Abstract:
A flat core brushless motor including a stator having a stator base with protruding poles, and a respective wound armature coil wrapped around each of the protruding poles, wherein the stator base includes at least one concave portion receiving the armature coils.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an improvement of a flat core brushless motor suitable for driving a spindle or a pickup used for a portable mini disk apparatus. 
     2. Description of the Related Art 
     A conventional flat core brushless spindle motor used for a portable mini disk apparatus is shown in FIG.  5 . That is, a brass bearing holder H is installed at a stator base B. A stator core C is formed by winding an armature coil N around a plurality of protruding poles, and is installed at the outer circumferential surface of the bearing holder H. A bearing J is installed inside the bearing holder H. A rotor R having a magnet M which is installed in a magnet holder Y facing the stator core C with a gap, is supported through a shaft S rotatably inserted in the bearing J. In the drawing, T denotes a turntable on which media is installed, which is integrally formed with the rotor R. 
     However, the flat spindle motor having the above structure is restricted in being made thinner by an expanded portion of the armature coil N wound around the protruding poles. Thus, the expanded portion of the armature coil is usually compressed and impregnated. Nevertheless, there is a problem of occasional disconnection or shorting of lines. 
     Also, when the expanded portion of the armature coil is not compressed and impregnated, the number of accumulated thickness units of a core must be reduced and thus the property of the motor is sacrificed. To solve this problem, a part of the core has an L shape. That is, a blade portion of the core is folded in an axial direction. However, this increases the manufacturing cost. 
     SUMMARY OF THE INVENTION 
     To solve the above problems, it is an objective of the present invention to provide a flat core brushless motor which can be made thin without compressing and reducing the expanded portion of an armature coil, to help reduce the effect of the stator base on the overall thickness of the motor, and without reducing the number of accumulated thickness units of a core, so that the properties of a motor are not sacrificed. 
     Accordingly, to achieve the above objective, there is provided a flat type core brushless motor formed by installing a stator which is made by winding an armature coil around each of a plurality of protruding poles at a stator base, in which a concave portion for escape of the armature coil is installed at the stator base. 
     It is preferred in the present invention that the concave portion for escape of the armature coil is a hole arranged at a circuit board attached to the stator base. 
     It is preferred in the present invention that the concave portion for escape of the armature coil is a hole arranged at a circuit board attached to the stator base and a hole installed at the stator base thereunder. 
     It is preferred in the present invention that the concave portion for escape of the armature coil is a hole arranged at a circuit board attached to the stator base and a hole installed at the stator base thereunder. 
     It is preferred in the present invention that the circuit board is formed of a thin flexible sheet to cover the edge of the hole formed in the stator base. 
     It is preferred in the present invention that a plurality of supports, which are lifted from the stator base by pressing processing, are used as a means for installing the stator and simultaneously a hole formed by the press processing for lifting the supports is used as part of the concave portion for escape of the armature coil. 
     It is preferred in the present invention that a rotation support portion is arranged inside the supports. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above objective and advantages of the present invention will become more apparent by describing in detail a preferred embodiment thereof with reference to the attached drawings in which: 
     FIG. 1 is a sectional view showing a flat core brushless motor according to a first preferred embodiment of the present invention; 
     FIG. 2 is a perspective view showing the assembly of major parts of the flat core brushless motor according to the first preferred embodiment of the present invention; 
     FIG. 3 is a sectional view showing a flat core brushless motor according to a second preferred embodiment of the present invention; 
     FIG. 4 is a sectional view showing a flat core brushless motor according to a third preferred embodiment of the present invention; and 
     FIG. 5 is a sectional view showing the general structure of a conventional flat core brushless motor. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, reference numeral  1  denotes a stator base of a thin rolled steel plate. A circuit board  2  of a polyamide or polyester film is attached to the stator base  1  by a double-sided adhesive film interposed therebetween. A shaft holder  1   a  is formed by a clamping process at the center of the stator base  1 . Supports  1   b  for maintaining a stator core  3  which will be described later are formed around the shaft holder  1   a  by being lifted, for each of protruding poles  3   a  of the stator core  3 . Prior to the lifting of the support  1   b , as shown in FIG. 2, a slightly enlarged hole, that is, a concave portion  1   c  for accommodating an expanded portion of an armature coil  3   b , is provided. In this case, the circuit board  2  is cut to make a concave portion  2   a  having a diameter less than that of the concave portion  1   c  for insulation so that the expanded portion of the armature coil  3   b  can easily extend therethrough. 
     Reference numeral  3  denotes a stator core formed by stacking five silicon steel plates. The stator core includes the plurality of protruding poles  3   a . Respective armature coils  3   b  are wound around the protruding poles  3   a . A recess  3   c  supported by an end portion  1   d  of the support  1   b  is located inside the stator core  3 . Also, although the stator core  3  is described as having five stacked silicon steel plates in the preferred embodiments shown in FIGS. 1 through 4, the number of silicon steel plates of the present invention is not limited thereto. 
     The stator core  3  is installed at the stator base  1  by fitting the support  1   b  into the recess  3   c . The stator core  3  is fixed by crushing a top portion  1   bb  of the support  1   b  or inserting a wedge between the end portion of the support  1   b  and the stator core  3 . Of course, the stator core  3  can be fixed by using an adhesive. A terminal of each armature coil  3   b  is connected to a predetermined pattern of the circuit board  2  by soldering, thus completing a stator. 
     Thus, the expanded portion of each of the armature coils  3   b , of which a part is accommodated in the concave portions  2   a  and  1   c , can have a low profile. Also, in the present embodiment, the shaft  4  is fixed by being directly pressed into and installed in the shaft holder  1   a.    
     A rotor includes a bearing  5  rotatably installed at the shaft  4 , a rotor case  6  installed at the bearing  5 , and a ring rubber magnet  7  which is pressed and fixedly installed inside the rotor case  6  by bending a plate to face the protruding poles  3   a , . . . of the stator core  3  with the gap in a radial direction. Further, the rotor case  6  is integrally formed with a turntable  8  on which a medium is installed. 
     A second preferred embodiment is shown in FIG. 3, which is suitable for a circuit board  22  that is relatively thick. That is, a concave portion  22   a  into which an expanded portion of an armature coil  3   b  can protrude is located only in the circuit board  22 . 
     In this case, the rotor R has a rotating shaft and a brass bearing holder  9  is installed at a stator base  11  by caulking. The rotor R includes a shaft  4  inserted in a bearing  55  installed inside a bearing holder  9 , a rotor case  66  which is pressed and fixedly installed at the shaft  4 , and a neodymium magnet  77  arranged inside the rotor case  66 . 
     FIG. 4 shows a third preferred embodiment of the present invention. In the present embodiment, a rotating shaft rotor is rotatably installed through a shaft  4  at a bearing  55  arranged inside a support  1   b . The bearing  55  may be directly pressed into and inserted in the support  1   b  or installed inside a stator core  3 . Here, as the rest of the structure is the same as that of the first preferred embodiment, the same reference numerals are used for the same elements and descriptions thereof are omitted. 
     It is noted that the present invention is not limited to the preferred embodiments described above, and it is apparent that variations and modifications by those skilled in the art can be effected within the spirit and scope of the present invention defined in the appended claims. 
     As described above, in a flat brushless motor according to the present invention formed by installing a stator made by winding an armature coil around each of a plurality of protruding poles at a stator base, because an expanded portion of the armature coil is received in a concave portion of the stator base, there is no need to restrict the armature coil and a flat brushless motor without problems such as disconnection or shorting of lines can be provided. 
     Also, the motor is suitable for a case in which the circuit board is relatively thick, while it can provide a flat core brushless motor when an expanded portion of the armature coil is considerably large. 
     Furthermore, the brass bearing holder is not needed and the structure is simplified by using fixed shaft motor. Thus, a flat core brushless motor with reduced the manufacturing cost can be provided.