Electromagnetic coil and electromagnetic clutch equipped therewith

Abstract

This invention provides an electromagnetic coil and an electromagnetic clutch equipped therewith that can easily and reliably prevent insulation failures even when a bobbinless coil is used. [Solution] The device comprises a magnetic coil case 11 having an annular storage groove 12, a coil 13 housed in the storage groove 12, and an electrically insulating insulating cover 15 fitted to the storage groove 12 to prevent contact between the coil 13 and the coil case 11. This reliably prevents insulation failure of the coil 13 that may occur due to contact between the coil 13 and the coil case 11. The side wall of the coil case 11 is provided with a retractable portion 33 that moves away from the coil 13 as it approaches the open end, and the insulating cover 15 is formed so as not to cover the retractable portion 33.

Description

Technical Field

[0001] The present invention relates to an electromagnetic coil used in an electromagnetic clutch or the like, and an electromagnetic clutch provided with this electromagnetic coil.

Background Art

[0002] In a compressor for an air conditioner mounted on a vehicle, an electromagnetic clutch is used to disconnect the connection between the vehicle drive engine and the compressor. This electromagnetic clutch includes a rotor rotatably attached to a compressor housing for transmitting the rotation of the vehicle engine, an exciting coil disposed radially inside the rotor and capable of exciting a magnetic field in the rotor, an armature plate provided close to the axial end face of the rotor and attracted to the end face of the rotor by the magnetic field excited by the exciting coil, and a hub for transmitting the rotation of the rotor to the drive shaft of the compressor via the armature plate. In a conventional exciting coil, a bobbin coil in which a winding is wound around a bobbin formed of resin or the like is used, and this is housed in an annular storage groove formed in a coil case, and further, resin is molded in the storage groove to ensure the water resistance of the coil.

[0003] However, a coil using such a bobbin has a problem that the size of the bobbin becomes larger than the coil itself, so that the entire exciting coil becomes larger. As a result, the electromagnetic clutch itself becomes larger, the weight increases, and it is also disadvantageous in terms of manufacturing cost. Therefore, bobbinless excitation coils, which do not involve winding the coil around a bobbin, have been proposed. For example, Patent Document 1 (Japanese Patent Publication No. 64-26032) discloses an excitation coil using a bobbinless coil in which the coil is wound without using a bobbin. The coil, wound in a ring shape, is restrained at several points of the ring portion by insulating tape to prevent unraveling. The insulating tape is wound to have a predetermined thickness, and by housing this coil in a storage groove of a coil case, the thickness of the insulating tape prevents contact between the housing and the coil, and also creates a gap between the coil housing and the coil, and by molding resin through this gap, the resin is spread throughout the storage groove of the coil case, thereby making the coil water-resistant. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 64-26032 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] However, in the above configuration employing a bobbinless coil, although the coil wire is wound in a ring shape and insulating tape is used to prevent unraveling, the coil wire itself is flexible, making it difficult to maintain a perfect circle. As a result, there was a possibility that the parts not wrapped in insulating tape would come into contact with the inner wall of the coil case. If such contact occurs, the enamel coating applied to the coil wire may peel off, potentially causing the coil wire to become electrically conductive with the coil case and leading to insulation failure. To solve this problem, one could consider increasing the thickness of the insulating tape or increasing the number of places where the insulating tape is wrapped. However, if these measures are taken, the manufacturing process becomes more complex, and the cycle time for coil manufacturing becomes longer, which is a disadvantage.

[0006] This invention has been made in view of the above circumstances, and its main objective is to provide an electromagnetic coil and an electromagnetic clutch equipped therewith that can easily and reliably prevent insulation failure even when a bobbinless coil is used without a bobbin. [Means for solving the problem]

[0007] To achieve the above objectives, the electromagnetic coil according to the present invention is A magnetic coil case having an annular storage groove, The coil housed in the aforementioned storage groove, An electrically insulating cover is fitted into the aforementioned storage groove to prevent contact between the coil and the coil case, It is characterized by having the following features.

[0008] Therefore, since the coil housed in the storage groove is prevented from contacting the inner wall of the coil case by the insulating cover fitted to the storage groove, insulation failure of the coil that could occur due to the coil wires contacting the coil case is reliably prevented. As a result, even if the coil is flexible and does not easily maintain a perfect circle, contact with the inner wall of the case is eliminated, and high insulation performance can be maintained.

[0009] Furthermore, the installation of an insulating cover eliminates the need for the conventional process of wrapping insulating tape around the entire circumference of the coil wire, thus simplifying the manufacturing process and enabling efficient coil production. As a result, the electromagnetic coil of the present invention not only improves reliability by preventing contact between the coil and the coil case, but also contributes to reducing manufacturing costs and shortening the manufacturing cycle time.

[0010] Furthermore, it is preferable to fill the storage groove with insulating resin and then resin-mold the coil. This resin molding integrates the coil with the insulating cover and coil case, preventing displacement of the coil due to vibration or external forces. In addition, the resin covering the entire coil improves moisture resistance, preventing a decrease in insulation performance due to moisture and dust from the external environment.

[0011] Furthermore, the coil case has a storage groove with a U-shaped cross-section that is open at one end, and the insulating cover fitted into the storage groove has an inner wall facing the inner side wall of the coil case, a bottom wall facing the bottom wall of the coil case, and an outer wall facing the outer side wall of the coil case, so that the entire coil case can be efficiently covered across the inner side wall, bottom wall, and outer side wall of the coil case. As a result, a reliable insulating layer is formed between the entire inner wall of the coil case and the coil, and even if the coil is flexible and does not easily maintain a perfect circle, contact with any part of the coil case is reliably avoided.

[0012] The coil case should have at least one of its inner and outer side walls provided with a retractable section that moves away from the coil as it approaches the open end, and the insulating cover should be formed so as not to cover the retractable section. With this configuration, the side wall of the coil case is sufficiently separated from the coil in the retracted section, eliminating the risk of contact between the coil and the coil case in that area, thus eliminating the need for insulation. Therefore, there is no particular problem even if the insulating cover does not cover the retracted section. Furthermore, by not covering the retracted section, it is possible to keep the height of the side wall of the insulating cover low, making it possible to make the insulating cover smaller.

[0013] In this configuration, it is preferable to provide a recessed groove around the entire circumference of the side wall of the coil case in the retracted section. Since the retracted section with the groove is not covered by the insulating cover, the insulating resin will reliably enter the groove, and the resin that solidifies within the groove will act as an anchor, allowing the resin to be firmly fixed to the housing section.

[0014] Furthermore, it is preferable that the outer wall of the insulating cover be provided with multiple reduced-diameter sections, which are radially reduced inward, spaced apart in the circumferential direction. This configuration allows for a space to be secured between the reduced-diameter portion of the insulating cover and the coil case, enabling the resin to be reliably filled between the insulating cover and the coil case all the way to the bottom wall. As a result, a large contact area can be secured between the insulating cover and the coil case and the resin, making it possible to firmly fix the insulating cover and the coil case together.

[0015] Furthermore, it is preferable to provide positioning means that fit together on the bottom wall of the coil case and the bottom wall of the insulating cover. Such positioning means may consist of a protrusion formed on one of the bottom walls of the coil case and the insulating cover, and a recess formed on the other that fits together with the protrusion. This configuration makes it easy to position the insulating cover when attaching it to the storage groove in the coil case. [Effects of the Invention]

[0016] As described above, the electromagnetic coil and electromagnetic clutch equipped therewith according to the present invention are designed so that an electrically insulating cover is fitted to the storage groove of a magnetic coil case having an annular storage groove, thereby reliably preventing the coil housed in the storage groove from coming into contact with the coil case. This makes it possible to easily and reliably avoid insulation failures and conductivity failures even when a bobbinless coil is used. Furthermore, by providing a retractable portion on at least one of the inner and outer side walls of the coil case, which moves away from the coil as it approaches the open end, it is possible to form a portion that is sufficiently separated from the coil. This makes it possible to reduce the height of the side walls of the insulating cover and thus miniaturize the entire insulating cover. In addition, by providing a groove in the retractable portion and filling it with resin, the resin solidified in the groove acts as an anchor, improving the fixing strength of the resin mold.

[0017] Furthermore, a reduced-diameter portion is provided on the outer wall of the insulating cover. This reduced-diameter portion forms a space between the resin, the coil case, and the insulating cover, enabling the injection of insulating resin. As a result, the entire coil can be reliably molded, and the fixing state and moisture-proof performance of the coil can be further improved. Moreover, by providing positioning means that fits between the bottom wall of the coil case and the bottom wall of the insulating cover, the positioning when mounting the insulating cover in the storage groove can be easily and accurately performed, thus improving the manufacturing accuracy and efficiency. As described above, according to the present invention, by preventing contact between the coil and the coil case, the insulation performance can be reliably improved, and at the same time, the efficiency of the manufacturing process can be increased, the manufacturing cost can be reduced, and furthermore, the reliability and durability of the entire electromagnetic clutch can be improved.

Brief Description of the Drawings

[0018] [Figure 1] It is a diagram showing a configuration example of an electromagnetic clutch provided with an electromagnetic coil according to the present invention. [Figure 2] It is a diagram showing a configuration example of the electromagnetic coil according to the present invention, as viewed from the open end of the coil case. [Figure 3] (a) is a cross-sectional view taken along the A-A line of the electromagnetic coil shown in FIG. 2, (b) is a cross-sectional view taken along the B-B line of the electromagnetic coil shown in FIG. 2, and (c) is a cross-sectional view taken along the C-C line of the electromagnetic coil shown in FIG. 2. [Figure 4] It is a diagram showing the coil case used for the electromagnetic coil according to the present invention. (a) is a perspective view seen from the bottom wall side, (b) is a perspective view seen from the opening end side, and (c) is a cross-sectional view taken along the A-A line of (a). [Figure 5] It is a diagram showing the insulating cover used for the electromagnetic coil according to the present invention. (a) is a side view seen from the bottom wall side, (b) is a perspective view seen from the bottom wall side, (c) is a side view seen from the opening end side, (d) is a perspective view seen from the bottom wall side, and (e) is a cross-sectional view taken along the A-A line of (a). [Figure 6] It is a diagram for explaining the process of assembling the electromagnetic coil. [Figure 7] These diagrams illustrate the flow of resin when filling the storage groove with insulating resin. (a) illustrates the flow of resin in the portion where a diameter reduction section is not provided, and (b) illustrates the flow of resin in the portion where a diameter reduction section is formed. [Modes for carrying out the invention]

[0019] Embodiments of the present invention will be described below with reference to the accompanying drawings. Note that the embodiments shown in the accompanying drawings are examples of the present invention, and the present invention is not limited to these embodiments.

[0020] First, let me describe the electromagnetic clutch 1 equipped with an electromagnetic coil according to the present invention.

[0021] As shown in Figure 1, the electromagnetic clutch 1 comprises an electromagnetic coil 10 (described later), a drive-side rotor 2 made of a magnetic material, a driven-side hub 3 that can rotate relative to the rotor 2, and an armature plate 4 made of a magnetic material, connected to the hub 3 and positioned opposite the side end face of the rotor 2 with a gap between them.

[0022] The electromagnetic coil 10 is fixed to the housing 5 (for example, the housing of a compressor) via a fixing plate 8 and is housed inside the rotor 2. When energized, the electromagnetic coil 10 forms a magnetic circuit via the rotor 2 and the armature plate 4, causing the armature plate 4 to be electromagnetically attracted to the rotor 2.

[0023] The hub 3 is mounted with respect to the rotating shaft 6, which protrudes from the housing 5, in such a way that its relative rotation is restricted.

[0024] Furthermore, the rotor 2 is an annular member centered on the centerline CL of the rotating shaft 6, and is composed of a pulley to which rotational power is transmitted via a belt from an external power source such as an engine. This rotor 2 is rotatably supported by a radial bearing 7 on the boss portion 5a of the housing 5.

[0025] The armature plate 4 is made of a magnetic material and is fixed to the hub 3 via an elastic member 9, and is positioned opposite the side end face of the rotor 2 with a gap in between. The armature plate 4 has a friction surface 4a that faces the side end face of the rotor 2. The friction surface 4a can come into close contact with the side end face of the rotor 2 by electromagnetic attraction due to the deformation of the elastic member 9.

[0026] Therefore, when the rotor 2 is belt-driven by an external power source, and the electromagnetic coil 10 is energized, the armature plate 4 is electromagnetically attracted (closely attached) to the rotor 2 and rotates together with the rotor 2, and the rotating shaft 6 rotates via the hub 3 which is integrated with the armature plate 4.

[0027] The electromagnetic coil 10 is fixed to a fixing plate 8 attached to the housing 5 and housed in a manner that ensures a predetermined clearance between it and the rotor 2 (pulley). Specifically, the rotor 2 has a housing recess 51 formed in an annular shape around the center line CL on the end face opposite to the end face facing the armature plate 4. The electromagnetic coil 10 is fixed to the fixing plate 8 positioned to face the open end of the housing recess 51 and is inserted into the housing recess 51 such that a gap is formed between it and the inner wall of the housing recess 51. Therefore, the rotor 2 can rotate without contacting the electromagnetic coil 10.

[0028] The electromagnetic coil 10 is formed in an annular shape with respect to the center line CL of the rotation axis 6, and as shown in Figures 2 and 3, it comprises a magnetic coil case 11 with an annular storage groove 12, a coil 13 housed in the storage groove 12, and an electrically insulating insulating cover 15 fitted to the storage groove 12 to prevent contact between the coil 13 and the coil case 11.

[0029] As shown in Figure 4, the coil case 11 is formed in a U-shape with an open end on the side opposite to the fixing plate 8, and comprises an inner side wall 11a, an outer side wall 11b, and a bottom wall 11c that connects the ends of these side walls 11a and 11b and closes the end on the fixing plate 8 side, and an annular storage groove 12 is defined by these side walls 11a and 11b and the bottom wall 11c.

[0030] A through-hole 22 is formed in a predetermined location in the bottom wall 11c, as shown in Figure 3(a), and is fitted with a grommet 21 through which the external wiring 20 is inserted. This through-hole 22 is positioned to align with the through-hole 8a provided in the fixing plate 8.

[0031] The insulating cover 15 fitted into the storage groove 12 is formed in an annular shape, as shown in Figure 5, and comprises an inner wall 15a facing the inner side wall 11a of the coil case 11, an outer wall 15b facing the outer side wall 11b of the coil case 11, and a bottom wall 15c facing the bottom wall 11c of the coil case 11 and connecting the inner wall 15a and the outer wall 15b.

[0032] A through-hole 15d is formed in the bottom wall 15c of the insulating cover 15 at a position aligned with the through-hole 22, and as shown in Figure 3(b), a boss receiver 16 is formed protruding from the inside of the insulating cover 15 to receive a boss portion 23 that has been machined to accommodate a screw fastening portion 11d (to which the terminals provided at the ends of the coil wires are screwed) provided on the surface side of the coil case 11. Furthermore, to prevent the insulating cover 15 from rotating relative to the coil case 11, positioning protrusions 17 are formed on the bottom wall 11c of the insulating cover 15, projecting outward (towards the bottom wall 11c of the coil case 11), as shown in Figure 3(c). These positioning protrusions 17 are formed in two locations on the bottom wall 15c of the insulating cover 15, separated by a 180-degree phase difference around the center line CL of the rotation axis 6. To avoid interference with the curved portion (R portion) on the inner periphery of the bottom wall 15c of the insulating cover 15, the cross-section is formed in a semicircular shape with the side facing the center line (CL) of the rotation axis 6 cut off. When the insulating cover 15 is formed by thermoforming, a cylindrical protrusion 18 and a pair of semicircular recesses 19 with a semicircular cross-section are formed on the back of the boss receiver 16 and the positioning protrusion 17 on the inner surface (inner surface of the bottom wall 15c).

[0033] The bottom wall 11c of the coil case 11 to which such an insulating cover 15 is attached is provided with a boss portion 23 that fits inside the boss portion receiver 16 of the insulating cover 15, and a recess 24 with a circular cross-section that receives the positioning projection 17 of the insulating cover 15. The boss portion 23 of the coil case 11 and the boss portion receiver 16 of the insulating cover 15 have a large assembly tolerance to account for molding errors. Similarly, the pair of positioning protrusions 17 of the insulating cover and the pair of recesses 24 of the coil case 11 also have a large assembly tolerance. However, the fit of the boss portion 23 and the boss portion receiver 16, and the pair of positioning protrusions 17 and the recesses 24 in three places suppresses circumferential rattle of the insulating cover 15 after it is mounted on the coil case 11, and defines the circumferential position of the insulating cover 15.

[0034] The outer wall 15b of the insulating cover 15 is capable of contacting the outer peripheral side wall 11b of the coil case 11, and the inner wall 15a of the insulating cover 15 is capable of contacting the inner peripheral side wall 11a of the coil case 11. Multiple (four in this example) diameter-reduced portions 31, which are formed by reducing the diameter radially inward, are provided on the outer peripheral side wall 11b of the insulating cover 15 at intervals in the circumferential direction. These diameter-reduced portions 31 are formed to a predetermined width, and when the insulating cover 15 is attached to the coil case 11, a space 32 is formed between the diameter-reduced portions 31 and the outer peripheral side wall 11b of the coil case 11.

[0035] Furthermore, the inner side wall 11a of the coil case 11 is provided with a retraction portion 33 that moves away from the coil 13 as it approaches the open end. This retraction portion 33 is formed around the entire inner surface of the coil case 11. In this embodiment, in the area up to partway towards the open end, it is shaped like a frustoconical cone, where the distance from the coil 13 gradually increases along the axial direction, and in the area from there to the open end, it is cylindrical, extending parallel to the center line of the coil case (a shape in which the distance from the coil is kept constant). Note that instead of a frustoconical shape, it is also possible to form a stepped or stepped shape to widen the distance from the coil 13 as it approaches the open end.

[0036] Given the shape of the coil case 11, the inner wall 15a of the insulating cover 25 is formed to be low in height from the bottom wall 15c so as not to cover the retracted portion 33. In this example, the outer wall 15b of the insulating cover is formed to be high enough to completely accommodate the coil, and the inner circumferential side wall is formed to be at the height of the boundary where the retracted portion 33 of the inner circumferential side wall 11a of the coil case 11 begins to form. Furthermore, the retractable portion 33, and in this particular example, the cylindrical portion following the frustoconical portion of the retractable portion, is provided with a recessed groove 34 extending around its entire circumference toward the outer surface of the coil case 11.

[0037] In the above configuration, to form the electromagnetic coil 10, as shown in Figure 6, the coil case 11 is set with its opening facing upwards on an assembly stand (not shown), and the insulating cover 15 is then fitted into the storage groove 12 with its opening facing upwards. At this time, the through hole 22 of the coil case 11 and the through hole 15d of the insulating cover 15 are aligned, the circumferential position of the insulating cover 15 is finely adjusted, and the boss portion 23 provided on the bottom wall 15c of the insulating cover 15 is fitted into the boss portion receiver 16, and the positioning protrusion 17 is fitted into the recess 24. As a result, the circumferential position of the insulating cover 15 is defined within the housing and then fixed without shifting position.

[0038] Subsequently, the coil 13, which has the coil wires bundled in a ring shape and partially wrapped with insulating tape at appropriate points around its circumference to prevent unraveling, and to which accessories such as diodes are connected, is inserted into the storage groove 12 of the coil case 11. At this time, the coil 13 is housed so as to rest on the boss support 16 provided on the bottom wall 11c of the coil case 11 and on accessories such as diodes placed between the bottom wall 15c of the insulating cover 15. As a result, the coil is housed in a state where it is floating above the bottom wall 15c of the insulating cover 15, but the lower surface of the coil 13 is supported at multiple points by the boss support 16 and accessories, so the inconvenience of the coil tilting is prevented. As described above, after housing the coil 13 in the insulating cover 15, accessories such as a thermal fuse β are installed on the upper surface of the coil 13, and then an electrically insulating thermosetting resin (insulating resin) α is poured through the opening of the coil case 11, and then heated to solidify it.

[0039] Therefore, with the above configuration, the housed coil 13 is only partially bundled with insulating tape without using a bobbin, and since the coil wire itself is flexible, it becomes difficult to maintain a perfect circle in the parts where the insulating tape is not wrapped. However, the coil 13 is positioned inside the insulating cover 15, so contact with the coil case 11 is reliably avoided. As a result, there is no risk of wear or peeling of the enamel coating on the surface of the coil wire due to contact with the coil case, and the occurrence of insulation failure caused by the coil 13 contacting the coil case 11 is prevented. Thus, in the above configuration, by reliably eliminating contact between the coil 13 and the coil case 11, it is possible to stably maintain the insulation performance of the coil even when a bobbinless coil is used.

[0040] Furthermore, while conventional methods required wrapping insulating tape around the entire circumference of the coil, this invention pre-installs an insulating cover in the storage groove and then houses the coil. This eliminates the need to increase the thickness of the insulating tape or the number of wrapping points, significantly simplifying the manufacturing process and enabling reductions in manufacturing costs and shorter manufacturing cycle times. Furthermore, in the above configuration, since the insulating cover 15 is provided with a diameter-reducing portion 31, the insulating resin α can easily flow through the space 32 formed between the coil case 11 and the diameter-reducing portion 31 to the bottom walls 11c and 15c, thereby ensuring a large contact area between the insulating resin α and the coil case 11 and insulating cover 15. As a result, after the insulating resin α has solidified, the resin exerts a strong fixing force, enabling the entire coil to be held stably.

[0041] Furthermore, the coil case 11 is provided with a retraction section 33 that moves away from the coil 13 as it approaches the open end, so that the coil 13 avoids contact with the coil case 11 at the retraction section 33. For this reason, there is no particular problem even if the height of the inner wall 15a of the insulating cover 15 is reduced so that it does not cover the retraction section. Rather, since the height of the inner wall 15a of the insulating cover 15 can be reduced, it becomes possible to miniaturize the insulating cover 15. In addition, since the retracted portion 33 is not covered by the insulating cover 15 and a groove 34 is provided in this retracted portion 33, the insulating resin α can be reliably filled into the groove during resin molding, and an anchoring effect can be achieved by the solidification of the insulating resin α. As a result, the bonding strength between the insulating resin α and the coil case 11 is further improved, and the coil will not shift position even under vibration or external force, maintaining long-term durability and reliability.

[0042] Furthermore, by forming a retracted portion 33 that is not covered by the insulating cover 15, it becomes possible to fill the space between the bottom surface of the coil 13 and the insulating cover 15 with insulating resin around its entire circumference. That is, as shown in Figure 7(a), in the portion of the insulating cover where the reduced diameter portion 31 is not formed, it becomes possible to flow insulating resin α between the coil 13 and the bottom wall 15c through the gap between the coil 13 and the outer wall 15b of the insulating cover 15, and as shown in Figure 7(b), in the portion where the reduced diameter portion 31 is formed, the insulating resin α that has flowed under the coil in the portion where the reduced diameter portion 31 is not formed moves in the circumferential direction, and it becomes possible to guide the insulating resin α under the coil through the space between the retracted portion 33 and the coil 13, so that the insulating resin α can be reliably filled inside the insulating cover around its entire circumference.

[0043] As described above, according to the electromagnetic coil 10 of this embodiment, even when a bobbinless coil 13 is used, the installation of the insulating cover 15 makes it possible to allow the coil wire to bend while reliably preventing contact between the coil 13 and the coil case 11. Therefore, it is possible to reliably prevent insulation failure with a simple structure.

[0044] In the above configuration, an example was shown in which the retractable portion 33 is provided on the inner side wall 11a of the coil case 11. However, the retractable portion 33 may also be provided on the outer side wall 11b of the coil case 11, or on both the inner side wall 11a and the outer side wall 11b. Therefore, the heights of the inner wall 15a and outer wall 15b of the insulating cover 15 should be adjusted as appropriate to match the retractable portion 33. [Explanation of Symbols]

[0045] 1. Electromagnetic clutch 2 rotors 3 Hubs 4 Armature Plate 10 Electromagnetic coils 11 Coil Cases 11a Inner side wall 11b Outer side wall 11c bottom wall 12 storage grooves 13 coils 15 Insulating cover 15a Inside wall 15b Outside wall 15c bottom wall 17 Positioning protrusion 24 recesses 33 Evacuation Section 34 grooves α insulating resin

Claims

1. A magnetic coil case (11) having an annular storage groove (12), The coil (13) is housed in the aforementioned storage groove (12), An electrically insulating insulating cover (15) is fitted into the storage groove (12) to prevent contact between the coil (13) and the coil case (11), An electromagnetic coil (10) characterized by comprising the above.

2. The electromagnetic coil (10) according to claim 1, characterized in that the storage groove (12) is filled with insulating resin (α) and the coil (13) is resin-molded.

3. The electromagnetic coil (10) according to claim 1, characterized in that the storage groove (12) is formed in a U-shape in cross-section and has one end open, and the insulating cover (15) fitted into the storage groove (12) comprises an inner wall (15a) facing the inner side wall (11a) of the coil case (11), an outer wall (15b) facing the outer side wall (11b) of the coil case (11), and a bottom wall (15c) facing the bottom wall (11c) of the coil case (11).

4. At least one of the inner side wall (11a) and the outer side wall (11b) of the coil case (11) is provided with a retractable portion (33) that moves away from the coil (13) as it approaches the open end. The insulating cover (15) is formed so as not to cover the retracted portion (33). The electromagnetic coil (10) according to feature 3.

5. The electromagnetic coil (10) according to claim 4, characterized in that the retracted portion (33) is provided with a recessed groove (34) extending around the entire circumference of the side walls (11a, 11b).

6. The electromagnetic coil (10) according to claim 3, characterized in that the outer wall (15b) of the insulating cover (15) is provided with a plurality of reduced-diameter portions (31) that are spaced apart in the circumferential direction, with the diameter being reduced toward the radially inward.

7. The electromagnetic coil (10) according to claim 3, characterized in that the bottom wall (11c) of the coil case (11) and the bottom wall (15c) of the insulating cover (15) are provided with positioning means that fit together with each other.

8. The electromagnetic coil (10) according to claim 7, characterized in that the positioning means comprises a positioning projection (17) formed on one of the bottom wall (11c) of the coil case (11) and the bottom wall (15c) of the insulating cover (15), and a recess (24) formed on the other that fits with the positioning projection.

9. An electromagnetic coil (10) according to any one of claims 1 to 8, A drive-side rotor (2) made of magnetic material, A driven hub (3) that is rotatable relative to the rotor (2), It comprises an armature plate (4) made of a magnetic material, connected to the hub (3), and positioned opposite the side end face of the rotor (2) with a gap between them, The electromagnetic coil (10) is housed inside the rotor (2) so as to be able to generate an attractive force that causes the armature plate (4) to be electromagnetically attracted to the rotor (2) by energizing the coil (13), thereby forming a magnetic circuit that passes through the rotor (2) and the armature plate (4). An electromagnetic clutch (1) characterized by the following.

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