Systems and methods for solenoids with permanent magnets

Abstract

To provide a solenoid eliminating the need to use two or more wire coils or coil bays to move an armature between two or more positions.SOLUTION: A solenoid includes a housing 102, a pole piece 104, a wire coil 140 arranged within the housing 102, a permanent magnet 109 arranged between the pole piece 104 and an end plate 106, an armature 108 configured to selectively move between a first position and a second position in response to a current applied to the wire coil 140, and a spring 144 configured to bias the armature 108. When the wire coil 140 is de-energized, the armature 108 is maintained in at least one of the first position and the second position. The first position is configured to be maintained by the spring 144, and the second position is configured to be maintained by magnetic attraction between the armature 108 and the permanent magnet 109 through engagement between the armature 108 and the pole piece 104.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application is based on and claims priority to U.S. Provisional Application No. 62 / 926,937, filed October 28, 2019, the entire contents of which are incorporated herein by reference.

[0002] <Statement Regarding Federally Sponsored Research> Not applicable. [Background technology]

[0003] Generally, a solenoid includes a coil of wire that can be selectively energized (ie, have current passed through it in a predetermined amount and direction) to move an armature between one or more positions. Summary of the Invention

[0004] In some aspects, the present disclosure provides a solenoid comprising a housing, pole pieces, end plates integral with or coupled to the housing, a wire coil disposed within the housing, a permanent magnet disposed between the pole pieces and the end plates, an armature configured to selectively move between a first position and a second position in response to a current applied to the wire coil, and a spring biased between the armature and the pole pieces. When the wire coil is not energized, the armature is maintained in at least one of the first and second positions. The first position is configured to be maintained by engagement with the spring, and the second position is configured to be maintained by a magnetic attractive force between the armature and the permanent magnet due to engagement between the armature and the pole pieces.

[0005] In another aspect, the present disclosure provides a solenoid including a housing, pole pieces, end plates integral with or coupled to the housing, a wire coil disposed within the housing, a permanent magnet disposed between the pole pieces and the end plate, an armature configured to move between a first position and a second position in response to a current applied to the wire coil, and a spring configured to bias the armature. When the wire coil is not energized, the armature is maintained in at least one of the first and second positions. The first position is configured to be maintained by the spring, and the second position is configured to be maintained by a magnetic attraction between the armature and the permanent magnet due to engagement between the armature and the pole pieces.

[0006] In some aspects, the present disclosure provides a solenoid including a housing, pole pieces, end plates integral with or coupled to the housing, a wire coil disposed within the housing, a permanent magnet axially disposed between the pole pieces and the end plates, an armature configured to move between a first position and a second position in response to a current applied to the wire coil, a pin coupled to the armature, and a spring configured to bias the armature. The pole pieces or end plates include bearing surfaces configured to slidably receive the pin. When the wire coil is not energized, the armature is maintained in at least one of the first and second positions. The first position is configured to be maintained by the spring, and the second position is configured to be maintained by a magnetic attractive force between the armature and the permanent magnet due to engagement between the armature and the pole pieces.

[0007] These and other aspects and advantages of the present disclosure will become apparent from the following description. The following description is set forth with reference to the accompanying drawings, which form a part hereof, and in which there are shown, for purposes of illustration, preferred configurations of the present disclosure. However, these configurations do not necessarily represent the full scope of the present disclosure, and reference should be made to the claims and this specification in interpreting the scope of the present disclosure.

[0008] The present invention will be better understood, and further aspects and advantages thereof will become apparent, by consideration of the following detailed description, which refers to the following drawings. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view of a solenoid according to one aspect of the present disclosure. [Figure 2] 2 is a cross-sectional view of the solenoid of FIG. 1 with the pole piece provided with an extension for a pin. [Figure 3] 3 is a cross-sectional view of the solenoid of FIG. 2 in which the end plate is integrally formed with the housing. [Figure 4] 3 is a cross-sectional view of the solenoid of FIG. 2 in which the top wall of the housing is formed as a separate piece. [Figure 5] 3 is a cross-sectional view of the solenoid of FIG. 2 showing magnetic flux lines. [Figure 6] 3 is a cross-sectional view of the solenoid of FIG. 2 with notches in the pole pieces and the armature in a first position. [Figure 7] FIG. 5 is a cross-sectional view of the solenoid of FIG. 4 with the armature in a second position. [Figure 8] 8 is a graph showing the force acting on the armature as a function of current for the solenoid of FIG. 7 in the extended or second position. DETAILED DESCRIPTION OF THE INVENTION

[0010] Before describing aspects of the present disclosure in detail, it is to be understood that the present disclosure is not limited in its application to the details of construction and arrangement of parts set forth in the following description or illustrated in the accompanying drawings. The present disclosure is capable of other forms and of being practiced or carried out in various ways. It is also to be understood that the phraseology and terminology used herein are for the purpose of description and not of limitation. The terms "including," "comprising," or "having" and variations thereof used herein are meant to encompass the previously listed elements, equivalents thereof, and additional elements. Unless otherwise expressly stated or limited, the terms "mounted," "connected," "supported," "coupled," and variations thereof are used broadly and encompass both direct and indirect mounting, connecting, supporting, and coupling. Furthermore, "connected" and "coupled" are not limited to physical or mechanical connections or couplings.

[0011] The following description is presented to enable those skilled in the art to make and use aspects of the present disclosure. Various modifications to the configurations shown will be apparent to those skilled in the art, and the generic principles described herein may be applied to other configurations and applications without departing from the aspects of the present disclosure. Thus, the aspects of the present disclosure should not be limited to the configurations shown, but are to be accorded the widest scope consistent with the principles and features disclosed herein. The following detailed description should be understood with reference to the drawings, in which like elements in different drawings are designated with like reference numerals. The drawings, which are not necessarily to scale, depict selected configurations and are not intended to limit the scope of the present disclosure. Those skilled in the art will recognize that there are many useful alternatives to the non-limiting examples shown herein that are also within the scope of the present disclosure.

[0012] The use of the term "axial" and variations thereof herein refers to a direction extending generally along an axis of symmetry, central axis, or elongation direction of a particular part or system. For example, an axially extending structure of a part may extend generally along a direction parallel to the axis of symmetry or elongation direction of the part. Similarly, the use of the term "radial" and variations thereof herein refers to a direction generally perpendicular to the corresponding axial direction. For example, a radially extending structure of a part may extend generally at least partially along a direction perpendicular to the longitudinal axis or central axis of the part. The use of the term "circumferential" and variations thereof herein refers to a direction extending generally around the periphery or edge of an object, or around an axis of symmetry, central axis, or elongation direction of a particular part or system.

[0013] The use of the term "spaced apart" herein refers to features that are spaced apart from one another. For example, axially spaced features of a component may be features that are spaced apart from one another along the axial direction. Unless otherwise specified or limited, the use of the term "spaced apart" does not require the features to be in any other particular alignment with respect to a reference direction. For example, axially spaced apart components may be generally axially spaced apart from one another, while being positioned or otherwise aligned along a common axially extending reference line, or while being otherwise unaligned. Similarly, for example, radially spaced apart components may be generally radially spaced apart from one another, while being axially spaced apart or not spaced apart from one another. Similarly, for example, circumferentially spaced apart components may be generally circumferentially spaced apart from one another, while being radially or axially spaced apart or not spaced apart from one another.

[0014] Generally, the present disclosure provides systems and methods for solenoids having permanent magnets. The permanent magnets may be axially polarized (i.e., the north and south poles of the magnets may be aligned in the axial or actuation direction defined by the solenoid) and may be positioned between two stationary components associated with the magnetic flux loops generated by a wire coil during actuation of the armature within the solenoid. In some non-limiting examples, the permanent magnets may be positioned adjacent to the axial ends of the solenoid, between the pole pieces and the end caps or end plates. This arrangement allows the permanent magnets to be positioned within the solenoid so that they do not axially overlap the axial actuation range defined by the stroke of the armature within the solenoid. This arrangement also allows for cost-effective utilization of magnetic material compared to conventional solenoids.

[0015] Typically, a solenoid may include an armature selectively movable between one or more positions. For example, the armature may be movable from a first position to a second position and vice versa. The armature may be held or maintained in the first position by physically engaging a biasing mechanism (e.g., a spring, linkage, or another mechanical device capable of exerting a biasing force on a surface), and the armature may be held or maintained in the second position by magnetic attraction provided by a permanent magnet.

[0016] 1 illustrates one non-limiting example of a solenoid 100 according to the present disclosure. The solenoid 100 may include a housing 102, a pole piece 104, an end plate or end cap 106, an armature 108, and a permanent magnet 109. Typically, the components of the solenoid may be arranged concentrically around a central axis 110.

[0017] In the illustrated non-limiting example, the housing 102 may define a generally cylindrical shape and may be fabricated from a magnetically conductive material (e.g., magnetic steel, iron, nickel, etc.). In other non-limiting examples, the housing 102 may define another shape as desired. The housing 102 may be formed as a single piece (i.e., as one piece of material) and may include an outer wall 112, a top wall 114, and an inner wall 116. The housing 102 may define a first end 118 and a second end 120 axially opposite the first end 118. The outer wall 112 may be attached or coupled to the end plate 106 at the first end 118. The outer wall 112 may extend axially from the first end 118 to a junction between the outer wall 112 and the top wall 114 at the second end 120. The top wall portion 114 may extend radially inward (i.e., radially toward the central axis 110) from the junction between the outer wall portion 112 and the top wall portion 114 to the junction between the top wall portion 114 and the inner wall portion 116. The inner wall portion 116 may extend axially from the junction between the top wall portion 114 and the inner wall portion 116 to a tapered end 122. The inner wall portion 116 may extend axially from the second end 120 toward the first end 118. The tapered end 122 of the inner wall portion 116 may be defined to have a gradually decreasing radial thickness as it extends axially toward the first end 118.

[0018] In some non-limiting examples, portions of the housing 102 may be formed by one or more separate components. For example, in some non-limiting examples, the inner wall 116 may be formed by a pole piece or another magnetically conductive component attached to or coupled to the housing 102 or by another component of the solenoid 100. In some non-limiting examples, the end plate 106 may be integrally formed (e.g., as a single piece) with the housing 102, the top wall 114 may be coupled to the housing 102 as an additional end cap, and the inner wall 116 may be integrally formed or coupled to the top wall 114.

[0019] The pole piece 104 may be at least partially disposed within the housing 102. The pole piece 104 may be fabricated from a magnetically conductive material (e.g., magnetic steel, iron, nickel, etc.). In the illustrated non-limiting example, the pole piece 104 may extend axially from the permanent magnet 109 toward the second end 120 of the housing 102. The pole piece 104 may include a tapered portion 124, an armature recess 126, and a spring recess 128. The tapered portion 124 may be disposed at one axial end of the pole piece 104 and may have a radial thickness that gradually decreases as the tapered portion 124 extends axially toward the second end 120. In the illustrated non-limiting example, an axial gap is provided between the tapered end 122 of the housing 102 and the tapered portion 124. The armature recess 126 may extend radially inward from a proximal end of the tapered portion 124 to define an armature face 130. The spring recess 128 may be axially spaced from the armature recess 126 and may extend radially inward further than the armature recess 126 to define a spring surface 131 .

[0020] The end plate 106 may be attached or coupled to the first end 118 of the housing 102. For example, the first end 118 of the housing 102 may be attached to the end plate 106 by gluing, swaging, welding, or a press fit. In either case, the end plate 106 may surround the generally open first end 118 of the housing 102. The end plate 106 may be fabricated from a magnetically conductive material (e.g., magnetic steel, iron, nickel, etc.). In the illustrated non-limiting example, the end plate 106 may define a generally annular shape including a bearing protrusion 132 extending axially from a center of the end plate 106. The bearing protrusion 132 extends axially away from the permanent magnet 109 and includes a bearing surface 134.

[0021] Typically, the armature 108 may be at least partially disposed within the housing 102 and may be movable from a first position to a second position and vice versa. The armature 108 may be fabricated from a magnetically conductive material (e.g., magnetic steel, iron, nickel, etc.). In the illustrated non-limiting example, the solenoid 100 may include an armature tube 136 within which the armature 108 may be movably housed. The armature tube 136 may be a thin-walled tube fabricated from a non-magnetically conductive material (e.g., non-magnetic steel, etc.). The armature 108 may include a pin 138 extending axially through at least a portion of the armature 108 and projecting axially therefrom. In the illustrated non-limiting example, the pin 138 projects axially from the armature 108 and may be configured to be slidably received by or slidably engage with a bearing surface 134 of the end plate 106. The pin 138 may further protrude axially outward from the bearing projection 132 of the end plate 106, thereby allowing the pin 138 to apply a force to or move an external component.

[0022] In the illustrated non-limiting example, the permanent magnet 109 may be axially disposed between the pole piece 104 and the end plate 106. The permanent magnet 109 may define an annular shape and may be axially magnetized (i.e., the north and south poles of the permanent magnet 109 are aligned with or parallel to the central axis 110).

[0023] Continuing to refer to FIG. 1 , the solenoid 100 may further include a wire coil 140 disposed within the housing 102. The wire coil 140 may be wound around a bobbin 142. The bobbin 142 may be made of a non-magnetically conductive material (e.g., plastic) and may be disposed within the housing 102 such that the wire coil 140 is wound around at least a portion of the armature 108. The wire coil 140 may be made, for example, from a copper coil configured to generate a magnetic field when the wire coil 140 is energized (i.e., when a current is passed through the wire coil 140), thereby applying a force to the armature 108. The magnitude and direction or polarity of the magnetic field and the force applied to the armature 108 are controlled by the amount and direction of the current passed through the wire coil 140. In some non-limiting examples, the wire coil 140 may be in electrical communication with a controller (not shown) via electrical contacts (not shown) on the solenoid 100. The controller may be configured to selectively pass electrical current through the wire coil 140 in a particular amount and direction.

[0024] Typically, solenoid 100 may further include a biasing mechanism engaged with armature 108 to maintain or hold armature 108 in one of the first and second positions. In the illustrated non-limiting example, solenoid 100 may include a spring 144 biased between armature 108 and pole piece 104. Specifically, spring 144 may be biased between and engaged with first surface 146 of armature 108 and spring surface 131 of pole piece 104. Spring 144 may be configured to exert an axial force on armature 108 such that armature 108 is biased toward the first position (e.g., axially upward in FIG. 1 ).

[0025] In some non-limiting examples, the pole piece 104 may provide a bearing surface for the pin 138. For example, FIG. 2 illustrates another non-limiting example of a solenoid 100 in which the end plate 106 does not include the bearing ridge 132 and bearing surface 134. Instead, the bearing ridge 132 and bearing surface 134 are formed as part of the pole piece 104. In this non-limiting example, the pole piece 104 includes a thin wall portion 150 that extends axially beyond the permanent magnet 109. As described herein, the housing 102 and the end plate 106 may be designated as being formed together or as separate components coupled to one another. FIG. 3 illustrates one non-limiting example of a solenoid 100 in which the end plate 106 is integrally formed with the housing 102, and the inner wall portion 116 may be integrally formed with the top wall portion 114 and coupled to the second end 120 of the housing 102. Alternatively, in the non-limiting example of FIG. 4, the outer wall 112 of the housing 102 is formed separately from the combination of the inner wall 116, the top wall 114 and the end plate 106.

[0026] Referring to FIG. 5 , in operation, the permanent magnet 109 and / or wire coil 140 may generate a magnetic flux path or loop 152 that imparts a force to the armature 108. Typically, the permanent magnet 109 may generate a magnetic flux path 152 that circulates around and within the housing 102, pole piece 104, and end plate 106. The magnetic field generated by the wire coil 140 supplements or opposes the magnetic flux path 152 generated by the permanent magnet 109, causing the armature 108 to move, depending on the polarity of the current supplied to the wire coil 140 and the polarity of the resulting magnetic field. It should be understood that the magnetic flux path 152 illustrated in FIG. 5 is applicable to all solenoid designs shown herein (i.e., FIGS. 1-4, 6, and 7). In configurations where the pole piece 104 includes a thin wall portion 150 that extends beyond the permanent magnet 109, the magnetic flux generated by the permanent magnet 109 may be shorted at the end plate 106 and pole piece 104, which is undesirable. This undesired shortness of the path is shown in Figure 5 as short flux loop 154. This short flux loop 154 ​​is shown for illustrative purposes only, and as described below, solenoid 100 is designed to reduce or eliminate the shortness of the magnetic flux generated by permanent magnet 109. It should be understood that in Figure 5, for illustrative purposes, magnetic flux path 152 and short flux loop 154 ​​are shown on opposite sides of solenoid 100. In operation, they will occur circumferentially around solenoid 100 (on either side of central axis 110 in Figure 5).

[0027] Short magnetic flux loops 154 can be reduced or eliminated by making the radial dimension of the thin walled portion 150 of the pole piece 104 as thin as possible within manufacturing tolerances. By making the dimension of the thin walled portion 150 such that the cross section (i.e., the area through which magnetic flux can pass) is thin in the radial direction, the magnetic flux generated by the permanent magnet 109 through the thin walled portion 150 is intentionally saturated, thereby reducing or eliminating the creation of short magnetic flux loops 154.

[0028] In some non-limiting examples, thin-walled section 150 may include various geometric features that help reduce the radial cross-section through which magnetic flux passes, which promotes magnetic shorting. For example, in the non-limiting example of solenoid 100 shown in Figures 6 and 7, thin-walled section 150 includes notches 156 that define radial recesses in thin-walled section 150. Notches 156 geometrically ensure that magnetic flux passing through thin-walled section 150 is saturated, thereby suppressing or eliminating short magnetic flux loops 154.

[0029] Regardless of the geometric configuration of the pole pieces 104 and end plates 106, the solenoid 100 may be configured to selectively move the armature 108 to move the pin 138 from a first or retracted position to a second or extended position, and vice versa. The general operation of the solenoid 100 will be described with reference to Figures 4 and 5. The following description of the operation of the solenoid 100 also applies to the solenoid design shown in Figures 1 and 2.

[0030] FIG. 6 illustrates the armature 108 in a first position and the pin 138 in a retracted position. When the wire coil 140 is de-energized (i.e., no current is passing through the wire coil 140), the armature 108 may be maintained or held in the first position by engagement between the spring 144 and the armature 108. The spring 144 may exert a force on the armature 108 (e.g., an upward direction in FIG. 6 ) to maintain the armature 108 in the first position. For example, the force of the spring 144 may be greater than the magnetic attraction between the armature 108 and the pole piece 104 provided by the magnetic flux path 152 generated by the permanent magnet 109. When it is desired to transition the armature 108 from the first position to the second position, a current may be passed through the wire coil 140 with a first polarity. A current having a first polarity passed through the wire coil 140 may supplement or augment the magnetic flux path 152 generated by the permanent magnet 109, thereby imparting an electromagnetic force to the armature 108 in a direction that opposes the force of the spring 144. In some non-limiting examples, the first polarity may be aligned with or the same as the polarity established by the permanent magnet 109. The additional electromagnetic force imparted by the wire coil 140 to the armature 108 (e.g., downward in FIG. 6 ) may overcome the force of the spring 144, and the armature 108 may move from the first position to the second position shown in FIG. 7 .

[0031] As shown in FIG. 7 , when the armature 108 is in the second position, the first surface 146 of the armature 108 may engage the armature surface 130 of the pole piece 104. Movement of the armature 108 from the first position to the second position may cause the pin 138 to extend axially. When the wire coil 140 is de-energized (i.e., no current is flowing through the wire coil 140), the armature 108 may be maintained or held in the second position by the magnetic attraction between the armature 108 and the permanent magnet 109 due to the engagement between the armature 108 and the pole piece 104. By disposing the permanent magnet 109 axially between the end plate 106 and the pole piece 104, the permanent magnet 109 does not come into direct contact with the moving element of the solenoid 100 (i.e., the armature 108). This arrangement is efficient from a magnetic standpoint because the stroke of the armature 108 does not axially overlap with the permanent magnet 109. That is, the permanent magnet 109 is axially spaced from the axial stroke traversed by the armature 108 as it moves between the first and second positions.

[0032] When it is desired to transition the armature 108 from the second position to the first position, a current may be passed through the wire coil 140 with a second polarity opposite to the first polarity. The current with the second polarity passed through the wire coil 140 may interfere with the magnetic flux path 152 generated by the permanent magnet 109, thereby reducing the force acting on the armature 108 in a direction (e.g., downward in FIG. 7 ) that holds the armature 108 engaged with the pole piece 104. The magnetic field generated by the wire coil 140 may interfere with the magnetic field of the permanent magnet 109, thereby reducing the force acting on the armature 108 by an amount sufficient to allow the spring 144 to move the armature 108 to the first position ( FIG. 6 ), thereby moving the pin 138 from the extended position to the retracted position.

[0033] As shown in FIG. 8, in the second or extended position (FIG. 7), the magnetic design of solenoid 100 may provide a predetermined amount of current having a second polarity such that magnetic flux path 152 generated by permanent magnet 109 is canceled and the force applied to armature 108 is zero, thereby allowing spring 144 to return armature 108 to the first position. With wire coil 140 in an unenergized state, magnetic flux path 152 may apply a force to armature 108 (0 A retaining force in FIG. 8) that maintains armature 108 in the second position (e.g., downward in FIG. 7) due to engagement between armature 108 and pole piece 109. The magnitude of this retaining force may be greater than the force applied to armature 108 by spring 144, thereby maintaining armature 108 in the second position with wire coil 140 in an unenergized state.

[0034] In some non-limiting examples, when the armature 108 is moved from the second position to the first position, a current having a second polarity and an amount equal to or within a predetermined tolerance of the predetermined current amount may be passed through the wire coil 140. By passing a current through the wire coil 140 in an amount equal to or within a predetermined tolerance of the predetermined current amount, the holding force acting on the armature 108 (e.g., a force urging the armature 108 downward into the pole piece 104) may be reduced sufficiently to allow the spring 144 to move the armature 108 to the first position. If the amount of current is not the predetermined amount or not within a specified tolerance of the predetermined current amount, the holding force acting on the armature 108 may be increased to prevent the armature 108 from moving to the first position.

[0035] Generally, the design of solenoid 100 provides a simplified design from a manufacturing and magnetic standpoint when compared to conventional solenoid designs. For example, the solenoid design may eliminate the need to use two or more wire coils or coil bays to move the armature between two or more positions.

[0036] While embodiments have been described herein for clarity and consistency, it will be understood that these embodiments can be combined or separated in various ways without departing from the invention. For example, it will be understood that all preferred features described herein are applicable to all aspects described herein.

[0037] Thus, while the invention has been described in connection with particular embodiments and examples, the invention is not so limited, and numerous other embodiments, examples, uses, and departures from the embodiments, examples, and uses are within the scope of the appended claims. Each patent document and publication cited herein is incorporated by reference in its entirety as if it were individually incorporated by reference herein.

[0038] Various features and advantages of the invention are set forth in the following claims.

Claims

1. Housing and A pole piece and an end plate integrally formed with or connected to the housing; a wire coil disposed within the housing; a permanent magnet disposed between the pole piece and the end plate; an armature configured to selectively move between a first position and a second position in response to an electrical current applied to the wire coil; a pin connected to the armature, The pole piece is provided with a bearing protrusion that extends axially from the end plate and includes a bearing surface that slidably receives the pin, A solenoid, wherein the pole piece includes a thin wall portion extending beyond the permanent magnet, the thin wall portion being sized so that magnetic flux emanating from the permanent magnet is saturated within the thin wall portion.

2. The solenoid of claim 1 , wherein the permanent magnet is axially disposed between the pole piece and the end plate.

3. 2. The solenoid of claim 1, wherein the permanent magnet is axially magnetized.

4. Housing and A pole piece and an end plate integrally formed with or connected to the housing; a wire coil disposed within the housing; a permanent magnet disposed between the pole piece and the end plate; an armature configured to move between a first position and a second position in response to a current applied to the wire coil; a pin connected to the armature; a spring configured to bias the armature, The pole piece is provided with a bearing protrusion that extends axially from the end plate and includes a bearing surface that slidably receives the pin, When the wire coil is not energized, the armature is maintained in at least one of the first position and the second position; the first position is configured to be maintained by the spring, and the second position is configured to be maintained by a magnetic attraction force between the armature and the permanent magnet due to engagement between the armature and the pole piece; A solenoid, wherein the pole piece includes a thin wall portion extending beyond the permanent magnet, the thin wall portion being sized so that magnetic flux emanating from the permanent magnet is saturated within the thin wall portion.

5. 5. The solenoid of claim 4, wherein said spring is biased between said armature and said pole piece.

6. the pole piece having an armature surface and a spring surface; the armature face is axially spaced from the spring face; The solenoid of claim 5 , wherein the spring engages the spring surface.

7. the permanent magnet is disposed axially between the pole piece and the end plate; 5. The solenoid of claim 4, wherein the permanent magnet is axially magnetized.

8. Housing and A pole piece and an end plate integrally formed with or connected to the housing; a wire coil disposed within the housing; a permanent magnet disposed axially between the pole piece and the end plate; an armature configured to move between a first position and a second position in response to a current applied to the wire coil; a pin connected to the armature; a solenoid including an armature tube capable of movably housing the armature, The pole piece is provided with a bearing protrusion that extends axially from the end plate and includes a bearing surface that slidably receives the pin, A solenoid, wherein the pole piece includes a thin wall portion extending axially beyond the permanent magnet, the thin wall portion being sized such that magnetic flux emanating from the permanent magnet is saturated within the thin wall portion.

9. the solenoid further comprises a spring configured to bias the armature; When the wire coil is not energized, the armature is maintained in at least one of the first position and the second position; 9. The solenoid of claim 8, wherein the first position is configured to be maintained by the spring, and the second position is configured to be maintained by magnetic attraction between the armature and the permanent magnet due to engagement between the armature and the pole piece.

10. 10. The solenoid of claim 9, wherein the spring is biased between the armature and the pole piece.

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