solenoid

Abstract

To provide a solenoid that can ensure thrust flatness over a wide range with a simple configuration. [Solution] The device comprises a coil, a fixed magnetic pole 2, and a movable magnetic pole 3. The fixed magnetic pole 2 has a first fixed magnetic pole portion 21 that forms an adsorption surface 21a to which the movable magnetic pole 3 is attracted when the coil is energized, and a second fixed magnetic pole portion 22 that is spaced apart from the first fixed magnetic pole portion 21 on the side of the movable magnetic pole 3 that is not attracted. The first cylindrical portion 21X of the first fixed magnetic pole portion 21 has an adsorption-side end face (first tip portion) 21c on the side of the second fixed magnetic pole portion 22, and the second cylindrical portion 22X of the second fixed magnetic pole portion 22 has a detachment-side end face (second tip portion) 22c on the adsorption side. An annular recess 30 extending in the circumferential direction is formed on the outer circumferential surface of the movable magnetic pole 3, and in the adsorption state S1 in which the movable magnetic pole 3 is attracted to the adsorption surface 21a, at least a part of the annular recess 30 is located on the adsorption side of the detachment-side end face (second tip portion) 22c.

Description

Technical Field

[0001] The present invention relates to a solenoid in which a movable magnetic pole operates with respect to a fixed magnetic pole.

Background Art

[0002] Conventionally, a solenoid as a functional component that converts electrical energy into mechanical motion by operating a movable magnetic pole (plunger) using electromagnetic force is generally known. Since the solenoid is an actuator with extremely excellent responsiveness, it is used in various scenes such as automobiles, home appliances, OA equipment, and electronic locks.

[0003] By the way, when the movable magnetic pole is attracted to the fixed magnetic pole in a solenoid, the thrust (attractive force) is inversely proportional to the square of the distance between the movable magnetic pole and the fixed magnetic pole. Therefore, as the movable magnetic pole approaches the adsorption position, the thrust of the movable magnetic pole rapidly increases. Particularly in a proportional solenoid, the region near the adsorption position where the thrust increases in this way cannot be used as a control stroke region. As a result, there may be a problem that the solenoid has to be enlarged in order to secure the control stroke region.

[0004] In view of such problems, Patent Document 1 discloses a technique for ensuring the flatness (stability) of the thrust in the region near the adsorption position and extending the control stroke region.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in recent years, the thrust required of solenoids has increased, which further increases the thrust in the region near the suction position. Therefore, there is a need for technology that can ensure even greater thrust flatness while keeping product costs down. [Means for solving the problem]

[0007] Therefore, the present invention provides a solenoid that can ensure thrust flatness over a wide range with a simple configuration.

[0008] A solenoid according to one aspect of the present invention comprises a coil, a fixed magnetic pole disposed near the coil, and a movable magnetic pole which is substantially cylindrical or columnar in shape and moves in its axial direction relative to the fixed magnetic pole when the coil is energized, wherein the fixed magnetic pole has a first fixed magnetic pole portion which forms an adsorption surface to which the movable magnetic pole is attracted when the coil is energized, and a second fixed magnetic pole portion which is spaced apart from the first fixed magnetic pole portion in the axial direction on the side from which the movable magnetic pole detaches from the adsorption surface, and the first fixed magnetic pole portion is such that a part of the movable magnetic pole enters when attracted The movable magnetic pole has a first cylindrical portion, the first cylindrical portion having a first tip portion on the side of the second fixed magnetic pole portion, the second fixed magnetic pole portion has a second cylindrical portion on its inside that holds at least a part of the movable magnetic pole, the second cylindrical portion having a second tip portion on the side of the first fixed magnetic pole portion, and an annular recess extending in the circumferential direction is formed on the outer circumferential surface of the movable magnetic pole, and in a state in which the movable magnetic pole is attracted to the first fixed magnetic pole portion (hereinafter referred to as the attracted state), at least a part of the annular recess is located on the side of the first fixed magnetic pole portion than the second tip portion.

[0009] In the above-described solenoid, in the adsorption state, at least a portion of the annular recess may be located on the side of the second fixed magnetic pole that is closer to the first tip.

[0010] In the solenoid described above, the annular recess is formed at a position away from the tip of the movable magnetic pole that is adsorbed to the adsorption surface, on the side of the second fixed magnetic pole, and in the detached state, when the movable magnetic pole has detached from the adsorption surface and is in the position closest to the second fixed magnetic pole, at least a portion of the annular recess may be located closer to the second fixed magnetic pole than the second tip.

[0011] In the above solenoid, the cross-sectional shape of the movable magnetic pole perpendicular to the axial direction is circular or annular, and the diameter of the bottom of the annular recess may be 90% or less of the diameter of the outer surface of the movable magnetic pole. [Effects of the Invention]

[0012] According to the solenoid described above, it is possible to ensure thrust flatness over a wide range with a simple configuration. [Brief explanation of the drawing]

[0013] [Figure 1] A longitudinal cross-sectional view of a solenoid according to an embodiment of the present invention, where (a) shows the adsorption state and (b) shows the detachment state. [Figure 2] This is a magnified longitudinal cross-sectional view of the vicinity of the annular recess, which is a key part of the solenoid, in the adsorption state. [Figure 3] This figure shows the magnetic flux generation state near the adsorption state when current is applied to the solenoid mentioned above. [Figure 4] This figure shows the magnetic flux generation state near the disconnection state when current is supplied to the solenoid mentioned above. [Figure 5] This figure shows experimental results confirming the effect of thrust flattening in the solenoid of the above embodiment through simulation, and represents the magnetic flux density of the movable magnetic pole in the adsorption state. (a) is a figure of an embodiment using a movable magnetic pole with an annular recess formed thereon, and (b) is a figure of a comparative example using a movable magnetic pole without an annular recess formed thereon. [Figure 6]This figure shows experimental results confirming the effect of thrust flattening in the solenoid of the above embodiment through simulation, and represents the magnetic flux density of the movable magnetic pole in an intermediate state. (a) is a figure of an embodiment using a movable magnetic pole with an annular recess formed therein, and (b) is a figure of a comparative example using a movable magnetic pole without an annular recess formed therein. [Figure 7] This figure shows experimental results confirming the effect of thrust flattening in the solenoid of the above embodiment through simulation, and represents the magnetic flux density of the movable magnetic pole in the detached state. (a) is a figure of an embodiment using a movable magnetic pole with an annular recess formed thereon, and (b) is a figure of a comparative example using a movable magnetic pole without an annular recess formed thereon. [Figure 8] The graph above shows the effect of thrust flattening obtained from the simulation, with the horizontal axis representing the distance from the adsorption surface to the movable magnetic pole and the vertical axis representing thrust (attraction force). [Modes for carrying out the invention]

[0014] Embodiments of the present invention will be described in detail below with reference to the drawings. (Overall structure) As shown in Figures 1(a) and 1(b), the solenoid 100 of this embodiment is a linear-acting (push-pull type) solenoid. Specifically, the solenoid 100 comprises a coil 1, a fixed magnetic pole 2 positioned near the coil 1, a movable magnetic pole 3 that is attracted to the fixed magnetic pole 2 when the coil 1 is energized, and a case 4 that supports the fixed magnetic pole 2 and houses the coil 1 and the movable magnetic pole 3 inside.

[0015] (movable magnetic pole) The movable magnetic pole 3 is a rod-shaped structure with a ring-shaped (or circular) cross-section centered on axis O, i.e., roughly cylindrical (or roughly cylindrical) in shape, extending in the axial direction D1, and a shaft 10, which also extends in the axial direction D1 centered on axis O, is inserted through it. The shaft 10 is fitted into the movable magnetic pole 3. Therefore, the axial direction D1 coincides with the longitudinal direction of both the movable magnetic pole 3 and the shaft 10.

[0016] On the outer peripheral surface of the movable magnetic pole 3, an annular concave portion 30 extending in the circumferential direction of the movable magnetic pole 3 (hereinafter simply referred to as the circumferential direction) is formed. As shown in FIG. 2, in this embodiment, the annular concave portion 30 has a planar bottom surface 31 and a pair of side surfaces 32 rising from both side edges of the bottom surface 31 in the axial direction D1 to the outside in the radial direction D2 (hereinafter simply referred to as the radial direction D2) of the movable magnetic pole 3, and has a groove shape with a substantially U-shaped cross section. The annular concave portion 30 is formed on the outer peripheral surface of the movable magnetic pole 3 at a position away from the other side in the axial direction D1 with respect to the front end surface (front end portion) 3a facing one side in the axial direction D1 of the movable magnetic pole 3, which is the side where the movable magnetic pole 3 is attracted to the fixed magnetic pole 2. The diameter dimension of the bottom surface 31 serving as the bottom of the annular concave portion 30 is preferably 90% or less of the diameter dimension of the outer peripheral surface of the movable magnetic pole 3. Therefore, the movable magnetic pole 3 is composed of a small-diameter region A1 where the annular concave portion 30 is formed and a large-diameter region A2 which is a region other than the small-diameter region A1.

[0017] (Fixed magnetic pole) The fixed magnetic pole 2 is provided so as to cover the movable magnetic pole 3 and the shaft 10 from the outer peripheral side. The fixed magnetic pole 2 has a first fixed magnetic pole portion 21 disposed on one side in the axial direction D1 (hereinafter referred to as the attracting side) and a second fixed magnetic pole portion 22 disposed at an interval on the other side in the axial direction D1 (hereinafter referred to as the separating side) with respect to the first fixed magnetic pole portion 21.

[0018] The first fixed magnetic pole portion 21 has a cylindrical shape centered on the axis O. The first fixed magnetic pole portion 21 forms an adsorption surface 21a on which the tip surface 3a of the movable magnetic pole 3 is adsorbed when current is supplied to the coil 1, which will be described in detail later. The first fixed magnetic pole portion 21 has a cylindrical first cylindrical portion 21X provided so that the adsorption surface 21a rises from the outer edge of the adsorption surface 21a so as to surround the periphery of the adsorption surface 21a from the outside in the radial direction of the movable magnetic pole 3. Therefore, the adsorption surface 21a defines the bottom of the first cylindrical portion 21X. In the adsorption state S1 where the tip surface 3a of the movable magnetic pole 3 is adsorbed on the adsorption surface 21a, a part of the movable magnetic pole 3 enters the inside of the first cylindrical portion 21X and the tip portion of the movable magnetic pole 3 is disposed, and the first cylindrical portion 21X and the outer peripheral surface of the movable magnetic pole 3 face each other. In this embodiment, an air gap bush 25 is provided on the adsorption surface 21a, and the adsorption surface 21a and the tip surface 3a of the movable magnetic pole 3 adsorb through this air gap bush 25, but this air gap bush 25 does not necessarily have to be provided.

[0019] Further, the first cylindrical portion 21X forms an adsorption-side end surface (first tip portion) 21c that is annular in the circumferential direction around the axis O as an end surface facing the separation side. In this embodiment, as the outer peripheral surface of the first cylindrical portion 21X, an inclined outer surface 21d that inclines from the adsorption-side end surface 21c toward the outside in the radial direction D2 and gradually expands the diameter of the first cylindrical portion 21X, and an adsorption-side outer surface 21e that extends in the axial direction D1 from the edge on the adsorption side of the inclined outer surface 21d to make the outer diameter of the first cylindrical portion 21X constant are formed. In the adsorption state S1, the whole (or a part) of the annular recess 30 in the movable magnetic pole 3 is located on the separation side with respect to the adsorption-side end surface 21c.

[0020] A shaft insertion hole 21b that penetrates in the axial direction D1 and opens to the adsorption surface 21a to insert the shaft 10 is formed in the first fixed magnetic pole portion 21. Returning to FIGS. 1(a) and 1(b), the first fixed magnetic pole portion 21 further has a flange portion 21Y that expands its own diameter at the adsorption-side end, and the first fixed magnetic pole portion 21 is fixed to a case 4, which will be described in detail later, through this flange portion 21Y.

[0021] The second fixed magnetic pole portion 22 is a bottomed cylindrical shape with the detachment side as the bottom, centered on the axis O, and has the movable magnetic pole 3 and a part of the shaft 10 arranged inside. The second fixed magnetic pole portion 22 has a second cylindrical portion 22X centered on the axis O that faces the outer circumferential surface of the movable magnetic pole 3, rising from the outer edge of the bottom surface 22a so as to surround the bottom surface 22a that faces the base end surface 3b of the movable magnetic pole 3 facing the detachment side in the axial direction D1. Therefore, at least a part of the movable magnetic pole 3 is arranged in the second cylindrical portion 22X. A circular recess 22b is formed in the bottom surface 22a centered on the axis O, and the shaft 10 is arranged in this recess 22b.

[0022] As shown in Figure 2, the second cylindrical portion 22X faces the adsorption side and forms a detachment end face (second tip) 22c that is annular in the circumferential direction. The detachment end face 22c faces the adsorption end face 21c with a gap in the axial direction D1. In the adsorption state S1, the entire annular recess 30 of the movable magnetic pole 3 is located on the adsorption side of the detachment end face 22c. However, it is not necessary for the entire annular recess 30 to be located on the adsorption side of the detachment end face 22c in the adsorption state S1; it is sufficient for at least a part of the annular recess 30 to be located on the adsorption side of the detachment end face 22c in the adsorption state S1.

[0023] (coil) Returning to Figures 1(a) and 1(b), coil 1 is provided between the first fixed pole portion 21 and the second fixed pole portion 22 so as to surround the fixed pole 2 from the outer circumference. Specifically, coil 1 is wound around a cylindrical coil bobbin 5 that covers the fixed pole 2 on the detached side of the flange portion 21Y of the first fixed pole portion 21. Power is supplied to coil 1 through lead wires (not shown). When current is supplied to coil 1, the tip surface 3a of the movable pole 3 is attracted to the adsorption surface 21a of the first fixed pole portion 21, and when the current to coil 1 is stopped, the tip surface 3a detaches from the adsorption surface 21a.

[0024] (case) Case 4 is cylindrical and is fixed to the outer circumferential surface of the flange portion 21Y of the first fixed magnetic pole portion 21, and is fixed to the second fixed magnetic pole portion 22 with the detachable end of the second fixed magnetic pole portion 22 protruding in the axial direction D1.

[0025] (Solenoid operation) When coil 1 is energized, a magnetic flux is generated such that the magnetic flux lines are directed from the second fixed magnetic pole portion 22 to the first fixed magnetic pole portion 21 via the movable magnetic pole 3, thereby generating thrust for the movable magnetic pole 3. In this embodiment, the solenoid 100 is a proportional solenoid that can be controlled to position the movable magnetic pole 3 at any desired location by adjusting the magnitude of the current flowing through coil 1, thereby balancing the biasing force from a biasing member (such as a spring) not shown. As a result, the movable magnetic pole 3 can reciprocate between an adsorption state S1 in which the tip surface 3a of the movable magnetic pole 3 is adsorbed to the adsorption surface 21a, and a detached state S2 in which the tip surface 3a of the movable magnetic pole 3 is detached from the adsorption surface 21a and the movable magnetic pole 3 is in the detached position. In the detached state S2, the shaft 10 is in contact with (or close to) the bottom surface of the recess 22b of the second fixed magnetic pole portion 22. In this detached state S2, the entire (or even a part of) annular recess 30 of the movable magnetic pole 3 is located on the detached side of the detached end face 22c of the fixed magnetic pole 2 (see Figure 4). Hereinafter, the state between the adsorption state S1 and the detachment state S2, where the distance between the tip surface 3a and the adsorption surface 21a is exactly half the distance in the adsorption state S1 and the distance in the detachment state S2, will be referred to as the "intermediate state".

[0026] Furthermore, it is preferable that the annular recess 30 is formed in a position, shape, and size such that it reduces the thrust (attraction force) of the movable magnetic pole 3 by 10% or more (more preferably 15% or more, even more preferably 20% or more) compared to the case where the annular recess 30 is absent in the adsorption state S1, and reduces the thrust (attraction force) of the movable magnetic pole 3 by less than 5% (more preferably less than 3%) compared to the case where the annular recess 30 is absent in the intermediate state.

[0027] (Effects and Benefits) As described above, with the solenoid 100 of this embodiment, when the movable magnetic pole 3 is attracted to the adsorption surface 21a by energizing the coil 1 and attempts to move to the adsorption side, a magnetic flux is generated such that the magnetic flux line B is directed from the second fixed magnetic pole portion 22 to the first fixed magnetic pole portion 21 via the movable magnetic pole 3, as shown in Figure 3. At this time, since an annular recess 30 is formed on the outer circumferential surface of the movable magnetic pole 3 so as to be located on the adsorption side of the detachment end face 22c in the adsorption state S1, the magnetic flux line B must pass through the small diameter region A1 of the movable magnetic pole 3 where the annular recess 30 is formed. For this reason, magnetic saturation is more likely to occur in the movable magnetic pole 3 compared to when the annular recess 30 is not formed, and as a result, it is possible to reduce the thrust of the movable magnetic pole 3 when approaching the adsorption state S1. In other words, with a very simple configuration such as forming an annular recess 30 on the movable magnetic pole 3, the thrust in the adsorption state S1 can be brought closer to the thrust in an intermediate state between the adsorption state S1 and the detachment state S2, and thrust flatness can be ensured over a wide area. Therefore, a wide control stroke range can be secured for the solenoid 100, and the axial dimension D1 of the product can be avoided. In particular, if the diameter of the bottom surface 31 of the annular recess 30 is 90% or less of the diameter of the outer surface of the movable magnetic pole 3, the occurrence of magnetic saturation in the movable magnetic pole 3 can be further promoted.

[0028] Furthermore, as shown in Figure 3, in the adsorption state S1, the annular recess 30 is located on the detachment side of the adsorption-side end face 21c. Therefore, as the device approaches the adsorption state S1, magnetic flux escapes radially outward from the large-diameter region A2 between the tip surface 3a of the movable magnetic pole 3 and the annular recess 30 toward the first cylindrical portion 21X of the first fixed magnetic pole portion 21, and as a result, the thrust can be further reduced. In addition, by forming the first cylindrical portion 21X on the first fixed magnetic pole portion 21, the distance between the movable magnetic pole 3 and the first fixed magnetic pole portion 21 near the detachment state S2 can be reduced compared to the case where the first cylindrical portion 21X does not exist, and the thrust near the detachment state S2 does not become too small. Thus, the control stroke region can be extended toward the detachment side as well.

[0029] Furthermore, as shown in Figure 4, in the detached state S2, the entire annular recess 30 is located further towards the detached side than the detached end face 22c. Therefore, in the vicinity of the detached state S2, magnetic flux can be generated such that the magnetic flux line B is directed from the second cylindrical portion 22X to the large-diameter region A2 between the tip surface 3a of the movable magnetic pole 3 and the annular recess 30. Thus, the magnetic flux line B is directed towards the large-diameter region A2 of the movable magnetic pole 3 without passing through the small-diameter region A1 of the movable magnetic pole 3, making it less likely for magnetic saturation to occur in the movable magnetic pole 3 in the vicinity of the detached state S2, and thus suppressing the decrease in thrust in the vicinity of the detached state S2.

[0030] Furthermore, in this embodiment, by forming the annular recess 30 in a position, shape, and size such that the thrust (attraction force) of the movable magnetic pole 3 is reduced by 10% or more (more preferably 15% or more, even more preferably 20% or more) in the adsorption state S1 compared to the case where the annular recess 30 is absent, and the thrust (attraction force) of the movable magnetic pole 3 is reduced by less than 5% (more preferably less than 3%) in the intermediate state compared to the case where the annular recess 30 is absent, the flatness of the thrust can be ensured over a wider area, and the control stroke area can be further expanded.

[0031] Herein, the present invention is not limited to the embodiments described above, and various modifications can be made without departing from the spirit of the invention. For example, the solenoid 100 is not limited to being a proportional solenoid, but may also be a tubular solenoid with a long stroke and requiring flat thrust.

[0032] Furthermore, the cross-sectional shape of the annular recess 30 is not limited to the above-described case; the cross-section may be trapezoidal or triangular such that the groove width gradually decreases towards the bottom of the annular recess 30.

[0033] Furthermore, the annular recess 30 is not limited to being formed in the position, shape, and size described above. It is sufficient if the annular recess 30 is formed in a position, shape, and size such that it reduces the thrust (attraction force) of the movable magnetic pole 3 by at least 10% (more preferably 15% or more, even more preferably 20% or more) compared to the case where the annular recess 30 is absent in the adsorption state S1, and reduces the thrust (attraction force) of the movable magnetic pole 3 by less than 5% (more preferably less than 3%) compared to the case where the annular recess 30 is absent in the intermediate state. [Examples]

[0034] The following describes the results of an experiment that confirmed the effect of thrust flattening in the solenoid 100 of the above-described embodiment through simulation. As shown in Figure 5(a), in the embodiment simulating the solenoid 100 described above, it was confirmed that in the adsorption state S1, the magnetic flux density was very high in the small-diameter region A1 where the annular recess 30 of the movable magnetic pole 3 was formed, making it easy for magnetic saturation to occur. On the other hand, as shown in Figure 5(b), in the comparative example simulating a solenoid 100H having a movable magnetic pole 3H without an annular recess 30, the magnetic flux density in the movable magnetic pole 3H was smaller than in the embodiment, and it was confirmed that magnetic saturation was less likely to occur compared to the embodiment.

[0035] Furthermore, as shown in Figures 6(a) and 6(b), in the intermediate state S3, there was no significant difference between the magnetic flux density at the movable magnetic pole 3 of the embodiment and the magnetic flux density at the movable magnetic pole 3H of the comparative example. It was confirmed that in both the embodiment and the comparative example, magnetic flux was generated such that the magnetic flux lines were directed from the movable magnetic poles 3 and 3H toward the first cylindrical portion 21X of the fixed magnetic pole 2.

[0036] Furthermore, as shown in Figures 7(a) and 7(b), even in the detached state S2, there was no significant difference between the magnetic flux density at the movable magnetic pole 3 of the embodiment and the magnetic flux density at the movable magnetic pole 3H of the comparative example. It was confirmed that in both the embodiment and the comparative example, magnetic flux was generated such that the magnetic flux lines were directed from the movable magnetic poles 3 and 3H toward the first cylindrical portion 21X of the fixed magnetic pole 2.

[0037] As shown in Figure 8, in the embodiment with the annular recess 30, compared to the comparative example without the annular recess 30, magnetic saturation is more likely to occur near the adsorption state S1, as described above. As a result, a thrust reduction effect of more than 20% is obtained in the adsorption state S1, while in the intermediate state S3, the thrust reduction is only about 0.2%, confirming the flattening of the thrust between the adsorption state S1 and the intermediate state S3. Furthermore, no significant difference in thrust was observed between the embodiment and the comparative example between the intermediate state S3 and the detachment state S2. Thus, it was found that forming the annular recess 30 on the movable magnetic pole 3 makes it possible to expand the control range. [Industrial applicability]

[0038] According to the solenoid of the present invention, it is possible to ensure thrust flatness over a wide range with a simple configuration. [Explanation of Symbols]

[0039] 1... Coil 2…Fixed magnetic pole 3, 3H…Movable magnetic pole 4…case 21...First fixed magnetic pole section 21X...First cylindrical part 21a…Adsorption surface 21c... Adsorption-side end face (first tip) 22...Second fixed magnetic pole section 22X...Second cylindrical part 22c... Detachable end face (second tip) 30…Annular recess 100, 100H... solenoid A1…Small diameter area A2…Large diameter area D1…Axis direction O…Axis line S1...Adsorption state S2... Departure state S3...Intermediate state

Claims

1. Coil and, A fixed magnetic pole positioned near the coil, A movable magnetic pole having a roughly cylindrical or columnar shape, which moves in its own axial direction relative to the fixed magnetic pole when current is passed to the coil, Equipped with, The aforementioned fixed magnetic pole is A first fixed magnetic pole portion that forms an adsorption surface to which the movable magnetic pole is attracted when current is supplied to the coil, A second fixed magnetic pole portion is positioned at a distance from the first fixed magnetic pole portion in the axial direction on the side from which the movable magnetic pole detaches from the adsorption surface, It has, The first fixed magnetic pole portion has a first cylindrical portion into which a part of the movable magnetic pole enters when attracted, The first cylindrical portion has a first tip portion on the side of the second fixed magnetic pole portion. The second fixed magnetic pole portion has a second cylindrical portion on which at least a part of the movable magnetic pole is arranged, The second cylindrical portion has a second tip portion on the side of the first fixed magnetic pole portion. An annular recess extending in the circumferential direction is formed on the outer surface of the movable magnetic pole. In a state in which the movable magnetic pole is attracted to the first fixed magnetic pole portion (hereinafter referred to as the attracted state), at least a portion of the annular recess is located on the side of the first fixed magnetic pole portion that is closer to the second tip portion of the solenoid.

2. The solenoid according to claim 1, wherein in the adsorption state, at least a portion of the annular recess is located on the side of the second fixed magnetic pole that is closer to the first tip.

3. The annular recess is formed at a position away from the tip of the movable magnetic pole that is adsorbed to the adsorption surface, on the side of the second fixed magnetic pole. The solenoid according to claim 1 or 2, wherein in the detached state, when the movable magnetic pole has detached from the adsorption surface and the movable magnetic pole is in the position closest to the second fixed magnetic pole, at least a portion of the annular recess is located closer to the second fixed magnetic pole than the second tip.

4. The cross-sectional shape of the movable magnetic pole perpendicular to the axial direction is circular or annular. The solenoid according to claim 1 or 2, wherein the diameter of the bottom of the annular recess is 90% or less of the diameter of the outer surface of the movable magnetic pole.

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