Abstract:
An electromagnetic clutch includes an electromagnet device housed in a rotor. The electromagnet device has a ring member having a containing chamber, a coil member having a bobbin and a coil element and housed in the containing chamber of the ring member, and a seal mechanism provided for enclosing the coil element in the containing chamber at a sealed-off condition. A desired seal mechanism is formed without using a molding resin. The productivity of manufacturing processes for the electromagnetic clutch may be increased by stopping use of a molding resin. Moreover, the proper insulation of the electromagnet device may be ensured by the desired seal mechanism.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an electromagnetic clutch, and more specifically, to an electromagnetic clutch suitable for use in compressors. 
     2. Description of Related Art 
     An electromagnetic clutch is used as a power transmission for a compressor. For example, a known structure of a scroll-type compressor having an electromagnetic clutch is constructed as depicted in FIG.  17 . In FIG. 17, electromagnetic clutch  100  is assembled around cylindrical projected portion  121   a  of front housing  121  of scroll-type compressor  120 . Electromagnetic clutch  100  includes rotor  101 , which is mounted upon projected portion  121   a  via bearing  123 . Rotor  101  has inner cylindrical portion  101   a , outer cylindrical portion  101   b , and bottom portion  101   c  connecting the ends of cylindrical portions  101   a  and  101   b . Containing space  101   d  is formed by portions  101   a ,  101   b  and  101   c . Electromagnet device  102  is enclosed within containing space  101   d  of rotor  101 . 
     Armature  103  is provided facing one end of rotor  101 . Armature  103  is connected to stopper plate  105  via plate spring  104 . Stopper plate  105  is fixed to boss portion  106  via rivets  107 . Boss portion  106  is fixed to end portion  122   a  of drive shaft  122  by threaded nut  108 . 
     In electromagnetic clutch  100 , a rotational torque is transmitted from an external power source (not shown) to rotor  101  via a V belt (not shown). When electromagnet device  102  is not energized, because armature  103  is urged by plate spring  104  away from rotor  101 , even if rotor  101  rotates, armature  103  does not rotate. Therefore, the rotational torque of rotor  101  is not transmitted to drive shaft  122 . When electromagnet device  102  is energized, armature  103  is attracted to the end of rotor  101  by the attracting force generated by electromagnet device  102 , in opposition to the urging force applied by plate spring  104 . Therefore, rotor  101  and armature  103  are integrated, and rotated together. The rotational torque of rotor  101  is transmitted to drive shaft  122  through stopper plate  105  and boss portion  106 , thereby driving compressor  120 . 
     FIG. 18 depicts an inclined plate-type compressor as another type of compressor. In FIG. 18, electromagnetic clutch  110  is assembled around of cylindrical projected portion  131   a  of front housing  131  of inclined plate-type compressor  130 . Electromagnetic clutch  110  may have a structure similar to that depicted in FIG.  17 . 
     FIG. 19 depicts an example of the detailed structure of the electromagnet device depicted in FIG. 17 or  18 . In FIG. 19, electromagnet device  102  has ring member  113  forming therein a containing chamber  113   a . Ring-like plate  114  is provided on one end outer surface of ring member  113  for fixing ring member  113  on a front housing of a compressor. Coil bobbin  112  provided with coil element  111  is housed within containing chamber  113   a  of ring member  113 . Coil bobbin  112  is enclosed within containing chamber  113   a  by charging resin  115 , such as an epoxy resin into containing chamber  113   a . Thus, in a known technology, a method for molding a resin is employed for preventing water or foreign material from entering into an electromagnetic clutch, including for ensuring the properties of vibration resistance, heat radiation resistance, and water proofing. 
     FIG. 20 depicts another example of the detailed structure of the electromagnet device depicted in FIG. 17 or  18 . In FIG. 20, electromagnet device  102 ′ has bobbin  116  formed as two separate parts. After coil element  111  is enclosed within the two parts of bobbin  116 , bobbin  116  is housed within containing chamber  113   a  of ring member  113 . Enclosed bobbin  116  then is fixed by caulked portions  117  formed at the partial inner edges of the opening portion of containing chamber  113   a.    
     In the known structure depicted in FIG. 19, however, because resin  115  for molding generally is a thermosetting resin, such as an epoxy resin, manufacturing electromagnet device  102  requires an expensive furnace for curing of the resin. Further, it takes a long period of time to cure the resin, thereby decreasing the productivity of manufacturing processes for such an electromagnetic clutch. 
     In the known structure depicted in FIG. 20, it is difficult to completely prevent water from entering into coil element  111  through a gap between the two parts of bobbin  116 . Therefore, there is a problem insulating coil element  111 . 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide an improved structure for an electromagnetic clutch that may increase the productivity of manufacturing processes by stopping use of a molding resin, and that may ensure the proper insulation of an electromagnet device. 
     To achieve the foregoing and other objects, an electromagnetic clutch according to the present invention is provided. The electromagnetic clutch includes an electromagnet device housed within a rotor. The electromagnet device comprises a ring member having a containing chamber, a coil member housed within the containing chamber of the ring member. The coil member comprises a bobbin and a coil element provided within the bobbin. The electromagnet device comprises a seal mechanism provided for enclosing the coil element within the containing chamber of the ring member in a sealed-off condition. 
     In the electromagnetic clutch, the seal mechanism comprises a seal plate to improve the seal formed between the bobbin and the ring member. The seal plate engages an engaging portion formed on an inner surface of the containing chamber of the ring member. The seal plate may comprise a side plate portion integral with the bobbin. Alternatively, the seal plate may comprise a resin plate provided separately from the bobbin. 
     The engaging portion may comprise a first groove formed on the inner surface of the containing chamber of the ring member. The first groove extends circumferentially about the ring member. Further, the engaging portion may comprise a stepped portion formed on the inner surface of the containing chamber of the ring member. The stepped portion extends circumferentially about the ring member. 
     The seal plate may have a projection extending circumferentially about the ring member. The projection engages the engaging portion formed on the inner surface of the containing chamber of the ring member. The projection may be brought into contact with the engaging portion. Further, the projection may be fitted into a second groove formed on the engaging portion. The second groove extends circumferentially about the ring member. 
     Further, the seal plate may have a V-shaped groove on its radial end surface, i.e., a radially outer end surface, or a radially inner end surface, or both. The seal plate may have a notch on its edge portion. The notch extends circumferentially about the seal plate. 
     The seal plate is fixed in the containing chamber of the ring member. For example, a part of the inner surface of the containing chamber of the ring member is crimped, and the seal plate is fixed in the containing chamber of the ring member by the crimping. Crimping may include the formation of a wave, bulge, crinkle, warp, or similar deformation in the ring member surface. A plurality of crimped portions may be disposed circumferentially about the ring member, or a crimped portion may extend continuously over the entire circumference of the ring member. The crimped portion, or portions, may be disposed on the inner surface of an outer cylindrical portion of the ring member, or an outer surface of an inner cylindrical portion of the ring member, or both. 
     An inner surface of of the containing chamber of the ring member positioned below the engaging portion, may be formed as a tapered surface causing a width of the containing chamber to gradually decrease. 
     The seal mechanism may comprise a protruded portion placed into contact with an inner surface of the containing chamber of the ring member. The protruded portion extends circumferentially about the ring member. The cross-sectional shape may be rectangular, semi-circular, triangular, or trapezoidal. 
     Such an electromagnetic clutch is used, for example, for a compressor. Any type of the compressor may be available. 
     In the electromagnetic clutch according to the present invention, the seal mechanism does not require a molding resin to achieve a desired quality of seal. The number of manufacturing steps may be decreased by stopping use of the molding resin, thereby reducing the cost for the manufacture of the electromagnetic clutch. 
     Further, because the seal mechanism may achieve a high quality of seal for the coil element without using a molding resin, the proper insulation of the coil element may be ensured readily and less expensively. 
     Further objects, features, and advantages of the present invention will be understood from the following detailed description of preferred embodiments of the present invention with reference to the accompanying figures. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the invention are now described with reference to the accompanying figures, which are given by way of example only, and are not intended to limit the present invention. 
     FIG. 1 is a perspective, cut-away view of an electromagnet device of an electromagnetic clutch according to a first embodiment of the present invention. 
     FIG. 2 is an enlarged, partial cross-sectional view of the electromagnet device depicted in FIG.  1 . 
     FIG. 3A is an exploded and enlarged, partial cross-sectional view and 
     FIG. 3B is an enlarged, partial cross-sectional view of a seal mechanism in the electromagnet device depicted in FIG. 2 according to a modification of the first embodiment. 
     FIG. 4A is an exploded and enlarged, partial cross-sectional view and 
     FIG. 4B is an enlarged, partial cross-sectional view of a seal mechanism in the electromagnet device depicted in FIG. 2 according to another modification of the first embodiment. 
     FIG. 5A is an exploded and enlarged, partial cross-sectional view and 
     FIG. 5B is an enlarged, partial cross-sectional view of a seal mechanism in the electromagnet device depicted in FIG. 2 according to a further modification of the first embodiment. 
     FIG. 6 is a partial, cross-sectional view of an electromagnet device of an electromagnetic clutch according to a second embodiment of the present invention. 
     FIG. 7A is an exploded and enlarged, partial cross-sectional view and 
     FIG. 7B is an enlarged, partial cross-sectional view of a seal mechanism in the electromagnet device depicted in FIG. 6 according to a modification of the second embodiment. 
     FIG. 8A is a partial, cross-sectional view of an electromagnet device of an electromagnetic clutch according to a third embodiment of the present invention. 
     FIGS. 8B-8D are enlarged, partial cross-sectional views of various modifications of the seal mechanism of the electromagnet device depicted in FIG.  8 A. 
     FIG. 9 is a partial, cross-sectional view of an electromagnet device of an electromagnetic clutch according to a fourth embodiment of the present invention. 
     FIG. 10 is an exploded cross-sectional view of the electromagnet device depicted in FIG. 9, showing the assembly of the electromagnet device. 
     FIG. 11 is a partial, cross-sectional view of an electromagnet device of an electromagnetic clutch according to a fifth embodiment of the present invention. 
     FIG. 12 is an exploded cross-sectional view of the electromagnet device depicted in FIG. 11, showing the assembly of the electromagnet device. 
     FIG. 13 is a partial, cross-sectional view of an electromagnet device of an electromagnetic clutch according to a sixth embodiment of the present invention. 
     FIG. 14 is an exploded cross-sectional view of the electromagnet device depicted in FIG. 13, showing the assembly of the electromagnet device. 
     FIG. 15 is a partial, cross-sectional view of an electromagnet device of an electromagnetic clutch according to a seventh embodiment of the present invention. 
     FIG. 16 is an exploded cross-sectional view of the electromagnet device depicted in FIG. 15, showing the assembly of the electromagnet device. 
     FIG. 17 is a cross-sectional view of a known scroll-type compressor including an electromagnetic clutch. 
     FIG. 18 is a cross-sectional view of a known inclined plate-type compressor including an electromagnetic clutch. 
     FIG. 19 is a partial, cross-sectional view of an example of an electromagnet device used in the electromagnetic clutch depicted in FIG. 17 or  18 . 
     FIG. 20 is a partial, cross-sectional view of another example of an electromagnet device used in the electromagnetic clutch depicted in FIG. 17 or  18 . 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     An electromagnetic clutch according to a first embodiment of the present invention is depicted in FIGS. 1 and 2. Referring to FIGS. 1 and 2, electromagnet device  10  provided in an electromagnetic clutch comprises ring member  5 , coil member  1 , and fastening member  6 . Ring member  5  has outer cylindrical portion  5   a , inner cylindrical portion  5   b , and bottom portion  5   c  connecting the ends of outer and inner cylindrical portions  5   a  and  5   b . Containing chamber  5   d  is formed as a ring-like groove portion in ring member  5  by respective portions  5   a - 5   c . Coil member  1  is contained in containing chamber  5   d . Fastening member  6  is fixed to a front housing of a compressor, as depicted in FIG. 17 or  18 . 
     Coil member  1  comprises ring-like bobbin  2 , made from a resin, and coil element  3  provided in bobbin  2 . Bobbin  2  has a U-shaped cross section formed by side plate portion  2   a  (a ceiling plate portion), the other side plate portion  2   c  (a bottom plate portion), and connecting plate portion  2   b . Coil element  3  is contained within the U-shaped bobbin  2 . 
     Engaging portion  7  is formed on the upper end portion of each of the radial inner surface of outer cylindrical portion  5   a  and the radial outer surface of inner cylindrical portion  5   b , at the opening portion of U-shaped ring member  5 . In this embodiment, engaging portion  7  is formed as a stepped portion extending circumferentially about ring member  5 . The radial outer and inner edges of side plate portion  2   a  of bobbin  2  engage engaging portion  7 . A part of the upper end of each of the radial inner surface of outer cylindrical portion  5   a  and the radial outer surface of inner cylindrical portion  5   b  above engaging portion  7  is crimped on each of the radial outer and inner edges of side plate portion  2   a  of bobbin  2 . A plurality of crimped portions  5   e  are disposed circumferentially about ring member  5  on the respective surfaces of outer and inner cylindrical portions  5   a  and  5   b.    
     By this crimping, coil member  1  may be securely fixed in ring member  5  at a condition in that bottom plate portion  2   c  of bobbin  2  is brought into contact with the upper surface of bottom portion  5   c  of ring member  5 . Referring to FIG. 2, the width of side plate portion  2   a  of bobbin  2  is slightly larger than the distance between the radial inner surface of outer cylindrical portion  5   a  and the radial outer surface of inner cylindrical portion  5   b , measured above engaging portion  7 . Therefore, side plate portion  2   a  of bobbin  2  is press fitted into the portion between outer and inner cylindrical portions  5   a  and  5   b , and both radial end surfaces of side plate portion  2   a  are press contacted to the radial inner surface of outer cylindrical portion  5   a  and the radial outer surface of inner cylindrical portion  5   b . From this configuration, coil member  1  is fixed in ring member  5  by the crimping. Thus, seal mechanism  11  is formed by side plate portion  2   a  of bobbin  2  engages portions  7  and includes crimped portions  5   e . Because seal mechanism  11  seals coil member  1  with press fitted side plate portion  2   a  of bobbin  2 , coil element  3  may be enclosed in containing chamber  5   d  of ring member  5  and substantially completely sealed-off from the outside. 
     In the embodiment of FIG. 2, it is not necessary to use a molding resin for sealing coil element  3 , which has required an extended period of time for curing and several steps. Therefore, the time and the number of steps for manufacturing the electromagnetic clutch may be decreased, and the cost for the manufacture may be reduced. Further, the desired insulation for coil element  3  may be achieved readily and less expensively without using a molding resin. 
     FIGS. 3A and 3B depict seal mechanism  11   a  according to a modification of the above-described first embodiment of the present invention. As depicted in FIG. 3A, in seal mechanism  11   a , a groove  7   a  extending over the entire circumference of ring member  5  is formed on the upper surface of engaging portion  7  formed on radial outer cylindrical portion  5   a , or radial inner cylindrical portion  5   b , or both (hereinafter, these portions are referred to as a “cylindrical portion  24 ”). Side plate portion  2   a  of bobbin  2  (hereinafter, referred to as a “seal plate  25 ”) has projection  25   a  extending over the entire circumference of seal plate  25 , at a position corresponding to the position of groove  7   a . Seal plate  25  has a width larger than the distance between the surfaces of cylindrical portions  24 , measured above engaging portion  7 . Seal plate  25  is inserted and press fitted into the opening portion of ring member  5 , as shown by the arrow in FIG.  3 A. 
     As depicted in FIG. 3B, after seal plate  25  is press fitted and projection  25   a  is inserted into groove  7   a  formed on engaging portion  7 , an inner upper edge portion of cylindrical portion  24  is crimped to form crimped portion  5   e . Thus, seal plate  25  is fixed in ring member  5 , and coil element  3  is enclosed in containing chamber  5   d  of ring member  5  in a completely sealed-off condition. 
     FIGS. 4A and 4B depict seal mechanism  11   b  according to another modification of the first embodiment of the present invention described above. As depicted in FIG. 4A, in seal mechanism  11   b , engaging portion  7  formed as a stepped portion extends over the entire circumference of ring member  5  on radial outer cylindrical portion  5   a , or radial inner cylindrical portion  5   b , or both (hereinafter, these portions are referred to as a “cylindrical portion  26 ”). Side plate portion  2   a  of bobbin  2  (hereinafter, referred to as a “seal plate  27 ”) has notch  27   a  extending over the entire circumference of seal plate  27 , at a position corresponding to the shoulder position of engaging portion  7 . The portion positioned below engaging portion  7  on the inner surface of cylindrical portion  26  is formed as a tapered surface  26   a  causing the width of containing portion  5   d  to gradually decrease. The edge portion of seal plate  27  having notch  27   a  engages engaging portion  7  including the upper portion of tapered inner surface  26   a  of cylindrical portion  26  by inserting and press fitting seal plate  27  into the opening portion of ring member  5 , as shown by the arrow in FIG.  4 A. 
     As depicted in FIG. 4B, after seal plate  27  is press fitted and notch  27   a  engages engaging portion  7  including the upper portion of tapered inner surface  26   a , an inner upper edge portion of cylindrical portion  26  is crimped to form crimped portion  5   e . Thus, seal plate  27  is fixed in ring member  5 , and coil element  3  is enclosed in containing chamber  5   d  of ring member  5  in a completely sealed-off condition. 
     FIGS. 5A and 5B depict seal mechanism  11   c  according to a further modification of the first embodiment of the present invention described above. As depicted in FIG. 5A, in seal mechanism lic, engaging portion  7  formed as a stepped portion extends over the entire circumference of ring member  5  on radial outer cylindrical portion  5   a , or radial inner cylindrical portion  5   b , or both (hereinafter, these portions are referred to as a “cylindrical portion  28 ”). Side plate portion  2   a  of bobbin  2  (hereinafter, referred to as a “seal plate  31 ”) has projection  31   a  extending over the entire circumference of seal plate  31  on its lower surface, at a position corresponding to the upper surface of engaging portion  7 . The edge portion of seal plate  31  engages engaging portion  7  as well as projection  31   a  and is placed into contact with the upper surface of engaging portion  7 , by inserting and press fitting seal plate  31  into the opening portion of ring member  5 , as shown by the arrow in FIG.  5 A. 
     As depicted in FIG. 5B, after seal plate  31  is press fitted and projection  31   a  is placed into contact with the upper surface of engaging portion  7 , an inner upper edge portion of cylindrical portion  28  is crimped to form crimped portion  5   e . Thus, seal plate  31  is fixed in ring member  5 , and coil element  3  is enclosed in containing chamber  5   d  of ring member  5  in a completely sealed-off condition. 
     FIG. 6 depicts an electromagnet device of an electromagnetic clutch according to a second embodiment of the present invention. In FIG. 6, electromagnet device  20  provided in an electromagnetic clutch comprises coil member  1 , ring member  5 , and fastening member  6 . Coil member  1  comprises ring-like bobbin  2 , and coil element  3  provided in bobbin  2 . Bobbin  2  has a U-shaped cross-section formed by side plate portion  2   a  (a ceiling plate portion), the other side plate portion  2   c  (a bottom plate portion), and connecting plate portion  2   b . Coil element  3  is contained within the U-shaped bobbin  2 . Side plate portion  2   a  has a width larger than the width of coil element  3 . 
     Ring member  5  has outer cylindrical portion  5   a , inner cylindrical portion  5   b , and bottom portion  5   c  connecting the ends of outer and inner cylindrical portions  5   a  and  5   b . Containing chamber  5   d  is formed as a ring-like groove portion in ring member  5  by respective portions  5   a - 5   c . Grooves  8  provided as engaging portions are formed on the radial inner surface of outer cylindrical portion  5   a  and the radial outer surface of inner cylindrical portion  5   b , at positions close to opening portion  5   f  of U-shaped containing chamber  5   d  of ring member  5 . The radial outer and inner edges of side plate portion  2   a  of bobbin  2  are completely fitted into grooves  8  to form seal mechanism  33 . 
     When the edges of side plate portion  2   a  of bobbin  2  are inserted into grooves  8 , the width of opening portion  5   f  may be expanded by elastically deforming cylindrical portions  5   a  and  5   b  by pressing side plate portion  2   a  into containing portion  5   d  through opening portion  5   f . Alternatively, the width of side plate portion  2   a  may be decreased by elastically deforming side plate portion  2   a  by applying a pressing force from both ends of side plate portion  2   a , so that the deformation of side plate portion  2   a  may be recovered by its elasticity after the edges of side plate portion  2   a  are inserted into grooves  8 . Further, the width of opening portion  5   f  may be expanded by using an appropriate jig (not shown). 
     Thus, seal mechanism  33  seals coil member  1  by engaging side plate portion  2   a  with grooves  8 . Coil element  3  may be enclosed in containing chamber  5   d  of ring member  5  and substantially completely sealed-off from the outside. In this embodiment, it is not necessary to use a molding resin for sealing coil element  3 , which has required an extended period of time for curing and several steps. Therefore, the time and the number of steps for manufacturing the electromagnetic clutch may be decreased, and the cost for the manufacture of the clutch may be reduced. Further, the desired insulation for coil element  3  may be achieved readily and less expensively without using a molding resin. 
     FIGS. 7A and 7B depict seal mechanism  33   a  according to a modification of the above-described second embodiment of the present invention. As depicted in FIG. 7A, in seal mechanism  33   a , a groove  8  extends over the entire circumference of ring member  5  and is formed as an engaging portion on the surfaces of radial outer cylindrical portion  5   a , or radial inner cylindrical portion  5   b , or both (hereinafter, these portions are referred to as a “cylindrical portion  22 ”). Side plate portion  2   a  of bobbin  2  (hereinafter, referred to as a “seal plate  23 ”) has V-shaped groove  23   a  on its radial end surface. V-shaped groove  23   a  extends over the entire circumference of seal plate  23 . Seal plate  23  has a width larger than the distance between the opposing bottom surfaces of grooves  8 . Seal plate  23  is inserted and press fitted into the opening portion of ring member  5 , as shown by the arrow in FIG.  7 A. 
     As depicted in FIG. 7B, when seal plate  23  is press fitted into groove  8 , pressure is applied to the edge of seal plate  23  having V-shaped groove  23   a . Consequently, the arms of V-shaped groove  23   a  are spread outwardly in groove  8  to form portions  23   b  deformed against the sides of groove  8 . Deformed portions  23   b  are brought into complete contact with both side surfaces of groove  8 . Thus, in seal mechanism  33   a , seal plate  23  is fixed in ring member  5  in complete contact with groove  8 , and coil element  3  is enclosed in containing chamber  5   d  of ring member  5  in a completely sealed-off condition. 
     FIG. 8A depicts an electromagnet device of an electromagnetic clutch according to a third embodiment of the present invention. In FIG. 8A, electromagnet device  30  provided in an electromagnetic clutch includes a ring member  5 , coil member  13 , and fastening member  6 . Coil member  13  comprises bobbin  12  formed from a resin having an elasticity, and coil element  3  provided in bobbin  12 . Bobbin  2  has a U-shaped cross-section formed by side plate portion  12   a  (a ceiling plate portion), the other side plate portion  12   c  (a bottom plate portion), and connecting plate portion  12   b . Coil element  3  is contained within the U-shaped bobbin  12 . Side plate portion  12   a  extends in the radial direction beyond the radial end of coil element  3 . Connecting plate portion  12   b  has protruded portion  12   d  extending over the entire circumference of bobbin  12  at an upper position on the outer surface of connecting plate portion  12   b  (a radially inner surface of bobbin  12 ). When bobbin  12  of coil member  13  is inserted into containing chamber  5   d  of ring member  5 , the radial outer edge of side plate portion  12   a  is fitted into groove  8  formed on the radial inner surface of outer cylindrical portion  5   a  of ring member  5  to form seal mechanism  33 . The corner portion of bobbin  12  between side plate portion  12   a  and connecting plate portion  12   b  is fixed by crimped portion  14  formed by a part of the surface portion of the upper edge of inner cylindrical portion  5   b  of ring member  5  to form seal mechanism  34 . Protruded portion  12   d  is press fitted onto the surface of inner cylindrical portion  5   b  at a position below seal mechanism  34  to further enhance the ability of this portion to seal containing chamber  5   d . At the same time, side plate portion  12   a  is pressed in a radially outer direction by the reactive force due to the press fitting between protruded portion  12   d  and the surface of inner cylindrical portion  5   b . Therefore, the radial outer edge of side plate portion  12   a  is fitted into groove  8  more securely. Further, even when there occurs a vibration in the electromagnetic clutch, for example, by a vibration of an engine of a vehicle, coil member  13  may be maintained within ring member  5  at a proper position more securely by providing protruded portion  12   d.    
     FIGS. 8B-8D depict various modifications with respect to the cross-sectional shape of protruded portion  12   d . As depicted in FIG. 8B, the cross-sectional shape of protruded portion  12   d , may be semi-circular. As depicted in FIG. 8C, the cross-sectional shape of protruded portion  12   d   2  may be rectangular or trapezoidal. As depicted in FIG. 8D, the cross-sectional shape of protruded portion  12   d   3  may be triangular. 
     FIG. 9 depicts an electromagnet device of an electromagnetic clutch according to a fourth embodiment of the present invention. In FIG. 9, electromagnet device  40  provided in an electromagnetic clutch includes a ring member  5 ; coil member  15 ; ring-like resin plate  17 , which is provided as a seal plate separately from bobbin  16 ; and fastening member  6 . Coil member  15  comprises bobbin  16  and coil element  3  provided in bobbin  16 . Bobbin  16  has a U-shaped cross-section formed by side plate portion  16   a  (a ceiling plate portion), the other side plate portion  16   c  (a bottom plate portion), and connecting plate portion  16   b . Coil element  3  is contained within the U-shaped bobbin  16 . Resin plate  17  is provided on side plate portion  16   a  of bobbin  16 . Resin plate  17  has a width greater than the width of containing chamber  5   d  of ring member  5 . The radial edge portions of resin plate  17  are engaged to engaging portions  7 , and fixed by crimped portions  5   e . Side plate portion  16   a  has a width less than the width of containing chamber  5   d.    
     As depicted in FIG. 10, after coil member  15  is inserted into containing chamber  5   d  of ring member  5  through its opening portion  5   f , elastic resin plate  17  is press fitted into containing chamber  5   d  through opening portion  5   f . Resin plate  17  is pressed onto engaging portions  7 . Then, a part of the radial inner edge portion of outer cylindrical portion  5   a  and a part of the radial outer edge portion of inner cylindrical portion  5   b  are crimped to form crimped portions  5   e . Thus, seal mechanism  11  is completed. Coil element  3  may be enclosed by seal mechanism  11  using resin plate  17  in a completely sealed-off condition. 
     In this embodiment, seal mechanisms similar to seal mechanisms  11   a - 11   c  shown in FIGS. 3-5 may be employed by substituting the seal plates depicted in FIGS. 3-5 with resin plate  17 . 
     FIG. 11 depicts an electromagnet device of an electromagnetic clutch according to a fifth embodiment of the present invention. In FIG. 11, electromagnet device  50  provided in an electromagnetic clutch includes a ring member  5 , coil member  15 , ring-like resin plate  17  provided as a seal plate separately from bobbin  16 , and fastening member  6 . Coil member  15  comprises bobbin  16 , and coil element  3  provided in bobbin  16 . Coil element  3  is contained within the U-shaped bobbin  16 . In this embodiment, grooves  8  are defined on the radial inner surface of outer cylindrical portion  5   a  of ring member  5  and on the radial outer surface of inner cylindrical portion  5   b  of ring member  5 . Resin plate  17  has a width slightly greater than the distance between the bottom portions of grooves  8  facing each other. The radial edge portions of resin plate  17  are press fitted into grooves  8 . Thus, seal mechanism  33  is formed. 
     As depicted in FIG. 12, after coil member  15  is inserted into containing chamber  5   d  of ring member  5  through its opening portion  5   f , resin plate  17  is press fitted into grooves  8  through opening portion  5   f . When resin plate  17  is inserted into containing chamber  5   d , cylindrical portions  5   a  and  5   b  may be elastically deformed, so that the width of opening portion  5   f  is temporarily enlarged, or resin plate  17  may be elastically deformed, so that the width of resin plate  17  is temporarily decreased. After the edges of resin plate  17  are press fitted into corresponding grooves  8 , elastically deformed opening portion  5   f , or elastically deformed resin plate  17 , may recover its original shape. Thus, seal mechanism  33  is completed. Coil element  3  may be enclosed by seal mechanism  33  using resin plate  17  in a completely sealed-off condition. 
     In this embodiment, a seal mechanism similar to seal mechanisms  33   a  shown in FIG. 7 may be employed by substituting the seal plate depicted in FIGS. 7 for resin plate  17 . Further, a jig (not shown) may be used for enlarging the width of opening portion  5   f  prior to inserting resin plate  17 . 
     FIG. 13 depicts an electromagnet device  60  of an electromagnetic clutch according to a sixth embodiment of the present invention. In FIG. 13, electromagnet device  60  provided in an electromagnetic clutch includes a ring member  5 ; coil member  21 ; ring-like resin plate  17 , which is provided as a seal plate separately from bobbin  18 ; and fastening member  6 . Coil member  21  comprises bobbin  18 , and coil element  3  provided in bobbin  18 . Coil element  3  is contained within the U-shaped bobbin  18 . In this embodiment, groove  8  is defined on the radial inner surface of outer cylindrical portion  5   a  of ring member  5 . The radially outer edge of resin plate  17  is fitted into groove  8 . Thus, seal mechanism  33  is formed. Side plate portion  18   a  (a ceiling portion) of bobbin  18  radially extends shorter than coil element  3  in the radially outward direction. Protruded portion  18   d  is provided on the outer surface of connecting portion  18   b  of bobbin  18 , similarly in the embodiment depicted in FIG.  8 A. Protruded portion  18   d  is pressed onto the radially outer surface of inner cylindrical portion  5   b  of ring member  5 . The inner edge of resin plate  17  is fixed by crimped portion  14 . Thus, seal mechanism  34  is formed. 
     As depicted in FIG. 14, after coil member  21  is inserted into containing chamber  5   d  of ring member  5  through its opening portion  5   f , resin plate  17  is inserted into containing chamber  5   d . The outer edge of resin plate  17  is fitted into groove  8 , and the inner edge of resin plate  17  is fixed by forming crimped portions  14 . Seal mechanisms  33  and  34  enclose coil member  21  in containing chamber  5   d  of ring member  5 . In particular, in seal mechanism  34 , even if water enters through a gap between caulked portions  14 , the entry of water may be interrupted by the engagement mechanism of protruded portion  18   d  pressed onto connecting portion  5   b  of ring member  5 . Therefore, coil element  3  may be enclosed in a completely sealed-off condition. 
     Protruded portion  18   d  may have another cross-sectional shape, such as a shape depicted in FIG. 8B,  8 C, or  8 D. 
     FIG. 15 depicts an electromagnet device  70  of an electromagnetic clutch according to a seventh embodiment of the present invention. In FIG. 15, electromagnet device  70  provided in an electromagnetic clutch includes a ring member  5 ; coil member  15 ; elastic ring-like resin cover  35  (a resin plate), which is provided as a seal plate separately from bobbin  16 ; and fastening member  6 . Coil member  15  comprises bobbin  16 , and coil element  3  provided in bobbin  16 . Coil element  3  is contained within the U-shaped bobbin  16 . In this embodiment, groove  8  is not formed on the surfaces of cylindrical portions  5   a  and  5   b  of ring member  5 . The surfaces of cylindrical portions  5   a  and  5   b  are tapered surfaces, so that the width of containing chamber  5   d  increases gradually towards its opening portion  5   f . Side plate portion  16   a  (a ceiling portion) of bobbin  16  extends in the radially outward direction less than coil element  3 . Resin cover  35  comprises upper plate portion  35   a , radial outer side portion  35   b , and radial inner side portion  35   c . Protruded portion  36 a extending over the entire circumference of ring cover is formed on the outer surface of radial outer side portion  35   b . Protruded portion  36   b  extending over the entire circumference of ring cover is formed on the outer surface of radial inner side portion  35   c . Resin cover  35  is press fitted into containing chamber  5   d . The inner edge of resin cover  35  is fixed by crimped portion  14 . Thus, seal mechanism  37  and seal mechanism  38  are formed. 
     As depicted in FIG. 16, after coil member  15  is inserted into containing chamber  5   d  of ring member  5  through its opening portion  5   f , elastic resin cover  35  is press fitted into containing chamber  5   d . Resin cover  35  then is fixed by a plurality of crimped portions  14 . Coil member  15  is sealed by the press fitting seal mechanisms between the radial inner surface of outer cylindrical portion  5   a  and protruded portion  36   a  and between the radial outer surface of inner cylindrical portion  5   b  and protruded portion  36   b . In particular, even if water enters through a gap between crimped portions  14 , the entry of water may be interrupted by pressed protruded portions  36   a  and  36   b . Therefore, coil element  3  may be enclosed in a completely sealed-off condition. 
     In this embodiment, crimped portion  14  may be provided at the outer edge side of resin cover  35  to fix resin cover  35 , or may be provided at both inner and outer edge side positions. 
     In the above-described embodiments, the number of crimped portions disposed circumferentially may be varied as appropriate to obtain the desired seal. Further, a crimped portion continuously extending over the entire circumference may be provided. 
     Although embodiments of the present invention have been described in detail herein, the scope of the invention is not limited thereto. It will be appreciated by those skilled in the art that various modifications may be made without departing from the scope of the invention. Accordingly, the embodiments disclosed herein are only exemplary. It is to be understood that the scope of the invention is not to be limited thereby, but is to be determined by the claims which follow.