Abstract:
A laminar electrical connector is provided that is formed from multiple superimposed strips of conductive material that form a stack having at least two ends. A second conductive material is used to join adjacent superimposed strips. The resultant connector has ends that are adapted to engage electrical terminals and provide an electrical communication therebetween. The resultant connector lacks a sheath on the ends or a grommet extending through the stack. Such a sheath or grommet limits the operative lifetime of the resulting connector and also creates current focusing that diminishes overall connector efficiency. A connector having a continuous layer of the second conductive material joining adjacent strips along the entire interface between the adjacent strips is also provided and improves connector performance in ways that are especially beneficial to applications associated with an electric vehicle or a hybrid vehicle.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention in general relates to an electrical connector and in particular to a laminar electrical connector having improved terminal conductivity and longevity. 
       BACKGROUND OF THE INVENTION 
       [0002]    Electrical connectors have long been made from superimposed plates or strips of conductive metal representative of these articles of those detailed in U.S. Pat. Nos. 710,532; 1,588,556; 2,074,810; and 2,092,505. The common characteristic of these earlier connectors is the inclusion of a sheath or grommet surrounding the hole in the connector, the hole engaging an electrical terminal. Securement of such a connector between two electrically insulated regions allowed these connectors to convey electrical current between the terminals. While prior art connections were well suited for a number of uses, technical innovations associated with electric and hybrid powered vehicles have created performance demands that existing electrical connectors are unable to satisfy. In particular, electrical current concentration around a sheath or grommet produces inefficient electrical transmission, localized heating that changes connector metal temper, and additional material interfaces that are prone to failure. All of these limitations of conventional connectors are made more pronounced by installation in a vehicle where weight considerations, environmental exposure, and vibration are accentuated relative to stationary uses. 
         [0003]    Thus, there exists a need for an electrical connector that provides superior performance and ease of manufacture through the exclusion of a sheath or grommet around a connector pole designed to engage an electrical terminal. 
       SUMMARY OF THE INVENTION 
       [0004]    A laminar electrical connector is provided that is formed from multiple superimposed strips of conductive material that form a stack having at least two ends. A second conductive material is used to join adjacent superimposed strips. The resultant connector has ends that are adapted to engage electrical terminals and provide an electrical communication therebetween. The resultant connector lacks a sheath on the ends or a grommet extending through the stack. Such a sheath or grommet limits the operative lifetime of the resulting connector and also creates current focusing that diminishes overall connector efficiency. A connector having a continuous layer of the second conductive material joining adjacent strips along the entire interface between the adjacent strips is also provided and improves connector performance in ways that are especially beneficial to applications associated with an electric vehicle or a hybrid vehicle. 
         [0005]    A process for manufacturing a laminar electrical connector stack includes superimposing strips of a first conductive material having a first material melting temperature to form a stack. A layer of second conductive material having second conductive material melting temperature less than the first conductive material melting temperature is placed between adjacent superimposed strips. Resistive heating of the stack to a temperature greater than two thirds of the second material melting temperature and less than the first conductive material melting temperature increases electrical conductivity and delamination strength of the stack in a direction transverse to the stack. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a simultaneous longitudinal and transverse cross-sectional view of an inventive dual end laminar electrical connector; and 
           [0007]      FIG. 2  is a perspective view of an inventive multiple ended laminar electrical connector. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0008]    The present invention has utility as an electrical connector. An inventive connector is particularly well-suited to operate in an environment associated with an electric or hybrid vehicle. Particularly beneficial features of an inventive connector include exclusion of a sheath or grommet surrounding a connector engagement with an extrinsic electrical terminal so as to limit current focusing and mechanical failure associated with the additional sheath or grommet. Additionally, an inventive connector includes layers of a lower melting temperature material relative to the strip material to improve performance of the resultant connector and provide a manufacturing scheme that does not rely on dipping connector ends into molten solder. 
         [0009]    The inventive electrical connector is shown generally at  10  in  FIG. 1 . The connector  10  is formed from multiple conductive material strips  12  that are superimposed to form a stack  14 . The connector  10  has ends at  16 A and  16 B. The ends  16 A and  16 B are each adapted to engage an extrinsic electrical terminal T to provide an electrical conduction path therebetween. It is appreciated that end  16 A or  16 B is amenable to functioning as an electrical contact with an electrical terminal T through a clamp that engages a stack  14 . Superior current flow characteristics are obtained in the end portion  16 A or  16 B, preferably, through formation of a hole  18  or notch  20  through the stack  14 . The hole  18  or notch  20  is adapted to engage an electrical terminal T or otherwise form a high surface area electrical contact with the electrical terminal T through insertion of a fastener F or other conventional component to the hole  18  or notch  20 , and into electrical communication with the electrical terminal T. It is appreciated that the presence, dimensions, and shape of a hole  18  or notch  20  in one end of an inventive connector  10  is wholly independent from those present in another end of the connector  10 . By way of example, a hole is circular, oblong or of a polygonal cross-sectional shape. The surface portions of the stack  14  intermediate between ends  16 A and  16 B are preferably covered with a polymeric electrical insulator. Polymeric electrical insulators  22  operative herein illustratively include Thermoplastic elastomers (TPE), Thermoplastic vulcanizates (TPV), poly vinyl chloride (PVC), Polytetrafluoroethylene, silicone, polyolefin, neoprene, and varnish. An inventive electrical conductor  10  is without a sheath surrounding the end portion  16  of stack  14  and also without a grommet, rivet, or ferrule surrounding a hole  18  or notch  20  formed in end  16 A or  16 B. 
         [0010]    A strip  12  used to form the stack  14  is chosen on a basis of electrical conductivity properties as well as operational longevity in the environment in which a given inventive electrical connector  10  is applied. Representative material suitable for the formation of a conductive strip  12  illustratively include copper, aluminum, iron, silver, and alloys thereof; steel; intermetallics; superconductors; pnictides, alloys thereof, and laminate thereof. Copper and copper alloys represent preferred compositions for a strip  12 . More preferably, half hard and spring tempered copper and copper alloys used to form a strip  12 , and in particular for a connector  10  operative in a vehicle application. To form a stack  14  multiple metal strips  12  are superimposed with complimentary contours so as to provide as a preferred embodiment to a stack  14  with limited voids between each of the strips  12  therein. 
         [0011]    A stack  14  of superimposed metal strips  12  are readily joined into a unified body both structurally and electrically by conventional techniques illustratively including: dipping an end into a molten solder with the solder having a lower melting temperature than the superimposed conductive strips  12  material; heating an end  16 A or  16 B to a temperature sufficient to fuse various strips  12  together through techniques, such as induction welding; and dipping an end  16 A or  16 B into a conductive paint to intercalate conductive particulate, such as carbon black or metallic flake into the interstitial planes between adjacent strips  12  and an adjoining strip. While these conventional techniques are operative to form an inventive electrical connector  10 , to conventional techniques has been found to limit overall connector performance. By way of example, solder dipping provides incomplete wetting, produces a stack with internal compressive stress, creates concentrated points of concurrent flow, leaves voids within the stack  14  and portions thereof that are not dipped into the solder bath. The other techniques of strip fusion and conductive paint application also suffer similar limitations. 
         [0012]    In order to provide a higher performance electrical connector, a second conductive material  24  is provided as a layer sandwiched between adjacent superimposed strips  12 . The second conductive material  24  preferably covers the majority of the surface interface between adjacent conducting strips  12 . More preferably, all of the surface interface is so covered by material  24 . The second conductive material  24  is chosen to have a melt temperature less than that of the conductive strip  12  such that upon heating a stack  14  having conductive material  24  sandwiched along the interface between two superimposed strips  12  to a temperature between the annealing temperature and just above melting temperature of the conductive material  24 , the stack  14  is physically and electrically joined through the thickness, t of the stack  14 . As used herein, the annealing temperature is defined as two thirds of the melt temperature for the second conductive material  24 , in degrees Kelvin. 
         [0013]    It is appreciated that a conductive material  24  is readily applied as a surface coating onto a sheet of material from which a strip  12  is formed. Alternatively, second conductive material  24  is applied as a powder, plating, or a dip coating on a strip  12 . Such a coating is also optionally applied to both opposing surfaces of a strip  12  such that the interface between superimposed strips  12  has a layering: (conductive strip material-second conductive material)/(second conductive material-conductive strip material). The use of dual surface coated strips with both strip surfaces surface being coated with conductive material are especially preferred since contact formation then involves like materials of second conductive material  24  becoming physically joined together and at a temperature that does not change the temper of the conductive strip material. In instances when the strips  12  are copper or copper alloys; tin, tin-based alloys, bismuth, and bismuth-based alloys represent preferred second conductive materials  24 . It is appreciated that the second conductive material  24  is formed of any of the material from which a strip  12  is formed with the proviso that the second conductive material  24  has a melt temperature below that of the conductive strip material. 
         [0014]    In a preferred process of forming inventive conductor  10 , a stack of superimposed conductive material strips  12  and the interface between adjacent superimposed strips including a second conductive material layer  24  are aligned and fixtured. An electrical current is applied to the fixtured stack so as to resistively heat the stack  14  to a temperature of between the annealing temperature and just above the melt temperature of the second conductive material  24 . Upon reduction of current input to the stack  14 , the second conductive material  24  hardens to form a joined stack  14 , with high strength and high conductivity relative to conventional joining techniques. It is appreciated that by controlling the current, the thermal profile of stack joining is controlled to mitigate interfacial stresses and control defect formation. 
         [0015]    An inventive connector  10  is formed from superimposing at least two strips  12 . Typically, between 2 and 50 strips  12  are superimposed. Preferably, between 2 and 20 strips  12  are superimposed to form a stack  14 . It is appreciated that a strip  12  need not have the same elemental composition as another strip  12  within the same stack  14 . 
         [0016]    An inventive connector well suited for electrically joining a vehicle battery with the components of an electrical or hybrid vehicle includes copper as the majority composition of the stack  14 . A stack  14  for a vehicle applications typically has a thickness, t of between 0.5 and 4 millimeters and a width, w of typically between 10 and 40 millimeters and has a current carrying capacity of a 8 to 0000 American Wire Gauge (AWG) standard circular cross section copper wire. 
         [0017]    Referring now to  FIG. 2  where like numerals correspond to the meaning ascribed to those numerals with respect to  FIG. 1 , a multiple-ended inventive conductor is shown generally at  30 . The connector  30  is formed from superimposed conductive strips that form a stack as detailed above with respect to  FIG. 1 . The strips used to form the connector  30  are stamped from a sheet and superimposed as detailed above with respect to  FIG. 1 . Connector  30  is noted to have three ends  32 A,  32 C, and  32 D. End  32 A has a circular hole  18  and  32 D has an oblong hole  18  therethrough. End  32 C includes a notch  20 . Connector  30  has ends of lesser thickness at  32 C and  32 D relative to end  32 A and is particularly well suited for current splitting to electrical terminals joined to ends  32 C and  32 D that require less current-carrying capacity. Bend regions  34  of electrical connector  30  are readily created any time during the process of electrical connector formation including stamping such contours into the strips, bending a joined stack or bending a joined stack already covered with polymeric insulator  22 . 
         [0018]    Patent documents and publications mentioned in the specification are indicative of the levels of those skilled in the art to which the invention pertains. These documents and publications are incorporated herein by reference to the same extent as if each individual document or publication was specifically and individually incorporated herein by reference. 
         [0019]    The foregoing description is illustrative of particular embodiments of the invention, but is not meant to be a limitation upon the practice thereof. The following claims, including all equivalents thereof, are intended to define the scope of the invention.