Abstract:
Method for fabricating a stator core and a back yoke of an outer rotor type BLDC motor in a direct coupling type washing machine, including the steps of providing a base metal of a circular electric sheet having a predetermined diameter, and pressing the base metal to form a back yoke at a periphery of the base metal, and divisional cores on an inside of the back yoke of the base metal, whereby forming the stator core and the back yoke at a time, to reduce working hours, and saving a material.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of Korean Application No. P2003-0089725 filed on Dec. 10, 2003, which is hereby incorporated by reference as if fully set forth herein.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to washing machines, and more particularly, to a method for fabricating a stator core of an outer rotor type BLDC motor applicable to a direct coupling type drum type washing machine.  
         [0004]     2. Discussion of the Related Art  
         [0005]     In general, a drum type washing machine washes laundry by using a friction force between a drum rotated by a driving power of a motor and laundry in a state detergent, washing water, and the laundry are introduced into the drum, shows almost no damage to, and entangling of the laundry, and has pounding, and rubbing washing effects.  
         [0006]     In the related art drum type washing machines, there are an indirect coupling type in which the driving power is transmitted from the motor to the drum through a belt wound on a motor pulley and a drum pulley indirectly, and a direct coupling type in which a rotor of a BLDC motor is coupled to the drum directly, to transmit the driving power from the motor to the drum, directly.  
         [0007]     The type in which the driving power of the motor is transmitted to the drum, not directly, but indirectly through the motor pulley and the drum pulley, has much energy loss in the course of power transmission, and causes much noise in the course of power transmission.  
         [0008]     According to this, for solving the problems of the indirect coupling type drum type washing machines, it is the present trend that use of the direct coupling type drum type washing machines with the BLDC motor is increasing.  
         [0009]      FIG. 1  illustrates a longitudinal section of a related art drum type washing machine.  
         [0010]     Referring to  FIG. 1 , the related art drum type washing machine is provided with a tub  2  mounted on an inside of a cabinet  1 , and a drum  3  rotatably mounted on a central portion of an inside of the tub  2 . There is a motor in rear of the tub  2 , wherein a stator  6  is secured to a rear wall of the tub, and a rotor  5  surrounds the stator  6 , and is connected to the drum  3  with a shaft passed through the tub.  
         [0011]     In the meantime, there are a door  21  mounted on a front of the cabinet  1 , and a gasket  22  between the door  21  and the tub  2 .  
         [0012]     There are hanging springs  23  between an inside surface of an upper portion of the cabinet  1 , and an upper portion of an outside circumferential surface of the tub  2 , and a friction damper  24  between the inside surface of a lower portion of the cabinet  1 , and a lower portion of the outside circumferential surface of the tub  2 .  
         [0013]      FIG. 2  illustrates a perspective exterior view of the stator in  FIG. 1 , and  FIG. 3  illustrates a reference drawing showing the steps of a process for fabricating a related art stator core.  
         [0014]     In a related art method for fabricating a divisional core DC type stator core, a sheet of metal plate, which is a base metal BM 1 , is punched out with a press to form a unit core having Ts  151 , a base portion  150 , and projected portions  500  on opposite side of the Ts  151  each for forming fastening hole  500   a  therein, the unit cores are stacked to a required height, to form a unit core assembly, the unit core assemblies are connected to each other in a circumferential direction, and the connected portions are welded, to complete fabrication of the stator core.  
         [0015]     The projected portion  500  on the unit core provides a fastening hole  500   a  for fastening the stator  6  to the rear wall of the tub, and serves to support a fastening force of a bolt.  
         [0016]     In the meantime,  FIG. 4  illustrates an enlarged view of ‘A’ part in  FIG. 1 , showing a rotor of plastic with a cylindrical frame, a back yoke  50  on an inside surface of the frame essentially required for providing a magnetic path, and magnets M attached to an inside surface of the back yoke  50 .  
         [0017]     Alike the core, the back yoke  50  is also fabricated by punching an electric sheet with a press.  
         [0018]     However, the related art has the following problems.  
         [0019]     The individual processes for fabricating the divisional core DC for fabricating the stator, and the back yoke  50 , not only require much working hours, but also result in waste of material.  
         [0020]     That is, the fabrication of the divisional core DC and the back yoke  50  by separate fabrication processes increases fabrication steps compared to a case both the divisional core DC and the back yoke  50  are fabricated at a time, and the separate provision and processing of base metal BM 1  for the divisional core DC and the base metal BM 1  for the back yoke  50  causes to increase wastes of the base metal with much loss of material.  
         [0021]     In the meantime, instead of the divisional core DC, though so called cylindrical core which is continuous in a circumferential direction without discontinuity may be applicable, in this case too, the back yoke  50  is still required to process separately, above problem can not be solved.  
       SUMMARY OF THE INVENTION  
       [0022]     Accordingly, the present invention is directed to a method for fabricating a stator core of an outer rotor type BLDC motor applicable to a direct coupling type drum type washing machine that substantially obviates one or more problems due to limitations and disadvantages of the related art.  
         [0023]     An object of the present invention is to provide a method for fabricating a stator core of an outer rotor type BLDC motor applicable to a direct coupling type drum type washing machine, in which a stator core and a back yoke are fabricated of one base metal and one time of processing, for reducing working hours and materials required for fabricating the stator core and the back yoke.  
         [0024]     Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.  
         [0025]     To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, a method for fabricating a stator core and a back yoke of an outer rotor type BLDC motor in a direct coupling type washing machine includes the steps of providing a base metal of an electric sheet, and pressing the base metal to form a back yoke at a periphery of the base metal, and a stator core on an inside of the back yoke of the base metal.  
         [0026]     In another aspect of the present invention, a method for fabricating a stator core and a back yoke of an outer rotor type BLDC motor in a direct coupling type washing machine includes the steps of providing a base metal of a circular electric sheet having a predetermined diameter, and pressing the base metal to form a back yoke at a periphery of the base metal, and divisional cores on an inside of the back yoke of the base metal.  
         [0027]     In another aspect of the present invention, a method for fabricating a stator core and a back yoke of an outer rotor type BLDC motor in a direct coupling type washing machine includes the steps of providing a base metal of a circular electric sheet having a predetermined diameter, and pressing the base metal to form a back yoke at a periphery of the base metal, and an one body of annular core on an inside of the back yoke of the base metal.  
         [0028]     It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0029]     The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings;  
         [0030]      FIG. 1  illustrates a longitudinal section of a related art drum type washing machine;  
         [0031]      FIG. 2  illustrates an exterior perspective view of the stator in  FIG. 1 ;  
         [0032]      FIG. 3  illustrates a reference drawing showing the steps of a method for fabricating a related art stator core;  
         [0033]      FIG. 4  illustrates an enlarged view of an ‘A’ part in  FIG. 1 ;  
         [0034]     FIGS.  5 A˜ 5 C illustrate a plan views showing the steps of a method for fabricating a stator core and a back yoke in accordance with a preferred embodiment of the present invention, wherein  
         [0035]      FIG. 5A  illustrates a plan view of a base metal provided,  
         [0036]      FIG. 5B  illustrates a plan view showing a state right after punching;  
         [0037]      FIG. 5C  illustrates a plan view showing a state unnecessary portions are removed; and  
         [0038]     FIGS.  6 A˜ 6 C illustrate plan views showing the steps of a method for fabricating a stator core and a back yoke in accordance with another preferred embodiment of the present invention, wherein  
         [0039]      FIG. 6A  illustrates a plan view of a base metal provided,  
         [0040]      FIG. 6B  illustrates a plan view showing a state right after punching;  
         [0041]      FIG. 6C  illustrates a plan view showing a state unnecessary portions are removed; and  
         [0042]      FIG. 7  illustrates a plan view of a joint of back yokes in accordance with another preferred embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0043]     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.  
         [0044]     A method for fabricating a stator core and a back yoke in accordance with a preferred embodiment of the present invention will be described with reference to FIGS.  5 ˜ 7 .  
         [0045]     FIGS.  5 A˜ 5 C illustrate a plan views showing the steps of a method for fabricating a stator core and a back yoke in accordance with a preferred embodiment of the present invention.  
         [0046]     Referring to  FIG. 5C , a base metal BM 2  of an electric sheet with required outside diameter Do and an inside diameter Di is provided for punching.  
         [0047]     In this instance, as shown, since the electric sheet has a central hole, it is preferable that the base metal BM 2  is annular, a full disc may be used, and a base metal with any geometry may be used as far as the base metal has an outside diameter grater than above outside diameter Do.  
         [0048]     After the base metal BM 2  is provided, the base metal is punched with a press (not shown) to form a separate stator core  60   a  and a back yoke  50  at a time.  
         [0049]     In this instance, the back yoke  50  is formed at a periphery of the base metal BM 2 , and the stator core is formed on an inside of the back yoke  50  of the base metal BM 2  in a divided shapes.  
         [0050]     In this instance, it is preferable that the divided stator cores are formed such that all circular arc angles α thereof are the same, for an example, 60°, 90°, or 120°.  
         [0051]     In the meantime, the back yoke  50 , and the stator core  60   a  are punched with a predetermined space L (where L=G+T) between the back yoke  50 , and the stator core  60   a , taking assembly of the stator core  6  and the rotor  5  into account.  
         [0052]     That is, in fabrication of the rotor  5 , because magnets  55  are attached to an inside of the back yoke, and it is required to maintain a predetermined gap G (see  FIG. 4 ) between an inside surface of the magnets  55  of the rotor  5  and an end of T  600  of the stator core  60   a  after assembly of the stator  6  and the rotor  5 , it is required to take a thickness (T see  FIG. 4 ) of the magnet  55 , and the gap G (air gap) required to be maintained between the rotor  5  and the stator  6  into account in a process the back yoke  50  and the stator core  60   a  are punched from the base metal BM 2  in advance.  
         [0053]     In other words, it is required to carry out the punching taking the thickness T of the magnet  55  to be attached to the inside surface of the back yoke  50 , and the gap G between the rotor  5  and the stator  6  into account in fabrication of the rotor  5 , for fabricating the outer rotor type BLDC motor in a state no discontinuity of magnetic path occurs at the back yoke  50  of the rotor  5 , or no interference occurs between the stator core  60   a  and the magnet  55 .  
         [0054]     Therefore, referring to  FIG. 5B , the back yoke  50  and the stator core  60   a  are punched in a state the back yoke  50  and the stator core  60   a  are spaced by a distance L (see  FIG. 4 ) which is a sum of the thickness T of the magnet  55  and the gap G required to be maintained between the rotor  5  and the stator  6 .  
         [0055]     Then, referring to  FIG. 5C , upon removal of unnecessary portion from the base metal BM 2  after the punching, on pair of the back yoke  50  and the stator core  60   a  is remained.  
         [0056]     In this instance, since the stator core is punched in a divided state, each of the core units are stacked, to form an assembly, and the assemblies are connected to one another in an annular shape, and connection portions are welded to complete fabrication of the stator core.  
         [0057]     FIGS.  6 A˜ 6 C illustrate plan views showing the steps of a method for fabricating a stator core and a back yoke in accordance with another preferred embodiment of the present invention. Because this embodiment has the same process with the foregoing embodiment in principle, detailed description will be omitted, while difference from the foregoing embodiment is described.  
         [0058]     In fabrication of the stator core and the back yoke  50  in accordance with the embodiment of the present invention, the stator core is punched, not in the divisional shape, but an annular whole shape, to form an annular whole core  60   b.    
         [0059]     Different from the divisional back yoke, what is required in this case is just stacking of the punched back yokes.  
         [0060]     In the meantime,  FIG. 7  illustrates a plan view of a joint of back yokes in accordance with another preferred embodiment of the present invention, wherein it can be noted that the joint of the back yokes  50  punched in divided shapes has a snake structure so that each ends are fit each other.  
         [0061]     It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the inventions. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.  
         [0062]     For an example, besides snake structure, the joint of the back yoke may be any shape as far as the shape has a geometric shape that fits adjacent back yoke  50 .  
         [0063]     Moreover, above embodiments describe formation from one sheet of base metal, it is of course possible that the punching is performed in a state a plurality of layers of the base metals are stacked, to form a stator core and a back yoke  50  stacked to required thickness.  
         [0064]     In the meantime, though the present invention has been described taking the drum type washing machine as an example, the present invention is also applicable to a stator core and a back yoke applied to a pulsator type direct coupling type motor.  
         [0065]     As has been described, the present invention has the following advantages.  
         [0066]     The formation of the stator core and the back yoke required for fabrication of a drum type washing machine BLDC motor at a time from one base metal permits to reduce a material required for fabrication of the stator core and the back yoke, and improve productivity different from a case when the stator core and the back yoke are processed separately because one pair of the stator core and the back yoke are formed by one time of pressing.