Abstract:
An electric machine and a method of forming a commutator for an electric machine includes forming a commutator assembly including a plurality of commutator bar members linked through a corresponding plurality of bridge elements, rolling the commutator assembly into a commutator form having a substantially continuous, uninterrupted, outer surface, introducing an internal support member that receives an end portion of each of the plurality of commutator bar members into an inner diameter of the commutator form, and separating the plurality of commutator bar members by removing each of the plurality of bridge elements creating a discontinuous outer surface.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    Exemplary embodiments pertain to the art of electric machines and, more particularly, to a method of constructing a commutator for an electric machine and an electric machine having a commutator constructed in accordance with the method. 
         [0002]    Many electric machines include a housing that supports a stator or field. An armature is arranged in the housing and rotates relative to the field. Generally, the armature includes a shaft that supports a commutator and a plurality of armature windings. The commutator is electrically connected to a plurality of armature windings. The commutator is connected to terminals on the housing through a set of brushes. The brushes ride on, and are in electrical contact with, an outer surface of the commutator. Typically, a spring biases the brushes onto the commutator to maintain the electrical contact. 
         [0003]    A commutator typically includes a set of individual contact bars fixed to the rotating shaft of a machine. In a motor, the electrical current flowing through the armature windings via the commutator and brushes interact with a stationary magnetic field produced in the field coil. The interaction of the current and stationary field produces a magnetic force that, in turn, produces a torque on the armature. The torque causes the armature to rotate about an axis defined by the shaft. In a generator, a mechanical torque applied to the shaft creates a motion of the armature windings through the field. Movement of the armature windings in the field induces a voltage that is passed through the commutator to the terminals via the brushes. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0004]    Disclosed is a method of constructing a commutator for an electric machine. The method includes forming a commutator assembly including a plurality of commutator bar members linked through a corresponding plurality of bridge elements, rolling the commutator assembly into a commutator form having a substantially continuous, uninterrupted, outer surface, introducing an internal support member that receives an end portion of each of the plurality of commutator bar members into an inner diameter of the commutator form, and separating the plurality of commutator bar members by removing each of the plurality of bridge elements creating a discontinuous outer surface. 
         [0005]    Also disclosed is an electric machine including an armature having a commutator constructed by a method including forming a commutator assembly including a plurality of commutator bar members linked through a corresponding plurality of bridge elements, rolling the commutator assembly into a commutator form having a substantially continuous, uninterrupted, outer surface, introducing an internal support member that receives an end portion of each of the plurality of commutator bar members into an inner diameter of the commutator form, and separating the plurality of commutator bar members by removing each of the plurality of bridge elements creating a discontinuous outer surface. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike: 
           [0007]      FIG. 1  depicts an electric machine including an armature having a commutator constructed in accordance with an exemplary embodiment; 
           [0008]      FIG. 2  depicts a commutator assembly including a plurality of commutator bar members joined by a plurality of bridge elements in accordance with an exemplary embodiment; 
           [0009]      FIG. 3  depicts the armature assembly of  FIG. 2  rolled into a commutator form; 
           [0010]      FIG. 4  depicts the armature assembly of  FIG. 3  with support rings installed in accordance with an exemplary embodiment; 
           [0011]      FIG. 5  depicts the armature assembly of  FIG. 4  with the internal support member installed; 
           [0012]      FIG. 6  depicts the armature assembly of  FIG. 5  following removal of bridge elements joining the plurality of commutator bar members; 
           [0013]      FIG. 7  depicts the armature assembly of  FIG. 6  following formation of a riser at an axial end thereof; and 
           [0014]      FIG. 8  is a perspective view of the commutator constructed in accordance with the method of the exemplary embodiments. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    A detailed description of one or more embodiments of the disclosed apparatus and method are presented herein by way of exemplification and not limitation with reference to the Figures. 
         [0016]    An electric machine in accordance with an exemplary embodiment is indicated generally at  2  in  FIG. 1 . Electric machine  2  includes a housing  4  having a first wall  6 , a second wall  7  and a third wall  8 . First, second and third walls  6 - 8  are connected and form an interior region  10  that houses a field  20  and an armature assembly  24 . Field  20  is mounted to an internal surface (not separately labeled) of first wall  6 . Armature assembly  24  is rotatably mounted relative to field  20 . Armature assembly  24  includes a shaft  30  having a first end  32  rotatably supported at second wall  7  through a first bearing  34  and a second end  36  rotatably supported at third wall  8  by a second bearing  38 . An armature winding assembly  42  is fixedly mounted to shaft  30 . 
         [0017]    Armature winding assembly  42  may include one or more windings or poles that are rotated relative to field  20 . Armature assembly  24  also includes a commutator  45  that is electrically connected to armature winding assembly  42  and a terminal block  46 . More specifically, commutator  45  is electrically connected to terminal block  46  through first and second brushes  48  and  49  via corresponding first and second conductors  56  and  57 . At this point it should be understood that while armature assembly  24  is described as being fixedly mounted to shaft  30 , shaft  30  may be fixedly mounted to housing  4  and armature assembly  24  may be rotatably mounted thereupon. Further, it should be understood that the number of brushes electrically connected to commutator  45  may vary. 
         [0018]    In accordance with an exemplary embodiment, commutator  45  is formed from a one-piece commutator assembly  80  illustrated in  FIG. 2 . One-piece commutator assembly  80  extends from a first end portion  82  to a second end portion  83  and includes a plurality of commutator bar members, one of which is indicated at  90 . Commutator bar members  90  are linked through a plurality of bridge elements, one of each is indicated at  92 . Each commutator bar member  90  includes a first end portion  94 , a second end portion  95  and an intermediate portion  97 . Second end portion  95  has a generally circular cross-section  99  while intermediate portion  97  includes a reduced thickness. More specifically, intermediate portion  97  has a thickness that is less than a thickness of first end portion  94  and a thickness of second end portion  95 . 
         [0019]    In accordance with an exemplary embodiment, one-piece commutator assembly  80  is formed into a commutator form  110  having a generally circular cross-section  111  and a substantially continuous outer surface  113  as shown in  FIG. 3 . Commutator form  110  does possess a discontinuity  114  in substantially continuous outer surface  113  at a region in which first end portion  82  and second end portion  83  come together. Commutator form  110  includes a first axial end  115  and an opposing second axial end  116 . Commutator form  110  is provided with an internal support member  120  as shown in  FIG. 4 . 
         [0020]    Internal support member  120  may be injection molded into commutator form  110  about intermediate portions  97 , second end portions  95  and a section of first end portions  94  of commutator bar members  90 . Internal support member  120  provides support to commutator bar members  90 . Internal support member  120  also physically locates each commutator bar member  90  relative to others of commutator bar members  90 . Internal support member  120  extends from a first end section  123 , that is positioned at first axial end  115 , to a second end section  124 . Second end section  124  is spaced from second axial end  116 . First end section  123  may be provided with a circumferential flange  127 . Internal support member  120  provides electrical isolation between the plurality of commutator bar members  90  upon the removal of bridge elements  92 , as will be discussed more fully below. Internal support member  120  also provides electrical isolation between the plurality of commutator bar members  90  and shaft  30  once commutator  45  is mounted to armature assembly  24 . 
         [0021]    As seen in  FIG. 5 , a first circumferential notch  134  is formed in substantially continuous outer surface  113  of commutator form  110  at first axial end  115 . A second circumferential notch  135  is formed in substantially continuous outer surface  113  between first axial end  115  and second axial end  116 . Each circumferential notch  134  and  135  has a fixed depth. The fixed depth may extend through each of the plurality of bridge elements  92  creating a localized discontinuity in substantially continuous outer surface  113 . The fixed depth does not however extend entirely through each of the plurality of commutator bar members  90 . A first fiberglass tape  140  is wrapped around commutator form  110  in first circumferential notch  134 . A second fiberglass tape  142  is wrapped around commutator form  110  in second circumferential notch  135 . First and second fiberglass tapes  140  and  142  provide radial support to commutator bars  90  when commutator  45  is subjected to centrifugal forces. 
         [0022]    As shown in  FIG. 6 , a plurality of slots, one of which is indicated at  145  is formed in commutator form  110 . Slots  145  are formed in first end portions  94  of corresponding ones of the plurality of commutator bar members  90 . In addition to forming slots  145 , each bridge element  92  is removed to physically separate each of the plurality of commutator bar members  90 . Once separated, second axial end  116  is folded, or bent, at a substantially right angle to form a riser  150  as shown in  FIG. 7 . Once riser  150  is formed, commutator  45  takes on an appearance as shown in  FIG. 8 . At this point, commutator  45  may be mounted on shaft  30  to form part of armature assembly  24 . When commutator  45  is installed on shaft  30 , riser  150  abuts armature winding assembly  42 . 
         [0023]    At this point it should be understood that the exemplary embodiments describe a method of constructing a commutator from a one-piece commutator assembly. More specifically, in place of the more labor intensive process of loading individual commutator bars into a fixture, joining the commutator bars and shaping the commutator bars, the exemplary embodiment employs a one-piece commutator assembly that simplifies the construction and manufacture of a commutator. It should also be understood that the one-piece commutator assembly can be formed using a variety of techniques including stamping, extrusion and the like. Also, while described as being wrapped with fiberglass tape, other materials may also be employed to wrap the commutator form. 
         [0024]    While the invention has been described with reference to an exemplary embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the claims.