Relief valve

Abstract

To provide a relief valve which enables reduction of a leak amount while reducing requirements related to processing accuracy of a plunger and a piston.SOLUTION: A relief valve 1 includes: a housing 11 including a valve passage 20 in which a working fluid flows; a plunger 12 which is movably housed in the housing so as to open or close the valve passage and receives inflow pressure in an opening direction in which the valve passage is opened; a differential pressure chamber 15 into which the inflow pressure of the valve passage is guided and which causes its fluid pressure to act on the plunger against the inflow pressure of the valve passage; a spring member 13 which biases the plunger in a closing direction; a piston 14 which is slidably installed on the plunger and moves in response to the fluid pressure of the differential pressure chamber to compress the spring member; and a damping chamber 16 which is connected to the differential pressure chamber and restricts movement of the piston in a compression direction in which the spring member is compressed. The piston includes a damping passage 24 connecting the differential pressure chamber with the damping chamber.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a relief valve having a pressure rise buffering function. [Background technology]

[0002] In construction machinery and the like, surge pressure occurs when braking a rotating body. In order to suppress the generation of surge pressure, a relief valve such as that disclosed in Patent Document 1 is known. In the relief valve of Patent Document 1, a damping chamber is provided to damp the stroke of a piston for buffering pressure rise. The damping chamber is connected to the inner hole of the piston via two throttles arranged in series. In the relief valve of Patent Document 1, the piston descends while discharging the working fluid in the damping chamber via the two throttles. Therefore, the flow rate of the working fluid discharged from the damping chamber is adjusted by the two throttles, so that the hydraulic pressure of the relieved working fluid can be gradually increased to the relief pressure. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Korean Patent No. 10-2151124 Summary of the Invention [Problem to be solved by the invention]

[0004] In the relief valve of Patent Document 1, the plunger and the piston are configured to be slidable against each other. This seals the gap between the plunger and the piston to prevent leakage of the hydraulic fluid. On the other hand, two throttles are formed in the plunger and the piston, respectively. The two throttles are connected via a slit formed on the outer circumferential surface of the plunger. The slit is formed so as to extend in the axial direction on the outer circumferential surface of the plunger. Therefore, the slit shortens the portion where the plunger and the piston slide against each other, that is, the seal width is shortened. Therefore, the accuracy of the clearance between the plunger and the piston is required to suppress the amount of leakage. This requires higher accuracy in machining the plunger and the piston.

[0005] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide a relief valve that can reduce the amount of leakage while satisfying requirements regarding the machining accuracy of the plunger and piston. [Means for solving the problem]

[0006] The relief valve of the present invention comprises a housing including a valve passage through which hydraulic fluid flows, a plunger movably accommodated in the housing to open and close the valve passage and receiving an inflow pressure of the valve passage in an opening direction to open the valve passage, a differential pressure chamber to which the inflow pressure of the valve passage is introduced and which causes the fluid pressure to act on the plunger against the inflow pressure of the valve passage, a spring member urging the plunger in a closing direction to close the valve passage, a piston slidably attached to the plunger and moving in response to the fluid pressure in the differential pressure chamber to compress the spring member, and a damping chamber connected to the differential pressure chamber and limiting movement of the piston in a compression direction to compress the spring member, the piston including a damping passage connecting the differential pressure chamber and the damping chamber.

[0007] According to the present invention, the piston includes a damping passage that connects the differential pressure chamber and the damping chamber. Therefore, the sliding portion where the plunger and the piston slide against each other can be made long. Therefore, the seal width between the plunger and the piston can be made long. This makes it possible to reduce the amount of leakage from between the plunger and the piston while suppressing the requirements for the machining accuracy of the plunger and the piston. Effect of the Invention

[0008] According to the present invention, it is possible to reduce the amount of leakage while reducing the requirements for machining accuracy of the plunger and piston. [Brief description of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view showing a relief valve according to a first embodiment of the present invention. [Diagram 2] 2 is an enlarged cross-sectional view showing a portion of the relief valve of FIG. 1. [Diagram 3] 2 is a graph showing a change over time in relief pressure in the relief valve of FIG. 1. [Figure 4] 3 is an enlarged cross-sectional view of the relief valve of FIG. 2, showing a state in which a piston has moved to a maximum compression position. FIG. [Diagram 5] FIG. 4 is a cross-sectional view showing a relief valve according to a second embodiment of the present invention. [Figure 6] FIG. 4 is a cross-sectional view showing a relief valve according to a third embodiment of the present invention. [Figure 7] FIG. 11 is a cross-sectional view showing a relief valve according to a fourth embodiment of the present invention. [Figure 8] FIG. 11 is a cross-sectional view showing a relief valve according to another embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, the relief valves 1, 1A to 1C according to the first to fourth embodiments of the present invention will be described with reference to the drawings described above. The concept of direction used in the following description is used for convenience in the description and does not limit the orientation of the configuration of the invention to that direction. Furthermore, the relief valve 1 described below is merely one embodiment of the present invention. Therefore, the present invention is not limited to the embodiments, and additions, deletions, and modifications are possible within the scope of the invention.

[0011] [First embodiment] The relief valve 1 shown in FIG. 1 is provided in, for example, a construction machine. The relief valve 1 brakes the torque of a hydraulic motor that drives a revolving body or the like in the construction machine. More specifically, the relief valve 1 brakes the torque of the hydraulic motor by maintaining the hydraulic pressure in a fluid passage (not shown) at or below a predetermined relief pressure. The relief valve 1 having such a function is mounted, for example, on a valve block 2. The valve block 2 has an inflow passage 2a, an outflow passage 2b, and an insertion hole 2c. The inflow passage 2a and the outflow passage 2b are connected to a fluid passage and a tank (both not shown), respectively. The inflow passage 2a and the outflow passage 2b are connected to the insertion hole 2c, respectively. The insertion hole 2c is formed along a predetermined axis L1, and the relief valve 1 is inserted into the insertion hole 2c. In this embodiment, the relief valve 1 is screwed into the insertion hole 2c.

[0012] The relief valve 1 is formed along a predetermined axis L1. When the hydraulic pressure in an inflow passage 2a connected to the hydraulic passage reaches a relief pressure, the relief valve 1 guides the hydraulic fluid in the hydraulic passage to an outflow passage 2b and discharges it to a tank. More specifically, the relief valve 1 mainly includes a housing 11, a plunger 12, a spring member 13, a piston 14, a differential pressure chamber 15, and a damping chamber 16. In this embodiment, the relief valve 1 further includes a sleeve 17.

[0013] The housing 11 also includes a valve passage 20 through which the hydraulic fluid flows. The housing 11 is formed, for example, in a cylindrical shape with a bottom. The housing 11 is screwed into the insertion hole 2c with its opening facing the inflow passage 2a. The valve passage 20 is connected to the inflow passage 2a and the outflow passage 2b, and the hydraulic fluid flowing in from the inflow passage 2a passes through the valve passage 20 and is discharged to the outflow passage 2b. More specifically, the housing 11 includes a housing main body 21, a cover 22, and a seat member 23.

[0014] The housing body 21 is formed in a generally cylindrical shape. The housing body 21 is screwed into the insertion hole 2c so that the opening on one axial side faces the inflow passage 2a. The axial direction is the direction in which the axis L1 extends. The housing body 21 also has a plurality of communication passages 21a on the outer circumferential surface on one axial side. The communication passages 21a are connected to an annular passage 21c, which will be described in detail later. The communication passages 21a also penetrate the housing body 21 in the radial direction, and communicate between the annular passage 21c and the outflow passage 2b. The cover 22 is screwed into the opening on the other axial side of the housing body 21. This blocks the opening on the other axial side of the housing body 21.

[0015] The seat member 23 is inserted into the opening on one axial side. The seat member 23 is formed, for example, in an annular shape. The seat member 23 has a flange 23a on one axial side. The seat member 23 is fixed to the valve block 2 by sandwiching the flange 23a between the housing body 21 and the valve block 2.

[0016] The inner hole 23b of the seat member 23 is connected to the inflow passage 2a and forms a part of the valve passage 20, as described later in detail. That is, the hydraulic fluid flows into the inner hole 23b of the seat member 23 from the inflow passage 2a. The seat member 23 is also formed with a valve seat 23d around the valve port 23c. The plunger 12, which will be described later in detail, can be seated on the valve seat 23d. The valve port 23c is an opening on the other axial side of the inner hole 23b of the seat member 23.

[0017] The plunger 12 is movably accommodated in the housing 11 so as to open and close the valve passage 20. More specifically, the plunger 12 opens the valve passage 20 by moving away from the valve seat 23d, and closes the valve passage 20 by sitting on the valve seat 23d. The plunger 12 receives an inflow pressure, which is the hydraulic pressure of the working fluid flowing into the valve passage 20, in an opening direction. Here, the opening direction is the direction in which the plunger 12 moves when opening the valve passage 20, i.e., the direction in which the valve passage 20 is opened. In this embodiment, the opening direction is the other axial direction.

[0018] More specifically, the plunger 12 is formed, for example, in a cylindrical shape. The plunger 12 has a through passage 12a, a guide portion 12b, and a valve portion 12c. The through passage 12a is an inner hole of the plunger 12 and penetrates the plunger 12 in the axial direction. The through passage 12a has a throttle 12d. The guide portion 12b is formed so as to protrude radially outward in the plunger 12. The guide portion 12b abuts against the inner peripheral surface of the housing body 21. As a result, the plunger 12 is guided by the inner peripheral surface of the housing body 21 to slide along the axis L1. The valve portion 12c is formed on the plunger 12 on the tip side of the guide portion 12b. The valve portion 12c is formed in a generally tapered shape. The plunger 12 closes the valve passage 20 by seating the valve portion 12c on a valve seat 23d.

[0019] The plunger 12 also forms an annular passage 21c between the guide portion 12b of the plunger 12 and the seat member 23. The annular passage 21c is an annular passage formed around the valve portion 12c. The annular passage 21c is connected to the multiple communication passages 21a, and constitutes the valve passage 20 together with the multiple communication passages 21a and the inner hole 23b of the seat member 23.

[0020] As shown in FIG. 2, the piston 14 is mounted on the plunger 12 so as to be slidable in the axial direction. In this embodiment, the piston 14 is formed in a substantially cylindrical shape. The piston 14 is mounted on the base end portion of the plunger 12 so as to be slidable. The piston 14 also has an outward flange 14a extending outward. The outward flange 14a is formed on the outer circumferential surface of the piston 14. In this embodiment, the outward flange 14a is formed on the other axial end side. The outward flange 14a forms a damping chamber 16, which will be described in detail later, on one axial side thereof.

[0021] The sleeve 17 is accommodated in the housing body 21 so as to guide the piston 14 in a sliding manner. In this embodiment, the sleeve 17 is formed in a substantially cylindrical shape. The sleeve 17 is fitted into the other axial end portion of the housing body 21. To explain in more detail, a step portion 21d is formed on the inner peripheral surface of the housing body 21. The sleeve 17 is sandwiched between the step portion 21d and the cover body 22 and fixed inside the housing body 21. The piston 14 is inserted into the sleeve 17 so as to be slidable in the axial direction. To explain in more detail, the piston 14 is inserted into the sleeve 17 so as to bring the outward flange 14a into contact with the inner peripheral surface of the sleeve 17.

[0022] The sleeve 17 also has an inward flange 17a. The inward flange 17a is formed on the inner peripheral surface of the sleeve 17 at one axial end side. The inward flange 17a slidably abuts on one axial end side portion of the piston 14, and the piston 14 slides along the inward flange 17a. The inward flange 17a faces the outward flange 14a and is disposed apart from the outward flange 14a. As a result, an annular damping chamber 16, which will be described later in detail, is formed between the inward flange 17a and the outward flange 14a. The inward flange 17a faces the guide portion 12b of the plunger 12 and is disposed apart from the guide portion 12b. An annular spring accommodating space 18 is formed between the inward flange 17a and the guide portion 12b.

[0023] The spring member 13 biases the plunger 12 in a closing direction as shown in FIG. 1. The closing direction is the direction in which the plunger 12 moves when closing the valve passage 20, that is, the direction in which the valve passage 20 is closed. In this embodiment, the closing direction is one axial direction. The spring member 13 is, for example, a compression coil spring. The spring member 13 is mounted on the plunger 12 in a compressed state and is accommodated in the spring accommodating space 18. One end of the spring member 13 abuts against the guide portion 12b of the plunger 12. The other end of the spring member 13 abuts against the piston 14 via a spring bearing member 25. The spring bearing member 25 is mounted on the plunger 12 so as to be movable in the axial direction, and is, for example, an annular spring bearing washer. The spring member 13 is disposed between the guide portion 12b and the piston 14 in a compressed state, and biases the plunger 12 in one axial direction as described above.

[0024] The inflow pressure of the valve passage 20 is introduced to the differential pressure chamber 15. More specifically, the differential pressure chamber 15 is formed in the housing 11 by the plunger 12 and the piston 14. In this embodiment, the differential pressure chamber 15 is formed between the plunger 12 and the piston 14 and the cover body 22. The differential pressure chamber 15 is also connected to the valve passage 20 via the through passage 12a of the plunger 12. As a result, the inflow pressure of the valve passage 20 is introduced to the differential pressure chamber 15. At this time, a sudden increase in pressure in the differential pressure chamber 15 is suppressed by the restriction 12d of the through passage 12a.

[0025] The differential pressure chamber 15 applies its fluid pressure to the plunger 12 so as to resist the inflow pressure of the valve passage 20. That is, the plunger 12 receives the fluid pressure of the differential pressure chamber 15 in the closing direction (i.e., one axial direction). Therefore, the plunger 12 receives the inflow pressure of the valve passage 20 and the fluid pressure of the differential pressure chamber 15 in directions opposing each other. In the plunger 12, the area of ​​the pressure-receiving surface that receives the inflow pressure is larger than the area of ​​the pressure-receiving surface that receives the fluid pressure of the differential pressure chamber 15. Therefore, when the inflow pressure of the valve passage 20 becomes high, the plunger 12 moves in the opening direction (i.e., the other axial direction) against the biasing force of the spring member 13. The piston 14 receives the fluid pressure of the differential pressure chamber 15 in the compression direction. Here, the compression direction is the direction in which the spring member 13 is compressed, which is one axial direction in this embodiment.

[0026] As described above, the damping chamber 16 is formed between the outward flange 14a and the inward flange 17a. The piston 14 can move in one axial direction by the damping chamber 16. In this embodiment, the piston 14 can move from a non-compressed position to a maximum compression position by the damping chamber 16. The non-compressed position is a position where the spring member 13 is not compressed by the piston 14, and in this embodiment, the tip of the piston 14 is retracted to the open end of the sleeve 17. On the other hand, the maximum compression position is a position when the piston 14 makes a full stroke, and is a position where the piston 14 protrudes most from the sleeve 17. The piston 14 moves in the axial direction according to the hydraulic pressure of the differential pressure chamber 15 that receives the pressure. As a result, the spring member 13 is further compressed, and the biasing force of the spring member 13 becomes even greater.

[0027] In addition, the damping chamber 16 is connected to the differential pressure chamber 15. This allows the damping chamber 16 to supply and discharge hydraulic fluid between the damping chamber 16 and the differential pressure chamber 15. This limits the movement of the piston 14 in one axial direction. To explain in more detail, when the piston 14 moves, the damping chamber 16 draws in hydraulic fluid from the differential pressure chamber 15 and discharges hydraulic fluid to the differential pressure chamber 15. This limits the movement of the piston 14 in one axial direction and the other.

[0028] The relief valve 1 thus constructed is further constructed as follows. That is, the piston 14 has a damping passage 24. The damping passage 24 connects the differential pressure chamber 15 and the damping chamber 16. This allows the damping chamber 16 to draw in and discharge working fluid between the differential pressure chamber 15 via the damping passage 24. In this embodiment, the damping passage 24 is formed in the outward flange 14a. To explain in more detail, the damping passage 24 includes a first passage portion 31, a communication portion 32, and a second passage portion 33.

[0029] The first passage portion 31 is connected to the differential pressure chamber 15. The first passage portion 31 is, for example, a communication hole and extends in the axial direction in the outward flange 14a. The first passage portion 31 opens at the other axial end face of the outward flange 14a that faces the differential pressure chamber 15. Therefore, the first passage portion 31 is connected to the differential pressure chamber 15.

[0030] The communication portion 32 is connected to the first passage portion 31. More specifically, the communication portion 32 is a groove formed on the outer peripheral surface of the outward flange 14a, and is formed over the entire circumferential direction. The communication portion 32 is formed at a position corresponding to the first passage portion 31. In this embodiment, the communication portion 32 is recessed radially inward from the position where the first passage portion 31 is formed on the outer peripheral surface of the outward flange 14a. The first passage portion 31 opens into the communication portion 32, and the first passage portion 31 and the communication portion 32 are connected to each other.

[0031] The second passage portion 33 is connected to the communication portion 32 and the damping chamber 16. The second passage portion 33 is, for example, a communication hole extending in the axial direction. The second passage portion 33 is formed at a position corresponding to the communication portion 32 and opens to the communication portion 32. In this embodiment, the second passage portion 33 is formed so as to overlap the first passage portion 31 when viewed from the other axial direction. That is, the second passage portion 33 is formed at the same position as the first passage portion 31 in the circumferential direction. In addition, the second passage portion 33 opens at one axial end face of the outward flange 14a facing the damping chamber 16. Therefore, the second passage portion 33 is connected to the damping chamber 16.

[0032] Furthermore, in this embodiment, each of the first passage portion 31 and the second passage portion 33 has a throttle 31a, 33a. Therefore, in the damping passage 24, two throttles 31a, 33a are interposed in series between the differential pressure chamber 15 and the damping chamber 16. This limits the flow rate of the working fluid discharged from the damping chamber 16, further limiting the axial movement of the piston 14. In this embodiment, the throttles 31a, 33a are formed on the communication portion 32 side of each of the passage portions 31, 33. However, the throttles 31a, 33a may be formed on the differential pressure chamber 15 side and the damping chamber 16 side.

[0033] <Relief valve operation> In the relief valve 1, the valve passage 20 is closed by the plunger 12 being seated on the valve seat 23d, and the valve passage 20 is opened by the increase in the hydraulic pressure in the inflow passage 2a, i.e., the inflow pressure in the valve passage 20. To explain in more detail, in the relief valve 1, a restriction 12d is formed in the through passage 12a. Therefore, a difference in the pressure increase occurs between the inflow passage 2a and the differential pressure chamber 15. As a result, the plunger 12 starts moving before the piston 14 starts moving. When the hydraulic pressure in the hydraulic passage, i.e., the inflow pressure in the valve passage 20, increases and exceeds a predetermined starting pressure (see time t1 in FIG. 3), the plunger 12 moves in the opening direction against the biasing force of the spring member 13. Then, the valve passage 20 opens. As a result, the inflow passage 2a and the outflow passage 2b communicate with each other. Then, the hydraulic fluid in the inflow passage 2a is discharged to the tank through the valve passage 20.

[0034] Thereafter, when the pressure in the differential pressure chamber 15 increases, the piston 14 moves in one axial direction and compresses the spring member 13. This increases the biasing force pushing the plunger 12 in the closing direction. This causes the working pressure to increase in order to operate the plunger 12 (see times t1 to t2 in FIG. 3). The working pressure continues to increase as the piston 14 moves toward the maximum compression position. Eventually, when the piston 14 reaches the maximum compression position (see FIG. 4), the working pressure reaches the relief pressure (see time t3 in FIG. 3). This causes the working fluid in the fluid passage to be discharged, and the pressure in the fluid passage can be maintained at or below the relief pressure (see time t3 and after in FIG. 3).

[0035] In addition, in the relief valve 1, after the inflow pressure exceeds the starting pressure and the valve passage 20 opens, the working pressure slowly rises from the starting pressure to the relief pressure over time. That is, the piston 14 moves from the non-compressed position to the maximum compression position while discharging the working fluid in the damping chamber 16 to the differential pressure chamber 15 via the damping passage 24. Therefore, the piston 14 moves slowly from the non-compressed position to the maximum compression position. Therefore, the working pressure rises slowly. This makes it possible to suppress a sudden rise in the working pressure and suppress the occurrence of a surge pressure when the relief pressure is reached (see time t3 in FIG. 3).

[0036] In such a relief valve 1, the discharge speed of the working fluid can be adjusted by the two passage portions 31, 33 of the damping passage 24. Therefore, the damping function for the piston 14 can be enhanced, that is, the moving speed of the piston 14 can be damped. This makes it possible to adjust the pressure rise buffer time, which is the time it takes for the working pressure to reach the relief pressure from the starting pressure.

[0037] In this embodiment, the passages 31 and 33 each have a throttle 31a, 33a. This makes it possible to suppress the discharge of hydraulic fluid from the damping chamber 16, thereby further attenuating the moving speed of the piston 14, i.e., lengthening the pressure rise buffering time. Furthermore, by forming the two throttles 31a and 33a, the permeation areas of the two passages 31 and 33 can be increased. This makes it possible to suppress clogging of the two passages 31 and 33 due to the inflow of contaminants, etc.

[0038] In the relief valve 1 of the first embodiment, the piston 14 includes a damping passage 24 that connects the differential pressure chamber 15 and the damping chamber 16. Therefore, the sliding portions 12e, 14b where the plunger 12 and the piston 14 slide against each other can be made long. Therefore, the seal width between the plunger 12 and the piston 14 can be made long. This makes it possible to suppress the amount of leakage from between the plunger 12 and the piston 14 while suppressing the requirements for the machining accuracy of the plunger 12 and the piston 14.

[0039] Furthermore, in the relief valve 1 of the first embodiment, the damping passage 24 has the first passage portion 31, the communication portion 32, and the second passage portion 33. Therefore, the differential pressure chamber 15 and the damping chamber 16 can be connected by the two passage portions 31, 33 that are connected in series. This makes it possible to increase the flow path cross section in each of the two passage portions 31, 33 compared to the case where they are connected by one passage portion. Therefore, the two passage portions 31, 33 can be easily machined.

[0040] Furthermore, in the relief valve 1 of the first embodiment, the damping passage 24 is formed in the outward flange 14a of the piston 14. Therefore, the damping passage 24 can be easily formed.

[0041] Furthermore, in the relief valve 1 of the first embodiment, the first passage portion 31 and the second passage portion 33 are communication holes formed in the outward flange 14a. It is relatively easy to control the flow path area of ​​the communication holes. Therefore, it is easy to control the flow rate of the working fluid discharged from the damping chamber 16, and it is possible to reduce the mechanical difference in the damping function between each relief valve 1.

[0042] Furthermore, in the relief valve 1 of the first embodiment, the first passage portion 31 and the second passage portion 33 have the throttles 31a, 33a. Therefore, it is possible to suppress the speed of the working fluid discharged from the damping chamber 16. This makes it possible to suppress the moving speed of the piston 14 and to lengthen the pressure rise buffering time.

[0043] [Second embodiment] A relief valve 1A of the second embodiment shown in Fig. 5 has a similar configuration to the relief valve 1 of the first embodiment. Therefore, the configuration of the relief valve 1A of the second embodiment will be mainly described with respect to the differences from the relief valve 1 of the first embodiment, and the same configuration will be denoted by the same reference numerals and description thereof will be omitted. The same applies to the relief valves 1B and 1C of the third and fourth embodiments described later.

[0044] The relief valve 1A of the second embodiment mainly includes a housing 11, a plunger 12, a spring member 13, a piston 14A, a differential pressure chamber 15, a damping chamber 16, and a sleeve 17. The piston 14A has an outward flange 14a and a damping passage 24A. The damping passage 24A includes a first passage portion 31A, a communication portion 32, and a second passage portion 33A. The first passage portion 31A and the second passage portion 33A are communication holes similar to the first passage portion 31 and the second passage portion 33 of the first embodiment, and are arranged at intervals from each other in the circumferential direction as viewed from one axial direction. In this embodiment, the first passage portion 31A and the second passage portion 33A are arranged to be shifted by 180 degrees in the circumferential direction as viewed from one axial direction.

[0045] In the relief valve 1A of the second embodiment, the first passage portion 31 and the second passage portion 33 are arranged to be shifted in the circumferential direction on the outward flange 14a. Therefore, it is possible to suppress the piston 14 from becoming eccentric due to the force from the working fluid flowing through the damping passage 24. This makes it possible to suppress the piston 14 from hitting on one side. In this embodiment, the first passage portion 31 and the second passage portion 33 are arranged to be shifted by 180 degrees in the circumferential direction on the outward flange 14a. Therefore, it is possible to further suppress the piston 14 from hitting on one side.

[0046] In addition, the relief valve 1A of the second embodiment has the same functions and effects as the relief valve 1 of the first embodiment.

[0047] [Third embodiment] The relief valve 1B of the third embodiment shown in FIG. 6 mainly includes a housing 11, a plunger 12, a spring member 13, a piston 14B, a differential pressure chamber 15, a damping chamber 16, and a sleeve 17. The piston 14B has an outward flange 14a and a damping passage 24B. The damping passage 24B includes a first passage portion 31B, a communication portion 32, and a second passage portion 33B. The first passage portion 31B and the second passage portion 33B are formed on the outer circumferential surface of the outward flange 14a. In this embodiment, the first passage portion 31B and the second passage portion 33B are notches. That is, the first passage portion 31B and the second passage portion 33B are grooves recessed radially inward on the outer circumferential surface of the outward flange 14a and extend in the axial direction. The first passage portion 31B communicates the differential pressure chamber 15 with the communication portion 32, and the second passage portion 33B communicates the communication portion 32 with the damping chamber 16. Each of the first passage portion 31B and the second passage portion 33B has the throttles 31a, 33a in a portion on the communication portion 32 side. In this embodiment, the first passage portion 31B and the second passage portion 33B are arranged so as to overlap each other when viewed from one axial direction, but they may be arranged so as to be shifted in the circumferential direction. Each of the first passage portion 31B and the second passage portion 33B may have the throttles 31a, 33a in a portion on the differential pressure chamber 15 side and a portion on the damping chamber 16 side, respectively.

[0048] In the relief valve 1B of the third embodiment, the first passage portion 31 and the second passage portion 33 are notches formed in the outer circumferential surface of the outward flange 14a. Therefore, the damping passage 24 can be easily formed.

[0049] In addition, the relief valve 1B of the third embodiment has the same functions and effects as the relief valve 1 of the first embodiment.

[0050] [Fourth embodiment] The relief valve 1C of the fourth embodiment shown in FIG. 7 mainly includes a housing 11, a plunger 12, a spring member 13, a piston 14C, a differential pressure chamber 15, a damping chamber 16, and a sleeve 17. The piston 14C has an outward flange 14a and a damping passage 24C. The damping passage 24C includes a first passage portion 31C, a communication portion 32, and a second passage portion 33C. The first passage portion 31C and the second passage portion 33C are formed on the outer circumferential surface of the outward flange 14a. In this embodiment, the first passage portion 31C and the second passage portion 33C are slits. That is, the first passage portion 31C and the second passage portion 33C are formed on the outer circumferential surface of the outward flange 14a by flattening a part of the outer circumferential surface of the outward flange 14a. The first passage portion 31C communicates between the differential pressure chamber 15 and the communication portion 32, and the second passage portion 33C communicates between the communication portion 32 and the damping chamber 16. Note that, although the first passage portion 31C and the second passage portion 33C are disposed at the same position in the circumferential direction in this embodiment, they may be disposed with a shift in the circumferential direction.

[0051] In the relief valve 1C of the fourth embodiment, the first passage portion 31 and the second passage portion 33 are slits formed in the outer circumferential surface of the outward flange 14a. Therefore, the damping passage 24 can be easily formed.

[0052] In addition, the relief valve 1C of the fourth embodiment has the same functions and effects as the relief valve 1 of the first embodiment.

[0053] [Other embodiments] The relief valves 1, 1A to 1C of the present embodiment are mainly used to brake a hydraulic motor that drives a rotating body of a construction machine, but the use is not necessarily limited thereto. That is, the relief valves 1, 1A to 1C may be used to brake a hydraulic motor that drives other devices, or may be used to brake other actuators. Furthermore, the relief valve 1 is not limited to being used for braking an actuator, and may be provided in a hydraulic circuit simply to limit the pressure in a hydraulic passage to a relief pressure or less.

[0054] Furthermore, a relief valve 1D of another embodiment may be configured as follows. That is, the relief valve 1D includes a damping passage 24D in a piston 14D as shown in Fig. 8. The damping passage 24D has a first passage portion 31D, a communication portion 32, and a second passage portion 33D. The first passage portion 31D and the second passage portion 33D may be inclined radially inward with respect to the axial direction.

[0055] Moreover, the first passage portion 31 and the second passage portion 33 do not necessarily have to have the same shape. For example, the first passage portion may be formed of a slit like the first passage portion 31C of the fourth embodiment, and the second passage portion may be formed of a communication hole like the second passage portion 33 of the first embodiment. Moreover, the first passage portions 31, 31A, 31B and the second passage portions 33, 33A, 33B do not necessarily have to have the throttles 31a, 33a, and either one or both of them may not have them. Moreover, the first passage portion 31C and the second passage portion 33C may be formed of a plurality of elongated grooves.

[0056] Exemplary embodiments A relief valve in a first aspect includes a housing including a valve passage through which hydraulic fluid flows, a plunger movably accommodated in the housing to open and close the valve passage and receiving an inflow pressure of the valve passage in an opening direction to open the valve passage, a differential pressure chamber to which the inflow pressure of the valve passage is introduced and which causes the fluid pressure to act on the plunger against the inflow pressure of the valve passage, a spring member urging the plunger in a closing direction to close the valve passage, a piston slidably attached to the plunger and moving in response to the fluid pressure in the differential pressure chamber to compress the spring member, and a damping chamber connected to the differential pressure chamber and limiting movement of the piston in a compression direction to compress the spring member, the piston including a damping passage connecting the differential pressure chamber and the damping chamber.

[0057] According to the above aspect, the piston includes a damping passage that connects the differential pressure chamber and the damping chamber. Therefore, the sliding portion where the plunger and the piston slide against each other can be made long. Therefore, the seal width between the plunger and the piston can be made long. This makes it possible to reduce the amount of leakage from between the plunger and the piston while suppressing the requirements for the machining accuracy of the plunger and the piston.

[0058] In a second aspect, the relief valve is the relief valve of the first aspect, wherein the damping passage has a first passage portion connected to the differential pressure chamber, a communication portion connected to the first passage portion, and a second passage portion connected to the communication portion and the damping chamber.

[0059] According to the above aspect, the damping passage has a first passage portion connected to the differential pressure chamber, a communication portion connected to the first passage portion, and a second passage portion connected to the communication portion and the damping chamber. Therefore, the differential pressure chamber and the damping chamber can be connected by two passage portions connected in series. This makes it possible to increase the flow path cross section of each of the two passage portions compared to a case where the differential pressure chamber and the damping passage are connected by one passage portion. Therefore, it is possible to easily process the two passage portions.

[0060] A relief valve in a third aspect is the relief valve of the second aspect, wherein the damping chamber is formed to surround the piston, the piston has an outward flange extending outward to form the damping chamber, and the damping passage is formed in the outward flange.

[0061] According to the above aspect, the damping passage is formed in the outward flange of the piston, so that the damping passage can be easily formed.

[0062] In a fourth aspect, the relief valve is the relief valve of the second or third aspect, wherein at least one of the first passage portion and the second passage portion is a communication hole.

[0063] According to the above aspect, at least one of the first passage portion and the second passage portion is a communication hole. It is relatively easy to control the flow path area of ​​the communication hole. Therefore, it is easy to control the flow rate of the working fluid discharged from the damping chamber, and it is possible to reduce the difference in the damping function between individual relief valves.

[0064] A relief valve in a fifth aspect is the relief valve of any one of the second to fourth aspects, wherein at least one of the first passage portion and the second passage portion has a throttle.

[0065] According to the above aspect, at least one of the first passage portion and the second passage portion has a throttle, so that the speed of the hydraulic fluid discharged from the damping chamber can be reduced, thereby reducing the moving speed of the piston and lengthening the pressure rise buffering time.

[0066] In a sixth aspect, in the relief valve of the third aspect, at least one of the first passage portion and the second passage portion is a notch formed in an outer peripheral surface of the outward flange.

[0067] According to the above aspect, at least one of the first passage portion and the second passage portion is a notch formed in the outer circumferential surface of the outward flange, so that the damping passage can be easily formed.

[0068] A relief valve in a seventh aspect is the relief valve of the third or sixth aspect, wherein at least one of the first passage portion and the second passage portion is a slit formed in an outer peripheral surface of the outward flange.

[0069] According to the above aspect, at least one of the first passage portion and the second passage portion is a slit formed in the outer circumferential surface of the outward flange, which makes it possible to easily form a damping passage.

[0070] A relief valve in an eighth aspect is the relief valve of the third, sixth or seventh aspect, wherein the first passage portion and the second passage portion are arranged to be shifted from each other in a circumferential direction.

[0071] According to the above aspect, the first passage portion and the second passage portion are arranged to be shifted in the circumferential direction on the outward flange. Therefore, it is possible to suppress the piston from being eccentric due to the force applied from the hydraulic fluid flowing through the damping passage. This makes it possible to suppress the piston from hitting one side. [Explanation of symbols]

[0072] 1,1A,1B,1C,1D Relief valve 11. Housing 12 Plunger 12d aperture 12e Sliding part 13 Spring material 14, 14A, 14B, 14C, 14D Piston 14a Outward flange 14b Sliding part 15 Differential pressure chamber 16 Dumping Room 20 Valve passage 24, 24A, 24B, 24C, 24D Dumping passage 31,31A,31B,31C,31D 1st passage section 31a Aperture 32 Communication part 33,33A,33B,33C,33D 2nd passage section 33a Aperture

Claims

1. a housing including a valve passage through which hydraulic fluid flows; a plunger that is movably accommodated in the housing to open and close the valve passage and that receives an inflow pressure of the valve passage in an opening direction to open the valve passage; a differential pressure chamber into which the inflow pressure of the valve passage is introduced and which applies the hydraulic pressure to the plunger against the inflow pressure of the valve passage; a spring member that biases the plunger in a closing direction to close the valve passage; a piston that is slidably attached to the plunger and moves in response to the hydraulic pressure in the differential pressure chamber to compress the spring member; a damping chamber connected to the differential pressure chamber and configured to limit movement of the piston in a compression direction that compresses the spring member, The piston includes a damping passage connecting the differential pressure chamber and the damping chamber.

2. 2. The relief valve according to claim 1, wherein the damping passage has a first passage portion connected to the differential pressure chamber, a communication portion connected to the first passage portion, and a second passage portion connected to the communication portion and the damping chamber.

3. The damping chamber is formed to surround the piston, The piston has an outwardly extending flange that defines the damping chamber.

3. The relief valve according to claim 2, wherein the damping passage is formed in the outward flange.

4. The relief valve according to claim 2 , wherein at least one of the first passage portion and the second passage portion is a communication hole.

5. 3. The relief valve according to claim 2, wherein at least one of the first passage portion and the second passage portion has a throttle.

6. 4. The relief valve according to claim 3, wherein at least one of the first passage portion and the second passage portion is a notch formed in an outer circumferential surface of the outward flange.

7. 4. The relief valve according to claim 3, wherein at least one of the first passage portion and the second passage portion is a slit formed in an outer circumferential surface of the outward flange.

8. The relief valve according to claim 3 , wherein the first passage portion and the second passage portion are arranged to be shifted from each other in a circumferential direction.

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