US3693136A

US3693136A - Electrical plug contact

Info

Publication number: US3693136A
Application number: US9636A
Authority: US
Inventors: Arthur I Appleton
Original assignee: Individual
Current assignee: Emerson Electric Co
Priority date: 1968-10-25
Filing date: 1970-02-09
Publication date: 1972-09-19
Anticipated expiration: 1989-09-19
Also published as: FR2021583A1; DE1953301B2; DE1953301A1; GB1285608A; DE1953302A1; DE1953302B2

Abstract

Electrical plug connectors of the male type, which are adapted to be matingly inserted into a female portion, wherein the male includes spring-biased, captive ball shaped members, preferably made of an insulating material such as a borosilicate glass for urging the male member against the corresponding arcuate contact surface of the female socket to which it is inserted with a relatively even distributed pressure, so that a substantial area of current contacting interface results. The male portion includes two different radii of curvature, at least one forming an arcuate contact surface in cross-section which subtends an arc of less than 180*.

Description

United States Patent Appleton [54] ELECTRICAL PLUG CONTACT [72] Inventor: Arthur I. Appleton, 1713 W. Wellington Ave., Northbrook, lll. 60613 [22] Filed: Feb. 9, 1970 [21] Appl.No.: 9,636

Related US. Application Data [63] Continuation-impart of Ser. No. 770,518, Oct.

25, 1968, abandoned.

[52] US. Cl ..339/9l B, 339/255 R [51] Int. Cl. ..H0lr 13/54 [58] Field ofSearch ..339/252255, 91 B, 339/91 P [56] References Cited UNITED STATES PATENTS 3,052,867 9/1962 Rogoff ..339/2l7 S FOREIGN PATENTS 0R APPLICATIONS 1,134,293 4/1957 France ..339/254 l,368,879 6/1964 France ..339/254 [15] 3,693,136 1 Sept. 19, 1972 OTHER PUBLICATIONS Electrical Manufacturing, Steinberg, 11- 1959, pp. 82- 88.

Primary Examiner-Joseph H. McGlynn Attorney-Wolfe, Hubbard, Leydig, Voit & Osann, Ltd.

[57] ABSTRACT Electrical plug connectors of the male type, which are adapted to be matingly inserted into a female portion, wherein the male includes spring-biased, captive ball shaped members, preferably made of an insulating material such as a borosilicate glass for urging the male member against the corresponding arcuate contact surface of the female socket to which it is inserted with a relatively even distributed pressure, so that a substantial area of current contacting interface results. The male portion includes two different radii of curvature, at least one forming an arcuate contact surface in cross-section which subtends an arc of less than 180.

1 Claim, 4 Drawing figures ELECTRICAL PLUG CONTACT This is a continuation in part of my co-pending U.S. application Ser. No. 770,518, filed Oct. 25, 1968 entitled Electrical Connectors, and now abandoned.

BACKGROUND OF THE INVENTION This invention relates primarily to the field of electrical connections and connectors, and more specifically, to improved plug connectors for making an electrical connection with a consistent and low voltage drop thereacross.

, Connectors of the multi-conductor type are most often used in conjunction with the transmission of small quantities of current. Typical applications include sensing equipment, measuring equipment, and other forms of delicate instrumentation where it is important that connectors do not transmit electrical noise which might disturb readings, etc. Also, there should not be a large and/or inconsistent voltage dropacross the various connections made by the multi-conductor, and all the connectors of a given size. in a manufacturers line should be relatively consistent in voltage drop.

Among the more widely used multi-conductor connectors utilizing male prongs received in a female receptacle, it has been found experimentally that the voltage drop betweenthe several connections in the same connector may vary as much as 40 percent. Also, most of these commonly used connectors are built to meet conservative military standards which specify the maximum millivolt drop permissible for each catagory of connector, and frequently these multi-conductor connectors include some connections or contact pairs which very closely approach this maximum. Manufacturers whose products so closely appraoch a given design criterion naturally must maintain a costly quality control to ensure that some do not exceed the permissible limits. Typical connectors made between a cylindrical male or prong and a tubular female or socket include some provision for holding the prong against the internal surface of the socket to thereby create electrical contact along a longitudinal line.

Not only iselectrical contact along a longitudinal line a rather poorconnection in theory, but something less than line contact is in fact achieved in practice. The reason for this is in part due to the fact that in small female receptacles, some of which are merely elongate holes in the neighborhood of one thirty-second of an inch in diameter, the openings are formed by drilling, and a drilled hole by itself is normally neither dimensionally true nor results in a smooth surface finish. Ordinary and relatively inexpensive machine operations cannot be employed to clean up the surface finish because of the small diameter of the hole. Thus, the contact between plug and receptacle amounts to only a few contact points, and the amount of resistance interjected into the electrical line by this poor contact between a given prong and receptacle is both undesirably high and unpredictable.

in several other well known connector variations, the female receptacle is produced from tubular copper stock which is cut to length and then longitudinally slit at what will laterbe in connection end to achieve flexibility and thereby provide for slight variability of the hole size. if the female is not made from material having good spring characteristics, a separate peripherally extending spring is used to bias the opposed halves or quarters of the partially slit tubing toward one another in order to ensure that there will always be some pressure exerted on the prong. It will be understood, however, that due to tolerancesthe inner diameter of the tubing must initially be slightly larger than the outer diameter of the prong or a possible interference fit would result. Thus, this construction also exhibits line contact at best, and possibly only multiple point contact. Additionally, in this slit tube form of the receptacle, the slotting operation usually leaves some burrs within the inner diameter of the tubing. If the tubing has a smaller diameter, these burrs normally are not removed, nor can they be removed with ordinary manufacturing techniques, if at all.

In larger sized connectors, it is a more common design to make a solid female of tubular material and to make the male by longitudinally slotting or longitudinally cross-slotting a slightly smaller diameter rod over a portion of its length. The slotted end of the prong is rounded or tapered and the segments formed by the slotting operation are bent slightly outwardly so that when the prong is pushed into the receptacle opening, the prong possesses some inherent resiliency and thereby bears against the internal sidewalls of the receptacle hole. Since the hole cannot be smaller than the original diameter of the prong, it must be larger. Thus, the actual contact between prong and receptacle is once again in the nature of several contact points, these points being near the leading end of the four prong segments.

It is therefore one of the principle objects of the invention to avoid these inherent disadvantages of known designs and to produce an electrical plug connector having a male element which minimizes voltage drop across the resultant connector in which it is utilized and maintains a consistent voltage drop among all similar connectors of a given size whether or not it is clustered. It is another basic object of the invention to provide a plug connector which is easier to work with in the field than those now available commercially.

It is another object to furnish a male plug member which is resiliently biased into good electrical contact with the wall of the female socketmember with which it is used, yet wherein scraping of the walls of the female by the biasing means is avoided. In this regard it is a related object to provide a male plug member of the foregoing type wherein said biasing means contacting the wall of the female avoids or precludes arcing therebetween that might lead to galling or pitting during insertion or withdrawal of the plug.

SUMMARY OF THE INVENTION The present invention minimizes or solves the problems discussed above by utilizing a male element with a contacting surface of identical mating shape to that of the receptacle so that there is an appreciable area of contact between plug and receptacle and novel captive biasing means carried by the plug for urging it against the receptacle.

In its preferred embodiment, the male plug portion includes at least one conductive element which has a contact surface of somewhat less than semicircular shape in cross section which is easily formed and plated. With this new construction, it has been found that an electrical connection with a reasonably predictable and low voltage loss thereacross can be manufactured by ordinary methods.

Because the connector in fact makes two connections instead of the usual one, it would be expected that the total millivolt loss across the entire connector assembly would be much larger than the loss experienced in known connectors having only one connection. However, the contact resistance is so low with these improved connections that the double connection yields less total resistance thereacross than the single connection of these other known connectors.

It should be noted here that the entire effect is due to the nature of the contactingsurfaces which lessens contact resistance and not to the bulk resistance because the component elements within the subject connectors are not any larger than known commercial constructions. Beyond having both less voltage drop and a more consistent voltage drop between all of the electrical connections in a connector assembly, the connector actually has, in some forms, less voltage drop between its extreme axial ends then a similar length of the same wire with which the connector is recommended.

Thus, a plug connector is disclosed herein that is particularly easy to work with and which exhibits both consistent and very low voltage drop. The individual plug connection presents an extremely close fitting interface to afford a substantial area of common contact, with the receptacle and the connection made exhibits a minimun of electrical noise.

While the invention has been described in connection with several illustrative embodiments, it will be understood that l do not intend to be limited to the embodiments shown, but, on the contrary, I intend to cover the various alternatives and equivalent arrangements included within the spirit and scope of the appended claims.

DESCRIPTION OF THE DRAWINGS Other objects and advantages of the invention will become apparent upon reading the attached detailed description and upon reference to the drawing in which:'

FIG. 1 is a partially cut away perspective view of a male connector embodying the features of the present invention;

FIG. 2 is a cross-sectional view of the connector shown in FIG. 1, taken substantially along the line 2-2 of FIG. 1;

FIG. 3 is a side elevation view of another form of the male connector shown in FIG. 1; and

FIG. '4 is a view taken substantially along the line 4- 4 of FIG. 3.

DESCRIPTION OF THE INVENTION Referring now to the drawings there is shown in FIGS. 1 and 2 a male portion of an examplary connector in accordance with the present invention usable with a tubular female having an internal contact surface of circular cross-section (not shown). In general, the male member includes a body 12 of generally cylindrical shape, having a prong portion 11 extending axially outwardly for engagement with the receptacle socket with which it is to be used. At the rear of the body 12, there is a longitudinally extending opening adapted to receive the insulation-striped end 14 of a conductor 16.

In carrying out the present invention, the prong portion is provided with radially outwardly biased captive mounted balls 18, which are adapted to be received within transversally extending bores 19, formed inas the prong portion 11, (FIG. 2). The balls 18 are each restrained from entirely escaping out of the bore 19 by the formation of a lip 21 which is extruded from the prong material by means of a staking operation. Resilient means (only one being shown in FIG. 2) herein shown as a spring 22 biases the ball 18 radially outward with respect to the outer periphery of the prong 11. In much as the balls 18 are depressed inwardly against the action of a spring when the prong is inserted into a receptacle, the reaction by the spring tends to drive the arcuate surface of the prong opposite from the balls against the corresponding arcuate surface of the receptacle socket.

In order to insure that a substantial area of current conducting interface results, referring particularly to FIG. 2, it will be noted that the cross-sectional shape of the prong is not circular, but, instead it is formed of two different radii, R1, and R2, generated from spaced apart axes and 24, respectively, and intersecting along a pair of lines 20. Ideally, the axis of the receptacle would be colinear with axis 23, and the radius of the mating female surface would be identical with the radius designated R1. The mating female surface, when a connection is made, would then be flush with the prong surface defined by radius R1 over the angle designated A" (this being less than and would continue around the prong along the dashed line 24 in FIG. 2.

Ball 18 has sufficient curvature and permissive travel, but its outermost portion juts outwardly and interferes with the receptacle during insertion. Being inwardly movable, it depresses upon initial insertion and rolls along the female contact surface until fully inserted. Thus, it causes no scraping or scoring of the wall of the female. The force of spring 22 maintains the proper contact pressure between the contacting surfaces.

It will be remembered that an advantage residing in a biased male is that it can be interchangeable with other plugs, which for the most part, are used in conjunction with non-expandable females. Unfortunately, the inner diameter of most cylindrical females already in use is not held to exacting dimensions since to do so still would not give better than the multiple point or line contact already achieved with the conventional male plugs used therewith. For example, the inner diameter of a k inch receptacle of a major manufacturer varies roughly between 0.500 and 0.502 inches. Such a variance is too great to assure large area contact between that receptacle and a dimensionally-closely-held prong designed in accordance with the present invention. Therefore, the radius R1 is held to a dimension slightly larger than the maximum radius of the female. However, the radius R2 on its axis or center 24 is adjusted so that the prongs can still be inserted into the female.

In other words, although R1 exceeds the radius of the female, no diameter" of the prong exceeds the diameter of the receptacle. Thus, upon insertion, each of the intersecting lines 20 are initially in line contact, but the relatively large angle A creates a wedging condition which increases the contact pressure. And, this highcontact pressure in conjunction with repeated insertions and withdrawals causes the lines 20 to wear and form larger and larger surface areas in common contact. This later is considerably more concentrated in this connector than it is in those displaying only single line contact.

In accordance with another of the important aspects of the invention, provision is made for insuring that no arcing occurs between the biasing means carried by the plug and the wall of the socket into which it is inserted, thereby avoiding any galling or pitting that might interfere with either the electrical contact or promote further damage to the contacting elements during sub sequent insertions or withdrawals of the plug. To this end, and with reference to FIGS. 3 and 4 there is herein shown a plug similar to that shown in FIG. 1 in that there is a body 26 of substantially cylindrical shape and prong portion 27 provided with radially outwardly biased captive mounted balls 28, which are received in bores 31 (FIG. 4). The balls 28 are each restrained from entirely escaping out of the bore 31 by the lip 32 the springs 30 used to resiliently bias the spheres are metal it precludes the passage of current through the spring which could result in a change in the spring characteristic, and alteration of the efficiency of the biasing feature. Furthermore, the insulating material of which the balls are constructed, is preferably a borosilicate glass, such as the products of Corning Glass Works sold under the tradename Pyrex, a glass that is resistent to heat, chemicals and electricity.

I claim as my invention:

1. An electrical plug connector of the type incorporating a male prong which is adapted to be insertable into a female receptacle having a side wall and a con nection surface of arcuate shape in cross-section, comprising, in combination, a plug body of substantially cylindrical shape adapted'to receive a conductor at one end and a substantially cylindrical prong portion at the opposite end, the prong portion having two different radii of curvature, at least one radius forming an arcuate connection surface in cross-section which subtends an arc of less than said prong arcuate shaped connection surface including substantially the same radius of curvature as the receptacle surface, and captive mounted biasing means including at least one spherical ball formed of an electrically insulating material, laterally movable and trapped within said prong and a resilient element for urging said spherical ball laterally outwardly to engage a receptacle side wall, the biasing means biasing a substantial portion of the length of the arcuate shape of said prong into engagement with a corresponding arcuate portion of said receptacle.

Claims

1. An electrical plug connector of the type incorporating a male prong which is adapted to be insertable into a female receptacle having a side wall and a connection surface of arcuate shape in cross-section, comprising, in combination, a plug body of substantially cylindrical shape adapted to receive a conductor at one end and a substantially cylindrical prong portion at the opposite end, the prong portion having two different radii of curvature, at least one radius forming an arcuate connection surface in cross-section which subtends an arc of less than 180*, said prong arcuate shaped connection surface including substantially the same radius of curvature as the receptacle surface, and captive mounted biasing means including at least one spherical ball formed of an electrically insulating material, laterally movable and trapped within said prong and a resilient element for urging said spherical ball laterally outwardly to engage a receptacle side wall, the biasing means biasing a substantial portion of the length of the arcuate shape of said prong into engagement with a corresponding arcuate portion of said receptacle.