Electromagnetic relief valve and poppet valve

Abstract

This electromagnetic relief valve is provided with: a housing that includes an intermediate pressure chamber, a drain passage, a communication passage, and a solenoid storage chamber; a main valve body that opens and closes a valve passage by stroking in accordance with a differential pressure between a hydraulic pressure of a main port and an intermediate pressure of the intermediate pressure chamber; an auxiliary valve body that opens and closes the communication passage and is pressurized by the intermediate pressure in the direction of opening the communication passage; a biasing member that biases the auxiliary valve body so as to resist the intermediate pressure; and a solenoid that is stored in the solenoid storage chamber. The solenoid storage chamber is located on one side in the axial direction, which is the opposite side of the intermediate pressure chamber with respect to the communication passage in the axial direction. The communication passage comprises a storage portion which is connected to the solenoid storage chamber and in which the auxiliary valve body is stored so as to be capable of stroking, and a communication hole portion which connects the storage portion and the drain passage. The communication hole portion comprises a first opening port connected to the storage portion, and a second opening port connected to the drain passage. The first opening port is disposed on one side in the axial direction with respect to the second opening port.

Description

Solenoid relief valves and poppet valves

[0001] The present disclosure relates to an electromagnetic relief valve that discharges hydraulic fluid into a tank and a poppet valve that opens and closes a communication passage.

[0002] An electromagnetic relief valve that discharges hydraulic fluid to a tank is known, for example, as disclosed in Patent Document 1. In the electromagnetic relief valve of Patent Document 1, a pilot poppet is biased by an adjustment spring. In the electromagnetic relief valve, when the pressure in the high-pressure oil line increases and exceeds the operating pressure of the pilot poppet, the pilot poppet rises, connecting the pilot chamber to the tank port via the drain passage and the communication hole. This causes the main poppet to rise, opening the communication between the high-pressure oil line and the tank port. The electromagnetic relief valve of Patent Document 1, configured in this manner, is equipped with a solenoid that generates an electromagnetic force in a direction against the biasing force of the adjustment spring, thereby adjusting the relief pressure.

[0003] JP 2014-127492 A

[0004] In the electromagnetic relief valve of Patent Document 1, each component, including the solenoid, is housed in a casing, and the casing, including the solenoid housing chamber in which the solenoid is housed, is filled with oil. In addition, in the electromagnetic relief valve of Patent Document 1, air is introduced from a tank, for example, through a drain passage and further through a communication hole to the poppet housing. Furthermore, air enters the solenoid housing chamber from the housing through the central hole. Air that enters the solenoid housing chamber causes hunting in the movable iron core. Therefore, it is desirable to prevent air from accumulating in the housing chamber that houses the poppet valve body.

[0005] Therefore, an object of the present disclosure is to provide an electromagnetic relief valve and a poppet valve that can prevent air from accumulating in the accommodation chamber.

[0006] The electromagnetic relief valve of the present disclosure is an electromagnetic relief valve that discharges hydraulic fluid from a main port to a tank port by opening a valve passage having the main port and a tank port, and includes a housing including an intermediate pressure chamber connected to the main port, a drain passage connected to the tank port, and a communication passage connecting the intermediate pressure chamber and the drain passage; a main valve element that is accommodated in the housing so as to be able to stroke in the axial direction and that strokes in response to a pressure difference between the hydraulic pressure of the main port and the intermediate pressure of the intermediate pressure chamber to open and close the valve passage; a sub-valve element that opens and closes the communication passage and receives intermediate pressure in a direction to open the communication passage; and a sub-valve element that resists the intermediate pressure. and a solenoid that generates an electromagnetic force in response to an input signal and that resists the biasing force, wherein the solenoid is provided in the housing so as to be located on one axial side of the communication passage that is opposite the intermediate pressure chamber in the axial direction, and the communication passage has a accommodating section that is connected to the solenoid and in which the sub-valve is accommodated so as to be able to stroke, and a communication hole section that connects the accommodating section to the drain passage, and the communication hole section has a first opening that is connected to the accommodating section and a second opening that is connected to the drain passage, and the first opening is located on the other axial side of the second opening.

[0007] According to the present disclosure, in the communication hole, the first opening, which is an opening on the housing side, is located on one axial side relative to the second opening, which is an opening on the drain passage side. Therefore, when air flows up the drain passage in one axial direction, the communication hole can prevent the air from being guided from the second opening to the first opening. This prevents air from flowing from the drain passage toward the housing, thereby preventing air from accumulating in the housing.

[0008] The poppet valve of the present disclosure comprises a housing including a drain passage connected to a tank and a communication passage connected to the drain passage, a poppet valve body that opens and closes the communication passage and receives an intermediate pressure in a direction that opens the communication passage, and a biasing member that biases the poppet valve body against the intermediate pressure, wherein the communication passage has a housing portion in which the poppet valve body is slidably housed, and a communication hole portion that connects the housing portion and the drain passage, and the communication hole portion has a first opening that connects to the housing portion and a second opening that connects to the drain passage, and the first opening is located on the other axial side of the second opening.

[0009] According to the present disclosure, in the communication hole, the first opening, which is an opening on the housing side, is located to one side in the axial direction with respect to the second opening, which is an opening on the drain passage side. Therefore, when air flows up the drain passage in one axial direction, the communication hole can prevent the air from being guided from the second opening to the first opening. This prevents the air from flowing from the drain passage toward the housing.

[0010] According to the electromagnetic relief valve of the present disclosure, it is possible to prevent air from accumulating in the accommodation chamber.

[0011] According to the poppet valve of the present disclosure, it is possible to prevent air from accumulating in the housing portion.

[0012] The above and other objects, features, and advantages of the present invention will become apparent from the following detailed description of preferred embodiments, which proceeds with reference to the accompanying drawings.

[0013] Fig. 1 is a cross-sectional view showing an electromagnetic relief valve according to a first embodiment of the present disclosure; Fig. 2 is a cross-sectional view showing an enlarged portion of the electromagnetic relief valve of Fig. 1; Fig. 3 is a cross-sectional view showing a flow of working fluid in the electromagnetic relief valve of Fig. 1; Fig. 4 is a cross-sectional view showing an electromagnetic relief valve according to a second embodiment of the present disclosure; Fig. 5 is a cross-sectional view showing an electromagnetic relief valve according to a third embodiment of the present disclosure;

[0014] Hereinafter, electromagnetic relief valves 1, 1A, and 1B according to first to third embodiments of the present disclosure will be described with reference to the drawings. Note that the concepts of directions used in the following description are used for convenience of explanation and do not limit the orientation of the configuration of the present invention to those directions. Furthermore, the electromagnetic relief valves 1, 1A, and 1B described below are merely one embodiment of the present disclosure. Therefore, the present disclosure is not limited to the embodiments, and additions, deletions, and modifications are possible within the scope of the spirit of the invention.

[0015] 1 connects a fluid passage (not shown) to a tank when the hydraulic pressure of hydraulic fluid (e.g., oil and water) flowing through the fluid passage exceeds a relief pressure. This allows the electromagnetic relief valve 1 to discharge a portion of the hydraulic fluid to the tank, thereby maintaining the hydraulic pressure in the fluid passage at the relief pressure. The electromagnetic relief valve 1 is provided in, for example, a valve block 2.

[0016] As shown in FIG. 2 , the valve block 2 includes a valve passage 2a in addition to the aforementioned liquid passage (not shown). The valve passage 2a has a main port 2b, a tank port 2c, and a valve hole 2d. The main port 2b is connected to the liquid passage, and the tank port 2c is connected to a tank (not shown). The valve hole 2d is located between the main port 2b and the tank port 2c. The valve hole 2d extends along a predetermined axis L1 in the valve block 2 and is formed, for example, as a bottomed hole. In this embodiment, the valve hole 2d has a valve port 2e on its bottom surface, and the main port 2b is connected to the valve hole 2d via the valve port 2e. The valve hole 2d also has a seat 2f formed around the valve port 2e. Furthermore, the tank port 2c opens to the circumferential surface of the valve hole 2d.

[0017] The electromagnetic relief valve 1 is provided in the valve block 2 so as to block the valve passage 2a. More specifically, the electromagnetic relief valve 1 is inserted into the valve hole 2d so as to block the valve passage 2a. In this embodiment, the electromagnetic relief valve 1 is inserted into the valve hole 2d so that a check valve element 17, which will be described in detail later, is seated on a seat 2f. The electromagnetic relief valve 1 also opens the valve passage 2a to discharge hydraulic fluid from the main port 2b to the tank port 2c. More specifically, when the hydraulic pressure in a fluid passage (not shown) exceeds a relief pressure, the electromagnetic relief valve 1 opens the valve passage 2a to discharge hydraulic fluid flowing through the fluid passage to the tank. The electromagnetic relief valve 1 thus configured includes a housing 11, a main valve element 12, a poppet valve element 13, a rod 14, a biasing member 15, and a solenoid 16. The electromagnetic relief valve 1 also includes a check valve element 17 and an air bleed valve 18. In this embodiment, the housing 11 , the poppet valve body 13 , and the biasing member 15 constitute a poppet valve 3 .

[0018] The housing 11 includes an intermediate pressure chamber 21, a drain passage 22, and a communication passage 23. The housing 11 also includes an air reservoir 25. The intermediate pressure chamber 21 is connected to the main port 2b, as described in detail below. The drain passage 22 is connected to the tank port 2c. The communication passage 23 connects the intermediate pressure chamber 21 and the drain passage 22. The air reservoir 25 is disposed between the drain passage 22 and the communication passage 23. The air reservoir 25 captures and stores air introduced from the drain passage 22 and the communication passage 23. The housing 11 is formed, for example, in a cylindrical shape, and is inserted into the valve hole 2d so that its axis coincides with the axis L1. In this embodiment, the housing 11 is mainly composed of a housing main body 31, a communication passage forming portion 32, and a plug 33.

[0019] The housing body 31 accommodates the main valve element 12, which will be described in detail later. More specifically, the housing body 31 accommodates the main valve element 12 and the check valve element 17. In this embodiment, the housing body 31 is formed in a cylindrical shape. More specifically, one end portion of the housing body 31 is formed with a larger diameter than the other end portion. The other end portion of the housing body 31 is inserted into the valve hole 2d and screwed onto the valve block 2.

[0020] The communication passage forming portion 32 has a communication passage 23 and is inserted into the housing main body 31. More specifically, the communication passage forming portion 32 is inserted into the axially middle portion of the housing main body 31 and divides the internal space 31a, which is the space within the housing main body 31, into one axial side and the other axial side. The communication passage forming portion 32, together with the main valve element 12 (described in detail later), forms the intermediate pressure chamber 21 on the other axial side of the internal space 31a. Here, the axial direction is the direction in which the axis L1 extends. In this embodiment, the one axial side is the upper side of the paper in FIG. 1 , and the other axial side is the lower side of the paper in FIG. 1 . In this embodiment, the communication passage forming portion 32 has a cylindrical shape with a bottom, and one end portion is formed in a flange shape. The other end portion of the communication passage forming portion 32 is inserted into the housing main body 31 from one axial side (i.e., one end side). On the other hand, the section from the other end side to the axially intermediate section of the communicating passage forming section 32 is formed with a smaller diameter than the one end side section, and is spaced radially away from the inner circumferential surface of the housing main body 31. A check valve element 17, which will be described in detail later, is slidably fitted on the outside of the section from the other end side to the axially intermediate section of the communicating passage forming section 32. In other words, the check valve element 17 is disposed between the communicating passage forming section 32 and the housing main body 31, and a cylindrical drain passage 22 is formed around the check valve element 17 and between it and the housing main body 31.

[0021] The communication passage forming portion 32 also has a communication passage 23 formed therein, which connects the drain passage 22 and the intermediate pressure chamber 21. More specifically, the communication passage 23 has an accommodating portion 23a and a plurality of communication holes 23b. The communication passage 23 also has a passage portion 23c. The passage portion 23c is connected to the intermediate pressure chamber 21. More specifically, the passage portion 23c is formed in the other end portion of the communication passage forming portion 32 and opens at the other end of the communication passage forming portion 32. In this embodiment, the passage portion 23c extends in the axial direction and is formed along the axis L1.

[0022] The accommodation portion 23a is connected to the inside of the solenoid 16, which will be described in detail later. The accommodation portion 23a is also connected to the passage portion 23c. More specifically, the accommodation portion 23a is formed from one end side portion to the axially middle portion of the communication passage forming portion 32, and opens at one end of the communication passage forming portion 32. In this embodiment, the accommodation portion 23a extends in the axial direction and is formed along the axis L1. The passage portion 23c opens at the bottom surface of the accommodation portion 23a, and the accommodation portion 23a has a sub-valve seat 23d on the bottom surface around the opening of the passage portion 23c.

[0023] The plurality of communication holes 23b connect the accommodation portion 23a and the drain passage 22. More specifically, the communication holes 23b are formed in an axially intermediate portion of the communication passage forming portion 32. In this embodiment, the communication holes 23b are formed radially outward of the accommodation portion 23a in the communication passage forming portion 32. The communication holes 23b have a first opening 23e and a second opening 23f. The first opening 23e is connected to the accommodation portion 23a, and the second opening 23f is connected to the drain passage 22. The first opening 23e is disposed on one axial side of the second opening 23f. More specifically, the first opening 23e is formed in the inner circumferential surface of the communication passage forming portion 32 (i.e., the inner circumferential surface of the accommodation portion 23a) and is disposed to correspond to the flow of hydraulic fluid ejected from the passage portion 23c. The second opening 23f is formed in the outer circumferential surface of the communication passage forming portion 32. In this embodiment, an annular groove 23g is formed in the axially intermediate portion of the outer peripheral surface of the communication passage forming portion 32, and the second opening 23f opens in the annular groove 23g. In this embodiment, the communication hole portion 23b is formed linearly so as to connect the two openings 23e, 23f. That is, the communication hole portion 23b is formed so as to incline toward one axial side as it extends radially outward.

[0024] Furthermore, the communication passage forming portion 32 forms an air reservoir 25 within the housing main body 31. The air reservoir 25 is connected to the drain passage 22 and the communication passage 23. The air reservoir 25 is located radially outward from the second opening 23f. The air reservoir 25 is located axially to one side from the drain passage 22 and the second opening 23f and is recessed in one axial direction. More specifically, the air reservoir 25 is formed in the housing 11 as follows. That is, one end portion between the axially intermediate portion of the communication passage forming portion 32 and the housing main body 31 forms the air reservoir 25. More specifically, the one end portion of the communication passage forming portion 32 is spaced axially away from the check valve element 17 and the second opening 23f. As a result, a recess is formed within the housing main body 31 on one axial side of the check valve element 17 and the second opening 23f, and this recess forms the air reservoir 25. Therefore, the air reservoir 25 can capture and store air guided from the drain passage 22 and the communication passage 23. Moreover, the air reservoir 25 is inclined toward one side in the axial direction as it extends radially outward. Therefore, the air discharged from the second opening 23f is guided in the air reservoir 25 radially outward, away from the second opening 23f.

[0025] The plug 33 accommodates the poppet valve element 13, which will be described in detail later. The plug 33 is inserted into one end portion of the housing body 31. More specifically, the plug 33 is inserted into one end portion of the housing body 31 so that the one end portion protrudes to one side in the axial direction. The plug 33 is formed, for example, in a cylindrical shape and has a poppet accommodating space 33a, which is its inner hole. The poppet accommodating space 33a is connected to the accommodating portion 23a of the communicating passage forming portion 32.

[0026] The check valve element 17 shown in FIG. 2 is accommodated in the housing 11 and is movable in the axial direction. More specifically, the check valve element 17 moves between a seated position where it is seated on the seat 2f and a disengaged position where it is lifted off the seat 2f. When in the disengaged position, the check valve element 17 opens the valve passage 2a at an opening degree corresponding to the stroke amount. Furthermore, the check valve element 17 forms a drain passage 22 between itself and the inner circumferential surface of the housing 11. More specifically, the check valve element 17 is formed, for example, in a cylindrical shape, and one end thereof is slidably and sealed and fitted to the axially middle portion of the communication passage forming portion 32. Meanwhile, the check valve element 17 is accommodated within the housing body 31, spaced radially inward from the inner circumferential surface of the housing body 31, forming an annular drain passage 22 between itself and the inner circumferential surface of the housing body 31.

[0027] The backflow valve element 17 receives tank pressure from the hydraulic fluid flowing through the drain passage 22 in a direction that causes the backflow valve element 17 to lift off the seat 2f, i.e., in one first direction. More specifically, the backflow valve element 17 has one end portion formed with a larger diameter than the other end portion, forming a step between the one end portion and the other end portion. The backflow valve element 17 receives tank pressure in one first direction at the step. Furthermore, as will be described in detail later, the backflow valve element 17 defines an intermediate pressure chamber 21 therein, and receives intermediate pressure in a direction that causes the backflow valve element 17 to seat on the seat 2f, i.e., in the other first direction. In other words, the backflow valve element 17 receives intermediate pressure in a direction against the tank pressure. The backflow valve element 17 lifts off from the seat 2f when the differential pressure, obtained by subtracting the intermediate pressure from the tank pressure, exceeds a predetermined pressure, and seats on the seat 2f when the differential pressure falls below the predetermined pressure.

[0028] Furthermore, the check valve element 17 has a main valve seat 17a and multiple connecting passages 17b. The main valve element 12 is seated on the main valve seat 17a, as will be described in detail later. More specifically, the main valve seat 17a is formed around the opening on the other axial side of the inner bore of the check valve element 17. The connecting passage 17b connects the tank port 2c to the inner bore of the check valve element 17. More specifically, the connecting passage 17b is formed in a position corresponding to the tank port 2c at the other end of the check valve element 17, and penetrates the other end of the check valve element 17 in the radial direction. As a result, the main port 2b and the tank port 2c are connected to each other via the connecting passage 17b and the inner bore of the check valve element 17, with the check valve element 17 seated on the seat 2f.

[0029] The main valve element 12 is accommodated in the housing 11 so as to be movable in the axial direction. More specifically, the main valve element 12 is accommodated in the check valve element 17 so as to be slidable in the axial direction. The main valve element 12 seats on the main valve seat 17a, thereby closing the valve passage 2a. More specifically, the main valve element 12 closes the inner bore of the check valve element 17 by seating on the main valve seat 17a. This closes the valve passage 2a. The main valve element 12 also moves in one axial direction within the check valve element 17, thereby lifting it off the main valve seat 17a. This opens the valve passage 2a. After lifting off the main valve seat 17a, the main valve element 12 opens the valve passage 2a by an amount corresponding to the stroke from the main valve seat 17a.

[0030] Explaining in more detail, the main valve element 12 is accommodated in the housing body 31 and is disposed on the other axial side of the communication passage forming portion 32, and forms an intermediate pressure chamber 21 between itself and the communication passage forming portion 32. In this embodiment, the main valve element 12 is accommodated within the check valve element 17, which is inserted together with the communication passage forming portion 32, and forms the intermediate pressure chamber 21 between itself and the communication passage forming portion 32 in the inner hole of the check valve element 17. Therefore, the main valve element 12 receives intermediate pressure on the other axial side, i.e., in a direction that causes it to seat on the main valve seat 17a.

[0031] The main valve element 12 also has a through passage 12a. The through passage 12a connects the intermediate pressure chamber 21 and the main port 2b. This allows the hydraulic fluid in the main port 2b to be introduced into the intermediate pressure chamber 21. The main valve element 12 strokes to open or close the valve passage 2a in response to the pressure difference between the hydraulic pressure in the main port 2b and the intermediate pressure in the intermediate pressure chamber 21. More specifically, the through passage 12a has a variable throttle 12b, as described in detail below, and connects the main port 2b and the intermediate pressure chamber 21 via the variable throttle 12b. The main valve element 12 is also biased toward the main valve seat 17a by a first spring member 41. In this way, the main valve element 12 strokes to a position where the hydraulic pressure in the main port 2b, the intermediate pressure in the intermediate pressure chamber 21, and the biasing force of the first spring member 41 are balanced. This opens or closes the valve passage 2a, and the valve passage 2a is opened by an amount corresponding to the stroke amount.

[0032] More specifically, the main valve element 12 includes a valve element portion 12c and a piston portion 12d. The valve element portion 12c is accommodated in the housing 11 and is movable in the axial direction. The valve element portion 12c is inserted into the backflow valve element 17 in a sealed state and slidable in the axial direction. The valve element portion 12c closes the valve passage 2a by seating on the main valve seat 17a and opens the valve passage 2a by lifting off the main valve seat 17a. The valve element portion 12c receives the hydraulic pressure and intermediate pressure of the main port 2b in opposing directions and is biased toward the seat portion 2f (i.e., in the other first direction) by the first spring member 41. Therefore, the valve element portion 12c strokes in response to the pressure difference between the hydraulic pressure of the main port 2b and the intermediate pressure in the intermediate pressure chamber 21 to open or close the valve passage 2a. In this embodiment, the valve body portion 12c is formed in a cylindrical shape, and the tip portion thereof is seated on the main valve seat 17a.

[0033] The piston portion 12d is slidably inserted into the inner bore of the valve body portion 12c. More specifically, the piston portion 12d is slidably inserted into the inner bore of the valve body portion 12c with its tip end portion protruding from the valve body portion 12c. The piston portion 12d also has a through passage 12a. The through passage 12a extends in the axial direction in the piston portion 12d. The through passage 12a has multiple openings 12e. The openings 12e are formed on the outer peripheral surface of the tip end portion of the piston portion 12d and are exposed at the tip of the valve body portion 12c. As the piston portion 12d slides in one axial direction within the valve body portion 12c, the openings 12e reduce the area exposed at the tip of the valve body portion 12c. That is, each of the openings 12e forms a variable throttle 12b, which throttles the through passage 12a in accordance with the stroke of the piston portion 12d. The through passage 12a opens at one end of the piston portion 12d, and is connected to the intermediate pressure chamber 21 at that end of the piston portion 12d. Like the valve body portion 12c, the piston portion 12d also receives the hydraulic pressure of the main port 2b and the intermediate pressure in opposing directions, and is urged in the other first direction by the second spring member 42. Therefore, the piston portion 12d adjusts the opening of the variable throttle 12b in accordance with the pressure difference between the hydraulic pressure of the main port 2b and the intermediate pressure of the intermediate pressure chamber 21.

[0034] The poppet valve element 13, which is an example of a sub-valve element, opens and closes the communication passage 23. More specifically, the poppet valve element 13 is accommodated in a housing portion 23a so as to be movable in the axial direction. In this embodiment, the poppet valve element 13 is inserted into the housing portion 23a so as to be slidable in the axial direction. More specifically, the poppet valve element 13 has a sliding portion 13a in the axially intermediate portion, and the sliding portion 13a is inserted into the housing portion 23a so as to be slidable in the axial direction. The tip portion of the poppet valve element 13 protrudes from the housing portion 23a into the passage portion 23c and seats on the sub-valve seat 23d, thereby closing the communication passage 23. More specifically, the tip portion of the poppet valve element 13 is tapered. The tip portion of the poppet valve element 13 is inserted into the passage portion 23c and seats on the sub-valve seat 23d, thereby closing the passage portion 23c. Furthermore, the tip of the poppet valve element 13 moves away from the sub-valve seat 23d as the poppet valve element 13 strokes to one side in the axial direction, thereby opening the communication passage 23.

[0035] The poppet valve element 13 receives the intermediate pressure in a direction that opens the communicating passage 23 (in this embodiment, one axial direction). More specifically, as described above, the tip end portion of the poppet valve element 13 protrudes into the passage portion 23c, and the tip end portion receives the intermediate pressure, which is the hydraulic pressure in the passage portion 23c, in one axial direction. The poppet valve element 13 is also biased by two spring members 43, 44. More specifically, the poppet valve element 13 protrudes from the accommodation portion 23a into the poppet accommodation space 33a, and the base end portion of the poppet valve element 13 is accommodated in the poppet accommodation space 33a. The third spring member 43 and the fourth spring member 44 are accommodated in the poppet accommodation space 33a. The third spring member 43 biases the poppet valve element 13 in a direction that causes it to seat on the sub-valve seat 23d. The fourth spring member 44 biases the poppet valve body 13 in a direction against the biasing force of the third spring member 43 so as to bias the poppet valve body 13 toward the rod 14, which will be described in detail later. Therefore, the poppet valve body 13 strokes in response to the intermediate pressure and the biasing forces of the two spring members 43, 44 to open and close the communication passage 23.

[0036] Furthermore, the poppet valve body 13 includes a conducting portion 13b. The conducting portion 13b connects the interior of the solenoid 16, which will be described in detail later, with the accommodation portion 23a. More specifically, the poppet valve body 13 separates the accommodation portion 23a (more specifically, the portion of the accommodation portion 23a on the other axial side) from the poppet accommodation space 33a by the sliding portion 13a. The conducting portion 13b is formed on the outer peripheral surface of the sliding portion 13a and connects the separated accommodation portion 23a with the poppet accommodation space 33a. The conducting portion 13b has a flow path area smaller than the flow path area of ​​the communication hole portion 23b. However, the conducting portion 13b may have a flow path area larger than the flow path area of ​​the communication hole portion 23b.

[0037] As shown in FIG. 1 , the rod 14 is accommodated in the housing 11 and is movable in the axial direction. The rod 14 contacts the poppet valve body 13 and pushes the poppet valve body 13 in the other axial direction. More specifically, the rod 14 is inserted through a solenoid 16, which will be described in detail later. The rod 14 is formed, for example, in a rod shape with a circular cross section, and its tip end protrudes from the solenoid 16 into the poppet accommodating space 33a. The rod 14 is pressed against the base end of the poppet valve body 13 by the biasing force of a biasing member 15, which will be described in detail later. More specifically, a cap 55, which will be described in detail later, is fitted into one end of the plug 33. The cap 55 has a rod insertion hole 55a, and the tip end of the rod 14 is inserted through the rod insertion hole 55a and is movable in the axial direction. The rod 14 also has a spring bearing member 14b at its base end.

[0038] The biasing member 15 biases the poppet valve body 13 against the intermediate pressure. More specifically, the biasing member 15 biases the poppet valve body 13 via the rod 14. In this embodiment, the biasing member 15 is provided inside the fixed magnetic pole 52, which will be described in detail later. The biasing member 15 is, for example, a coil spring, and is provided in the spring receiving member 14b to bias the rod 14 in the other axial direction. As a result, the rod 14 is pressed against the base end of the poppet valve body 13, further pushing the poppet valve body 13 in the other axial direction.

[0039] The solenoid 16 shown in FIG. 1 generates an electromagnetic force in response to an input signal that resists the biasing force of the biasing member 15. In this way, the solenoid 16 adjusts the biasing force of the biasing member 15 in response to the input signal. The solenoid 16 is provided in the housing 11 so as to be located on one axial side of the communicating passage 23, opposite the intermediate pressure chamber 21 in the axial direction. More specifically, the solenoid 16 is provided in the plug 33 of the housing 11. In this embodiment, the solenoid 16 includes a solenoid cover 50, a coil member 51, and a solenoid tube 56.

[0040] The solenoid cover 50 accommodates a coil member 51, which will be described in detail later, and a solenoid tube 56 is inserted therein. The solenoid cover 50 is, for example, cylindrical and includes an accommodation chamber 60, which is its internal space. The accommodation chamber 60 has an inner bore 60a and a coil accommodation portion 60b. The inner bore 60a is a hole that penetrates the solenoid cover 50 in the axial direction along the axis L1. The coil accommodation portion 60b is an annular space formed around the inner bore 60a in the axially intermediate portion of the solenoid cover 50. More specifically, the solenoid cover 50 has inner flanges 50a, 50b that protrude radially inward at both axial ends, and the coil accommodation portion 60b is a space formed between the two inner flanges 50a, 50b. The solenoid cover 50 is provided at one end portion of the plug 33 so that its opening is abutted against an opening in the plug 33. Furthermore, in this embodiment, the solenoid cover 50 is provided at one end side portion of the plug 33 so that its axis coincides with the axis L1.

[0041] The coil member 51 generates a magnetic field in response to an input signal. More specifically, the coil member 51 has a cylindrical coil bobbin 51 a and a winding 51 b, and is configured by winding the winding 51 b around the coil bobbin 51 a. The coil member 51 is formed in a cylindrical shape and is housed in the coil housing portion 60 b of the solenoid cover 50.

[0042] The solenoid tube 56 includes a fixed magnetic pole 52, a guide member 54, a cap 55, and a movable iron core 53. The solenoid tube 56 is configured by assembling the fixed magnetic pole 52, the movable iron core 53, the guide member 54, and the cap 55 in advance to form a unit. The solenoid tube 56 is inserted through the solenoid cover 50, and both axial ends thereof protrude from the solenoid cover 50 in one axial direction and the other axial direction, respectively. In this embodiment, the solenoid tube 56 is inserted through an inner hole 60a of the accommodation chamber 60 (more specifically, within the coil member 51). The other axial end of the solenoid tube 56 is attached to the plug 33 by being threadedly engaged with the plug 33. Each component of the solenoid tube 56 will be described below.

[0043] The fixed magnetic pole 52 is made of a magnetic material. The fixed magnetic pole 52 is located on one axial side of the solenoid tube 56. In this embodiment, the fixed magnetic pole 52 is located on an inner flange 50a on one end of the solenoid cover 50. The fixed magnetic pole 52 is inserted into the coil member 51 and extends from the coil member 51 to one axial side of the solenoid cover 50. The fixed magnetic pole 52 is formed, for example, in a cylindrical shape and has an inner through-hole 52a. The aforementioned biasing member 15 is housed in the through-hole 52a. More specifically, the base end portion of the rod 14 is inserted into the through-hole 52a from the other axial side. A slide bearing 46 is provided in the through-hole 52a, and the base end portion of the rod 14 is supported by the through-hole 52a via the slide bearing 46. As described above, the biasing member 15 is attached to the base end of the rod 14 (more specifically, the spring receiving member 14 b ) and is disposed in the through hole 52 a of the fixed magnetic pole 52 .

[0044] The guide member 54 is made of a non-magnetic material and guides the movable iron core 53, which will be described in detail later, in the axial direction. More specifically, the guide member 54 is cylindrical. The guide member 54 is connected to the fixed magnetic pole 52 via a sleeve 57. More specifically, the sleeve 57 is cylindrical, for example. The other end of the fixed magnetic pole 52 is fitted into one end of the sleeve 57, and the one end of the guide member 54 is fitted into the other end. In this way, the guide member 54 and the fixed magnetic pole 52 are connected via the sleeve 57.

[0045] The cap 55 is provided at the opening on the other end side of the guide member 54 and closes the guide member 54. As a result, an internal space 56a is formed inside the solenoid tube 56, surrounded by the fixed magnetic pole 52, the guide member 54, and the cap 55. The cap 55 also protrudes from the guide member 54 in the other axial direction, and the protruding portion is screwed onto one end side of the plug 33 in a sealed state. In this way, the cap 55 is attached to the plug 33.

[0046] The cap 55 is formed, for example, in a cylindrical shape and has a rod insertion hole 55a as its inner hole. As described above, the rod 14 is inserted through the rod insertion hole 55a, and the tip of the rod 14 protrudes from the rod insertion hole 55a and is pressed against the base end of the poppet valve body 13. A gap is provided between the rod 14 and the inner circumferential surface of the rod insertion hole 55a, and an annular gap 14a is formed between the rod 14 and the inner circumferential surface of the rod insertion hole 55a. This allows hydraulic fluid to flow from one axial side to the other axial side within the rod insertion hole 55a through the annular gap 14a. Note that a slide bearing may be disposed between the rod 14 and the inner circumferential surface of the rod insertion hole 55a, and the rod 14 may be slidably disposed in the rod insertion hole 55a via the slide bearing. In this case, for example, the gap within the slide bearing has the same function as the annular gap 14a, that is, it allows the hydraulic fluid to flow from one axial side to the other axial side within the rod insertion hole 55a.

[0047] The movable core 53 is mounted on the rod 14 so as to be immovable relative to the rod 14 in the axial direction. More specifically, the movable core 53 is fixed to an axially intermediate portion of the rod 14 and slidably inserted into the guide member 54 so as to move axially together with the rod 14. That is, the movable core 53 is disposed between the fixed magnetic pole 52 and the plug 33 and moves axially therebetween in accordance with the movement of the rod 14. The movable core 53 is made of a magnetic material and is attracted to the fixed magnetic pole 52 when the coil member 51 generates a magnetic field. As a result, the movable core 53 applies an electromagnetic force to the rod 14 that resists the biasing force of the biasing member 15. This adjusts the biasing force applied to the poppet valve element 13 via the rod 14.

[0048] As described above, the movable core 53 is slidably housed in the guide member 54, separating the interior of the solenoid 16 (more specifically, the interior of the solenoid tube 56) into one end portion and the other end portion. The movable core 53 has a communication passage 53a. The communication passage 53a passes through the movable core 53 in the axial direction and connects the one end portion and the other end portion of the internal space 56a. This allows the working fluid to flow from the one end portion to the other end portion in the internal space 56a, filling the internal space 56a with working fluid.

[0049] As described above, the solenoid tube 56 configured in this manner is formed by assembling the fixed magnetic pole 52, the movable iron core 53, the guide member 54, and the cap 55 into a unit, for example. The solenoid tube 56 configured in this manner is formed, for example, in a cylindrical shape. The solenoid tube 56 is inserted into the solenoid cover 50 as follows. That is, the other axial end of the fixed magnetic pole 52 and the movable iron core 53 of the solenoid tube 56 are inserted into the solenoid cover 50. The solenoid tube 56 has one axial end portion of the fixed magnetic pole 52 protruding in one axial direction from the solenoid cover 50, and the cap 55 protruding in the other axial direction from the solenoid cover 50. The solenoid tube 56 is attached to the plug 33 by threading the cap 55 at the other axial end of the solenoid tube 56 onto the plug 33.

[0050] The air bleed valve 18 is a valve for releasing air introduced into the solenoid 16 (more specifically, into the solenoid tube 56). More specifically, the air bleed valve 18 is provided on one end side of the through hole 52a of the fixed magnetic pole 52. In this embodiment, the air bleed valve 18 includes a casing 18a and an air bleed valve body 18b. The casing 18a is formed in a cylindrical shape and has an air bleed passage 18c as its inner hole. The casing 18a is fitted into one end side of the through hole 52a in a sealed state, and the air bleed passage 18c is connected to the through hole 52a. The air bleed valve body 18b is threadedly engaged with the base end side of the air bleed passage 18c, and its tip end is seated on an air bleed valve seat 18d formed in the air bleed passage 18c. This closes the air bleed passage 18c. The air bleed valve body 18b can be separated from the air bleed valve seat 18d by rotating it and moving it in one axial direction. The air bleed valve body 18b has an internal passage 18e therein, and when separated from its seat, the working fluid is discharged from the electromagnetic relief valve 1 together with air through the internal passage 18e.

[0051] <Solenoid Oil Immersion and Air Bleeding Operations> In the electromagnetic relief valve 1 configured as described above, hydraulic fluid is introduced into the solenoid 16, and the solenoid tube 56 is filled with hydraulic fluid. More specifically, in the electromagnetic relief valve 1, hydraulic fluid is introduced into the solenoid tube 56, and the solenoid tube 56 is filled with hydraulic fluid. The movable iron core 53 within the solenoid tube 56 is immersed in hydraulic fluid. The following describes the oil immersion operation of introducing hydraulic fluid into the solenoid tube 56 and filling it with hydraulic fluid. In the oil immersion operation, hydraulic fluid is supplied to the main port 2b. The hydraulic fluid supplied to the main port 2b is introduced into the intermediate pressure chamber 21 through the through passage 12a, and the intermediate pressure eventually increases, opening the communication passage 23. Then, the hydraulic fluid is introduced into the other axial side of the accommodation portion 23a through the passage portion 23c and further into the poppet accommodation space 33a through the conducting portion 13b of the poppet valve body 13. Furthermore, the hydraulic fluid passes through the gap around the rod 14 in the rod insertion hole 55a and is guided into the solenoid tube 56, filling the inside of the solenoid tube 56. At this time, the hydraulic fluid is first guided to the other end side of the movable iron core 53 in the solenoid tube 56. Thereafter, the hydraulic fluid passes through the communication passage 53a and reaches the one end side of the movable iron core 53. As a result, the entire inside of the solenoid tube 56 is filled with hydraulic fluid.

[0052] Furthermore, during the oil immersion operation, the air bleed valve body 18b is separated from the air bleed valve seat 18d. Therefore, the working fluid introduced into one end portion of the solenoid tube 56 passes further from the through-hole 52a of the fixed magnetic pole 52 through the air bleed passage 18c and the inner passage 18e and is discharged to the outside of the electromagnetic relief valve 1. At this time, the working fluid pushes out the air in the communicating passage 23 and the solenoid tube 56 to the outside of the electromagnetic relief valve 1. As a result, the solenoid tube 56 is filled with working fluid, and the air in the communicating passage 23 and the solenoid tube 56 is bled.

[0053] <Operation of the Electromagnetic Relief Valve> In the electromagnetic relief valve 1, as shown by the two-dot chain line in FIG. 3 , the working fluid in the main port 2b is guided to the intermediate pressure chamber 21 through the through passage 12a. When the intermediate pressure exceeds the working pressure corresponding to the biasing force of the biasing member 15, the poppet valve element 13 lifts off from the sub-valve seat 23d, opening the communication passage 23. As a result, the working fluid in the intermediate pressure chamber 21 is discharged from the communication passage 23 through the drain passage 22 to the tank port 2c and then to the tank via the tank port 2c. As the working fluid is discharged from the intermediate pressure chamber 21 to the tank, the working fluid in the main port 2b is guided to the intermediate pressure chamber 21 through the through passage 12a. However, because the variable throttle 12b is formed in the through passage 12a, a pressure difference occurs between the fluid pressure in the main port 2b and the intermediate pressure. When a pressure difference occurs, the main valve element 12 is lifted in one axial direction and lifted off from the main valve seat 17a, opening the valve passage 2a. As a result, the hydraulic fluid in the main port 2b is discharged to the tank port 2c (see the thick line in FIG. 3), and the hydraulic pressure in the main port 2b is maintained at a relief pressure corresponding to the hydraulic pressure.

[0054] Furthermore, when the hydraulic pressure in the main port 2b drops below the relief pressure, the intermediate pressure decreases, and the poppet valve element 13 eventually seats on the sub-valve seat 23d. This causes the intermediate pressure to rise, reducing the pressure difference between the hydraulic pressure in the main port 2b and the intermediate pressure. This causes the main valve element 12 to move downward in the other axial direction and seat on the main valve seat 17a, closing the valve passage 2a. This stops the hydraulic fluid in the main port 2b from being discharged to the tank port 2c.

[0055] Furthermore, the electromagnetic relief valve 1 operates as follows when the hydraulic pressure at the main port 2b becomes lower than the tank pressure. That is, as the intermediate pressure decreases, the differential pressure obtained by subtracting the intermediate pressure from the tank pressure eventually exceeds a predetermined pressure. When this occurs, the check valve element 17 lifts off the seat 2f. This opens the valve passage 2a, and hydraulic fluid is guided from the tank port 2c to the main port 2b. This makes it possible to prevent cavitation from occurring due to a shortage of hydraulic fluid in the fluid passage connected to the main port 2b.

[0056] In the electromagnetic relief valve 1 configured as described above, air may be introduced from the tank into the drain passage 22 via the tank port 2c. Therefore, when the electromagnetic relief valve 1 is disposed so that one end thereof is positioned upward, the air rises in one axial direction through the drain passage 22 due to its buoyancy. The rising air eventually leaves the drain passage 22 and reaches the air reservoir 25, where it is captured. The air reservoir 25 is formed so as to be recessed toward one axial side of the second opening 23f. Therefore, the air captured in the air reservoir 25 is prevented from reaching the second opening 23f from the air reservoir 25. This prevents air from being introduced into the communicating passage 23 and from accumulating in the accommodation portion 23a.

[0057] Furthermore, in the electromagnetic relief valve 1, air may be contained in the hydraulic fluid that flows from the main port 2b through the through passage 12a and further via the intermediate pressure chamber 21 to the communicating passage 23. In the communicating passage 23, when the hydraulic fluid is ejected from the passage portion 23c into the accommodation portion 23a, the tip of the poppet valve body 13 causes the hydraulic fluid to have a velocity component in the radial direction, i.e., to flow so as to spread radially outward (see the two-dot chain line near the tip of the poppet valve body 13 in FIG. 3 ). Such hydraulic fluid flows toward the first opening 23e, which is positioned lower than the conduit portion 13b, and more hydraulic fluid flows into the first opening 23e. More specifically, because the first opening 23e is positioned to correspond to the flow of hydraulic fluid with a velocity component in the radial direction, more hydraulic fluid flows into the first opening 23e. This prevents air from accumulating in the accommodation portion 23a. Therefore, air contained in the hydraulic fluid is prevented from being introduced into the conducting portion 13b, and is also prevented from being introduced into the solenoid tube 56 via the conducting portion 13b.

[0058] Furthermore, when the electromagnetic relief valve 1 is positioned so that one end thereof is positioned upward, the air rises in one axial direction due to its buoyancy. In the electromagnetic relief valve 1, the second opening 23f, which is the outlet side of the communication hole portion 23b, is positioned on one axial side of the first opening 23e, so that air is prevented from returning from the second opening 23f to the first opening 23e through the communication hole portion 23b. Furthermore, in this embodiment, the communication hole portion 23b is inclined in one axial direction as it advances radially outward. Therefore, air introduced into the first opening 23e flows through the communication hole portion 23b toward the second opening 23f, preventing the air from returning to the storage portion 23a. This prevents air from accumulating in the storage portion 23a.

[0059] Furthermore, air flowing through the communication hole portion 23b is discharged through the second opening 23f and then captured in the air reservoir portion 25. The air reservoir portion 25 is recessed toward one axial side of the second opening 23f. Therefore, air is stored away from the second opening 23f, preventing the air from returning to the second opening 23f. This prevents air from accumulating in the storage portion 23a. Furthermore, the air reservoir portion 25 is inclined toward one axial direction as it extends radially outward, allowing air discharged from the second opening 23f to accumulate radially outward. This allows the air reservoir portion 25 to accumulate air at a position away from the second opening 23f, further preventing the air from returning to the second opening 23f. This prevents air from accumulating in the storage portion 23a.

[0060] In the electromagnetic relief valve 1 of this embodiment, the first opening 23e in the communication hole portion 23b is located on one side in the axial direction relative to the second opening 23f. Therefore, when air flows up the drain passage 22 in one axial direction, the communication hole portion 23b can prevent the air from being guided from the second opening 23f to the first opening 23e. This prevents air from flowing from the drain passage 22 toward the accommodation portion 23a, thereby preventing air from accumulating in the accommodation portion 23a. This prevents air from entering the solenoid tube 56.

[0061] Furthermore, in the electromagnetic relief valve 1 of this embodiment, the air reservoir 25 is located on one axial side of the second opening 23f and is recessed in one axial direction. Therefore, the air reservoir 25 can capture air that has risen in one axial direction through the drain passage 22. This prevents air from accumulating in the accommodation portion 23a. This further prevents air from entering the solenoid tube 56.

[0062] Furthermore, in the electromagnetic relief valve 1 of this embodiment, the second opening 23f opens radially inward of the drain passage 22, and the air reservoir 25 is inclined in one axial direction as it extends radially outward. Therefore, air accumulates radially outward of the air reservoir 25, and air is prevented from being introduced into the second opening 23f. This prevents air from being introduced into the communicating passage 23, further preventing air from accumulating in the accommodation portion 23a. Therefore, air is further prevented from entering the solenoid tube 56.

[0063] Furthermore, in the electromagnetic relief valve 1 of this embodiment, the passage portion 23c extends in one axial direction, and the poppet valve element 13 has a tapered tip that is inserted into the passage portion 23c to close the passage portion 23c. Therefore, when the passage portion 23c is opened, the hydraulic fluid flowing from the passage portion 23c to the housing portion 23a strikes the poppet valve element 13 and is directed radially outward. When directed radially outward, the communicating hole portion 23b extends obliquely toward one axial direction as it moves radially outward. Therefore, the hydraulic fluid can flow smoothly through the communicating hole portion 23b. This allows air to easily flow into the communicating hole portion 23b along with the hydraulic fluid, thereby preventing air from remaining in the housing portion 23a. This further prevents air from accumulating in the housing portion 23a and further prevents air from entering the solenoid tube 56.

[0064] Furthermore, in the electromagnetic relief valve 1 of this embodiment, the communication hole portion 23b extends radially inward from the drain passage 22 toward the accommodation portion 23a and is inclined toward the other axial direction as it travels from the drain passage 22 toward the accommodation portion 23a. Therefore, even if air flows up the drain passage 22 in the other axial direction, the air can be prevented from traveling through the communication hole portion 23b. This prevents air from traveling from the drain passage 22 toward the accommodation portion 23a, further preventing air from accumulating in the accommodation portion 23a. This further prevents air from entering the solenoid tube 56.

[0065] Furthermore, in the electromagnetic relief valve 1 of this embodiment, the conducting portion 13b has a flow path area smaller than the flow path area of ​​the communication hole portion 23b, which makes it possible to prevent air from being introduced into the solenoid tube 56 from the accommodation portion 23a via the conducting portion 13b.

[0066] Furthermore, in the poppet valve 3 of this embodiment, the first opening 23e in the communication hole portion 23b is located on one side of the axial direction relative to the second opening 23f. Therefore, when air flows up the drain passage 22 in one axial direction, the communication hole portion 23b can prevent the air from being guided from the second opening 23f to the first opening 23e. This prevents the air from flowing from the drain passage 22 toward the accommodation portion 23a. This prevents air from accumulating in the accommodation portion 23a.

[0067] [Second embodiment] An electromagnetic relief valve 1A of a second embodiment shown in Fig. 4 is similar in configuration to the electromagnetic relief valve 1 of the first embodiment. Therefore, with regard to the configuration of the electromagnetic relief valve 1A of the second embodiment, differences from the electromagnetic relief valve 1 of the first embodiment will mainly be described, and the same components will be assigned the same reference numerals and descriptions thereof will be omitted. The same applies to an electromagnetic relief valve 1B of a third embodiment etc., which will be described later.

[0068] The electromagnetic relief valve 1A of the second embodiment includes a housing 11, a main valve element 12, a poppet valve element 13A, a rod 14, a biasing member 15, a solenoid 16, a check valve element 17, and an air vent valve 18. The conducting portion 13c of the poppet valve element 13A connects the accommodation portion 23a to the inside of the solenoid 16 (more specifically, the inside of the solenoid tube 56), and is configured as follows in this embodiment. That is, the conducting portion 13c extends along the axis of the poppet valve element 13A (along the axis L1 in this embodiment). The conducting portion 13c has a plurality of tip-side openings 13d and a plurality of base-side openings 13e on the outer circumferential surface of the poppet valve element 13A.

[0069] The tip-side opening 13d is formed on the outer peripheral surface of the poppet valve body 13A, closer to the tip than the sliding portion 13a, and is connected to the communication passage 23 (more specifically, the accommodation portion 23a). On the other hand, the base-side opening 13e is formed on the outer peripheral surface of the poppet valve body 13A, closer to the base than the sliding portion 13a, and is connected to the poppet accommodation space 33a. Therefore, the conducting portion 13c also connects the communication passage 23 to the poppet accommodation space 33a and further to the inside of the solenoid tube 56 via the rod insertion hole 55a. In this embodiment, for example, four tip-side openings 13d and four base-side openings 13e are formed on the outer peripheral surface, and are arranged at equal intervals in the circumferential direction. Furthermore, like the conducting portion 13b in the first embodiment, the conducting portion 13c has a flow passage area smaller than the flow passage area of ​​the communicating hole portion 23b, making it difficult for air to enter.

[0070] In addition, the electromagnetic relief valve 1A of the second embodiment has the same functions and effects as the electromagnetic relief valve 1 of the first embodiment.

[0071] 5, the electromagnetic relief valve 1B of the third embodiment includes a housing 11, a main valve element 12, a poppet valve element 13B, a rod 14, a biasing member 15, a solenoid 16, a check valve element 17, and an air vent valve 18. The conducting portion 13f of the poppet valve element 13B connects the accommodation portion 23a with the inside of the solenoid 16 (more specifically, the inside of the solenoid tube 56), and is configured as follows in this embodiment. That is, the conducting portion 13f is a groove formed in the outer peripheral surface of the poppet valve element 13B, and is arranged in a spiral shape on the outer peripheral surface of the poppet valve element 13B. The base end of the conducting portion 13f is connected to the communicating passage 23 (more specifically, the accommodation portion 23a), and the base end is connected to the poppet accommodation space 33a. Therefore, the conducting portion 13f also connects the communication passage 23 to the poppet accommodating space 33a and further to the inside of the solenoid tube 56 via the rod insertion hole 55a. Also, like the conducting portion 13b in the first embodiment, the conducting portion 13f has a flow path area smaller than the flow path area of ​​the communication hole portion 23b, making it difficult for air to enter.

[0072] In addition, the electromagnetic relief valve 1B of the third embodiment has the same functions and effects as the electromagnetic relief valve 1 of the first embodiment.

[0073] [Other Embodiments] In the electromagnetic relief valves 1, 1A, and 1B of the first to third embodiments, the housing 11 includes the air reservoir 25, but this does not necessarily have to be the case. The shape of the air reservoir 25 is not limited to the shape described above. The communication hole 23b is formed to be inclined, but may be formed in a crank shape or a curved shape, as long as the opening on the accommodating portion 23a side is located closer to the other end than the opening on the drain passage side. The electromagnetic relief valves 1, 1A, and 1B of the first to third embodiments employ a pull-type solenoid 16, but a push-type solenoid may also be employed. The electromagnetic relief valves 1, 1A, and 1B of the first to third embodiments employ a main valve element 12 that includes the piston portion 12d, but may instead comprise only the valve element portion 12c.

[0074] In the electromagnetic relief valves 1, 1A, and 1B of the first to third embodiments, the entire air reservoir 25 is located radially outward from the second opening 23 f, but it is sufficient if at least a portion of the air reservoir 25 is located radially outward from the second opening 23 f. In addition, the solenoid tube 56 is configured by assembling the fixed magnetic pole 52, the movable iron core 53, the guide member 54, and the cap 55 in advance, but this is not necessarily required.

[0075] <Exemplary Embodiment> An electromagnetic relief valve according to a first aspect is an electromagnetic relief valve that discharges hydraulic fluid from a main port to a tank port by opening a valve passage having the main port and a tank port, and includes a housing including an intermediate pressure chamber connected to the main port, a drain passage connected to the tank port, and a communication passage connecting the intermediate pressure chamber and the drain passage; a main valve element that is accommodated in the housing so as to be movable in an axial direction and that strokes in response to a pressure difference between a hydraulic pressure at the main port and an intermediate pressure in the intermediate pressure chamber to open and close the valve passage; a sub-valve element that opens and closes the communication passage and receives intermediate pressure in a direction to open the communication passage; the solenoid is provided in a housing so as to be located on one axial side of the communication passage, opposite the intermediate pressure chamber in the axial direction, and the communication passage has a accommodating section connected to the solenoid and in which the sub-valve is accommodated so as to be able to stroke, and a communication hole section connecting the accommodating section to the drain passage, the communication hole section having a first opening connected to the accommodating section and a second opening connected to the drain passage, the first opening being located on the other axial side of the second opening.

[0076] According to the above aspect, in the communication hole, the first opening, which is an opening on the housing side, is located on one side in the axial direction with respect to the second opening, which is an opening on the drain passage side. Therefore, when air flows up the drain passage in one axial direction, the communication hole can prevent the air from being guided from the second opening to the first opening. This prevents the air from flowing from the drain passage toward the housing, thereby preventing the air from accumulating in the housing.

[0077] In a second aspect, the electromagnetic relief valve is the electromagnetic relief valve of the first aspect, wherein the housing includes an air reservoir portion disposed between the drain passage and the communication passage, and the air reservoir portion is located axially to one side from the drain passage and the second opening and is recessed in one axial direction.

[0078] According to the above aspect, the air reservoir is located on one side of the second opening in the axial direction and is recessed in that direction. Therefore, the air reservoir can capture air that has risen up the drain passage in that direction, thereby further preventing air from accumulating in the storage portion.

[0079] An electromagnetic relief valve in a third aspect is the electromagnetic relief valve of the second aspect, wherein the air reservoir portion is located radially outward of the second opening and is inclined toward one side in the axial direction as it extends radially outward.

[0080] According to the above aspect, the air reservoir is located radially outward of the second opening and is inclined in one axial direction as it extends radially outward. Therefore, air accumulates radially outward of the air reservoir, preventing air from being introduced into the second opening. This prevents air from being introduced into the communication passage, further preventing air from accumulating in the storage portion.

[0081] The electromagnetic relief valve in a fourth aspect is the electromagnetic relief valve of any one of the first to third aspects, wherein the communicating passage has a passage portion connected to the intermediate pressure chamber, the sub-valve body is a poppet valve body whose tip portion is formed in a tapered shape and whose tip portion is inserted into the passage portion to close the passage portion, the passage portion extends in the axial direction, and the communicating hole portion extends obliquely toward one side in the axial direction as it progresses radially outward.

[0082] According to the above aspect, the passage extends in one axial direction, and the poppet valve element has a tapered tip that is inserted into the passage to close the passage. Therefore, when the passage is opened, hydraulic fluid flowing from the passage to the housing strikes the poppet valve element and is directed radially outward. When directed radially outward, the hydraulic fluid has a communicating hole that extends obliquely toward one axial direction. Therefore, the hydraulic fluid can flow smoothly through the communicating hole. This allows air to easily flow into the communicating hole along with the hydraulic fluid, thereby preventing air from remaining in the housing. This further prevents air from accumulating in the housing.

[0083] The electromagnetic relief valve in a fifth aspect is the electromagnetic relief valve of any one of the first to fourth aspects, wherein the sub-valve body includes a conducting portion, the accommodating portion and the inside of the solenoid are connected to each other via the conducting portion, and the conducting portion has a flow path area smaller than the flow path area of ​​the communicating hole portion.

[0084] According to the above aspect, the conducting portion has a flow path area smaller than the flow path area of ​​the communication hole portion, so that it is possible to prevent air from being introduced from the accommodation portion into the solenoid via the conducting portion.

[0085] In a sixth aspect, a poppet valve includes a housing including a drain passage connected to a tank and a communication passage connected to the drain passage, a poppet valve body that opens and closes the communication passage and receives an intermediate pressure in a direction to open the communication passage, and a biasing member that biases the poppet valve body against the intermediate pressure, wherein the communication passage has a housing portion in which the poppet valve body is slidably housed, and a communication hole portion that connects the housing portion and the drain passage, and the communication hole portion has a first opening connected to the housing portion and a second opening connected to the drain passage, and the first opening is located on the other axial side of the second opening.

[0086] According to the above aspect, in the communication hole, the first opening, which is an opening on the housing side, is located on one axial side with respect to the second opening, which is an opening on the drain passage side. Therefore, when air flows up the drain passage in one axial direction, the communication hole can prevent the air from being guided from the second opening to the first opening. This can prevent the air from flowing from the drain passage toward the housing.

[0087] From the above description, many modifications and other embodiments of the present invention will be apparent to those skilled in the art. Therefore, the above description should be construed as illustrative only and is provided for the purpose of teaching those skilled in the art the best mode for carrying out the present invention. Details of the structure and / or function thereof may be substantially changed without departing from the spirit of the present invention.

Claims

1. An electromagnetic relief valve that discharges hydraulic fluid from a main port to a tank port by opening a valve passage having the main port and a tank port, comprising: a housing including an intermediate pressure chamber connected to the main port, a drain passage connected to the tank port, and a communication passage connecting the intermediate pressure chamber and the drain passage; a main valve element that is accommodated in the housing and can move axially and strokes in response to a pressure difference between the hydraulic pressure of the main port and the intermediate pressure of the intermediate pressure chamber to open and close the valve passage; a sub-valve element that opens and closes the communication passage and receives intermediate pressure in a direction to open the communication passage; a biasing member that biases the sub-valve element against the intermediate pressure; and a solenoid that generates an electromagnetic force in response to an input signal and against the biasing force, the solenoid being provided in the housing so as to be located on one axial side of the communication passage opposite the intermediate pressure chamber in the axial direction, the communication passage has a housing portion that is connected to the solenoid and that houses the sub-valve element so as to be able to stroke, and a communication hole portion that connects the housing portion to the drain passage, the communication hole portion having a first opening that is connected to the housing portion and a second opening that is connected to the drain passage, the first opening being located on the other axial side of the second opening, an electromagnetic relief valve.

2. An electromagnetic relief valve as set forth in claim 1, wherein the housing includes an air reservoir portion disposed between the drain passage and the communication passage, the air reservoir portion being located on one side of the axial direction from the drain passage and the second opening and recessed in one axial direction.

3. An electromagnetic relief valve as set forth in claim 2, wherein the air reservoir is located radially outward of the second opening and is inclined radially outward toward one side in the axial direction.

4. An electromagnetic relief valve as described in claim 1, wherein the communicating passage has a passage portion connected to the intermediate pressure chamber, the sub-valve body is a poppet valve body whose tip portion is formed in a tapered shape and whose tip portion is inserted into the passage portion to close the passage portion, the passage portion extends in the axial direction, and the communicating hole portion extends obliquely towards one side in the axial direction as it progresses radially outward.

5. An electromagnetic relief valve as described in claim 1, wherein the sub-valve element includes a conducting portion, the accommodating portion and the interior of the solenoid are connected to each other via the conducting portion, and the conducting portion has a flow path area smaller than the flow path area of ​​the communicating hole portion.

6. A poppet valve comprising: a housing including a drain passage connected to a tank and a communication passage connected to the drain passage; a poppet valve element that opens and closes the communication passage and receives an intermediate pressure in a direction that opens the communication passage; and a biasing member that biases the poppet valve element against the intermediate pressure, wherein the communication passage has a housing portion in which the poppet valve element is slidably housed, and a communication hole portion that connects the housing portion and the drain passage, and the communication hole portion has a first opening that connects to the housing portion and a second opening that connects to the drain passage, and the first opening is located on the other axial side of the second opening.

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