US 2791755 A
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Description (OCR text may contain errors)
May 7, 1957 K. M. HAMMELL ELECTRICAL CONNECTOR Fiied April 20, 1955 5 JM&L 5 m\\ m m 0% l/A% 7/1 2 MH a m mwfi m.
A vAMI II' ELECTRICAL CONNECTOR Kemper M. Hammell, Harrisburg, Pa., assignor to AMP Incorporated, a corporation of New Jersey Application April 20, 1955, Serial No. 502,697
4 Claims. (Cl. 339-258) This invention relates to electrical connectors and more particularly, in a connector assembly wherein the parts are designed for fast and permanent assemblage, to an improved sheet metal receptacle which grips under spring pressure a mating sheet metal tab. 7
In the art of coupling a pair of conductors with solderless connectors wherein the parts forming the assembly are secured together by the friction afforded through one part having spring means bearing against a surface on the other part, adequate spring pressure must be provided to satisfy mechanical requirements, e. g. stability against accidental disconnection, while a sufiicient area of electrical contact must also be provided to attain the currentcarrying capacity usually desired of such connectors.
The amount of metal in the receptacle available to obtain both the mechanical and electrical characteristics desired, however, is limited. It has been the practice, therefore, to concentrate all the available spring pressure at points or along lines of the tab to achieve a good mechanical connection, assuming that good electrical characteristics flow from the high contact pressure thereby obtained.
Reducing the places of contact to lines and points, albeit at high contact pressure, more or less reduces the current rating of the connection, but more disadvantageously such contact is highly subject to corrosion in use even under good conditions, primarily due to accelerated oxidation caused by the heat inherently generated in the assembly. Thus, although a connection in which reliance is placed on line and point contact under high pressure may initially perform satisfactorily even under fairly heavy current loads, such a connection tends to deteriorate at a fairly high rate and to fall from cor lGSlOIl.
It is, therefore, an object of the present invention to provide an electrical connector assembly wherein the parts may be quickly assembled in permanent installation yielding a connection which retains high quality mechanical and electrical characteristics throughout the life expectancy of the equipment associated therewith. Another object is to provide in an electrical connector assembly an improved sheet metal receptacle for receiving under spring pressure a mating tab. To these purposes an optimum area of contact between the elements is provided without reducing the contact pressure below the minimum necessary to secure the assembly from disconnection in normal use whereby, while the perimeter of the contact area may be subject to corrosion, a central portion of such area will be insulated and protected from corrosive factors thus assuring an electrical connection of long life and high quality.
Other objects and attainments of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings in which there is shown and described a preferred embodiment; it is to be understood, however, that this embodiment is not intended to be exhaustive or limiting of the invention but is given for purposes of illustration in order that others skilled in the art may fully understand the invention and the principles thereof and the manner of applying it in practical use so that they may modify it in various forms, each as may be best suited to the conditions of a particular use.
In the drawings:
Figure 1 is a perspective view of the two elements of a connector assembly illustrating the invention;
Figure 2 is a sectional view of the receptacle elemen taken at line 2-2 of Figure 1;
Figure 3 is a sectional view similar to that of Figure 2 but with the tab element in connective relationship with the receptacle element;
Figure 4 is a sectional view taken at line 44 of Figure 3;
Figure 5 is a sectional view taken at line 5-5 of Figure 2; and
Figures 6a to 6d are fragmentary cross-sectional views taken from Figure 3 for illustrating certain mechanical deficiencies encountered in the forming process of the connector assembly.
A connector assembly illustrative of the invention includes a tab element and a receptacle element for receiving and frictionally gripping the tab, generally designated at 1 and 3 respectively in Figure l, the elements being provided with ferrule means by which each is attached in electrical connection with the ends respectively of a pair of leads 5 to be coupled. Typically such ferrule means include barrels 7, each having a pair of ears 9, curled about and compressed into tight mechanical and electrical engagement with the hated ends of leads 5 and barrels 11, each having a pair of cars 13 wrapped around and supporting the insulation of the leads.
The connector elements 1 and 3 may conveniently be fabricated accordingto conventional blankingand forming techniques from any suitable malleable sheet metal stock, such as half to three-quarters hard brass, bronze or the like, which will increase in resilience and hardness upon being subjected to a cold-forging or coining operation. As thus fabricated, in the illustrated embodiment of my invention element 1 takes the form of a substantially flat rectangular tab having stop shoulders 15 which engage the front sidewalls of receptacle element 3 thereby to define the limit of insertion of the tab within the receptacle. An indentation or dimple 17 is centrally located on at least one, and preferably both active surfaces of tab 1 to form with boss 19 in receptacle 3 a detent means to be more particularly described.
a To provide for receiving and retaining tab 1 in springlocked electrical and mechanical engagement, receptacle element 3 includes a base or floor portion 21 from opposed side edges of which extend a pair of flanges 23 having inturned ends 25 overlying and spatially disposed from base portion 21, as best shown in Figures 2 to 5. As thus arranged, base portion 21 and flanges 23 define an open-ended channel of slightly greater width and height than tab 1 which may therein be inserted. Suitably anchored at longitudinally spaced points along base portion 21 is a spring 27 in the form of a'flat strip which is bowed out of the plane of base portion 21 and into the channel of the receptacle thereby to bias under pressure tab 1 into engagement with ends 25 of fiange-23. Spring 27 may conveniently be fashioned integrally with base portion 21 in the forming operations for the receptacle. To this end a pair of substantially parallel longitudinal: Slts29 cut in base portion 21 define the spring strip 27-which thus has -its-ends integral with' base 21. Also in the forming operation strip 27 is reduced in thickness as compared to the original thickness of the sheet metal stock by a cold-forging or coining operation where by to impart the desired spring characteristics thereto, such as hardness-and resilience.
As thus constructed-insertion,oftab 1 inthereceptacle depresses spring 27 -which.,bears against the undersurface .of the tab that is intturn supported by. flange ends 25. A centrally located boss 19,.preferably raised on the sur- .face of spring 27 during the. coining operation performed thereon, cooperates with eitheriofindenta-tions 17 .of tab 1 to provide a detent which adds to the tensile or pullotf strength of the connection. It willbexobservedfrom Figures 3 and 4 that in order to be Withdrawnfrorn its connected relationship .with .the receptacle, tab 1 must depress spring 27 an amount equal to the height of the .boss above the planeof the spring thereby adding to the spring pressure which has to beovercome. :Boss 19 and indentation 17 may takeany suitable complementary form which will mm in the smooth camming of spring 27 downwardly upon either insertion or withdrawal of the tab. For example, the boss and indentation may .over boss 19 which thenis free frorncontact with the tab. -As a result, area contact between-the tab and spring surfaces may be achieved, as will be explained. In this connection in Figure 3 the undersides 31 of ends 25 are shown in flat abutment in area contact with the upper surface of-tab 1. While this may be desirable from an electrical conductivity standpoint, such area contact is extremely difficult-to achieve in practice; surfaces 31 must be precisely coplanar while tab 1 must be ab- .solutelyflat and free from the edge curvature due to blank- .ing or burrsalong thetab sides as aresult of employing stamping operations in the forming process. Neither of these conditions can be satisfiedl practically where .blanking and forming processes are employed, hence, in realityonly a line contact on. the tab is obtained with surface 31, various possible conditions being shown in Figuresfia to 6d, such vcontactbeing unreliable electrically due-stoits vulnerability to corrosion.
As shown in Figure 5, spring 27 is bowed inwardly of .the receptacle channel about radii :of curvature R1 at the extremities that are substantially less than the radius of curvatureRz of the .centraLportionof the strip to define a central slightly-bowed plateau which is flattened, Figure 4, upondepressionof the spring by tab 1. The-central portion of the area of contact thus attained is sufiiciently isolated from all points which may be attacked by corrosionthat the connection may support high current loads over a prolonged period. To gain as much area of contact as possible without unduly decreasing contact pressure, slots '29 should be located as near as possible to-the side edges-of base portion 21, thus increasing the width of the contact area while adding to the volume of metal comprising the spring.
The primary'conductive path between thetab and receptacle is seen to be the flattened upper surfaceof spring 27 and the'contacted portion-of the undersur face of the tab. Thus,'spri ng 27 has the dual functionof mechanically'locking, and electrically contactingthe tab. :Mechanically, the spring may vary in form and dimension so longas electrically anninimum area ofocontact isassured. In this connection the length dimension of the contact area is not critical since the minimum requirements in this respect are usually greatly exceeded. For example, the edge contact illustrated in Figure 6 extends substantially the length of the tab, but the contact width along the surfaces shown has been found in practice not to exceed 0.015 inch, and usually less, which is inadequate. Oxide penetrations from both sides of such line contact results in complete failure of the connection within 500 hours in life tests simulating actual service by temperature cycling. A contact width of 0.030 inch, however, has been found to be satisfactory in that the connection will not fail in temperature cycling until after at least 1500 hours time which is the lowest cornmercially acceptable limit. Preferably the contact width is 0060-0080 inch which provides an adequate safety factor and operable time of at least 3500 hours for exceeding in all probability the life of any device utilizing the connection.
To achieve a contact width of 0060-0080 inch, in view of the small size for the receptacle portion of receptacle element 3, typically in the ;order of 0.400 inch which may accommodate a spring 0.300 inchin length, the plateau of spring 27 must be nearly flatwith only a slight bow or crown at radiu R2. ,ln areceptacle of this size a maximum spring deflection.of- 0,.008 inch. will typically accommodate the thickness of the tab .and the height of boss 19, but in 0.300 inch this .amountof spring deflection cannot be absorbed by. a springv bowed in accordance with radius R2 without .beingforced over'center. The radius, of curvature R1, at the. spring extremities must be sufiiciently smaller than radius R2 to raise the nearly flat spring plateau above the plane of fioor 21 far enough to avoid depression of the spring below the plane of the floor, thus effectively increasing the spring length.
1. An electrical connector for receiving a substantially flat rectangular tab having an indentation in at least one .face comprising a base portion, oppositely disposed side flanges overhanging and forming with said base portion a receptacle for receiving the tab, a boss on said base portion adapted to fit within the indentation to provide a detent for resisting withdrawal of the tab from'the receptacle, said boss having dimensions smaller than the indentation, relative to the general plane of the contact surfaceslof said base portion and the tab respectively, so asto be free from forceful engagementwith the tab upon centering the indentation over said boss.
2. An electrical connector for receiving a substantially flat rectangular tab having an indentation in at least one face comprising a base portion, oppositely disposed side flanges overhanging and forming with said base portion a a receptacle for receiving the tab, said base portion including a resilient strip convexly bowed lengthwise of said receptacleand adapted to spring-bias-the tab against said flanges and to be at least partially flattened to provide an area of electrical contact with the tab, a boss on said member adapted to fit within the indentation to provide a detent obstructing removal of the tab from thc receptacle, the corresponding dimensions of said boss being smaller than the indentation so as to be free from forceful engagement with the tabupon centering the indentation thereover.
3. An electrical connector substantially as set forth in claim 2 wherein said strip is defined by two parallel slots in said base portion and is bowed out of the plane of said base portion with radii of curvature atthe end portions substantially smaller than the radius of curvature of the central portion thereof.
4. An electrical connection comprising areceptacle having a base portionandv opposed side fiangesoverhanging .saidbase portion, said base. portion including aresilient ,strip convexly bowed lengthwise of said receptacle, and a substantially fiat tab received within said receptacle and spring-biased by said strip against said flanges causing said strip to become flattened over a central portion of its length, detent means for resisting removal of said tab including a boss and dimple respectively on said strip and tab within the flattened part of said strip, the corresponding dimensions of said boss being smaller than said dimple so as to be free from forceful engagement with the tab.
References Cited in the file of this patent UNITED STATES PATENTS Batcheller May 31, 1949 Batcheller June 10, 1952 Batcheller June 10, 1952 Martines Feb. 21, 1956