Abstract:
Brush spring assemblies for heavy-duty use are addressed. Such assemblies may include constant-force springs used to bias carbon brushes into contact with commutator surfaces. They additionally may include temporary capture mechanisms for the springs, allowing the springs to be retracted—and retained in a retracted position—while brackets containing the springs are inserted into brush holders. Post insertion, the capture mechanisms may be manipulated so as to release the springs, permitting the springs thereafter to bias brushes toward the commutator surfaces.

Description:
FIELD OF THE INVENTION 
   This invention relates to holders, or cards, for devices typically called carbon brushes and more particularly to components of such holders, including retainers for springs included in the holders. The invention is especially, although not exclusively, useful for heavy-duty brush holders deployed on vehicles such as trains. 
   BACKGROUND OF THE INVENTION 
   U.S. Pat. No. 6,246,144 to Hockaday, et al., incorporated herein in its entirety by this reference, illustrates an exemplary holder assembly for two carbon brushes. A pair of coil springs is included within the assembly, with each spring biasing an associated brush toward the surface of a commutator or other rotating machine element. Because the coil springs likely are designed only for light-duty use, the force provided by such springs presumably may easily be overcome by compressing the springs manually. 
   By contrast, brush holders intended for use with locomotives, for example, must withstand much heavier duty. Consequently, their designs differ significantly from that of the Hockaday patent. Moreover, the severity of the environment in which train-mounted brush holders are placed has precluded use of conventional constant-force holders for these purposes. Instead, variable-force holders traditionally are used, notwithstanding that such holders could result in non-uniform performance and life, elevated brush wear, sparking, and increased potential for flash-over. 
   Drive motors for locomotives, furthermore, typically are integral with the drive trains and mounted on the undercarriages of the locomotives. Significant spatial constraints thus exist for the associated brush holders in connection both with their placement for use and their removal for brush replacement. To accommodate these constraints, “finger”-style brush holders have been created. Finger-style holders have low profiles and are easily disengaged from the corresponding brushes so as to facilitate replacement thereof when worn to unacceptable levels. They are, however, non-constant-force devices, as the spatial constraints prevent easy retraction of the their springs when brushes need to be removed and replacement brushes and spring brackets need to be returned to the holders. Indeed, in the past, extraordinary manual force has been required to counteract the spring forces and push spring brackets into brush holders. 
   SUMMARY OF THE INVENTION 
   The present invention resolves the problems created by having to provide extensive manual force to push spring brackets into heavy-duty brush holders (whether for locomotive use or otherwise). Assemblies of the invention include temporary capture mechanisms for the brush springs, allowing the springs to be retracted—and retained in a retracted position—while the brackets are inserted into the holders. Post insertion, the capture mechanisms may be manipulated so as to release the springs, permitting the springs thereafter to bias corresponding brushes toward commutator surfaces. This arrangement permits constant-force springs to be used, further avoiding issues associated with utilizing conventional variable-force springs. 
   Preferred capture mechanisms of the invention include a pair of arms and a sliding retainer. The arms are formed with portions extending outside the footprint of the retainer. As a result, when the retainer slides toward the arms, it tends to force them inward, allowing them to capture the free end of a spring. When the retainer is slid away from the arms, by contrast, the tensioned arms move outward, thereby releasing the free end of the spring. Capture mechanisms of the invention may, however, differ from the presently-preferred version and omit either the arms, retainer, or both the arms and retainer in favor of any other suitable design. 
   Assemblies of the invention additionally may include a generally V-shaped base, with an end of the spring fastened adjacent an end of a first leg of the “V.” Fastened at the other end of the first “V” leg is the capture mechanism. The second leg of the “V” may, if desired, have a complex shape. Such shape, if present, may be designed to latch the assembly in place within a holder while allowing easy removal thereof for repair or brush replacement. 
   It thus is an optional, non-exclusive object of the present invention to provide mechanisms for retracting springs (or other biasing devices) and at least temporarily retaining them in retracted positions. 
   It is another optional, non-exclusive object of the present invention to provide such mechanisms which may release the springs after being inserted into brush holders for use. 
   It is also an optional, non-exclusive object of the present invention to provide brush assemblies permitting constant-force springs to be used with locomotives and in other extreme environments. 
   It is, furthermore, an optional, non-exclusive object of the present invention to provide assemblies that may easily be removed from holders when necessary or desired. 
   Other objects, features, and advantages of the present invention will be apparent to those skilled in the relevant art with reference to the remaining text and drawings of this application. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1A  illustrates an exemplary brush spring assembly of the present invention with the spring unretracted. 
       FIG. 1B  illustrates the brush spring assembly of  FIG. 1A  with the spring retracted. 
       FIG. 2  illustrates an exemplary heavy-duty brush holder adapted to hold three brushes as well as three brush spring assemblies consistent with  FIGS. 1A-B . 
       FIG. 3  illustrates the brush spring assembly of  FIG. 1B  immediately prior to release of the spring. 
       FIG. 4  illustrates the brush spring assembly of  FIG. 1B  immediately after the release of the spring. 
       FIGS. 5A-C  illustrate an exemplary process that may be used to capture the spring of the brush spring assembly of  FIG. 1B . 
       FIG. 6  illustrates an exemplary first alternative brush spring assembly of the present invention. 
       FIG. 7  illustrates an exemplary second alternative brush spring assembly of the present invention. 
       FIG. 8  depicts a generic brush capable of use with a brush holder described herein. 
   

   DETAILED DESCRIPTION 
     FIGS. 1A-1B  detail exemplary brush spring assembly  10  of the present invention. Preferably included as part of assembly  10  are spring  14 , base  18 , and capture mechanism  22 . Also shown in  FIGS. 1A-1B  are one or more fasteners  26 , which function to attach end  30  of spring  14  to base  18 . Although rivets  34  and bar  38  (see  FIG. 2 ) constitute preferred fasteners  26 , those skilled in the art will recognize that numerous other fastening mechanisms may be used instead. 
     FIG. 1A  details metallic spring  14  in a rolled, unretracted position. In this rolled position, it is available to contact and bias an associated brush toward a commutator surface. Further, because of its construction, spring  14  may provide relatively constant bias force to the brush, avoiding problems related to utilizing non-constant-force springs. 
   By contrast,  FIG. 1B  illustrates spring  14  in a partially unrolled, retracted position. In this position, spring  14  defines two portions: a generally linear portion  42  and a rolled portion  46 . As shown in  FIG. 1B , rolled portion  46  may be retained by capture mechanism  22 , a significant feature of the present invention. When portion  46  is so retained, assembly  10  may be fitted manually into holder  50  (see  FIG. 2 ) without the installer having to apply force to counteract that of spring  14 . 
   Shown in  FIG. 2  is an exemplary holder  50 . As illustrated, holder  50  accepts three brushes and three corresponding assemblies  10 , one each in areas  54 A,  54 B, and  54 C. Holder  50  need not accept exactly three brushes, however, and instead may accept fewer or greater than this number. Likewise, neither holder  50  nor insulator pins  58  need be configured as detailed in  FIG. 2 . 
   Also shown in  FIG. 2  are three assemblies  10  in differing states of readiness for use. Assembly  10 A, for example, has been prepared for insertion into area  54 A, with spring  14  retained by capture mechanism  22  in a retracted position. Assembly  10 C is illustrated as inserted into area  54 C, with spring  14  having been released from capture mechanism  22  so as to contact a face of a brush (not shown) below. Assembly  10 B, by contrast, is in process of being removed from area  54 B as, for example, when it must be repaired or its associated brush must be replaced. 
     FIGS. 1-4  also detail aspects of exemplary base  18 . Base  18  may (but need not necessarily) comprise a generally “V” shape made of metal, with legs  62  and  66  terminating at vertex  70 . Leg  62 , further, preferably may be substantially flat or linearly-oriented, while leg  66  preferably has a more complex shape. Base  18  may be made of metal or any other material allowing legs  62  and  66  manually to be forced closer together, as by an installer pushing leg  66  toward leg  62  in the direction of arrow A. Thus, if recessed segment  74  helps latch assembly  10  in position within holder  50 , the latching may be undone merely by having the installer push flange  78 , thereby causing leg  66  to travel in the direction of arrow A. 
     FIGS. 1-4  similarly show features of a retaining means such as capture mechanism  22 . Like spring  14 , mechanism  22  preferably is connected to base  18 . Mechanism  22  also preferably is connected to leg  62  of base  18  opposite vertex  70 . Consequently, some distance D exists between mechanism  22  and end  30  of spring  14 , thereby allowing portion  42  to be unrolled approximately distance D before being captured by mechanism  22 . Mechanism  22  may be made of polyetherimide obtained from, e.g., Polymer Resources, Ltd., or any other suitable material. 
   Certain embodiments of mechanism  22  comprise arms  82  and  86 , retainer  90 , and foot  94 . Foot  94  is fastened in any appropriate way to leg  62 , and arms  82  and  82  are either connected to or integrally formed with foot  94 . Generally U-shaped retainer  90  includes channels positioned about arms  82  and  86  and is configured so as to be able to slide forward and back along arms  82  and  86 .  FIG. 3  illustrates retainer  90  in its forward position, while  FIG. 4  depicts the retainer  90  in its rearward position. Protrusion  98 , if present, may be employed to facilitate sliding retainer  90  using a thumb or finger of an installer. Mechanism  22  further is configured in any manner suitable to prevent retainer  90  from separating entirely from foot  94 . 
   As illustrated especially in assembly  10 C of  FIG. 2  and in  FIG. 4 , arms  82  and  86  may cant outward, beyond the footprint of retainer  90 . As a result, as retainer  90  slides forward, it forces arms  82  and  86  inward, as shown by assemblies  10 A and  10 B of  FIG. 2  and in  FIG. 3 . Sliding retainer  90  rearward, therefore, allows arms  82  and  86  to spring out, back to their normal (canted) positions. 
   Arms  82  and  86  include respective fingers  102  and  106 . As arms  82  and  86  are forced inward, so too are fingers  102  and  106  until they project well into space  110  (see  FIG. 1B ) formed by rolled portion  46 . As so projecting, fingers  102  and  106  function to lock rolled portion  46  in place, thereby retaining spring  14  in its retracted position. 
   Detailed in  FIGS. 5A-C  are sequential operations that may be employed to prepare spring  14  for retention within capture mechanism  22 . Shown in these figures is a table T with a vertical surface V terminating in lower edge E. If assembly  10  is moved toward table T (as shown by directional arrow B in  FIG. 5A ), spring  14  eventually will contact surface V. Further movement of assembly  10  in direction B, with leg  62  passing below edge E, will result in surface V forcing spring  14  to begin unrolling ( FIG. 5B ) in the direction of arrow C. Continued movement of assembly  10  in direction B results in further unrolling of spring  14 , creating linear portion  42  and placing rolled portion  46  in position for capture by mechanism  22  ( FIG. 5C ). 
   Reference to table T, surface V, and edge E herein is for explanatory purposes only. Persons skilled in the art will recognize that numerous alternate methods of appropriately positioning spring  14  exist for capture by mechanism  22 . Although some of these methods conceivably could employ a table or vertical surfaces, they need not necessarily do so. 
     FIGS. 6 and 7  illustrate respective alternate assemblies  10 ′ and  10 ″. Like assembly  10 , each of assemblies  10 ′ and  10 ″ may incorporate spring  14 , respective bases  18 ′ and  18 ″, and respective capture mechanisms  22 ′ and  22 ″. Mechanisms  22 ′ and  22 ″, further, may include respective pairs of arms  82 ′,  86 ′,  82 ″, and  86 ″ and fingers  102 ′,  106 ′,  102 ″, and  106 ″. Unlike arms  82  and  86 , however, arms  82 ′,  86 ′,  82 ″, and  86 ″ may be canted inward and, effectively, hinged. Pivoting arms  82 ′,  86 ′,  82 ″, and  86 ″ outward allows release of a retained spring  14  or positions the arms appropriately to capture rolled portion  46 . 
   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.