Patent Abstract:
An electromagnetic clutch for separably coupling a drive source and a rotary shaft has a rotor to be disposed in the outside of the rotary shaft concentrically therewith. The rotor is rotated by a drive source and accommodates an electromagnetic coil. The electromagnetic clutch has an armature plate that is attracted toward the rotor by an electromagnetic force generated by the electromagnetic coil so as to adhere to the rotor. Furthermore, the electromagnetic clutch has a coupler for coupling the armature plate and the rotary shaft to each other. The coupler includes a center part to be coupled to the rotary shaft and an elastically-deformable outer part for coupling the center part to the armature plate, the outer part being extended from the center part and elastically deformed when the armature plate is attracted to the rotor.

Full Description:
This Nonprovisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 2003-305179 filed in Japan on Aug. 28, 2003, the entire contents of which are hereby incorporated by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an electromagnetic clutch, and more particularly to an electromagnetic clutch suitable for a compressor of a vehicle air-conditioning system. 
   2. Description of the Related Art 
   An electromagnetic clutch of this type is suitable for a compressor of a vehicle air-conditioning system and capable of intermittently transmitting a driving force from the engine to the main shaft of the compressor. For instance, the well-known electromagnetic clutch disclosed in Unexamined Japanese Patent Publication No. 11-63021 is provided with a rotor that is rotatably supported by the end of the housing of the compressor. The rotor has an electromagnetic coil inside, and a driving belt is put round the outer periphery of the rotor with an engine pulley. Disposed coaxially with the rotor is an annular armature plate. The armature plate is contactable to and separatable from the end wall of the rotor and is also rotatable integrally with the main shaft of the compressor. More specifically, the armature plate is coupled to the main shaft through a coupling member and plate springs, and is elastically supported by the plate springs. 
   According to this electromagnetic clutch, when the electromagnetic coil is not excited, the armature plate is located at the OFF position that is away from the rotor due to the urging force of the plate springs. When the electromagnetic coil is excited, however, the armature plate is displaced from the OFF position to the ON position in which it is joined to the rotor. In other words, the armature plate is displaced toward the rotor, resisting the urging force of the plate springs due to the attraction of the electromagnetic coil, and is pressed against the rotor. At this point, the rotor is driven to rotate through the driving belt, so that the rotor brings the armature plate to rotate therewith through the use of a frictional force, to thereby rotate the main shaft of the compressor through the plate springs and the coupling portion. 
   The above-described electromagnetic clutch requires that the armature plate be disposed parallel to the rotor with high accuracy in order to achieve the secure couplement of the armature plate with the rotor. For this reason, both the coupling member and the plate springs supporting the armature plate require high accuracy not only in their shapes and dimensions but also in assembly. 
   In case that the supporting means of the armature plate is constructed with the coupling member and the plate springs, there occurs a problem that the number of components of the supporting means are increased, and that it is difficult to improve the accuracy in assembly. 
   SUMMARY OF THE INVENTION 
   An object of the present invention consists in providing an electromagnetic clutch in which it is possible to reduce the number of components by forming a coupling member and plate springs integrally and to dispose an armature plate parallel to a rotor securely and easily. 
   To accomplish the above object, the present invention provides an electromagnetic clutch for separably coupling a drive source and a rotary shaft. The electromagnetic clutch comprises: a rotor to be disposed in the outside of the rotary shaft concentrically therewith and rotated by the drive source; an electromagnetic coil accommodated in the rotor; an armature plate attracted toward the rotor by an electromagnetic force generated by the electromagnetic coil so as to adhere to the rotor; and a coupler for coupling the armature plate and the rotary shaft to each other, the coupler including a center part to be coupled to the rotary shaft and an elastically-deformable outer part for coupling the center part to the armature plate, the outer part being extended from the center part and elastically deformed when the armature plate is attracted to the rotor. 
   In concrete terms, the center part of the coupler includes a metal sleeve that is coupled to the rotary shaft, and the outer part is made of resin that is insert-molded with the sleeve. 
   With the aforementioned structure, the coupler is made as an one-piece member, and this heightens disposition accuracy of the armature plate in relation to the rotary shaft. Therefore, it is possible to arrange the armature plate parallel to the rotor without fail. Since the coupler is made up of one component, and the total number of all components is accordingly small, the assemble of the electromagnetic clutch is easy. Furthermore, the insert molding facilitates production of the coupler and achieves high accuracy in a shape and dimensions of the coupler. In addition, the production cost can be reduced. 
   The outer part is preferably made of heat-hardening resin. In this case, the coupler has an excellent heat resistance. 
   It is also preferable that the coupler further includes a boss part integrally formed with the outer part, the boss part being mounted on said sleeve. Since the boss part is thicker than the outer part, elastic deformation of the boss part is prevented. It is then possible to suppress a reduction in coupling strength between the outer part and the sleeve through the boss part. 
   Preferably, one of the sleeve and boss part has a groove and the other has a projection engaged with the groove. In this case, there generates no relative rotation between the outer part and the sleeve, so that a rotating force of the rotor can be reliably transmitted to the rotary shaft. 
   In a concrete embodiment, the outer part includes a plurality of straight elastic pieces. Each of the elastic pieces has a tip end fixed to an outer peripheral part of the armature plate. The elastic piece also has an axis intersecting a rotating direction of the armature plate at either an obtuse angle or an acute angle. 
   In another concrete embodiment, the outer part includes a plurality of straight elastic pieces. The tip end of each elastic piece is fixed to the outer peripheral part of the armature plate, and the elastic piece also has an axis intersecting the rotating direction of the armature plate at a right angle. The outer part further includes an elastic ring that couples the tip ends of the elastic pieces to one another. 
   In still another concrete embodiment, the coupler is further provided with a plurality of rivets for coupling the outer part to the armature plate. A part of each rivet is embedded in the outer part by insert molding. 
   It is preferable that the coupler further have a plurality of metal rings embedded in the outer part by insert molding, and a plurality of rivets passing through the corresponding metal ring to join the outer part and the armature plate to each other. 
   A further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific example, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitative of the present invention, and wherein: 
       FIG. 1  is a vertical section of an electromagnetic clutch according to a first embodiment, which is mounted on a compressor; 
       FIG. 2  is an elevation view of a coupler applied to the electromagnetic clutch of  FIG. 1  with an armature plate fixed thereto; 
       FIG. 3  is an enlarged partial section taken along line III-III of  FIG. 2 ; 
       FIG. 4  is an elevation view of a coupler according to a second embodiment with the armature plate fixed thereto; 
       FIG. 5  is a section taken along line V-V of  FIG. 4 ; 
       FIG. 6  is an enlarged partial section taken along line VI-VI of  FIG. 4 ; 
       FIG. 7  is an elevation view of a coupler according to a third embodiment with the armature plate fixed thereto; 
       FIG. 8  is a section taken along line VIII-VIII of  FIG. 7 ; 
       FIG. 9  is an elevation view of a coupler according to a fourth embodiment with the armature plate fixed thereto; and 
       FIG. 10  is a section taken along line X-X of  FIG. 9 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  shows a refrigerating circuit of a vehicle air-conditioning system. In a circulation line of the refrigerating circuit, there are interposed a compressor  10 , a condenser  12 , a receiver  14 , an expansion valve  16  and an evaporator  18  in the order named, with respect to a direction in that a refrigerant circulates. The compressor  10  is provided with an electromagnetic clutch  20  of a first embodiment, and a driving force from an engine, not shown, is intermittently transmitted through the electromagnetic clutch  20  to a main shaft of the compressor  10 . A compression unit, not shown, of the compressor  10  is driven with rotation of the main shaft  22 , to thereby circulate the refrigerant in the refrigerating circuit. The compressor  10  may be either of a scroll-type or of a swash plate-type. 
   The electromagnetic clutch  20  includes a rotor  25 . The rotor  25  is rotatably supported by an end portion  26  of a housing of the compressor  10  through a ball bearing  28 . Concretely, the rotor  25  has an inner peripheral wall  30  and an outer peripheral wall  32 . The inner peripheral wall  30  integrally continues to the outer peripheral wall  32  with an annular end wall  34  therebetween. Formed in the end wall  34  are a plurality of slits  36 . The slits  36  extend intermittently in a circumferential direction to regulate magnetic flux. There is formed a belt groove  38  in an outer peripheral surface of the outer peripheral wall  32 . A driving belt, not shown, for transmitting the driving force from the engine is fit into the belt groove  38 . 
   The rotor  25  accommodates an electromagnetic coil  24  between the inner peripheral wall  30  and the outer peripheral wall  32  with a stator  33  fitted thereto. The stator  33  is fixed to the housing of the compressor  10  through a bracket  35  and kept in slide contact with the inner peripheral wall  30  and the outer peripheral wall  32 . 
   An annular armature plate  40  is coaxially arranged on the end wall  34  side of the rotor  25  and is made of a magnetic material, such as an iron-based material. The armature plate  40  is supported by the main shaft  22  of the compressor  10  through a coupler  42  so that the armature plate  40  is allowed to contact with and separate from the rotor  25  and integrally rotate with the main shaft  22 . The armature plate  40  is also provided with a slit  44  extending intermittently in a circumferential direction. 
   The coupler  42  of the armature plate  40  includes a hard sleeve  46  made of metal. The sleeve  46  extends from the end portion  26  of the housing, passing through the armature plate  40 , and an end portion of the main shaft  22  is screwed therein. The end portion of the main shaft  22  passes through the sleeve  46 , and a nut  48  is fastened to a tip end of the main shaft  22  to prevent the sleeve  46  from coming off. 
   The coupler  42  includes a coupling member  50 . The coupling member  50  is made of heat-hardening resin having elasticity. The sleeve  46  and a plurality of rivets  52  are integrally included in the coupling member  50  by insert molding. In concrete terms, the coupler  50  includes a boss  54 , a flange  56  and a plurality of arms  58 , which are integrally molded, the boss  54  being integrally mounted with an outer end portion of the sleeve  46  from the outside in a radial direction thereof. Provided in between the sleeve  46  and the boss  54  are an engaging projection  60  and an engaging groove  62  serving in combination as engaging means for inhibiting relative rotation. Concretely, in the coupler  42 , the engaging projection  60  is integrally formed in the boss  54 , and the engaging groove  62  in the sleeve  46 . 
   The flange  56  is integrally formed in a portion of the boss  54 , which protrudes from an outer surface of the armature plate  40 . As illustrated in  FIG. 2 , the flange  56  is formed into a substantially triangular plate, and the boss  54  passes through the flange  56  at a substantial center thereof in a normal direction thereof. 
   Each of the arms  58  extends from an apex area of the flange  56  outward, with respect to a radial direction of the boss  54 . The arms  58  are arranged at regular intervals in a circumferential direction of the boss  54 . A tip end of each arm  58  is positioned near an outer periphery of the outer surface of the armature plate  40 . Herein, each arm  58  has a step  59  near a base end thereof and also includes a region that straightly expands from the step  59  to the tip end thereof with a fixed width. As illustrated in  FIG. 3 , although having a fixed thickness, the region is thinner than the base end of the arm  58  and functions as an elastic piece. Therefore, the region of the arm  58  is hereinafter referred to as a plate spring  64 . In addition, the base end of the arm  58  has the same thickness as the flange  56 . 
   Referring to  FIG. 1 , there is provided a through-hole in the base end of each arm  58 , and a rubber cushion  66  is interfitted in the through-hole. Each rubber cushion  66  projects by a given length toward the armature plate  40 , and a projecting end thereof is brought into contact with the armature plate  40 . In other words, the rubber cushions  66  provide a fixed space between the base ends of the arms  58 , namely the flange  56 , and the armature plate  40 . The plate spring  64 , as shown in  FIG. 3 , continues to the base end of the arm  58  through the step  59  and contacts with the outer surface of the armature plate  40 . 
   Integrally mounted on a tip end of the plate spring  64  is the corresponding rivet  52 . The coupler  42  is joined to the armature plate  40  by the rivets  52 . More specifically, each of the rivets  52  has an axial portion  68  embedded in the tip end of the plate spring  64  by insert molding. The rivet  52  has legs  70  protruding from the plate spring  64  and engaged with an engaging aperture  72  of the armature plate  40 . The legs  70  of the rivet  52  are bent in the engaging aperture  72  of the armature plate  40 , thereby preventing disengagement of the legs  70 . 
   Herein, the plate spring  64  has an axis that obliquely intersects rotating directions R1 and R2 of the armature plate  40 . Concretely, as illustrated in  FIG. 2 , when the coupler  42  rotates in the rotating direction R1, θ1 is an obtuse angle, where L is a tangent with respect to the armature plate  40  at an intersection between the axis of the plate spring  64  and an outer peripheral edge of the armature plate  40 , and where θ1 is an angle between the axis of the plate spring  64  and the tangent L. In case that the coupler  42  rotates in the rotating direction R2, θ2 is an acute angle, where θ2 is an angle between the axis of the plate spring  64  and the tangent L. 
   According to the electromagnetic clutch  20 , when the electromagnetic coil  24  is not applied with current, the armature plate  40  is located at an OFF position that is away from the rotor  25  due to an urging force of the plate springs  64 , so that a rotating force of the rotor  25  is not transmitted to the armature plate  40 . 
   On the contrary, when the electromagnetic coil  24  is applied with current, the armature plate  40  is located at an ON position that is in contact with the rotor  25  due to a magnetic field generated by the electromagnetic coil  24 . More specifically, while the current is applied to the electromagnetic coil  24 , the magnetic field of the electromagnetic coil  24  makes the rotor  25  an electromagnet. Thus, the armature plate  40  magnetically adheres to the end wall  34  of the rotor  25 , resisting the urging force of the plate springs  64 , thereby joining the rotor  25  and the armature plate  40  to each other. As a result, the rotating force of the rotor  25  is transmitted to the armature plate  40  due to friction. The rotating force is then transmitted sequentially to the plate springs  64  (arms  58 ), the flange.  56 , the sleeve  46  and the main shaft  22 . Consequently, by using the rotating force transmitted to the main shaft  22  as a driving force, the compression unit of the compressor  10  performs intake and compression of the refrigerant. Therefore, the refrigerant is circulated in the refrigerating circuit. 
   According to the electromagnetic clutch  20 , the coupler  42  is made as an one-piece member, which heightens deposition accuracy of the armature plate  40  in relation to the main shaft  22 . It is then possible to dispose the armature plate  40  precisely parallel to the rotor  25 . When the armature plate  40  is at the OFF position, an appropriate gap is secured between the armature plate  40  and the rotor  25 . Furthermore, since the coupler  42  is made up of one component, and the total number of all components is accordingly small, assemble of the electromagnetic clutch  20  is easy. Additionally, the insert molding facilitates production of the coupler and heightens accuracy in a shape and dimensions thereof. 
   The electromagnetic clutch  20  is light in weight because of the coupling member  50  made of resin, and also has excellent heat resistance due to a heat-hardening characteristic of the resin. 
   According to the electromagnetic clutch  20 , since the thickness of the plate spring  64  is smaller than that of the flange  56 , elastic deformation takes place only in the plate spring  64  when the armature plate  40  is displaced from the OFF position to the ON position. Thus, elastic deformation of the flange  56  and the boss  54  is suppressed, thereby preventing a reduction in coupling strength between the boss  54  and the sleeve  46 . 
   According to the electromagnetic clutch  20 , the sleeve  46  is made of a hard material, such as metal, which prevent a reduction in coupling strength between the main shaft  22  and the sleeve  46  and furthermore improves abrasion-resistance of the sleeve  46  to the main shaft  22 . 
   According to the electromagnetic clutch  20 , the boss  54  and the sleeve  46  are engaged with each other by way of the engaging groove  62  and the engaging projection  60 . Thus, there generates no relative rotation between the boss  54  and the sleeve  46 , so that it is possible to reliably transmit the rotating force of the rotor  25  to the main shaft  22 . 
   The present invention is not limited to the aforementioned embodiment and may be modified in various ways. For instance,  FIGS. 4 ,  5  and  6  each show a coupler  80  of a second embodiment with the armature plate  40 . Identical components to those in the first embodiment are denoted by the same reference numerals, and a redundant explanation thereof will be omitted. 
   In the coupler  80 , there are formed six engaging projections  60  and respective engaging grooves  62  in between the sleeve  46  and the boss  54 . The engaging projections  60  and the corresponding engaging grooves  62  are arranged at regular intervals in the circumferential direction of the boss  54 . In this case, the engaging projections  60  and the engaging grooves  62  further improve the coupling strength between the sleeve  46  and the main shaft  22 . This makes it possible to entirely prevent the relative rotation between the boss  54  and the sleeve  46 . 
   There is no rubber cushion attached to the base end of the arm  58 , and the coupling member  50  is in tight contact to an opposite outer portion of the armature plate  40 . The arm  58 , as illustrated in  FIG. 6 , has a ridgeline  82  orthogonal to an axis thereof near the base end. A region expanding from the ridgeline  82  to the tip end is formed as a plate spring  84 . The plate spring  84  gets thinner in thickness from the ridgeline  82  toward the tip end thereof. When the plate springs  84  are bent, stress is applied mainly to the flange  56  having great thickness. This elongates the life of the plate springs  84 . 
     FIGS. 7 and 8  show a coupler  90  of a third embodiment with the armature plate  40 . 
   The coupler  90  includes a block  92  serving as a sleeve, which is formed in the shape of a triangle pole. The block  92  has a screw hole, and screwed in the screw hole is an end portion of the main shaft  22 . The block  92  is integrally included in a coupling member  96  by insert molding together with a plurality of hard metal rings  94 . 
   The coupling member  96  is made of heat-hardening resin having elasticity and has a shape similar to a steering wheel. In other words, the coupling member  96  includes a boss  98 , six arms  100  and a rim  102 , which are molded integrally. The boss  98  is formed into a substantially orthohexagonal pole that is rounded, and is integrally mounted on an outer end portion of the block  92  from the outside in a radial direction thereof. 
   The arms  100  radially extend from the respective apexes of the boss  98  up to a rim  102 . Accordingly, each arm  100  has an axis orthogonal to the tangent L at the intersection between the axis and the outer peripheral edge of the armature plate  40 . As illustrated in  FIG. 8 , the arm  100  is smaller in thickness than the boss  98  and gets thinner by degrees from the boss  98  toward the tip end thereof. 
   The rim  102  is supported by the boss  98  through the arms  100  and disposed concentrically with the boss  98 . The rim  102  is formed in an annular shape to be substantially level with the outer surface of the armature plate  40 , and has the same thickness as the tip ends of the arms  100 . The rim  102  also has an external diameter that is substantially equal to an external diameter of the armature plate  40  and expands along the outer peripheral edge of the armature plate  40 . The rim  102  is provided with the rings  94  and through-holes alternating at positions located in a circumferential direction in which the arms  100  are joined to one another. Fixed to the rings  94  are rivets  104 , and each rivet has a head that is crushed in the engaging aperture  72  of the armature plate  40 . Therefore, the armature plate  40  and the coupler  90  are fixed to each other by the rivets  104 . Moreover, rubber cushions  106  are interfitted in the respective through-holes. 
   In the coupler  90 , each arm  100  functions as a straight elastic piece, and the rim  102  as an annular elastic piece. Since the tip ends of the arms  100  are coupled to the rim  102 , the arms  100  and the rim  102  act in consort as one elastic body  108 . Thus, if there is a minor difference in elastic force between the arms  100  due to variation of shapes and sizes of the arms  100 , an urging force is uniformized in the entire elastic body  108 . This makes it possible to evenly urge the entire armature plate  40 . 
   Furthermore, mounting portions for the rivets  104 , located in the rim  102 , are reinforced by the rings  94 , so that stress is not focused on the rim  102 , to thereby prevent damage to the rim  102 . 
     FIGS. 9 and 10  show a coupler  110  of a fourth embodiment with the armature plate  40 . 
   In the coupler  110 , a boss  112  is formed into a cylinder and has no arm extending from the boss  112  toward the rivets  104 . The coupler  110  is different from the coupler  90  in the respect that each arm  116  is broad. 
   According to the coupler  110 , there is a long distance between the boss  112  and the rivet  104  through the arm  116  and the rim  102 , or between the boss  112  and a coupling portion that is coupled to the armature plate  40 . This means that the urging force of the entire elastic body  108  is increased. Therefore, if the coupler  110  is applied to the electromagnetic clutch  20 , it is possible to securely carry out the contact and separation of the armature plate  40  with respect to the rotor  25 .

Technology Classification (CPC): 5