Abstract:
In accordance with one embodiment, the present technique provides a bushing that is configured to electrically and mechanically couple a conductor bar of a rotor assembly to an end ring of the rotor assembly. The exemplary bushing has an interior surface that is configured to abut against the conductor bar and an exterior surface that is configured to abut the perimetric surface of an end slot. Advantageously, the bushing, because of a good fit in the end slot and around the conductor bar, provides a good electrical connection between the conductor bar and the end ring. Moreover, the exemplary bushing also provides interferences fits that at least partially secure the end ring to the rotor core.

Description:
BACKGROUND  
       [0001]     The present technique relates generally to the field of electric motors and particularly to rotors for induction motors, such as a fabricated squirrel cage rotor, for example.  
         [0002]     Electric motors of various types are commonly found in industrial, commercial and consumer settings. In industry, such motors are employed to drive various kinds of machinery, such as pumps, conveyors, compressors, fans and so forth, to mention only a few. Conventional alternating current (ac) electric motors may be constructed for single- or, multiple-phase power and are typically designed to operate at predetermined speeds or revolutions per minute (rpm), such as 3600 rpm, 1800 rpm, 1200 rpm and so on. Such motors generally include a stator comprising a multiplicity of windings surrounding a rotor, which is supported by bearings for rotation in the motor frame. Typically, the rotor comprises a core formed of a series of magnetically conductive laminations arranged to form a lamination stack caped at each end by electrically conductive end rings. Additionally, typical rotors include a series of conductors that are formed of a nonmagnetic, electrically conductive material and that extend through the rotor core. These conductors are electrically coupled to one another via the end rings, thereby forming one or more closed electrical pathways.  
         [0003]     In the case of ac motors, applying ac power to the stator windings induces a current in the rotor, specifically in the conductors. The electromagnetic relationships between the rotor and the stator cause the rotor to rotate. The speed of this rotation is typically a function of the frequency of ac input power (i.e., frequency) and of the motor design (i.e., the number of poles defined by the stator windings). A rotor shaft extending through the motor housing takes advantage of this produced rotation and translates the rotor&#39;s movement into a driving force for a given piece of machinery. That is, rotation of the shaft drives the machine to which it is coupled.  
         [0004]     Often, design parameters call for relatively high rotor rotation rates, i.e., high rpm. By way of example, a rotor within an induction motor may operate at rates as high as 10,000 rpm, and beyond. Based on the diameter of the rotor, operation at such rpm translates into relatively high surface speeds on the rotor. Again, by way of example, these rotor surface speeds can reach values of 100 meters per second (mps), and beyond. During operation, particularly during high-speed operation, produced centripetal and centrifugal forces strain various components of the rotor assembly. For example, if not properly accounted for, the centripetal and centrifugal forces developed in the end ring may cause the end ring to prematurely malfunction. Moreover, these centripetal and centrifugal forces may, overtime, negatively affect the mechanical integrity of the rotor, leading to a lessening of performance and, in certain instances, failure of the motor. Undeniably, loss of performance and motor failure are events that can lead to unwanted costs and delays.  
         [0005]     In traditional motors, the end ring and the electrical conductors extending through the rotor core are mechanically and electrically coupled via a brazing process By way of example, the conductor and the end ring may be brazed together using a hard brazing rod with a high melting point. Unfortunately, heat generated during a brazing process can negatively affect the material of the end rings and/or the conductor. For example, developed heat can cause annealing in the end rings and/or conductors. In turn, such annealing reduces the yield strength of the annealed material, thereby increasing the likelihood of damage due to centripetal and centrifugal forces within the rotor, for instance.  
         [0006]     There exists a need, therefore, for a method and apparatus for improved rotor construction and integrity.  
       BRIEF DESCRIPTION  
       [0007]     According to one exemplary embodiment, the present technique provides a bushing for use with a motor rotor. The exemplary bushing includes a body that has an interior section, which is configured to receive a portion of a conductive member, and an exterior section. In the exemplary bushing, the interior section abuts the conductive member, and the exterior section abuts the end slot of an end member. Accordingly, the exemplary body at least partially secures the end member to the rotor core and electrically couples the conductive member to the end member. Advantageously, the exemplary bushing facilitates a mechanical connection between the end member and conductive member that secures the end member to the rotor core. Moreover, the securing member electrically couples the conductive member to the end member. Accordingly, the exemplary securing member facilitates electrical and mechanical connections of various components of the rotor without the introduction of relatively high amounts of heat, for instance.  
         [0008]     In accordance with another embodiment, the present technique provides a rotor for an electric motor. The rotor comprises a rotor core, which includes a plurality of rotor slots extending therethrough, and first and second end members disposed on opposite ends of the rotor core. In the exemplary rotor, each end member has a plurality of end slots that extend therethrough. These end slots cooperate with the rotor slots to define a plurality of rotor channels that extend through both the rotor core and the first and second end members. These exemplary rotor channels each supports a conductive member, which is disposed in and extends through the rotor channel. To mechanically secure the end members with respect to the rotor core, and to electrically couple the conductive members to the end member, the exemplary rotor includes securing members that are disposed in each of the end slots and at least partially about a conductive member. Accordingly, the exemplary securing member forms an interference fit in cooperation with the conductive member and in cooperation with the end slot of the end member, thereby mechanically securing the end member to the rotor core and electrically coupling the conductive member to the end member. Advantageously, the exemplary securing member facilitates retention of the mechanical integrity of the conductive member and the end member that, by way of example, may be lost due to heat produced during a brazing process, for instance. In turn, retention of the mechanical integrity of the various rotor components facilitates an increase in the integrity of the rotor during high speed operation and, as such, reduces the likelihood of failure due to centripetal and centrifugal forces produced during operation, for instance. In other words, the exemplary embodiments facilitate the construction of a more robust rotor and motor.  
         [0009]     In accordance with another exemplary embodiment, the present technique provides a method of manufacturing a rotor. The method includes the act of aligning an end member with a rotor core such that a rotor slot extending through the rotor core cooperates with an end slot in the end member to form a rotor channel that extends through the rotor core and the end member. The exemplary method also includes disposing a conductive member in the rotor channel. Additionally, the exemplary method includes disposing a securing member in the end slot and at least partially about the conductive member such that the securing member electrically couples the end member and the conductive member. Advantageously, the exemplary securing member abuts against the end slot and the conductive member, thereby creating a pair of interference fits. These interference fits, in the exemplary method, mechanically secure the end member to the rotor core. 
     
    
     DRAWINGS  
       [0010]     These and other features, aspects and advantages of the present technique will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:  
         [0011]      FIG. 1  is a perspective view of an induction motor, in accordance with an embodiment of the present technique;  
         [0012]      FIG. 2  is a partial cross-sectional view of the motor of  FIG. 1  along line  2 - 2 ;  
         [0013]      FIG. 3  is an exploded perspective view of a rotor, in accordance with an embodiment of the present technique;  
         [0014]      FIG. 4  is a cross-sectional view of an end member of the rotor of  FIG. 3  along line  4 - 4 ;  
         [0015]      FIG. 5  is a detail, perspective and cross-sectional view of a portion of rotor assembly, in accordance with an embodiment of the present technique; and  
         [0016]      FIG. 6  is a flow chart representative of an exemplary process for manufacturing a rotor, in accordance with an embodiment of the present technique.  
     
    
     DETAILED DESCRIPTION  
       [0017]     As discussed in detail below, embodiments of the present technique provide apparatus and methods related to rotors for induction motors. Although the following discussion focuses on induction motors, the present technique also affords benefits to a number of applications in which rotor integrity and design is a concern. Indeed, the present technique is applicable to induction generators, among other types of device constructions. Accordingly, the following discussion provides exemplary embodiments of the present technique and, as such, should not be viewed as limiting the appended claims to the embodiments described.  
         [0018]     Additionally, as a preliminary matter, the definition of the term “or” for the purposes of the following discussion and the appended claims is intended to be an inclusive “or.” That is, the term “or” is not intended to differentiate between two mutually exclusive alternatives. Rather, the term “or” when employed as a conjunction between two elements is defined as including one element by itself, the other element itself, and combinations and permutations of the elements. For example, a discussion or recitation employing the terminology “‘A’ or ‘B’” includes: “A” by itself, “B” by itself, and any combination thereof, such as “AB” and/or “BA.” 
         [0019]     Turning to the drawings,  FIG. 1  illustrates an exemplary electric motor  10 . The exemplary motor  10  is an induction motor housed in a motor housing and includes a frame  12  capped at each end by end caps  14  and  16 , respectively. The frame  12  and the endcaps  14  and  16  may be formed of various materials, such as cast iron, steel, aluminum or any other suitable structural material. Advantageously, the end caps  14  and  16  may include mounting and transportation features, such as the illustrated mounting feet  18  and eyehooks  20 . Those skilled at the art will appreciate in light of the following description that a wide variety motor configurations and devices may employ the techniques outlined below.  
         [0020]     To induce rotation of the exemplary rotor, current is routed through stator windings  32  disposed in the stator. (See  FIG. 2 .) These stator windings are electrically interconnected to form groups, which are, in turn, interconnected in a manner generally known in the pertinent art. The stator windings are further coupled to terminal leads, which electrical connect the stator windings to an external power source  22 . By way of example, the external power source  22  may comprise an ac pulse with modulated (PWM) inverter. As yet another example, the external power source  22  may comprise a single-phase or a three-phase ac power source. In any event, a conduit box  24  houses the electrical connection between the terminal leads and the external power source  22  for the exemplary motor  10 . The exemplary conduit box  24  is formed of metal or plastic material and, advantageously, provides access to certain electrical components of the motor  10 .  
         [0021]     When electrical current from the external power source  22  is routed through the stator windings, a magnetic field that induces rotation of the rotor is produced. Specifically, a magnetic field is produced and, resultantly, current is induced the rotor bars  44  (see  FIG. 3 ). This induced current generates another magnetic field, and the interaction between these magnetic fields causes rotation of the rotor. A rotor shaft  26 , which is coupled to the rotor, rotates in conjunction with the rotor. That is, rotation of the rotor translates into a corresponding rotation of the rotor shaft  26 . To support and facilitate rotation of the rotor and the rotor shaft  26 , the exemplary motor  10  includes bearing sets that are carried within the end caps  14  and  16 , respectively. (See  FIG. 2 .) As will be appreciated by those of ordinary skill in the art, the rotor shaft  26  may couple to any number of drive machine elements, thereby transmitting torque to the given drive machine element. By way of example, machines such as pumps, compressors, fans, conveyers and so forth, may harness the rotational motion of the rotor shaft  26  for operation.  
         [0022]      FIG. 2  provides a partial cross-section view of the exemplary motor  10  of  FIG. 1  along line  2 - 2 . For the sake of simplicity, only the top portion of the motor is illustrated, as the structure of the exemplary motor  10  is essentially mirrored along it&#39;s centerline. The exemplary motor  10  includes a plurality of stator laminations  28  that are juxtaposed and aligned with respect to one another to form a stator core  30 . Each exemplary stator lamination  28  includes features that cooperate with features of adjacent stator laminations  28  to form cumulative features that extend the length of the stator core  30 . For example, each stator lamination  28  has an aperture the extends through the lamination and that cooperates with apertures of adjacent stator laminations form slots that extend the length of the stator core  30  and that are configured to receive one or more turns of a coil winding, which are illustrated as coil ends  32  in  FIG. 2 . Each stator lamination  28  also has a central aperture, which, when aligned with the central apertures of adjacent stator laminations  28 , forms a contiguous rotor chamber  34  that extends through the stator core  30 .  
         [0023]     In the exemplary motor  10 , a rotor  36  resides within this rotor chamber  34 . Similar to the stator core  30 , the exemplary rotor  36  is formed of a plurality of rotor laminations  38  that are aligned and adjacently placed with respect to one another. Thus, the rotor laminations  38  cooperate to form the contiguous rotor core  40 . The exemplary rotor  36  also includes end members, such as the illustrated end rings  42 , that are disposed on opposite ends of the rotor core  40 . These end rings  42  cooperate with other components to secure the rotor laminations  38  with respect to one another, as discussed further below. The exemplary rotor  36  also includes electrically conductive members, such as the illustrated conductor bars  44 , that extend the length of the rotor  36 . In the exemplary motor  10 , the end rings  42 , in cooperation with securing members  46  disposed in end slots (see  FIG. 3 ) of the end rings  42 , electrical couple the conductor bars to the end ring  42  and, as such, one another. To facilitate electrical communications, the exemplary conductor bars  44 , the exemplary end rings  42  and the exemplary securing members  46  are formed of non-magnetic, yet electrically conductive materials. Indeed, the conductor bars  44  and the exemplary end rings  42  and/or the securing members  46  may be formed of a high-strength material, thereby facilitating use in higher stress applications.  
         [0024]     To support the rotor  36  and the rotor shaft  26 , the exemplary motor  10  includes bearing sets  48  and  50  that are each disposed in the respective end caps  14  and  16  and that are each secured to the rotor shaft  26 . The exemplary bearings sets  48  and  50  facilitate rotation of the rotor shaft  26  and rotor  36  within the stator core  30 . By way of example, the exemplary bearing sets  48  and  50  have a ball bearing construction; however, the bearing sets  48  and  50  may have a sleeve bearing construction, among other types of bearing constructions. Advantageously, the end caps  14  and  16  include features, such as the illustrated inner bearing caps  52  that secure the bearing sets  48  and  50  within their respective end caps  14  and  16 . These exemplary inner bearing caps  52  include fasteners, such as bolts or other types of suitable fasteners, that are releasibly secured to the end caps  14  and  16 . The bearing sets  48  and  50  receive and transfer the radial and thrust loads produced by the rotor shaft  26  and the rotor  36  during operation of the motor to the motor housing, i.e., the frame  12  and the end caps  14  and  16 .  
         [0025]     Each exemplary bearing set  48  and  50  includes an inner race  54  disposed circumferentially about the rotor shaft  26 . The fit between the inner races  54  and the rotor shaft  26  causes the inner races  54  of each bearing set to rotate in conjunction with the rotor shaft  26 . Each exemplary bearing set  48  and  50  also includes an outer race  56  and rolling elements  58 , which are disposed between the inner race  54  and the outer race  56 . The rolling elements  58  facilitate rotation of the inner races  54 , while the outer races  56  remain stationarlily mounted with respect to the end caps  14  and  16 . Thus, the bearing sets  48  and  50  facilitate rotation of the rotor shaft  26  and the rotor  36  and provide a support structure for the rotor  36  and rotor shaft  26  within the motor housing. In the exemplary motor  10 , a lubricant coats the rolling elements  58  and races  54  and  56  of each bearing set  48  and  50 , thereby providing a separating film between the various components of the bearing sets. Advantageously, this lubricant mitigates the likelihood of seizing, galling, welding, excessive friction and/or excessive wear, to name but a few adverse effects.  
         [0026]      FIG. 3  presents an exploded view of an exemplary rotor  36 , which includes a series of rotor laminations  38  disposed between a pair of end rings  42 . To maintain symmetry, the rotor laminations  38  and the end rings  42  are disposed concentrically along an axial centerline  60  of the rotor  36 . That is, the axial centerline  60  of the rotor  36  passes through the center of each of the end rings  42  and each of the rotor laminations  38 . Accordingly, the axial centerline  60  defines an axis of rotation for the assembled rotor  36 .  
         [0027]     Focusing on the exemplary rotor laminations  38 , each rotor lamination  38  presents a generally circular cross-section and is formed of a magnetically conductive material, such as an electrical steel. Extending from end-to-end, i.e., transverse to the cross-section, each rotor lamination  38  includes features that cooperate with corresponding features of adjacent rotor laminations  38  to form cumulative features that extend the length of the rotor core  40 . For example, each rotor laminations  38  has a circular shaft aperture  62  that is located in the center of the rotor lamination  38  and that extends from end-to-end. The shaft apertures  60  of adjacent rotor laminations  38  cooperate to form a shaft chamber configured to receive the rotor shaft  26  (See  FIG. 2 ) therethrough. Additionally, each rotor lamination  38  has a series of rotor slots  64  that are concentrically arranged with respect to one another and about the centerline  60 . In the illustrated rotor laminations  38 , thirty-six rotor slots  64  are arranged in a slot pattern and are at equiangular and symmetric positions with respect to one another. As will be appreciated by one of ordinary skill in the art in view of this discussion, other slot patterns and arrangements may also be envisaged. For example, the rotor laminations  38  may have twenty-four rotor slots that are arranged in any number of configurations. When the rotor laminations  38  are assembled with respect to one another the rotor slots cooperate to form rotor channels (See  FIG. 2 ) that extend through the rotor core  40 . These rotor channels are configured to receive electrically conductive and non-magnetic members (i.e., conductor bars  44 ) therethrough.  
         [0028]     The end rings  42 , which are disposed on opposite ends of the rotor core  40 , also present features that are advantageous to the rotor  36 . For example, each exemplary end ring  42  has a series of end slots  66  that are arranged concentrically with respect to one another and that extend through the end ring  42 . (See  FIG. 4 ). As illustrated, each exemplary end ring  42  has thirty-six end slots  66  that are arranged in a slot pattern that corresponds with the slot pattern of the rotor laminations  38 . Accordingly, when aligned and assembled, the end slots  66  and the rotor slots  64  cooperate to define a plurality of rotor channels (see  FIG. 2 ) that extend through the rotor core  40  and the end rings  42  and that receive the conductor bars  44  therethrough. (See  FIG. 2 .)  
         [0029]     As illustrated in  FIG. 5 , the end rings  42  are secured to the rotor core  40  by exemplary securing members  46  that are each disposed in an end slot  66  and circumscribed about a conductive member  44 . In the exemplary embodiment, each securing member  46  has a cylindrical body that includes an inner surface  70  that abuts against the conductor bar  44  and an outer surface  72  that abuts against the perimetric surface  73  of the end slot  66 . However, as will be appreciated for those of ordinary skill in the art in view of the present description, the securing member  46  may present a number of shapes and profiles. For example, the body need not be limited to a cylindrical shape. Additionally, the body may comprise a single piece in abutment with both the conductor bar  44  and the end slot  66  or may comprise an assembly of pieces that abuts the conductor bar  44 , in turn, the perimeter of the end slot  66 .  
         [0030]     The securing members  46 , by way of example, establish a series of interference fits between the inner surface  72  and the conductor bar  44  as well as between the outer surface  74  and the perimetric surface  73  of the end slot  66 . In turn, these interference fits, in cooperation with interference fits on the opposite end ring  42 , restrict movement of the end rings  42  with respect to the rotor core  40  and, as such, secure the end rings  42  to the rotor core  40 . Additionally, the abutment of the exemplary securing member  46  with the conductor bar  44  and the end ring  42  facilitates electrical conductivity between the end ring  42  and the conductor bar  44 . That is, the exemplary securing member  46  electrically couples the conductor bar  44  to the end ring  42 , and, in turn, electrically couples the conductor bars  44  to one another. Advantageously, the interference fits provide a mechanical connection between the conductor bars  44  and the end ring  42 , thereby electrically and physically connecting the end members and conductor bars  44  with respect to one another without affecting the material properties of either structure. To help facilitate the engagement between the securing members  46  and the conductor bars  44 , the interior surface  70  of the exemplary securing member  46  tapers in a manner corresponding to the tapered end  76  of the conductor bar  44 .  
         [0031]     In the exemplary embodiment, the securing member  46  is formed of a malleable and electrically conductive material, such as copper. As one example, the securing member  46  is formed of a copper having a hardness of H0 (as measured in accordance with the standards of the American Society for Testing and Material or ASTM). The securing member  46  may have a hardness rating (i.e., lower yield strength) than the conductors bars  44 , because the securing members  46  are sandwiched between the conductor bars  44  and the end slots  66  and, as such, receive support from these elements of the rotor assembly. Advantageously, the malleability of the securing members  46  facilitates the correction of manufacturing errors and increases acceptable tolerances with respect to the conductor bars  44  and the end members  42  (e.g., end slots  66 ). In other words, the malleable material of the securing members  46  accommodates for dimensional discrepancies between the planned and manufactured components of the rotor, for instance. As an additional benefit, using a material with lower yield strength for the securing members  46 , as compared to the conductor bars  44 , can facilitate a reduction in manufacturing costs, for example.  
         [0032]     With  FIGS. 1-5  in mind,  FIG. 6  diagrammatically illustrates an exemplary process for manufacturing a rotor in accordance with an embodiment of the present technique. The exemplary process includes the act of fabricating the rotor laminations  38 , as is represented by block  80 . By way of example, the rotor laminations  38  may be fabricated via a stamping process, in which a pattern is stamped on a thin sheet of metal blank (e.g., lamination). The exemplary process also includes the act of aligning and arranging the laminations with respect to one another, as represented by block  82 . Once aligned, the rotor laminations  38  cooperate to form the cumulative features of the rotor core  40 , such as shaft chamber discussed above. While the rotor laminations are maintained under compression, end rings members  42  are aligned and arranged with respect to the rotor core  40 , as represented by block  84 . Once aligned, the end slots  66  of the end rings  42  cooperate with the rotor slots  64  to form rotor channels that extend the length axial length of the rotor assembly. As represented by block  86 , the exemplary process also includes the act of disposing the conductor bars  44  into to rotor channels. To secure the end rings  42  to the rotor core  40 , securing members  46  are inserted into the end slots  66  and about the conductor bars  44 , as represented by block  88  of the exemplary process. The securing members  46 , in the exemplary process, are inserted using mechanical assistance, such as a hydraulic press, for example. Upon insertion, the exemplary securing members  46  create interference fits in cooperation with the end slot  66  and the conductor bars  44 , thereby mechanically coupling the end rings  42  to the rotor core  40  and electrically coupling the end rings  42  to the conductor bars  44  and, as such, the conductors bars  44  to one another. Indeed, the inner surface  72  of the retaining member establishes interference fits with the conductor bar  44 , and the outer surface  74  establishes interference fits with the perimetric surface  73  of the end slot  66 . These fits are formed as the retaining member  46  is axially pressed into engagement with the tapered male end  76  of the conductor bar  44 . These interference fits provide the mechanical and electrical coupling for the various components of the rotor and, as such, mitigate the need for the introduction of heat, which is typically used for a brazing process and which can negatively impact structural properties of the rotor. Because the securing members  46  retain the end rings  42  in position with respect to the rotor core  40 , the external compression is removed, as represented by block  90  of the exemplary process.  
         [0033]     While only certain features of the technique have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the technique.