Abstract:
Brush card or holder assemblies are disclosed. The assemblies avoid any need for a separate plastic cap and utilize a lead wire (which could be or include a rod or other electrically-conductive device) both electrically to connect a brush to an external component and mechanically to fix the position of one end of a mechanism, such as a spring, for biasing the brush toward the surface of a commutator or other rotating machine element.

Description:
FIELD OF THE INVENTION 
     This invention relates to assemblies including holders, or cards, for devices typically called carbon brushes and more particularly to holders for such brushes in which a lead functions not only to carry electricity to or from a brush but also to compress a spring or other mechanism used to bias the brush toward a rotating mechanism such as a commutator. 
     BACKGROUND OF THE INVENTION 
     U.S. Pat. No. 5,621,262 to Han, incorporated herein in its entirety by this reference, illustrates in its FIGS. 1 and 2 exemplary existing carbon brush holders. Both holders include (unlettered) caps, typically formed of plastic like material B of FIG. 1. Additionally shown in FIG. 2 are a brush C to which a lead is attached or embedded, with the lead in turn being connected to terminal G. An (unlettered) spring biases brush C (downward in the drawing) toward the surface of a rotating commutator, with the cap of the holder serving to compress the spring and effectively fix the position of one of its ends. 
     Also disclosed in the Han patent are various embodiments of a brush holder in which a flexible copper lead connects a brush to an element denoted a “brush terminal,” which brush terminal in turn contacts an element called the “lead terminal.” Like the brush holder of FIG. 2 of the Han patent, these other embodiments may contain a spring useful to bias the brush to contact the surface of a commutator. As illustrated in FIG. 15 of the Han patent, for example, the position of one end of the spring (the upper end shown in the drawing) is fixed by the brush terminal and underside of a cap screwed into the holder body, while its other end abuts a carbon brush. According to the Han patent, the cap is plastic and functions also to press together the lead and brush terminals. 
     Other commercially-available designs involving torsion springs include seventeen components, while those utilizing leaf and coil springs may contain as many as thirteen components. Typical coil-spring designs, for example, require not only a card and dual shunted brushes, but also two brush boxes, two coil springs, two lead wires, and four terminals (two to the brush boxes and two to external switches). Assembly of these coil-spring designs requires two repetitions of eight steps, including (1) inserting a spring into a brush box, (2) inserting a brush into the brush box, (3) bonding the shunt wire to the brush box, (4) bending the tab of the brush box to retain the brush and spring within the box, (5) bonding one end of a lead wire to a terminal (to the brush box), (6) bonding the other end of the lead wire to a terminal (to an external switch), (7) mounting the brush box assembly to a brush card, and (8) inserting a lead wire and terminal into a terminal of the brush box. Although assembly of existing leaf-spring designs necessitates two repetitions of fewer steps (six rather than eight), it nonetheless continues to require steps of bonding of lead wires and leaf springs to terminals or mounts and interconnecting the components via the terminals. 
     SUMMARY OF THE INVENTION 
     The present invention, by contrast, encompasses assemblies of brush cards or holders containing as few as nine components in some dual-brush embodiments and whose assembly is less complex than those techniques described in the preceding section. It additionally avoids any need to use a separate plastic cap such as that of the brush holders of the Han patent. Instead, a single lead wire (which could be or include a rod or other electrically-conductive device) not only electrically connects the brush and an external switch but also mechanically fixes the position of one end of a biasing mechanism such as a spring. By utilizing a lead wire with sufficient rigidity to withstand the expansive force of the spring without significant deformation and securing its position vis-a-vis the abutting end of the spring, the cards of the present invention provide simpler devices for holding functional carbon brushes. 
     Certain embodiments of the present invention contemplate placement of two conductive blocks such as brushes in a card or holder, each designed to contact the same rotating object (e.g. a commutator) in use. However, to complete an electrical connection between the commutator and an external device (such as but not limited to a switch), only a single block or brush is necessary. Thus, for a shunted brush, only a card, biasing means, and a lead wire are necessary to convey electricity reliably from the commutator to an external device (or vice-versa). Typically one end of the lead wire is connected to the shunt, while the other connects directly or indirectly (through, e.g., a terminal) to the external device. 
     In addition to being connected to the shunt, the lead wire of the present invention may also be secured to the brush card itself. Embodiments of the invention are designed for the lead wire to be the subject of an interference fit with a slot in the card. However, those skilled in the art will recognize that other means (including adhesive as one of multiple examples) may be employed to retain the lead wire in position respecting the brush card. 
     Assuming the biasing means is a coil spring, one end of the spring abuts the end of the brush opposite the commutator to allow the spring force to press against the commutator surface. The other end of the spring directly (or indirectly if appropriate) abuts the lead wire, typically in an insulated area of the wire. Because the lead wire is selected to withstand the expansive force of the spring without significant deformation, it provides an essentially immovable base against which the spring can expand in the opposite direction. 
     It is therefore an object of the present invention to provide a card or holder for an electrically-conductive brush. 
     It is also an object of the present invention to provide a brush card assembly which is simpler to assemble and requires fewer components than analogous conventional assemblies. 
     It is another object of the present invention to provide a brush card assembly which does not require any plastic cap. 
     It is an additional object of the present invention to provide a brush card assembly in which a lead wire not only electrically connects to the brush but also mechanically fixes the position of one end of a mechanism (such as a spring) used to bias the brush against the surface of a rotating machine such as a commutator. 
     It is a further object of the present invention to provide an assembly in which the lead wire is sufficiently rigid to withstand the expansive force of a spring without significant deformation. 
     It is yet another object of the present invention to provide an assembly in which the lead wire is secured to the brush card as, for example, by an interference fit. 
     Other objects, features, and advantages of the present invention will be apparent with reference to the remaining text and the drawings of this application. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is an exploded perspective view of a section of a dual-brush embodiment of a card assembly of the present invention. 
    
    
     DETAILED DESCRIPTION 
     Illustrated in FIG. 1 is an exemplary assembly  10  of the present invention. As shown in the sectional view of FIG. 1, assembly  10  may comprise holder or card  14 , brushes  18 A and  18 B, coil springs  22 A and  22 B, and lead wires  26 A and  26 B. Also illustrated in FIG. 1 are terminals  30 A and  30 B and shunts  34 A and  34 B, the latter of which are embedded or otherwise electrically connected respectively to brushes  18 A and  18 B. 
     Card  14  typically defines an opening  38  designed to surround or circumscribe a commutator of an electric motor. Either or both of brushes  18 A and  18 B contact the surface of the commutator in use, with their edges  42 A and  42 B wearing over time because of, among other phenomena, the frictional contact with the commutator. Protruding typically (although not necessarily) from a face at or near the opposite edge  46 A of brush  18 A is shunt  34 A, used to carry electricity to or from the brush  18 A. Brush  18 B may be similarly configured, with current-carrying shunt  34 B protruding either from edge  46 B of the brush  18 B or from a face of the brush other than edge  42 B. Because each of brushes  18 A and  18 B is made of electrically conductive material (carbon or graphite of low electrical resistance, for example), electrical current can flow from shunt  34 A or  34 B through the associated brush  18 A or  18 B to the commutator surface (or vice-versa). 
     Card  14  also defines slots, often oriented in a common plane, into which brushes  18 A and  18 B may be fitted. FIG. 1 illustrates brush  18 A as fitted into its corresponding slot, while a portion of slot  50  for brush  18 B is visible in the drawing. Additionally positioned within these slots are springs  22 A and  22 B, each having a respective end  54 A or  54 B designed to urge brush  18 A or  18 B against the commutator surface. 
     Defined as part of card  14 , moreover, are a second set of slots (typically but not necessarily oriented generally perpendicularly to slots  50 ) into which lead wires  26 A and  26 B may be fitted. FIG. 1 details a portion of one of these slots  58 , each of which in some embodiments receives a lead wire  26 A or  26 B and retains the wire in place with an interference fit. As so fitted, lead wires  26 A and  26 B abut respective ends  62 A and  62 B of springs  22 A and  22 B. Thus, by forming lead wires  26 A and  26 B of material sufficiently rigid to withstand the expansive force of their associated springs  22 A and  22 B without significant deformation, the wires  26 A and  26 B can function as relatively immobile bases (or boundaries) for the springs  22 A and  22 B. As a consequence, no other component, such as a plastic cap or other non-deformable part, is required to retain the springs  22 A and  22 B in slots  50 . 
     Although slot  58  and an interference fit are presently preferred methods of securing lead wires  26 A and  26 B to card  14 , those skilled in the art will recognize that other suitable methods of affixing the lead wires  26 A and  26 B to the card  14  may exist. As noted above, the present invention contemplates securing each of lead wires  26 A and  26 B in position with sufficient force to withstand (and overcome) attempted expansion of springs  22 A and  22 B by movement of their ends  62 A and  62 B. Any such securing means that provides this force, therefore, may be used when necessary or desired. 
     In addition to serving as bases for springs  22 A and  22 B, lead wires  26 A and  26 B function to convey electricity to or from respective brushes  18 A and  18 B. Uninsulated portion  66 A of lead wire  26 A is thus shown electrically connected to shunt  34 A, while corresponding portion  66 B of lead wire  26 B electrically connects to shunt  34 B. The electrical connections may be made directly (as, for example, by adhering or bonding the lead wires  26 A and  26 B into contact with respective shunts  34 A and  34 B) or indirectly using any appropriate means of establishing such connections. 
     Each of lead wires  26 A and  26 B typically terminates in a terminal  30 A or  30 B (often crimped about or bonded to the wire) for connection to an external switch or other device or component. Because shunts  34 A and  34 B are flexible, they can continue to connect lead wires  26 A and  26 B to brushes  18 A and  18 B, respectively, notwithstanding wear of edges  42 A and  42 B and movement of the brushes  18 A and  18 B under the force of springs  22 A and  22 B. Electrical communication between brushes  18 A and  18 B and lead wires  26 A and  26 B alternatively could occur through springs  22 A and  22 B (if such springs are made of conductive material such as uninsulated metal and insulation  70  is removed from the lead wires), although such electrical communication is not as reliable as when the shunts  34 A and  34 B are employed. 
     Although coil springs  22 A and  22 B are shown in FIG. 1, they are not the only means of biasing brushes  18 A and  18 B useable in connection with the present invention. Instead, any mechanism (for example mechanical or electrical) capable of urging brushes  18 A and  18 B toward opening  38  could in some cases be appropriate. Furthermore, assembly  10  need not incorporate two brushes  18 A and  18 B, as assemblies having only one brush  18 A may be made consistent with the present invention. In such case assembly  10  would not necessarily include any of brush  18 B, spring  22 B, lead wire  26 B, or terminal  30 B, nor would one each of slots  50  and  58  associated with these components be needed. Of course, assembly  10  alternatively may include more than two brushes  18 A and  18 B when desired. 
     Building assembly  10  is straightforward. One assembly method begins by inserting brush  18 A, followed by spring  22 A, into card  14 . Lead wire  26 A is then pressed (fitted) into its corresponding slot  58  and shunt  34 A is electrically connected to portion  66 A of the lead wire  26 A. If terminal  30 A is used, it can then be crimped or bonded onto (or otherwise attached to) lead wire  26 A. These steps may, of course, be repeated if brush  18 B is utilized in card  14  and varied or reordered as necessary or desired. 
     The foregoing is provided for purposes of illustrating, explaining, and describing embodiments of the present invention. Modifications and adaptations to these embodiments will be apparent to those skilled in the art and may be made without departing from the scope or spirit of the invention.