Abstract:
Disclosed herein relates to a dynamoelectric machine brush. The brush comprising, a first brush surface electrically engagable with a rotatable conductor of a dynamoelectric machine in response to the brush being urged toward the rotatable conductor, and a contoured brush surface on a side of the brush opposite the first brush surface. The contoured brush surface further having at least one recess receptive of and complementary in shape to a biasing member that urges the brush towards a rotatable conductor of a dynamoelectric machine.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    Brush holder assemblies in dynamoelectric machines are sometimes attached to a plate. Each of the brush holder assemblies accommodates a brush that may be electrically connected to a flexible conductor. The flexible conductor connected to the brush is routed through a hole or slot in a brush holder of the brush holder assembly. The end of the flexible conductor that is not connected to the brush may be electrically connected to a rigid conductor that sealably extends through a housing of the machine. Preventing the flexible and the rigid conductors from inadvertently shorting out against other conductive components of the dynamoelectric machine that carry alternate electrical potentials than that which is carried by the flexible or rigid conductors, is necessary for the proper operation of the dynamoelectric machine. 
         [0002]    Brush holder assemblies typically also include a biasing spring for urging the brushes toward a commutator. The biasing force created by such springs can vary depending upon how the spring is seated against a surface of the brush, for example. Such variations in spring force can have a detrimental affect on the durability of the machine as well as have a detrimental affect on the audible and electrical noise emitted from the machine. It may, therefore, be desirable to minimize variations in brush spring force. 
         [0003]    Mechanisms that attach the brush holders to the plates of dynamoelectric machines can also affect the brush spring force. In machines, in which the spring is compressed between the brush and the brush holder, variability in the positional attachment of the brush holder to the plate can affect the contact force of the brush against the commutator. It may therefore be advantageous to minimize the number of features involved in attaching the brush holder to the metal plate. 
         [0004]    Another factor that affects not only the durability of the brush holder assembly but the complete dynamoelectric machine is the temperature at which the machine operates. The current that flows through the flexible connectors, brushes, commutator and windings of the machine can influence the operational temperature of the machine with higher currents causing higher operational temperatures. The amount of current that flows is affected by operational conditions of the dynamoelectric machine such as mechanical loading and friction, for example, and is therefore an unavoidable condition, which should be accommodated. Durability failures that result from over temperature operation can require replacement of the entire machine at a considerably higher cost than if only the brush holder assembly required replacement. 
         [0005]    Over temperature operation can also result in fires. Some bush holder assemblies use the flexible conductors as fusible links, however, the flexible nature of such conductors may cause them to have a variation in current draw at which the open circuit occurs, resulting in premature failures of the conductors on some devices while permitting overheating on others. It may therefore be desirable to have a failure include an opening of the circuit at a more controlled current level than that which is available with the flexible conductors and to have the brush holder assemblies fail prior to the failure of the complete dynamoelectric machine. 
         [0006]    Therefore, the art of brush holder assemblies is in need of simpler and less costly ways to prevent internal electrical short circuits, more reliable spring biasing forces, and integration of fusible links with tight control of overload currents. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0007]    Disclosed herein relates to a dynamoelectric machine brush. The brush comprising, a first brush surface electrically engagable with a rotatable conductor of a dynamoelectric machine in response to the brush being urged toward the rotatable conductor, and a contoured brush surface on a side of the brush opposite the first brush surface. The contoured brush surface further having at least one recess receptive of and complementary in shape to a biasing member that urges the brush towards a rotatable conductor of a dynamoelectric machine. 
         [0008]    Further disclosed herein relates to a starter motor brush. The brush comprising, a plurality of arcuate grooves in a surface of the brush receptive of a coil spring. 
         [0009]    Further disclosed herein is a method that relates to maintaining alignment of a dynamoelectric machine brush biasing member. The method comprising, controlling lateral movement of an end of the biasing member in contact with the brush with a contoured surface of the brush receptive of the end of the biasing member in contact with the contoured brush surface. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike: 
           [0011]      FIG. 1  depicts a perspective view of a brush holder assembly disclosed herein; 
           [0012]      FIG. 2  depicts a perspective view of a rigid conductor disclosed herein; 
           [0013]      FIG. 3  depicts a graphical relationship of time versus current to electrically interrupt a circuit for different conductors; 
           [0014]      FIG. 4  depicts a perspective view of a grommet disclosed herein; 
           [0015]      FIG. 5  depicts a perspective view of a partial assembly of a brush holder assembly disclosed herein; 
           [0016]      FIG. 6  depicts a partial cross sectional view of a brush and brush holder shown in  FIG. 1 ; 
           [0017]      FIG. 7  depicts a perspective view of a brush disclosed herein; 
           [0018]      FIG. 8  depicts a perspective view of an alternate brush disclosed herein; 
           [0019]      FIG. 9  depicts a perspective view of a brush to base plate assembly disclosed herein; and 
           [0020]      FIG. 10  depicts a radial view of a brush to base plate assembly disclosed herein. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]    Referring to  FIG. 1 , a perspective view of one embodiment of a brush holder assembly disclosed herein is shown generally at  10 . The brush holder assembly  10  includes a base plate  14 , to which four brush holders  18  are attached. The brush holders  18  each have a cavity  22  in which a brush biasing member  26 , depicted here as a compression spring, and a brush  30  are located. The biasing member  26  is compressed within the cavity  22  to thereby create a biasing force on the brush  30  urging the brush  30  in a radially inward direction. Each brush  30  has a ground flexible conductor  34  or a positive flexible conductor  36  attached thereto to provide an electrical connection to the brush  30 . The positive flexible conductors  36 , attached to two of the brushes  30  located across from each other on the base plate  14 , are electrically connected to a rigid conductor  38 , depicted here as a bus bar. The rigid conductor  38  has an arcuate shape with a radially outward protrusion  42  to which an external flexible conductor  46  is electrically attached. A grommet  50  includes an aperture  54 , which is slit shaped, through which the protrusion  42  is positioned and sealed. The grommet  50  seals the protrusion  42  to a housing (not shown) of the dynamoelectric machine. 
         [0022]    The four brushes  30  are radially inwardly biased towards a rotatable conductor  58 , depicted here as a commutator. The brushes  30  make electrical contact with the rotatable conductor  58 , which provides electrical current to a rotor of the dynamoelectric machine during operation of the machine. The two brushes  30  not connected to the rigid conductor  38  are instead connected to the base plate  14  through the two ground flexible conductors  34 . The base plate  14  may be made of an electrically conductive material such as metal, for example, and is connected to electrical ground of the machine. The rigid conductor  38  is connected to a direct current (DC) source of electrical power such as a battery, for example, through the positive flexible conductor  36 . 
         [0023]    A dynamoelectric machine using the above described brush holder assembly can convert DC electrical energy into rotational energy and vice versa. In a vehicle starter motor, for example, DC current flows to the motor&#39;s rotor through the flexible conductor  46 , the rigid conductor  38 , the positive flexible conductors  36 , and the brushes  30 . Simultaneously, the DC current flows from the machine&#39;s rotor through the brushes  30 , the ground flexible conductors  34 , and the base plate  14  to electrical ground. As more rotational energy, through increases in torque, for example, is demanded, more electrical energy, through increases in current, for example, will be drawn. 
         [0024]    The current carrying components of a dynamoelectric machine have limits as to how much current they can carry before they fail. Such failures are typically due to overheating that accompanies high current draw. Failures may include increased audible noise, decreased efficiency, shortened durability and even complete inoperability, for example. It may therefore be desirable to implement a fusible link in the machine that will interrupt or open the electrical circuit before more costly failures can occur. 
         [0025]    Referring to  FIG. 2  a perspective view of the rigid conductor  38 , or bus bar, is shown, which incorporates a fused portion as will now be described in detail. The rigid conductor  38  comprises an arcuate elongated arm  62 , formed from metal stamping, with a central portion  66  from which the protrusion  42  extends. The protrusion  42  has the external flexible conductor  46  electrically connected to a connectable site  44  by a method such as welding or soldering ( FIG. 1 ). The rigid conductor  38  extends in opposite directions from the central portion  66 , and has a first extension  70  with a first end  74  and a second extension  80  with a second end  84 . The first end  74  and the second end  84  each have a positive flexible conductor  36  electrically connected to a connectable site  44  thereon by welding or soldering (FIG.  1 ). Between the central portion  66  and the end  74  is a first reduced cross sectional area  78 . Similarly, between the central portion  66  and the end  84  is a second reduced cross sectional area  88 . The reduced cross sectional areas  78  and  88  are formed by orifices  79  and  89  respectively. The orifices  79 ,  89  leave two thin walled sections  92  of the base material of the rigid conductor  38 . The total cross sectional area of each of the reduced cross sectional areas  78 ,  88  are selected to melt at current loads that do not cause damage to the other current carrying components, thereby creating fused portions and providing overload protection in the rigid conductor  38 . 
         [0026]    The overload protection can have various relationships of time versus current at which the protection is triggered. This relationship is determined in part by the reduced cross sectional areas  78 ,  88 , and in part by the material from which the rigid conductor  38  is manufactured. Referring now to  FIG. 3 , three examples of time versus current load are graphed. The first line is for a copper bus bar with a 1.5 mm 2  cross sectional area, the second line is for a brass bus bar with a 1.5 mm 2  cross sectional area, and the third is for a brass bus bar with a 2.0 mm 2  cross sectional area. It is, therefore, possible, within limits, to tailor the time versus current load to open the circuit to the specific needs of each application by selection of material and cross sectional loads. Additionally, the reduced cross sectional areas  78 ,  88  provide a means of more accurately controlling the overload protection than is available using the flexible conductors  34 ,  36 , and  46 , for example. As such, the reduced cross sectional areas  78 ,  88  are selected to melt to an opened circuit at lower current loads than the flexible conductors  34 ,  36 , and  46 . 
         [0027]    To maintain accurate control of the current load protection it may be desirable to coat the metal of the rigid conductor  38  with plating such as tin, lead tin or silver, for example. By plating the rigid conductor  38 , reduction in the cross sectional area of the reduced cross sectional areas  78 ,  88  due to corrosion, can be significantly slowed thereby maintaining the original reduced cross sectional areas  78 ,  88 , and the corresponding current load protection they afford, for a longer period of time. 
         [0028]    Referring now to  FIG. 4 , the grommet  50 , which incorporates features to prevent electrical short circuits within the machine, will be described in further detail. The grommet  50  creates a sealable passageway for electrical power from the outside to the inside of the dynamoelectric machine. A body portion  110  of the grommet  50  sealable engages with an opening (not shown) in a rigid surface of the dynamoelectric machine. The body portion  110  is arcuate shaped to match the rigid surface of the machine to which it will be sealed. The body portion  110  includes an outer larger area portion  114  and an inner larger area portion  118  at greater and lesser radial dimensions respectively than the radial dimension coincident with the rigid surface of the machine to thereby lock the grommet  50  in the correct radial position relative to the machine. 
         [0029]    A slit shaped aperture  54  extends radially through a central area of the body portion  110  of the grommet  50 . The protrusion  42  extends through the aperture  54  with an interference fit that creates a seal between the grommet  50  and the protrusion  42 . Thus, the protrusion  42  is positioned to conduct electrical energy from outside the machine to inside the machine through the seal it has with the grommet  50 . Sealing the dynamoelectric machine is desirable to prevent incursion of contaminants into the machine that can adversely effect the operation and durability of the machine. A locating notch  122  is formed on an inner surface of the grommet  50  to receive a tab (not shown) on the base plate  14  to fix the grommet axially relative to the machine. 
         [0030]    A first projection  126  and a second projection  128  extend from opposite sides of the body portion  110  of the grommet  50 . The projections  126  and  128  have a “C” shaped cross section, thereby forming a channel, with the open portion of the “C” shape directed radially inwardly. A recessed portion of the “C” shape of the projections  126 ,  128  continue, in an uninterrupted fashion, across the body portion  110 . The projections  126  and  128  continue the arcuate shape of the body portion  110 , from which they extend, and substantially match the arcuate shape and length of the rigid conductor  38 . The rigid conductor  38  is located in the arcuate recess in the grommet  50  and the protrusion  42  is sealedly positioned within the aperture  54  thereby rotationally fixing the rigid conductor  38  to the grommet  50 . To radially attach the projections  126 ,  128 , of the grommet  50 , to the extensions  70 ,  80 , of the rigid conductor  38 , optional wings  130 ,  132 , of the grommet  50 , located near the ends  74 ,  84  of the rigid conductor  38  may be employed. A first wing  130  and a second wing  132  extend axially towards one another in opposite directions to partially close the open portion of the “C” shaped projections  126 ,  128 . An opening  134  between the wings  130 ,  132  is smaller than the axial width of the rigid conductor  38  thereby retaining the ends  74 ,  84  in the extensions  70 ,  80 . The grommet  50  is made of an elastomer and is therefore elastic to enhance sealablity and to allow it to be flexed from its original shape, if necessary, to assemble it into the rigid surface of the machine. The material of the grommet  50  is electrically nonconductive and the projections  126  and  128  provide insulation to the rigid conductor  38  to prevent shorting of the rigid conductor  38  with components of alternate electrical potential that could otherwise contact the rigid conductor  38  directly. 
         [0031]    Although the embodiments described herein incorporate a square “C” shaped cross section other cross sectional shapes could also be utilized while remaining within the scope of the present invention, such as a circular cross section with a slit along a length, for example. Similarly, the opened portion of the “C” shape could be directed axially rather then radially inwardly as disclosed herein. 
         [0032]    Referring to  FIG. 5  the rigid conductor  38  is further prevented from making inadvertent contact with components within the dynamoelectric machine by an interface with brush holders  136 . The brush holders  136  are molded, for example by injection molding, from a nonconductive plastic resin. A groove  140  is integrated into the brush holder  136 . The groove  140  is formed circumferentially relative to the dynamoelectric machine with the opened portion of the groove directed radially outwardly. The groove  140  is sized to receive the rigid conductor  38  with the projection  126  or  128  covering the rigid conductor  38 . A small interference between the walls of the groove and the projections  126 ,  128  may by used to prevent relative movement of the rigid conductor  38  within the groove  140 . It should be noted that other embodiments could have grooves sized to receive the rigid conductor  38  directly without an insulative layer being present. The groove  140  is positioned relative to a cavity  142 , slidably receptive of a brush  30 , such that the groove  140  and the cavity  142  do not overlap axially at all to thereby allow the full cross sectional shape of the cavity  142  to extend fully to the outer most radial dimension of the base plate  14 . Such a construction would allow for maximization of the overall brush  30  length, which may be desirable for reasons such as increased durability, for example. 
         [0033]    Referring to  FIGS. 6 and 1 , in an alternate embodiment the groove  140  may partially overlap axially with the cavity  22 . Such a partial overlap may permit use of a biasing member  26  with a large diameter  146 , such as a compression spring, for example, to be located symmetrically relative to the brush  30 . The large diameter  146  of the biasing member  26 , and its symmetrical orientation to the brush  30 , facilitates even loading of the brush to the rotatable conductor  58  ( FIG. 1 ), which may be advantageous for durability of the brushes  30  and even brush  30  wear. Additionally, by axially extending the groove  140  beyond the axial dimension of the cavity  22 , even if only partially, the axial width of the groove  140  can be made longer than if it were to not extend beyond the axial dimension of the cavity  22 . A longer axial length of the groove  140  may be desirable to accommodate a rigid conductor  38  with a long axial dimension. 
         [0034]    Even loading of the brush  30  to the rotatable conductor  58 , as mentioned above, can contribute to long brush  30  life. Even brush loading can also contribute to more consistent and reliable electrical contact between a brush surface  150  and the rotatable conductor  58 . In addition to even loading, equal loading force between the multiple brushes  30  that contact the rotatable conductor  58  can have an affect on the quality of the electrical contact and brush durability, with more equal brush forces correlating with improved contact quality and increased durability. Accurately positioning an end  154  of the biasing member  26  that is in contact with the brush  30  may, therefore, be desirable. 
         [0035]    Referring again to  FIG. 6 , a surface  158  of the brush  30  is contoured to complementarily receive the end  154  of the biasing member  26 . The contoured surface  158  may include such features as, a partial hollow cylindrical recess  162 , or a pair of grooves  166 , for example, which may be parallel to one another, as are shown in  FIG. 7 . Both the cylindrical recess  162  and the pair of grooves  166  configurations provide alignment of the biasing member  26  to the brush  30  to thereby consistently distribute the force of the biasing member  26  into the brush  30 . Additional alignment may be provided by sizing the recess  162  or the pair of grooves  166  such that an outer side wall  168  or an inner side wall  169  or both side walls  168 ,  169  interfere with the biasing member  26 . Such an arrangement may require that the biasing member  26  be flexed to engage the contoured surface  158  thereby providing even greater alignment between the brush  30  and the biasing member  26 . 
         [0036]    Referring to  FIG. 8  in yet another embodiment the brush  30  has a partially cylindrical shaped recess  163  with outer walls  164  on contoured surface  158 . Unlike the recess in  FIG. 7 , the recess in  FIG. 8  is not of a hollow cylindrical shape but instead is of a solid cylindrical shape. The coil spring biasing member  26  engages either loosely with the outer walls  164  or engages tightly with an interference fit with the outer walls  164 . It should be noted that, although embodiments disclosed herein describe specific shapes of the contoured surface  158 , specifically cylindrical or grooves, it should be noted that alternate shapes may be used on the contoured surface  158  while still being covered by the scope of the present invention. 
         [0037]    High contact area between the brush surface  150  and the rotatable conductor  58  may also improve the quality of the electrical contact. Consequently, the brushes  30  are manufactured with a brush surface  150  that is shaped to maximize surface contact with the rotatable conductor  58  at initial start of the machine. The cross sectional shape of the brushes  30  and the cavities  22 ,  142  are made noncircular to prevent rotation of the brushes  30  within the cavities  22 ,  142  to thereby present the brush surface  150  to the rotatable conductor  58  in the same orientation over time. This nonrotatable brush  30  feature also assures that a hole  170  in the brushes  30  into which the flexible conductors  34 ,  36  attach is properly oriented to minimize stress loading on the flexible conductors  34 ,  36  and the attachment points on either end of the conductors  34 ,  36 . 
         [0038]    The ground flexible conductors  34  have one end electrically attached to the base plate  14  of the brush holder assembly  10  as shown in  FIG. 1 . The brush holders  18 ,  136  are also attached to the base plate  14 . How the brush holders  18 ,  136  are attached to the base plate  14  is more easily seen in  FIGS. 5 ,  6  and  9  with references now being made thereto. Each brush holder  18 ,  136  has a mounting surface  174  that slidably contacts a surface  178  on the base plate  14 . Each brush holder  18 ,  136  also has a pair of protrusions  182  that project in opposite directions from the brush holders  18 ,  136  along the surface  174 . 
         [0039]    A plurality of tangs  186 , formed in the base plate  14  in pairs, hold the protrusions  182  to the base plate  14 . Each tang  186  is formed from a tab  190  that includes an axially directed portion  194  and a radially inwardly directed portion  198 . Thus each tang  186  is radially inwardly open and radially outwardly closed. The axially directed portion  194  positions the radially inwardly directed portion  198  above the base plate surface  178  a distance substantially equal to the axial thickness of the protrusions  182 . The brush holders  18 ,  136  are attached to the base plate  14  by sliding the brush holders  18 ,  136  radially outwardly while the surface  174  of the brush holders  18 ,  136  is butted against the surface  178  of the base plate  14  to thereby engage the protrusions  182  with the tangs  186 . The distance between the two tangs  186  that form a pair is substantially equal to the distance across the each brush holder  18 ,  136  where the protrusions  182  protrude from the brush holder  18 ,  136 , thereby locking the brush holders  18 ,  136  from moving circumferentially relative to the base plate  14 . 
         [0040]    The axially directed portion  194  of the tabs  190  form a stop to locate the brush holders  18 ,  136  in a radial position relative to the base plate  14  such that an outer surface  202  of the brush holders  18 ,  136  is generally aligned with an outer circumferential surface  206  of the base plate  14 . The force of the biasing members  26  acting to urge the brushes  30  toward the rotatable conductor  58  is also acting to urge the brush holders  18 ,  136  radially outwardly. This radially outwardly directed force keeps the protrusions  182  in contact with the axially directed portion  194  of the tabs  190  to thereby positively locate the brush holders  18 ,  136  relative to the base plate  14 . Additionally, the base plate  14  may include a flexible tab  210  that protrudes axially from the base plate  14  and engages with a notch  214  formed in the surface  174  of the brush holders  18 ,  136  to lock the brush holders  18 ,  136  to the base plate  14 . 
         [0041]    Additional retainment of the brush holder  18 ,  136  to the base plate  14  can be achieved by locating the brush holders  18 ,  136  between a pair of protuberances  218  that extend axially from the base plate  14  radially outwardly of the tabs  190 . By positioning the protuberances  218  from one another a distance substantially equal to a width of the brush holder  18 ,  136  across the surface  174  the protuberances  218  may decrease vibrational movement in a side-to-side fashion. 
         [0042]    Referring to  FIG. 10  a view directed radially inwardly towards an alternate embodiment base plate  222  with the brush holder  18 ,  136  assembled thereon is depicted. The base plate  222  includes an axially projecting lip  226  extending from the surface  178  around at least a portion of the circumference of the base plate  222 . The lip  226  has dovetail cutout portions  230  shaped to substantially complementarily match a dovetail portion  234  of the brush holders  18 ,  136 . The dovetail cutout portions  230  in addition to providing retainment of the brush holders  18 ,  136  in a side-to-side fashion also provide retainment in and axial direction. That is, the radially outer most portion of the brush holder  18 ,  136  is held axially against the surface  178  by the engagement of the dovetail portion  234  with the dovetail cutout portion  230 . Such retainment may aid in reducing vibration of the brush holders  18 ,  136  in an axial direction. 
         [0043]    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.