Abstract:
A method of contouring a motor brush includes mounting a brush in a brush card and contouring the brush. The brushes are retracted and a contour wheel is placed proximate the brushes such that when the brushes are released, the brushes contact the contour wheel. The contour wheel includes an abrasive surface and when rotated the wheel wears-in the brushes. Accordingly, the brushes are worn-in to a commutator before the commutator is installed in the motor. Upon initial motor run, the contoured brushes allow the motor to run quieter than a motor without contoured brushes.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates generally to dynamoelectric machines and, more particularly, to brush commutated direct current (DC) motors.  
           [0002]    Brush commutated motors typically include a motor housing, a rotor assembly, a stator including one or more field windings or one or more permanent magnets. The rotor assembly includes a rotor core and a rotor shaft extending through the rotor core. The rotor core includes a plurality of armature windings attached to a commutator mounted to the rotor shaft. The commutator includes a plurality of commutator segments or bars extending radially out from the shaft and electrically insulated from each other by a plurality of insulators.  
           [0003]    The motor housing includes at least one endshield and houses at least a portion of the rotor assembly. Electric motors also typically include at least one bearing sized to receive and support the rotor shaft, and at least one inner bearing cap separated from the bearing. Typically, the bearing is positioned between an endshield and an inner bearing cap and facilitates rotation of the rotor shaft when the field windings are energized. A yoke or brush card including a plurality of brushes is mounted within the housing such that the brushes make slideable contact with the commutator. In a motor having field windings, the field windings are energized producing a plurality of fixed stator poles. In a permanent magnet motor, the permanent magnets produce a plurality of fixed stator poles.  
           [0004]    In both permanent magnet motors and motors with field windings, the brushes and commutator are positioned such that the current flow through the armature windings generates a plurality of magnetic rotor poles that oppose the fixed stator poles causing the shaft to rotate. The commutator bars are arranged to alternate the current direction through the armature windings such that, while the armature windings physically rotate, the magnetic poles produced by the armature windings are substantially stationary. Accordingly, a torque is continuously provided.  
           [0005]    Typically, the brushes of a motor are generally shaped or contoured to the shape of the commutator. The brushes are less expensive to repair and replace than the commutator and, accordingly, the brushes are manufactured “softer” than the commutator such that the brushes wear more than the commutator does. As the brushes wear-in, the brushes become contoured to the shape of the commutator and the motor runs quieter than the motor ran initially. Additionally, a motor with brushes that have worn-in or seated to the commutator is beneficial because the initial non-symmetric brush commutator contact of a new motor can reduce performance, lead to thermal overload, and cause application deficiency.  
           [0006]    Motor manufacturers have employed several methods to wear-in the brushes. One method is to run a new motor at a no-load condition for an extended period of time which extends the manufacturing time and raises manufacturing costs. Another method is to apply an abrasive material such as a seating stone between the brushes and the commutator. The material causes the brushes to wear-in quicker but raises manufacturing costs because the material must be applied and then removed from the commutator and the brushes after the brushes have worn-in to the commutator. Additionally, utilizing an abrasive material at the commutator-brush interface can lead to bearing contamination that can shorten the operating life of a motor.  
         BRIEF SUMMARY OF THE INVENTION  
         [0007]    A method of contouring a motor brush includes mounting a brush in a brush card and mounting the brush card to at least one of a stator and an endshield. The brushes are retracted and a contour wheel is placed proximate the brushes such that when the brushes are released, the brushes contact the contour wheel. The contour wheel includes an abrasive surface and a handle to facilitate a rotation of the wheel. The wheel is rotated one-half turn in a first direction and one-half turn in a second direction. The brushes are retracted and the contour wheel is replaced with a commutator sized approximately equal to the contour wheel. Accordingly, the brushes are worn-in to the commutator before the commutator is installed in the motor. Upon initial motor run, a motor with contoured brushes runs quieter than a motor without contoured brushes.  
           [0008]    Apparatus for contouring a brush for a motor includes a contour wheel including an abrasive surface and a shaft extending substantially perpendicular to the contour wheel. A top plate is attached to the shaft opposite the wheel and away from an end of the shaft such that the shaft extends through the top plate. The top plate can be engaged with at least one of a stator and an endshield. The top plate includes at least one bearing to rotatably support the shaft.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is top view, with parts cut away, of one embodiment of a contour apparatus;  
         [0010]    [0010]FIG. 2 is a top view, with parts cut away, of an alternative embodiment of a contour apparatus; and  
         [0011]    [0011]FIG. 3 is a cross sectional view of a motor. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0012]    [0012]FIG. 1 is a top view, with parts cut away, of one embodiment of a contour apparatus  10  including a handle  12  and a shaft  14  extending from handle  12  to a contour wheel  16  including an axis  17 . Contour apparatus  10  further includes at least one bearing  18  and a top plate  20  extending substantially perpendicular to axis  17  such that axis  17  is substantially centered in top plate  20 . Shaft  14  extends through top plate  20  and is rotatably supported by bearing  18 . In an exemplary embodiment, contour apparatus  10  includes a plurality of bearings  18  to provide a proper wheel alignment of contour wheel  16  with a plurality of brushes  22  attached to a brush card  24 . Brushes  22  can be positioned in a normal position and a retracted position. Brushes  22  are resiliently mounted to brush card  24  such that a plurality of brush springs (not shown) bias brushes  22  toward their normal position.  
         [0013]    Brush card  24  is attached to an endshield  26  of a motor (not shown in FIG. 1). Endshield  26  includes a rabbet  28  to which a housing body (not shown in FIG. 1) is attached to fabricate the motor. Top plate  20  includes a bearing portion  30  that houses bearings  18 . Bearing portion  30  is substantially centered on top plate  20  and top plate  20  is sized to fit within rabbet  28  such that shaft  14  is substantially centered between brushes  22 . Contour wheel  16  is substantially circular and is sized approximately equal in radius to a commutator (not shown in FIG. 1) of the motor. Contour wheel  16  includes an abrasive surface  32 . In an exemplary embodiment, abrasive surface  32  has a grit size of 320 or less using the CAMI (Coated Abrasives Manufacturer&#39;s Institute) standard. In an alternative embodiment, abrasive surface  32  has a grit size of 240 or less.  
         [0014]    Contour apparatus  10  is utilized by retracting brushes  22  and positioning top plate  20  within rabbet  28  such that contour wheel  16  is proximate to brushes  22  and will contact brushes  22  when brushes  22  are released from their retracted position. Since brushes  22  are resiliently mounted, brushes  22  are biased toward their normal positions when released from their retracted positions. After brushes  22  are released from their retracted position, handle  12  is rotated causing contour wheel  16  to rotate against brushes  22 . Since contour wheel  16  includes an abrasive surface  32 , brushes  22  wear-in to contour wheel  16 . Additionally, since contour wheel  16  is sized approximately equal to the commutator, brushes  22  wear-in to the commutator prior to the commutator being mounted in the motor.  
         [0015]    In an exemplary embodiment, handle  12  and contour wheel  16  are rotated one-half turn in one direction, such as, for example, clockwise, and one-half turn in a second direction, such as, for example, counter-clockwise, such that brushes  22  wear-in from rotatably contacting abrasive surface  32  in both directions. Brushes  22  are retracted and contour apparatus  10  is removed to facilitate further fabrication of the motor. Accordingly, brushes  22  are contoured while in their assembled locations and initial motor noise is reduced. After contouring a plurality of brushes, a dust may form on abrasive surface  32  that is removed by releasing compressed air proximate to abrasive surface  32  such that the dust is blown from abrasive surface  32 . Alternatively, a vacuum (not shown) is utilized to remove the dust from abrasive surface  32 .  
         [0016]    [0016]FIG. 2 is a top view, with parts cut away, of an alternative embodiment of a contour apparatus  50 . Contour apparatus  50  is substantially similar to contour apparatus  10  shown in FIG. 1, and components in contour apparatus  50  that are identical to components in contour apparatus  10  are identified in FIG. 2 using the same reference numerals used in FIG. 1. Accordingly, contour apparatus  50  includes a handle  12  and a shaft  14  extending from handle  12  to a contour wheel  16  including an axis  17 . Contour apparatus  50  further includes at least one bearing  18  and a top plate  20  extending substantially perpendicular to axis  17  such that axis  17  is substantially centered in top plate  20 . Shaft  14  extends through top plate  20  and is rotatably supported by bearing  18 . In an exemplary embodiment, contour apparatus  50  includes a plurality of bearings  18  to provide a proper wheel alignment of contour wheel  16  with a plurality of brushes  22  attached to a brush card  24 . Brushes  22  can be positioned in a normal position and a retracted position. A plurality of brush springs (not shown) bias brushes  22  in their normal position.  
         [0017]    Brush card  24  is attached to a retaining tab  52  mounted in a stator housing  54 . Top plate  20  includes a bearing portion  30  that houses bearings  18 . Bearing portion  30  is substantially centered on top plate  20  and top plate  20  is sized to fit around housing  54  such that shaft  14  is substantially centered between brushes  22 . Contour wheel  16  is substantially circular and is sized approximately equal in radius to a commutator (not shown). Contour wheel  16  includes an abrasive surface  32 . In an exemplary embodiment, abrasive surface  32  has a grit size of 320 or less using the CAMI (Coated Abrasives Manufacturer&#39;s Institute) standard. In an alternative embodiment, abrasive surface  32  has a grit size of 240 or less.  
         [0018]    Contour apparatus  50  is utilized by retracting brushes  22  and positioning top plate  20  around housing  54  such that contour wheel  16  is proximate to brushes  22  and will contact brushes  22  when brushes  22  are released from their retracted position and biased toward their normal position. After brushes  22  are released from their retracted position, handle  12  is rotated causing contour wheel  16  to rotate against brushes  22 . Since contour wheel  16  includes an abrasive surface  32 , brushes  22  wear-in to contour wheel  16 . Additionally, since contour wheel  16  is sized approximately equal to the commutator, brushes  22  wear-in to the commutator prior to the commutator being mounted in the motor.  
         [0019]    In an exemplary embodiment, handle  12  and contour wheel  16  are rotated one-half turn in one direction, such as, for example, clockwise, and one-half turn in a second direction, such as, for example, counter-clockwise, such that brushes  22  wear-in from rotatably contacting abrasive surface  32  in both directions. Brushes  22  are retracted and contour apparatus  50  is removed to facilitate further fabrication of the motor. Accordingly, brushes  22  are contoured while in their assembled locations and initial motor noise is reduced. After contouring a plurality of brushes, a dust may form on abrasive surface  32  that is removed by releasing compressed air proximate to abrasive surface  32  such that the dust is blown from abrasive surface  32 . Alternatively, a vacuum (not shown) is utilized to remove the dust from abrasive surface  32 .  
         [0020]    [0020]FIG. 3 is a cross sectional view of a motor  70  including a plurality of contoured brushes  72  resiliently attached to a brush card  74  such that each brush  72  is biased toward a normal position. Each brush  72  can be retracted to a retracted position. When brushes  72  are in their normal positions, a contoured surface  76  of each brush  72  rotatably contacts a commutator  78  including a plurality of commutator bars  80 . Brushes  72  were contoured using contour apparatus  10  (shown in FIG. 1). Each commutator bar  80  is connected to a rotor core  84  including a plurality of armature windings (not shown). Rotor core  84  and commutator  78  are attached to a rotor shaft  86  mounted in a plurality of endshields  88  including a first endshield  90 . Rotor shaft  86  is rotatably supported by a plurality of bearings  92  held in place with a plurality of inner bearing caps  93 . Brush card  74  is attached to first endshield  90 . Each endshield  88  includes a rabbet  94  that attaches each endshield  88  to a housing  96  including a stator  98  mounted therein and including a bore  100  therethrough. Stator  98  includes a plurality of stator windings (not shown). Housing  96  further includes a first end  102  and a second end  104 . In an alternative embodiment of motor  70 , brush card  74  is attached to stator  98  rather than first endshield  90 .  
         [0021]    During fabrication of motor  70 , brush card  74  including brushes  72  is attached to first endshield  90  and each brush  72  is retracted to a retracted position a first time. Top plate  20  (shown in FIG. 1) is positioned within rabbet  94  of first endshield  90  such that contour wheel  16  is substantially centered among brushes  72  and brushes  72  are released from the retracted positions. Since brushes  72  are biased toward their normal positions, brushes  72  contact contour wheel  16 . Handle  12  is turned one-half turn in a first direction and one-half turn in a second direction. Since contour wheel  16  includes abrasive surface  32 , brushes  72  wear-in to contour wheel  16 . Brushes  72  are retracted a second time and contour wheel  16  is removed. Rotor shaft  86  including commutator  78  is positioned in motor  70  and brushes  72  are released from the retracted positions. Since brushes  72  are biased toward their normal positions, brushes  72  contact commutator  78 . Furthermore, since commutator  78  is substantially sized equally in radius to contour wheel  16 , brushes  72  are worn-in to commutator  78  before initially contacting commutator  78 . After fabricating a plurality of motors, a dust may form on abrasive surface  32  that is removed by releasing compressed air proximate to abrasive surface  32  such that the dust is blown from abrasive surface  32 . Alternatively, a vacuum (not shown) is utilized to remove the dust from abrasive surface  32 .  
         [0022]    During initial operation of motor  70 , the stator windings are energized producing a plurality of stator poles and the armature windings are energized producing a plurality of rotor poles that oppose the fixed stator poles causing rotor shaft  86  to rotate. The commutator bars are arranged to alternate the current direction through the armature windings such that a torque is continuously provided. Since brushes  72  have been contoured to commutator  80  through the use of contour apparatus  10 , brushes  72  are worn-in already and motor  70  generates less noise than a motor without contoured brushes.  
         [0023]    While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.