Abstract:
Disclosed herein are methods and apparatus for providing a strain relief for use in the assembly of an electrical connector on an end of an electrical conductor having at least an outer braided portion, which may be surrounded by an insulating cover. The methods and apparatus disclosed herein provide a low cost approach for installation using minimal tooling, while providing a precise and robust relief that ensures electrical performance.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority under 35 U.S.C. 119(e) to U.S. Provisional Patent Application No. 60/379,353, filed May 10, 2002. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to electrical connectors and, more particularly, to a strain relief used in an electrical connector and conductor assembly. 
     2. Brief Description of Prior Developments 
     In some conventional electrical connector and cable assemblies, the most common way to electrically join the cable braid to the metal shell is to crimp a metal ferrule over the braid, and compress the ferrule slightly when the shell is closed. Typically, crimping is completed manually, and therefore is imprecise. 
     There is a concern with this type of system in that over crimping the wire pairs could damage the dielectric, such as in the case where too great a crimping force is applied. For example, degradation in electrical performance can result from applying excessive force during the crimping. There is also a concern that crimping to the soft jacket is not a reliable strain relief should the cable be pulled away from the connector. 
     SUMMARY OF THE INVENTION 
     The present invention provides a solution to these problems and others. The techniques disclosed herein provide for a strain relief that can be tailored to meet a specific need. With better control over aspects of the manufacture and installation of the strain relief, better control over electrical performance and other aspects are achieved. 
     In embodiments of the strain relief disclosed herein, the strain relief provides additional benefits. For example, in one embodiment of the strain relief disclosed herein, little or no additional tooling is required for installation of the strain relief, thus improving installation time and reducing installation expenses while maintaining electrical performance. Multiple strain reliefs may be manufactured, with little additional expense. Furthermore, distribution of multiple size strain reliefs can be accomplished with minimal handling. 
     In one embodiment, an overmolded strain relief is provided. The use of a low pressure overmolding process does not damage the wires of the cable. In an alternate embodiment of the present invention, rather than overmolding the strain relief onto the cable, a slip-on strain relief is provided and is subsequently slipped onto the cable. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of an end of an electrical connector and cable assembly incorporating features of the present invention; 
     FIG. 2 is a perspective view of the cable and strain relief shown in FIG. 1 before attachment to the electrical connector; 
     FIG. 3 is a perspective view of the strain relief shown in FIG. 1; 
     FIG. 4 is a rear elevational view of the strain relief shown in FIG. 3; 
     FIG. 5 is a side elevational view of the strain relief shown in FIG. 3; 
     FIG. 6 is a front elevational view of the strain relief shown in FIG. 3; 
     FIG. 7 is a perspective view of a second embodiment of the strain relief where three strain reliefs appear on a single strip; 
     FIG. 8 is a rear elevational view of a single strain relief as shown in FIG. 7; 
     FIG. 9 is a front elevational view of a single strain relief as shown in FIG. 7; 
     FIG. 10 is a side view of a single strain relief as shown in FIG. 7; and, 
     FIG. 11 is a partially exploded perspective view of the electrical connector and cable assembly shown in FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, there is shown a perspective view of an end of an electrical connector and cable assembly  10  incorporating features of the present invention. Although the present invention will be described with reference to the exemplary embodiments shown in the drawings, it should be understood that the present invention can be embodied in many alternate forms of embodiments. In addition, any suitable size, shape or type of elements or materials could be used. 
     The strain relief is generally discussed in reference to FIGS. 2-6 as a one-piece overmolded strain relief  18 . Further aspects of a second and preferred embodiment, that of a slip-on strain relief  77 ,  79 ,  81 , are discussed in reference to FIGS. 7-10. 
     The electrical connector and cable assembly  10  generally comprises an electrical conductor assembly  12  and an electrical connector  14 . Referring also to FIG. 2, the electrical conductor assembly  12  generally comprises an electrical conductor cable  16 , and a low pressure overmolded strain relief  18 . The cable  16  is a common electrical conductor cable. The cable  16  generally comprises a plurality of electrical conductors  20 , an inner insulator  22 , an electrically conductive outer braid  24 , and an outer insulator cover  26 . In the embodiment shown, the cable comprises pairs of conductors surrounded by individual insulating covers and a cover over each pair of conductors and covers. However, in alternate embodiments, any suitable type of electrically conductive cable could be provided. 
     In one embodiment, the strain relief  18  is overmolded onto the outer insulator cover  26 . In one embodiment, the strain relief  18  is overmolded by a low pressure molding process. A mold is closed over the cable  16 . A low pressure material, such as a thermoplastic, fills the cavity of the mold. Non-limiting examples of suitable materials include polypropylene and 6-6 Nylon™. After curing, the mold is opened leaving the remaining casting  18 . 
     Referring also to FIGS. 3-6, the strain relief  18  is formed as a one-piece molded plastic or polymer member. The strain relief  18  generally comprises a rear section  28 , a front section  30 , a recessed area  32  between the front section and the rear section, and a center aperture  34 . The center aperture  34  extends through the strain relief  18  between its front end and its rear end. 
     The rear section  28 , in the embodiment shown, comprises a general round ring shape. The rear section comprises a generally flat or smooth exterior end surface portion. However, in alternate embodiments, any suitable shape could be provided. The front section  30  comprises a general ring shape with a general hexagon outer shape. The front section also comprises a generally flat or smooth exterior end surface portion. The hexagon outer shape provides flat surfaces  36  on the outer sides of the front section. In alternate embodiments, the front section could comprise any suitable type of polygonal shape, or could comprise any suitable type of shape which includes at least one flat surface or a surface contoured to mate with a mating surface of the electrical connector shell (with a portion of the braid  24  therebetween) as further described below. 
     Referring to FIG. 7, a second embodiment of the strain relief is shown. In FIG. 7, a set of three strain reliefs  77 ,  79 ,  81  are shown as produced together in one separate molding process. The strain reliefs  77 ,  79 ,  81  are shown as connected by excess material in the form of flashing  87  resulting from molding. The flashing  87  may be left in place for neatly grouping the strain reliefs  77 ,  79 ,  81 , such as for distribution purposes. In one embodiment, an array of various size strain reliefs  77 ,  79 ,  81  are produced as a set, wherein the set is distributed as shown in FIG.  7 . This embodiment may be useful in various situations, such as where a user needs to ensure availability of an appropriately sized strain relief  77 ,  79 ,  81  during assembly of connectors for various cable sizes. 
     As shown in FIG. 7, a slip-on strain relief  77 ,  79 ,  81  includes certain features not included in the overmolded strain relief  18 . The slip-on strain relief  77 ,  79 ,  81  generally has a hollow cylindrical form, which includes a gap  85  along one side of the strain relief  77 ,  79 ,  81 . Teeth  83  may be included for providing gripping power relative to the insulation  26  of the cable  16 . In order to install the strain relief  77 ,  79 ,  81 , and to provide for proper form once under compression, the slip-on strain relief  77 ,  79 ,  81  includes a gap  85 . The gap  85  runs from the front section  30  to the rear section  28 , thus creating a break in the wall of the strain relief  81 . Accordingly, the slip-on strain relief  77 ,  79 ,  81  has a “C” cross sectional shape. Aspects of the gap  85  may be determined based upon factors such as, without limitation, the size of the cable  16 , and the degree of compression desired for use with a given connector  14 . 
     As shown in FIG. 8, the rear elevational view of the strain relief  81 , a detent  89  may be included. The detent  89  is located on the interior portion of the strain relief  77 ,  79 ,  81  along the center aperture  34 . The detent  89  may be incorporated to provide flexibility in the strain relief  77 ,  79 ,  81 . The flexibility may be advantageous for permitting a greater width of the gap  85  during installation. That is, the detent  89  makes it easier to separate the walls of the strain relief  81  and to increase the size of the gap  85 . More or less than one detent  89  may be included. The detent  89  generally runs the length of the strain relief  81 , however, the detent  89  may be shorter than the entire length of the strain relief  77 ,  79 ,  81 . 
     In one embodiment, the detent  89  is sized or otherwise configured so that the strain relief  81  is balanced under compression. That is, the detent  89  is configured so as to mimic the properties of the gap  85 . In other embodiments, the reverse is true. That is, the gap  85  is configured to provide balanced compression in light of requirements for the detent  89 . 
     Also shown in FIG. 8, four teeth  83  are present. The teeth  83  are located on the interior portion of the strain relief  81  along the center aperture  34 . The teeth  83  may be more or less in number. Referring back to FIG. 7, the teeth  83  are also shown as being of one course. In other embodiments, more than one course of teeth  83  may be used. Further, in the embodiment shown in FIG. 8, the teeth  83  are circumferentially distributed, or placed, so as each one is separated about 90° from the next. In other embodiments, the teeth  83  are otherwise circumferentially distributed. 
     FIG. 9 provides a front elevational view of the strain relief  81 . In this view, other features of the strain relief  81  are apparent, such as the flat surfaces  36  that are shown in the embodiment depicted in FIG.  6 . 
     FIG. 10 provides a side view of the strain relief  81 . In this side view, indicia  90  are also shown. The indicia  90  may be applied as a recess during the separate molding, may be stamped, embossed, or otherwise applied to the strain relief  77 ,  79 ,  81 . The indicia  90 , or multiples thereof, may be used for coding and conveying a variety of information. For example, in one embodiment, a code conveys size information to a user, in another embodiment, a code conveys lot information to a manufacturer. In other embodiments, color coding techniques may be used, wherein aspects of the strain relief  77 ,  79 ,  81  may be determined according to the color of the strain relief  77 ,  79 ,  81 . The smooth or flat front end surface  92  and the smooth or flat rear end surface  94  are shown in FIG.  10 . 
     Mounting the strain relief may be accomplished manually or remotely with appropriate tooling. In some embodiments, the slip-on strain relief  81  may be slipped on over an end of a cable  16 , at an appropriate time such as prior to conductor assembly. In other embodiments, the gap  85  of the slip-on strain relief  77 ,  79 ,  81  is forced at least partially open so as to provide for lateral insertion of the cable  16  into the strain relief  77 ,  79 ,  81 . The opening force on the strain relief  77 ,  79 ,  81  is subsequently released. Then, the strain relief  77 ,  79 ,  81  substantially returns to the form of the strain relief  77 ,  79 ,  81  prior to application of the opening force. In this manner, the strain relief  77 ,  79 ,  81  is “slipped” onto the cable  16 . Preferably, the strain relief  77 ,  79 ,  81  does not snap onto or lock into itself. 
     Referring now to FIG. 11, the conductor assembly  12  is shown partially attached to the electrical connector  14 . The electrical connector  14  generally comprises a plurality of electrical contacts  38 , a housing  40 , and an electrically conductive shell  42 . The shell  42 , in the embodiment shown, comprises two half pieces  44 ,  46  which are attached to each other over the housing  40  by fasteners  48 . In alternate embodiments, the shell could comprise any suitable number of pieces, the pieces could comprise any suitable size or shape, and the pieces could be fixedly attached to each other and/or the housing by any suitable means. In the embodiment shown in FIG. 11 the first half piece  44  of the shell  42  is shown removed from the connector to show the connection of the conductor assembly  12  with the connector  14 . The half pieces  44 ,  46  comprises interior facing flat sections  52  and projecting ribs  54  which oppose each other. The ribs  54  are formed by the inwardly projecting rear end walls of the shell pieces  44 ,  46 . 
     The electrical conductors  20  of the cable  16  are attached to the electrical contacts  38  of the connector  14 . A suitable portion of the outer cover  26  of the cable  16  in front of the overmolded strain relief  18  or the slip-on strain relief  77 ,  79 ,  81  is removed to allow the exposed section of the braid  24  to be folded backward onto the strain relief  18 ,  77 ,  79 ,  81 . The braid  24  is folded back over the front section  30  and into the recessed area  32 . 
     In the embodiment shown, the conductor assembly  12  further comprises electrically conductive tape  50 . The tape  50  is attached to the braid  24  to prevent strands of the braid from spreading out. In a preferred embodiment, the electrically conductive tape comprises a metallized copper tape. However, in alternate embodiments, any suitable type of electrically conductive fastener for fixedly retaining the braid  24  at the front section  30  and the recessed area  32  of the strain relief  18 ,  77 ,  79 ,  81  could be provided. In an alternate embodiment, the tape or other braid end fastener might not be provided. 
     When the half pieces  44 ,  46  of the shell  42  are attached to each other in the finalized assembly, the projecting ribs  54  extend into the recessed area  32  of the strain relief to sandwich a portion of the braid  24  between the strain relief  18 ,  77 ,  79 ,  81  and the shell  42  in the recessed area  32 . If the tape  50  is located at the recessed area  32 , that portion of the tape is also sandwiched between the strain relief  18 ,  77 ,  79 ,  81  and the shell  42 . The flat sections  52  of the shell  42  sandwich the tape  50  and the braid  24  between the shell  42  and the strain relief  18 ,  81  against two opposite ones of the flat surfaces  36  of the front section  30  of the strain relief  18 ,  77 ,  79 ,  81 . This causes the shell  42  to capture the strain relief  77 ,  79 ,  81 , compress it into its final position, thus forming an electrical connection between the braid and the shell. 
     In the embodiment shown, the strain relief  18 ,  77 ,  79 ,  81  is a one-piece member, but serves three purposes. The hexagon shape of the front section  30  creates the form where the cable braid can be compressed by the metal shells. The center recessed area is used to trap the metal braid with the metal shells to prevent the cable from being pulled out of the connector  14 . The rear section  28  prevents the cable  12  from being pushed into the connector  14 , and perhaps damaging the connection between the conductors  20  and the contacts  38 . 
     In some conventional electrical connector and cable assemblies, the most common way to electrically join the cable braid to the metal shell is to crimp a metal ferrule over the braid, and compress the ferrule slightly when the shell is closed. There is a concern with this type of system in that crimping over the wire pairs could damage the dielectric; causing degradation in the cable assembly performance. There is also a concern that crimping to the soft jacket  26  is not a reliable strain relief should the cable be pulled away from the connector. 
     The present invention provides a solution to these problems by providing a plastic strain relief. The plastic strain relief may be overmolded onto the cable  16 . The use of a low pressure overmolding process does not damage the wires of the cable. In an alternate embodiment of the present invention, rather than overmolding the strain relief  18  onto the cable  16 , a slip-on strain relief  77 ,  79 ,  81  is supplied which is subsequently slipped onto the cable  16 . 
     It should be understood that the foregoing description is only illustrative of the invention. Various alternatives and modifications can be devised by those skilled in the art without departing from the invention. Accordingly, the present invention is intended to embrace all such alternatives, modifications and variances which fall within the scope of the appended claims.