Relief valve

Abstract

To provide a relief valve for allowing the regulation of a relief pressure while suppressing a pressure required as a pilot pressure.SOLUTION: A relief valve 100 includes a housing 10 in which a pilot chamber 51 and an oil chamber 52 are formed, a valve element 20, an energizing member 30 for energizing the valve element 20 toward an inflow flow path 101a, and a piston 40 including a first piston member 41 for pressing the energizing member 30 with the pressure of pilot oil in the pilot chamber 51 to change the warping amount of the energizing member 30. At least part of the first piston member 41 is arranged in the oil chamber 52 for partitioning the oil chamber 52 into a first oil chamber 52a and a second oil chamber 52b. The first piston member 41 has a first pressure receiving surface 41d for receiving a pressure from working oil in the first oil chamber 52a to one of the axial direction, and a second pressure receiving surface 41e for receiving a pressure from working oil in the second oil chamber 52b to the other of the axial direction.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a relief valve, and more particularly to a relief valve that changes the amount of deflection of a biasing member according to the pressure of pilot oil. [Background technology]

[0002] BACKGROUND ART Conventionally, a relief valve is known in which the amount of deflection of a biasing member is changed by the pressure of pilot oil (see, for example, Patent Document 1).

[0003] The above-mentioned Patent Document 1 discloses a relief valve for a hydraulic control device. The relief valve includes a valve slide that blocks the connection between an inlet terminal and a tank terminal, a pilot valve cone that presses the valve slide, a control spring that presses the valve slide in the closing direction via the pilot valve cone, and a tension piston that presses the control spring with pilot pressure and changes the amount of deflection of the control spring. A force due to the pilot pressure acts on the tension piston in one axial direction. The relief pressure is adjusted by changing the amount of deflection of the control spring using the tension piston.

[0004] The pilot valve cone has a passage penetrating in the axial direction, and the other axial end of the pilot valve cone is inserted into a recess in the tension piston. Pressurized fluid is introduced via the passage in the pilot valve cone into a control chamber defined by the recess in the tension piston and the other axial end of the pilot valve cone. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] European Patent No. 1781952 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the relief valve described in Patent Document 1, because the pressure fluid is introduced into the control chamber, the force of the pressure fluid in the control chamber acts on the tension piston in the other axial direction, counteracting the pilot pressure. In this case, if the relief pressure is to be adjusted using the pilot pressure, the pilot pressure must be strong enough to push back the force of the pressure fluid. This poses a problem in that it is difficult to adjust the relief pressure while suppressing the pressure required as the pilot pressure.

[0007] This disclosure has been made to solve the above-mentioned problems, and one object of this disclosure is to provide a relief valve that is capable of adjusting the relief pressure while suppressing the pressure required as the pilot pressure. [Means for solving the problem]

[0008] In order to achieve the above object, a relief valve according to a first aspect of this disclosure comprises: a housing in which a pilot chamber and an oil chamber are formed; a valve body that connects or blocks an inlet flow path into which hydraulic oil flows and an outlet flow path from which hydraulic oil flows out, the valve body including a first surface facing the inlet flow path, a second surface facing the oil chamber, and a through passage connecting the first surface and the second surface; a biasing member that biases the valve body toward the inlet flow path; and a piston including a first piston member that presses the biasing member with the pressure of pilot oil in the pilot chamber and changes the amount of deflection of the biasing member, at least a portion of the first piston member being disposed within the oil chamber and dividing the oil chamber into a first oil chamber and a second oil chamber, the first piston member having a first pressure-receiving surface that receives pressure in one axial direction from the hydraulic oil in the first oil chamber and a second pressure-receiving surface that receives pressure in the other axial direction from the hydraulic oil in the second oil chamber.

[0009] In the relief valve according to the first aspect of this disclosure, as described above, the first piston member has a first pressure-receiving surface that receives pressure in one axial direction from the hydraulic oil in the first oil chamber and a second pressure-receiving surface that receives pressure in the other axial direction from the hydraulic oil in the second oil chamber. This allows the force acting on the first piston member in one axial direction due to the hydraulic oil pressure to counteract the force acting on the first piston member in the other axial direction due to the hydraulic oil pressure, thereby reducing the force acting in the other axial direction counteracting the pilot oil pressure. As a result, the pilot oil pressure does not need to be high enough to push back all of the force acting on the first piston member in the other axial direction due to the hydraulic oil pressure. This makes it possible to adjust the relief pressure while suppressing the pressure required as the pilot pressure.

[0010] A relief valve according to a second aspect of this disclosure comprises: a housing in which a pilot chamber, an oil chamber, and an open-to-atmosphere chamber are formed; a valve body that connects or blocks an inlet flow path into which hydraulic oil flows and an outlet flow path from which hydraulic oil flows out, the valve body including a first surface facing the inlet flow path, a second surface facing the oil chamber, and a through passage connecting the first surface and the second surface; a biasing member that biases the valve body toward the inlet flow path; and a piston including a first pilot piston member that changes the amount of deflection of the biasing member by the pressure of pilot oil in the pilot chamber, wherein the other axial surface of the first pilot piston member faces the pilot chamber and the one axial surface of the first pilot piston member faces the open-to-atmosphere chamber.

[0011] In the relief valve according to the second aspect of this disclosure, as described above, the other axial surface of the first pilot piston member faces the pilot chamber, and the one axial surface of the first pilot piston member faces the open-to-atmosphere chamber. This means that, unlike when the one axial surface of the first pilot piston member faces the backpressure chamber, the one axial surface of the first pilot piston member is open to the atmosphere, preventing a force acting on the one axial surface of the first pilot piston member in the other axial direction due to backpressure, which counteracts the pressure of the pilot oil. As a result, the relief pressure can be adjusted while suppressing the pressure required as the pilot pressure. Furthermore, because the effect of backpressure can be reduced, the relief pressure can be adjusted accurately even when the backpressure fluctuates significantly. [Effects of the Invention]

[0012] According to the present disclosure, the relief pressure can be adjusted while suppressing the pressure required as the pilot pressure. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a vertical cross-sectional view showing a relief valve according to a first embodiment. [Figure 2] FIG. 2 is a partially enlarged view of FIG. [Figure 3] FIG. 6 is a vertical cross-sectional view showing a relief valve according to a second embodiment. [Figure 4] FIG. 3 is a partially enlarged view of FIG. 2. [Figure 5] FIG. 10 is a vertical cross-sectional view showing a relief valve according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, embodiments embodying the present disclosure will be described with reference to the drawings.

[0015] [First embodiment] The configuration of a relief valve 100 according to a first embodiment will be described with reference to Figures 1 and 2. In the figures, the Z direction represents the axial direction, the Z1 direction represents one axial direction, and the Z2 direction represents the other axial direction. The Y direction represents the radial direction perpendicular to the axial direction.

[0016] The relief valve 100 shown in Fig. 1 is a relief valve that regulates the maximum pressure of a hydraulic circuit through which hydraulic oil flows. The relief valve 100 is used in construction machinery vehicles, industrial vehicles, and the like. As will be described later, the relief valve 100 is a direct-acting, differential pressure type variable relief valve that can adjust the relief pressure. The relief valve 100 is attached to a valve block 101.

[0017] The relief valve 100 includes a housing 10, a valve element 20, a biasing member 30, and a piston 40. The valve element 20, the biasing member 30, and the piston 40 are accommodated inside the housing 10. Furthermore, the relief valve 100 is not a balanced piston type that includes a main valve and a subsidiary valve, but is a direct acting type that has a single valve element 20. Therefore, the structure of the relief valve 100 can be simplified compared to a balanced piston type that has a large number of parts and a complex structure. This makes it possible to reduce the occurrence of foreign matter, such as dust mixed in the hydraulic oil, getting caught in the gaps between the parts that make up the relief valve 100.

[0018] The housing 10 is attached to a valve block 101. The valve block 101 is formed with an inlet passage 101a through which hydraulic oil flows in and an outlet passage 101b through which hydraulic oil flows out. The inlet passage 101a is connected to an inlet port. High-pressure hydraulic oil from the hydraulic circuit flows into the inlet passage 101a. The inlet pressure of the relief valve 100 acts on the inlet passage 101a. The outlet passage 101b is connected to an outlet port. The back pressure of the relief valve 100 acts on the outlet passage 101b. For example, if the outlet passage 101b is connected to a tank of the hydraulic circuit, the back pressure of the relief valve 100 is equal to the tank pressure.

[0019] The housing 10 also includes a valve seat member 11 and housing members 12 to 15. The valve seat member 11 and the housing members 12 to 15 are arranged in roughly this order from one axial direction to the other axial direction, and together form the exterior of the relief valve 100.

[0020] The valve seat member 11 has a valve seat 11a. The valve seat 11a is formed to surround the passage 10a connected to the inlet flow passage 101a. The valve element 20 seats on and moves away from the valve seat 11a. The valve seat 11a is formed at the other axial end of the annular valve seat member 11. The passage 10a is formed as an inner hole of the valve seat member 11. The valve seat member 11 may be omitted, in which case the valve seat 11a may be formed directly in the valve block 101.

[0021] The housing member 12 is a cylindrical member extending along the axial direction. A valve seat member 11 is attached to one axial end of the housing member 12. A passage 10b connected to an outlet flow path 101b is formed on the side surface of one axial end of the housing member 12. The housing member 12 is screwed into the valve block 101 via a screw 12a.

[0022] The housing member 13 is a cylindrical member extending along the axial direction. The diameter of at least a portion of the housing member 13 is smaller than the diameter of the housing member 12. One axial portion of the housing member 13 is inserted into the inner hole of the housing member 12 in the axial direction and is screwed into the inner hole of the housing member 12 via a screw 13a. The other axial portion of the housing member 13 protrudes from the inner hole of the housing member 12 in the other axial direction and has a nut 16 screwed onto its outer periphery. The housing member 13 is fastened and fixed to the housing member 12 by the nut 16. A cylindrical retaining member 17 is disposed in the inner hole of the housing member 13 and is fitted with a first piston member 41 (described later) of the piston 40. The first piston member 41 is fitted into the inner hole of the retaining member 17, and the outer periphery of the retaining member 17 is fitted with the housing member 13.

[0023] The housing member 14 has a small-diameter structure 14a and a large-diameter structure 14b with a larger diameter than the small-diameter structure 14a. Both the small-diameter structure 14a and the large-diameter structure 14b have a cylindrical shape extending along the axial direction. The small-diameter structure 14a is inserted into the inner hole of the housing member 13 in one axial direction, threaded into the inner hole of the housing member 13 via a screw 14c, and fastened to the housing member 13 via a retaining member 17. The large-diameter structure 14b is connected to the other axial portion of the small-diameter structure 14a and protrudes from the inner hole of the housing member 13 in the other axial direction.

[0024] The housing member 15 is inserted into the inner hole of the large-diameter structure 14b in one axial direction and is screwed to the large-diameter structure 14b via a screw 15a. The housing member 15 also protrudes from the inner hole of the large-diameter structure 14b in the other axial direction, and a nut 18 is screwed onto its outer periphery. The housing member 15 is fastened and fixed to the housing member 14b by the nut 18. The housing member 15 is also formed with a pilot port 15b that supplies pilot oil. The pressure of the pilot oil is the pressure used to operate objects in the hydraulic circuit, including the relief valve 100. In this embodiment, the hydraulic oil in the main circuit for driving actuators, etc. is simply referred to as "hydraulic oil," and the operating hydraulic oil is referred to as "pilot oil."

[0025] The housing 10 is provided with a pilot chamber 51 into which the pressure of the pilot oil is introduced, an oil chamber 52 into which the pressure of the hydraulic oil is introduced, a biasing member chamber 53 in which the biasing member 30 is disposed, a back pressure chamber 54, and an atmosphere-open chamber 55 that is open to the atmosphere. The pilot chamber 51 is connected to the pilot port 15b. Therefore, the pilot oil pressure of the pilot port 15b acts on the pilot chamber 51. The pilot chamber 51 is defined by the recessed structure of the housing member 15 and a second piston member 42 of the piston 40, which will be described later. The oil chamber 52 is connected to a through passage 20c of the valve body 20, which will be described later. Therefore, the inlet pressure of the relief valve 100 acts on the oil chamber 52. The oil chamber 52 is defined by the housing member 13 and a first piston member 41 of the piston 40, which will be described later.

[0026] The biasing member chamber 53 is connected to the outflow passage 101b via a passage 12b of the housing member 12. Therefore, the back pressure of the relief valve 100 acts on the biasing member chamber 53. The biasing member chamber 53 is also defined by the housing member 12 and the valve body 20.

[0027] The back pressure chamber 54 is connected to the biasing member chamber 53 via a passage 13b of the housing member 13 and a passage 17a of the holding member 17. Therefore, the back pressure of the relief valve 100 acts on the back pressure chamber 54. The back pressure chamber 54 is also defined by the housing member 14, the holding member 17, and a first piston member 41 and a third piston member 43 of the piston 40, which will be described later.

[0028] The open-to-atmosphere chamber 55 is connected to the atmosphere via a passage 14d of the housing member 14. Therefore, the pressure of the hydraulic oil does not act on the open-to-atmosphere chamber 55. The open-to-atmosphere chamber 55 is partitioned by the housing member 14, the housing member 15, and a second piston member 42 and a third piston member 43 of the piston 40, which will be described later.

[0029] The biasing member chamber 53, the oil chamber 52, the back pressure chamber 54, the atmosphere-open chamber 55, and the pilot chamber 51 are arranged in this order from one axial direction to the other axial direction. The biasing member chamber 53 is arranged in a position radially overlapping with a portion of the valve body 20. The oil chamber 52 is arranged on the other axial side of the biasing member chamber 53 and in a position radially overlapping with a portion of the first piston member 41 of the piston 40. The back pressure chamber 54 is arranged on the other axial side of the oil chamber 52 and in a position radially overlapping with a portion of the first piston member 41 and the third piston member 43 of the piston 40. The atmosphere-open chamber 55 is arranged on the other axial side of the back pressure chamber 54 and in a position radially overlapping with a portion of the second piston member 42 and the third piston member 43 of the piston 40. The pilot chamber 51 is arranged on the other axial side of the atmosphere-open chamber 55. At least a portion of the pilot chamber 51 is arranged on the other axial side of the second piston member 42 of the piston 40.

[0030] The valve body 20 connects or blocks the inflow passage 101a and the outflow passage 101b. The valve body 20 includes a first surface 20a facing the inflow passage 101a, a second surface 20b facing a second oil chamber 52b (described later) of the oil chamber 52, and a through passage 20c connecting the first surface 20a and the second surface 20b. The valve body 20 also includes an enlarged structure 20d seated on the valve seat 11a and a shaft 20e extending from the enlarged structure 20d in the other axial direction. The first surface 20a is formed on one axial end surface of the enlarged structure 20d of the valve body 20. The second surface 20b is formed on the other axial end surface of the shaft 20e. The through passage 20c passes through the valve body 20 in the axial direction from the first surface 20a to the second surface 20b, and guides the hydraulic oil in the inlet passage 101a to the second oil chamber 52b of the oil chamber 52. A throttle 20f is also formed in the through passage 20c. The throttle 20f suppresses sudden changes in the pressure in the oil chamber 52.

[0031] Here, the relief valve 100 is a differential pressure type that cancels the pressure-receiving area of ​​the valve element 20 by guiding the hydraulic oil through the through passage 20c. Specifically, the first surface 20a of the valve element 20 receives pressure in the other axial direction from the hydraulic oil in the inlet flow passage 101a, and the second surface 20b receives pressure in the one axial direction from the hydraulic oil in the oil chamber 52. Therefore, the effective pressure-receiving area of ​​the valve element 20 is the area obtained by subtracting the pressure-receiving area of ​​the second surface 20b from the pressure-receiving area of ​​the first surface 20a. In other words, the effective pressure-receiving area of ​​the valve element 20 is expressed by the following equation (1). Furthermore, because the relief valve 100 is a differential pressure type, the biasing member 30 can be made smaller even when a large flow rate of hydraulic oil is circulated, and the valve element 20 can also accommodate a large flow rate. A1=(d1 2 -d2 2 )×π / 4 (1) where: A1: Effective pressure-receiving area of ​​the valve body 20 d1: diameter of the first surface 20a facing the inflow channel 101a d2: diameter of the second surface 20b facing the oil chamber 52 is.

[0032] The biasing member 30 biases the valve element 20 toward the inlet flow passage 101a and the valve seat 11a to set the relief pressure. In the relief valve 100, the biasing member 30 is disposed axially further from the first piston member 41 of the piston 40 and the housing member 13. The biasing member 30 is a coil spring. However, the biasing member 30 is not limited to a coil spring and may be, for example, a leaf spring. The biasing member 30 is held between the spring seat 60 and the enlarged structure 20d in the biasing member chamber 53. The biasing member 30 is compressed in the biasing member chamber 53 so as to press the spring seat 60 in the other axial direction and press the enlarged structure 20d in one axial direction. When the pressure of the hydraulic oil in the inlet flow path 101a of the relief valve 100 rises to the relief pressure, the valve element 20 moves in the other axial direction against the biasing force of the biasing member 30, and the inlet flow path 101a and the outlet flow path 101b are connected. This allows the hydraulic oil to flow out, and the inlet pressure and flow rate of the relief valve 100 are controlled.

[0033] The piston 40 is provided to variably adjust the relief pressure. Specifically, the piston 40 presses the biasing member 30 by the pressure of the pilot oil in the pilot chamber 51, changing the amount of deflection of the biasing member 30. In this way, the piston 40 variably adjusts the relief pressure according to the pressure of the pilot oil. The more the biasing member 30 is deflected, the greater the biasing force that biases the valve element 20 by the biasing member 30, and the relief pressure is adjusted to be higher. The piston 40 can variably adjust the relief pressure within a set pressure range.

[0034] The basic relief pressure is adjusted by the housing member 13. Specifically, the amount of deflection of the biasing member 30 is changed by the amount by which the housing member 13 is inserted into the housing member 12 by the screw 13a. The basic relief pressure is set by fixing the housing member 13 with the nut 16. The piston 40 variably adjusts the relief pressure while the basic relief pressure is adjusted by the housing member 13.

[0035] Furthermore, the movable range of piston 40, i.e., the range over which the relief pressure can be variably adjusted by deflecting biasing member 30, is adjusted by housing member 15. Specifically, the movable range of second piston member 42 formed by housing member 14 and housing member 15 is set by the amount of insertion of housing member 15 into housing member 14 by screw 15a. Then, by fixing housing member 15 with nut 18, the movable range of second piston member 42 is set, and the range over which piston 40 can variably adjust the relief pressure by deflecting biasing member 30 is adjusted.

[0036] As shown in FIGS. 1 and 2 , the piston 40 includes a first piston member 41, a second piston member 42, and a third piston member 43. The first piston member 41, the second piston member 42, and the third piston member 43 are separate components. The first piston member 41 is disposed on one axial side of the piston 40 and presses the biasing member 30 in the one axial direction via a spring seat 60. The first piston member 41 has an annular structure 41b having a recessed structure 41a recessed in the other axial direction and into which the other axial end of the shaft 20e of the valve body 20 is inserted, and a protruding structure 41c having a smaller diameter than the annular structure 41b and protruding in the other axial direction from the annular structure 41b. The annular structure 41b is slidably fitted in a liquid-tight manner in the inner hole of the housing member 13. The other axial end of the shaft 20e of the valve body 20 is slidably fitted in a liquid-tight manner in the recessed structure 41a of the annular structure 41b. Convex structure 41c is slidably fitted in a liquid-tight manner into the inner hole of holding member 17. Second piston member 42 is an example of a first pilot piston member, and third piston member 43 is an example of a second pilot piston member.

[0037] The second piston member 42 is disposed on the other axial side of the piston 40, and receives pressure in one axial direction from pilot oil in a pilot chamber 51. The second piston member 42 presses and moves the first piston member 41 in one axial direction via the third piston member 43. The second piston member 42 has a larger diameter than the first piston member 41 and the third piston member 43. The second piston member 42 is slidably fitted into a recessed structure of the housing member 15 that is recessed in the other axial direction.

[0038] The third piston member 43 is disposed between the first piston member 41 and the second piston member 42 in the axial direction, and is pressed by the second piston member 42 to press and move the first piston member 41 in one axial direction. The third piston member 43 has a smaller diameter than the convex structure 41c of the first piston member 41 and the third piston member 43. The second piston member 42 is slidably fitted into the inner hole of the small-diameter structure 14a.

[0039] In the first embodiment, at least a portion of the first piston member 41 is disposed within the oil chamber 52, and the first piston member 41 divides the oil chamber 52 into a first oil chamber 52a and a second oil chamber 52b. The first piston member 41 has a first pressure-receiving surface 41d that receives pressure in one axial direction from the hydraulic oil in the first oil chamber 52a, and a second pressure-receiving surface 41e that receives pressure in the other axial direction from the hydraulic oil in the second oil chamber 52b. In the first embodiment, when viewed from the axial direction, the annular surface between the outer periphery of the annular structure 41b and the outer periphery of the convex structure 41c constitutes the first pressure-receiving surface 41d. The annular surface faces the first oil chamber 52a. The surface of the concave structure 41a that faces the second surface 20b constitutes the second pressure-receiving surface 41e. The opposing surface of the concave structure 41a faces the second oil chamber 52b. The opposing surface of the recessed structure 41a is the surface of the recessed structure 41a defined by the diameter d2, and in the first embodiment, is the bottom surface of the recessed structure 41a.

[0040] The first oil chamber 52a is disposed radially outward from the annular structure 41b and is defined by the annular structure 41b, the retaining member 17, and the housing member 13. The second oil chamber 52b is disposed radially inward from the annular structure 41b and is defined by the recessed structure 41a and the other axial end of the shaft 20e of the valve body 20. The first piston member 41 has a communication hole 41f connecting the first oil chamber 52a and the second oil chamber 52b. The communication hole 41f is formed in the annular structure 41b and penetrates the annular structure 41b in the radial direction. The inlet pressure of the relief valve 100 is introduced into the second oil chamber 52b from the inlet flow passage 101a via the through passage 20c. The inlet pressure of the relief valve 100 is introduced into the first oil chamber 52a from the second oil chamber 52b via the communication hole 41f.

[0041] In the first embodiment, the pressure-receiving area of ​​the first pressure-receiving surface 41d and the pressure-receiving area of ​​the second pressure-receiving surface 41e are equal to each other in the first piston member 41. In the present embodiment, the pressure-receiving area of ​​the first pressure-receiving surface 41d and the pressure-receiving area of ​​the second pressure-receiving surface 41e being equal to each other means that the area ratio between the first pressure-receiving surface 41d and the second pressure-receiving surface 41e is between 0.9 and 1.1. When the pressure-receiving area of ​​the first pressure-receiving surface 41d and the pressure-receiving area of ​​the second pressure-receiving surface 41e are equal to each other, the effective pressure-receiving area of ​​the first piston member 41 formed by the first pressure-receiving surface 41d and the second pressure-receiving surface 41e is zero or close to zero. In this case, the axial force acting on the first piston member 41 due to the pressure of the hydraulic oil can be suppressed.

[0042] This point will be explained using mathematical formulas. Because the inlet pressure of the relief valve 100 acts on the first oil chamber 52a, the force acting on the first pressure-receiving surface 41d due to the pressure of the hydraulic oil in the first oil chamber 52a is expressed by the following formula (2). Because the inlet pressure of the relief valve 100 acts on the second oil chamber 52b, the force acting on the second pressure-receiving surface 41e due to the pressure of the hydraulic oil in the second oil chamber 52b is expressed by the following formula (3). When one axial direction is defined as the positive direction, the total force acting on the first piston member 41 due to the pressure of the hydraulic oil is expressed by formula (4). When the pressure-receiving area of ​​the first pressure-receiving surface 41d and the pressure-receiving area of ​​the second pressure-receiving surface 41e are equal, the effective pressure-receiving area is zero or close to zero, as expressed by the following formula (5), and therefore the force acting on the first piston member 41 due to the pressure of the hydraulic oil can be suppressed. The inner diameter d2 of the annular structure 41b, the outer diameter d3 of the annular structure 41b, and the diameter d4 of the convex structure 41c are set so as to suppress the influence of the pressure of the hydraulic oil acting on the first piston member 41. (d3 2 -d4 2 )×π / 4×PP (2) d2 2 ×π / 4×PP (3) (d3 2 -d4 2 )×π / 4×PP-d2 2 ×π / 4×PP=(d3 2 -d4 2 -d2 2 )×π / 4×PP (4) A2=(d3 2 -d4 2 -d2 2 )×π / 4≒0 (5) where: d2: inner diameter of the annular structure 41b d3: outer diameter of the annular structure 41b d4: diameter of the convex structure 41c PP: Inlet pressure of relief valve 100 A2: Effective pressure receiving area of ​​the first piston member 41 with respect to the inlet pressure of the relief valve 100 is.

[0043] In the first embodiment, the first piston member 41 has a third pressure-receiving surface 41g that receives pressure in one axial direction from the hydraulic oil in the backpressure chamber 54 and a fourth pressure-receiving surface 41h that receives pressure in the other axial direction from the hydraulic oil in the biasing member chamber 53. In the first embodiment, when viewed from the axial direction, the other axial surface of the convex structure 41c constitutes the third pressure-receiving surface 41g. The other axial surface of the convex structure 41c faces the backpressure chamber 54. Note that an oil passage such as a slit is formed in the other axial surface of the convex structure 41c and in one axial surface of the third piston member 43, so that the backpressure of the hydraulic oil in the backpressure chamber 54 acts on each of these surfaces. In addition, the one axial surface of the annular structure 41b constitutes the fourth pressure-receiving surface 41h. The one axial surface of the annular structure 41b receives the backpressure of the hydraulic oil in the biasing member chamber 53 via the spring seat 60.

[0044] In the first embodiment, the pressure-receiving area of ​​the third pressure-receiving surface 41g and the pressure-receiving area of ​​the fourth pressure-receiving surface 41h are equal to each other in the first piston member 41. In the present embodiment, the pressure-receiving area of ​​the third pressure-receiving surface 41g and the pressure-receiving area of ​​the fourth pressure-receiving surface 41h being equal to each other means that the area ratio between the third pressure-receiving surface 41g and the fourth pressure-receiving surface 41h is between 0.9 and 1.1. When the pressure-receiving area of ​​the third pressure-receiving surface 41g and the pressure-receiving area of ​​the fourth pressure-receiving surface 41h are equal to each other, the effective pressure-receiving area of ​​the first piston member 41 formed by the third pressure-receiving surface 41g and the fourth pressure-receiving surface 41h is zero or close to zero. In this case, the axial force acting on the first piston member 41 due to the pressure of the hydraulic oil can be suppressed.

[0045] This point will be explained using mathematical formulas. Because the back pressure of the relief valve 100 acts on the back pressure chamber 54, the force acting on the third pressure-receiving surface 41g due to the pressure of the hydraulic oil in the back pressure chamber 54 is expressed by the following formula (6). Furthermore, because the back pressure of the relief valve 100 acts on the biasing member chamber 53, the force acting on the fourth pressure-receiving surface 41h due to the back pressure of the hydraulic oil in the biasing member chamber 53 is expressed by the following formula (7). When the other axial direction is the positive direction, the total force acting on the first piston member 41 due to the back pressure of the hydraulic oil is expressed by formula (8). Furthermore, when the pressure-receiving area of ​​the third pressure-receiving surface 41g and the pressure-receiving area of ​​the fourth pressure-receiving surface 41h are equal, the effective pressure-receiving area is zero or close to zero, as expressed by the following formula (9), and therefore the force acting on the first piston member 41 due to the back pressure of the hydraulic oil can be suppressed. The inner diameter d2 of the annular structure 41b, the outer diameter d3 of the annular structure 41b, and the diameter d4 of the convex structure 41c are set so as to suppress the influence of the back pressure of the hydraulic oil acting on the first piston member 41. d4 2 ×π / 4×PR (6) (d3 2 -d2 2 )×π / 4×PR (7) (d3 2 -d2 2 )×π / 4×PR-d4 2 ×π / 4×PR=(d3 2 -d2 2 -d4 2 )×π / 4×PR (8) A3=(d3 2 -d2 2 -d4 2 )×π / 4≒0 (9) where: d2: inner diameter of the annular structure 41b d3: outer diameter of the annular structure 41b d4: diameter of the convex structure 41c PR: Back pressure of relief valve 100 A3: Effective pressure receiving area of ​​the first piston member 41 against the back pressure of the relief valve 100 is.

[0046] Moreover, in the first embodiment, the second piston member 42 has an atmosphere open surface 42a that faces the atmosphere open chamber 55 on one side in the axial direction, and a pilot pressure receiving surface 42b that faces the pilot chamber 51 on the other side in the axial direction. The atmosphere open surface 42a is a surface on one side in the axial direction of the second piston member 42, and is in contact with the atmosphere inside the atmosphere open chamber 55. The atmosphere open surface 42a does not receive pressure in the other side in the axial direction from the hydraulic oil. The pilot pressure receiving surface 42b is a surface on the other side in the axial direction of the second piston member 42, and receives pressure in one side in the axial direction from the pilot oil in the pilot chamber 51. Since the atmosphere open surface 42a faces the atmosphere open chamber 55, the second piston member 42 is configured to be less likely to be pushed back by the back pressure of the relief valve 100 that counteracts the pressure of the pilot oil.

[0047] Moreover, in the first embodiment, one axial surface of the third piston member 43 faces the back pressure chamber 54. The one axial surface of the third piston member 43 receives back pressure in the other axial direction from the hydraulic oil in the back pressure chamber 54. The area of ​​the one axial surface of the third piston member 43 is smaller than the area of ​​the pilot pressure receiving surface 42b. That is, the relationship between the area of ​​the one axial surface of the third piston member 43 and the area of ​​the pilot pressure receiving surface 42b is expressed by the following equation (10). The diameter d6 of the second piston member 42 and the diameter d5 of the third piston member 43 are set so as to reduce the effect of the back pressure acting on the second piston member 42. d5 2 ×π / 4 <d6 2 ×π / 4 (10) where: d5: diameter of the third piston member 43 d6: diameter of the second piston member 42 is.

[0048] Furthermore, the area of ​​the pilot pressure receiving surface 42b of the second piston member 42 can be changed by changing the diameter d6. That is, the area of ​​the pilot pressure receiving surface 42b of the relief valve 100 can be changed by changing the second piston member 42 to a second piston member 42 with a different diameter d6. This makes it possible to change the slope between the pilot oil pressure and the relief pressure, and therefore makes it possible to configure a relief valve 100 in which the slope between the pilot oil pressure and the relief pressure varies.

[0049] [Effects of the first embodiment] In the first embodiment, the following effects can be obtained.

[0050] In the first embodiment, as described above, the relief valve 100 includes the housing 10 in which the pilot chamber 51 and the oil chamber 52 are formed, the valve element 20 communicating or blocking an inflow passage 101a through which the hydraulic oil flows and an outflow passage 101b through which the hydraulic oil flows, the valve element 20 including a first surface 20a facing the inflow passage 101a, a second surface 20b facing the oil chamber 52, and a through passage 20c connecting the first surface 20a and the second surface 20b, the biasing member 30 biasing the valve element 20 toward the inflow passage 101a, and the pilot chamber 51. and a piston (40) including a first piston member (41) that presses the biasing member (30) with the pressure of pilot oil in the first piston member (41) and changes the amount of deflection of the biasing member (30), at least a portion of the first piston member (41) being disposed within the oil chamber (52) and dividing the oil chamber (52) into a first oil chamber (52a) and a second oil chamber (52b), and the first piston member (41) has a first pressure-receiving surface (41d) that receives pressure in one axial direction from the hydraulic oil in the first oil chamber (52a) and a second pressure-receiving surface (41e) that receives pressure in the other axial direction from the hydraulic oil in the second oil chamber (52b).

[0051] With the above configuration, the force acting on the first piston member 41 in one axial direction due to the pressure of the hydraulic oil can be made to counteract the force acting on the first piston member 41 in the other axial direction due to the pressure of the hydraulic oil, thereby reducing the force acting in the other axial direction counteracting the pressure of the pilot oil. As a result, the pilot oil pressure does not need to be high enough to push back all of the force acting on the first piston member 41 in the other axial direction due to the pressure of the hydraulic oil. This makes it possible to adjust the relief pressure while suppressing the pressure required as the pilot pressure.

[0052] In the first embodiment, as described above, the relief valve 100 includes the housing 10 in which the pilot chamber 51, the oil chamber 52, and the open-to-atmosphere chamber 55 are formed, and the valve element 20 which connects or blocks the inflow passage 101a through which the hydraulic oil flows and the outflow passage 101b through which the hydraulic oil flows, and has a first surface 20a facing the inflow passage 101a, a second surface 20b facing the oil chamber 52, and a through passage 20c connecting the first surface 20a and the second surface 20b. a valve body (20) including a second piston member (42) that changes the amount of deflection of the first piston member (30) by the pressure of pilot oil in the pilot chamber, a valve body (20) including a valve member (20) that includes a second piston member (42) that changes the amount of deflection of the first piston member (30) by the pressure of pilot oil in the pilot chamber, and a pilot pressure receiving surface (42b) on the other axial side of the second piston member (42) faces the pilot chamber (51), and an atmosphere open surface (42a) on one axial side of the second piston member (42) faces the atmosphere open chamber (55).

[0053] With the above configuration, unlike when the atmosphere-opened surface 42a on one axial side of the second piston member 42 faces the back pressure chamber 54, the atmosphere-opened surface 42a on one axial side of the second piston member 42 is open to the atmosphere. This prevents a force acting on the atmosphere-opened surface 42a on one axial side of the second piston member 42 in the other axial direction due to back pressure, which counteracts the pressure of the pilot oil. As a result, the relief pressure can be adjusted while suppressing the pressure required as the pilot pressure. Furthermore, since the influence of back pressure can be reduced, the relief pressure can be accurately adjusted even when the back pressure fluctuates significantly. Furthermore, when the relief valve 100 is used on a rotating body that is prone to back pressure fluctuations during rotation, being able to reduce the influence of back pressure is extremely effective.

[0054] Furthermore, in the first embodiment, as described above, the first piston member 41 has an annular structure 41b having a concave structure 41a that is recessed in the other axial direction and into which the other axial end of the valve body 20 is inserted, and a convex structure 41c that is smaller in diameter than the annular structure 41b and protrudes in the other axial direction from the annular structure 41b, and when viewed from the axial direction, the annular surface between the outer periphery of the annular structure 41b and the outer periphery of the convex structure 41c constitutes the first pressure-receiving surface 41d, and the surface of the concave structure 41a that faces the second surface 20b constitutes the second pressure-receiving surface 41e. This makes it possible to form the first pressure-receiving surface 41d and the second pressure-receiving surface 41e with a simple structure, thereby realizing a configuration that adjusts the relief pressure while suppressing the pressure required as the pilot pressure with a simple structure.

[0055] In the first embodiment, as described above, the first piston member 41 has a communication hole 41f that connects the first oil chamber 52a and the second oil chamber 52b. This allows the first oil chamber 52a and the second oil chamber 52b to be connected by the communication hole 41f, making it possible to easily guide the hydraulic oil to the first oil chamber 52a and the second oil chamber 52b. Furthermore, since the communication hole 41f is formed in the first piston member 41, the structure can be made less complicated than when a passage for guiding the hydraulic oil is formed in the housing 10 or the like.

[0056] Furthermore, in the first embodiment, as described above, the pressure-receiving area of ​​the first pressure-receiving surface 41d and the pressure-receiving area of ​​the second pressure-receiving surface 41e in the first piston member 41 are equal. This allows the force acting on the first piston member 41 in one axial direction due to the pressure of the hydraulic oil and the force acting on the first piston member 41 in the other axial direction due to the pressure of the hydraulic oil to be offset, thereby suppressing the force acting in the other axial direction that counteracts the pressure of the pilot oil. As a result, the pilot pressure required to adjust the relief pressure can be suppressed.

[0057] Furthermore, in the first embodiment, as described above, the housing 10 is provided with a biasing member chamber 53 connected to the outflow passage 101b and a backpressure chamber 54 connected to the outflow passage 101b. The first piston member 41 has a third pressure-receiving surface 41g that receives pressure (back pressure) in one axial direction from the hydraulic oil in the backpressure chamber 54 and a fourth pressure-receiving surface 41h that receives pressure (back pressure) in the other axial direction from the hydraulic oil in the biasing member chamber 53. This achieves the same effect with respect to the hydraulic oil backpressure as with the hydraulic oil pressure in the oil chamber 52. That is, the force acting on the first piston member 41 in one axial direction due to the hydraulic oil backpressure and the force acting on the first piston member 41 in the other axial direction due to the hydraulic oil backpressure can be made to counteract each other, thereby reducing the force acting in the other axial direction counteracting the pilot oil pressure. As a result, the relief pressure can be adjusted while further suppressing the pilot pressure. Furthermore, since the influence of the back pressure acting on the first piston member 41 can be reduced, the relief pressure can be adjusted with high precision even when the back pressure fluctuates greatly.

[0058] Furthermore, in the first embodiment, as described above, the first piston member 41 has an annular structure 41b having a concave structure 41a that is recessed in the other axial direction and into which the other axial end of the valve body 20 is inserted, and a convex structure 41c that is smaller in diameter than the annular structure 41b and protrudes in the other axial direction from the annular structure 41b, with the other axial surface of the convex structure 41c forming the third pressure-receiving surface 41g and the one axial surface of the annular structure 41b forming the fourth pressure-receiving surface 41h. This makes it possible to form the third pressure-receiving surface 41g and the fourth pressure-receiving surface 41h with a simple structure, thereby realizing a configuration that adjusts the relief pressure while suppressing the pressure required as the pilot pressure with a simple structure.

[0059] Furthermore, in the first embodiment, as described above, the pressure-receiving area of ​​the third pressure-receiving surface 41g and the pressure-receiving area of ​​the fourth pressure-receiving surface 41h in the first piston member 41 are equal. This allows the force acting on the first piston member 41 in one axial direction due to the back pressure of the hydraulic oil and the force acting on the first piston member 41 in the other axial direction due to the back pressure of the hydraulic oil to be offset, thereby suppressing the force acting in the other axial direction that opposes the pressure of the pilot oil. As a result, the relief pressure can be adjusted while further suppressing the pilot pressure, and the relief pressure can be adjusted more accurately without being dependent on fluctuations in the back pressure.

[0060] Furthermore, in the first embodiment, as described above, the piston 40 includes the third piston member 43 disposed between the first piston member 41 and the second piston member 42, and a back pressure chamber 54 facing one axial surface of the third piston member 43 and connected to the outflow passage 101b is formed inside the housing 10, and the area of ​​the one axial surface of the third piston member 43 is smaller than the area of ​​the pilot pressure receiving surface 42b. As a result, because the area of ​​the one axial surface of the third piston member 43 is smaller than the area of ​​the pilot pressure receiving surface 42b, even when back pressure acts in the other axial direction against the pressure of the pilot oil, the effect of the back pressure acting on the one axial surface of the third piston member 43 can be reduced.

[0061] [Second embodiment] A relief valve 200 according to a second embodiment will be described with reference to Figures 3 and 4. Note that the same components as those in the first embodiment will be given the same reference numerals and detailed description thereof will be omitted.

[0062] As shown in FIGS. 3 and 4, a relief valve 200 according to the second embodiment includes a first piston member 141 instead of the first piston member 41 of the first embodiment. In the second embodiment, the first piston member 141 divides the oil chamber 52 into a first oil chamber 152a and two second oil chambers 152b and 152c. The first piston member 141 also includes a first pressure-receiving surface 141d that receives pressure in one axial direction from the hydraulic oil in the first oil chamber 152a, and a second pressure-receiving surface 141e that receives pressure in the other axial direction from the hydraulic oil in the second oil chambers 152b and 152c. The first piston member 141 also includes an annular structure 41b, a convex structure 41c, and a flange 141i. The flange 141i has a larger diameter than the annular structure 41b and protrudes radially outward from the annular structure 41b. The flange 141i is slidably fitted into the inner hole of the housing member 13 in a liquid-tight manner.

[0063] The first oil chamber 152a is located on the other axial side of the flange 141i, and is defined by the flange 141i, the retaining member 17, and the housing member 13. The second oil chamber 152b is located radially inward of the annular structure 41b, and is defined by the recessed structure 41a and the other axial end of the shaft 20e of the valve body 20. The second oil chamber 152c is located radially outward of the annular structure 41b and on one axial side of the flange 141i, and is defined by the annular structure 41b, the flange 141i, and the housing member 13.

[0064] In the second embodiment, the first piston member 141 has a first communication hole 141j connecting the second oil chamber 152b and the second oil chamber 152c, and a second communication hole 141k connecting the first oil chamber 152a and the second oil chamber 152b. The first communication hole 141j is formed in the annular structure 41b and penetrates the annular structure 41b in the radial direction. The second communication hole 141k is formed in the convex structure 41c and penetrates the convex structure 41c in the radial direction. Hydraulic oil flows into the second oil chamber 152b from the inlet flow passage 101a via the through-passage 20c. Hydraulic oil flows into the second oil chamber 152c from the second oil chamber 152b via the first communication hole 141j. Hydraulic oil flows into the first oil chamber 152a from the second oil chamber 152b via the second communication hole 141k.

[0065] In the second embodiment, the first oil chamber 152a faces an annular surface between the outer periphery of the annular structure 41b and the outer periphery of the convex structure 41c when viewed in the axial direction, and faces the other axial surface of the flange 141i. The second oil chamber 152b faces a surface of the concave structure 41a that faces the second surface 20b. The second oil chamber 152c faces one axial surface of the flange 141i radially outward from the annular structure 41b. In the second embodiment, the annular surface and the other axial surface of the flange 141i form a first pressure-receiving surface 141d. The surface of the concave structure 41a that faces the second surface 20b and one axial surface of the flange 141i form a second pressure-receiving surface 141e.

[0066] In addition, in a range R (see FIG. 4) radially outward from the annular structure 41b of the flange 141i, the pressure of the hydraulic oil acts from both sides in the axial direction, and therefore the force due to the pressure of the hydraulic oil is canceled. Therefore, in the first piston member 141 as well, the pressure-receiving area of ​​the first pressure-receiving surface 141d and the pressure-receiving area of ​​the second pressure-receiving surface 141e are equal, similar to the first piston member 41 of the first embodiment.

[0067] The other configurations of the second embodiment are the same as those of the first embodiment.

[0068] [Effects of the second embodiment] In the second embodiment, the following effects can be obtained.

[0069] In the second embodiment, as described above, the first piston member 141 has a first pressure-receiving surface 141d and a second pressure-receiving surface 141e. This makes it possible to adjust the relief pressure while suppressing the pressure required as the pilot pressure, similar to the first embodiment. Also, in the second embodiment, as described above, the pilot pressure-receiving surface 42b on the other axial side of the second piston member 42 faces the pilot chamber 51, and the atmosphere-opened surface 42a on one axial side of the second piston member 42 faces the atmosphere-opened chamber 55. This makes it possible to adjust the relief pressure while suppressing the pressure required as the pilot pressure, similar to the first embodiment, and also makes it possible to adjust the relief pressure with high accuracy even when the back pressure fluctuates greatly.

[0070] Furthermore, in the second embodiment, as described above, the first piston member 141 divides the oil chamber 52 into a first oil chamber 152a and two second oil chambers 152b, 152c, and the first piston member 141 has a larger diameter than the annular structure 41b and further includes a flange 141i protruding outward from the annular structure 41b, a first communicating hole 141j connecting the second oil chamber 152b and the second oil chamber 152c, and a second communicating hole 141k connecting the first oil chamber 152a and the second oil chamber 152b, and the first oil chamber 152a faces the annular surface and the other axial surface of the flange 141i, the second oil chamber 152b faces the surface opposite the second surface 20b in the recessed structure 41a, and the second oil chamber 152c faces one axial surface of the flange 141i outside the annular structure 41b. As a result, the first pressure-receiving surface 141d is formed by the annular surface and the other axial surface of the flange 141i, and the second pressure-receiving surface 141e is formed by the surface facing the second surface 20b in the recessed structure 41a and one axial surface of the flange 141i, so that the first pressure-receiving surface 141d and the second pressure-receiving surface 141e can be formed with a simple structure.

[0071] The other effects of the second embodiment are the same as those of the first embodiment.

[0072] [Third embodiment] A relief valve 300 according to the third embodiment will be described with reference to Fig. 5. Note that the same components as those in the first and second embodiments will be given the same reference numerals and detailed description thereof will be omitted.

[0073] 5, in a relief valve 300 according to the third embodiment, a pilot port 101c is formed in the valve block 101, unlike the first and second embodiments in which the pilot port 15b is formed in the housing member 15. In the third embodiment, the pressure of the pilot oil is introduced from the pilot port 101c into the pilot chamber 51 via the passage 12c of the housing member 12, the passage 13c of the housing member 13, the passage 17b of the holding member 17, the passage 243a of the third piston member 243, and the passage 242c of the second piston member 242. In the relief valve 300 of the third embodiment, the pilot port 101c is formed in the valve block 101, and therefore, unlike the case in which the pilot port 15b is formed in the housing member 15, it is possible to reduce the piping for guiding the pilot oil to the pilot port 15b.

[0074] In the third embodiment, the relief valve 300 includes a second piston member 242 and a third piston member 243 instead of the second piston member 42 and the third piston member 43 of the first and second embodiments. The second piston member 242 and the third piston member 243 are integrally configured as a single part. Passages 242c and 243b that guide pilot oil to the pilot chamber 51 are formed inside the second piston member 242 and the third piston member 243. In the third embodiment, a back pressure chamber 54 is formed inside the retaining member 17. The second piston member 242 is an example of a first pilot piston member. The third piston member 243 is an example of a second pilot piston member.

[0075] The other configurations of the third embodiment are the same as those of the first and second embodiments.

[0076] [Effects of the third embodiment] In the third embodiment, the following effects can be obtained.

[0077] In the third embodiment, as described above, the first piston member 141 has a first pressure-receiving surface 141d and a second pressure-receiving surface 141e. As a result, similar to the first and second embodiments, the relief pressure can be adjusted while suppressing the pressure required as the pilot pressure. Furthermore, in the second embodiment, as described above, the pilot pressure-receiving surface 42b on the other axial side of the second piston member 42 faces the pilot chamber 51, and the atmosphere-opened surface 42a on one axial side of the second piston member 42 faces the atmosphere-opened chamber 55. As a result, similar to the first and second embodiments, the relief pressure can be adjusted while suppressing the pressure required as the pilot pressure, and the relief pressure can be adjusted accurately even when the back pressure fluctuates greatly.

[0078] The other effects of the third embodiment are the same as those of the first and second embodiments.

[0079] [Variations] It should be noted that the embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present disclosure is defined by the claims rather than the description of the above embodiments, and further includes all modifications (variations) within the meaning and scope equivalent to the claims.

[0080] For example, in the first to third embodiments described above, an example was shown in which the effective pressure-receiving area of ​​the first piston member formed by the first pressure-receiving surface and the second pressure-receiving surface was zero or near zero, but the present disclosure is not limited to this. In the present disclosure, the effective pressure-receiving area of ​​the first piston member formed by the first pressure-receiving surface and the second pressure-receiving surface does not have to be zero or near zero. For example, in a work machine in which the pilot oil pressure is relatively high, even if the effective pressure-receiving area of ​​the first piston member formed by the first pressure-receiving surface and the second pressure-receiving surface is not as small as zero or near zero (i.e., even if the pressure-receiving area of ​​the first pressure-receiving surface and the pressure-receiving area of ​​the second pressure-receiving surface are not equal), the cancellation effect of the force due to the pressure of the hydraulic oil in the first piston member can be sufficiently exhibited. In this case, for example, the pressure-receiving area of ​​the first pressure-receiving surface and the pressure-receiving area of ​​the second pressure-receiving surface may differ by up to 30%.

[0081] Furthermore, in the above-described first to third embodiments, an example was shown in which the effective pressure-receiving area of ​​the first piston member formed by the third pressure-receiving surface and the fourth pressure-receiving surface was zero or near zero, but the present disclosure is not limited thereto. In the present disclosure, the effective pressure-receiving area of ​​the first piston member formed by the third pressure-receiving surface and the fourth pressure-receiving surface does not have to be zero or near zero. For example, in a work machine in which the pilot oil pressure is relatively high, even if the effective pressure-receiving area of ​​the third piston member formed by the third pressure-receiving surface and the fourth pressure-receiving surface is not as small as zero or near zero (i.e., even if the pressure-receiving area of ​​the third pressure-receiving surface and the pressure-receiving area of ​​the fourth pressure-receiving surface are not equal), the effect of canceling the force due to the back pressure of the hydraulic oil in the third piston member can be sufficiently exhibited. In this case, for example, the pressure-receiving area of ​​the third pressure-receiving surface and the pressure-receiving area of ​​the fourth pressure-receiving surface may differ by up to 30%.

[0082] In addition, although the first embodiment described above illustrates an example in which the first piston member includes an annular structure and a convex structure, and the second and third embodiments described examples in which the first piston member includes an annular structure, a convex structure, and a flange, the present disclosure is not limited thereto. In the present disclosure, the first piston member may have any shape as long as it has a first pressure-receiving surface and a second pressure-receiving surface.

[0083] In addition, in the first embodiment, an example was shown in which the first piston member, the second piston member, and the third piston member were separate members, and in the second and third embodiments, an example was shown in which the second piston member and the third piston member were an integrated member, but the present disclosure is not limited to this. In the present disclosure, the first piston member and the second piston member may be an integrated member, or the first piston member, the second piston member, and the third piston member may be an integrated member.

[0084] In addition, in the first to third embodiments, an example was shown in which one axial surface of the second piston member faces the open-to-atmosphere chamber, but the present disclosure is not limited to this. In the present disclosure, one axial surface of the second piston member may face the back pressure chamber.

[0085] Furthermore, in the first to third embodiments, an example was shown in which the recessed structure had the same diameter as diameter d2 in the second oil chamber portion, but the present disclosure is not limited to this. In the present disclosure, the recessed structure may have a diameter larger than diameter d2 in the second oil chamber portion. In this case, the pressure of the hydraulic oil acts on both sides in the axial direction in the portion of the recessed structure radially outward of diameter d2, thereby canceling the force due to the pressure of the hydraulic oil. Therefore, even in a first piston member having a recessed structure with a diameter larger than diameter d2 in the second oil chamber portion, the pressure-receiving area of ​​the first pressure-receiving surface and the pressure-receiving area of ​​the second pressure-receiving surface are equal, as in the first piston members of the first to third embodiments.

[0086] Furthermore, the first pressure-receiving surface and the second pressure-receiving surface shown in the first to third embodiments are merely examples, and the shapes and arrangements of the first pressure-receiving surface and the second pressure-receiving surface are not limited to these and can be modified as desired. The first pressure-receiving surface may be any surface that receives pressure in one axial direction from the hydraulic oil in the first oil chamber, and may include various surfaces such as a surface perpendicular to the axial direction, a surface inclined with respect to the axial direction, a stepped surface, and a curved surface. The first pressure-receiving surface may also be a combination of these surfaces. The second pressure-receiving surface may be any surface that receives pressure in the other axial direction from the hydraulic oil in the second oil chamber, and may include various surfaces such as a surface perpendicular to the axial direction, a surface inclined with respect to the axial direction, a stepped surface, and a curved surface. The second pressure-receiving surface may also be a combination of these surfaces.

[0087] Furthermore, the third pressure-receiving surface and the fourth pressure-receiving surface shown in the first to third embodiments are merely examples, and the shapes and arrangements of the third pressure-receiving surface and the fourth pressure-receiving surface are not limited to these and can be modified as desired. The third pressure-receiving surface may be any surface that receives pressure in one axial direction from the hydraulic oil in the back pressure chamber, and may include various surfaces such as a surface perpendicular to the axial direction, a surface inclined with respect to the axial direction, a stepped surface, and a curved surface. The third pressure-receiving surface may also be a combination of these surfaces. The fourth pressure-receiving surface may be any surface that receives pressure in the other axial direction from the hydraulic oil in the biasing member chamber, and may include various surfaces such as a surface perpendicular to the axial direction, a surface inclined with respect to the axial direction, a stepped surface, and a curved surface. The fourth pressure-receiving surface may also be a combination of these surfaces. [Explanation of symbols]

[0088] 10. Housing 20 Valve body 20a Page 1 20b 2nd side 20c through passage 30 biasing member 40 pistons 41, 141 First piston member 41a Concave structure 41b Ring structure 41c Convex structure 41d, 141d First pressure surface 41e, 141e Second pressure surface 41f communication hole 41g 3rd pressure surface 41h 4th pressure surface 42, 242 Second piston member (first pilot piston member) 42a Open to the atmosphere 42b Pilot pressure receiving surface 43, 243 Third piston member (second pilot piston member) 51 Pilot's Room 52 Oil room 52a, 152a 1st oil chamber 52b, 152b, 152c 2nd oil chamber 53 biasing member chamber 54 Back pressure chamber 55 Open-air chamber 100, 200, 300 relief valve 101a Inlet channel 101b Outlet channel 141i flange 141j 1st communication hole 141k 2nd communication hole

Claims

1. a housing having a pilot chamber and an oil chamber formed therein; a valve body that connects or blocks an inflow passage through which hydraulic oil flows in and an outflow passage through which hydraulic oil flows out, the valve body including a first surface facing the inflow passage, a second surface facing the oil chamber, and a through passage connecting the first surface and the second surface; a biasing member that biases the valve body toward the inflow channel; a piston including a first piston member that presses the biasing member by the pressure of the pilot oil in the pilot chamber and changes the deflection amount of the biasing member, the first piston member is at least partially disposed within the oil chamber and divides the oil chamber into a first oil chamber and a second oil chamber; a relief valve, the first piston member having a first pressure-receiving surface that receives pressure in one axial direction from the hydraulic oil in the first oil chamber, and a second pressure-receiving surface that receives pressure in the other axial direction from the hydraulic oil in the second oil chamber.

2. The first piston member is an annular structure having a recessed structure recessed in the other axial direction and into which the other axial end of the valve body is inserted; a convex structure having a smaller diameter than the annular structure and protruding from the annular structure in the other axial direction; and When viewed from the axial direction, an annular surface between an outer periphery of the annular structure and an outer periphery of the convex structure constitutes the first pressure-receiving surface, The relief valve according to claim 1 , wherein a surface of the recessed structure facing the second surface constitutes the second pressure-receiving surface.

3. The relief valve according to claim 1 or 2, wherein the first piston member has a communication hole connecting the first oil chamber and the second oil chamber.

4. the first piston member divides the oil chamber into the first oil chamber and two second oil chambers, The first piston member is a flange having a diameter larger than that of the annular structure and projecting outwardly from the annular structure; a first communication hole connecting one side of the second oil chamber and the other side of the second oil chamber; a second communication hole connecting the first oil chamber and one of the second oil chambers; and the first oil chamber faces the annular surface and the other axial surface of the flange, one side of the second oil chamber faces a surface of the recessed structure opposite to the second surface, The relief valve according to claim 2 , wherein the other of the second oil chambers faces one axial surface of the flange outside the annular structure.

5. 5. The relief valve according to claim 1, wherein in the first piston member, a pressure receiving area of ​​the first pressure receiving surface is equal to a pressure receiving area of ​​the second pressure receiving surface.

6. Inside the housing: a biasing member chamber connected to the outflow passage; a back pressure chamber connected to the outflow passage; is further formed, The first piston member is a third pressure receiving surface that receives pressure in one axial direction from the hydraulic oil in the back pressure chamber; a fourth pressure-receiving surface that receives pressure in the other axial direction from the hydraulic oil in the biasing member chamber; The relief valve according to any one of claims 1 to 5, comprising:

7. The first piston member is an annular structure having a recessed structure recessed in the other axial direction and into which the end of the valve body in the other axial direction is inserted; a convex structure having a smaller diameter than the annular structure and protruding from the annular structure in the other axial direction; and the other axial surface of the convex structure constitutes the third pressure-receiving surface, The relief valve according to claim 6 , wherein one axial surface of the annular structure constitutes the fourth pressure-receiving surface.

8. 8. The relief valve according to claim 6, wherein in the first piston member, a pressure receiving area of ​​the third pressure receiving surface is equal to a pressure receiving area of ​​the fourth pressure receiving surface.

9. An atmosphere-open chamber that is open to the atmosphere is further formed inside the housing, the piston further includes a second piston member disposed on the other side of the first piston member in the axial direction and pressing the first piston member to move it in the one axial direction, 9. The relief valve according to claim 1, wherein the second piston member has an atmosphere open surface facing the atmosphere open chamber on one side in the axial direction, and a pilot pressure receiving surface facing the pilot chamber on the other side in the axial direction.

10. the piston further includes a third piston member disposed between the first piston member and the second piston member; a back pressure chamber is further formed inside the housing, the back pressure chamber facing one axial surface of the third piston member and connected to the outflow passage; 10. The relief valve according to claim 9, wherein an area of ​​one axial surface of the third piston member is smaller than an area of ​​the pilot pressure receiving surface.

11. a housing having a pilot chamber, an oil chamber, and an open-to-atmosphere chamber formed therein; a valve body that connects or blocks an inflow passage through which hydraulic oil flows in and an outflow passage through which hydraulic oil flows out, the valve body including a first surface facing the inflow passage, a second surface facing the oil chamber, and a through passage connecting the first surface and the second surface; a biasing member that biases the valve body toward the inflow channel; a piston including a first pilot piston member that changes the deflection amount of the biasing member by the pressure of the pilot oil in the pilot chamber, the other axial surface of the first pilot piston member faces the pilot chamber, a relief valve, wherein one axial surface of the first pilot piston member faces the atmosphere open chamber;

12. The piston further includes a second pilot piston member disposed axially on one side of the first pilot piston member, a back pressure chamber is further formed inside the housing, the back pressure chamber facing one axial surface of the second pilot piston member and connected to the outflow passage; 12. The relief valve according to claim 11, wherein an area of ​​one axial surface of the second pilot piston member is smaller than an area of ​​the other axial surface of the first pilot piston member.

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