US 3474380 A
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Qct. 21, i969 E. A, MILLER 3,474,380
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izw' fl, fuller United States Patent O 3,47 4,380 ELECTRICAL CONNECTORS Edwin A. Miller, 11 Old Elm Road, Fairfield, Conn. 06430 Filed Feb. 19, 1968, Ser. No. 706,250 Int. Cl. Hk 1/12; H01r 11/22, 13/50 U.S. Cl. 339-17 11 Claims ABSTRACT OF THE DISCLOSURE In order to avoid sustaining arc damage to a connector contact structure entirely across its breadth, one or more elements are provided which are confined to less than the full lateral extent of the contact and which protrude forwardly of the main current-carrying body. These elements absorb and delimit the damage caused by the initial arc so that the main body of the contact is kept free of arc damage entirely.
FIELD OF THE INVENTION The invention relates generally to the eld of arc darnage avoidance, particularly as it relates to plug-in electrical connectors.
THE PRIOR ART When a contact structure for an electrical connector emerges from its nal fabrication operation, and the contact has not yet been used to make or break an electrical circuit, its surfresistance is then about as low as it will ever be. The surface is relatively free of oxides, dirt, and chemical contaminants, and no arc has yet been drawn to blacken the contact surface with carbon deposits, to erode or transfer metal at the surface, or to vaporize or voxidize metal due to the heat of the arc. In subsequent use, contacts must eventually face this kind of damage from arcing upon making or breaking an electrical circuit. In high power switch gear, the problems are so severe that they are dealt with by elaborate arc-suppression mechanisms, such as oil baths or gas blasts.
But in the case of small light duty electrical plug connectors, such measures are not feasible within the limitations of space and cost. Therefore, the contacts in plug assemblies of this type are subjected to arc damage, and the only safeguard is the design of the mating contacts so that a good wiping action takes place upon plug-in, to keep the mating surfaces as clean as possible.
'Ihe wiping action, however, is not an unmixed blessing. Although it renews the contact surface to some eX- tent, it also distributes the carbon deposits, oxides, dirt, and other contaminants in a direction rearwardly of the initial point of contact between electrodes. The prior art has not suggested a way to confine the arc damage to a fraction of the contact breadth, leaving the remainder of the contact breadth free of such arc damage.
SUMMARY OF THE INVENTION The present invention provides a contact structure for use in plug type electrical connectors, which is designed to confine arc damage to a sacrificial sector of the contact breadth, and to exclude such arc damage entirely from the remainder of the contact breadth so as to preserve its surface resistance at the relatively low level encountered prior to arcing.
BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a perspective view, with parts broken away for greater visibility, of a first embodiment of a contact structure in accordance with this invention.
FIG. 2 is a side elevational View, with parts sectioned, of a plug connector employing the contact structure of FIG. l, this view showing the moment of initial Contact with a mating contact.
FIG. 3 is a similar side elevational view of the plug connector and contact structure of the previous figure, showing nearly complete engagement with the mating contact.
FIG. 4 is a sectional view, taken along the lines 4-4, of the structure in FIG. 3.
FIG. 5 is a perspective view of another embodiment of a Contact structure in accordance with this invention.
FIG. 6 is a side elevational view, with parts sectioned, of a plug connector employing the contact structure of FIG. 5, and showing the initial stages of contact with a mating contact.
FIG. 7 is a similar side elevational view of the plug and contact combination of FIG. 6, showing nearly complete engagement with the mating contact.
FIG. 8 is a sectional View, taken along the lines 8-8, of the structure of FIG. 6.
FIG. 9 is a sectional view, taken along the lines 9--9, of the structure of FIG. 7.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an electrical contact 10 fabricated of a unitary strip of resilient metal. At one end of the contact strip 10 is a tail piece 12 which comprises a at clamping section 14 and an end section 16. FIG. 2 shows that the fiat clamping section 14 is held firmly between two halves 18 and 20 of a connector plug housing 22. This housing 22 is molded of any conventional insulating plastic material, and forms an enclosure about the contact structure 10. The end section 16 of the contact structure protrudes beyond the rear of the plug housing 22, as seen in FIG. 2, to form an external electrical terminal. An opening 24 provides a convenient place for soldering a lead wire to the terminal.
Just beyond the clamping section 14, the contact structure 10 has a right angle section 26 which merges into an arm 28 projecting forwardly, i.e. to the left, which is also the direction of plug-in motion of the plug assembly 10, 22. At the front of the contact structure 10, i.e. near the point of initial contact with a mating electrode, the arm 28 merges into a substantially U-shaped bend which forms the leading surface 32 of the contact structure, i.e. that part of the contact structure 10 which rst approaches the mating electrode. The leading surface 32 merges into a main contact arm 34. The latter terminates in a turned-up end 36 which prevents scoring of the mating electrode when the latter is withdrawn to the left of FIGS. 2 and 3.
The main support of the contact structure 10 comes from the clamping relationship with the plug housing 22 at clamping section 14. The bend 26 is substantially parallel to and braced against the adjacent face of the plug housing 22. The angle between bend 26 and arm 28 is such that arm 2S is biased downwardly by inherent resiliency so that the arm 34 rests against the adjacent face of the lower plug housing section 20. This serves to increase contact pressure with a mating electrode inserted between the arm 34 and plug section 20, and thereby generate a good wiping contact, in accordance with conventional contact design practice.
The plug housing 22 opens to the left to admit a mating structure 39, in this instance a printed circuit board cornprising a phenolic base 40 plated with a conductive metal electrode layer 42. The board 39 is inserted by sliding it to the right along the shelf provided by the lower plug section 20. The metal plating 42 establishes initial electrical communication, i.e. an arc, with some portion of the convex leading surface 32.
Contact must be made below the inection point of the curvature of leading surface 32, so that the entire contact structure is cammed upwardly, permitting the printed circuit board 39 to slide underneath the contact arm 34 to the position illustrated in FIG. 3. As this happens the arm 28 of contact structure 10 is exed upwardly against a spacing shim 44 which may be integrally molded with the upper plug section 18. When the arm 28 has been driven fully into abutment with the shim 44 as shown in FIG. 3, then the lower arm 34 is fiexed, and its inherent resilience causes contact pressure to be exerted against the mating electrode 42, so that there is a firm wiping contact between the arm 34 and the metal plating 42 as they slide across one another.
A protruding element 50 is struck from the body of the convexly curved leading surface 32, leaving a cut 51 on three sides of the element 50. The radius of curvature of that protruding element 50 is greater than the radius of curvature of the remaining side portions 52 on either side of the central protruding element 50 to establish the protruding relationship. Conversely, the tighter radius of curvature of the two side portions 52 makes them trailing elements of the leading surface 32. This protrudingtrailing relationship dictates that, as the mating electrode 42 approaches the contact structure 10 from the left, it makes initial contact with the central protruding element 50 and subsequent contact with the trailing side elements 52.
This means that the arc drawn at the moment of initial (or final) electrical communication will be confined to the protruding element 50 and excluded from the trailing elements 32. Moreover, when the carbon deposits, oxidation products, loose metal particles, and other surface contaminants which result from the arcing are spread rearwardly of the initial arc area as the printed circuit board 39 continues its wiping passage from the position of FIG. 2 rearwardly toward the position of FIG. 3, these contaminants are confined to a sacrificial central sector of the contact 10. The arm 34 provides the principal contact with the electrode 42 once the position of FIG. 3 has been reached. Therefore, the outer sections of arm 34, which line up behind the trailing elements 52, will be entirely free of arcing products, and those products will be confined entirely to the central section of arm 34, which lines up behind the protruding element 50.
In addition, the central section of the main contact arm 34 can be removed entirely as shown in FIGS. 1, 2 and 4 to leave a vacancy 60 behind the protruding element 50. Thus, no portion of the main contact arm 34 which lines up behind the element 50 is employed for subsequent electrical communication with the mating electrode 52. This further avoids the problem of establishing electrical communication through a film of carbon, metal oxide, loose metal particles and other arc deposits. In addition, it avoids spreading such deposits over a larger-than-necessary area of the mating electrode 42 as the latter moves fully into engagement with the contact structure 10, i.e. from the position of FIG. 2 to the position of FIG. 3.
It will be apparent that the basic principle of this 1nvention is realized whenever there are protruding and trailing elements in electrical communications with each other which are laterally displaced from each other in a direction transverse to the plug-in direction, and that the invention is not limited to any particular number or arrangement of protruding and trailing elements. To take a specifc example, FIG. 5 shows another embodiment of a contact structure in accordance with this invention. Here a contact structure 210 has a clamping seat 212 and a terminal end 216 formed with a lead connection hole 224. The clamping seat 212 merges into a bend 226 and then into a resilient arm 228. The latter merges with a convexly curved leading surface 232 which in turn merges with a main contact arm 234 ending in a bent tail 236.
In this embodiment the two outer elements 252 of the leading surface 232 have the greater radius of curvature and are therefore the protruding elements. The central section 250 has the smaller, tighter radius of curvature and hence forms the trailing element which remains free of arc damage due to the sacrifice of the protruding elements 252. In this embodiment the central section 250 is not struck from the curved surface like the tongue 50 of the previous embodiment, but is separated from the outer sections by slits 254. Another diference in this embodiment is represented by the fact that the main contact arm 234 lacks the central vacancy 60, and has instead downwardly protruding rib 262.
The insulating plug housing 222 is quite similar to the housing 22 of the previous figures. It has upper and lower halves 218 and 220 respectively, which clamp the contact structure 210 at the clamping area 214. The end section 216 protrudes rearwardly to form an electrical terminal. The bend 226 is braced against the adjacent surface of the plug housing 222. An integrally molded shim 244 limits upward movement of the contact structure 210 when it is cammed upwardly by the plugging in of the printed circuit board 239 (phenolic base 240 and metal plating 242).
Initial arcing contact of the mating electrode 242 with the outer protruding elements 252 is illustrated in FIG. 6, while subsequent insertion into full engagement With the main contact arm 234 is illustrated in FIG. 7. The latter view shows that the downwardly projecting central rib 262 confines the area of contact with the mating electrode 242 to the central region of the main contact arm 234. This is seen again in the sectional view of FIG. 9 which shows how the rib 262 maintains contact with the electrode 242 in the central region of arm 234 but holds the anking outer regions on either side of it up out of contact with the electrode 242. Thus, in this embodiment arc damage is confined to the outer sections of main contact arm 234 which line up behind the protruding elements 252, and these sections are also held out of contact with the electrode 242. This minimizes the distribution of carbon deposits, oxides and other surface contaminants over the metal electrode 242 as it is inserted fully into engagement with the main contact arm 234.
In either embodiment of the invention, a sacrificial portion of the leading surface bears the entire brunt of the arc damage, and a corresponding sacrifical portion of the main contact arm which follows the leading surface into engagement with the mating electrodes is kept out of electrical contact with the mating electrode entirely so as to avoid attempting to establish electrical communication through a film of arc product deposits and to avoid unnecessary distribution of such deposits over the mating electrode. In this way, the invention establishes a new approach to the problem of avoiding high contact resistances as a result of arc damage.
Therefore the following claims, the function of which is to define the scope of patent protection to which this invention is entitled, should be given a latitude of interpretation which is consistent with the inventive principles emerging from the foregoing disclosure.
The invention claimed is:
1. A contact structure for an electrical connector plug for electrical connection to a conductive metal electrode layer printed on and extending to an edge of one planar side of the insulating base of a printed circuit board through sliding engagement in a plug-in direction parallel to said side of said base and transverse to its said edge, said contact structure being formed of a unitary strip of resilient metal bent into generally U-shape to form a forward bight and resilient mounting and contact arms extending rearwardly from said bight and comprising at least two resilient conductive elements electrically connected to each other and displaced from each other in a lateral direction transverse to said plug-in direction, at least one of said elements protruding ahead of a trailing one of said elements and ahead of any other part of said contact structure which is electrically connected to said protruding element, said protruding and trailing elements each having an inclined leading surface forming a part of said bight :for camming and flexing engagement with the edge of said layer, said leading surface of said protruding element protruding forward relative to said plug-in direction with respect to said leading surface of said trailing element, whereby rst make and break arcing Contact is made with said edge of said layer by said protruding leading surface, said resilient contact arm having a trailing contact surface in following relation to said trailing leading surface laterally offset from said protruding leading surface for contacting a surface of said layer laterally offset from the surface first engaged by said protruding leading surface, and said resilient contact arm being devoid of any contact surface in followingl aligned relation to said protruding leading surface and disposed in the plane of said laterally offset trailing contact surface.
2. A contact structure as in claim 1, wherein said protruding element is substantially centrally located relative to said lateral direction, and there is one of said trailing elements of either side of said protruding element.
3. A contact structure as in claim 1, wherein said trailing element is substantially centrally located relative to said lateral direction, and there is one of said protruding elements on either side of said trailing element.
4. A contact structure as in claim 1, wherein said contact arm of said metal strip forms resiliently cantilevered contact ar-m extending rearwardly from said bight relative to said plug-in direction and positioned for yieldably engaging said conductive layer after initial contact is established therewith by said protruding leading surface.
5. A contact structure as in claim 4 wherein said contact arm is cut away in an area following said protruding leading surface to minimize contact in that area with said conductive layer.
6. A contact structure as in claim 4 wherein said contact arm is formed with a raised longitudinal rib following said trailing leading surface, said vrib protruding in a direction to Contact said conductive layer when the latter is in said engaged relationship with said contact arm, whereby to hold out of engagement with said conducting layer that portion of said contact arm which follows said protruding leading surface.
7. A contact structure as in claim 4, wherein said mounting arm includes a at clamping area for clamping said contact element in a connector plug.
8. A contact structure as in claim 7, in combination with an insulating connector plug structure arranged in clamping relationship thereto at said clamping area.
9. The combination of claim 8 wherein said plug structure is arranged to form an insulating enclosure about said contact element, said enclosure having an opening located to admit said circuit board along said plug-in direction to make initial contact with said protruding leading surface and subsequent contact with said contact arm.
10. The combination of claim 9 wherein said plug structure is arranged to confine the motion of said mating conductor upon insertion into said structure enclosure, and to limit movement of said second end of said metal strip in response to engagement of said mating conductor with said contact arm during such insertion, and said contact arm is oriented so as to be resiliently deflected by engagement with said mating conductor during such insertion so as to provide a wiping pressure contact therewith.
11. The combination of claim 10 wherein said second end of said metal strip extends beyond said plug structure to form an external electrical terminal.
References Cited UNITED STATES PATENTS 680,981 8/1901 Johnson 200--146 896,210 8/1908 James 200-146 1,216,420 2/1917 Dodgson 200-166 3,040,291 6/ 1962 Schweitzer 339-17 X FOREIGN PATENTS 1,046,137 12/ 1958 Germany.
RICHARD E. MOORE, Primary Examiner U.S. Cl. X.R. 339--l49, 252, 278