Relief valve

Abstract

To prevent the behavior of the pilot valve body from becoming unstable. [Solution] The electromagnetic relief valve 100 comprises a pilot poppet 20 that operates in response to the pressure of hydraulic oil in a pilot passage P1 and connects or blocks communication between the pilot passage P1 and a discharge passage, a pilot piston 51 that is provided in the main poppet 5 and moves in response to the pressure difference between the pressure in the high-pressure passage H and the pressure in the back-pressure chamber 8, a first communication passage 10 that is provided in the pilot piston 51 and connects the high-pressure passage H and the back-pressure chamber 8, and a first orifice 52 that is provided in the first communication passage 10 and generates a pressure difference that acts on the pilot piston 51. When the pilot piston 51 moves due to the pressure difference and the valve portion 51c of the pilot piston 51 seats on the second seat portion 7j of the sleeve 7, the hydraulic oil that has been guided from the high-pressure passage H to the first communication passage 10 passes only through the second orifice 55 and flows from the back-pressure chamber 8 to the pilot passage P1.

Description

[Technical Field]

[0001] The present invention relates to a relief valve. [Background technology]

[0002] Patent Document 1 discloses a relief valve including: a main poppet that communicates and blocks the flow of working fluid between a high-pressure passage and a low-pressure passage; a sleeve that defines a back pressure chamber between itself and the main poppet; a pilot passage that is provided in the main poppet and faces the high-pressure passage and the back pressure chamber; a drain chamber that is provided in the sleeve and from which working fluid in the back pressure chamber is discharged; a first passage that is provided in the sleeve to communicate between the drain chamber and the back pressure chamber; a second passage that is configured to communicate between the pilot passage and the back pressure chamber and is provided with a throttle that applies resistance to the working fluid passing through; and a pilot poppet that opens and closes the first passage.

[0003] In the relief valve described in Patent Document 1, when the pilot piston makes a full stroke against the biasing force of the spring, the tapered portion of the pilot piston comes into line contact with the seat portion provided on the sleeve, thereby blocking the flow of hydraulic oil from the back pressure chamber through the gap between the tapered portion and the seat portion to the first passage, and the hydraulic oil in the back pressure chamber flows out into the first passage and drain chamber through the second passage and pilot passage. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-12406 Summary of the Invention [Problem to be solved by the invention]

[0005] In the relief valve described in Patent Document 1, when the pilot poppet opens, the hydraulic oil that has flowed from the high-pressure passage into the first passage flows out into the drain chamber, and the hydraulic oil that has flowed from the back-pressure chamber into the first passage through the second passage also flows out into the drain chamber, resulting in an increase in the flow rate of hydraulic oil flowing through the first passage.

[0006] For this reason, the relief valve described in Patent Document 1 requires a large pilot poppet opening. However, if the pilot poppet opening is large, the behavior of the pilot poppet becomes unstable, and the flow rate of hydraulic oil discharged from the first passage to the drain chamber fluctuates greatly. This causes the pressure in the back pressure chamber to fluctuate, which may cause the behavior of the main poppet to become unstable.

[0007] The present invention has been made in view of the above-mentioned problems, and has an object to suppress the behavior of the pilot valve element from becoming unstable. [Means for solving the problem]

[0008] The present invention includes a main valve element that connects or blocks a high-pressure side passage and a low-pressure side passage, a back pressure chamber into which working fluid is introduced that urges the main valve element in a valve closing direction, a sleeve that partitions the back pressure chamber between itself and the main valve element, a pilot passage provided in the sleeve that connects the back pressure chamber and a discharge passage for discharging the working fluid, a pilot valve element that operates in response to the pressure of the working fluid in the pilot passage and connects or blocks the pilot passage and the discharge passage, a biasing portion that urges the pilot valve element in a valve closing direction, and a pilot piston that is slidably provided in a slide hole provided in the main valve element and moves in response to the pressure difference between the pressure in the high-pressure side passage and the pressure in the back pressure chamber. a first communication passage provided in the pilot piston and communicating between the high-pressure side passage and the back pressure chamber; a first throttle provided in the first communication passage and generating a differential pressure acting on the pilot piston; a valve provided in the pilot piston and opening to the back pressure chamber side of the first communication passage; and a seat provided in the sleeve and against which the valve of the pilot piston abuts, wherein when the pilot piston moves due to the differential pressure and the valve of the pilot piston seats on the seat of the sleeve, the working fluid guided from the high-pressure side passage to the first communication passage passes only through the second throttle and flows from the back pressure chamber to the pilot passage.

[0009] In this invention, when the relief valve operates, the valve portion of the pilot piston seats on the seat portion of the sleeve, so that hydraulic oil flowing from the high-pressure passage to the back pressure chamber passes only through the second orifice. This provides resistance to the hydraulic oil flowing from the high-pressure passage to the back pressure chamber through the first and second orifices, reducing the flow rate of hydraulic oil from the high-pressure passage to the back pressure chamber. This reduces the flow rate of hydraulic oil discharged from the back pressure chamber to the discharge flow path through the pilot passage, allowing the opening of the pilot valve element to be reduced. This prevents the pilot valve element from becoming unstable.

[0010] The present invention is also characterized in that it further comprises a second communication passage provided between an outer peripheral surface of the pilot piston and an inner peripheral surface of a sliding hole provided in the main valve body, the second communication passage communicating with the back pressure chamber, and the second throttle is an annular throttle provided in the second communication passage.

[0011] In this invention, the second throttle is configured as an annular throttle, so that it is possible to easily configure a throttle with a small flow passage area compared to when the second throttle is configured as an orifice.

[0012] The present invention is also characterized in that the second throttle is a groove provided in at least one of the valve portion of the pilot piston and the seat portion of the sleeve.

[0013] In this invention, the second throttle is formed by, for example, a groove provided in one of the pilot piston and the sleeve, so that the second throttle can be easily manufactured. [Effects of the Invention]

[0014] According to the present invention, it is possible to prevent the behavior of the pilot valve element from becoming unstable. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic diagram of an electromagnetic relief valve according to an embodiment of the present invention, showing a state in which a main poppet and a pilot poppet are closed. [Figure 2] FIG. 2 is a schematic configuration diagram of the electromagnetic relief valve according to the embodiment of the present invention, showing a state in which the pilot poppet is open and the valve portion of the pilot piston is seated on the seat of the sleeve. [Figure 3] FIG. 3 is a schematic diagram of the electromagnetic relief valve according to the embodiment of the present invention, showing a state in which the main poppet and the pilot poppet are open. [Figure 4] FIG. 4 is a schematic diagram of an electromagnetic relief valve according to a modified example. [Figure 5] FIG. 5 is an enlarged view of the vicinity of the second throttle of an electromagnetic relief valve according to another modified example. DETAILED DESCRIPTION OF THE INVENTION

[0016] An electromagnetic relief valve 100 according to an embodiment of the present invention will be described with reference to FIGS. 1 to 3. FIG.

[0017] The electromagnetic relief valve 100 is an inverse proportional type electromagnetic relief valve. An inverse proportional type is a relief valve configured so that the relief pressure decreases as the value of current applied to a solenoid, which will be described later, increases.

[0018] The electromagnetic relief valve 100 is provided, for example, in a hydraulic control circuit that controls the operation of construction machinery. The electromagnetic relief valve 100 opens when the pressure of the hydraulic oil in the high-pressure passage H reaches a set pressure (relief pressure), and by releasing the hydraulic oil from the high-pressure passage H to the low-pressure passage L, it prevents the pressure of the hydraulic oil in the high-pressure passage H from becoming abnormally high. The electromagnetic relief valve 100 also has an anti-void function, and opens when the high-pressure passage H becomes negative pressure, and by supplying the hydraulic oil from the low-pressure passage L to the high-pressure passage H, it prevents the occurrence of cavitation.

[0019] As shown in FIG. 1 , the electromagnetic relief valve 100 is attached to an equipment body 1 by screw fastening. The equipment body 1 is the body of a hydraulic device such as a hydraulic cylinder, a hydraulic pump, a hydraulic motor, or a valve block having a plurality of valves. Note that, in this embodiment, an example is shown in which the electromagnetic relief valve 100 is attached to the equipment body 1, but this is not limiting, and the electromagnetic relief valve 100 can be applied to various devices, pipelines, and the like. Also, in this embodiment, an example is described in which hydraulic oil is used as the working fluid of the equipment body 1, but the working fluid may be other liquids such as hydraulic water, or may be gas such as compressed air.

[0020] The device body 1 is provided with a high-pressure passage H and a low-pressure passage L, with the electromagnetic relief valve 100 as the boundary. The device body 1 is provided with a seat portion 1a between the high-pressure passage H and the low-pressure passage L, on which a suction poppet 3, which will be described later, is seated. Note that the device body 1 is not limited to the main body of a hydraulic device, and may be a block body or the like installed between hydraulic devices.

[0021] As shown in FIG. 1, the electromagnetic relief valve 100 includes a valve portion V for connecting or disconnecting a high-pressure passage H and a low-pressure passage L, and a solenoid portion S as a biasing portion for adjusting a set pressure (relief pressure).

[0022] As shown in FIG. 1 , the valve section V includes a valve housing 2 attached to a device main body 1 in which a high-pressure passage H and a low-pressure passage L are provided, a suction poppet 3 provided in the valve housing 2 and configured to connect or disconnect the high-pressure passage H and the low-pressure passage L by lifting off or seating on a seat 1a, a main poppet 5 provided in the suction poppet 3 as a main valve element and configured to connect or disconnect the high-pressure passage H and the low-pressure passage L by lifting off or seating on a seat 3f formed on the suction poppet 3 as a second valve seat, and a valve element 5 provided in the suction poppet 3 by lifting off or seating on a seat 3f. a back pressure chamber 8 into which hydraulic oil is introduced for urging the main poppet 5 in the valve closing direction; a sleeve 7 that separates the back pressure chamber 8 from the main poppet 5; a drain chamber 12 that is provided within the sleeve 7 and from which the hydraulic oil in the back pressure chamber 8 is discharged; a pilot passage P1 that is provided in the sleeve 7 and connects the drain chamber 12 to the back pressure chamber 8; a pilot poppet 20 that is provided within the sleeve 7 and serves as a pilot valve body that opens and closes the pilot passage P1; and a pilot piston 51 that is slidably provided within a slide hole 50a provided in the main poppet 5 and moves in accordance with the pressure difference between the pressure in the high pressure passage H and the pressure in the back pressure chamber 8.

[0023] As shown in FIG. 1, the valve housing 2 is a cylindrical member having a first cylindrical portion 2a attached to the device main body 1 and a second cylindrical portion 2b connected to the base member 71 of the solenoid portion S on the opposite side from the first cylindrical portion 2a.

[0024] The suction poppet 3 is a cylindrical member with a bottom, having a cylindrical portion 3a and a bottom portion 3b. The suction poppet 3 is provided axially movable within the valve housing 2, with a portion of it protruding from the opening of the first cylindrical portion 2a of the valve housing 2. A high-pressure port 3H communicating with the high-pressure passage H is provided in the bottom portion 3b of the suction poppet 3, and a low-pressure port 3L communicating with the low-pressure passage L is provided near the bottom portion 3b of the cylindrical portion 3a.

[0025] A corner 3c between the cylindrical portion 3a and the bottom portion 3b of the suction poppet 3 is formed in a tapered shape, and when this corner 3c is seated on the seat portion 1a of the equipment body 1, communication between the high-pressure passage H and the low-pressure passage L through the equipment body 1 and the suction poppet 3 is blocked. A first accommodating hole 3d is provided on the bottom portion 3b side of the suction poppet 3 to accommodate a main poppet 5, and a second accommodating hole 3e, which has a larger diameter than the first accommodating hole 3d and accommodates a sleeve 7, is provided at the end opposite the bottom portion 3b. A communicating passage 4, which communicates with the low-pressure passage L, is provided between an outer peripheral surface 3g of the suction poppet 3 and an inner peripheral surface 2c of the valve housing 2.

[0026] The main poppet 5 has a main body portion 50 that is slidable within the first accommodating hole 3d, and a slide hole 50a that is formed in the main body portion 50 so as to penetrate therethrough in the axial direction.

[0027] The main body 50 has a valve portion 50b that seats on a seat portion 3f formed inside a corner 3c of the suction poppet 3. When the valve portion 50b seats on the seat portion 3f, communication between the high-pressure passage H and the low-pressure passage L through the space between the suction poppet 3 and the main poppet 5 is blocked. A seal member (O-ring) is provided between the outer peripheral surface of the main body 50 and the inner peripheral surface of the suction poppet 3 to seal the gap between the main body 50 and the suction poppet 3.

[0028] The pilot piston 51 has a flange portion 51a that faces the back pressure chamber 8, which is a space defined by the inner circumferential surface of the suction poppet 3, the main poppet 5, and the sleeve 7, and a cylindrical shaft portion 51b that extends axially from the flange portion 51a and is inserted into the slide hole 50a. The tip of the shaft portion 51b protrudes from the tip surface of the main body portion 50 that faces the high-pressure passage H. The shaft portion 51b is formed so that the outer diameter of the tip side is approximately the same as the inner diameter of the slide hole 50a. This creates a nearly sealed state between the shaft portion 51b and the slide hole 50a.

[0029] The pilot piston 51 is provided with a first communication passage 10 that passes through the pilot piston 51 in the axial direction and that connects the high-pressure passage H and the back pressure chamber 8.

[0030] A first throttle 52 is provided near the opening of the first communication passage 10 on the side of the high-pressure passage H to apply resistance to the hydraulic oil flowing through the first communication passage 10. The first throttle 52 generates a pressure difference acting on the pilot piston 51.

[0031] A second communication passage 53 that communicates between the first communication passage 10 and the back pressure chamber 8 is provided between the outer peripheral surface of the pilot piston 51 and the inner peripheral surface of a slide hole 50a provided in the main poppet 5. The second communication passage 53 is formed by reducing the diameter of a part of the shaft portion 51b of the pilot piston 51. The second communication passage 53 communicates with the first communication passage 10 via a through hole 54 that is provided so as to radially penetrate the shaft portion 51b of the pilot piston 51.

[0032] An annular second orifice 55 is provided in the second communication passage 53. The second orifice 55 is formed by making a portion of the outer peripheral surface of the shaft portion 51b in the region where the second communication passage 53 is formed protrude in an annular shape, thereby narrowing the gap between the outer peripheral surface of the pilot piston 51 and the inner peripheral surface of a slide hole 50a provided in the main poppet 5. The second orifice 55 is provided between the through hole 54 and the back pressure chamber 8. The effective cross-sectional area of ​​the second orifice 55 is smaller than the effective cross-sectional area of ​​the first orifice 52.

[0033] The sleeve 7 has a base portion 7a inserted into the suction poppet 3, a connecting portion 7b coupled to the base member 71, an accommodating hole 7c opening at the axial end opposite the base portion 7a, an intermediate portion 7d provided between the base portion 7a and the connecting portion 7b and having an outer circumferential surface exposed between the suction poppet 3 and the base member 71, a through-hole 7e passing through the connecting portion 7b in the axial direction, a protruding portion 7f protruding from the base portion 7a toward the back pressure chamber 8, and a second seat portion 7j provided at the tip of the protruding portion 7f and on which the valve portion 51c of the pilot piston 51 is seated.

[0034] The base portion 7a of the sleeve 7 slidably supports the suction poppet 3. A seal member (O-ring) that seals the gap between the sleeve 7 and the suction poppet 3 is provided between the outer peripheral surface of the base portion 7a of the sleeve 7 and the inner peripheral surface of the suction poppet 3.

[0035] The sleeve 7 is also provided with a first seat 7g, which is provided on the bottom surface of the accommodating hole 7c and on which the valve portion 23 of the pilot poppet 20 seats and unseats, a first passage 7h which extends axially from the first seat 7g toward the protruding portion 7f, and a second passage 7i which opens onto the outer peripheral surface of the protruding portion 7f and connects the back pressure chamber 8 and the first passage 7h. In this embodiment, the first passage 7h and the second passage 7i form a pilot passage P1. The first seat 7g is formed coaxially with the accommodating hole 7c so that its central axis coincides with the central axis of the accommodating hole 7c.

[0036] The drain chamber 12 is a space defined in the accommodation hole 7c between the bottom surface of the accommodation hole 7c and the pilot poppet 20, and the hydraulic oil discharged from the back pressure chamber 8 through the pilot passage P1 flows into the drain chamber 12.

[0037] 1 and other figures, the pilot poppet 20 is a member formed in a substantially cylindrical shape and slidably received in the receiving hole 7c of the sleeve 7. The pilot poppet 20 slides on the inner circumferential surface of the receiving hole 7c and includes a first sliding portion 21 and a second sliding portion 22 arranged side by side in this order from the solenoid portion S side, a conical valve portion 23 protruding in the axial direction from the second sliding portion 22, an annular groove 24 provided between the first sliding portion 21 and the second sliding portion 22, a plurality of communication holes 25 opening into the bottom surface of the annular groove 24, a communication passage 26 communicating with the communication holes 25 and extending in the axial direction of the pilot poppet 20, and a rod portion 27 having a smaller diameter than the first sliding portion 21 and extending from the end face of the first sliding portion 21 toward the plunger 72.

[0038] The first sliding portion 21 is formed so that its outer diameter is approximately the same as the inner diameter of the receiving hole 7c, thereby creating a nearly sealed state between the first sliding portion 21 and the receiving hole 7c.

[0039] A communication passage 22a formed by a groove or a flat notch is provided in the axial direction on the outer peripheral surface of the second sliding part 22. As a result, the hydraulic oil discharged from the pilot passage P1 (first passage 7h) to the drain chamber 12 flows into the annular groove 24 through the communication passage 22a provided on the outer peripheral surface of the second sliding part 22. As described above, the space between the first sliding part 21 and the accommodating hole 7c is substantially sealed, so the hydraulic oil that has flowed into the annular groove 24 is guided to the communication passage 26 through the communication hole 25.

[0040] 1, a spring 81 is provided between the flange portion 51a of the pilot piston 51 and the sleeve 7, and a spring 82 is provided between the suction poppet 3 and the base member 71. The spring 81 urges the pilot piston 51 so that the flange portion 51a abuts against the main body portion 50 of the main poppet 5, and also urges the main body portion 50 via the flange portion 51a so that the main body portion 50 seats on the seat portion 3f of the suction poppet 3. On the other hand, the spring 82 urges the suction poppet 3 so that the corner portion 3c of the suction poppet 3 seats on the seat portion 1a of the equipment main body 1.

[0041] Next, the solenoid section S will be described.

[0042] The solenoid section S has a base member 71, a plunger 72 as a plunger section that is slidably housed within the base member 71 and presses the pilot poppet 20, a spring 74 that is provided on the opposite side of the plunger 72 from the pilot poppet 20 and serves as a biasing member that biases the pilot poppet 20 in the valve-closing direction via the plunger 72, a coil 75 that is supported by the base member 71 and that, when a current is applied, applies a reaction force to the plunger 72 that opposes the biasing force of the spring 74, a yoke 76 that is provided to surround the coil 75, a fixed iron core 77 attached to the yoke 76, and an adjustment member 79 that is attached to the fixed iron core 77 and is free to move in the axial direction. In this embodiment, the solenoid section S is configured by the base member 71, the plunger 72, the coil 75, the yoke 76, and the fixed iron core 77.

[0043] The base member 71 is a cylindrical member made of a magnetic material. The base member 71 has a cylindrical portion 71a that is inserted into the yoke 76, a flange portion 71b that is larger in diameter than the cylindrical portion 71a and that restricts axial movement of the coil 75, an accommodating hole 71c that is formed across the cylindrical portion 71a and the flange portion 71b and that accommodates the plunger 72, and a connecting portion 71d that is provided on the opposite side of the flange portion 71b from the cylindrical portion 71a.

[0044] The cylindrical portion 71a is connected to the fixed core 77 via a tube member 91. A guide member 90 that slidably supports the plunger 72 is provided in the accommodation hole 71c.

[0045] The connecting portion 71d is formed in a cylindrical shape. An internal thread is formed on the inner peripheral surface of the connecting portion 71d, and an external thread is formed on the outer peripheral surface. The internal thread formed on the inner peripheral surface of the connecting portion 71d threads into the external thread formed on the outer peripheral surface of the connecting portion 7b of the sleeve 7, thereby connecting the sleeve 7 and the base member 71. Furthermore, the external thread formed on the outer peripheral surface of the connecting portion 71d threads into the internal thread formed on the inner peripheral surface of the second cylindrical portion 2b of the valve housing 2, thereby connecting the valve housing 2 and the base member 71.

[0046] The solenoid portion S is provided inside the connecting portion 71d and further includes a spring 83 that biases the pilot poppet 20 in the valve closing direction, and a spring seat 30 that supports one end of the spring 83. The spring seat 30 is provided with an insertion hole 30a through which the rod portion 27 of the pilot poppet 20 is inserted, and a plurality of through holes 30b through which the hydraulic oil passes.

[0047] The plunger 72 is made of a magnetic material and has through holes 72a and 72b extending in the axial direction, through which hydraulic oil flows.

[0048] The spring 74 is formed of a coil spring, and one end is supported by the adjustment member 79 and the other end is supported by the plunger 72. The biasing force of the spring 74 acts to bias the pilot poppet 20 in the valve closing direction via the plunger 72. In other words, the spring 74 biases the pilot poppet 20 so that the valve portion 23 of the pilot poppet 20 is seated on the first seat portion 7g.

[0049] When current is applied to the coil 75, the coil 75 applies a thrust to the plunger 72 that counteracts the biasing force of the spring 74. As the current applied to the coil 75 increases, the biasing force of the spring 74 acting on the pilot poppet 20 via the plunger 72 decreases. As a result, the pressure required to separate the valve portion 23 of the pilot poppet 20 from the first seat portion 7g, known as the valve opening pressure (cracking pressure), decreases. In the electromagnetic relief valve 100, the set pressure (relief pressure) at which the pilot poppet 20 opens can be changed by controlling the current applied to the coil 75 to change the biasing force of the spring 74 acting on the pilot poppet 20.

[0050] The fixed core 77 is made of a magnetic material. The fixed core 77 has a through hole 77a. An internal thread is provided on the outer side of the through hole 77a to be threadedly engaged with the adjustment member 79. A spring chamber 78 is formed in the through hole 77a of the fixed core 77 between the plunger 72 and the adjustment member 79, and serves as a biasing member chamber in which the spring 74 is housed.

[0051] The adjustment member 79 is a so-called flat-point set screw, in which a male thread is formed on the outer peripheral surface of a cylindrical member. The adjustment member 79 has an end surface 79a against which one end of the spring 74 abuts. The biasing force of the spring 74 can be adjusted by moving the adjustment member 79 in the axial direction relative to the fixed iron core 77. The axial movement of the adjustment member 79 is restricted by tightening a lock nut 80.

[0052] Next, the operation of the electromagnetic relief valve 100 will be described.

[0053] The hydraulic oil in the high-pressure passage H is guided to the pilot passage P1 through the first communication passage 10 and the back pressure chamber 8. When the pressure of the hydraulic oil guided to the pilot passage P1 reaches the valve-opening pressure (cracking pressure) of the pilot poppet 20 set by the solenoid section S, in other words, when the biasing force on the pilot poppet 20 in the valve-opening direction due to the pressure of the hydraulic oil guided to the pilot passage P1 becomes greater than the biasing force on the pilot poppet 20 in the valve-closing direction due to the solenoid section S, the valve section 23 of the pilot poppet 20 lifts off from the first seat 7g.

[0054] When the valve portion 23 of the pilot poppet 20 leaves the first seat portion 7g, the hydraulic oil in the back pressure chamber 8 flows through the pilot passage P1, the drain chamber 12, the communicating passage 22a, the annular groove 24, the communicating hole 25, the communicating passage 26, and the through hole 72a into the spring chamber 78. The hydraulic oil that has flowed into the spring chamber 78 is discharged to the low pressure passage L through the through hole 72b, the through hole 30b, the through hole 7e, the region outside the intermediate portion 7d, and the communicating passage 4. In this embodiment, the flow path from the drain chamber 12 to the low pressure passage L corresponds to the "discharge flow path" in the claims.

[0055] Hydraulic oil is constantly supplied to the back pressure chamber 8 from the high pressure passage H through the first communication passage 10. However, the supply of hydraulic oil from the high pressure passage H to the back pressure chamber 8 is restricted by the first throttle 52 provided in the first communication passage 10. Therefore, when the valve element 23 separates from the first seat 7g and the hydraulic oil in the back pressure chamber 8 is discharged, the pressure in the back pressure chamber 8 gradually becomes lower than the pressure in the high pressure passage H.

[0056] In this way, when the pressure in the back pressure chamber 8 decreases, a pressure difference acts on the pilot piston 51. Specifically, when the biasing force due to the pressure in the high-pressure passage H becomes greater than the sum of the biasing force due to the pressure in the back pressure chamber 8 and the biasing force of the spring 81, the pilot piston 51 moves toward the sleeve 7, and the valve portion 51c of the pilot piston 51 seats on the second seat portion 7j of the sleeve 7 (see FIG. 2). As a result, the opening of the first communication passage 10 on the back pressure chamber 8 side is closed, and the hydraulic oil that has flowed into the first communication passage 10 from the high-pressure passage H through the first throttle 52 flows into the second communication passage 53 through the through-hole 54. The hydraulic oil that has flowed into the second communication passage 53 then passes through the second throttle 55 and flows into the back pressure chamber 8.

[0057] In this manner, when the valve portion 51c of the pilot piston 51 is seated on the second seat 7j of the sleeve 7, resistance is applied to the hydraulic oil flowing from the high-pressure passage H toward the back-pressure chamber 8 by the first orifice 52 and the second orifice 55, reducing the flow rate of the hydraulic oil from the high-pressure passage H toward the back-pressure chamber 8. This further reduces the pressure in the back-pressure chamber 8, further reducing the biasing force of the pressure in the back-pressure chamber 8 that acts in a direction to seat the body portion 50 of the main poppet 5 on the seat 3f of the suction poppet 3. When the pressure difference (differential pressure) between the pressure in the back-pressure chamber 8 and the pressure in the high-pressure passage H exceeds a predetermined pressure difference, the body portion 50 of the main poppet 5 lifts off the seat 3f of the suction poppet 3, and the main poppet 5 opens (see FIG. 3). This allows the hydraulic oil to be discharged from the high-pressure passage H to the low-pressure passage L. In this manner, the electromagnetic relief valve 100 prevents the pressure in the high-pressure passage H from becoming abnormally high.

[0058] When the flow rate from the pilot passage P1 to the drain chamber 12 is high, it is necessary to increase the opening of the pilot poppet 20. However, as the opening of the pilot poppet 20 increases, the behavior of the pilot poppet 20 becomes unstable, resulting in greater fluctuations in the flow rate of hydraulic oil discharged from the pilot passage P1 to the drain chamber 12. This causes the pressure in the backpressure chamber 8 to fluctuate, potentially destabilizing the behavior of the main poppet 5. More specifically, a larger opening of the pilot poppet 20 also results in greater fluctuations in the pilot flow rate. If the pilot poppet 20 suddenly opens and closes, a sudden increase or decrease in the pilot flow rate occurs, which can cause hunting or other phenomena in the pilot poppet 20 and lead to unstable operation of the pilot poppet 20. Furthermore, a sudden increase or decrease in the pilot flow rate can easily cause a sudden increase or decrease in the differential pressure across the main poppet 5, which can cause hunting or other phenomena in the main poppet 5 and lead to unstable operation.

[0059] In contrast, in the electromagnetic relief valve 100 of the present embodiment, when the pilot poppet 20 opens, the valve portion 51c of the pilot piston 51 seats on the second seat portion 7j of the sleeve 7, so that the hydraulic oil guided from the high-pressure passage H to the first communication passage 10 passes through the first orifice 52 and the second orifice 55 and flows into the back pressure chamber 8. This reduces the flow rate of hydraulic oil flowing from the high-pressure passage H into the back pressure chamber 8, and therefore reduces the flow rate of hydraulic oil discharged from the back pressure chamber 8 to the drain chamber 12 through the pilot passage P1. Therefore, according to the electromagnetic relief valve 100, the opening degree of the pilot poppet 20 can be reduced during the relief operation, so that the behavior of the pilot poppet 20 can be prevented from becoming unstable.

[0060] Furthermore, in the electromagnetic relief valve 100 of this embodiment, the hydraulic oil can be discharged in one direction from the high-pressure passage H through the first communication passage 10, the second communication passage 53, the back pressure chamber 8, and the pilot passage P1, thereby making the flow of the hydraulic oil smooth.

[0061] When the main poppet 5 opens and the hydraulic oil in the high-pressure passage H is discharged into the low-pressure passage L, the pressure of the hydraulic oil in the high-pressure passage H drops to the set pressure (relief pressure), and the pressure in the backpressure chamber 8 and the pilot passage P1 drops to the valve-opening pressure (cracking pressure) of the pilot poppet 20. This causes the pilot poppet 20 to close, and the pressure in the high-pressure passage H becomes equal to the pressure in the backpressure chamber 8, causing the main poppet 5 to close due to the biasing force of the spring 82.

[0062] In the above embodiment, the electromagnetic relief valve 100 including the solenoid portion S as the biasing portion has been described as an example, but this is not limiting. The biasing portion of the relief valve may be configured only by a spring. Note that the type of spring is not limited to mechanical springs such as coil springs and disc springs, and may also be a spring using a compressible fluid such as an air spring.

[0063] In the above embodiment, the second seat portion 7j of the sleeve 7 is tapered, and the tip of the second seat portion 7j is configured to fit into the first communication passage 10. Alternatively, as shown in FIG. 4, the valve portion 51c of the pilot piston 51 may be tapered, and the second seat portion 7j of the sleeve 7 may be cylindrical, and the tip of the valve portion 51c of the pilot piston 51 may fit into the second seat portion 7j of the sleeve 7.

[0064] Furthermore, in the above embodiment, the second communication passage 53 is provided between the outer peripheral surface of the pilot piston 51 and the inner peripheral surface of the slide hole 50a formed in the main poppet 5, and the annular second throttle 55 is provided in the second communication passage 53. However, this is not limited to this. For example, as shown in FIG. 5 , the second communication passage 53 may not be provided, and a second throttle 155 formed by a groove may be provided in the valve portion 51c of the pilot piston 51. In this case, when the valve portion 51c of the pilot piston 51 seats on the second seat portion 7j of the sleeve 7, the opening of the groove is covered, thereby forming the second throttle 155. When the valve portion 51c of the pilot piston 51 seats on the second seat portion 7j of the sleeve 7, the hydraulic oil flowing from the first communication passage 10 toward the back pressure chamber 8 passes only through the second throttle 155. 5, when the electromagnetic relief valve 100 operates, the first orifice 52 and the second orifice 155 can provide resistance to the hydraulic oil flowing from the high-pressure passage H to the back-pressure chamber 8, thereby reducing the flow rate of the hydraulic oil flowing from the high-pressure passage H to the back-pressure chamber 8. Therefore, similar to the embodiment shown in FIGS. 1 to 4, the behavior of the pilot poppet 20 can be prevented from becoming unstable.

[0065] Although not shown, instead of providing a groove in the valve portion 51c of the pilot piston 51, the second throttle 155 may be configured by providing a groove in the second seat portion 7j of the sleeve 7, or by providing grooves in both the valve portion 51c of the pilot piston 51 and the second seat portion 7j of the sleeve 7.

[0066] The configuration, operation, and effects of the embodiment of the present invention configured as above will be described below.

[0067] The electromagnetic relief valve 100 (relief valve) comprises a main poppet 5 (main valve element) that connects or blocks a high-pressure passage H (high-pressure side passage) and a low-pressure passage L (low-pressure side passage), a back pressure chamber 8 into which hydraulic oil (working fluid) is introduced to urge the main poppet 5 (main valve element) in a valve-closing direction, a sleeve 7 that partitions the back pressure chamber 8 between the main poppet 5 (main valve element), a pilot passage P1 that is provided in the sleeve 7 and connects the back pressure chamber 8 to a discharge passage for discharging the hydraulic oil (working fluid), a pilot poppet 20 (pilot valve element) that operates in response to the pressure of the hydraulic oil (working fluid) in the pilot passage P1 to connect or block the pilot passage P1 and the discharge passage, a solenoid portion S (biasing portion) that urges the pilot poppet 20 (pilot valve element) in a valve-closing direction, and a solenoid portion S that is slidably provided in a slide hole 50a provided in the main poppet 5 (main valve element) and connects the high-pressure passage H (high-pressure side passage) to a low-pressure passage L (low-pressure side passage). a first communication passage 10 provided in the pilot piston 51 and communicating between the high-pressure passage H (high-pressure side passage) and the back-pressure chamber 8; a first orifice 52 provided in the first communication passage 10 and generating a pressure difference acting on the pilot piston 51; a valve portion 51c provided in the pilot piston 51 and opening to the back-pressure chamber 8 side of the first communication passage 10; and a second seat portion 7j (seat portion) provided in the sleeve 7 and against which the valve portion 51c of the pilot piston 51 abuts. When the pilot piston 51 moves due to the pressure difference and the valve portion 51c of the pilot piston 51 seats on the second seat portion 7j (seat portion) of the sleeve 7, the working oil (working fluid) guided from the high-pressure passage H (high-pressure side passage) to the first communication passage 10 passes only through the second orifices 55, 155 and flows from the back-pressure chamber 8 to the pilot passage P1.

[0068] In this configuration, when the electromagnetic relief valve 100 (relief valve) operates, the valve portion 51c of the pilot piston 51 seats on the second seat portion 7j (seat portion) of the sleeve 7, so that the hydraulic oil flowing from the high-pressure passage H to the back-pressure chamber 8 passes only through the second orifice 55, 155. As a result, resistance is applied to the hydraulic oil flowing from the high-pressure passage H to the back-pressure chamber 8 by the first orifice 52 and the second orifice 55, 155, so the flow rate of the hydraulic oil flowing from the high-pressure passage H to the back-pressure chamber 8 can be reduced. As a result, the flow rate of the hydraulic oil discharged from the back-pressure chamber 8 to the drain chamber 12 through the pilot passage P1 decreases, so the opening degree of the pilot poppet 20 can be reduced. This prevents the behavior of the pilot poppet 20 from becoming unstable.

[0069] The electromagnetic relief valve 100 (relief valve) further includes a second communication passage 53 that is provided between the outer peripheral surface of the pilot piston 51 and the inner peripheral surface of a sliding hole 50a provided in the main poppet 5 (main valve body) and that connects the first communication passage 10 with the back pressure chamber 8, and the second orifice 55 is an annular orifice provided in the second communication passage 53.

[0070] In this configuration, the second throttle 55 is configured as an annular throttle, so that it is possible to easily configure a throttle with a small flow passage area compared to when the second throttle 55 is configured as an orifice.

[0071] In the electromagnetic relief valve 100 (relief valve), the second throttle 155 is a groove provided in at least one of the valve portion 51c of the pilot piston 51 and the second seat portion 7j (seat portion) of the sleeve 7.

[0072] In this configuration, the second orifice 155 is formed by, for example, a groove provided in one of the valve portion 51c of the pilot piston 51 and the second seat portion 7j (seat portion) of the sleeve 7, so that the second orifice 155 can be easily manufactured.

[0073] Although the embodiments of the present invention have been described above, the above embodiments merely illustrate some of the application examples of the present invention, and it is not intended that the technical scope of the present invention be limited to the specific configurations of the above embodiments.

[0074] In the above embodiment, the second orifice 55 is an annular orifice, but this is not limiting. For example, the diameter of the through-hole 54 may be adjusted to form the second orifice. Alternatively, the second orifice 55 may be formed by a groove provided on the outer periphery of the pilot piston 51.

[0075] In addition, in the relief valve 100 shown in FIG. 4, instead of the configuration in which the through hole 54 and the second throttle 55 are provided, an orifice equivalent to the second throttle 55 may be provided so as to penetrate the cylindrical portion of the second seat portion 7j. [Explanation of symbols]

[0076] 100···Solenoid relief valve (relief valve), 5···Main poppet (main valve element), 7···Sleeve, 7f···Protrusion, 7g···First seat portion, 7j···Second seat portion (seat portion), 8···Back pressure chamber, 10···Pilot passage, 20···Pilot poppet (pilot valve element), 51···Pilot piston, 51c···Valve portion, 52···First restriction, 53···Second communication passage, 54···Through hole, 55, 155···Second restriction, H···High pressure passage, L···Low pressure passage, P1···Pilot passage, S···Solenoid portion, V···Valve portion

Claims

1. a main valve body that connects or disconnects a high-pressure side passage and a low-pressure side passage; a back pressure chamber into which a working fluid is introduced to bias the main valve element in a valve closing direction; a sleeve that defines the back pressure chamber between itself and the main valve body; a pilot passage provided in the sleeve and connecting the back pressure chamber with a discharge passage for discharging the working fluid; a pilot valve body that operates in response to the pressure of the working fluid in the pilot passage and connects or disconnects the pilot passage and the discharge passage; a biasing portion that biases the pilot valve element in a valve closing direction; a pilot piston slidably provided in a slide hole formed in the main valve body, the pilot piston moving in response to a pressure difference between the pressure in the high-pressure passage and the pressure in the back pressure chamber; a first communication passage provided in the pilot piston and communicating the high-pressure side passage with the back pressure chamber; a first throttle provided in the first communication passage for generating the pressure difference acting on the pilot piston; a valve portion provided in the pilot piston, the valve portion opening to the back pressure chamber side of the first communication passage; a seat portion provided in the sleeve and against which the valve portion of the pilot piston abuts, when the pilot piston moves due to the pressure difference and the valve portion of the pilot piston seats on the seat portion of the sleeve, the working fluid guided from the high-pressure side passage to the first communication passage passes only through the second throttle and flows from the back pressure chamber to the pilot passage.

2. 2. The relief valve according to claim 1, a second communication passage provided between an outer peripheral surface of the pilot piston and an inner peripheral surface of the slide hole provided in the main valve body, the second communication passage communicating with the first communication passage and the back pressure chamber; The relief valve is characterized in that the second throttle is an annular throttle provided in the second communication passage.

3. 2. The relief valve according to claim 1, a second restriction formed in at least one of the valve portion of the pilot piston and the seat portion of the sleeve;

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