Abstract:
A rotor comprises a rotor core comprising a rotational axis and a plurality of slots, a plurality of rotor bars inserted in the plurality of slots, and a plurality of holders arranged around a rotational axis of the rotor. Each holder comprises an insertion groove configured to receive and engage with an end of one of the plurality of rotor bars. An end of another rotor bar among the plurality of rotor bars is interposed between and coupled to two immediately neighboring holders among the plurality of holders.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of priority to Korean Patent Application No. 10-2013-0122482 filed on Oct. 15, 2013, the entire contents of which are incorporated herein by reference. 
       TECHNICAL FIELD 
       [0002]    The present disclosure relates to an end-ring for an induction motor and a rotor with the end-ring, and particularly, to a structure of an end-ring coupled with rotor bars of a rotor of an induction motor. 
       BACKGROUND 
       [0003]    A rotor of an induction motor is configured of an electrical sheet, a rotor bar, and end-ring. In the case of a typical induction machine, since the rotor bar and the end-ring are made of an aluminum material, the rotor bar and the end-ring are simultaneously manufactured to integrate the rotor bar and the end-ring by aluminum die casting. Recently, in order to improve efficiency of an induction motor, it is inclined to use copper having low resistivity instead of using aluminum. 
         [0004]    However, in the case of using copper instead of aluminum, it is very difficult to manufacture the induction motor by copper (Cu) die casting. The reason is that a boiling point of aluminum is 700° C. but a boiling point of copper is 1300° C. In the case of manufacturing the induction motor by the copper die casting, an expensive die casting equipment is required and since a manufacturing technology of only the copper die casting is required, a domestic/foreign place which may manufacture the induction motor is very restricted. 
         [0005]    For this reason, the copper rotor bar has been typically used. In this case, after the copper rotor bar fitted for a shape of the electrical sheet is manufactured and is inserted into the electrical sheet, upper and lower copper rotor bars and the end-ring portion are coupled with each other by brazing. 
       SUMMARY 
       [0006]    An aspect of the present inventive concept relates to an end-ring for an induction motor configuring a rotor without using an expensive star-like end-ring and a rotor having the same. 
         [0007]    Another aspect of the present inventive concept is directed to an end-ring for an induction motor capable of improving mass production of the induction motor having a copper rotor bar even though the end-ring of a copper piece type is applied and a rotor having the same. 
         [0008]    Other objects and advantages of the present inventive concept can be understood by the following description, and become apparent with reference to the embodiments of the present inventive concept. Also, it is obvious to those skilled in the art to which the present inventive concept pertains that the objects and advantages of the present inventive concept can be realized by the means as claimed and combinations thereof. 
         [0009]    In accordance with an aspect of the present inventive concept, an end-ring for an induction motor, wherein the end-ring has an outside provided with an insertion groove and is configured of a plurality of separate pieces. 
         [0010]    A material of the plurality of pieces may be copper (Cu). 
         [0011]    A material of the plurality of pieces may be aluminum (Al). 
         [0012]    The plurality of pieces may have a “         ”-shape. 
         [0013]    The plurality of pieces may be configured of 34. 
         [0014]    In accordance with an aspect of the present inventive concept, a rotor includes: a pair of end-rings for an induction motor; a plurality of rotor bars configured to be coupled with insertion grooves of the plurality of pieces; and a rotor core configured to be coupled with the plurality of rotor bars. 
         [0015]    A material of the rotor bar may be copper (Cu). 
         [0016]    A material of the rotor bar may be aluminum (Al). 
         [0017]    The insertion grooves formed in the plurality of pieces may be coupled between the rotor bars from an inside direction of the rotor toward an outside direction. 
         [0018]    The end-ring and the plurality of rotor bars may be bonded to each other by brazing. 
         [0019]    An area width of the end-ring for an induction motor may be a sum of a width of the rotor bar with an inside width of the plurality of pieces. 
         [0020]    The plurality of pieces may have a “         ”-shape. 
         [0021]    The plurality of pieces may be configured of 34. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIGS. 1A-1C  are diagrams illustrating a coupling structure of a rotor bar using a star-like end-ring with the end-ring. 
           [0023]      FIG. 2  is a perspective view of the end-ring in accordance with an embodiment of the present inventive concept. 
           [0024]      FIG. 3  is a cross-sectional view taken along an X-X′ axis illustrated in  FIG. 2 . 
           [0025]      FIG. 4  is an assembled view of end-rings  421  and  422  in accordance with an embodiment of the present inventive concept with a rotor bar  410 . 
           [0026]      FIG. 5  is a diagram illustrating an area of the end-ring coupled with the rotor bar illustrated in  FIG. 4 . 
           [0027]      FIG. 6  is a perspective view of a rotor having the end-ring structure in accordance with an embodiment of the present inventive concept. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]    Since the present inventive concept may be variously modified and have several embodiments, specific embodiments will be shown in the accompanying drawings and be described in detail in a detailed description. However, it is to be understood that the present inventive concept is not limited to the specific embodiments, but includes all modifications, equivalents, and substitutions included in the spirit and the scope of the present inventive concept. 
         [0029]    Throughout the accompanying drawings, the same reference numerals will be used to describe the same components. 
         [0030]    Terms used in the specification, ‘first’, ‘second’, etc., may be used to describe various components, but the components are not to be construed as being limited to the terms. That is, the terms are used to distinguish one component from another component. 
         [0031]    For example, the ‘first’ component may be named the ‘second’ component and the ‘second’ component may also be similarly named the ‘first’ component, without departing from the scope of the present inventive concept. The term ‘and/or’ includes a combination of a plurality of items or any one of a plurality of terms. 
         [0032]    Unless indicated otherwise, it is to be understood that all the terms used in the specification including technical and scientific terms have the same meaning as those that are understood by those who skilled in the art. 
         [0033]    It must be understood that the terms defined by the dictionary are identical with the meanings within the context of the related art, and they should not be ideally or excessively formally defined unless the context clearly dictates otherwise. 
         [0034]    Hereinafter, an end-ring for an induction motor and a rotor having the same in accordance with an embodiment of the present inventive concept will be described in detail with reference to the accompanying drawings. 
         [0035]    Generally, coupling the end-ring with the copper rotor bar by making the end-ring shape an annular (donut) shape is the simplest method. However, in the case of a driving motor for a green car, since the driving motor is a motor driven at a high speed, the end-ring may be separated from the copper rotor bar at a high speed when the annular end-ring is applied. Due to the problem, a method of manufacturing the end-ring in a star type fitted for the shape of the copper rotor bar and coupling the end-ring with the copper rotor bar has been mainly used. 
         [0036]    This is shown in  FIGS. 1A-1C . Referring to  FIG. 1A , a copper rotor bar  110  is inserted, and star-like end-rings  120  are inserted into upper and lower portions of the copper rotor bar  110  and then the end-rings  120  are coupled with the copper rotor bar  110  by brazing. The coupling structure is shown in  FIG. 1B . 
         [0037]      FIG. 1C  illustrates a structure of the star-like end-ring  120 . To manufacture the end-ring shape in the star type, since the end-ring is manufactured by wire cutting, additional time and costs are required. 
         [0038]    In other words, the structure is to prevent the end-ring from separating from the copper rotor bar at the time of high speed driving, but since the star-like end-ring needs to be wire cut, processing cost is expensive and much processing time is required. That is, mass production may be reduced. 
         [0039]    Further, there is a method of forming the end-ring by collecting squared copper pieces as another end-ring structure. In other words, as a method of inserting a plurality of squared copper pieces between the respective copper rotor bars, there is a method of coupling an end-ring with a copper rotor bar. 
         [0040]    However, in the end-ring structure, since the plurality of copper pieces are inserted between the copper rotor bars one by one, manufacturing time may be long and an area of the end-ring may be reduced. Further, a copper loss may be increased due to the reduction in the area of the end-ring. 
         [0041]    Generally, in other words, a current flowing in several copper rotor bars flows in other copper rotor bars through the end-ring and therefore the area of the end-ring between the cooper rotor bars needs to be larger than that of the copper rotor bar. However, in the case of using the copper pieces, since the area of the copper rotor bar is the same as the area of the end-ring, a larger amount of heat may be generated in the end-ring than in the copper rotor bar and the efficiency may be reduced. 
         [0042]    Further, after the brazing, there is a need to process both of the inside of the end-ring part and the outside of the rotor. 
         [0043]    Further, when the copper rotor bar is applied, since a density of copper is 3.3 times as large as that of aluminum, the number of copper rotor bars is increased to secure a safety factor of the rotor. Therefore, when the number of copper rotor bars is 68, since the copper pieces are required at both of the upper and lower portions of the rotor,  136  copper pieces are required, but since a person inserts the  136  copper pieces between the copper rotor bars, a great deal of time may be required and there are many problems in manufacturing ability. 
         [0044]      FIG. 2  is a perspective view of an end-ring in accordance with an embodiment of the present inventive concept. Referring to  FIG. 2 , the end-ring  200  is formed by collecting a plurality of pieces  210 . Further, the plurality of pieces  210  are not connected to each other, but are independently separated from each other. Further, an assembled shape of the number of pieces  210  becomes a circle. Further, a material of the plurality of pieces  210  may be copper (Cu) but is not limited thereto, and therefore aluminum (Al) may be used. The plurality of pieces  210  are configured of 34. Therefore, when the end-ring is formed at both sides, the number of pieces  210  becomes a total of 64. Therefore, the number of pieces is more reduced than the existing 136 pieces. 
         [0045]      FIG. 3  is a cross-sectional view taken along an X-X′ axis illustrated in  FIG. 2 . Referring to  FIG. 3 , a “         ”-shaped or “C”-shaped piece  210  is provided with an insertion groove  310  which is formed in an outside direction. Therefore, the insertion grooves  310  formed in the plurality of pieces  210  are coupled in the outside direction of the rotor from an inside direction thereof between the rotor bars, which is illustrated in  FIG. 5 . Matters of  FIG. 5  will be described below. 
         [0046]      FIG. 4  is an assembled view of end-rings  421  and  422  in accordance with an exemplar embodiment of the present inventive concept with a rotor bar  410 . Referring to  FIG. 4 , the end-ring  200  illustrated in  FIGS. 2 and 3  which is configured in pair is coupled with upper and lower ends of the rotor bar  410 . That is, the first end-ring  421  is coupled with a lower end of the rotor bar  410  and the second end-ring  422  is coupled with an upper end of the rotor bar  410 . Further, the rotor bars  410  are also provided in plural, and as a material thereof, copper (Cu) is mainly used but is not limited thereto and therefore aluminum (Al) may be used. 
         [0047]    Generally, the rotor (illustrated in  FIG. 5  and described below) of the induction motor is largely configured of a rotor core (otherwise, called an electrical sheet), the rotor bar  410 , and the end-rings  421  and  422 . 
         [0048]    Therefore, the rotor bar  410  is inserted in the rotor core and the “         ”-shaped piece  210  is inserted between the rotor bars  410  from the inside of the rotor toward the outside thereof and then is brazed at the outside of the rotor, such that the rotor bar  410  is bonded to the end-rings  421  and  422 . 
         [0049]    Based on the foregoing scheme, when the copper rotor bar is applied to the upper and lower portions of the rotor by the same operation, the rotor of the induction motor may be manufactured. The rotor is shown in  FIG. 5 . In particular,  FIG. 5  is a diagram illustrating the area of the end-ring coupled with the rotor bar illustrated in  FIG. 4 .  FIG. 5  illustrates that a rotor core  520  is assembled in an inner surface of the rotor bar  410  and an end-ring width  500  is disposed on the end-ring  421  assembled at the upper end of the rotor bar  410 . The end-ring width  500  becomes a sum of the width  520  of the rotor bar with the inside width  520  of the piece  210 . 
         [0050]    Like the rotor bar illustrated in  FIG. 5 , since the “         ”-shaped pieces  210  requires only half the number of rotor bars  410 , the operation time required to insert the pieces is reduced and thus productivity is improved. 
         [0051]    Further, since the end-ring width  500  in which current flows is larger than the area of the rotor bar, a current density at the end-rings  421  and  422  may be reduced, thereby reducing the heat generation and improving the efficiency. 
         [0052]      FIG. 6  is a perspective view of the rotor having the end-ring structure in accordance with the embodiment of the present inventive concept. When a phase balance current electrically having a phase difference of 120° is applied to a primary side stator (not illustrated) of the induction motor, a coil is wound around the stator with the phase difference of 120° and therefore a rotating magnetic field is generated. 
         [0053]    Since the rotor bar cuts off a magnetic flux of the rotating magnetic field, that is, changes a magnetic flux of the rotating magnetic field, a voltage is induced and since the “         ”-shaped piece configures a closed circuit, a current flows. 
         [0054]    The rotor is applied with force by the current and the rotating magnetic field and thus rotates. Therefore, the rotor necessarily includes the “         ”-shaped pieces configuring the closed circuit. 
         [0055]    In accordance with the embodiments of the present inventive concept, since the area of the end-ring may be increased by configuring the end-ring in the “         ”-shaped copper pieces, the secondary-side copper loss may be reduced and since the heat generation is reduced with the reduction in loss and thus the burden on the cooling system is reduced, the overall performance of the system may be improved. 
         [0056]    Further, as another effect of the present inventive concept, since the copper pieces are inserted between the rotor bars and thus the number of copper pieces is required as many as the number of rotor bars, the process may be simple and the mass production time may be shortened. 
         [0057]    In addition, as another effect of the present inventive concept, since the expensive star-like end-ring is not applied, the production cost may be reduced. 
         [0058]    While the present inventive concept has been described with respect to the specific embodiments, it will be apparent to 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.