Abstract:
In the disclosed electromagnetic clutch, a bent porion ( 15   a ) of a plate ( 15 ) comes into contact with an armature ( 6 ) attempting to move beyond a predetermined movable range, thereby restricting the movement of the armature ( 6 ). As a result, if an elastic member ( 14 ) is fused, a trouble is prevented which otherwise might be caused by the movement of the now-unsupported armature ( 6 ) beyond a predetermined movable range.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an electromagnetic clutch, for transmitting and interrupting a rotational driving force, suitably used to interrupt the operation of a compressor of an air conditioning system of an automobile, etc. 
   2. Description of the Prior Art 
   A conventionally known technique for an electromagnetic clutch is disclosed in Japanese Unexamined Patent Publication No. 2000-161389.  FIG. 9  is a sectional view of such an electromagnetic clutch  101 . In  FIG. 9 , the left side in the drawing is designated as the front side and the right side in the drawing as the rear side of the electromagnetic clutch  101 . 
   The electromagnetic clutch  101  is mounted on a compressor  110  through an annular support member  109  and comprises an electromagnetic coil  103  built in a stator  102 , a rotor  104  freely rotatable around the electromagnetic coil  103 , a pulley  114  rotated integrally with the rotor  104  for transmitting the power from the engine not shown, an armature  105  adapted to be attracted to the rotor  104  by the magnetic force generated in the electromagnetic coil  103  and a cylindrical hub  106  adapted to rotate with the armature  105 . 
   The hub  106  is connected to a leaf spring member  111  by a rivet  113 . The rear side of the leaf spring member  111  is bonded to the front side of an elastic member  107  by baking. The rear side of the elastic member  107 , on the other hand, is bonded to the front side of the armature  105  by baking. The hub  106  is integrally fitted in the rotational direction of a rotary shaft  108  of the compressor by a bolt  112 . 
   The armature  105 , which is arranged in an opposed relationship, with a predetermined minuscule gap therebetween, with the friction surface of the rotor  104 , is formed of an annular magnetic material such as iron. The rear side of the elastic member  107  is bonded by baking to the front side of the armature  105 . By the elastic deformation of the leaf spring member  111 , bonded by baking to the front side of the elastic member  107 , the armature  105  and the elastic member  107  can be moved along the axial direction of the rotary shaft  108 , so that when current flows in the electromagnetic coil  103 , the armature  105  is attracted to the rotor  104  by the magnetic force of the electromagnetic coil  103 . The impact sound generated at this time by the collision between the friction surfaces of the armature  105  and the rotor  104  is absorbed by the elastic member  107 . 
   Also, once the compressor  110  is “locked”, by foreign matter or otherwise, the armature  105  connected to the hub  106  integrally rotating with the rotary shaft of the compressor  110  also ceases to rotate, and heat is generated by fiction with the rotor  103  still continuing to rotate. This heat is transmitted through the armature  105  to the elastic member  107 . As a result, the elastic member  107  is fused, and the armature  105  is separated from the members of the compressor  110  such as the leaf spring member  111 , the hub  106  and the rotary shaft  108  which are stopped by the locking of the compressor  110 . In this way, the troubles such as a belt being broken or the temperature being abnormally increased due to a protracted overloaded state can be prevented. In other words, the electromagnetic clutch  101  has also the function of a torque limiter. 
   In the case where the compressor  110  is locked due to foreign matter or otherwise, the torque limiter mechanism of the electromagnetic clutch works to separate the armature  105  from the rotary shaft  108 . In the process, the elastic member  107  that has thus far supported the armature  105  is fused. Therefore, the armature  105  is left supported while being attracted to the rotor  104  by the magnetic field generated in the electromagnetic coil  103 . As a result, the armature  105  moves in a radial direction by means of a centrifugal force, and this may cause an abnormal noise to be generated by the contact with a rotating inner hub  115 . 
   In the case where the rivet  113  is broken by the overload torque imposed on the electromagnetic clutch  101  before the elastic member  107  is fused by the locking of the compressor  110 , the armature  105  moves axially toward the front side of the electromagnetic clutch  101  and may come off. 
   SUMMARY OF THE INVENTION 
   This invention has been developed in view of the above-mentioned situation, and the object thereof is to provide an electromagnetic clutch capable of preventing an abnormal sound or other troubles which may be caused by the movement of the armature  105  in radial or axial direction beyond a predetermined movable range at the time of a malfunction. 
   In order to achieve the object described above, according to a first aspect of the invention, there is provided an electromagnetic clutch comprising restriction means ( 15   a ,  20 ,  18 ,  15   b ,  7   d ) for restricting the radial movement of the armature ( 6 ) when it is disconnected from the hub ( 7 ). 
   In this aspect of the invention, preferably, the movement of the armature ( 6 ) in the radial direction is restricted by bringing a part ( 15   a ,  15   b ) of a plate ( 15 ) into contact with the armature ( 6 ). 
   In this aspect of the invention, preferably, the movement of the armature ( 6 ) in the radial direction is restricted by bringing a part of mounting means ( 18 ) into contact with the armature ( 6 ). 
   In this aspect of the invention, preferably, the movement of the armature ( 6 ) in the radial direction is restricted by bringing a part ( 7   d ) of a hub ( 7 ) into contact with the armature ( 6 ). 
   As described above, according to this invention, the provision of the restriction means ( 15   a ,  20 ,  18 ,  15   b ,  7   d ) for restricting the movement of the armature ( 6 ) in the radial direction thereof prevents the armature ( 6 ) moving beyond a predetermined movable range when disconnected from the hub ( 7 ). 
   According to another aspect of the invention, there is provided an electromagnetic clutch comprising restriction means ( 15   a ,  6   a ,  7   a ) for restricting the movement of the armature ( 6 ) along the axis of the hub ( 7 ) when disconnected with the hub ( 7 ). 
   In this aspect of the invention, the hub ( 7 ) includes a flange portion ( 7   a ) having the outer diameter larger than the inner diameter of a part ( 15   a ) of a plate ( 15 ), and the movement of the armature ( 6 ) along the axis of the hub ( 7 ) is restricted by bringing a part ( 15   a ) of the plate ( 15 ) into contact with the flange portion ( 7   a ). 
   In this aspect of the invention, the outer diameter of the flange portion ( 7   a ) is larger than the inner diameter portion ( 6   a ) of the armature ( 6 ), and the movement of the armature ( 6 ) along the axis of the hub ( 7 ) is restricted by bringing the flange ( 7   a ) into contact with the inner diameter portion ( 6   a ) of the armature ( 6 ). 
   As described above, according to this invention, the provision of the restriction means ( 15   a ) for restricting the movement of the armature ( 6 ) along the axis of the hub ( 7 ) prevents the armature ( 6 ) moving beyond a predetermined movable range when disconnected with the hub ( 7 ). 
   The reference numerals in the parentheses attached to the component parts described above designate an example of correspondence with the specific means described in the embodiments of the invention described later. 
   The present invention may be more fully understood from the description of preferred embodiments of the invention, as set forth below, together with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a sectional view of an electromagnetic clutch according to a first embodiment of the invention. 
       FIG. 2  is a diagram showing the connection of a hub  7  with a leaf spring member  12 , a plate  15 , an elastic member  14  and an armature  6  as viewed from the front side according to the first embodiment of the invention. 
       FIG. 3  is a sectional view showing the connection of a hub  7  with a leaf spring member  12 , a plate  15 , an elastic member  14  and an armature  6  according to a second embodiment of the invention. 
       FIG. 4  is a sectional view showing the connection of a hub  7  with a leaf spring member  12 , a plate  15 , an elastic member  14  and an armature  6  according to a third embodiment of the invention. 
       FIG. 5  is a sectional view showing the connection of a hub  7  with a leaf spring member  12 , a plate  15 , an elastic member  14  and an armature  6  according to a fourth embodiment of the invention. 
       FIG. 6  is an enlarged view of  FIG. 1  showing the relation between the outer diameter φA of the flange portion  7   a , the inner diameter φB of the bent plate portion  15   a  and the inner diameter portion  6   a  of the armature according to the first embodiment. 
       FIG. 7  is an enlarged view showing the relation between the outer diameter φA of the flange portion  7   a  and the inner diameter φC of the inner diameter portion  6   a  of the armature according to the second, third and fourth embodiments. 
       FIG. 8  is a sectional view showing the connection of a hub  7  with a leaf spring member  12 , a plate  15 , an elastic member  14  and an armature  6  according to a fifth embodiment of the invention. 
       FIG. 9  is a sectional view of an electromagnetic clutch  101  according to the prior art. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   (First Embodiment) 
     FIGS. 1 and 2  are diagrams showing a first embodiment, in which  FIG. 1  is a partly cutaway sectional view of an electromagnetic clutch  1 , mounted on a refrigerant compressor  8  (hereinafter referred to as the compressor) for the refrigeration cycle of an automotive air conditioning system, for interrupting the power from a drive source. In the description that follows, the surface of the electromagnetic clutch  1  viewed from the left side in  FIG. 1  is referred to as the front side, and the surface thereof viewed from the right side in  FIG. 1  as the rear side of the electromagnetic clutch  1 . 
   The electromagnetic clutch  1  is configured mainly of an electromagnetic coil  3 , a rotor  4 , an armature  6  and a hub  7 . 
   The electromagnetic coil  3  is fixed on a compressor  8  through an annular support member  10 , and accommodated in a stator  2  formed of a magnetic material such as iron having a V-shaped cross section. Also, the electromagnetic coil  3  is wound around a resin bobbin  3   a  and fixedly molded and electrically insulated using an insulating resin material such as epoxy resin. 
   The rotor  4  has a bearing  21  on the inner peripheral portion thereof and is rotatably supported on the outer peripheral surface of a cylindrical boss  8   a  of the housing of the compressor  8  by the bearing  21 . The rotor  4  constitutes a drive-side rotary member for receiving the turning effort from the vehicular engine (not shown) providing a drive source. The rotor  4  has a pulley  5  with a V-belt (not shown) suspended on the outer peripheral portion thereof, and is rotated by the turning effort of the engine transmitted thereto through the V-belt. Also, the rotor  4  is formed of a magnetic material such as iron, and formed with a U-shaped cross section in slightly spaced relation with the stator  2 . 
   The armature  6  is formed as a disk of a magnetic material such as iron. In the deenergized state of the electromagnetic coil  3 , the end surface on the rear side of the armature  6  is arranged in opposed relation, with a minuscule gap (say, about 0.5 mm) therebetween, to the friction surface  4   a  of the rotor  4 , and is attracted to the friction surface  4   a  of the rotor  4  by the magnetic force generated in the electromagnetic coil  3  accommodated in the rotor  4 . The rear side of the elastic member  14  is bonded by baking to the front side of the armature  6  and, further is connected to the leaf spring member  12  through the plate  15  (described later) bonded by baking to the front side of the elastic member  14 . The function of the spring portion  12   a  of the leaf spring member  12  makes it possible for the armature  6  to move only a predetermined amount along the axis of the rotary shaft  9  integral with the elastic member  14  and the plate  15 . 
   The hub  7  has an inner hub  7   b  formed, cylindrically, of an iron metal. A spline fitting portion  7   c  is formed on the inner peripheral surface of the cylindrical portion of the inner hub  7   b , and the hub  7  is integrally fitted with the rotary shaft  9  by the spline fitting portion  7   c . The hub  7  is integrally molded with a mounting flange portion  7   a  extending radially outward of an end along the axis of the cylindrical portion of the inner hub  7   b . This hub  7  is connected to the rotary shaft  9  of the refrigerant compressor  8  providing a driven unit, and has the function of transmitting the turning effort of the rotor  4  and the rotating armature  6  to the compressor  8  when the armature  6  is attracted to the friction surface  4   a  of the rotor  4 . 
   The elastic member  14  is a disc with a hole formed in the central portion thereof, and is held between, and bonded by baking to, the rear side of a disc plate  15  with a hole formed in the central portion thereof and the front side of the armature  6 . The rubber material used for the elastic member  14  preferably exhibits superior characteristics of torque transmission and torque variation absorption (vibration attenuation) in the wide temperature range (−30° C. to 120° C.) of the automotive operating environment. Specifically, butyl rubber chloride, acrylonitrile, butadiene rubber, ethylene propylene rubber or the like is recommended. 
   A bent plate portion  15   a  is arranged on the inner diameter side of the plate  15 , and shown in the enlarged view of  FIG. 6 . The bent plate portion  15   a  is bent to the rear side under the inner diameter portion  6   a  of the armature  6 . Specifically, the bent plate portion  15   a  is formed so that the inner peripheral portion of the armature  6  extends from the front side toward the rear side. 
   The outer diameter φA of the discal mounting flange portion  7   a  of the hub  7  is larger than the inner diameter φB of the bent plate portion  15   a.    
   The outer peripheral portion of the leaf spring member  12  is fixed on the plate  15  by outer rivets  19 , and the inner peripheral portion thereof on the hub  7  by inner rivets  18 .  FIG. 2  is diagram showing the connection of the hub  7  with the leaf spring member  12  and the plate  15  as viewed from the front side. The leaf spring member  12  is substantially triangular in shape and has punched portions  16  with a spring portion  12   a  formed at the intermediate portion between the apexes of the triangle. 
   The plate  15  is formed with plate hole portions  15   c , from which a part of the elastic member  14  is projected thereby to form stoppers  17 . The initial displacement of the spring portion  12   a  is secured by bending the spring portion  12   a  while keeping the stoppers  17  and the outer rivets  19  in predetermined relative positions. When the electromagnetic coil  3  is deenergized, therefore, the elastic member  14  and the armature  6  connected by the leaf spring member  12  are supported at a position slightly spaced from the rotor  4  by the elastic restoration of the spring portion  12   a.    
   (Operation of this Embodiment) 
   As long as the electromagnetic coil is kept deenergized, the armature  6  is arranged in an opposed relation, with a very small gap therebetween, to the friction surface  4   a  of the rotor  4 . Even in the case where the rotor  4  is rotated by the turning effort of the engine, therefore, the armature  6  is not rotated. Thus, neither the hub  7  nor the rotary shaft  9  rotates, and the compressor  8  is not driven. 
   Once the electromagnetic coil  3  is energized, however, the armature  6  is attracted toward the rotor  4  by the magnetic force generated in the electromagnetic coil  3 , and the spring portion  12   a  of the leaf spring member  12  is elastically deformed. The armature  6  is attached to the friction surface  4   a  of the rotor  4  and begins to rotate integrally with the rotor  4 . In the process, the elastic member  14  held between the armature  6  and the plate  15  functions to alleviate the impact sound generated by the attachment of the armature  6  to the friction surface  4   a  of the rotor  4 . 
   An explanation of the torque limiter function in which the transmission of the overload torque from the compressor  8  is interrupted thereby to protect the V-belt (not shown) and other engine auxiliary machines, in the case where the compressor  8  is locked by biting foreign matter or otherwise, is given below. In the case where the rotary shaft  9  ceases to rotate due to the locking of the compressor  8 , the friction heat is generated between the armature  6  that is connected to the rotary shaft  9  through the hub  7  and the leaf spring member  12  and has ceased to rotate on the one hand and the friction surface  4   a  of the rotor  4  still continuing to be rotated by receiving the turning effort from the engine on the other hand. 
   This heat is transmitted to the elastic member  14  through the armature  6  and fuses the elastic member  14 . Thus, the torque transmission from the plate  15  to the armature  6  is interrupted and the armature  6  is released from the rotary shaft  9  of the compressor  8 . As a result, the overload thus far imposed on the electromagnetic clutch  1  is eliminated. 
   (Effects of this Embodiment) 
   The elastic member  14  that has thus far supported the armature  6 , once fused by the operation of the torque limiter mechanism described above, is removed, and the armature  6  is left attached on the fiction surface  4   a  of the rotor  4  by the electromagnetic force generated in the electromagnetic coil  3 . In such a situation, the armature  6  may tend to move in the radial direction by the centrifugal force or the like. As shown in  FIG. 6 , however, the bent plate portion  15   a  is in contact with the inner portion  6   a  of the armature, and therefore the armature  6  is prevented from moving further in the radial direction. As a result, abnormal noise or other troubles, which otherwise might be caused as the armature  6  is moved in the radial direction without being supported and the armature  6  comes into contact with the rotating inner hub  7   b  after the operation of the torque limiter mechanism, are prevented. 
   In the case where the leaf spring member  12  or the inner rivets  18  are broken under the overload torque, on the other hand, the plate  5 , the elastic member  14  and the armature  6  connected to each other may move axially toward the front side and come off. As the outer diameter φA of the flange portion  7   a  of the hub  7  is larger than the inner diameter φB of the bent plate portion  15   a , however, the tendency of the plate  15  to move axially toward the front side causes the bent plate portion  15   a  to come into contact with the flange portion  7   a . Therefore, the movement of the plate  15  axially toward the front side is also restricted. 
   Further, the spring portion  12   a  is provided with an initial displacement by bringing the stoppers  17  into contact with the central portion of the spring portion  12   a . Therefore, the spring portion  12   a  can be displaced uniformly about each stopper  17 . Thus, the elasticity of the spring portion  12   a  can be utilized to the maximum degree. 
   (Second Embodiment) 
     FIG. 3  is a sectional view of the hub  7 , the leaf spring member  12 , the plate  15 , the elastic member  14  and the armature  6  according to a second embodiment. Unlike in the first embodiment wherein the plate  15  is provided with the bent portion  15   a , according to this embodiment, an independent restricting portion  20  is fixedly held between the rear side of the flange portion  7   a  of the hub  7  and the inner rivets  18 . After the operation of the torque limiter mechanism, therefore, the movement of the armature  6  in the radial direction is restricted. This independent restricting portion  20 , which is disc-shaped and has a hole formed in the central portion thereof, has the outer diameter portion thereof bent to contact with the inner diameter portion  6   a  of the armature  6 . 
   (Third Embodiment) 
     FIG. 4  is a sectional view of the hub  7 , the spring plate member  12 , the plate  15 , the elastic member  14  and the armature  6  according to a third embodiment. Unlike in the first and second embodiments, according to this embodiment, the rear side of each inner rivet  18  is so shaped that the tendency of the armature  6  to move in the radial direction causes the rear side of the inner rivets  18  to extend to a position in contact with the inner diameter portion  6   a  of the armature  6 , thereby restricting the movement of the armature  6  in the radial direction. 
   (Fourth Embodiment) 
     FIG. 5  is a sectional view of the hub  7 , the leaf spring member  12 , the plate  15 , the elastic member  14  and the armature  6  according to a fourth embodiment. According to this embodiment, the outer diameter portion  15   b  of the plate  15  is bent toward the armature  6 , and thus restricts the movement of the armature  6  in the radial direction from the outside. 
   In the second, third and fourth embodiments described above, the outer diameter φA of the flange portion  7   a  of the hub  7  is larger than the inner diameter φC of the inner diameter portion  6   a  of the armature  6 , as shown in  FIG. 7 . 
   In the case where the leaf spring member  12  or the inner rivets  18  are broken under an overload torque, the plate  15 , the elastic member  14  and the armature connected to each other tend to move axially toward the front side and come off. As the outer diameter φA of the flange portion  7   a  of the hub  7  is larger than the inner diameter φC of the inner diameter portion  6   a  of the armature  6 , however, the tendency of the plate  15  to move axially toward the front side brings the inner diameter portion  6   a  of the armature  6  into contact with the flange portion  7   a . Thus, the axial movement of the armature  6  toward the front side is also restricted. 
   (Fifth Embodiment) 
     FIG. 8  is a sectional view of the hub  7 , the leaf spring member  12 , the plate  15 , the elastic member  14  and the armature  6  according to a fifth embodiment. According to this embodiment, the flange portion  7   a  is bent to form a bent flange portion  7   d  to thereby restrict the movement of the armature  6  in the radial direction. 
   While the invention has been described by reference to specific embodiments chosen for purposes of illustration, it should be apparent that numerous modifications could be made thereto by those skilled in the art without departing from the basic concept and scope of the invention.