Abstract:
A rotor of an induction motor includes a core assembly including a plurality of core discs formed with a plurality of slots; a plurality of conductive bars passing through the slots, each of the conductive bars having a first end and a second end respectively extended out of a first end surface and a second end surface of the core assembly; a first end ring assembly including a plurality of first conductive rings stacked on each other and penetrated by the first ends of the conductive bars; and a second end ring assembly including a plurality of second conductive rings stacked on each other and penetrated by the second ends of the conductive bars; wherein the first conductive rings and the second conductive rings are respectively welded to the first ends and the second ends of the conductive bars by electron beam welding or laser welding.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a rotor of an induction motor, and more particularly, to a rotor of an induction motor with end ring assemblies formed by electron beam welding or laser welding. 
     2. Description of the Prior Art 
     A rotor of an induction motor generally comprises a shaft and a laminated magnetic core mounted to the shaft. The laminated magnetic core is formed with a plurality of slots for allowing a plurality of conductive bars to pass through. The conductive bars extend out of both ends of the laminated magnetic core, and an end ring or end cap at either end of the laminated magnetic core is configured to mechanically and electrically connect to the conductive bars. 
     In one well known method of rotor production, the conductive bars and the end rings are integrally formed by casting. However, the conductive bars may shrink after formation, such that the conductive bars are loose in the slots. In addition, bubbles may form in structures of the conductive bars and the end rings, and layers of insulation material on surfaces of the laminated magnetic core may be damaged during the casting process. The prior art provides several techniques for solving the above problem by forming the conductive bars and the end rings (or end caps) separately. For example, US patent application number 2014/0339950 discloses a rotor assembly with end caps welded to conductive bars by electron beam welding. However, the end caps are formed by forging, which requires more complex manufacturing processes. Moreover, each of the conductive bars is welded to the end cap at one single position, thus connection reliability between the conductive bars and the end caps may not be sufficient for long term operation. 
     SUMMARY OF THE INVENTION 
     The present invention provides a rotor of an induction motor, comprising a core assembly comprising a plurality of core discs stacked on each other, each of the core discs being formed with a plurality of slots; a plurality of conductive bars passing through the slots of the plurality of core discs, each of the conductive bars having a first end extended out of a first end surface of the core assembly, and a second end extended out of a second end surface of the core assembly; a first end ring assembly adjacent to the first end surface of the core assembly, the first end ring assembly comprising a plurality of first conductive rings stacked on each other and penetrated by the first ends of the conductive bars; and a second end ring assembly adjacent to the second end surface of the core assembly, the second end ring assembly comprising a plurality of second conductive rings stacked on each other and penetrated by the second ends of the conductive bars; wherein the first conductive rings are welded to the first ends of the conductive bars by electron beam welding or laser welding, and the second conductive rings are welded to the second ends of the conductive bars by electron beam welding or laser welding; and wherein a quantity of the first conductive rings is equal to or greater than 2, and a quantity of the second conductive rings is equal to or greater than 2. 
     The present invention further provides a method for manufacturing a rotor of an induction motor. The method comprises providing a core assembly that comprises a plurality of core discs stacked on each other, wherein each of the core discs is formed with a plurality of slots; inserting a plurality of conductive bars into the plurality of slots, wherein each of the conductive bars has a first end extended out of a first end surface of the core assembly, and a second end extended out of a second end surface of the core assembly; mounting a first end ring assembly and a second end ring assembly respectively to the first ends and the second ends of the conductive bars, wherein the first end ring assembly comprises a plurality of first conductive rings stacked on each other and penetrated by the first ends of the conductive bars, and the second end ring assembly comprises a plurality of second conductive rings stacked on each other and penetrated by the second ends of the conductive bars; welding the first conductive rings to the first ends of the conductive bars by electron beam welding or laser welding; and welding the second conductive rings to the second ends of the conductive bars by electron beam welding or laser welding. 
     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing a rotor of an induction motor of the present invention. 
         FIG. 2  is a diagram showing a core disc of a core assembly of the present invention. 
         FIG. 3  is a diagram showing a conductive ring of an end ring assembly of the present invention. 
         FIG. 4  is a partial exploded view of the rotor in  FIG. 1 . 
         FIG. 5  is a detailed view of the slots of the core disc of the present invention. 
         FIG. 6  is a detailed view of the enclosed slots of the conductive ring of the present invention. 
         FIG. 7  is a cross-sectional view of a conductive bar of the present invention. 
         FIG. 8  is a diagram illustrating a welding process of the end ring assembly of the present invention. 
         FIG. 9  is a diagram showing a welding zone during the welding process. 
         FIG. 10  is a diagram showing the rotor after the welding process. 
     
    
    
     DETAILED DESCRIPTION 
     Please refer to  FIG. 1  to  FIG. 3 .  FIG. 1  is a diagram showing a rotor of an induction motor of the present invention.  FIG. 2  is a diagram showing a core disc of a core assembly of the present invention.  FIG. 3  is a diagram showing a conductive ring of an end ring assembly of the present invention. The rotor  100  of the induction motor of the present invention comprises a core assembly  110 , a first end ring assembly  120 , and a second end ring assembly  130 . The core assembly  110  comprises a plurality of core discs  112  stacked on each other. The core discs  112  are mutually connected through the connecting points  114 . For example, the core discs  112  can be riveted together through the connecting points  114 . Each of the core discs  112  is formed with a plurality of slots S 1 . The core discs  112  of the core assembly  110  can be formed by stamping. Preferably, the core discs  112  can be made of steel. 
     The first end ring assembly  120  is adjacent to a first end surface  116  of the core assembly  110 . The second end ring assembly  130  is adjacent to a second end surface  118  of the core assembly  110 . Both the first end ring assembly  120  and the second end ring assembly  130  comprise a plurality of conductive rings  140  stacked on each other. Specifically, a quantity of the conductive rings  140  of the first end ring assembly  120  is equal to or greater than 2, and a quantity of the conductive rings  140  of the second end ring assembly  130  is equal to or greater than 2. Each of the conductive rings  140  is formed with a plurality of enclosed slots S 2 . The conductive rings  140  of the first end ring assembly  120  and the second end ring assembly  130  can be formed by stamping, in order to simply manufacturing processes of the rotor  100  of the present invention. Preferably, the conductive rings  140  can be made of copper. 
     In addition, as shown in  FIG. 1 , a notch n 2 , n 3 , n 4  is formed on a joint area between outer edges of two adjacent conductive rings  140  of the first end ring assembly  120 , and a notch n 6 , n 7 , n 8  is formed on a joint area between outer edges of two adjacent conductive rings  140  of the second end ring assembly  130 . Moreover, a notch n 1  is formed on a joint area between outer edges of the core assembly  110  and the first end ring assembly  120 , and a notch n 5  is formed on a joint area between outer edges of the core assembly  110  and the second end ring assembly  130 . 
     Furthermore, a layer of insulation material can be arranged on the first end surface  116  of the core assembly  110  for preventing conduction between the first end ring assembly  120  and the core assembly  110 . Similarly, a layer of insulation material can also be arranged on the second end surface  118  of the core assembly  110  for preventing conduction between the second end ring assembly  130  and the core assembly  110 . 
     Please refer to  FIG. 4 , and refer to  FIG. 1  to  FIG. 3  as well.  FIG. 4  is a partial exploded view of the rotor in  FIG. 1 . The rotor  100  of the present invention further comprises a plurality of conductive bars  150 . The conductive bars  150  can be formed by extrusion molding. Preferably, the conductive bars  150  can be made of copper. The conductive bars  150  pass through the slots S 1  of the plurality of core discs  112 . First ends of the conductive bars  150  extend out of the first end surface  116  of the core assembly  110 . The enclosed slots S 2  of the conductive rings  140  of the first end ring assembly  120  allow the first ends of the conductive bars  150  to penetrate through. The enclosed slot S 2  of the conductive ring  140  of the first end ring assembly  120  is configured to completely enclose a periphery of the first end of a corresponding conductive bar  150 , so as to improve conductivity and structural strength between the first end ring assembly  120  and the conductive bars  150 . Moreover, since the rotor  100  is symmetrically arranged, second ends (not shown) of the conductive bars  150  also extend out of the second end surface  118  of the core assembly  110 . Similarly, the enclosed slots S 2  of the conductive rings  140  of the second end ring assembly  130  allow the second ends of the conductive bars  150  to penetrate through. The enclosed slot S 2  of the conductive ring  140  of the second end ring assembly  130  is configured to completely enclose a periphery of the second end of a corresponding conductive bar  150 , so as to improve conductivity and structural strength between the second end ring assembly  130  and the conductive bars  150 . 
     Please refer to  FIG. 5  to  FIG. 7 .  FIG. 5  is a detailed view of the slots of the core disc of the present invention.  FIG. 6  is a detailed view of the enclosed slots of the conductive ring of the present invention.  FIG. 7  is a cross-sectional view of a conductive bar of the present invention. The conductive bar  150  has essentially the same shape as the slot S 1  of the core disc and the enclosed slot S 2  of the conductive ring. Dimensions of the conductive bar  150  are slightly smaller than dimensions of the slot S 1  and the enclosed slot S 2 , this allows the conductive bar  150  to pass through the slot S 1  and the enclosed slot S 2 . Since the core disc  112  and the conductive ring  140  are formed by stamping, the conductive bar  150  can be precisely fit with the slot S 1  and the enclosed slot S 2 . 
     Please refer to  FIG. 8 .  FIG. 8  is a diagram illustrating a welding process of the end ring assembly of the present invention. Once the first end ring assembly  120  and the second end ring assembly  130  are respectively mounted to the first ends and the second ends of the conductive bars, a fixture  200  can be utilized for fixing both ends of the rotor  100 . A welding machine  300  is further utilized for welding the conductive rings  140  of the first end ring assembly  120  to the first ends of the conductive bars  150 , and for welding the conductive rings  140  of the second end ring assembly  130  to the second ends of the conductive bars  150 . For example, the welding machine  300  can direct an electron or laser beam toward the notch n 2  on the joint area between outer edges of two adjacent conductive rings  140  of the first end ring assembly  120  for welding the two conductive rings  140 , which are adjacent to the notch n 2 , to the first end of one of the conductive bars  150 . The rotor  100  is then rotated by the fixture  200  for directing the electron or laser beam toward other positions on the notch n 2 , for sequentially welding the conductive rings  140  adjacent to the notch n 2  to the first ends of the rest conductive bars  150 . Meanwhile, the two conductive rings adjacent to the notch n 2  are also welded to each other. Thereafter, the welding machine  300  (and/or the rotor  100 ) can be moved along a direction X parallel to a rotational axis of the rotor  100 , and the welding machine  300  then directs an electron or laser beam toward the notch n 3  on the joint area between outer edges of two adjacent conductive rings  140  of the first end ring assembly  120  for welding the two conductive rings  140 , which are adjacent to the notch n 3 , to the first end of one of the conductive bars  150 . The rotor  100  is then rotated by the fixture  200  for directing the electron or laser beam toward other positions on the notch n 3 , for sequentially welding the conductive rings adjacent to the notch n 3  to the first ends of the rest conductive bars. Meanwhile, the two conductive rings adjacent to the notch n 3  are also welded to each other. Similarly, the welding machine  300  can further direct electron or laser beams toward the notch n 4  for welding the conductive rings  140 , which are adjacent to the notch n 4 , to the first ends of the conductive bars  150 , and welding the conductive rings  140  adjacent to the notch n 4  together. As such, the process of welding the conductive rings  140  of the first end ring assembly  120  together and the process of welding the conductive rings  140  of the first end ring assembly  120  to the first ends of the conductive bars  150  can be completed simultaneously. Moreover, the conductive ring  140  adjacent to the first end surface  116  of the core assembly  110  is not welded to the first end surface  116  of the core assembly  110 . 
     After welding all of the conductive rings  140  of the first end ring assembly  120  to the first ends of the conductive bars  150 , the welding machine  300  can sequentially direct electron or laser beams toward the notches n 6 -n 8  in order to weld the conductive rings  140  of the second end ring assembly  130  to the second ends of the rest conductive bars  150 , and welding the conductive rings  140  of the second end ring assembly  130  together. The process of welding the conductive rings  140  of the second end ring assembly  130  to the second ends of the conductive bars  150  is similar to the process of welding the conductive rings  140  of the first end ring assembly  120  to the first ends of the conductive bars  150 , thus no further illustration is provided. Similarly, the process of welding the conductive rings  140  of the second end ring assembly  130  together and the process of welding the conductive rings  140  of the second end ring assembly  130  to the second ends of the conductive bars  150  can be completed simultaneously. Moreover, the conductive ring  140  adjacent to the second end surface  118  of the core assembly  110  is not welded to the second end surface  118  of the core assembly  110 . 
     According to the above welding process, each of the conductive bars  150  is respectively welded to the first end ring assembly  120  and the second end ring assembly  130  at multiple positions, such that connection reliability between the conductive bars  150  and the first and second end ring assemblies  120 ,  130  can be increased. Moreover, welding between the adjacent conductive rings  140  of the first and second end ring assemblies  120 ,  130  and welding between the conductive rings  140  and the conductive bars  150  are completed at a same time, such that manufacturing processes of the rotor  100  can be simplified. 
     In the present invention, power of the electron beam welding or laser welding is between 4 kw and 20 kw. In addition, for increasing welding efficiency, two welding machines can be utilized for welding the conductive rings  140  of the first end ring assembly  120  and the second end ring assembly  130  respectively to the first ends and the second ends of the conductive bars  150  simultaneously. 
     Please refer to  FIG. 9 .  FIG. 9  is a diagram showing a welding zone  160  during the welding process. Energy of the electron or laser beam can be directed to the welding zone  160  ranging from a circumferential side surface of the conductive ring  140  to an outer edge of the conductive bar  150 . A depth of the welding zone  160  is preferably between 4 mm to 6 mm. Since the electron or laser beams are directed to the notches n 2 -n 4  and n 6 -n 8 , energy of the electron or laser beam can be easily directed to the outer edge of the conductive bar  150  through the notches n 2 -n 4  and n 6 -n 8  without significant energy loss, in order to further increase the connection reliability between the conductive bar  150  and the first and second end ring assemblies  120 ,  130 . 
     Please refer to  FIG. 10 .  FIG. 10  is a diagram showing the rotor after the welding process. After the welding process, surfaces of the rotor  100  can be grinded for removing uneven edges at the welding positions. On the other hand, the core assembly  110  of the rotor  100  can be further mounted to a shaft (not shown) after the welding process. 
     In contrast to the prior art, the rotor of the present invention comprises end ring assemblies consisted of a plurality of conductive rings formed by stamping to have enclosed slots precisely fitting with the conductive bars, such that the conductivity and structural strength between the end ring assemblies and the conductive bars can be improved. Further, each of the conductive bars is welded to the end ring assemblies at multiple positions by electron beam welding or laser welding, thus the connection reliability between the conductive bars and the end ring assemblies can be increased. Moreover, welding between the adjacent conductive rings of the end ring assemblies and welding between the conductive rings of the end ring assemblies and the conductive bars are completed at the same time, such that the manufacturing processes of the rotor can be simplified. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.