 22A, thereby preventing the spring 56 from moving unexpectedly.

[0047] An overflow valve 43 is connected to the first main passage 7b on the control valve side, which opens when the pressure in the first main passage 7b on the control valve side reaches a predetermined pressure.

[0048] Next, mainly refer to Figure 3 The switching valve 22 will be described in detail. Figure 3 This is a cross-sectional view of the load holding mechanism 20, showing a state where the pilot pressure is not directed to the pilot chamber 23 and the switching valve 22 is in the blocked position 22A. Figure 3 In the middle, it is marked with Figure 2 The component of the same symbol shown is the same as... Figure 2 The structure shown is the same as the one described.

[0049] The switching valve 22 is assembled to the main body 60 of the load holding mechanism 20. A spool valve hole 60a is formed on the main body 60, and a generally cylindrical sleeve 61 is inserted into the spool valve hole 60a. A spool valve 56 is assembled freely within the sleeve 61.

[0050] A spring chamber 54 is defined on the side of one end face 56a of the slide valve 56 by a cover 57. The spring chamber 54 is connected to the second drain passage 76b via a notch 61a formed on the end face of the sleeve 61. Working fluid that leaks into the spring chamber 54 is discharged to the fluid tank T through the second drain passage 76b.

[0051] The spring chamber 54 houses a first annular spring support member 45 and a second annular spring support member 46. The end face of the first spring support member 45 abuts against one end face 56a of the slide valve 56, and a pin portion 56c protruding from one end face 56a of the slide valve 56 is inserted into the hollow portion. The second spring support member 46 is disposed near the bottom of the cover 57. The spring 36 is clamped between the first spring support member 45 and the second spring support member 46 in a compressed state, and clamps the first spring support member 45 to apply force to the slide valve 56 in the closing direction.

[0052] The axial position of the second spring support member 46 within the spring chamber 54 is set by abutting the top end of an adjusting bolt 47, which is screwed through the bottom of the cover 57, against the back of the second spring support member 46. By screwing in the adjusting bolt 47, the second spring support member 46 is moved closer to the first spring support member 45. Therefore, by adjusting the amount of screwing in the adjusting bolt 47, the initial spring load of the spring 36 can be adjusted. The adjusting bolt 47 is secured by a nut 48.

[0053] A pilot chamber 23 is defined on the side of the other end face 56b of the slide valve 56. The pilot chamber 23 is divided by a piston hole 60b formed in communication with the slide valve hole 60a and a cover 58 that closes the piston hole 60b. Pilot pressure is guided to the pilot chamber 23 via a pilot passage 52 formed in the main body 60. A piston 50 is slidably housed in the pilot chamber 23, the piston 50 bearing the pilot pressure on its back side and applying a thrust to the slide valve 56 that overcomes the force of the spring 36.

[0054] A drain chamber 51 is divided within the piston orifice 60b by a slide valve 56 and a piston 50. The drain chamber 51 is connected to a first drain passage 76a. Working fluid that leaks into the drain chamber 51 is discharged from the first drain passage 76a to the fluid tank T.

[0055] The piston 50 has: a sliding portion 50a, the outer peripheral surface of which slides along the inner peripheral surface of the piston hole 60b; a top end portion 50b, which is formed with a smaller diameter compared to the sliding portion 50a and faces the other end face 56b of the slide valve 56; and a base end portion 50c, which is formed with a smaller diameter compared to the sliding portion 50a and faces the top end face of the cover 58.

[0056] When pilot fluid is supplied to the pilot chamber 23 via pilot passage 52, pilot pressure acts on the back side of the base end 50c and the annular back side of the sliding portion 50a. This causes the piston 50 to advance, and the top end 50b abuts against the other end face 56b of the slide valve 56, causing the slide valve 56 to move. Thus, the slide valve 56 withstands the thrust of the piston 50 generated by the pilot pressure acting on the back side of the piston 50, thereby overcoming the force of the spring 36 and moving. Even when the back side of the base end 50c abuts against the top face of the cover 58, because the base end 50c has a smaller diameter than the sliding portion 50a, the pilot pressure acts on the annular back side of the sliding portion 50a, therefore, the piston 50 can still advance.

[0057] Since one end of the piston 50 faces the pilot chamber 23 and the other end faces the drain chamber 51 connected to the fluid tank T, the thrust of the piston 50 generated by the pilot pressure of the pilot chamber 23 is efficiently transmitted to the slide valve 56.

[0058] The slide valve 56 stops at a position where the force of the spring 36 acting on 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 set at the stopping position of the slide valve 56.

[0059] A bypass passage 30 is formed on the switching valve 61 (see reference). Figure 2 The first supply port 32, which is connected to the back pressure passage 31 (see reference), Figure 2 The second supply port 33, which is connected to the downstream passage 38 (see reference) Figure 2 The three ports 3 and 4 are connected to the discharge port.

[0060] The outer peripheral surface of the slide valve 56 is partially cut into an annular shape, forming a first pressure chamber 64, a second pressure chamber 65, a third pressure chamber 66, and a fourth pressure chamber 67 through the cut portion and the inner peripheral surface of the sleeve 61. The first pressure chamber 64 is always in communication with the discharge port 34.

[0061] The third pressure chamber 66 is always connected to the first supply port 32. Multiple throttling sections 37 are formed on the outer peripheral surface of the shoulder 72 of the slide valve 56. These multiple throttling sections 37 move by the slide valve 56 overcoming the force of the spring 36, thereby connecting the third pressure chamber 66 and the second pressure chamber 65.

[0062] The fourth pressure chamber 67 is always in communication with the second pressure chamber 65 via a pressure-conducting passage 68 formed axially in the slide valve 56.

[0063] When the pilot pressure is not guided to the pilot chamber 23, the lift valve 70 formed in the slide valve 56 is pressed against the valve seat 71 formed on the inner circumference of the sleeve 61 by the force of the spring 36, thereby blocking the communication between the second pressure chamber 65 and the first pressure chamber 64. Therefore, the communication between the first supply port 32 and the discharge port 34 is blocked. This prevents the working fluid in the rod-side chamber 2a from leaking to the discharge port 34. This state corresponds to the blocked position 22A of the switching valve 22. With the lift valve 70 seated on the valve seat 71 by the force of the spring 36, a small gap exists between the end face of the first spring bearing member 45 and the end face of the sleeve 61. Therefore, the lift valve 70 is reliably sealed relative to the valve seat 71 by the force of the spring 36.

[0064] When the pilot pressure is guided to the pilot chamber 23 and the thrust of the piston 50 acting on the slide valve 56 is greater than the force of the spring 36, the slide valve 56 moves against the force of the spring 36. This causes the lift valve 70 to separate from the valve seat 71, and the third pressure chamber 66 and the second pressure chamber 65 are connected via multiple throttling sections 37. Therefore, the first supply port 32 is connected to the discharge port 34 via the third pressure chamber 66, the second pressure chamber 65, and the first pressure chamber 64. Through the connection between the first supply port 32 and the discharge port 34, the working fluid in the rod-side chamber 2a flows downstream through the throttling section 37 to the downstream passage 38 (see reference). Figure 2 The switch valve 22 is guided. This state corresponds to the first connected position 22B of the switching valve 22.

[0065] When the pilot pressure guided to the pilot chamber 23 increases, the slide valve 56 moves further against the force of the spring 36, and the fourth pressure chamber 67 connects to the second supply port 33. Herein, the second supply port 33 connects to the discharge port 34 via the fourth pressure chamber 67, the pressure guiding passage 68, the second pressure chamber 65, and the first pressure chamber 64. Through the connection between the second supply port 33 and the discharge port 34, the working fluid in the back pressure chamber 25 flows downstream through the throttling section 37 to the downstream passage 38 (see reference). Figure 2 The valve is guided. This state corresponds to the second connected position 22C of the switching valve 22.

[0066] Next, while referring to Figure 2 as well as Figure 3 The operation of the hydraulic control device 100 will be explained.

[0067] With control valve 6 in the neutral position 6C, the working fluid sprayed by pump 4 is not supplied to cylinder 2. At this time, the pilot pressure is not guided to the pilot chamber 23 of switching valve 22, therefore, switching valve 22 is in the blocked position 22A.

[0068] 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-bearing area in the valve core 24 in the valve-closing direction (the area of ​​the back side of the valve core 24) is greater than the pressure-bearing area in the valve-closing direction, i.e., the area of ​​the second pressure-bearing surface 24b, the valve core 24 is seated in the seat portion 28 by the load acting on the back side of the valve core 24 generated by the pressure of the back pressure chamber 25 and the force of the spring 27. In this way, by operating the check valve 21, leakage of the working fluid in the rod-side chamber 2a is prevented, and the boom 1 is kept in a stopped state.

[0069] When the operating handle 10 is actuated, pilot pressure is introduced from the pilot control valve 9 to the pilot chamber 6a of the control valve 6. The control valve 6 then switches to the retracted position 6A by an amount corresponding to the pilot pressure. When the control valve 6 switches to the retracted position 6A, the ejection pressure of the pump 4 acts on the first pressure-bearing surface 24a of the operating check valve 21. At this time, the switching valve 22 is not introducing pilot pressure to the pilot chamber 23 and is in the blocked 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. When the load acting on the first pressure-bearing surface 24a is greater than the combined load of the load acting on the back of the valve core 24 generated by the pressure of the back pressure chamber 25 and the force of the spring 27, the valve core 24 separates from the seat portion 28. Thus, if the operating check valve 21 is opened, the working fluid ejected from the pump 4 is supplied to the rod-side chamber 2a, and the cylinder 2 retracts. This causes the boom 1 to... Figure 1 The direction of arrow 80 shown is upward.

[0070] When the operating handle 10 is actuated, pilot pressure is directed from the pilot control valve 9 to the pilot chamber 6b of the control valve 6. The control valve 6 then switches to the extended position 6B by an amount corresponding to the pilot pressure. At the same time, pilot pressure is also directed to the pilot chamber 23. Therefore, the switching valve 22 switches to either the first connected position 22B or the second connected position 22C depending on the supplied pilot pressure.

[0071] When the pilot pressure guided to the pilot chamber 23 is above the first predetermined pressure but below the second predetermined pressure, the switching valve 22 switches to the first connected position 22B. In this case, the connection between the second supply port 33 and the discharge port 34 is blocked, therefore, 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 remains closed.

[0072] On the other hand, the first supply port 32 is connected to the discharge port 34, so the working fluid in the rod-side chamber 2a is guided from the bypass passage 30 through the throttling section 37 to the downstream passage 38, and discharged from the first main passage 7b on the control valve side to the fluid tank T via the control valve 6. Additionally, the working fluid ejected from the pump 4 is supplied to the opposite side chamber 2b of the rod, thus extending the cylinder 2. This allows the stick 1 to extend... Figure 1 The direction of arrow 81 shown is downward.

[0073] Here, switching valve 22 to the first connected position 22B is primarily for crane operations where the conveyed material installed on bucket 13 is unloaded to the destination. This is because, during crane operations, cylinder 2 needs to extend at a low speed to slowly lower boom 1 in the direction of arrow 81. Therefore, the pilot pressure in pilot chamber 6b of control valve 6 is relatively low, and control valve 6 is slightly switched to the extended position 6B. Consequently, the pilot pressure in pilot chamber 23 of switching valve 22 is also relatively low, above the first predetermined pressure but below the second predetermined pressure, and switching valve 22 is only switched to the first connected position 22B. Therefore, the working fluid in boom-side chamber 2a flows through throttling section 37 and is discharged, and boom 1 descends at a low speed suitable for crane operations.

[0074] Furthermore, even if the working fluid leaks to the outside due to a situation such as a rupture in the first main passage 7b on the control valve side, when the switching valve 22 is in the first connected position 22B, the flow rate of the working fluid discharged from the rod side chamber 2a is limited by the throttling section 37, thus suppressing the descent speed of the bucket 13. This function is called instrument metering control. Therefore, before the bucket 13 falls to the ground, the switching valve 22 can be switched to the blocking position 22A, thereby preventing the bucket 13 from falling rapidly.

[0075] Thus, the throttle section 37 is used to suppress the descent speed of cylinder 2 when the one-way valve 21 is closed, and to suppress the descent speed of bucket 13 when the first main passage 7b on the control valve side is broken.

[0076] When the pilot pressure guided to the pilot chamber 23 is above the second predetermined pressure, the switching valve 22 switches to the second connection position 22C. In this case, the second supply port 33 is connected to the discharge port 34, so the working fluid of the back pressure chamber 25 of the operating check valve 21 is guided from the back pressure passage 31 to the downstream passage 38 through the bypass throttling section 37, and discharged from the first main passage 7b on the control valve side to the fluid tank T via the control valve 6. Hereby, a pressure difference is generated before and after the throttling section 26a, the pressure in the back pressure chamber 25 decreases, so the force acting on the valve core 24 in the valve closing direction decreases, the valve core 24 separates from the seat 28, thereby deactivating the function of the operating check valve 21 as a check valve.

[0077] In this way, the one-way valve 21 is operated to allow the working fluid to flow from the control valve 6 to the rod-side chamber 2a, and on the other hand, the working fluid is allowed to flow from the rod-side chamber 2a to the control valve 6 according to the back pressure, which is the pressure of the back pressure chamber 25.

[0078] When the one-way valve 21 is opened, the working fluid in the rod-side chamber 2a is discharged to the fluid tank T via the first main passage 7, causing the cylinder 2 to extend rapidly. That is, when the switching valve 22 is switched to the second connection position 22C, the flow rate of the working fluid discharged from the rod-side chamber 2a increases, thus increasing the flow rate of the working fluid supplied to the opposite-side chamber 2b, and accelerating the extension speed of the cylinder 2. Consequently, the boom 1 descends rapidly in the direction of arrow 81.

[0079] When switching valve 22 is switched to the second connected position 22C, such as during excavation operations, the pilot pressure in the pilot chamber 6b of control valve 6 is relatively high, and control valve 6 is switched to the extended position 6B to a greater extent. Therefore, the pilot pressure in the pilot chamber 23 of switching valve 22 is also relatively high, exceeding the second predetermined pressure. Thus, switching valve 22 is only switched to the second connected position 22C.

[0080] Here, the operator operates the lever 10 to guide pilot pressure to the pilot chamber 23 and move the slide valve 56 in the opening direction. When the lever 2 is extended and the pressure in the lever-side chamber 2a rises, causing the overflow valve 41 to open, the overflow fluid discharged from the overflow valve 41 is discharged to the fluid tank T via the third drain passage 76c. On the other hand, it is also guided to the drain chamber 51 and the spring chamber 54 via the first drain passage 76a and the second drain passage 76b. Because the overflow fluid is guided to the drain chamber 51, the piston 50 sometimes moves in the direction of separation from the slide valve 56. In this case, the thrust of the piston 50 generated by the pilot pressure is not transmitted to the slide valve 56; therefore, the slide valve 56 moves in the closing direction due to the force of the spring 36. As a result, even though the operator operates the lever 10 to guide pilot pressure to the pilot chamber 6b and the pilot chamber 23, the desired extension speed of the cylinder 2 cannot be obtained.

[0081] On the other hand, even when the slide valve 56 moves in the closed direction, the pilot pressure is guided to the pilot chamber 6b of the control valve 6. Therefore, the downstream passage 38, which is downstream of the slide valve 56, and the first main passage 7b on the control valve side are in a state of communication with the fluid tank T via the control valve 6. As a result, the working fluid inside the downstream passage 38 and the first main passage 7b on the control valve side is discharged into the fluid tank T, and the pressure decreases. Since the working fluid in the downstream passage 38 and the first main passage 7b on the control valve side flows into the fluid tank T due to its own weight, the interior of the downstream passage 38 and the first main passage 7b on the control valve side sometimes becomes negative pressure.

[0082] In this situation, to achieve the desired elongation speed, the operator operates the operating handle 10 in a manner that increases the pilot pressure acting on the slide valve 56, causing the slide valve 56 to move again in the opening direction. At this time, because the slide valve 56 has moved in the closing direction, the working fluid flows forcefully to the downstream passage 38 on the downstream side of the slide valve 56, which has a reduced pressure, and to the first main passage 7b on the control valve side, causing the cylinder 2 to temporarily accelerate rapidly in the elongation direction.

[0083] As a countermeasure, in this embodiment, such as Figure 2 as well as Figure 3 As shown, the switching valve 22 has: a pressure-conducting passage 90 that connects the drain passage 76 and the downstream side of the slide valve 56; and a one-way valve 91 disposed in the pressure-conducting passage 90 that allows only the flow of working fluid from the drain passage 76 to the downstream side of the slide valve 56. The following is a detailed description.

[0084] In this embodiment, one end of the pressure guiding passage 90 is connected to the second drainage passage 76b via the spring chamber 54, and the other end is connected to the downstream passage 38. One end of the pressure guiding passage 90 is connected to the spring chamber 54 via a notch 61a formed on the end face of the sleeve 61. The connection of one end of the pressure guiding passage 90 to the second drainage passage 76b via the spring chamber 54 is not limited; it can be directly connected to the second drainage passage 76b without going through the spring chamber 54, or it can be connected to the first drainage passage 76a, the third drainage passage 76c, or the fourth drainage passage 76d. Furthermore, the other end of the pressure guiding passage 90 can be connected to the downstream side of the slide valve 56, or it can be connected to the first main passage 7b on the control valve side.

[0085] like Figure 3 As shown, the one-way valve 91 includes: a lift valve 92, which is housed in a pressure-conducting passage 90 in a freely movable manner; a valve seat 93, which is formed in the pressure-conducting passage 90; a plug 94, which closes the opening of the pressure-conducting passage 90, which opens on the outer surface of the main body 60; a spring 95, which is a force-applying component, is housed between the lift valve 92 and the plug 94 in a compressed manner, and applies force to the lift valve 92 toward the valve seat 93; and an annular sealing component 96, which is provided on the outer peripheral surface of the plug 94.

[0086] When the pressure in the drain passage 76 is greater than the pressure in the downstream passage 38, the lift valve 92 moves against the force of the spring 95 and opens. This allows the working fluid to flow from the drain passage 76 to the downstream passage 38 via the pressure-conducting passage 90. Conversely, when the pressure in the downstream passage 38 is greater than the pressure in the drain passage 76, the spring 95 causes the lift valve 92 to sit on the valve seat 93 and open, thus blocking the flow of the working fluid from the downstream passage 38 to the drain passage 76 via the pressure-conducting passage 90. Furthermore, the check valve 91 is not limited to a lift type; it can be a ball type, or it can be an operating check valve that uses the pressure on the upstream side as the lift pressure to open.

[0087] The switching valve 22 has a pressure-conducting passage 90 and a one-way valve 91, thereby achieving the following effects.

[0088] The operator operates the operating handle 10 to guide pilot pressure into the pilot chamber 23, causing the slide valve 56 to move in the opening direction. When the cylinder 2 is extended and the pressure in the rod-side chamber 2a rises, causing the relief valve 41 to open, the slide valve 56 moves in the closing direction as described above. At this time, the downstream passage 38, which is downstream of the slide valve 56, is connected to the fluid tank T via the control valve 6, thus reducing the pressure. Furthermore, when the pressure in the drain passage 76 is greater than the pressure in the downstream passage 38, the check valve 91 opens, guiding working fluid from the drain passage 76 to the downstream passage 38 via the pressure-conducting passage 90. This reduces the pressure in the drain passage 76, and also reduces the pressure in the drain chamber 51 and the spring chamber 54. Additionally, by guiding working fluid from the drain passage 76 to the downstream side of the slide valve 56 via the pressure-conducting passage 90, the pressure reduction in the downstream passage 38 and the first main passage 7b on the control valve side is suppressed.

[0089] Therefore, when the slide valve 56 moves in the closed direction, if the operator operates the operating handle 10 to increase the pilot pressure acting on the slide valve 56 in order to obtain the desired extension speed, the slide valve 56 moves smoothly in the open direction due to the pressure reduction in the drain chamber 51 and the spring chamber 54. Thus, the extension speed desired by the operator can be obtained quickly. Furthermore, since the pressure reduction in the downstream passage 38 and the first main passage 7b on the control valve side is suppressed, the situation where the working fluid forcefully flows to the downstream side of the slide valve 56 when the slide valve 56 moves in the open direction, causing the cylinder 2 to temporarily accelerate rapidly in the extension direction, can be prevented. In addition, since the pressure reduction in the downstream passage 38 and the first main passage 7b on the control valve side is suppressed, the downstream passage 38 and the first main passage 7b on the control valve side become negative pressure, preventing cavitation and thus improving the responsiveness when operating the operating handle 10.

[0090] According to the first embodiment described above, the following effects are achieved.

[0091] Because a one-way valve 91, which only allows the working fluid to flow from the drain passage 76 to the downstream side of the slide valve 56, is provided on the pressure-conducting passage 90 connecting the drain passage 76 and the downstream side of the slide valve 56, even when the overflow valve 41 is open during the process of the operator extending the cylinder 2 by operating the handle, the overflow pressure fluid is guided to the downstream side of the slide valve 56 via the pressure-conducting passage 90. This reduces the pressure in the drain passage 76, as well as the pressure in the drain chamber 51 and the spring chamber 54. Furthermore, it suppresses the pressure drop on the downstream side of the slide valve 56. Therefore, when the overflow valve 41 is open and the slide valve 56 moves in the closed direction, even if the operator operates the operating handle 10 to increase the pilot pressure acting on the slide valve 56 in order to obtain the desired extension speed, rapid acceleration of the cylinder 2 can be prevented.

[0092] Hereinafter, variations of the above embodiments will be described. These variations are also within the scope of the present invention, and it is possible to combine these variations with the structures of the above embodiments or to combine these variations with each other.

[0093] (1) The drainage passage 76 is not limited to the structure described in the above embodiment. For example, as... Figure 4 As shown, it is also possible to have a structure where the fourth drainage passage 76d is not provided, and the first drainage passage 76a, the second drainage passage 76b, and the third drainage passage 76c are directly connected. Additionally, as... Figure 5 As shown, a structure can also be constructed where the first drainage passage 76a and the third drainage passage 76c are connected, while the second drainage passage 76b is provided independently. In this structure, the pressure-conducting passage 90 is connected to the drainage passage 76 having the first drainage passage 76a and the third drainage passage 76c. Additionally, as... Figure 6 As shown, the second drainage passage 76b and the third drainage passage 76c can be connected, while the first drainage passage 76a is provided independently. In this structure, the pressure guiding passage 90 is connected to the drainage passage 76 having the second drainage passage 76b and the third drainage passage 76c. That is, the pressure guiding passage 90 is connected to the overflow valve 41 and to the drainage passage 76 connected to at least one of the drainage chamber 51 and the spring chamber 54.

[0094] (2)Reference Figure 7 as well as Figure 8 The following describes variations of the above embodiments. Figure 7 This is a hydraulic circuit diagram of the hydraulic control device 101 involved in this modified example. Figure 8 This is a cross-sectional view of the load holding mechanism 20 of the hydraulic control device 101 involved in this modification. Figure 7 as well as Figure 8 In this variation, structures having the same functions as those in the above embodiments are labeled with the same symbols as in the above embodiments, and their descriptions are omitted. In this variation, the piston 50 of the above embodiments is not provided, and the pilot chamber 23 and the drain chamber 51 are configured as a common space.

[0095] A throttling orifice 97, acting as a throttling element, is provided in the passage connecting the drain chamber 51 and the spring chamber 54 in the drain passage 76 to exert resistance on the flowing working fluid. Specifically, in this modified example, a first drain passage 76a connected to the drain chamber 51 and a second drain passage 76b connected to the spring chamber 54 are connected, and a throttling orifice 97 is provided in this connected passage. Thus, when the working fluid is guided to the pilot chamber 23 via the pilot passage 52, the pressure upstream of the throttling orifice 97 acts on the pilot chamber 23, and the pressure downstream of the throttling orifice 97 acts on the drain chamber 51. Therefore, the slide valve 56 moves by balancing the load generated by the pressure difference across the throttling orifice 97 and the force of the spring 36.

[0096] The operator operates the operating handle 10 to guide pilot pressure into the pilot chamber 23, causing the slide valve 56 to move in the opening direction. With the cylinder 2 extended and the pressure in the rod-side chamber 2a rising, the overflow valve 41 opens. The overflow fluid discharged from the overflow valve 41 is then guided to the drain chamber 51 and the spring chamber 54. Since the piston 50 is not provided in this modification, the overflow fluid guided to the drain chamber 51 does not reduce the thrust of the slide valve 56 generated by the pilot pressure. However, the overflow fluid guided to the spring chamber 54 causes a force in the closing direction to act on the slide valve 56; therefore, as in the above embodiment, a force in the closing direction acts on the slide valve 56. Thus, in this modification, the pressure passage 90 and the check valve 91 also function in the same way as in the above embodiment.

[0097] (3) In Figure 9 It shows Figure 7 as well as Figure 8 Examples of variations of the shape shown. For example... Figure 9 As shown, the drainage passage 76 can also be a structure in which a first drainage passage 76a connected to the drainage chamber 51 is not provided, a third drainage passage 76c connected to the overflow valve 41 and a second drainage passage 76b connected to the spring chamber 54 are connected. In this modified example, the pressure guiding passage 90 and the one-way valve 91 also perform the same function as in the above embodiment.

[0098] The structure, function, and effects of the embodiments of the present invention are summarized and explained below.

[0099] A fluid pressure control device 100 for controlling the extension and retraction of cylinder 2, which drives load 1, includes: a control valve 6 that controls the supply of working fluid from fluid pressure supply source 4 to cylinder 2; a pilot control valve 9 that controls the pilot pressure guided from pilot pressure supply source 5 to control valve 6; a main passage 7b that connects the load-side pressure chamber 2a of cylinder 2, which operates under the load pressure generated by load 1 when control valve 6 is in the neutral position 6C, to control valve 6; and a load holding mechanism 20 provided in the main passage 7b, which includes: an operating check valve 21 that allows working fluid to flow from control valve 6 to load-side pressure chamber 2a, and on the other hand, allows working fluid to flow from load-side pressure chamber 2a to control valve 6 based on back pressure; and a switching valve 22 that is connected to control valve 6 by the pilot pressure guided via pilot control valve 9. The switching valve 22 is operated in conjunction with the following: a pilot chamber 23 guided by a pilot control valve 9 to a pilot pressure; a spool valve 56 that moves according to the pilot pressure of the pilot chamber 23; a spring chamber 54 housing a force-applying member 36 that applies force to the spool valve 56 in the closing direction; a drain chamber 51 sandwiching the spool valve 56 and disposed on the side opposite to the spring chamber 54; a drain passage 76 connected to the overflow valve 41 and connected to at least one of the drain chamber 51 and the spring chamber 54; a pressure-conducting passage 90 connecting the drain passage 76 and the downstream side of the spool valve 56; and a check valve 91 disposed in the pressure-conducting passage 90 and allowing only the working fluid to flow from the drain passage 76 to the downstream side of the spool valve 56.

[0100] In addition, the switching valve 22 also has a piston 50, which bears pilot pressure on the back and applies a thrust to the slide valve 56 to overcome the force of the force-applying component 36. The drain chamber 51 is divided by the slide valve 56 and the piston 50.

[0101] In addition, the pilot chamber 23 and the drain chamber 51 are common, and a throttling section 97 that applies resistance to the flowing working fluid is provided in the passage connecting the drain chamber 51 and the spring chamber 54 in the drain passage 76.

[0102] Because the above structure includes a check valve 91 on the pressure-conducting passage 90 connecting the drain passage 76 and the downstream side of the slide valve 56, which only allows the working fluid to flow from the drain passage 76 to the downstream side of the slide valve 56, when the operator extends the cylinder 2 towards the load-side pressure chamber 2a by operating the handle and the overflow valve 41 is open, the overflow fluid is guided to the downstream side of the slide valve 56 via the pressure-conducting passage 90. This prevents sudden acceleration of the cylinder 2.

[0103] The embodiments of the present invention have been described above. However, the above embodiments are merely some examples of the application of the present invention and are not intended to limit the technical scope of the present invention to the specific structures of the above embodiments.

[0104] This application claims priority based on Japanese Patent Application No. 2021-130616 filed with the Japan Patent Office on August 10, 2021, the entire contents of which are incorporated herein by reference.

Claims

1. A fluid pressure control device for controlling the extension and retraction of a cylinder driving a load, wherein, have: A control valve that controls the supply of working fluid from a fluid pressure supply source to the cylinder; A pilot control valve that controls the pilot pressure directed from a pilot pressure supply source to the control valve; The main passage connects the load-side pressure chamber of the cylinder, which is affected by the load pressure generated by the load when the control valve is in the neutral position, to the control valve. A load holding mechanism is provided in the main passage. The load holding mechanism has: The one-way valve is operated to allow the working fluid to flow from the control valve to the load-side pressure chamber, and on the other hand, to allow the working fluid to flow from the load-side pressure chamber to the control valve according to the back pressure. A switching valve, which operates in conjunction with the control valve by a pilot pressure guided via the pilot control valve, and is used to switch the operation of the actuating check valve; The relief valve opens when the pressure in the load-side pressure chamber reaches a predetermined pressure. The switching valve has: The pilot chamber, which is guided by the pilot control valve to pilot pressure; A spool valve that moves according to the pilot pressure in the pilot chamber; A spring chamber, which houses a force-applying component that applies force to the slide valve in the closing direction; A drain chamber, which sandwiches the slide valve, is located on the opposite side of the spring chamber; A drainage passage, which is connected to the overflow valve and to at least one of the drainage chamber and the spring chamber; A pressure-conducting passage connects the drainage passage to the downstream side of the slide valve; A one-way valve is provided in the pressure passage and allows working fluid to flow only from the drain passage to the downstream side of the slide valve.

2. The fluid pressure control device as described in claim 1, wherein, It also includes a piston that receives pilot pressure on its back side and applies a thrust to the slide valve that overcomes the force exerted by the force-applying component. The drainage chamber is divided by the slide valve and the piston.

3. The fluid pressure control device as described in claim 1, wherein, The pilot chamber and the drainage chamber are interconnected. A throttling section is provided in the drainage passage connecting the drainage chamber and the spring chamber to apply resistance to the flowing working fluid.

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