Abstract:
Detailed are brush assemblies for electric motors. The assemblies may include retention springs or other mechanisms designed to bias brushes away from surfaces of commutators during assembly of the motors. Such retention mechanisms additionally may be fitted into cavities in associated cover plates following motor assembly. The cover plates further may include tabs which, in use of the motor, assist in supporting side surfaces of the brushes and in orienting the plate relative to a corresponding brush card.

Description:
FIELD OF THE INVENTION 
   This invention relates to brush assemblies for electric motors and more particularly, although not necessarily exclusively, to such assemblies incorporating components for retaining brushes in selected positions during assembly of electric motors. 
   BACKGROUND OF THE INVENTION 
   Disclosed in U.S. Pat. No. 6,664,701 to Ortt, et al., whose contents are incorporated herein in their entirety by this reference, is an example of a brush assembly for an electric motor. FIG. 2 of the Ortt patent illustrates the assembly, which includes a brush, an electrical connector for the brush, and a spring. As noted in the Ortt patent, the spring functions to bias the brush into contact with an outer surface of a commutator and thereby “complete the electrical circuit between the rotating commutator and a power source.” See Ortt, col. 1, 11.26–27. 
   U.S. Pat. No. 5,990,594 to Hyatt, Jr., et al., whose contents, by this reference, are also incorporated herein in their entirety, details another brush assembly for use as part of an electric motor. In this assembly, coil springs are positioned within brush sleeves so as to bias brushes into contact with a commutator. Consistent with many conventional brush assemblies, however, neither the assembly of the Ortt patent nor that of the Hyatt, Jr. patent utilizes springs or other resilient materials to bias brushes away from any commutator surface during motor assembly or otherwise. 
   SUMMARY OF THE INVENTION 
   The present invention provides alternative brush assemblies for electric motors. Included among components of the assemblies are springs, or other mechanisms, designed to bias brushes away from surfaces of a commutator during assembly of a motor. Also included in each assembly may be a cover plate with a cavity into which a retention spring may be fitted following formation of the motor. If present, the plate additionally may (if desired) incorporate one or more tabs which, in use of the motor, assist in supporting side surfaces of the brushes and in orienting the plate relative to a corresponding brush card. 
   Prior to operation of the assembled electric motor, the retention spring operates to counteract—and either balance or overcome—forces provided by coil or other springs used to bias brushes toward commutator surfaces. Consequently, before operation of the motor the brushes are not biased toward a commutator surface. This lack of bias greatly facilitates assembly of the motor, as it allows insertion of the commutator into the card carrying the brushes without undesired contact between the commutator and brushes. By contrast, in many conventional assemblies, a separate plastic tube is used temporarily to restrain the brushes so that the commutator may be positioned appropriately relevant to the card. The present invention thus also avoids the need for a separate tube to be used for this purpose. 
   Further, although the retention spring of the invention is not needed after a motor is assembled, it need not be removed from the assembly. Instead, the retention spring may be fitted into a cavity in the associated cover plate and retained there throughout the life of the motor. Indeed, in preferred embodiments, the act of inserting the brush card itself onto the motor causes a commutator to move the retention spring into the cavity, so that no further effort is required to fit the spring there. Hence, no separate operation to remove the retention spring is necessary. 
   One proposed embodiment of the retention spring is generally circular, but with a flattened (straightened) end segment and flanges protruding from an open opposite end. The flattened end, which abuts a corresponding surface of the brush card, helps orient the spring relative to the card so that the flanges are aligned with (nominally) vertical channels in the opposite end of the card. When the retention spring is subjected to vertical forces, the flanges may travel within the channels while the flattened end slides along its abutting surface. Should its flanges exit the channels, the retention spring will expand and be captured by the cavity in the cover plate. However, absent the existence of such vertical forces acting on the retention spring, movement of the retention spring will be constrained relative to the brush card, with its curved surfaces restraining movement of the brushes within the card. 
   To facilitate placement of brushes within cards and provide electrical access to the brushes, many brush cards omit much of one side wall of each brush housing. A consequence of this omission is lack of complete support for the brushes within the housings, particularly on the side where parts of the walls are omitted. Hence, included in some embodiments of the cover plate are one or more tabs protruding toward the brush card. Such tabs, if present, may function as partial walls for the brush housings within the card, further supporting respective side surfaces of the brushes. As noted above they also may orient the cover plate relative to the brush card. 
   It thus is an optional, non-exclusive object of the present invention to provide brush assemblies in which brushes are constrained within an associated card prior to assembly of an electric motor. 
   It also is an optional, non-exclusive object of the present invention to provide brush assemblies in which the brush-constraint mechanism need not be removed to complete assembly of the electric motor. 
   It is another optional, non-exclusive object of the present invention to provide retention mechanisms for brushes that may be fitted into brush cards. 
   It is, moreover, an optional, non-exclusive object of the present invention to provide retention mechanisms in the form of springs having flanges fitted into the brush cards. 
   It is a further optional, non-exclusive object of the present invention to provide brush assemblies with cover plates having cavities (recesses) into which retention mechanisms may be fitted following assembly of the electric motors. 
   It is yet another optional, non-exclusive object of the present invention to provide cover plates having one or more tabs protruding therefrom, which tabs form portions of walls for brush housings of the brush cards. 
   Other objects, features, and advantages of the present invention will be apparent to those skilled in the relevant fields with reference to the remaining text and drawings of this application. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates, in plan view, an exemplary retention mechanism of the present invention. 
       FIG. 2  presents an exploded view of a brush assembly of the present invention including the retention mechanism of  FIG. 1 . 
       FIG. 3  illustrates the brush assembly of  FIG. 2  prior to incorporation into a motor. 
       FIG. 4  shows the brush assembly of  FIGS. 2–3  following incorporation into a motor. 
   

   DETAILED DESCRIPTION 
   Depicted in  FIG. 1  is retention mechanism  10  of the present invention. Mechanism  10  is preferably (although not necessarily) in the form of a spring with end section  14 , opposed resilient legs  18  and  22 , and flanges  26  and  30 .  FIG. 1  illustrates mechanism  10  in two positions, with legs  18  and  22  “closed” (in solid lines) and “open” (in dotted lines). 
   Versions of mechanism  10  consistent with  FIG. 1  appear generally circular or U-shaped, with an open area opposite end section  14 . End section  14  may include a flat or straight segment  34  and transitional segments  38  and  42  connecting flat segment  34  to respective legs  18  and  22 . Segment  34  is designed to abut a corresponding surface of an associated brush card. Those skilled in the relevant art will, however, recognize that segment  34  need not necessarily be flat, but rather may be shaped differently depending on the shape of the corresponding surface of the card (or otherwise as appropriate or desired). 
   Legs  18  and  22  beneficially are curved so that, when in the closed position, their curvature generally matches the internal curvature of the associated brush card. In the embodiment of  FIG. 1 , legs  18  and  22  terminate at respective flanges  26  and  30  at the open end of mechanism  10 , with such flanges  26  and  30  designed to fit into corresponding channels of the brush card so as to compress legs  18  and  22 . Again, however, those skilled in the relevant fields will understand that legs  18  and  22  need not necessarily terminate in flanges  26  and  30  and that other methods of engaging the brush card may be utilized instead. Because mechanism  10  is wider in its “open” state, clear from  FIG. 1  is that it thus will exert outward force radially when legs  18  and  22  are compressed radially into the “closed” state. This outward radial force exerted by legs  18  and  22  functions to counteract opposite spring forces acting on the brushes within a card, thus retaining the brushes in a desired position during assembly of the electric motor. 
   Illustrated in  FIG. 2  are components of a brush assembly  50  of the present invention. Assembly  50  incorporates retention mechanism  10  as well as at least brush card  54 , plate  58 , and one or more brushes  62 . Also shown in  FIG. 2  are subassemblies  66 A and  66 B to which brushes  62  are connected, springs  70  (one associated with each brush  62 ), and end cap assembly  74 . Although four brushes  62  and springs  70  are illustrated in  FIG. 2 , more or fewer brushes and springs may be included instead. 
     FIG. 2  also details novel aspects of brush card  54 , including its interior surface  76 . As shown in  FIG. 2 , card  54  may contain channels  78  and  82  extending from surface  76  and whose major axes are generally perpendicular to the major plane of card  54 . (Stated differently, if card  54  is positioned horizontal to a surface, then channels  78  and  82  will be positioned more or less vertically.) Although channels  78  and  82  need not be oriented as depicted in  FIG. 2 , this orientation is preferred, as it facilitates desired movement of retention mechanism  10  after a motor is assembled. When retention mechanism  10  is in use, legs  18  and  22  are compressed and fitted into, respectively, channels  78  and  82  so that mechanism  10  is in the “closed” state. 
   Included as well in brush card  54  are recess  86 , whose surface  90  abuts (or otherwise engages) segment  34  of mechanism  10 , and housings  94 , one for each of brushes  62 . Depicted in  FIG. 2  is that housings  94  are incomplete, in that they do not fully envelop their associated brushes. For example, housings  94  intentionally lack wall structure at interior surface  76  so that brushes  62  may contact a commutator placed in the space bounded by surface  76 . Each housing  94  additionally may have an incomplete side wall  98  and an open end  102  to permit a brush  62  to be placed therein and a corresponding electrical lead  106  to extend therefrom. 
   Plate  58  may be attached to card  54  (using fasteners such as bolts B or other attachment means) so as to cover open ends  102  of housings  94 . In this way, brushes  62  may be precluded from escaping housings  94  through ends  102 . Further, however, plate  58  may include one or more tabs  110  protruding therefrom, preferably one tab  110  for each side wall  98 . If present, such tabs  110  may be positioned so as partially to complete the incomplete side walls  98 , thereby enveloping and supporting more of each brush  62 . Because tabs  110  would be designed to fit into the incomplete areas of walls  98 , they also could facilitate properly orienting plate  58  for attachment to card  54 . 
   Side  114  of plate  58  opposite card  54  beneficially includes cavity  118  (divided into recessed sections  118 A and  118 B). If retention mechanism  10  is pushed or otherwise forced toward plate  58 , compressed legs  18  and  22  will begin travelling within channels  78  and  82  toward plate  58  as well. Once at the open ends of channels  78  and  82 , legs  18  and  22  will expand into, respectively, recesses  118 A and  118 B and thus be “captured” by cavity  118 . Cavity  118  hence provides a resting place for retention mechanism  10  after it is no longer needed to restrain brushes  62 . End cap  122  of cap assembly  74  may be fitted over plate  58  so as to cover, among other things, recess  118  and thereby prevent retention mechanism  10  from exiting assembly  50 . 
     FIG. 3  shows mechanism  10  in its operational position, with legs  18  and  22  restraining brushes  62 . Because springs  70  bias brushes  62  toward the open area bounded by surface  76 , absent intervention brushes  62  would tend to protrude into that open area. Their doing so could, in turn, hinder insertion of a commutator into that area. Retention mechanism  10  provides such intervention, with the outward radial force exerted by legs  18  and  22  overcoming (or at least balancing) the force of springs  70 , thereby preventing brushes  62  from extending substantially out of housings  94  into the open area. 
     FIG. 4  illustrates retention mechanism  10  in its resting position within cavity  118  following incorporation of brush assembly  50  into a motor. (For clarity, end cap assembly  74  has been omitted from this drawing.) Visible in  FIG. 4  is commutator C of the motor. Upon insertion of brush assembly  10  onto the motor, commutator C engages retention mechanism  10  and pushes it toward plate  58 . This in turn causes flanges  26  and  30  to travel within channels  78  and  82  until they exit therefrom into recesses  118 A and  118 B, at which time legs  18  and  22  extend, precluding flanges  26  and  30  from returning to the channels  78  and  82 . Retention mechanism  10  thus need not be removed from brush assembly  50 , but thereafter may rest in cavity  118  and not impede proper functioning of the motor. 
   The foregoing is provided for purposes of illustrating, explaining, and describing exemplary embodiments and certain benefits of the present invention. Modifications and adaptations to the illustrated and described embodiments will be apparent to those skilled in the relevant art and may be made without departing from the scope or spirit of the invention.