Systems and methods for solenoids with permanent magnets

Abstract

A solenoid is provided. The solenoid includes a housing, a pole piece, an end plate formed with or coupled 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 a current applied to the wire coil, and a spring configured to bias the armature. When the wire coil is de-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 magnetic attraction between the armature and the permanent magnet through engagement between the armature and the pole piece.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application is based upon and claims priority to U.S. Provisional Patent Application No. 62 / 926,937, filed on October 28, 2019, which is incorporated herein by reference in its entirety.

[0003] A note about federally funded research

[0004] not applicable. Technical Field

[0005] The present application relates to solenoids. Background Art

[0006] A solenoid generally includes a coil of wire that can be selectively energized (ie, supplied with an electric current of a specific magnitude and direction) to move an armature between one or more positions. Summary of the invention

[0007] In some aspects, the present disclosure provides a solenoid comprising a housing, a pole piece, an end plate formed with or coupled 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 a current applied to the wire coil, and a spring biased between the armature and the pole piece. When the wire coil is de-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 engagement with the spring, and the second position is configured to be maintained by magnetic attraction between the armature and the permanent magnet through engagement between the armature and the pole piece.

[0008] In another aspect, the present disclosure provides a solenoid comprising a housing, a pole piece, an end plate formed with or coupled 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, and a spring configured to bias the armature. When the wire coil is de-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 magnetic attraction between the armature and the permanent magnet through engagement between the armature and the pole piece.

[0009] In some aspects, the present disclosure provides a solenoid comprising a housing, a pole piece, an end plate formed with or coupled 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 coupled to the armature, and a spring configured to bias the armature. The pole piece or the end plate comprises a bearing surface configured to slidably receive the pin. When the wire coil is de-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 magnetic attraction between the armature and the permanent magnet through engagement between the armature and the pole piece.

[0010] The foregoing and other aspects and advantages of the present disclosure will become apparent from the following description. In the specification, reference is made to the accompanying drawings which form a part thereof and which illustrate preferred configurations of the present disclosure by way of illustration. However, such configurations do not necessarily represent the full scope of the present disclosure, and therefore reference is made to the claims and this document to interpret the scope of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The present invention will be better understood when considering the following detailed description, and features, aspects and advantages other than those set forth above will become apparent.Such detailed description refers to the following drawings.

[0012] Figure 1 is a cross-sectional view of a solenoid according to one aspect of the present disclosure.

[0013] Figure 2 is a pole piece having a pin extending therefrom Figure 1 Cross-sectional view of a solenoid.

[0014] Figure 3 Has end plates formed integrally with the housing Figure 2 Cross-sectional view of a solenoid.

[0015] Figure 4 A case in which the top wall portion of the housing is formed as a separate component Figure 2 Cross-sectional view of a solenoid.

[0016] Figure 5 is a graph showing the magnetic flux lines Figure 2 Cross-sectional view of a solenoid.

[0017] Figure 6 The armature is in the first position with a notched portion in the pole piece. Figure 2Cross-sectional view of a solenoid.

[0018] Figure 7 The armature is in the second position Figure 4 Cross-sectional view of a solenoid.

[0019] Figure 8 It is shown Figure 7 A graph of the force on the armature of a solenoid as a function of current in the extended position or second position. DETAILED DESCRIPTION

[0020] Before explaining any aspect of the present disclosure in detail, it should be understood that the present disclosure is not limited in its application to the construction details and component arrangements set forth in the following specification or shown in the following drawings. The present disclosure can have other configurations, or be practiced or executed in various ways. In addition, it should be understood that the wording and terminology used herein are for descriptive purposes and should not be considered restrictive. In this article, "including", "comprising" or "having" and its variants are meant to cover the items listed later and their equivalents and other items. Unless otherwise specified or limited, the terms "install", "connect", "support" and "couple" and their variants are widely used and cover direct and indirect installation, connection, support and coupling. In addition, "connect" and "couple" are not limited to physical or mechanical connections or couplings.

[0021] The following discussion is provided to enable those skilled in the art to make and use various aspects of the present disclosure. Various modifications to the configuration shown will be apparent to those skilled in the art, and the general principles herein may be applied to other configurations and applications without departing from various aspects of the present disclosure. Therefore, various aspects of the present disclosure are not intended to be limited to the configuration shown, but will be given the broadest scope consistent with the principles and features disclosed herein. The following specific embodiments are read with reference to the accompanying drawings, in which similar elements in different drawings have similar numbers. The drawings, which are not necessarily drawn 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 the non-limiting examples provided herein have many useful alternatives and fall within the scope of the present disclosure.

[0022] As used herein, the term "axial" and its variations refer to a direction that generally extends along an axis of symmetry, a central axis, or a direction of elongation of a particular component or system. For example, an axially extending structure of a component may generally extend in a direction parallel to the axis of symmetry or the direction of elongation of the component. Similarly, as used herein, the term "radial" and its variations refer to a direction that is generally perpendicular to the corresponding axial direction. For example, a radially extending structure of a component may generally extend at least partially in a direction perpendicular to the longitudinal axis or central axis of the component. As used herein, the term "circumferential" and its variations refer to a direction that generally extends around the circumference or periphery of an object, around an axis of symmetry, around a central axis, or around the direction of elongation of a particular component or system.

[0023] The term "separated" as used herein refers to features that are spaced apart from one another. For example, an axially separated feature of a component may be a feature that is spaced apart from one another in an axial direction. Unless otherwise specified or limited, the use of the term "separated" is not intended to require any other specific alignment of the feature relative to a reference direction. For example, axially separated components may generally be spaced apart from one another relative to an axial direction while being disposed or otherwise aligned along a common axially extending reference line or not disposed or otherwise aligned along a common axially extending reference line. Similarly, for example, radially separated components may generally be spaced apart from one another relative to a radial direction while being separated from one another or not separated from one another relative to an axial direction. Similarly, for example, circumferentially separated components may generally be spaced apart from one another relative to a circumferential direction while being separated from one another or not separated from one another relative to a radial direction or an axial direction.

[0024] In general, the present disclosure provides systems and methods for solenoids with permanent magnets. The permanent magnet can be axially magnetized (i.e., the north and south poles of the magnet can be aligned with the axial direction or actuation direction defined by the solenoid) and can be arranged between two immovable components that participate in the magnetic flux loop generated by the wire coil during actuation of the armature in the solenoid. In some non-limiting examples, the permanent magnet can be arranged adjacent to the axial end of the solenoid between the pole piece and the end cap or end plate. The arrangement can position the permanent magnet within the solenoid so that the permanent magnet does not axially overlap with the axial actuation range defined by the stroke of the armature in the solenoid. Compared with conventional solenoids, the arrangement can provide cost-effectiveness and efficient use of magnetic materials.

[0025] Typically, a solenoid may include an armature that is selectively movable between one or more positions. For example, the armature may be movable from a first position to a second position, and may be movable from a second position to a first position. The armature may be held or maintained in a first position by physical engagement with a biasing mechanism (e.g., a spring, a connecting rod, or other mechanical device capable of providing a biasing force on a surface), and the armature may be held or maintained in a second position by magnetic attraction provided by a permanent magnet.

[0026] Figure 1 A non-limiting example of a solenoid 100 according to the present disclosure is shown. The solenoid 100 can include a housing 102, a pole piece 104, an end plate or end cap 106, an armature 108, and a permanent magnet 109. Generally, the components of the solenoid can be arranged concentrically about a central axis 110.

[0027] In the non-limiting example shown, the housing 102 can define a generally cylindrical shape and can be made of a magnetically permeable material (e.g., magnetic steel, iron, nickel, etc.). In other non-limiting examples, the housing 102 can define other shapes as desired. The housing 102 can be formed as an integral component (i.e., a single piece of material) and can include an outer wall portion 112, a top wall portion 114, and an inner wall portion 116. The housing 102 can define a first end 118 and a second end 120 axially disposed opposite the first end 118. The outer wall portion 112 can be attached or coupled to the end plate 106 at the first end 118. The outer wall portion 112 can extend axially from the first end 118 to a junction between the outer wall portion 112 and the top wall portion 114 at the second end 120. The top wall portion 114 can extend radially inward (e.g., radially toward the central axis 110) from the junction between the outer wall portion 112 and the top wall portion 114 to a junction between the top wall portion 114 and the inner wall portion 116. The inner wall portion 116 can extend axially from a junction between the top wall portion 114 and the inner wall portion 116 to a tapered end 122. The inner wall portion 116 can extend axially from the second end 120 toward the first end 118. The tapered end 122 of the inner wall portion 116 can define a gradual decrease in radial thickness as it extends axially toward the first end 118.

[0028] In some non-limiting examples, portions of the housing 102 can be formed from one or more separate components. For example, in some non-limiting examples, the inner wall portion 116 can be formed from a pole piece or another magnetically permeable component attached or coupled to the housing 102, or another component of the solenoid 100. In some non-limiting examples, the end plate 106 can be formed with the housing 102 (e.g., as an integral component), and the top wall portion 114 can be coupled to the housing 102 as an additional end cap, and the inner wall portion 116 can be integrally formed with or coupled to the top wall portion 114.

[0029] The pole piece 104 can be at least partially arranged within the housing 102. The pole piece 104 can be made of a magnetically permeable material (e.g., magnetic steel, iron, nickel, etc.). In the non-limiting example shown, the pole piece 104 can extend axially from the permanent magnet 109 toward the second end 120 of the housing 102. The pole piece 104 can include a tapered portion 124, an armature groove 126, and a spring groove 128. The tapered portion 124 can be arranged at one axial end of the pole piece 104, and can define a gradually decreasing radial thickness when the tapered portion 124 extends axially toward the second end 120. In the non-limiting example shown, an axial gap is arranged between the tapered end 122 of the housing 102 and the tapered portion 124. The armature groove 126 can extend radially inward from the proximal end of the tapered portion 124 to define an armature surface 130. The spring groove 128 may be axially separated from the armature groove 126 and may extend radially inwardly further than the armature groove 126 to define a spring surface 131 .

[0030] The end plate 106 can be attached or coupled to the first end 118 of the housing 102. For example, the first end 118 of the housing 102 can be adhesively attached, crimped, welded, or press-fitted onto the end plate 106. In any case, the end plate 106 can enclose the normally open first end 118 of the housing 102. The end plate 106 can be made of a magnetically permeable material (e.g., magnetic steel, iron, nickel, etc.). In the non-limiting example shown, the end plate 106 can define a generally annular shape that includes a bearing protrusion 132 extending axially from a central portion of the end plate 106. The bearing protrusion 132 extends axially away from the permanent magnet 109 and includes a bearing surface 134.

[0031] Typically, the armature 108 can be at least partially disposed within the housing 102 and can be movable from a first position to a second position, and from a second position to a first position. The armature 108 can be made of a magnetically permeable material (e.g., magnetic steel, iron, nickel, etc.). In the non-limiting example shown, the solenoid 100 can include an armature tube 136 in which the armature 108 is movably received. The armature tube 136 can be a thin-walled tube made of a non-magnetically permeable material (e.g., non-magnetically permeable stainless steel). The armature 108 can include a pin 138 that extends axially through at least a portion of the armature 108 and protrudes axially from the armature 108. In the non-limiting example shown, the pin 138 can protrude axially from the armature 108 and can be slidably received by or engaged with a bearing surface 134 of the end plate 106. The pin 138 may further protrude axially from the bearing protrusion 132 of the end plate 106 , which allows the pin 138 to provide a force or displacement to an external component.

[0032] In the non-limiting example shown, permanent magnet 109 may be disposed axially between pole piece 104 and end plate 106. Permanent magnet 109 may define an annular shape and may be axially magnetized (i.e., the north and south poles of permanent magnet 109 are aligned with or parallel to central axis 110).

[0033] Continue to refer Figure 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. For example, the wire coil 140 may be made of a copper coil configured to generate a magnetic field, thereby applying a force to the armature 108 in response to the wire coil 140 being energized (i.e., current being applied to the wire coil 140). The magnitude and direction or polarity of the magnetic field, as well as the force applied to the armature 108, may be controlled by the magnitude and direction of the current applied to 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 apply current to the wire coil 140 in a specific magnitude and direction.

[0034] In general, the solenoid 100 can further include a biasing mechanism that engages the armature 108 to maintain or hold the armature 108 in one of the first position and the second position. In the non-limiting example shown, the solenoid 100 can include a spring 144 that is biased between the armature 108 and the pole piece 104. Specifically, the spring 144 can be biased between and engage the first surface 146 of the armature 108 and the spring surface 131 of the pole piece 104. The spring 144 can be configured to apply an axial force to the armature 108 so that the armature 108 is biased toward the first position (e.g., from Figure 1 axially upward from the perspective of the

[0035] In some non-limiting examples, pole piece 104 may provide a bearing surface for pin 138. For example, Figure 2 Another non-limiting example of a solenoid 100 is shown in which the end plate 106 does not include the bearing protrusion 132 and the bearing surface 134. Instead, the bearing protrusion 132 and the 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 over the permanent magnet 109. As described herein, the housing 102 and the end plate 104 can be designed to be formed together or as separate components that are coupled together. Figure 3A non-limiting example of a solenoid 100 is shown in which the end plate 106 is formed with the housing 102, and the inner wall portion 116 can be integrally formed with the top wall portion 114 and coupled to the second end 120 of the housing 102. Alternatively, Figure 4 A non-limiting example is shown in which the outer wall portion 112 of the housing 102 is formed separately from the combination of the inner wall portion 116 , the top wall portion 114 , and the end plate 106 .

[0036] refer to Figure 5 In operation, the permanent magnets 109 and / or the wire coils 140 can generate a magnetic flux path or loop 152 that provides a force to the armature 108. In general, the permanent magnets 109 can generate a magnetic flux path 152 that circulates around and through the housing 102, the pole pieces 104, and the end plates 106. The magnetic field generated by the wire coils 140 can supplement or interrupt the magnetic flux path 152 generated by the permanent magnets 109 to affect the movement of the armature 108, depending on the polarity of the current supplied to the wire coils 140 and the polarity of the magnetic field generated. It should be understood that Figure 5 The magnetic flux path 152 shown in FIG. 1 is applicable to all solenoid designs shown herein (i.e., Figure 1-Figure 4 , Figure 6 and Figure 7 In a configuration where the pole piece 104 includes a thin wall portion 150 that extends over the permanent magnet 109 , the magnetic flux generated by the permanent magnet 109 may pass through the end plate 106 and the pole piece 104 and undesirably short circuit. Figure 5 The undesirable short circuit is shown by the shorted magnetic flux loop 154. The shorted magnetic flux loop 154 ​​is shown for illustrative purposes only, and as described herein, the solenoid 100 is designed to prevent or eliminate the short circuiting of the magnetic flux from the permanent magnet 109. It should be understood that in Figure 5 The magnetic flux paths 152 and short-circuit magnetic flux loops 154 on opposite sides of the solenoid 100 are shown for illustrative purposes only. In operation, these will occur circumferentially around the solenoid 100 (i.e., between Figure 5 on both sides of the central axis 110 in FIG. 1 ).

[0037] By dimensioning the thin-walled portion 150 of the pole piece 104 to be as radially thin as possible within manufacturing tolerances, short-circuit magnetic flux loops 154 can be prevented or eliminated. By dimensioning the thin-walled portion 150 to be radially thin in cross-section (i.e., the area through which magnetic flux can travel), the magnetic flux generated by the permanent magnet 109 flowing through the thin-walled portion 150 can be intentionally saturated, thereby preventing or eliminating the generation of short-circuit magnetic flux loops 154.

[0038] In some non-limiting examples, the thin-walled portion 150 may include various geometric features that help reduce the radial cross-section through which magnetic flux may flow. For example, Figure 6 and Figure 7 A non-limiting example of a solenoid 100 is shown where the thin wall portion 150 includes a notch 156 defining a radial groove in the thin wall portion 150. The notch 156 geometrically ensures that the magnetic flux traveling through the thin wall portion 150 is saturated, which prevents or eliminates shorting magnetic flux loops 154.

[0039] Regardless of the geometry of the pole piece 104 and the end plate 106, the solenoid 100 can be configured to selectively move the armature 108 between a first position or retracted position and a second position or extended position, thereby selectively moving the pin 138 between a first position or retracted position and a second position or extended position, and vice versa. The general operation of the solenoid 100 will be described with reference to Figure 4 and Figure 5 The following description of the operation of the solenoid 100 also applies to Figure 1 and Figure 2 The solenoid design shown in .

[0040] Figure 6 The armature 108 is shown in a first position, wherein the pin 138 is in a retracted position. When the wire coil 140 is de-energized (i.e., no current is supplied to the wire coil 140), the armature 108 can be maintained or held in the first position by engagement between the spring 144 and the armature 108. The spring 144 can provide a force to the armature 108 (e.g., from Figure 6 109) which maintains the armature 108 in the first position. For example, the force of the spring 144 can 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 can be applied to the wire coil 140 with a first polarity. The current having the first polarity applied to the wire coil 140 can supplement or increase the magnetic flux path 152 generated by the permanent magnet 109, which provides an electromagnetic force on the armature 108 in a direction opposite to the force of the spring 144. In some non-limiting examples, the first polarity can be aligned with or the same as the polarity defined by the permanent magnet 109. The additional electromagnetic force on the armature 108 provided by the wire coil 140 (e.g., from Figure 6 in the downward direction) can overcome the force of the spring 144, and the armature 108 can be moved from the first position to Figure 7 The second position is shown.

[0041] like Figure 7As shown, when the armature 108 is in the second position, the first surface 146 of the armature 108 can engage the armature surface 130 of the pole piece 104. The movement of the armature 108 from the first position to the second position can axially extend the pin 138. When the wire coil 140 is de-energized (i.e., no current is supplied to the wire coil 140), the armature 108 can be maintained or held in the second position by magnetic attraction between the armature 108 and the permanent magnet 109 through the engagement between the armature 108 and the pole piece 104. The axial arrangement of the permanent magnet 109 between the end plate 106 and the pole piece 104 arranges the permanent magnet 109 to not be in direct contact with the moving element of the solenoid 100 (i.e., the armature 108). From a magnetic point of view, this arrangement is effective because the stroke of the armature 108 does not overlap axially with the permanent magnet 109. That is, the permanent magnets 109 are axially separated from the axial stroke traversed by the armature 108 as the armature 108 moves between the first position and the second position.

[0042] When it is desired to switch the armature 108 from the second position to the first position, a current may be applied to the wire coil 140 at a second polarity opposite to the first polarity. The current having the second polarity applied to the wire coil 140 may interrupt the magnetic flux path 152 generated by the permanent magnet 109, which may reduce the magnetic flux in the direction acting to keep the armature 108 engaged with the pole piece 104 (e.g., from the Figure 7 The interruption of the magnetic field of the permanent magnet 109 by the magnetic field generated by the wire coil 140 can reduce the force on the armature 108 by a sufficient amount to allow the spring 144 to move the armature 108 to the first position ( Figure 6 ), which moves the pin 138 from the extended position to the retracted position.

[0043] like Figure 8 As shown, in the second or extended position ( Figure 7 ), the magnetic design of the solenoid 100 can provide a predefined current magnitude with a second polarity at which the magnetic flux path 152 generated by the permanent magnet 109 is canceled and the magnetic force applied to the armature 108 is zero, thereby allowing the spring 144 to move the armature 108 back to the first position. When the wire coil 140 is de-energized, due to the engagement between the armature 108 and the pole piece 109 ( Figure 8 0A holding force), the flux path 152 can generate a force on the armature 108 that acts to maintain the armature 108 in the second position (e.g., from Figure 7 The magnitude of the retaining force can be greater than the force on the armature 108 provided by the spring 144, which maintains the armature 108 in the second position when the wire coil 140 is de-energized.

[0044] In some non-limiting examples, when the armature 108 moves from the second position to the first position, a current having a second polarity whose magnitude is equal to, or within a predefined tolerance of, a predefined current magnitude can be supplied to the wire coil 140. By supplying a current to the wire coil 140 whose magnitude is equal to, or within a predefined tolerance of, the predefined current magnitude, the holding force on the armature 108 (e.g., the force pushing the armature 108 downward into the pole piece 104) can be sufficiently reduced to allow the spring 144 to move the armature 108 to the first position. If the magnitude of the current is not at, or within a predefined tolerance of, the predefined current magnitude, the holding force on the armature 108 increases and prevents the armature 108 from moving to the first position.

[0045] Generally, the design of solenoid 100 can provide a simplified design from a manufacturing and magnetic perspective compared to conventional solenoid designs. For example, the design of the solenoid can eliminate the need to use two or more wire coils or coil carriers for moving the armature between two or more positions.

[0046] In this specification, the embodiments of the present specification have been described in a manner that enables a clear and concise description to be written, but it is intended and will be understood that the embodiments may be combined or separated in different ways without departing from the present invention. For example, it should be understood that all preferred features described herein are applicable to all aspects of the invention described herein.

[0047] Therefore, although the invention has been described in conjunction with particular embodiments and examples, the invention is not necessarily so limited, and many other embodiments, examples, uses, modifications, and deviations from the described embodiments, examples, and uses are intended to be covered by the appended claims. The entire disclosure of each patent and publication cited herein is incorporated herein by reference, as if each such patent or publication was individually incorporated herein by reference.

[0048] Various features and advantages of the invention are set forth in the following claims.

Claims

1. A solenoid comprising: shell; Pole piece; an end plate formed with or coupled 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 electric current applied to the wire coil; as well as a pin coupled to the armature, wherein the pole piece includes a bearing projection extending axially from the end plate and including a bearing surface that slidably receives the pin, Wherein the pole piece comprises a thin-walled portion extending through the permanent magnet and being dimensioned such that a magnetic flux generated by the permanent magnet is saturated in the thin-walled portion.

2. The solenoid according to claim 1, characterized in that The permanent magnet is arranged axially between the pole piece and the end plate.

3. The solenoid according to claim 1, characterized in that The permanent magnet is axially magnetized.

4. The solenoid according to claim 1, wherein: The solenoid further includes a spring positioned between the armature and the pole piece, wherein when the wire coil is de-energized, the armature is maintained in at least one of the first position and the second position, and 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 through engagement between the armature and the pole piece.

5. The solenoid according to claim 1, wherein: The thin-walled portion is configured to retain a permanent magnet on the end plate.

6. The solenoid according to claim 1, wherein: The thin-walled portion defines a radial groove to further reduce the radial cross-section at the thin-walled portion.

7. The solenoid according to claim 6, characterized in that The radial groove is provided on the radial inner surface of the thin-walled portion.

8. A solenoid comprising: shell; Pole piece; an end plate formed with or coupled 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 an electric current applied to the wire coil; a pin coupled to the armature, wherein the pole piece includes a bearing projection extending axially from the end plate and including a bearing surface that slidably receives the pin; as well as a spring configured to bias the armature, wherein the armature is maintained in at least one of the first position and the second position when the wire coil is de-energized, and 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 through engagement between the armature and the pole piece, Wherein the pole piece comprises a thin-walled portion extending through the permanent magnet and being dimensioned such that a magnetic flux generated by the permanent magnet is saturated in the thin-walled portion.

9. The solenoid according to claim 8, characterized in that The spring is positioned between the armature and the pole piece.

10. The solenoid according to claim 9, characterized in that The pole piece includes an armature surface and a spring surface, and wherein the armature surface is axially separated from the spring surface and the spring engages the spring surface.

11. The solenoid according to claim 8, wherein The permanent magnet is arranged axially between the pole piece and the end plate, and wherein the permanent magnet is axially magnetized.

12. The solenoid of claim 8, wherein: The thin-walled portion is configured to retain a permanent magnet on the end plate.

13. A solenoid comprising: shell; Pole piece; an end plate formed with or coupled 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 an electric current applied to the wire coil; a pin coupled to the armature, wherein the pole piece or the end plate includes a bearing protrusion extending axially from the end plate and including a bearing surface configured to slidably receive the pin; as well as an armature tube, the armature tube movably receiving the armature, Wherein the pole piece comprises a thin-walled portion extending through the permanent magnet and being dimensioned such that a magnetic flux generated by the permanent magnet is saturated in the thin-walled portion.

14. The solenoid of claim 13, wherein: The permanent magnet is arranged axially between the pole piece and the end plate, and wherein the permanent magnet is axially magnetized.

15. The solenoid of claim 13, wherein: The solenoid further includes a spring configured to bias the armature, wherein the armature is maintained in at least one of the first position and the second position when the wire coil is de-energized, and 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 through engagement between the armature and the pole piece.

16. The solenoid of claim 13, wherein: The thin-walled portion defines a radial groove to further reduce the radial cross-section at the thin-walled portion.

17. The solenoid of claim 16, wherein: The radial groove is provided on the radial inner surface of the thin-walled portion.

18. The solenoid of claim 13, wherein: The thin-walled portion is configured to retain a permanent magnet on the end plate.

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