solenoid

Abstract

To provide a solenoid that can exert the desired magnetic force. [Solution] A solenoid 1 comprising a coil 39 disposed inside a cylindrical case 30 and covered by a resin molded part 2, a fixed iron core 32 having a small diameter part 32b and a large diameter part 32c and inserted into the central hole 31a of the coil 39, a movable iron core 4 disposed inside the fixed iron core 32, and a plate 33 embedded in the resin molded part 2 so as to overlap radially with the fixed iron core 32 and form a magnetic path between the case 30 and the fixed iron core 32, wherein the axial width L1 of the inner circumferential surface 35a of the plate 33 is larger than the axial width L2 of the outer circumferential surface part 34 of the plate 33, and the inner circumferential surface 35a of the plate 33 extends across the small diameter part 32b and the large diameter part 32c of the fixed iron core 32.

Description

Technical Field

[0001] The present invention relates to a solenoid, for example, a solenoid that drives a movable iron core by a magnetic action when an electric current is applied to a coil.

Background Art

[0002] In various industrial fields, solenoids are used as means for operating various devices such as valves and machines. When an electric current is applied to a coil, a solenoid moves a movable iron core accommodated so as to be reciprocable electromagnetically, thereby operating various devices.

[0003] For example, in the solenoid shown in Patent Document 1, a coil in which a conducting wire is wound around a bobbin is molded together with a plate by resin, and the structural strength of the molded coil is high. The molded coil has a bottomed cylindrical shape and is inserted into a solenoid case. A bottomed cylindrical fixed iron core is disposed on the bottom side inside the molded coil, and a center post is disposed on the opening side inside the molded coil. A plunger is disposed in a space surrounded by the molded coil, the fixed iron core, and the center post. When an electric current is applied to the molded coil, a magnetic circuit is formed by the center post, the case, the plate, the fixed iron core, and the plunger, and the plunger is magnetically attracted to the center post.

[0004] The fixed iron core is provided with a stepped portion composed of a large-diameter portion extending in the axial direction along the inner peripheral surface of the coil and a small-diameter portion extending in the axial direction from the large-diameter portion toward the bottom of the fixed iron core and overlapping the plate in the radial direction. Since the tip side of the fixed iron core is narrowed by the small-diameter portion, it is possible to avoid contact with the resin molding portion of the coil when inserting the fixed iron core into the center hole of the coil. Further, the small-diameter portion of the fixed iron core is configured to avoid contact with the resin molding portion even when the resin molding portion thermally expands and contracts during use of the solenoid.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] International Publication No. 2016 / 125629 (page 5, Figure 1) [Overview of the project] [Problems that the invention aims to solve]

[0006] However, in the solenoid described above, variations in the axial assembly position between the upper fixed core and the coil occur due to differences in manufacturing and assembly precision of each component. As a result, the radial overlap between the large-diameter portion of the fixed core and the plate becomes insufficient, which could lead to inadequate transmission of magnetic flux and a decrease in the function of the magnetic circuit. Furthermore, if the large-diameter portion of the fixed core is inserted beyond the plate to a position where it radially overlaps with the resin molded portion, the resin molded portion, which expands and contracts due to heat during use, may come into contact with the large-diameter portion of the upper fixed core, potentially overloading the fixed core and causing deformation of the fixed core, which could lead to a loss of function in the magnetic circuit.

[0007] This invention was made in view of these problems, and aims to provide a solenoid that can exert the desired magnetic force. [Means for solving the problem]

[0008] To solve the above problems, the solenoid of the present invention is A solenoid comprising: a coil disposed within a cylindrical case and covered by a resin molded portion; a fixed iron core having a small diameter portion and a large diameter portion and inserted into the central hole of the coil; a movable iron core disposed within the fixed iron core; and a plate embedded in the resin molded portion so as to overlap radially with the fixed iron core and form a magnetic path between the case and the fixed iron core, The axial width of the inner circumferential surface of the plate is greater than the axial width of the portion on the outer circumferential surface side of the plate. The inner circumferential surface of the plate extends across the small diameter portion and the large diameter portion of the fixed iron core. According to this design, the large-diameter portion of the fixed core is positioned offset from the resin molded portion in the axial direction, thus preventing the resin molded portion from contacting the large-diameter portion of the fixed core due to thermal expansion and contraction during use. Therefore, no external force from the resin acts on the fixed core, and a magnetic circuit that can exert the desired magnetic force can be constructed. Furthermore, the large-diameter portion of the fixed core can be extended in the axial direction, and since it is positioned so that the axial overlap between the upper surface of the plate and the large-diameter portion of the fixed core is large, even if the axial overlap between the large-diameter portion of the fixed core and the plate is insufficient, the effect on magnetic flux transmission can be reduced. Therefore, a magnetic circuit that can exert the desired magnetic force can be constructed. In addition, since the axial width of the inner circumferential surface of the plate is large, a large axial region where the plate and the large-diameter portion of the fixed core overlap radially can be secured, ensuring reliable transmission of magnetic flux between the plate and the fixed core.

[0009] The plate may include a radial portion extending radially with a constant width, and an axial portion extending axially from the inner diameter end of the radial portion toward the small diameter side of the fixed iron core. According to this, a large area can be secured in the axial direction where the plate and the large-diameter portion of the fixed iron core overlap radially. In addition, the step difference between the axial portion and the radial portion can suppress thermal expansion and contraction toward the inner diameter side of the resin molded portion.

[0010] The plate may be in contact with the inner circumferential surface of the case. According to this, the case makes contact with a highly rigid plate, which stabilizes the connection between the coil and the case.

[0011] The plate may be placed on a stepped portion provided on the inner circumference of the case. According to this design, the stepped portion allows for axial positioning of the plate relative to the case. Furthermore, since the plate contacts the inner circumferential surface and end surface of the case, magnetic flux can be transferred efficiently.

[0012] The fixed core may be integrally formed with the movable core at one end in the direction of movement and the other end. According to this, since the structural strength of the fixed core is high, it is possible to suppress breakage when inserting into the central hole of the coil.

Brief Description of the Drawings

[0013] [Figure 1] It is a longitudinal sectional view showing the solenoid in Embodiment 1 of the present invention. [Figure 2] It is an enlarged view of the main part of FIG. 1. [Figure 3] It is a schematic sectional view showing the solenoid in Embodiment 2 of the present invention. [Figure 4] It is a schematic sectional view showing the solenoid in Embodiment 3 of the present invention. [Figure 5] It is a schematic sectional view showing the solenoid in Embodiment 4 of the present invention.

Mode for Carrying Out the Invention

[0014] A mode for carrying out the solenoid according to the present invention will be described below based on examples.

Examples

[0015] The solenoid according to Embodiment 1 will be described with reference to FIGS. 1 and 2.

[0016] The solenoid 1 of the present Embodiment 1 will be described as a solenoid used for the solenoid valve V. Note that the solenoid 1 is not limited to the solenoid valve V and may be used for a solenoid actuator that operates any load.

[0017] As shown in FIG. 1, the solenoid valve V is configured by integrally attaching the solenoid 1 and a valve (not shown) that adjusts the fluid flow rate. Note that FIG. 1 shows the off state of the solenoid valve V when no current is applied to the coil 39.

[0018] The solenoid 1 is mainly composed of a solenoid molded body 31, a fixed iron core 32, and a plunger 4 as a movable iron core. This solenoid 1 is housed in a solenoid case 30 on the side of the mounting device (not shown).

[0019] The solenoid case 30 is formed in a stepped cylindrical shape from a metal material having magnetism such as iron. Note that the solenoid case 30 is not limited to a cylindrical shape, and may be a tubular shape with a different cross-sectional shape such as a square tubular shape. Furthermore, the solenoid case 30 may be integral with a mounting device (not shown) or may be connected to a mounting device.

[0020] An annular stepped portion 30A that projects downward on the inner diameter side is formed on the inner circumference of the upper end portion of the solenoid case 30. The stepped portion 30A is composed of an upper inner circumferential surface 30a, an end surface 30b that extends in the inner diameter direction from the lower end of the upper inner circumferential surface 30a, and a lower inner circumferential surface 30c that extends downward from the inner diameter end of the end surface 30b.

[0021] The solenoid molded body 31 is disposed above the solenoid case 30. Also, a valve (not shown) is disposed below the solenoid 1 in the solenoid case 30.

[0022] The solenoid molded body 31 is formed in a bottomed cylindrical shape by molding a coil 39 in which a plurality of conductive wires are wound around a bobbin 36 formed of an insulator and an annular plate 33 composed of a magnetic member with a resin molding portion 2. The plate 33 is insert-molded into the bobbin 36.

[0023] Specifically, the resin molding portion 2 covers the outer peripheral surface of the coil 39 and the outer peripheral surface of the annular base portion 36a at the upper part of the bobbin 36, and closes the upper part of the annular base portion 36a. Thereby, a central hole 31a that opens downward is provided in the center of the solenoid molded body 31.

[0024] A power line is embedded above the resin molded part 2, and power is supplied to the coil 39 from the outside through the connector terminal 40 to which the power line is connected.

[0025] The plate 33 is an annular and substantially flat magnetic material, formed from a magnetic metal material such as iron, and is configured to form a magnetic path between the fixed core 32 and the solenoid case 30. The plate 33, fixed core 32, and solenoid case 30 may be made of different materials or the same material.

[0026] More specifically, as shown in Figure 2, the plate 33 has an annular radial portion 34 extending substantially horizontally with a constant width in the radial direction, and an axial portion 35 extending substantially vertically upward from the inner diameter edge of the radial portion 34, and has a substantially L-shaped cross-section. The axial width L1 of the axial portion 35 is greater than the axial width L2 of the radial portion 34 (L1 > L2).

[0027] As shown in Figures 1 and 2, the inner circumferential surface 35a of the axial portion 35, the inner circumferential surface 36c of the bobbin 36, and the inner circumferential surface 2a of the resin molding portion 2 constitute the inner circumferential surface of the solenoid molded body 31. The inner circumferential surface 35a of the axial portion 35 has a slightly smaller diameter than the inner circumferential surface 36c of the bobbin 36 and the inner circumferential surface 2a of the resin molding portion 2.

[0028] The plate 33 is positioned inside the bobbin 36 by insert molding. A portion of the outer circumferential surface 34a of the radial portion 34 (see Figure 2) is in contact with the upper inner circumferential surface 30a of the stepped portion 30A of the solenoid case 30. The lower outer edge surface of the radial portion 34 is in contact with the end face 30b of the stepped portion 30A of the solenoid case 30. As a result, the solenoid molded body 31 is positioned vertically relative to the solenoid case 30.

[0029] Returning to Figure 1, the fixed iron core 32 is a bottomed cylindrical shape made of magnetic material.

[0030] The fixed iron core 32 has an integral structure consisting of a large-diameter peripheral wall 32A, an annular side wall 32B, a small-diameter peripheral wall 32C, and a bottom wall 32D, in that order from bottom to top.

[0031] The large-diameter circumferential wall 32A is cylindrical in shape and extends in the axial direction. The large-diameter circumferential wall 32A is screw-fixed to the inner circumferential surface of the solenoid case 30.

[0032] The annular side wall 32B extends inward from the upper end of the large-diameter circumferential wall 32A.

[0033] The small-diameter circumferential wall 32C is an outer stepped cylindrical shape that extends upward from the inner diameter end of the annular side wall 32B. The small-diameter circumferential wall 32C is provided with a thin-walled portion 32a in which the outer surface is recessed in the inner diameter direction in an isosceles trapezoidal shape when viewed in cross-section, thereby reducing the thickness of the plate.

[0034] Furthermore, near the upper end of the outer circumferential surface of the small-diameter circumferential wall 32C, an annular stepped portion 32d is formed, with the upper part being a small-diameter portion 32b and the lower part being a large-diameter portion 32c (see Figure 2). The large-diameter portion 32c is the part that extends upward from a position radially opposite to the coil 39 and is the outermost diameter portion of the small-diameter circumferential wall 32C. This small-diameter circumferential wall 32C is inserted from below into the central hole 31a of the solenoid molded body 31. Note that the outer circumferential surface of the large-diameter portion 32c is smaller in diameter than the inner circumferential surface 36c of the bobbin 36, and a radial gap is formed between the outer circumferential surface of the large-diameter portion 32c and the inner circumferential surface 36c of the bobbin 36.

[0035] When assembling the fixed core 32 into the central hole 31a of the solenoid molded body 31, the small diameter portion 32b at the tip of the fixed core 32 makes it easy to insert the fixed core 32 into the central hole 31a without it coming into contact with the inner circumferential surface of the solenoid molded body 31.

[0036] The bottom wall 32D is continuous with the upper end of the small-diameter peripheral wall 32C and closes the upper end of the small-diameter peripheral wall 32C.

[0037] Below the plunger 4 and below the thin-walled portion 32a inside the small-diameter peripheral wall 32C, an annular magnetic member 37 is positioned, thereby closing off the space within the small-diameter peripheral wall 32C.

[0038] The plunger 4 is formed in a cylindrical shape from a magnetic metal material such as iron. This plunger 4 is positioned to move vertically within the space surrounded by the small-diameter peripheral wall 32C of the fixed iron core 32 and the magnetic member 37.

[0039] A through-hole 4a is formed in the center of the plunger 4, extending axially. A rod 5 is fitted into this through-hole 4a. The rod 5 extends from both the upper and lower sides of the plunger 4.

[0040] The upper end of the rod 5 is inserted through a bearing 9 fixed to the bottom wall 32D of the fixed iron core 32. The lower end 5b of the rod 5 is inserted through a bearing 9' fixed to a through hole 37a of the magnetic member 37. The lower end surface of the rod 5 is positioned to move toward and away from a valve body constituting a valve (not shown).

[0041] The solenoid case 30, plate 33, fixed iron core 32, plunger 4, and magnetic member 37 form a magnetic path.

[0042] By energizing the coil 39, a magnetic circuit is formed, generating a magnetic force between the magnetic member 37 and the plunger 4, causing the plunger 4 to move downward (not shown). Furthermore, because the thin-walled portion 32a of the fixed core 32 has high magnetic resistance, magnetic flux is easily transmitted from the fixed core 32 to the plunger 4.

[0043] Next, we will explain the details of the assembled state of solenoid 1 using Figure 2.

[0044] As shown in Figure 2, in the assembled state of the solenoid 1, the stepped portion 32d of the fixed core 32 radially overlaps with the inner circumferential surface 35a of the axial portion 35 of the plate 33. In other words, the axial portion 35 extends vertically so as to radially overlap the large diameter portion 32c and the small diameter portion 32b of the fixed core 32.

[0045] According to this, since the small-diameter portion 32b of the fixed iron core 32 faces radially against the inner circumferential surface 2a of the resin molded portion 2, even if the resin molded portion 2 expands and contracts inward due to thermal expansion when the solenoid valve V is used, the resin molded portion 2 does not come into contact with the fixed iron core 32.

[0046] In other words, because the large-diameter portion 32c of the fixed core 32 is positioned lower than the resin molded portion 2, contact with the large-diameter portion 32c of the fixed core 32 is avoided even if the resin molded portion 2 expands and contracts due to heat during use. Therefore, no external force acts on the fixed core 32 from the resin molded portion 2. In other words, external forces from the resin molded portion 2 prevent the fixed core 32 from shifting position or the resin molded portion 2 from getting stuck between the large-diameter portion 32c of the fixed core 32 and the plate 33. This allows the magnetic circuit to be properly configured and the desired magnetic force to be exerted.

[0047] In this embodiment, the inner circumferential surface 35a of the plate 33 and the large-diameter portion 32c are in contact, but a radial gap may be formed with a width smaller than the radial gap between the inner circumferential surface 2a of the resin molded portion 2 and the small-diameter portion 32b.

[0048] Furthermore, since the axial width L1 of the inner circumferential surface of the plate 33, i.e., the inner circumferential surface 35a of the axial portion 35, is larger than the axial width L2 of the outer circumferential surface of the plate 33, i.e., the outer circumferential surface 34a of the radial portion 34, a large area where the plate 33 and the large-diameter portion 32c of the fixed core 32 overlap in the radial direction can be secured in the axial direction, ensuring reliable transmission of magnetic flux between the plate 33 and the fixed core 32.

[0049] Specifically, by ensuring a large axial width L1 of the inner circumferential surface 35a of the axial portion 35, variations in the axial assembly position between the fixed iron core 32 and the solenoid molded body 31, which occur due to the manufacturing and assembly accuracy of each component constituting the solenoid valve V, can be tolerated by an axial width L3, which is the difference between the axial width L1 and the axial width L2.

[0050] Furthermore, even if the bobbin 36 attempts to deform inward due to thermal expansion and contraction of the resin molded portion 2 located on the outer circumference of the bobbin 36, this deformation is restricted by the step between the axial portion 35 and the radial portion 34. Therefore, deformation of the resin molded portion 2 and the entire bobbin 36 inward can be restricted. Moreover, since the resin molded portion 2 located on the inner circumference of the annular base portion 36a of the bobbin 36 is positioned to overlap radially with the small diameter portion 32b of the fixed iron core 32, no external force acts on the fixed iron core 32 from the resin molded portion 2.

[0051] Furthermore, the outer circumferential surface 34a of the radial portion 34 of the plate 33 is in contact with the upper inner circumferential surface 30a of the stepped portion 30A of the solenoid case 30. As a result, since the plate 33, which has higher rigidity than the resin molded portion 2, is in contact with the solenoid case 30, the connection between the solenoid molded body 31 and the solenoid case 30 can be stabilized.

[0052] Furthermore, the plate 33 is positioned on the stepped portion 30A of the solenoid case 30, with the outer peripheral surface 34a of the radial portion 34 contacting the upper inner peripheral surface 30a of the stepped portion 30A, and the lower outer edge surface of the axial portion 35 abutting against the end face 30b of the stepped portion 30A, thus enabling good transfer of magnetic flux between the plate 33 and the solenoid case 30. In addition, the solenoid molded body 31 is positioned vertically relative to the solenoid case 30.

[0053] Furthermore, the fixed core 32 is integrally formed with an annular side wall 32B that forms a magnetic path between the magnetic member 37, which is the side to which the plunger 4 is attracted, and the solenoid case 30, and a small-diameter peripheral wall 32C that extends to the opposite side from the magnetic member 37. As a result, the structural strength of the fixed core 32 is higher than that of a fixed core with a segmented structure, which suppresses damage when inserting the fixed core 32 into the central hole 31a of the solenoid molded body 31, and also provides high assembly accuracy and dimensional accuracy of the inner surface of the fixed core 32.

[0054] Furthermore, the fixed iron core is configured to surround the inner diameter side, one axial end side, and outer diameter side of the coil in the solenoid molded body, and the outer diameter side is magnetically connected to the plate, so that the solenoid case is not used as a magnetic circuit (see Figure 5).

[0055] Furthermore, the solenoid case 30, the fixed core 32, and the plate 33 may be made of the same material. In this case, since the thermal expansion coefficient and thermal contraction coefficient of the solenoid case 30, the fixed core 32, and the plate 33 are the same, no stress will be generated even if each component expands or contracts due to heat. [Examples]

[0056] Next, the solenoid according to Example 2 will be described with reference to Figure 3. Note that the description of components that are identical to those in Example 1 and therefore redundant will be omitted.

[0057] As shown in Figure 3, the solenoid 200 of this embodiment 2 has a plate 233 that is substantially disc-shaped, and its upper surface 233a is a tapered surface that slopes downward from the inner diameter side to the outer diameter side.

[0058] The plate 233 is formed such that the axial width L10 of the inner circumferential surface 233b is larger than the axial width L20 of the outer circumferential surface 233c. This ensures that even if there is variation in the axial assembly position between the fixed core 232 and the solenoid molded body 231, the inner circumferential surface 233b of the plate 233 can be positioned across the large diameter portion 232c and the small diameter portion 232b of the fixed core 232.

[0059] Furthermore, the simple structure of the plate 233 results in excellent workability. Note that the upper surface 233a of the plate 233 is not limited to a straight line; for example, it may be a curved surface that convex downwards or upwards. [Examples]

[0060] Next, the solenoid according to Example 3 will be described with reference to Figure 4. Note that the description of components that are identical to those in Example 1 and therefore redundant will be omitted.

[0061] As shown in Figure 4, the plate 333 of the solenoid 300 in this embodiment 3 is composed of a radial portion 334 extending substantially horizontally, an axial portion 335 extending upward from the inner diameter edge of the radial portion 334, and an axial portion 338 extending upward from the outer diameter edge of the radial portion 334, and has a cross-section that is substantially upward U-shaped. The radial portion 334 is the portion on the outer circumference side of the axial portion 335.

[0062] The axial width L11 of the axial portion 335 on the inner diameter side and the axial width L11' of the axial portion 338 on the outer diameter side are the same (L11 = L11').

[0063] According to this, the region where the plate 333 and the large-diameter portion 332c of the fixed iron core 332 overlap radially, and the region where the plate 333 and the solenoid case 330 overlap radially, can be secured in the axial direction to ensure reliable transmission of magnetic flux.

[0064] Furthermore, the outer surface of the axial portion 335, the upper surface of the radial portion 334, and the inner surface of the axial portion 338 may be smoothly connected in a curved manner. [Examples]

[0065] Next, the solenoid according to Example 4 will be described with reference to Figure 5. Note that the description of components that are identical to those in Example 1 and therefore redundant will be omitted.

[0066] As shown in Figure 5, the fixed core 532 of the solenoid 500 in this embodiment 4 has a divided structure consisting of an upper magnetic body 532A, a lower magnetic body 532B, and a cylindrical body 532C. The cylindrical body 532C is made of a non-magnetic material and is positioned between the upper magnetic body 532A and the lower magnetic body 532B. The portion of the cylindrical body 532C positioned between the upper magnetic body 532A and the lower magnetic body 532B is a portion of the fixed core 532 with high magnetic resistance.

[0067] The lower magnetic body 532B has a portion 532Ba located on the inner diameter side of the coil 36 in the solenoid molded body 531, a portion 532Bb located on the lower end side of the coil 36, and a portion 532Bc located on the outer diameter side of the coil 36. The upper end of portion 532Bc is magnetically connected to the plate 533. The coil 36 in the solenoid molded body 531 is surrounded by portions 532Ba, 532Bb, 532Bc and the plate 533. In other words, the solenoid case 530 is not used as a magnetic circuit.

[0068] Furthermore, the solenoid case 530 in this embodiment 4 is a component on the solenoid 500 side. The solenoid 500 is constructed by assembling the solenoid case 530, solenoid molded body 531, fixed iron core 532, and plunger 504 with respect to the internal components 550 on the mounting equipment side, while adjusting their respective positions.

[0069] Although embodiments of the present invention have been described above with reference to the drawings, the specific configurations are not limited to these embodiments, and any changes or additions that do not depart from the spirit of the present invention are also included.

[0070] For example, in the above embodiments 1 to 4, a configuration in which the inner diameter side of the plate is longer in the axial direction than the outer diameter side was illustrated, but the invention is not limited to this, and for example, it may have a constant thickness and extend in the radial direction.

[0071] Furthermore, while the above-described embodiments 1 to 4 illustrate a configuration in which the axial portion extends upward from the radial portion, i.e., toward the insertion direction of the fixed core, the axial portion may also extend downward, i.e., toward the withdrawal direction of the fixed core. [Explanation of symbols]

[0072] 1 Solenoid 2 Resin molding section 4. Plunger (movable iron core) 30 Solenoid Case (Case) 30A stepped section 30a Upper inner surface 30b end face 31 Solenoid molded body 31a center hole 32 Fixed iron core 32C Small diameter peripheral wall 32a Thin wall part 32b Small diameter section 32c Large diameter section 32d stepped section 33 plates 34 Radial portion 34a Outer surface 35 Axial location 35a Inner surface 36 bobbins 36a Annular base 37 Magnetic material 39 coils V Solenoid Valve

Claims

1. A solenoid comprising: a coil disposed within a cylindrical case and covered by a resin molded portion; a fixed iron core having a small diameter portion and a large diameter portion and inserted into the central hole of the coil; a movable iron core disposed within the fixed iron core; and a plate embedded in the resin molded portion so as to overlap radially with the fixed iron core and form a magnetic path between the case and the fixed iron core, The axial width of the inner circumferential surface of the plate is greater than the axial width of the portion on the outer circumferential surface side of the plate. The inner circumferential surface of the plate is a solenoid that extends from the small diameter portion to the large diameter portion of the fixed iron core.

2. The solenoid according to claim 1, wherein the plate comprises a radial portion extending radially with a constant width, and an axial portion extending axially from the inner diameter end of the radial portion toward the small diameter side of the fixed core.

3. The solenoid according to claim 1, wherein the plate is in contact with the inner circumferential surface of the case.

4. The solenoid according to claim 3, wherein the plate is arranged on a stepped portion provided on the inner circumference of the case.

5. The solenoid according to claim 1, wherein the fixed core is integrally formed with one end and the other end of the movable core in the direction of movement.

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