US 3902154 A
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Description (OCR text may contain errors)
[451 Aug. 26, 1975 United States Patent [1 1 McKee 1 1 STRAIN RELIEF  Inventor: William H. McKee, West Covina, 'f E'mmlrfer joseph AS51810!!! E.\'ammer.lames W. Davie Altorney, Agent, or FirmLawrence S. Cohen  Assignee: TRW Inc., Cleveland, Ohio  Filed: Feb. 19, 1974 ABSTRACT Appl. No.: 443,730
A relief wire terminating system with particular regard to a strain relief means provided as an integral part of the system. At the rearward or termination portion of  U.S. 339/223 R; 339/103 R  Int. Cl. H01R 15/12 Field of Search 339/223 R, 103 R, 103 M. the system, side walls define a channel for receiving an insulated wire. At the rearmost extremity, a tab ex- 339/223 S, 97 R, 97 P, 98, 99 R tends from the top of each wall at an angle, downward References Cited and inward into the space. The tabs terminate in edges UNITED STATES PATENTS defining a wire passing space between them, and
below them, a wire restraining space. The tabs act on the wire to take up strain.
2,668,279 Epstein 339/103 R 3,824,530 Roberts et 339/99 R FOREIGN PATENTS OR APPLICATIONS 13 Claims, 6 Drawing Figures 1,008,995 11/1965 United Kingdom............. 339/223 R PATENTEI] M182 6 I975 sum 2 [If 2 ll STRAIN RELIEF BACKGROUND OF THE INVENTION,
1. Field of the Invention The invention relates to wire termination systems. It particularly relates to strain relief means' assoeiate'd with wire termination systems. I
2. Description of'the Prior Art,
It has long been considered desirable and often imperative that in terminating a wire, some strain relief means be provided. This is true of wire to wire and wire to connector terminations, and, in fact, with regard to all terminations. The degree of handling expected, the level of reliability and the life expectancy of the termination are some of the factors which effect the level of efficacy required of a strain relief means. i V
Most strain relief means for connectors are .built into the insulators which retain the terminations and/or the contact members. In other cases, strain relief is accomplished by additional hardware such as clamps. These usually operate by squeezing or otherwise gripping the wire and holding it firm at a point to the rear of the point of termination. It is the general desire to avoid the transmittal of forces on the wire or movement of the wire to the point of actual termination.
The advent of miniaturized high density connectors, in fact of miniaturized electrical and electronic components in general, has produced problems in the design of strain relief means strong enough to be able to effec tively take up the strains expected, while being'constructed in the space and of the materials associated with such components. It is apparent that miniaturization means the use of small, thin, and relatively weak items. Yet, in use, the forces imposed on the item s usually are not proportionately reduced.
These problems as well as problems in high volume production of 'molded insulator bodies have been recognized. For example, in the high contact density ribbon type connector described in US. Pat. No. 3,747,050 a connector is illustrated with terminal elements on 85 mil. centers and termination materials constructed of 6 mil. thick metal.
In addition, the very recent advent of solderless termination means for such connectors has incrased the need for effective strain relief and magnifies the problems associated generally with reliable, economic termination systems. With the delicate construction of miniaturized electrical components has also come the need for increased reliability as well as, at point of electrical terminations, very rigid adherence to low contact resistance change. This latter requirement is especially appreciated by those familiar with the telecommunications industry where strict criteria are established and only very small contact resistance change at the point of termination are permitted. For example, in a typical telecommunication high density miniaturized connector a contact resistance change not to exceed 0.25 miliohms in not more than, in 10,000 contact elements with a 95% confidence level, has been specified.
The termination system described herein and particularly the strain relief means eliminate or reduce the majority of these problems while providing an economical form. It is especially useful with high density miniaturized connectors of the type commonly used in cable to-cable and rack and panel installations in telecommunications systems having the above specification. These items are required to be produced in very high volumes with severe criteria for reliability and adherence to specifications as noted above.
SUMMARY OF THE INVENTION A wire termination system, in particular a strain relief as an integral part of the termination system where an insulated wire is retained in a wire receiving channel between side walls by tabs extending from the upper edge of the side walls angularly downward and converging. The terminal edges of the tabs are spaced apart defining a wire passing space between them for the installation of a wire therethrough and to resist take up strains imposed upon the wire.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial perspective view of a preferred embodiment of the invention.
FIG. 2 is a partial side view of a preferred embodiment of the invention.
FIG. 3 is a partial top view of a preferred embodiment of the invention.
FIG. 4 is a sectional view through line IVIV of FIG. 2 of a preferred embodiment of the invention. 7 v
FIG. 5 is a sectional perspective view of a high contact density ribbon type connector employing a preferred embodiment of the invention.
FIG. 6 is a perspective view of a high contact density ribbon type contact element employing a preferred embodiment of the invention with wires assembled.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring generally to FIGS. 1 through 7, the strain relief means of the invention is illustrated. as part of the wire receiving or termination portion of a ribbon type contact element employed as shown in FIG. 5 in a high contact density ribbon type connector.
In understanding and describing the invention, it is convenient to explain at the outset that the ribbon type contact is formed from a single sheet of metal by punching, bending, forming and otherwise working the sheet into the desired shape. In an exemplary application, 0.006 inch thick cadmium bronze sheet metal is used.
In the illustrations, reference numerals having a sub- 0 refer to identical reversed items as are identified by the major numeral. In the discussion, only the major reference numeral will be cited, but it will be understood to also comprehend the sub -a numerals, unless otherwise noted.
The wire receiving portion has a channel-like body defined by sides 2, and a bottom 3 into which the wire 4 is fitted. The wire 4 is terminated for electrical contact between the jaws 5, formed-in from the sides 2. A more detailed description of this termination means is contained in co-pending application Ser. No. 443,678 filed Feb. 19, I974.
.The strain relief means is located to the rear of the termination means and is separated therefrom by a slot 6, in the sides. This separation permits limited resilient flexing of the strain relief means without transmitting movement forwardly to the electrical termination points, as will be more fully explained later. The sides 2 in the strain relief area are spaced so as to easily but firmly receive the insulated wire 4 in the channel. Formed over from the top of the sides 2 are tabs 7. These tabs extend at an angle downward and convergently into the channel. The terminal edges 8 of the tabs are opposed and spaced apart a distance smaller than the wire intended to be received in the channel, defining between them a wire passing space and beneath them a wire receiving space. The wire passing space should be larger than the conductor of the wire but smaller than the outside diameter of the insulation of the wire.
Dimples 9 are formed in the sides 2 immediately behind the tabs and substantially proximate to the terminal edges 8. It has been found preferable to form the tabs 7 in contact with the respective dimples 9.
In an exemplary case, when the termination system and strain relief is designed for insulated 24 gauge solid wire, the wire passing space between the terminal edges 8 of the tabs 7 is 0.012 inches. The sides 2 are spaced apart 0.038 inch. The dimples 9 extend 0.003 inch into the wire receiving space. The diameter of 24 gauge solid wire is 0.020 inch. Due to the outward movement permitted as described below, the wire passing space after insertion is increased to about 0.023 inches.
In use, an insulated wire 4 is positioned over the strain relief portion and with a segment over the electrical termination portion. The wire 4 is then pushed downward into the channel usually by a specially designed apparatus. As the wire 4 passes the tabs 7 and especially their terminal edges 8 they are urged to separate somewhat to permit it to pass. The diples 9 prevent collapse of the tabs 7 against the sides 2. The tabs 7 therefore retain their angular orientation convergently downward and into the wire receiving space. As the wire is inserted into the channel, its insulative cover deforms elastically somewhat as illustrated in FIG. 4.
It is desirable that as the wire enters the strain relief portion, the terminal edges 8 be able to move apart somewhat to permit the wire to pass. However, this movement apart should be at least somewhat within the resiliency of the structure, and also should exploit the ability of the elastomeric insulative coating of the wire to deform/This could be achieved, in part, by forming the tabs 7 slightly away from the dimples 9, although it has been found preferable to form the tabs 7 touching the dimples 9. It may also be achieved by permitting slight outward movement of the sides 2 as they reside in the insulator 10 (FIG. 5). In order to prevent this movement and other strains from being transmitted to the termination portions, the slots 6 have been formed in the sides 2.
FIG. 2 is a view taken at the section IV-IV shown in FIG. 2. Some deformation of the insulative cover of the wire is seen, indicating the type of snug fit achieved. The tabs 7 are firmly holding the wire in place against upward movement.
Referring to FIG. 5, the ribbon type contact element 11 is shown installed in an insulating high density connector body I0. The sides 2 of the strain relief are supported by ribs 12. In the area of the strain relief, the ribs 12 are formed slightly thinner providing a larger opening in order to permit the slight outward movement of the sides as the wire is inserted, as explained above. In the area of the formed-in jaws 5, the fit in the ribs 12 is more intimate since movement there is undesirable.
With the attendant rigidity provided by the side walls 2, the strain relief means will absorb movements and forces which would degrade or destroy the efficacy of the electrical contact at the termination portion.
The sides 2 of the wire receiving channel are pressed by the insulative cover of the wire 4 against the surrounding insulator 10. Altogether a reliable strain relief is formed able to handle the normal forces and movement imposed in use especially upward movement but in the space and with the materials normally associated with miniaturized elements. Of particular note is the construction of the strain relief as an integral part of the termination system itself, in this preferred embodiment including the formed-in jaws 5 and in addition the entire contact element 11.
In a test in which 24 gauge and 26 gauge wire insulated wire was inserted into a contact element of the type described the wires were pulled upward at a angle until they stripped out of the strain relief. The force necessary to remove the wire was measured and found to be well within the desired value. It is also possible to reuse the contact after stripping a wire out, thus preventing loss of an entire connector in the event of failure of a single contact. In addition, in performance tests under hostile environments, thermal aging, thermal shock and flexure, the termination system and strain relief has been found to perform well within specifications.
While the above description relates to certain embodiments now known to and preferred by the inventor, it is possible for persons skilled in the art to make certain additions, changes and modifications. It is intended by the appended claims to cover such additions, changes and modifications as fall within the scope and spirit of the invention.
1. In an electrical termination system having a termination means for receiving and maintaining a wire in electrical contact;
a strain relief as an integral part of the termination system comprising,
spaced apart facing sides defining a wire receiving channel rearward of the termination means;
a wire passing means extending from the upper portion of at least one of the sides, defining a wire passing space effective to resiliently permit passage through it by movement transverse to its axis, of a wire having a diameter greater than the wire passing space and the wire passing means also defining a wire restraining space below it in the channel for restraining movement out of the channel of a wire inserted in the wire restraining space.
2. The electrical termination system of claim 1 wherein the wire passing means is a tab extending from the upper edge of at least one side angularly downward into the wire receiving space and toward the other side and terminating to define the wire passing space.
3. The electrical termination system of claim 2 wherein a tab as defined extends from each side substantially oppositely and convergently defining the wire passing space between them.
4. The electrical termination system of claim 3 further comprising protuberance means in each of the sides extending into the wire receiving channel adjacently behind and toward the tabs to limit their outward movement relative to their respective channel sides.
5. The electrical termination system of claim 2 further comprising a protuberance in the side from which the tab extends into the wire receiving space adjacently behind and toward the tab to limit its outward movement. 7
6. In an electrical connector of the type having an insulating housing adapted to receive a plurality of contact elements for mating connection with a mating connector and a plurality of contact elements mounted in the housing, each element having a contact portion for mating with a mating connector and a termination means for receiving and maintaining a wire in electrical contact, a strain relief means as an integral part of the contact element comprising;
spaced apart facing sides defining a wire receiving channel rearward of the termination portion, tab means extending from the upper edge of each side oppositely and convergently into the wire receiving channel at an angle downward and away from their respective sides and terminating to define a wire restraining space below them and a narrowed wire passing space between them; the tab means being effective to resiliently permit passage through the wire passing space of a wire having a diameter greater than the wire passing space, moved transversely of its axis, and to restrain movement out of the channel of a wire inserted into the wire restraining space. 7. The electrical connector of claim 6 further comprising means permitting limited resilient outward movement of the terminal ends of the tab means when a wire is passed downward past them into the wire restraining space.
8. The electrical connector of claim 6 further comprising protuberances in each of the sides extending into the wire receiving channel adjacent and toward the tab means in order to limit their outward movement relative to the sides.
9. The electrical connector of claim 7 wherein the insulating housing has integral walls adjacent the sides of each contact for locating the contact elements and which walls are spaced slightly away from the contact elements at the area of the sides of the strain relief means in order to permit slight movement of the sides and thereby at least in part the resilient movement of the terminal ends of the tab means.
10. The electrical connector of claim 8 wherein the insulating housing has integral walls adjacent the sides of each contact for locating the contact elements and which walls are spaced slightly away from the contact elements at the area of the sides of the strain relief means in order to permit slight flexing of the sides and thereby at least in part the resilient movement of the terminal ends of the tab means.
11. The electrical connector of claim 10 wherein the contact elements are arranged in at least one row and the walls are defined by ribs separating the contact elements in the row.
12. A ribbon type electrical contact element formed from thin sheet comprising;
a contact portion for mating with a mating member;
a termination portion comprising a termination means and a strain relief means and spaced apart facing sides defining a wire receiving channel;
the termination means comprising at least one pair of wire contacting jaws, the jaws being oppositely positioned and formed-in from the sides and extending into the wire receiving channel; and
the strain relief means comprising;
tab means extending oppositely from the upper edge of each side angularly downward and convergently into the wire receiving channel and terminating to define a wire passing space between them and a wire restraining space below them; the tab means being effective to resiliently permit passage through the wire passing space of a wire having a diameter greater than the wire passing space. moved transversely of its axis, and to restrain movement out of the channel of a wire inserted into the wire restraining space;
protuberances in each of the sides extending into the wire receiving channel adjacently behind and toward the tab means in order to limit their outward movement relative to the sides.
13. The contact element of claim 12 further comprising slots in the sides separating the strain relief means from the termination means.