Abstract:
In an electromagnetic clutch having a rotating component, groove portions ( 21   a   , 21   b ) are made on a surface of the rotating component to induce air flow during rotation of the rotating component. The air flow enhances radiation of heat from the electromagnetic clutch. It is preferable that the groove portion is formed at each of axial ends of a driving rotor or pulley ( 12 ) included as the rotating component in the electromagnetic clutch.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an electromagnetic clutch and a compressor comprising the same. 
     An electromagnetic clutch is widely used in various devices such as compressor. A conventional electromagnetic clutch comprises a driving rotator driven to rotate, an armature facing the driving rotator in an axial direction, a driven rotator supporting the armature movably in the axial direction, and a coil for generating electromagnetic force when charged with electricity. By controlling the electricity to the coil, the armature is brought in and out of contact with the driving rotator, thus accomplishing the intermittent transmission of the rotating force. For instance, when the coil is charged with electricity, the armature is pressed against the driving rotator by an electromagnetic force, transmitting by friction the rotating force of the driving rotator to the driven rotator via the armature. When the coil is not charged with electricity, the armature is away from the driving rotator, and the rotating force of the driving rotator is not transmitted to the driven rotator. 
     The conventional electromagnetic clutch has a problem of heat generation. That is, the coil generates heat while it is charged with electricity. Further, bearings which rotatably support respective driving and driven rotators also generate heat. 
     However, the conventional electromagnetic clutches have not been provided with almost any provisions for radiating such heat. In other words, they were simply left to effect a self-cooling. Accordingly, there was a possibility of short-circuits caused by a temperature rise at the coil. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide an electromagnetic clutch in which improvement is made about radiation of heat therefrom. 
     It is another object of the present invention to provide a compressor which comprises the electromagnetic clutch. 
     Other objects of the present invention will become clear as the description proceeds. 
     An electromagnetic clutch to which the present invention is applicable comprises a rotating component. In the electromagnetic clutch, the rotating component has a groove portion which induces air flow during rotation of the rotating component. The air flow enhances radiation of heat from the electromagnetic clutch. 
     A compressor to which the present invention is applicable comprises the electromagnetic clutch described above and a compression mechanism driven through the electromagnetic clutch to compress gaseous fluid. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a sectional view of a scroll type compressor comprising an electromagnetic clutch according to an embodiment of the present invention, and 
     FIG. 2 shows a sectional view of a pulley included in the electromagnetic clutch of FIG. 1 as taken along the line II—II in FIG.  1 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference to FIG. 1, description will be made as regards a scroll type compressor comprising an electromagnetic clutch according to an embodiment of the present invention. 
     The scroll type compressor is for bringing about a refrigerant flow in a refrigerating circuit of a car air conditioning apparatus and comprises a casing  1  with its one end open and a front end plate  2  which closes the opening of the casing  1 . Arranged within the casing  1  are a fixed scroll  4  and a movable or orbiting scroll  5  interfitting each other to define compression chambers  3  between them. The fixed scroll  4  is fixed to the casing  1 . The orbiting scroll  5  revolves through an orbit without rotation, by rotation of a driving shaft  7  which is rotatably supported on the front end plate  2  via radial bearing  6 . In cooperation with the fixed scroll  4 , the orbiting scroll  5  causes the compression chambers  3  to move towards the center of the fixed scroll  4 . As a result, the compression chambers  3  are decreased with their volumes. thus, refrigerant gas taken in the compression chambers  3  from the periphery of the orbiting scroll  5  is compressed in the compression chambers  3  before it is ejected to an ejecting chamber  8 . A combination of the fixed and the orbiting scrolls  4  and  5  is referred to a compression mechanism. 
     An electromagnetic clutch  10  is provided at the front of the scroll type compressor. The front end plate  2  has a cylindrical portion  9  protruding forward. The electromagnetic clutch  10  comprises a pulley  12  serving as a driving rotator which is rotatably mounted on the cylindrical portion  9  of the front end plate  2  via a radial bearing  11 , an armature  13  facing the pulley  12  in the axial direction, a boss  14  serving as a driven rotator which is fixed on the driving shaft  7 , a plate spring  17  serving as an elastic supporting member for supporting the armature  13  onto the boss  14  by means of rivets  15  and  16  in such a manner that the armature  13  can move in the axial direction, and a coil  18  for generating electromagnetic force to bring the armature  13  in and out of contact with the pulley  12 . An automobile engine drives the pulley  12  via a belt in the manner known in the art. A reference numeral  19  designates a plurality of slits for effectively forming a magnetic path or circuit. 
     When the electricity is charged on the coil  18 , the electromagnetic force causes the armature  13  to be pressed against the axial end face of the pulley  12  with elastically bending the plate spring  17 . Therefore, the rotating force of the pulley  12  is transmitted to the boss  14  and the driving shaft  7  via the armature  13  by friction between the pulley  12  and the armature  13 . When the electricity to the coil  18  is off, the armature  13  is withdrawn from the pulley  12  by reaction force of the plate spring  17 , thereby preventing the transmission of the rotating force of the pulley  12  to the boss  14  and the driving shaft  7 . In this way, the electromagnetic clutch  10  accomplishes the intermittent transmission of the power to the above-described compression mechanism. 
     Meanwhile, the coil  18  generates heat while charged with electricity. The bearing  11  also generates heat while the pulley  12  is rotating. 
     With reference to FIG. 2 showing the pulley  12  as viewed from the compressor side, the description will be made as regards a countermeasure for such heat. 
     The pulley  12  is provided with a plurality of groove portions  21   a  and  21   b  which are formed in both axial end faces  12   a  and  12   b  thereof, respectively. Each of the groove portions  21   a  and  21   b  extends in a direction intersecting both radial and tangential directions. In FIG. 2, the groove portions  21   a  shown by solid lines are formed on one end face  12   a , and the groove portions  21   b  shown by broken lines are formed on the other end face  12   b . The arrow  22  indicates the rotating direction of the pulley  12 . 
     As can be seen from FIG. 2, the groove portions  21   a ,  21   b  are formed in such a manner as to induce air flow outwards, thereby enhancing the heat radiation. Since the heat radiation capacity is increased, the problem of heat accumulation at the coil  18  and radial bearing  11  is solved. Namely, the coil  18  and the radial bearing  11  are forcibly cooled by air flow, and the temperature rise at these locations are restrained. 
     While the present invention has thus far been described in connection with a single embodiment thereof, it will readily be possible for those skilled in the art to put this invention into practice in various other manners. For example, it is possible to modify the number of the groove portions. The electromagnetic clutch can be used in another type compressor such as a swash plate type compressor.