Abstract:
A unique electrical machine includes a plurality of fasteners extending only partially into a rotor core of an induction rotor through a short circuit ring, wherein the fasteners cooperate to balance the induction rotor and/or mechanically support the short-circuit ring. A unique method of assembling an electrical rotor machine includes extending fasteners into a rotor core of a rotor through a component, and employing the fasteners to balance the rotor and/or mechanically support the component. Other embodiments include apparatuses, systems, devices, hardware, methods, and combinations for electrical rotor machines. Further embodiments, forms, features, aspects, benefits, and advantages of the present application will become apparent from the description and figures provided herewith.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims benefit of U.S. Provisional Patent Application No. 61/800,646 filed Mar. 15, 2013, entitled HIGH SPEED INDUCTION MOTOR ROTOR, which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to electrical rotor machines, and in particular, high-speed induction machines such as high speed induction motors and/or generators. 
       BACKGROUND 
       [0003]    Induction rotor machines, such as induction motors and generators, are employed in a wide variety of machines and systems. The structural integrity and balancing of induction rotors remains an area of interest. Some existing systems have various shortcomings, drawbacks, and disadvantages relative to certain applications. Accordingly, there remains a need for further contributions in this area of technology. 
       SUMMARY 
       [0004]    One embodiment of the present invention includes a unique electrical machine having a plurality of fasteners extending only partially into a rotor core of an induction rotor through a short circuit ring. One embodiment of the present invention includes a unique method of assembling an electrical rotor machine, including extending fasteners into a rotor core of an induction rotor through a component. Other embodiments include apparatuses, systems, devices, hardware, methods, and combinations for electrical rotor machines. Further embodiments, forms, features, aspects, benefits, and advantages of the present application will become apparent from the description and figures provided herewith. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views, and wherein: 
           [0006]      FIG. 1  schematically depicts some aspects of a non-limiting example of an electrical rotor machine in accordance with an embodiment of the present invention. 
           [0007]      FIG. 2  depicts some aspects of a non-limiting example of a rotor of an electrical rotor machine in accordance with an embodiment of the present invention. 
           [0008]      FIG. 3  is a cross-sectional view of the rotor of  FIG. 2 . 
           [0009]      FIG. 4  is a partial cross-section illustrating some aspects of a non-limiting example of a rotor for an electrical rotor machine in accordance with an embodiment of the present invention. 
           [0010]      FIG. 5  is a partial cross-section illustrating some aspects of a non-limiting example of a rotor for an electrical rotor machine in accordance with another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    For purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings, and specific language will be used to describe the same. It will nonetheless be understood that no limitation of the scope of the invention is intended by the illustration and description of certain embodiments of the invention. In addition, any alterations and/or modifications of the illustrated and/or described embodiment(s) are contemplated as being within the scope of the present invention. Further, any other applications of the principles of the invention, as illustrated and/or described herein, as would normally occur to one skilled in the art to which the invention pertains, are contemplated as being within the scope of the present invention. 
         [0012]    In one aspect, the present invention pertains to electrical machines, i.e., electrical rotor machines, such as electric induction motors and/or generators, and particularly, but not exclusively, to electrical machine rotors, e.g., for use in such machines, with improved mass balancing features and/or improved structural features. An induction rotor may include coated steel layers (e.g., a lamination rotor), a squirrel cage, and a shaft. The squirrel cage may include a number of conductors, e.g., aligned along the axis of the rotor or aligned at an angle to the axis of the rotor; and a short-circuit ring or shorting ring, e.g., at each end of the rotor. The short-circuit rings contact the conductors at both ends of the rotor. Squirrel cages may be made, for example, by casting aluminum into the rotor core, although other manufacturing techniques may be employed. Aluminum is often used for the squirrel cage because of its good electrical conductivity. However, the mechanical properties of aluminum are a tradeoff to its electrical conductivity, as aluminum is typically weaker than other metals/alloys having lesser conductivity. 
         [0013]    In addition to electrical machines and electrical machine rotors having improved balance features and/or improved short-circuit rings or support for short-circuit rings, aspects of the present invention include methods of balancing a rotor of an electrical machine, and methods of supporting the short-circuit ring to effectively improve the mechanical strength of the short-circuit ring. In some embodiments, the aforementioned methods may be combined. Although relating to electrical machines, the invention has particular applicability to, but is not limited to, high speed electrical machines, such as high-speed induction rotors. 
         [0014]    At high speeds, the short-circuit ring of an induction rotor is highly mechanically strained during the operation of the motor. In one aspect of the invention, the short-circuit ring is supported by fasteners, e.g., pins or bolts attached to the rotor. These fasteners may also be utilized as fastening mechanisms for adding and/or removing balancing mass. The fasteners may be attached to the rotor core, through the short-circuit ring. The size of the holes in the short-circuit ring relative to the size of the portion of the fastener disposed within the short-circuit ring may be optimized for improved mechanical support of the short-circuit ring without adding critical sources of thermal stress (e.g., between the different materials of the rotor). The mechanical capacity of a rotor is an important design issue in high-speed motors, as the forces exerted on the rotor can be great. The mechanical capacity of the short-circuit rings is also an important design feature of high-speed rotors, due to the mechanical properties of aluminum. In addition to mechanically induced strain, an aluminum short-circuit ring is also exposed to thermal strain, resulting from mechanical contact between the rotor and short-circuit ring, and the difference in thermal expansion coefficients between the short-circuit ring and the rotor core, e.g., a laminated rotor core. Aluminum has a relatively small Young&#39;s modulus (approximately 70 GPa) and a small yield stress value (approximately 40-120 MPa—depending on the fabrication process). Aluminum is also sensitive to fatigue degradation as it deforms plastically relatively easily by both fast-rate and slow-rate strains. Accordingly, short-circuit rings of high-speed induction rotors may be exposed to large mechanical loads, and may be easily degraded or broken by high-speed rotation. 
         [0015]    A rotor of an induction electrical machine, such as a motor and/or generator, may be mass compensated and balanced for improved rotation about the axis of the shaft and for reduced loading on the bearings. This may be done, for example, by either adding or removing mass, e.g., at one or both of the rotor ends. High-speed motors preferably receive more accurate mass balancing than conventional low-speed motors. However, an accurate mass compensation/balance is difficult, in practice, for many reasons. In addition, the shape and the mechanical strength of the short-circuit rings impose additional challenges, e.g., because they are made of aluminum, and e.g., cover a large portion of the rotor ends. 
         [0016]    Some aspects of the present invention ease the process of mass balancing by adding additional mass to desired locations on the rotor rather than removing mass from a solid short-circuit ring, and by removing mass by shortening removable pins and/or bolts rather than removing mass from the solid short-circuit ring. In some aspects of the present invention, mechanical support may also or alternatively be added to the short-circuit rings, e.g., via the use of pins and/or bolts. 
         [0017]    Referring to the drawings, and in particular  FIG. 1 , some aspects of a non-limiting example of an electrical machine  10  in accordance with an embodiment of the present invention are schematically depicted. In one form, electrical machine  10  is an induction motor. In other embodiments, electrical machine  10  may take other forms. Electrical machine  10  includes a casing  12 , a stator  14 , a shaft  16 , an induction rotor  18  and bearings  20 . Casing  12  is configured to house stator  14 , shaft  16 , induction rotor  18  and bearings  20 . In one form, bearings  20  are mounted in casing  12 , e.g., an end plate of casing  12 . In other embodiments, bearings  20  may be mounted and coupled to casing  12  via one or more other structures. Bearings  20  are structured to radially support induction rotor  18 , and to react inductor rotor  18  thrust loads. 
         [0018]    Stator  14  includes a plurality of stator windings  22  and a stator core  24 . Induction rotor  18  is disposed radially inward of stator core  24 . In one form, stator  14  circumferentially encompasses induction rotor  18 , although in other embodiments, stator  14  may only partially encompass induction rotor  18  e.g., in the form of segments disposed circumferentially around stator  14 . Induction rotor  18  is configured for electromagnetic cooperation with stator  14 , e.g., to convert electrical power into mechanical power for delivery via shaft  16  in some embodiment and/or convert mechanical power received from shaft  16  into electrical power for delivery via stator  14  in other embodiments. 
         [0019]    Referring now to  FIGS. 2 and 3 , some aspects of a non-limiting example of induction rotor  18  in accordance with an embodiment of the present invention are schematically illustrated. Rotor  18  includes a rotor core  26 , a plurality of conductors  28  circumferentially spaced apart about rotor core  26 , and short-circuit shorting rings  30 . Inductor rotor  18  rotates about an axis of rotation  32 . In one form, rotor core  26  is a laminated rotor core formed of a plurality of laminations of, e.g., steel or iron-based sheets having nonconductive coatings, which are stacked and affixed together to form the rotor. In other embodiments, rotor core  26  may take other forms. In the illustrated example, two short-circuit rings are depicted. It will be understood that in other embodiments, any number of short-circuit rings may be employed. Short-circuit rings  30  are in electrical communication with each of conductors  28 . In one form, short-circuit rings  30  and conductors  28  are integral, e.g., integrally formed about rotor core  26 , such as by casting. In other embodiments, short-circuit rings  30  may be brazed to conductors  28 , welded to conductors  28  or otherwise mechanically attached or affixed to conductors  28 , including via the use of pins, bolts, or other fasteners. Although described using the term “ring,” and depicted in the FIGS. generally in the shape of a ring, it will be understood that short-circuit rings  30  may be of any suitable shape. 
         [0020]    Referring to  FIGS. 4 and 5 , some aspects of a non-limiting example of induction rotor  18  in accordance with an embodiment of the present invention are schematically illustrated. In the embodiments of  FIGS. 4 and 5 , rotor core  26  includes a plurality of holes  34 . In one form, holes  34  are formed on each end of rotor core  26 . In other embodiments, holes  34  may be formed on only a single end of rotor core  26 . Holes  34  extend into rotor core  26 , e.g., in an axial direction parallel to the axis of rotation  32 . Holes  34  are spaced apart from conductors  28 . In one form, holes  34  extend only partially into rotor core  26 . In other embodiments, holes  34  may extend through the axial length of rotor core  26 . Each short-circuit ring  30  includes a plurality of holes  36  that extend therethrough, e.g., in the axial direction, and which are aligned with holes  34  of rotor core  26 . 
         [0021]    Installed into and disposed at least partially in holes  34  and  36  are a plurality of fasteners  38 . In one form, by virtue of the locations of holes  34  and  36 , fasteners  38  are spaced apart from conductors  28 . In other embodiments, some or all of holes  34  and  36  may be partially or fully aligned with and formed into conductors  28 . In such embodiments, a corresponding some or all fasteners  38  may be in electrical communication with respective conductors  28 . In one form, fasteners  38  are formed of a ferrous material, e.g., in order to reduce or eliminate changes in the magnetic properties of induction rotor  18  stemming from the provision of fasteners  38 , holes  34  and/or holes  36 . In other embodiments, other materials may be used in addition to or in place of a ferrous material. In various embodiments, fasteners  38  may take one or more of a plurality of forms. For example, fasteners  38  may be pins and/or bolts. Fasteners  38  include a shank  40 . In one form, shanks  40  and holes  36  are sized to yield a gap  42  therebetween. Gap  42  extends radially outward from axis of rotation and  32 , and in various may also extend in other directions. In one form, gap  42  is disposed between a surface  44  of holes  36  and a surface  46  of shanks  40 , wherein surfaces  44  and  46  are those surfaces of respective holes  36  and shanks  40  that would come into closer proximity with each other under conditions of increasing rotor speed and/or temperature (and in some embodiments, other factors, as well) as would cause short-circuit ring  30  to radially expand at a greater rate than rotor core  26 . In various embodiments, gap  42  may extend fully or partially around the circumference of shank  40  and hole  36 . In one form, gap  42  is sized, e.g., via the respective geometric sizes of shanks  40  and holes  36 , to prevent a mechanical contact or interference, at least in the radial direction, between holes  36  and shanks  40  under selected conditions. In one form, the selected conditions include maximum operating speed of induction rotor  18  coupled with the maximum operating temperature of induction rotor  18 , e.g., as measured in short-circuit ring  30  and the end portions of rotor core  26  and conductors  28  that are adjacent to short-circuit ring  30 . By preventing the aforementioned mechanical interference, undesirable stress fields within short-circuit ring  30  may be avoided, and fretting damage to short-circuit ring  30  may be avoided. In other embodiments, the size and geometry of gap  42  may vary with the needs of the application. In still other embodiments, a gap may not be formed between shank  40  and holes  36 . 
         [0022]    In some embodiments, fasteners  38  include a head  48  having a clamping surface  50  that is operative to engage a corresponding clamping surface  52  on short-circuit ring  30  for transmitting clamping loads into short-circuit ring  30  to clamp short-circuit ring  30  against rotor core  26  and/or conductors  28  to thereby support short-circuit ring  30 . In some embodiments, fasteners  38  are used to clamp short-circuit ring  30  against rotor core  26  or against conductors  28 , instead of clamping short-circuit ring  30  against both rotor core  26  and against conductors  28 . By clamping short-circuit ring  30  against rotor core  26  and/or conductors  28 , short-circuit ring  30  centrifugal loads are transferred to the corresponding rotor core  26  and/or conductors  28 , e.g., via friction at the mechanical interface between short-circuit ring  30  and rotor core  26  and/or conductors  28 . This effectively strengthens short-circuit ring  30  by reducing its centrifugally induced stresses, which thus increases the life of short-circuit ring  30 . 
         [0023]    Fasteners  38  include a retention feature  54 . Holes  34  include a retention feature  56 . Retention features  54  and  56  are configured to engage each other to retain fasteners  38  in holes  34 . In some embodiments, retention feature  54  and  56  are configured to engage each other sufficiently to pretension fasteners  38  and clamp short-circuit ring  30  against rotor core  26  and/or conductors  28 . The amount of pretension may vary with the needs of the application. In one form, retention features  54  and  56  are threads. In some embodiments, retention feature  54  and  56  may be geometric features, such as cylinders and corresponding cylindrical openings, respectively, that form an interference fit when engaged, e.g., upon installation of fasteners into holes  34 . In other embodiments, retention features  54  and  56  may take other forms. 
         [0024]    During the operation of electrical machine  10 , induction rotor  18  may achieve high rotational speeds, which imparts centrifugal loading into short-circuit rings  30 . In order to reduce imbalance loads and wear on bearings  20 , it is desirable to mass compensate induction rotor  18  to balance induction rotor  18 , e.g., by adding balance mass at selected locations to induction rotor  18  or by removing balance mass from selected locations on induction rotor  18 . Although it may be possible to balance induction rotor  18 , for example, by selectively removing material from one or both short-circuit rings  30 , e.g., by grinding or another machining process, doing so may be time consuming, expensive (particularly when too much material is inadvertently removed), and may result in, for example, the formation of crack initiation sites, stress risers, undesirable reductions in cross-sectional area, and potentially degraded material properties in the vicinity of the removed material e.g. by virtue of a heat affected zone generated by high temperatures stemming from the use of an improper, worn or otherwise unsuitable or undesirable machining implement. Accordingly, in some embodiments of the present invention, fasteners  38  are used for balancing induction rotor  18 . In some embodiments, fasteners  38  may be used for both clamping short-circuit ring  30  to rotor core  26  and/or conductors  28  and for balancing induction rotor  18 . In other embodiments, fasteners  38  may be used only for balancing induction rotor  18  or only for clamping short-circuit ring  30  to rotor core  26  and/or conductors  28 . 
         [0025]    In some embodiments, fasteners  38  may be used to attach a balance weight  58  at selected radial and circumferential locations on induction rotor  18 , e.g., wherein the balance weight  58  is retained by head  48  of fasteners  38 , as depicted in  FIG. 4 . In other embodiments, balance weight  58  may take other forms, and/or may be retained by head  48  or may be retained by other means and/or may be disposed in other locations. In other embodiments, fasteners  38  may include a balance portion  60 , e.g., extending from shank  40 . For example, in some embodiments, all or part of balance portion  60  may be removed from selected fasteners  38 , e.g., via grinding or other machining, in order to balance induction rotor  18 , an example of which is depicted in  FIG. 5 , which illustrates two fasteners  38 , wherein the upper fasteners  38  includes a balance portion  60  that has been machined to remove some of its mass, whereas the lower fastener  38  balance portion retains its full length. In other embodiments, fasteners  38  may be manufactured with balance portions  60  having various masses. In such embodiments, the balancing of induction rotor  18  may include selecting desired fasteners  38 , based on mass, and installing the desired fasteners  38  at the requisite hole  34 ,  36  locations to achieve the desired balance. In these embodiments, fine-tuning may be achieved by grinding the desired fasteners to remove additional mass from the balance portions  60 . Although  FIG. 5  illustrates balance portion  60  as being disposed within rotor core  26 , it will be understood that in various embodiments, balance portion  60  may be disposed at any convenient location. 
         [0026]    Embodiments of the present invention include electrical machine, comprising: a stator; a shaft configured to rotate about an axis of rotation, wherein said axis of rotation defines an axial direction; an induction rotor for electromagnetic cooperation with the stator, wherein the induction rotor is coupled to the shaft and includes: a rotor core extending in the axial direction and having a plurality of first holes; and a squirrel cage having a plurality of conductors and a short-circuit ring in electrical communication with the plurality of conductors and having a plurality of second holes spaced apart from the conductors; wherein the induction rotor includes a plurality of fasteners extending through the second holes in the short-circuit ring, extending into the first holes only partially into the rotor core, and cooperating to balance the induction rotor and/or mechanically support the short-circuit ring; and a bearing structured to radially support the induction rotor via the shaft. 
         [0027]    In a refinement, the fasteners are configured to clamp the short-circuit ring against the rotor core and/or the conductors. 
         [0028]    In another refinement, the first holes include a first threaded portion; and the fasteners include a second threaded portion in threading engagement the first threaded portion. 
         [0029]    In yet another refinement, the fasteners include a head configured to axially engage the short-circuit ring for clamping the short-circuit ring to the rotor core and/or the conductors. 
         [0030]    In still another refinement, the fasteners include a first damping surface; the short-circuit ring includes a second clamping surface in mating engagement with the first clamping surface; and the first clamping surface engages the second damping surface to clamp the short-circuit ring against the rotor core and/or the conductors. 
         [0031]    In yet still another refinement, the fastener includes a shank, and wherein the second holes and the shank form a gap therebetween. 
         [0032]    In a further refinement, the gap extends at least in a radial direction. 
         [0033]    In a yet further refinement, at least one of the fasteners is configured to secure a balance mass to the induction rotor. 
         [0034]    In a still further refinement, the balance mass is a washer. 
         [0035]    In a yet still further refinement, wherein the balance mass is a portion of the at least one fastener. 
         [0036]    In an additional refinement, the fasteners are configured to clamp the short-circuit ring against the rotor core and/or the conductors, and wherein at least one of the fasteners is configured to secure a balance mass to the induction rotor. 
         [0037]    In another refinement, wherein the fasteners have an interference fit with the first holes in the rotor core. 
         [0038]    Embodiments of the present invention include a method of assembling an electrical machine, comprising: forming a rotor having a rotor core and a component disposed adjacent a face of the rotor core; forming first holes in a rotor core, wherein the first holes extend at least partially into the rotor core; forming second holes in the component; extending fasteners through the second holes and into the first holes, only partially into the rotor core; and employing the fasteners to balance the rotor and/or mechanically support the component. 
         [0039]    In a refinement, the method also includes forming threads in the first holes; forming threads on the fasteners; and threadingly engaging the fasteners with the first holes. 
         [0040]    In another refinement, the method also includes forming the first holes and the fasteners to generate an interference fit between the first holes and the fasteners. 
         [0041]    In yet another refinement, the method also includes clamping the component against the rotor core. 
         [0042]    In still another refinement, the method also includes balancing the rotor, wherein the balancing includes securing a balance mass to the rotor with at least one of the fasteners. 
         [0043]    In yet still another refinement, the balancing includes removing a portion of at least one of the fasteners and/or selecting for installation into the rotor a fastener having a lesser mass than another fastener. 
         [0044]    In a further refinement, the method also includes clamping the component against the rotor core; and balancing the rotor, wherein the balancing of the rotor includes securing a balance mass to the rotor with at least one of the fasteners and/or removing a portion of at least one of the fasteners. 
         [0045]    Embodiments of the present invention include an electrical machine, comprising: a stator; a shaft configured to rotate about an axis of rotation, wherein said axis of rotation defines an axial direction; an induction rotor coupled to the shaft, wherein the induction rotor includes a squirrel cage having a plurality of conductors and a short-circuit ring in electrical communication with the plurality of conductors, wherein the induction rotor includes a rotor core extending along the axis of rotation; a bearing structured to radially support the induction rotor via the shaft; and means for supporting the short-circuit ring and/or balancing the induction rotor. 
         [0046]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment(s), but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as permitted under the law. Furthermore it should be understood that while the use of the word preferable, preferably, or preferred in the description above indicates that feature so described may be more desirable, it nonetheless may not be necessary and any embodiment lacking the same may be contemplated as within the scope of the invention, that scope being defined by the claims that follow. In reading the claims it is intended that when words such as “a,” “an,” “at least one” and “at least a portion” are used, there is no intention to limit the claim to only one item unless specifically stated to the contrary in the claim. Further, when the language “at least a portion” and/or “a portion” is used the item may include a portion and/or the entire item unless specifically stated to the contrary.