Multiple internal shield termination system

Abstract: A conductive yoke is provided insertable into a backshell adapter to provide a convenient shielding termination system for grounding braids and shields of conductors in a multiconductor cable to be connected to and grounded at a multipin electrical connector, the yoke providing ease of connection of such braids and shields to it and having direct electrical contact to the grounded surface of the connector.

Description: The present invention relates to a lightweight wire or cable shielding termination system and most particularly to the use of a yoke disposed between a connector backshell adapter and the back of an electrical connector to provide a direct ground connection for ground leads of multiconductor cables to the rear face of the connector, considered the grounding point. There is a constant search for better grounding of the shield wires, woven braids about individual data or power carrying wires of a multiconductor cable as well as strain relief wires of a cable braid while also providing good electrical shielding. Such terminations particularly those for military use and commercial conduits, are required to prevent undesirable electromagnetic radiation. Although there are currently many different devices and systems for providing grounding and shielding, the search goes on for a lightweight system that has excellent electrical shield grounding characteristics and is quick and easy to install and repair. There is an additional problem with cables that also requires attention. The exterior surface of many of the individual conductors of of multiconductor cables are made of Teflon (a DuPont trademark). The cables normally pass through a backshell connector to a multicontact electrical connector. The cable is clamped at the point of entry onto the backshell connector by various types of clamps such as saddle clamps. As a result of the Teflon coating the cables, when subject to severe vibration, such as encountered in aircraft, tanks and like vehicles, may slip and slide and place a severe strain on the individual wire leads. The integrity of the cable under such circumstances is dependent upon the weakest wire lead or solder joint much as a chain is only as strong as its weakest link. The use of the saddle clamp and the like is an attempt to relieve the strain on the individual wires but such attempt is not always successful. EP-0546657-A discloses an electrical cable connector for an electric cable having a plurality of conductors surrounded by respective shields. The cable connector includes a backshell for receiving a cable through a front end, and an annular cable transition element for insertion into the back end of the backshell. In use, these outer shields are formed into pigtails and clamped to the outside of the cable transition element. It is an object of the present invention to provide a lightweight wire shielding and termination system that provides excellent grounding of the electrical shield conductors and cable braids that is quick and easy to install and insensitive to shock and vibration. It is another object of the present invention to provide a lightweight wire shielding termination system in which metallized plastic shielding material may be used to reduce weight. It is another object of the present invention to provide a termination shielding system providing very low ground path resistance between a shield and a connector to which it is coupled. It is yet another object of the present invention to provide a wire shield termination system resistant to corrosion and damage from heat cycling. It is another object of the present invention to provide a highly efficient braid grounding system that is both lightweight and strong. Yet another object of the present invention is to provide a cable shielding system that cooperates with a cable shield termination system to provide continuous electrical shielding from a cable through a termination system contained within a backshell adapter to an electrical connector. It is also an important object of the present invention to provide a replaceable yoke for insertion into a backshell adapter employed to provide the interface between a multiconductor cable and the back of an electrical connector whereby to establish a multi-wire braid termination grounding system. Still another object of the present invention is to provide strain relief of the wires of a cable subject to severe shock and vibration whereby to prevent breakage of one or more of the wires of a cable. The present invention provides a device according to claims 1, 3, 6 and a method according to claim 11. The present invention includes as a major component an annular termination yoke insertable into the front end of a conventional backshell adapter of the type usually employed to physically connect a multiconductor cable to the back of a multicontact electrical connector. The yoke is preferably a lightweight aluminium or metalized plastic ring with teeth on one end for mating with the teeth at the back of an electrical connector and for maintaining electrical continuity of the ground path. The other end or back of the yoke provides various methods for connecting multiple shield grounding leads to the yoke, the yoke providing continuity to the teeth of the connector (where teeth are employed) through teeth on the front of the yoke. Quick installation of the ground leads may be accomplished by various means such as holes in an annular wall at the back of the yoke to receive pins on the ends of the shielding braids, holes in the front of the yoke to receive ground wires that have passed through the center opening of the yoke or as another example, a ground lead bandolier grounding tape onto which numerous ground leads have been presoldered. The tape is soldered or clamped to the ring of the yoke. The tape rides on ridges of metal to insure excellent grounding, the grounding resistance being of the order of 0.001 ohms. The yoke snaps into a plastic adapter plated with metal or a lightweight metal backshell adapter to provide shielding, the adapter being secured to the cable. The yoke is adapted not only to ground the shield braids of individual wires but also the braid disposed about the cable where such is employed. Specifically, bulk shielding of the communication or power wires may be achieved with a lightweight metallized cloth (braid) woven from threads of, for instance, copper, aluminum or a copper plated polymer substrate. The cloth may be formed as a tube disposed about a cable to be shielded. The tube may have wires for grounding the tube to the aforesaid yoke or may be formed into a pigtail and secured to the yoke directly or indirectly. Strain relief of the wires of a cable carrying data or electricity may be achieved by attaching the shield braids to the yoke. If the length of the shield braids from the saddle clamp at the entry to the backshell adapter to the yoke is sufficiently less than the length of the cable wires from the saddle clamp to the multipin connection, the cable wires will have slack, and all shield braids would have to fail before strain is placed on the wires. The invention will now be further described by way of example only with reference to the drawings in which:- Figures 1 and 1a illustrate one version of the yoke of the present invention; Figures 2 and 2a illustrate another version of the yoke which is a comparative example and not the invention. Figure 3 illustrates a second version of a termination yoke employed with a bandolier grounding tape; Figures 4 and 4a illustrate a third version of the yoke of the present invention; Figures 5 and 5a illustrate still another construction of the yoke, according to the invention; Figure 6 illustrates the assembled cable and termination structure partially in section; Figure 7 is a detailed view of one structure for retaining the yoke in the backshell adapter; Figure 8 is a partially cut-away side view of a prior art cable using a saddle clamp to provide strain relief; and Figure 9 is a sectional view of a structure for relieving strain on the individual wires of a cable. Referring now specifically to Figure 1, there is illustrated one form of yoke generally designated by the reference numeral 2. The yoke is an annulus having a large center opening 4 and in this configuration a plurality of apertures 6 formed in a rear wall 8 of the yoke 2; the wall 8 being transverse to the axis of the annulus. The apertures 8 have indents (or notches) 10 that cooperate with ridge 12 on pins 14 secured to the ends of conductors 16 to be terminated in (grounded at) the yoke 2. The conductors 16 are the braids of the individual cable conductors and the grounding wires for the cable braid. The front of the yoke 2 has teeth 18 to engage teeth conventionally found on the back of a multipin connector, see Figure 6 teeth 126. The yoke may be a lightweight metal such as aluminum, a lightweight plastic with metalized coating or a lightweight plastic with metallic inserts to provide continuity from the grounding leads to a connector. Referring now to Figure 2 of the accompanying drawings, given as a comparative example a yoke 19 has a skirt 20 at its back end; the skirt 20 having a knurled surface 22. Ground leads such as a lead 24, may be clamped to the skirt 20 by a strap 26, preferably but not necessarily conductive. The yoke 19 has teeth 28 as does the yoke of Figure 1. Referring specifically to Figure 3 of the accompanying drawings, a termination yoke 30 is also in the form of a ring having a toothed front face 32 adapted to interface with an electrical connector (Figure 6) in conventional fashion. The face 32 has teeth 34 to provide good electrical contact with an electrical connector. A grounding lead bandolier 36 (hereinafter "tape 36") constitutes a flexible metal band 38 to which is soldered a plurality of wire leads 40 to be employed to ground various components of the assembly. The tape 36 may be made up in any convenient length and may be cut to provide the number of leads required for a particular application. The tape is wrapped around and may be soldered or strapped to a rearwardly located circular region or ring 42 of the yoke 30. The ring may have protrusions 44 thereon to insure firm contact between the ring and the tape. The grounding leads are illustrated as having Solder Sleeves® 46 or the like, connected to their ends remote from the ring 42. (Solder Sleeves is a registered trademark of Raychem Corporation.) Referring now to Figure 4 of the accompanying drawings, a yoke 48 has teeth 50 at its front end formed on an annular shoulder 52. The interface between a region 54 of reduced diameter of the yoke and the shoulder 52 defines a sloping wall 56 between the outer perimeter of the shoulder 52 and the region 54. A plurality of holes 58 extend through the shoulder 52 below the teeth 50 from the front of the yoke through to the region 54. Leads 59 to be terminated in the yoke 48 are passed through a large passage 60 through the main body of the yoke and are then reversed and inserted into and through the holes 58 and preferably into contact with an annular shoulder 62 at the back of the region 54. The leads 59 may be clamped against the surface of the region 54 by a strap 64. Referring now to Figure 5 of the accompanying drawings, a yoke 66 is quite similar to the yoke of Figure 1 with the exception of a ring of holes 68 about annular skirt 70 behind an outwardly sloping region 72 of the yoke. On the front of the yoke teeth 74 are formed for engagement with mating teeth on the back of an electrical connector to be engaged by the yoke. The yoke has a further ring of holes 76 into which ground leads, such as lead 78, are to be inserted. The holes 68 and 76 intersect for several reasons, first a technician assembling the device can determine if the end of the lead is fully inserted into its hole 76 and secondly, if desired, a length of solder wire may be inserted into hole 68 and heated to solder the wire in place. Alternatively, a short length of solder wire may be inserted into a hole 76, melted and then lead 78 inserted until viewed through hole 68. Heavily tinned wires may also be used as well as a conductive mastic. Referring now to Figure 6 of the accompanying drawings an assembled structure incorporating an electric cable backshell adapter, yoke and electrical connector is illustrated. A cable 80 is disposed in a conduit 82 and is included in Figure 6 to demonstrate the full capability of the yoke. The cable 80 has shielded wires 84 extending from the cable through a backshell adapter 86, thence through an adapter coupling nut 88, and a yoke 90 to the back of a conventional cable connector 92. Outer shields (braids) (not illustrated) of the wires 84 are connected by Solder Sleeves 94 to ground leads 96 connected to surface 95 of the yoke 90, for instance, by the bandolier of Figure 4, reference numeral 36. The cable and conduit are secured to a reduced diameter region 98 of the adapter 86 by a termination strap 100 that clamps strain relief filaments 102 of the cable, a metal cloth shielding braid 104, and grounding drain wires 108 of the conduit to the region 98 of the adapter 86. The interface between the conduit 82 and adapter body 86 is covered by a heat shrink sleeve 110 to protect against the environment. The adapter 86 may be a plastic having a metallized coating to provide shielding in its region but does not provide a grounding function. The grounding of the braid 104 and drain wires 108 are affected by folding the drain wires back on themselves (see length 108a), clamping them to the adapter 86 on an annulus 112, formed on the back thereof, by the strap 100 and bringing the wire 108 out from under the termination strap and to a Solder Sleeve 114 to one of the grounding leads 96. Thus there is complete continuity from the metal cloth shield 104, braids of the leads 84, and drain wires (strain relief wires) 108 to surface 95 of the yoke, the yoke in turn being grounded via the connector body 92 to system ground. Referring now to adapter 86, coupling nut 88, is secured to the adapter 86 by a snap ring 116 recessed in a circular slot 118 in the outer surface of the adapter. The yoke 90, when the system is assembled, is seated in the adapter 86 with its surface 117 in engagement with the surface 119 of the adapter, whereby teeth 121 of the yoke can engage teeth 123 (if provided) of the connector 92. The left region of the adapter coupling nut 88 as viewed in Figure 6, is threaded to mate with threads 120 on the connector 92. The yoke 90 has a radial hole 122 formed in its surface 123 which hole mates with a pin 124 (only half being shown in Figure 6, see Figure 7) to retain the yoke in the adapter. The slot and pin arrangement is oriented to not be dislodged by rotation of adapter coupling nut 88. All regions at the interface between the conduit and electrical connector are fully electrically shielded and are environmentally sealed by an O-ring 125 as well as by sleeve 110. The materials employed throughout are lightweight such as aluminum or plated plastics. As a result of light weight and positive coupling the structure is resistant to shock and vibration while the environmental shielding reduces corrosion and choice of materials reduces effects of heat. EMI protection is provided as indicated above. In the event the back of the electrical connector does not have teeth the yoke may have teeth or may have a flat surface providing high pressure contact between the yoke and connector. The yoke surface may be roughened for better contact. Referring to Figure 7 of the accompanying drawings, the same reference numerals are used as in Figure 6. The yoke 90 is illustrated as inserted into the end of the adapter 86. To secure the yoke in the adapter 86 the slot 122 is aligned with the pin 124 and the pin is depressed so as to enter slot 122. The yoke is now fixed in place and provides, when the nut 88 is screwed onto threads 120 of the adapter 92, direct engagement with teeth 126 of the connector, thus providing continuity of the grounding path. An additional feature is the ease of repair of the assembly. The only element that would normally require replacement in the event of major repair would be the heat shrink sleeve 41 although some of the Solder Sleeves might require replacement. The termination strap may be a standard cable tie and can be readily replaced if necessary. Referring now specifically to Figure 8 of the accompanying drawings, a prior art cable termination system is illustrated. As illustrated four Teflon coated cables 130 enter a backshell connector 132 through a rubber or the like collar 134. A saddle clamp 136 tighlty binds the collar 134 about cables 130 to prevent movement of the cables relative to the backshell connector 132. The outer braids 138 of the individual cables 130 are brought out of the ends of the cables 130, looped back over the saddle clamp 136 and secured to an annuluar area 140 of the backshell connector to the left, of the clamp 136, as viewed in Figure 8. The braids 138 are secured to the area 140 by, in this instance, a hose clamp 142. The backshell connector is secured to a multipin electrical connector 144 in conventional fashion. Wires 146 of the cables 130 are connected to the multipin connector 144 as can be seen in the breakaway region of the backshell connector. The problem with this arrangement resides in the fact that such a cable high vibration can cause the cables 130 to pull back away from the electrical connector 144 and place a strain on the wires 146. The braids 138 are of no help in preventing strain on the wires 146 since when the cables pull back the strain on the braids is reduced since the exit of the braids from the cables are forward of the clamp 136 and are loosened as the cables retreat. Thus strain is placed on the individual wires 146 and can cause failure of one or more wires. Referring now specifically to Figure 9 of the accompanying drawings, there is illustrated a system for transferring strain on the wires; that is, conductors, to the braids all of which would have to fail before strain is placed on the conductors. Cables 150 enter a backshell connector 152 through a saddle or like clamp 154. The cables have braided shields 156 that are removed from the cables and formed into pigtails 158. The pigtails are attached to a yoke 159 while conductors 160 of the cables are connected to a multipin electrical connector 162. Note that the conductors 160 are illustrated as being wavey to indicate that they are slack while the braids are straight to indicate they are taut. Each cable 150 has its braid pigtailed and attached to the yoke. Thus as a practical matter all braids would have to break or become unsoldered before strain is palced on any of the leads. Since the braids are stronger than the conductors the potential for damage to the conductors is greatly reduced.

Claims: A device for terminating a cable which comprises conductors and shielding for each of said conductors, the device comprising: an adapter (86) defining a passage, the passage being for receiving an end of the cable; an annular yoke (2; 19; 30; 48; 66; 90) having a back portion for insertion into a front end of the adapter, said yoke (2; 19; 30; 48; 66; 90) being electrically conductive; low resistance means for electrically connecting said shielding to said yoke (2; 19; 30; 48; 66; 90); means for providing a low loss electrical path between the yoke (2; 19; 30; 48; 66; 90) and a reference potential, characterized in that said low resistance means includes: a first surface (8) of said yoke (2; 66) adjacent said back portion thereof, said first surface being generally perpendicular to an axis of the yoke, and a plurality of holes (6; 76) extending into said first surface (8), said holes being arranged in an arcuate path along said first surface (8), whereby said plurality of holes (6; 76) can receive the ends of respective leads which are either portions of the shielding of the cable or elements separate from the cable but put into contact with the shielding. A device according to claim 1 wherein said yoke (66) further includes: a region (70) providing a substantially constant outer diameter surface; a plurality of radial holes (68) extending through said constant diameter surface and intersecting said holes (76) in said first surface. A device for terminating a cable which comprises conductors and shielding for each of said conductors, the device comprising: an adapter (86) defining a passage, the passage being for receiving an end of the cable; an annular yoke (2; 19; 30; 48; 66; 90) having a back portion for insertion into a front end of the adapter, said yoke (2; 19; 30; 48; 66; 90) being electrically conductive, low resistance means for electrically connecting said shielding to said yoke (2; 19; 30; 48; 66; 90); means for providing a low loss electrical path between the yoke (2; 19; 30; 48; 66; 90) and a reference potential, characterized in that said low resistance means includes: a region (42) of the yoke (30) providing a substantially constant diameter outer surface, and a conductive tape (36) for securement to said outer surface, whereby the conductive tape can be secured to said outer surface, and electrically connected, in spaced relation along the length of the tape, to respective grounding leads (40) which either portions of the shielding of the cable or elements separate from the cable but put into contact with the shielding. A device according to claim 3 further comprising a strap for securing said tape (36) to said outer surface. A device according to claim 4 wherein said tape (36) is suitable for securement to said outer surface by a fusible conductive material. A device for terminating a cable which comprises conductors and shielding for each of said conductors, the device comprising: an adapter (86) defining a passage, the passage being for receiving an end of the cable; an annular yoke (2; 19; 30; 48; 66; 90) having a back portion for insertion into a front end of the adapter, said yoke (2; 19; 30; 48; 66; 90) being electrically conductive, low resistance means for electrically connecting said shielding to said yoke (2; 19; 30; 48; 66; 90); means for providing a low loss electrical path between the yoke (2; 19; 30; 48; 66; 90) and a reference potential, characterized in that said low resistance means includes: a second surface (56) of said yoke at a front end thereof at a sharp angle to the axis of said yoke; and a plurality of holes (58) formed in said second surface (56). A combination of a device according to claim 1 and a cable (80) having a plurality of conductors (84), shielding for each of said conductors, and electrically conductive leads within said shielding, said passage being centrally located in said adapter; said yoke (90) being configured to have its back portion fit into said front end of said adapter with a front portion of said yoke protruding therefrom, an end of said cable (80) being received within a back end of said passage; and said low resistance means securing and electrically connecting the conductive leads to said yoke (90). A combination according to claim 7 further comprising means (100) for securing the cable to the adapter. A combination according to claim 8 further comprising means for physically coupling said adapter to a multi-pin electrical connector with said yoke (90) in electrical contact with the electrical connector. A combination according to claim 9 in which said conductive leads and conductors are of such a length that when the conductive leads are in tension, and said conductors are in contact with respective pins of the multi-pin connector, there is a slack in the conductors adjacent the multi-pin connector. A method for terminating a cable (80) which comprises a plurality of conductors and shielding for each of said conductors, the method comprising the steps of: locating a back portion of an annular yoke in the front end of the adapter, the annular yoke being electrically conductive; inserting an end of the cable into a back end of a passage defined by an adapter; electrically connecting said shielding to said yoke; and providing a low loss electrical path between the yoke and a reference potential, characterized in that said electrical connection step includes: inserting respective ends of a plurality of grounding wires, which are either portions of the shielding of the cable or elements separate from the cable but put into contact with the shielding, into holes in a back wall of the yoke; inserting solder into radial holes intersecting the holes in the back wall of the yoke, and heating the solder to its fusion temperature.

Inventors: GOETT EDWARD P, SPRATT ROBERT F, WOEHL ROGER, GOETT, EDWARD P., SPRATT, ROBERT F., WOEHL, ROGER
Applicants: ENGINEERED TRANSITIONS, ENGINEERED TRANSITIONS CO., INC.
Application year: 1996
Main classification: H01R9
IPC codes: H01R13, H01R9