Electromagnetic clutch
BACKGROUND OF THE INVENTION 
     This invention relates to an electromagnetic clutch, particularly an electromagnetic clutch for selectively transmitting rotation of an automobile engine to a compressor used for automobile cooling apparatus. 
     This kind of electromagnetic clutch usually comprises a clutch disc connected to a rotary shaft; a rotor or pulley means including a belt receiving portion, an annular portion facing the clutch disc with a gap and a cylindrical bearing receiving portion; and a stator which is secured to the compressor and includes an electromagnet and a cylindrical portion rotatably supporting the rotor through a bearing. The stator of this type is shown in U.S. Pat. No. 3,703,227, wherein the stator except windings, that is, a stator frame has a flange (71) and ring (75) as a U-shaped core for containing a winding therein; a flat portion 74; and a small ring (76). The small ring (76) supports the bearing receiving portion of the rotor through the bearing, and the outer face of the bearing receiving portion faces the inner face of the ring (75) with a small air gap to establish a magnetic flux passage, so that the inner face of the ring (75) and the outer face of the small ring (76) must be precisely finished. Further the flange ( 71) face also faces the stator with a small gap to establish a magnetic flux passage, so that a precise relation between the flange (71), the ring (75) and the small ring (76) must be made. 
     The stator flame comprises three parts and need two junctures, so that assemblying of the stator flame is laborious. 
     As stated above, the stator flame has a plurality of faces which each belong to different parts and need accurated concentricity to each other. Therefore, on bases of one of the faces the other faces need be machined precisely, so that the machining is laborious. 
     Further, the stator flame is made such that a part of the stator flame bridging from the flange (71) to the small ring (75) is made of one piece of low carbon steel, and the small ring (76) also is made low carbon steel since the piece is junctioned by friction welding and the juncture must be strong. Therefore, since the magnetic circuit results in magnetic flux passing through the small ring, a resultant loss of magnetic flux amounting to about 17-18% occurs whereby the electromagnetic clutch effects decreased performance. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide an electromagnetic clutch which has a high productibility without decrease of frictional clutch force. 
     Another object of the invention is to provide an electromagnetic clutch which has a high productibility with less juncture as compared with the prior art as mentioned above. 
     Another object of the invention is to provide an electromagnetic clutch which has a high productibility with less machining portions. 
     Another object of the invention is to provide an electromagnetic clutch which is small in magnetic flux loss. 
     A feature of an electromagnetic clutch according to the present invention is that a core member of one piece and a supporting member of one piece are tightly inserted and made a stator flame assembly. The stator flame is fixed to a machine or apparatus, support rotatably rotor means, such as a pulley member, and holds therein an exciting coil. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a section view of an embodiment of an electromagnetic clutch according to the present invention; 
     FIG. 2 is a section view of a stator flame assembly employed in the electromagnetic clutch in FIG. 1; 
     FIG. 3 is a section view of another embodiment of the stator flame assembly as shown in FIG. 2; and 
     FIG. 4 is a section view of another embodiment of the electromagnetic clutch according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIGS. 1 and 2, an embodiment of the electromagnetic clutch according to the present invention will be described hereinafter in detail. 
     In FIG. 1 the electromagnetic clutch comprises a clutch disc including armature 1 connected to a rotary shaft 2, a rotor of a pulley 3, an electromagnet 4, and a supporting member 5. Torque of the pulley 3 driven by a driving source such as an engine, motor, etc., is selectively transmitted to the rotary shaft 2 by frictional engagement of the armature 1 with pulley 3. A force for the frictional engagement is generated by selectively energizing of the electromagnet 4. 
     The armature 1 with an annular shape is made of magnetic material and mounted on a holding plate 7 through leaf springs 6 thereby permitting the armature 1 to limitedly move axially of the rotary shaft 2. The holding plate 7 is secured to a hub 8 fixed to the rotary shaft 2 by a key 9 and a screw means 10. 
     The electromagnet 4 is generally cylindrical and comprises a core member 41 which is cylindrical as a whole, U-shaped in its section and has an annular space 41d defined by an inner cylindrical portion 41c, a bottom portion 41a spreading out from one end of the inner cylindrical portion 41c and an outer cylindrical portion 41b, and an exciting coil 42 which is inserted in the annular space 41d and burried with insulating resin 43. The core member 41 is made of annular plate of low carbon steel by press working. When formed the inner and outer cylindrical portions 41c and 41b are made precisely coaxially. 
     The supporting member 5 has a sleeve portion 5a, a flange portion 5b spreading out from one end of the sleeve portion 5a, and a bent portion 5c formed at the outer end of the flange portion 5b. The supporting member 5 is made of aluminum alloy by cold or hot forging. The supporting member 5 is tightly inserted to be press-fitted in the core member 41 from the bottom portion 41a to make a stator flame assembly. The stator flame assembly has an annular space defined by the supporting member 5 and the inner cylindrical portion 41c of the core member 41. 
     After assembled in the stator flame assembly, a face E of the supporting member 5 is finished by machining on a basis of faces A and B of the core member 41, whereby faces A, B and C are made precisely coaxially. An inner face C of the bent portion 5c and a face D perpendicular to the face C are finished precisely by machining on a basis of the faces A and B, thereby providing a recess for engagement with a machine part such as a compressor casing 12. The exciting coil 42 is inserted in the annular space 41d and fixed with the insulating resin 43 whereby an assembly of the electromagnet 4 and supporting member 5 is completed. The assembly of the electromagnet 4 and supporting member 5 is fitted to the machine part 12 by screw means 11. 
     The supporting member 5 carries a bearing 13 fitted to the sleeve portion 5a and supports the pulley member 3 through the bearing 13. 
     The pulley member 3 comprises a cylindrical portion of a rim 3a with a belt receiving grooves 3b, a sleeve portion 3d mounting the bearing 13 thereon and an annular pole portion 3c portion engages with the armature 1. The cylindrical portion 3a and the sleeve portion 3d of the pulley member 3 face to the outer and inner cylindrical portion with small air gaps α and β, respectively, so that magnetic flux produced in the core member 41 flows into the pulley member 3 through the air gaps α and β, as shown by a dotted line I. 
     A face F of the supporting member 5 is finished by forging, an air gap γ is larger than the air gaps α and β. 
     Upon energizing the electromagnet 4, the magnetic flux produced in the core follows along the dotted line 1, which results in causing the armature 1 to contact with the pole portion of the pulley member to make a frictional coupling between the pulley member 3 and the armature 1, whereby torque of the pulley member is transmitted to the rotary shaft 2 through the plate springs 6, the holding plate 7 and the hub 8. 
     In order to make resistance of the magnetic circuit small, it is necessary to make each of the air gaps α and β small. Therefore, the outer and inner cylindrical portions 41b and 41c of the core member 41, the cylindrical portion 3a, and sleeve portion 3d of the pulley member 3 and the sleeve portion 5a of the supporting member 5 are made strictly coaxially. 
     In the above embodiment of the present invention, the assembly of the core member 41 and the supporting member 5a corresponding to the stator flame comprises two parts assembled so that the juncture of them is one. Therefore, assembling of the two parts is extremely simplified. 
     Further, the assembly of the core member 41 and supporting member 5 which concentricity is needed comprises two parts one of which is precisely finished by press-forming without machining, so that the other part only needs machining. Additionally, the two portion of the part to be finished by machining is done machining on a basis of the same faces. Therefore, finishing can be done efficiently. 
     Still further, since the supporting member is made of non-magnetic material of aluminum alloy, magnetic flux loss followed in magnetic circuits II, III is reduced (to 5-10% in a result really measured). Accordingly, the electromagnetic clutch is raised in its performance. 
     The core member 41 and the supporting member 5 can be joined by welding, in such a case the supporting member of the same material as the core member is preferred. Even in the case of use of low carbon steel, the magnetic flux loss is reduced by about 5% as compared with one in the prior electromagnetic clutch. 
     In the supporting member 5, it is capable to make the recess 14 defined by the bent portion 5c and the flange portion 15b deeper (as shown by L in FIG. 2) by forging longer bent portion 15c, whereby the electromagnetic clutch is tightly fixed to the casing 12 so that eccentricity due to vibration is not brought and its liability and life are improved. 
     Next, another embodiment of the present invention will be described referring to FIG. 3. In FIG. 3, a supporting member 51 comprises a sleeve portion 51c and a flange portion 51b. The core member 41 has a recess portion 41e made in the inner cylindrical portion 41c thereof. The supporting member 51 is secured to the core member 41 with flange portion end 51c of the supporting member 51 tightly inserted in the inner cylindrical portion 41c on a basis of the faces A and B. 
     Machining of a face E of the supporting member 51 is done in the same manner as one in FIG. 2, but faces C and D defining an engagement recess 14 is not necessary to machine because the faces C and D is made at right angle. The supporting member 51 has no bent portions at the end of the flange portion 51b so that forging is easy. 
     Further, another embodiment of the present invention will be described referring to FIG. 4. In this embodiment, an electromagnet 4 only is different from one shown in FIGS. 1 and 2. The electromagnet 4 has a core member 15 which is L-shaped in section and has an inner cylindrical portion 15b, a bottom portion 15a spreading out from the inner cylindrical portion 15b, and an exciting coil 16 which is put on the inner cylindrical portion 15b and burried with resin 17. The bottom portion 15a is more thick than the inner cylindrical portion, and the end 15c of the bottom is cylindrical and opposes to the cylindrical portion 3a of the pulley member 3 with a small air gap, whereby the magnetic flux produced in the core member 15 flows into the pulley member 3 through the air gap.