Abstract:
Detailed are brush assemblies for electric motors. The assemblies may include lead frames to which leaded electrical components are mounted directly. The lead frames additionally may include two or more conductors and be positioned remote from the brushes of the assemblies.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to brush assemblies for electric motors and more particularly, although not necessarily exclusively, to such assemblies in which leaded electrical components are mounted directly to lead frames.  
       BACKGROUND OF THE INVENTION  
       [0002]     Brush assemblies for use as parts of electric motors are disclosed in numerous patents. Two of many examples of such patents are U.S. Pat. No. 6,664,701 to Ortt, et al. and U.S. Pat. No. 5,990,594 to Hyatt, Jr., et al., the contents of which are incorporated herein in their entireties by this reference. Considered generally, such assemblies house brushes which, in operation, contact a commutator to complete an electrical circuit between the commutator and a power source and cause the commutator to rotate.  
         [0003]     Some existing brush assemblies include brush card housings in which electrical components are mounted, typically for radio-frequency interference (RFI) suppression. Examples of such components include inductors and varistors, either or both of which may be mounted adjacent the brushes of an assembly and connected relatively directly thereto. These mountings may be difficult to effect, however, given the geometries and space limitations of the housings involved. Mounting the components in this manner likewise may be more expensive than optimal.  
         [0004]     Recent alternative approaches to these existing mountings attempt to relocate the electrical components farther from the brushes and their associated housing so as to avoid close proximity to high temperatures. One such relocation approach involves mounting electrical components to a printed circuit board (PCB) and connecting the PCB to a lead frame forming part of the brush card assembly. Existing space limitations mandate that the electrical components be surface-mount, rather than leaded, devices, however. These limitations result in inadequate performance of the RFI suppression components in certain conditions.  
         [0005]     Another approach, recently devised for certain fuel pump modules, includes mounting a single leaded electrical component directly to a two-conductor lead frame. Retainer guides extending opposite the legs of the lead frame are utilized to guide insertion of the component and thereafter maintain its position during various manufacturing processes. Although preferable in some respects to other approaches, this approach—with retainer guides and only two-conductor lead frames—is not optimal for at least some brush assemblies.  
       SUMMARY OF THE INVENTION  
       [0006]     The present invention seeks to resolve issues arising with these and other mounting approaches. Consistent with some approaches, those of the present invention involve relocating electrical components away from brushes and adjacent the lead frame of a brush card assembly. Instead of utilizing a PCB, however, approaches of the invention include directly mounting components to the lead frame. Similarly, rather than relocating only one component to the vicinity of a two-conductor lead frame, the present invention comprises mounting multiple such components to a three-conductor lead frame. Although retainer guides conceivably could be utilized as part of the invention, they need not necessarily be used because of differing manufacturing processes also to be employed.  
         [0007]     Presently preferred manufacturing techniques associated with the invention permit pre-assembly of the lead frame. As a result, multiple leaded electrical components may be securely connected to the lead frame prior to its incorporation into the brush card assembly. Thereafter, the pre-assembled lead frame may have a housing molded around it or be placed into a cavity of a pre-molded brush card housing and a cover molded over the lead frame. Brushes, springs, and other ancillary equipment then may be added within the housing and all electrical connections welded or soldered together. Because the electrical components of the lead frame need be stabilized only during the overmolding process, tooling associated with the molding (rather than retainer guides) may effect any needed stabilization of the components.  
         [0008]     At least one brush card assembly consistent with the present invention includes integral brush card and lead frame housings. Incorporated into the brush card housing are (at least) two brushes and associated biasing mechanisms such as springs. Also included in the brush card housing and electrically connected to the brushes is a thermal circuit breaker designed to cease current flow should its temperature reach a selected threshold.  
         [0009]     Removed from the brush card housing in this embodiment are all electrical components typically used for RFI suppression. The components instead are welded, or otherwise mounted, directly to a lead frame. Additionally, the lead frame is designed to include three conductors (plus, minus, and “ground”), with the ground conductor preferably (but not necessarily) positioned intermediate the others. For the particular components likely to be utilized in connection with commercial versions of the invention, this design facilitates their mounting to the lead frame. Blades of the lead frame are electrically connected to the brushes of the assembly, while the legs connect ultimately to a power source and the ground conductor connects to the motor can itself. Two-conductor lead frames may be utilized instead of the three-conductor versions mentioned above, however, as may lead frames having more than three conductors (if necessary or desired).  
         [0010]     It thus is an optional, non-exclusive object of the present invention to provide brush card assemblies in which leaded electrical components are mounted directly to lead frames.  
         [0011]     It is another optional, non-exclusive object of the present invention to provide brush card assemblies in which lead frames having two or more conductors are employed.  
         [0012]     It also is an optional, non-exclusive object of the present invention to provide brush card assemblies in which lead frames may be pre-assembled and which retainer guides need not necessarily be utilized.  
         [0013]     It is a further optional, non-exclusive object of the present invention to provide brush card assemblies omitting PCBs and surface-mount components yet continuing to provide RFI suppression.  
         [0014]     It is, moreover, an optional, non-exclusive object of the present invention to provide RFI suppression components mounted in a lead frame housing remote from the brushes of the brush card assembly.  
         [0015]     Other objects, features, and advantages of the present invention will be apparent to those skilled in the appropriate art with reference to the remaining text and drawings of this application. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]      FIG. 1  illustrates, in plan view, an exemplary brush card assembly of the present invention together with a commutator.  
         [0017]      FIG. 2  is a cross-sectional view of the brush card assembly (and commutator) taken along lines C-C of  FIG. 1 .  
         [0018]      FIG. 3  is an isometric view of a lead frame, to which electrical components have been mounted, which may form part of the brush card assembly of  FIG. 1 .  
         [0019]      FIG. 4  is a plan view of the lead frame of  FIG. 3 .  
         [0020]      FIG. 5  is an elevational view of the lead frame of  FIG. 3 .  
         [0021]      FIG. 6  is a plan view of the lead frame of  FIG. 3  showing portions of the lead frame opposite those depicted in  FIG. 4 . 
     
    
     DETAILED DESCRIPTION  
       [0022]     Shown in  FIGS. 1-2  is an exemplary brush card assembly  10  of the present invention together with commutator C of an electric motor. Assembly  10  includes housing  14 , which may comprise brush card housing  18  and lead frame housing  22 . Housing  14  preferably is formed of molded plastic or other thermoplastic material that is electrically insulating, although other materials may be utilized instead if appropriate or desired. Additionally, brush card housing  18  and lead frame housing  22  preferably are integrally formed, although they need not necessarily be so created.  
         [0023]     Also depicted in  FIGS. 1-2  is seal material  26 . Frequently made of Santoprene, seal material  26  is friction fitted or otherwise attached to housing  14 . When assembly  10  is positioned within a device for use as part of an electric motor, material  26  may effectively seal against a surface of the device and thereby inhibit debris from entering housing  14 . Those skilled in the relevant art will recognize that seal material  26  need not necessarily be made of Santoprene and need not necessarily form part of assembly  10 , particularly if other means for inhibiting entry of debris into housing  14  exist.  
         [0024]     Positioned within brush card housing  18  may be brushes  30 , two of which are detailed in  FIGS. 1-2 , and associated springs  34 . As is already well known, springs  34  function to bias brushes  30  into contact with commutator C. Wires  38  serve to convey electricity to brushes  30 , the output of one of which may be connected via thermal breaker  42 . Breaker  42 , if present, operates to open the electrical circuit including brushes  30  if its temperature passes a selected threshold.  
         [0025]     Absent from the version of brush card housing  18  illustrated in  FIGS. 1-2  are any inductors or varistors typically employed for RFI suppression. Instead, electrical components  46  in the form of capacitors preferably provide this suppression and are positioned within lead frame housing  22 . Such components  46 , whether or not capacitors, advantageously are leaded and, for example, are not surface-mounted to a PCB.  
         [0026]     Detailed in  FIGS. 3-6  is lead frame  50 . Lead frame  50  is housed within lead frame housing  22  and is beneficially made of tin-plated copper, although other electrically-conductive materials may be used instead. Forming parts of lead frame  50  are legs  54 A and  54 B, blades  58 A and  58 B, and conductors  62 A,  62 B, and  62 C. Conductor  62 A connects leg  54 A to blade  58 A, while conductor  62 B connects leg  54 B to blade  58 B. Conductor  62 C, by contrast, preferably connects to an associated motor can via connector  66 . During the manufacturing process, portions of lead frame  50  marked “A” and “B” may be removed in order to isolate electrically each of conductors  62 A,  62 B, and  62 C from the others.  
         [0027]     As noted in  FIGS. 3-6 , components  46  and connector  66  extend from conductors  62 A-C in the direction opposite legs  54 A-B. However, because conductors  62 A-C include lead holes  70 , leads  74  of electrical components  46  may extend through the holes  70  and be welded, or otherwise connected, to the side  78  from which legs  54 A-B protrude. Depending on the application for assembly  10 , holes  70  may be either custom-formed in lead frame  50  or generically cut therein.  
         [0028]     Blades  58 A-B extend into brush card housing  18 , each for electrical connection (direct or indirect) to a brush  30 . Blades  58 A-B optionally may include guide holes  82  useful for aligning tooling or other equipment during manufacturing processes. Legs  54 A-B are adapted for connection to a source of electrical power so as to allow current to flow to brushes  30  and cause commutator C to rotate. Preferably legs  54 A-B are inserted into openings in a molded connector housing, although they may be electrically connected in any suitable manner to the power source.  
         [0029]     Assembly  10  may be manufactured using any appropriate process. Beneficially, however, lead frame  50  may be created (with portions “A” and “B” intact) and connected to electrical components  46  prior to being positioned within housing  14 . Pre-assembling lead frame  50  and components  46  avoids, among other things, having to weld components  46  within the small area available to do so after lead frame  50  is included within lead frame housing  22 .  
         [0030]     Assembled lead frame  50  may then be positioned within cavity  86  (see  FIG. 2 ) of lead frame housing  22  as the housing  22  is molded around the lead frame  50 . Typically thereafter, seal material  26  will be added if to be included as part of assembly  10 . Because, by this time, handling of electronic components  46  is complete, only brushes  30 , springs  34 , thermal breaker  42 , and their associated wiring need be inserted into brush card housing  18 . Completing the wiring connections and coupling the wiring to blades  58 A and  58 B finishes electrical circuitry associated with assembly  10 .  
         [0031]     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.