Abstract:
An outer rotor type motor provides a rotor of an outer rotor type motor with an optimal and simple structure that can be assembled easily. A rotation shaft is supported in a bearing housing and a stator is formed of a field winding. A rotor disposed outside the stator to house the stator therein, has a yoke surface on which a permanent magnet for performing a magnetic interaction with the filed winding of the stator is installed. The rotor rotates around the stator. A shaft bushing connects the rotor and the rotation shaft. The shaft bushing to be fastened to a central portion of the rotor is formed to have a polygonal shape to prevent a loss of a rotary power of the rotation shaft and has an insulation member for an electrical insulation of the motor.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a rotor of an outer rotor type motor; and, more particularly, to a rotor of an outer rotor type motor for use in a drum type washing machine, wherein the rotor is fabricated and assembled simply, thus improving productivity.  
       BACKGROUND OF THE INVENTION  
       [0002]     With regard to various driving methods for a motor, there is a motor type driven by an induced electromotive force (hereinafter, this motor type will be referred to as an electric induction motor). Such an electric induction motor is a kind of AC motor in which a rotary power is generated by an interaction between a rotating magnetic field generated in a stator and an inductive magnetic field generated in the rotor. Also, this electric induction motor is of a rotating magnetic field type.  
         [0003]     The electric induction motor can be designed in various ways, i.e., it can be designed as a three-phase induction motor, a three-phase winding type induction motor and so forth as well as a single-phase induction motor. It is one of AC motors easy to use, so it has been widely employed in various household electric appliances.  
         [0004]     Given that it has a constant rotational speed depending on a load imposed thereon and a long lifetime, the electric induction motor is adequate as a power supply motor. As a small-sized motor, in particular, a single-phase type capacitor motor has been most widely utilized.  
         [0005]     The electric induction motor basically includes a housing; a stator fixed in the housing; and a rotator connected with a rotation shaft rotatably supported in the housing via a bearing. The stator generates an induced magnetism by receiving a power from outside via a winding coil, and the rotor rotates along with the rotation shaft due to the induced magnetism generated by the stator.  
         [0006]     In the electric induction motor with the above-described configuration, an electric current is induced to a secondary winding by an electromagnetic induction of a primary winding which is connected to a power supply, and a rotary power is obtained by an interaction between the current induced at the secondary winding and a rotating magnetic field. Such an electric induction motor can be classified into an inner rotor type or an outer rotor type depending on relative locations of the stator and the rotor.  
         [0007]     Recently, an outer rotor type induction motor having a rotor installed outside a stator has wide applications, because it is capable of increasing a torque at a same volume, and, by using the outer rotor type motor, it is possible to use the inner space of the stator for another purpose.  
         [0008]     In the outer rotor type induction motor, a rotor having a driving shaft, a magnet, a rotor case, and so forth rotates outside a stator which is formed of an iron core, a core, a base, a bearing, and so forth. That is, the rotor rotates around the stator.  
         [0009]     The rotor of the outer rotor type induction motor is illustrated in  FIG. 1 .  
         [0010]     In the figure, a rotor  1  is made of a steel material and forms a casing of the motor by being press-molded. The rotor  1  includes a rotor core  2  and a rotor bushing  3 . The rotor core  2  has a laminated iron core  2   a  which is press-fitted to the inner peripheral surface of the rotor  1  after being fabricated by blanking; and a ring-shaped ending member  2   b  installed at an upper and a lower end of the laminated core  2   a . The rotor bushing  3  is for connecting the rotor  1  with a rotation shaft (not shown).  
         [0011]     As mentioned, the rotor  1  employs the rotor bushing  3  to deliver its rotary power to the rotation shaft. The coupling of the rotor  1  and the rotor bushing  3  is illustrated in  FIG. 2 .  
         [0012]     As shown in  FIG. 2 , the rotation shaft  4  is inserted into the rotor bushing  3  and is fixed to the rotator bushing  3  via a bolt  6 . When the rotation shaft  4  and the rotor bushing  3  are connected to each other, the rotor bushing  3  is fastened to the rotor  1  via a fixing protrusion  7  or a bolt  8 .  
         [0013]     However, with regard to the above-described configuration of the rotor  1 , the whole assembly process has been difficult because the rotor core  2  having the laminated iron core  2   a  and the ending members  2   b  need to be press-fitted to the rotor  1 . Furthermore, since the rotor bushing  3  and the rotor  1  are connected via the additional volt  6 , a fastening force therebetween may not be strong enough, resulting in a reduction in stability of the rotor  1 .  
       SUMMARY OF THE INVENTION  
       [0014]     It is, therefore, an object of the present invention to provide a rotor of an outer rotor type motor with an optimal and simple structure that can be assembled easily, wherein the rotor is capable of stabilizing a transfer of its rotary power to a rotation shaft.  
         [0015]     In accordance with a preferred embodiment of the present invention, there is provided an outer rotor type motor which includes a rotation shaft supported in a bearing housing; a stator formed of a field winding; a rotor disposed outside the stator to house the stator therein and having a yoke surface  15  on which a permanent magnet  20  for performing a magnetic interaction with the filed winding of the stator is installed, the rotor  10  rotating around the stator; and a shaft bushing  30  for connecting the rotor  10  and the rotation shaft  50 , wherein the shaft bushing  30  to be fastened to a central portion of the rotor  10  is formed to have a polygonal shape to prevent a loss of a rotary power of the rotation shaft  50  and has an insulation member for an electrical insulation of the motor. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     The above and other objects and features of the present invention will become apparent from the following description of preferred embodiments given in conjunction with the accompanying drawings, in which:  
         [0017]      FIG. 1  is a perspective view of a conventional rotor;  
         [0018]      FIG. 2  sets forth a cross sectional view to illustrate the conventional rotor connected with a rotation shaft;  
         [0019]      FIG. 3  presents a perspective view in accordance with the present invention; and  
         [0020]      FIG. 4  depicts a cross sectional view to illustrate the rotor of the present invention connected with a rotation shaft. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]     The technical essence of the present invention resides in that a rotor for use in an outer rotor type commutatorless DC motor is fabricated to have a simple structure which is optimal in the aspect of strength and function of the rotor. Thus, manufacturing costs of the rotor can be reduced, and a stable transfer of a rotary power is enabled.  
         [0022]     A rotor having such advantageous characteristics in accordance with the present invention is illustrated in  FIG. 3 .  
         [0023]     A rotor  10  of an outer rotor type motor in accordance with the present invention is formed to have a cylindrical shape as a whole by press-molding an iron material. Substructures of the rotor  10  are formed through a simple post-process after the press-molding process.  
         [0024]     Specifically, in the post-process for forming the substructures, an engagement hole  12  is formed in a base portion  18  of the rotor  10  of the cylindrical shape which is press-molded.  
         [0025]     Then, a polygonal shaft bushing  30  for preventing a loss of a rotary power of a shaft is press-fitted into the engagement hole  12  or molded into the engagement hole  12  by insert-injection. The shaft bushing  30  also includes an insulating member for the electric insulation of the motor.  
         [0026]     The shaft bushing  30  is configured to include a insulation portion  32  formed by injecting a polygonal resin material; and a bushing portion  35  press-fitted into the insulation portion  32  through a sinter-molding. The bushing portion  35  serves to receive the shaft  50  inserted thereinto. As mentioned above, the insulation portion  32  connected with the bushing portion  35  is fastened into the engagement hole  12  by press-fitting or insert-injection.  
         [0027]     Meanwhile, formed inside the engagement hole  12  is a stepped portion  19  for confining an installation depth of the shaft bushing  30  inserted into the engagement hole  12 .  
         [0028]     Further, the bushing portion  35  of the shaft bushing  30  is provided on its inner peripheral surface with a serration  34 . The presence of the serration  34  prevents a loss of a rotary power transferred to the shaft.  
         [0029]     Also, a permanent magnet attachment surface  15  is extended along the inner sidewall of the rotor  10 , and a permanent magnet  20  for performing a magnetic interaction with a field winding of a stator is attached to the permanent magnet attachment surface  10 . At this time, the permanent magnet  20  is firmly attached to the permanent magnet attachment surface  15  by a bonding or the like such that it is not separated from the attachment surface  15  when the rotor  10  rotates.  
         [0030]     Meanwhile, an outer end portion of the permanent magnet attachment surface  15  is curved outward, and a bent portion  22  is formed lower than the height of the permanent magnet  20 . That is, the height between the base portion  18  and the bent portion  22  is delimited such that a part of the permanent magnet  15  projects higher than the top end of the permanent magnet attachment surface  15  when it is attached to the permanent magnet attachment surface  15 . As a result, the permanent magnet  20  can be attached to the attachment surface  15  more firmly.  
         [0031]     Further, an inclined surface  24  is formed at a joint portion between the permanent magnet attachment surface  15  and the base portion  18  of the rotor  10 . The inclined surface  24  is provided to ease the control of the attachment position of the permanent magnet  20  when the magnet  20  is attached to the permanent magnet attachment surface  15 .  
         [0032]     A fastening unit of a motor using the shaft bushing  30  configured as described above is illustrated in  FIG. 4 .  
         [0033]     In  FIG. 4 , a driving motor for a drum type washing machine is employed as a power source for providing a high-output rotary power with a constant rotational speed. When the motor is installed in a main body of, e.g., a drum type washing machine, it is connected to a rotation shaft  50  of the washing machine which is extended downward from the washing machine main body.  
         [0034]     The rotation shaft  50  is supported in a bearing housing  16  below the washing machine main body, and a joint bolt  6  is provided at an end portion of the rotation shaft  50 .  
         [0035]     The rotation shaft  50  is fastened to the rotor  10  for generating the rotary power of the motor via the joint bolt  14 , which will be described in detail hereinbelow.  
         [0036]     To connect the rotor  10  with the rotation shaft  50 , the shaft  50  is inserted into the engagement hole  12  of the rotor  10  and is fixed therein by the joint bolt  14 .  
         [0037]     The rotation shaft  50  is engaged with the serration  34  provided on the inner peripheral surface of the bushing portion  30  inside the shaft bushing  30 , so that the rotary power can be transferred between the rotor  10  and the rotation shaft  50  without suffering from a loss of the rotary power. The shaft bushing  30  having the insulation portion  32  and the bushing portion  35  is fitted into the engagement hole  12  with the bushing portion  35  inserted into the polygonal insulation portion  32  to be fixed therein. Further, when the shaft bushing  35  is fitted into the engagement hole  12 , the installation depth thereof is confined by the presence of the stepped portion  19  in the lower portion of the engagement hole  12 . That is, the shaft bushing  30  is prevented from being inserted too deeply below the base portion  18  of the rotor  10 .  
         [0038]     Moreover, the permanent magnet  20  attached to the inner wall surface of the cylindrical rotor  10  performs a magnetic interaction with a stator (not shown) disposed inside the rotor  10 .  
         [0039]     As described above, the rotor  10  is formed of the base portion  18  forming a bottom portion of the cylindrical body and the permanent magnet attachment surface  15  forming the vertical wall surface of the cylindrical body. The rotor  10  having this configuration can be simply fabricated by press-molding, and is installed inside the drum type washing machine.  
         [0040]     By fitting the shaft bushing  30  into the engagement hole  12 , the shaft bushing  50  is connected to the rotor  10 , so that the rotary power of the rotor  10  can be transferred to the rotation shaft  50 .  
         [0041]     If the drum type washing machine is operated by the motor in which the above-described rotor  10  in accordance with the present invention is installed, the position of the permanent magnet  20  is set optimally by the presence of the inclined surface  24  on the permanent magnet attachment surface  15  of the rotor  10 . Thus, the permanent magnet  20  is allowed to perform an optimal magnetic interaction with the stator, whereby the rotor  10  is made to rotate with an optimum rotary power, and its rotary power is delivered to the shaft bushing  30  connected with the engagement hole  12  as one body.  
         [0042]     Meanwhile, by the presence of the bent portion  22  formed on the outer wall surface of the rotor  10 , a strain that might be caused by the rotary power of the rotor  10  is prevented, so that the rotary power can be maintained stably.  
         [0043]     Then, the rotary power delivered to the shaft bushing  30  is transferred to the rotation shaft  50  and, then, to a drum formed as one body with the rotation shaft  50 , thus making the drum rotate. As a result of the rotation of the drum, washing of laundry accommodated in the drum is carried out.  
         [0044]     Moreover, since the insulation portion  32  of the shaft bushing  30  is formed of a resin material, a current leakage that might occur during the rotation of the motor can be avoided and, also, a current leakage due to an electrical defect of the rotor  10  can be prevented.  
         [0045]     As described above, since the rotor  10  of the motor for use in the drum type washing machine is formed by press-molding the base portion  18  and the lateral permanent magnet attachment surface  16  as one body, the fabrication of the rotor  10  becomes easier. Further, since the inclined surface  24  is provided on the permanent magnet attachment surface  15  of the rotor  10 , the setting of the installation position of the permanent magnet also gets easier. In addition, by using the shaft bushing  30  including the insulation portion  32  formed of a resin material, a current leakage of the rotor  10  can be prevented.  
         [0046]     In accordance with the present invention, a rotor for use in an outer rotor type commutatorless DC motor to be used in a drum type washing machine is fabricated to have a simple structure which is optimal in the aspect of strength and function. Thus, manufacturing costs of the rotor can be reduced, and a stable transfer of a rotary power is enabled. Moreover, a current leakage that might be caused by an electrical defect of the motor can be prevented, so that reliability of the drum type washing machine is improved.  
         [0047]     While the invention has been shown and described with respect to the preferred embodiments, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.